Title of Invention	EVAPORATION INDUCED LITHOGRAPHY
Abstract	A method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising providing solution/dispersion of said material in a volatile solvent on a flat surface;placing at least one mask on droplet of said solution/dispersion;exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask;depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; removing the mask without disturbing the pattern formed along the mask. The process is entirely evaporation based producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. The process also includes formation of patterns of more than one layer including reaction of two species along the TEM grid lines (mask).

Title of Invention

EVAPORATION INDUCED LITHOGRAPHY

Abstract

A method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising providing solution/dispersion of said material in a volatile solvent on a flat surface;placing at least one mask on droplet of said solution/dispersion;exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask;depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; removing the mask without disturbing the pattern formed along the mask. The process is entirely evaporation based producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. The process also includes formation of patterns of more than one layer including reaction of two species along the TEM grid lines (mask).

Full Text	Field of Invention The present invention relates to lithographic pattern formation upon evaporation of a liquid drop containing solute (molecules) or dispersed particles, referred herein as Evaporation Induced Lithography. More particularly the process of the present invention is entirely evaporation based producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. The process also includes formation of patterns of more than one layer including reaction of two species along the TEM grid lines Background and Prior Art Jumping Zhang, Yan Liu, Yonggang Ke, and Hao Yan Nano Letters,2006, teaches organization of periodic square-like gold nanoparticles arrays, templated by self assembled two dimension DNA nanogrids on a surface. Reference of lithographically patterned devices of nanocrystals can be found in Yi Cui, Mikael T. Bjork, J.Alexander Liddle, Carsten Sonnichsen, Benjamin Boussert, and A. Paul Alivisatos, Nano Letters, 2004. Further, Richard D. Piner, Jin Zhu, Feng Xu, Seunghun Hong,Chad A. Mirkin Science. 1999, teaches the development of a direct-write "dippen"nanolithography (DPN) to deliver molecules in a positive printing mode. An atomic force microscope (AFM) tip was used to write alkanethiols with 30-nanometer linewidth resolution on a gold thin film in a manner analogous to that of a dip-pen. Molecules are delivered from the AFM tip to a solid substrate of interest via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices. Site-specific fabrication of organic, inorganic, and hybrid solid-state nanostructures though a novel combination of electron beam lithography (eBL) and spin coating of liquid and sol-gel precursors, termed as soft eBL were discussed in Suresh Dontu, Zixiao Pan, Benjamin Myers, Gajendra Shekhawat, Nianqiang Wu, and Vinayak Dravid Nano Letters. 2005, Younan Xia, George M. Whitesides Angewandte Chemie. 1998, teaches the process of softlithography using elastomeric stamps and molds . Maria-Victoria Meli, Antonella Badia, Peter Grutter, and R. Bruce Lennox, Nano Letters 2002, discusses a methodology to create nanometer-scale patterns with a diblock copolymer mask with an intrinsic topological nanopattern. It is described in Bartosz A. Grzybowski, Kyle J. M. Bishop, Christopher J. Campbell, Marcin Fialkowski and Stoyan K. Smoukov Soft Matter. 2 2005, that an experimental method that allows precise control of reaction-diffusion processes at small scales based on two - dimensional microgeometries from which reactions are initiated; and provide a facile route to complex micro- and nano-structures. A review on colloidal lithography by Seung-Man Yang, Se Gyu Jang, Dae-Geun Choi, Sarah Kim, and Hyung Kyun Yu Small. 2006, where self-assembly of colloids and the spontaneous formation of well-ordered colloidal arrays is discussed. The review presents the versatility of the self assembled colloidal masks in fabricating novel nanopatterns such as nanocups, hollow shells, and multifaceted materials. US 7,018,944 describes a method for generating a mask: having a nanoscale pattern, the method comprises a suspension liquid (containing periodically arranged objects), being placed on top of a supporting liquid that is placed on a substrate surface. The periodic arrangement of the objects in the suspension liquid has to be maintained over a given area using the apparatus. These ordered objects in the suspension create a mask and deposit a material through interstices contained in the mask so as to create a pattern on the substrate. The deposition of the material is carried out by one of the processes like sputtering, evaporation and spraying of a colloidal solution. It does not have the rigidity of the grid in depositing patterns. Further, the primary aim of the above patent is to organize particles on a substrate by placing the original particles on a liquid, which upon drainage leads to arrangement of the particles on the substrate surface. In this way layer of particles are arranged on the substrate surface based on their natural separation depending on the diameters of the particles. In addition, depositions of materials in the interstices of the particles followed by removal of the particles generate patterns of the new materials. US 6,709,929 demonstrates a method of selective etching preferably using the etching template to produce nanoscale patterns. It describes a technique of forming selfassembled nanoporous anodic aluminum oxide thin films. Celio et al ("Patterned Assembly of Colloidal particles by Confined Dewetting Lithography" Langmuir: Vol. 22, No. 26: December 19, 2006, pp 11426- 11435) reports the assembly of colloidal particles into confined arrangements and patterns on various cleaned and chemically modified solid substrates using a method which the term 3 authors term as"confined dewetting lithography". It teaches use of functionalized substrate surfaces with positively charge materials so that negatively charge polystyrene spheres could be better deposited. This art teaches use of polystyrene spheres of micrometer sizes to deposit the same in patterned formats as per the pattern of the grid (which is a cell) on ITO/glass and Si/SiO2 surfaces. The drawbacks of the prior art methods of lithography is one or more of the following: (a) they are limited by the diffraction wavelength of light (photolithography); (b the pattern formation could be made on specific substrates and requires high vacuum conditions (electron and ion beam lithography or X-ray lithography); (c) the speed of writing any particular high-resolution large scale structure is very low (dip-pen lithography); (d) the structures obtained by the conventional method (soft lithography) have either low resolution or are not applicable to a large set of materials constituting the structure; (e) there is no systematic way of controlling the patterns of structures especially at the large scale and those that are not formed by reaction diffusion (pattern formation by reaction diffusion waves); (f) there is limited flexibility in terms of various pattern formation or systematic pattern generation (nanosphere lithography); (g) organized single-molecule patterns on substrates are either not possible or difficult to achieve, (h) does not have rigidity of the grids in depositing patterns. Thus there is need for a fast, efficient single method where colloidal particles or solute particles can be systematically patterned on substrate surfaces, and the nature of the patterns can be controlled by external parameters and also layer-by-layer deposition of patterned structures could be obtained. Objects of Invention Thus the main objective of the present invention is to generate scalable patterned assembly of colloidal particles and molecular materials deposited on a substrate surface such as glass slides by evaporating a liquid drop, containing the colloidal particles or molecular materials, onto which a metallic grid mask (TEM grid) is placed for guided pattern formation. 4 Summary of Invention According to main aspect of the present invention there is provided a method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising: i) providing solution/dispersion of said material in a volatile solvent on a flat surface; ii) placing at least one mask on droplet of said solution/dispersion; iii) exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask;, iv) depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; i) removing the mask without disturbing the pattern formed along the mask Detailed Description Of Invention Brief description of the accompanying drawings Figure 1a: Optical micrograph of a metallic (TEM) Grid (Copper). Figure 1b: Optical micrograph of a metallic (TEM) Grid (Nickel). Figure 2: Schematic of a drop evaporating in a restricted geometry used in the present method of pattern generation. Figure 3: Optical micrographs of (A) deposits of two-dimensional arrays of AuNPs (using Copper TEM grid) on glass slide. (B) An expanded view of (A). Figure 4: AFM image of the pattern of the two dimensional arrays of AuNPs (using Nickel TEM grid). Figure 5a: : Two dimensional arrays of of AuNPs (using Nickel TEM grid).). Figure 5b: EDX of the pattern of two dimensional arrays of AuNPs (using Nickel TEM grid). Figure 6: Two dimensional arrays of Rhodamine B dye generated using the present method with Copper TEM grid. 5 Figure 7: Two dimensional arrays of Nile Red dye deposited using the present method with Copper TEM grid. Figure 8: (A) Two dimensional arrays of CdCI2 deposited using the present method. (B) An expanded view of A. Figure 9: Two dimensional arrays of polyvinyl pyrrolidone (PVP) on glass deposited using the present method. (A) is deposited using a copper grid. (B) is deposited using a Nickel grid. Figure 10: Optical micrographs of layer-by-layer deposited three dimensional arrays AuNPs (using Nickel TEM grid) on glass slide. Here one layer was deposited over another by the method described in the text. (B) is an expanded view of (A). Figure 11: Optical micrographs of two-dimensional arrays of CdS quantum dots obtained by reaction between CdCI2 and Na2S. (B) is an expanded view of (A). Figure 12: Optical micrographs of two-dimensional cross patterns of arrays of AuNPs on glass generated using the present methods. (A) Two separate deposits were performed one afteranother. (B) Double-grid deposition was used for one-time deposition. Figure 13: Patterns by using a membrane with CdS quantum dots Unlike the prior art the present invention does not use any films. The grids used do not form cells and no charged particles of use of chemical charge for deposition is used. The rigidity of the grids used is also unlike that of prior art. More particularly the process of the present invention is entirely evaporation based and the sidewall of the glass slide on which the process is carried out is not even bounded and no supporting or suspension liquids are used unlike the prior art. Further the TEM grid is not pretreated before its usage. Moreover the application of present method for producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. Additionally the formation of patterns by reaction two species along the TEM grid lines (CdS nanoparticles by reaction between CdCI2 and Na2S) is demonstrated. 6 The method developed by the present inventors has the unique advantage of patterned deposition of molecular and colloidal particles on the substrate surface by evaporation at room temperature where the pattern is guided by the structure of the mask -metallic grid (TEM grid) and the structure is formed by assembly of the materials along the patterned lines. The mask could also be membrane and the deposition pattern in that case follows the porous structure of the membrane. It is a facile, versatile and a general method for the generation of micron and submicron scale patterns of molecular and nanoscale materials assembled on a substrate surface. The primary condition for generating patterns of any materials is that the substance, whose pattern is to be generated, should be soluble or dispersible in a volatile liquid like water and toluene. The substances, the patterns of which can be generated are nanoscale particles of metal such as gold (Au), silver (Ag) and copper (Cu) or other metal nanoparticles that are dispersible in a volatile solvent and semiconductors such as CdS, Mn2+ doped CdS and ZnS or other semiconductor nanoparticles that are dispersible in a volatile solvent, solutions of single molecules such as an organic dye (Rhodamine B, Nile Red), solution of inorganic materials such as CdCI2, solution/dispersion of polymers like polyvinyl pyrrolidone (PVP), or other polymers that are soluble or dispersible in a volatile solvent. The droplets of these solutions / dispersions, upon evaporation in the presence of a metallic grid mask such as a transmission electron microscope (TEM) grid, lead to the deposition of patterned assembly of molecular and nanoscale materials on the surface of glass slides (substrates) where the droplets were placed. The pattern of the assembly follow that of the TEM grid with dimensions of lines far reduced than those of the TEM grids. Smaller lines and arrays may be deposited using membrane as mask for deposition where the deposited pattern follows the pattern of the porous structure as shown in Figure 13 According to a preferred aspect the method produces layer-by-layer three-dimensional deposition of assembled materials on the substrate surface. The patterns of the second layer of deposition can be made at a chosen angle to that of the first layer patterns. 7 The materials of the second layer is same or different from that of the first layer. For example, when the first layer of patterned deposition is made of assembly of metal nanoparticles, the second layer is of semiconductor nanoparticles (quantum dots). If the first patterned layer is made of a reactant the second patterned layer is made of a second reactant, where the second reactant reacts with the first one at the overlapping regions and produces the product at the intersections, which constitute the reaction sites. Hence, present invention of patterns generation by restricted evaporation using a TEM grid or any other similar mask opens a new approach to the growth of organized multidimensional arrays of colloidal particles in general. The present invention reveals the versatility of the simple evaporation process for aligning nanometer-to-micrometer- sized objects. The striking simplicity of the present restricted evaporation process finds use in the fabrication of biological devices, semiconductors and other electronic devices. This facile method of arranging particles in two and three - dimensional arrays is considered as a general method of patterned deposition of particles of various sizes and nature. The method may be used as basis for higher hierarchical device structures and opens up the possibility of making large-scale electronic devices with individually addressable nanoscopic and or molecular components. The details of the method are mentioned below. The potential applications of this simple method range from optoelectronic devices to micro and nano arrays of DNA, proteins etc. The principle behind this new technique is to evaporate a droplet of the solution (dispersion) containing the materials, of which pattern is to be generated, placed on a substrate surface (flat) in the presence of a metallic grid mask placed on top of the droplet. The invention is now defined by way of following non-limiting illustrative examples: 8 Grids used in the examples Commercially available TEM grid is used as the metallic grid mask. TEM grids are used are made of copper or nickel metals. The grids made of copper had regular arrays of rectangular openings of 45 micron x 45 micron with the metallic arms of the rectangle having dimensions of 45 microns x 5 microns (Figure 1a). Overall, the grid is circular with a diameter of about 3 mm. On the other hand, the grids made of nickel has regular arrays of rectangular openings of 100 micron x100 micron with the metallic arms of the rectangle having dimensions of 100 microns x 10 microns (Figure 1b). Overall, the grid is circular with a diameter of about 3 mm. More than one such grids may be attached and used together. Example 1 The present example demonstrates generation of patterned structures of AuNPs on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then air-dried. A colloidal solution of Au nanoparticles is prepared by treating 5 mL aqueous HAuCI4 (0.1 mM) with 1 mM of NaBH4. A drop (20 uL) of an aqueous solution of the colloidal Au nanoparticles is then placed onto the glass slide. A TEM copper grid is then placed carefully onto the drop such that the grid stays on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide are minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy, atomic force microscopy, scanning electron microscopy etc. The details of the micrographs are shown in Figures 3, 4, 5a and 5b. These two dimensional arrays are 0.4-0.6 micron in height with a width of 4-6 micron. When the above evaporation is carried out in the presence of a commercially available IR light lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 2 micron instead of 4-6 micron) and the evaporation process is completed in 10 min instead of 30 min. 9 Example 2 The present example demonstrates generation of patterned structures of Rhodamine B dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then air-dried. An aqueous solution of Rhodamine B dye was prepared by dissolving 100 uL of 0.1 M dye in 10 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of the Rhodamine B dye was then placed onto the glass slide. A TEM copper / nickel grid was then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 6. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. Example 3 This example demonstrates generation of patterned structures of Nile Red dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. An aqueous solution of Nile Red dye is prepared by dissolving 0.1 mg of the dye in 5ml of toluene. A drop (20 uL) of an aqueous solution of the Nile Red dye is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed.The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 7. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines were thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. 10 Example 4 The present example demonstrates generation of patterned structures of CdCI2 on a substrate surface. A glass microscope slide of size 1 cm x 1 cm was first cleaned by ethanol solution and then dried. An aqueous solution of 1.1 x 10-4 M of CdCI2 is prepared. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min using such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 8. When the above evaporation was carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. Example 5 The present example demonstrates generation of patterned structures of PVP on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. An aqueous solution of PVP is prepared by dissolving 15 mg of PVP in 2 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of PVP is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 9. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. 11 The above methods provide two-dimensional micron line patterns, consisting of arrays of colloidal particles, on glass substrate surfaces. As can be seen from the figures there are three kinds of deposits as results of evaporation under the above conditions. They are as follows: (a) Single line deposits of materials along the TEM grid lines with thickness on the order of 6.01 microns. These lines have typical heights on the order of 0.45 microns on the substrate (glass) surface. (Figures 3A and 3B) (b) Double line deposits of materials (with a spacing of 20 micron) along the TEM grid lines with thickness on the order of 2 micron or less. These lines have typical heights on the order of 1 micron. (Figure 5a) (c) Plate -like continuous deposits of materials along the TEM grid lines with thickness on the order of 4 microns or less. These plates have typical heights on the order of 1 micron. (Figures8A, 8B.9A, 9B, 6) Example 6 The, deposition of two layers of patterned materials one on top of the other is demonstrated as follows. The first layer of material (Au nanoparticles) is deposited on a glass slide as mentioned above using a TEM grid on top of a drop of an aqueous solution of AuNPs. When the deposited material is completely dried in 30 min (after removal of the grid) another drop of the same solution is again placed at the place where the original drop was there (that led to the formation of first grid patterns). A TEM grid is likewise placed on top of this drop followed by evaporation of the same. The process finally led to the formation of double-layered patterns where one layer of patterned deposits is placed on top of a previous layer of patterned deposits. The deposition of the first patterned layer is same (similar) as those described earlier. The deposition of the second patterned layer is typically thinner than the first layer. In other words, the lines corresponding to the patterned deposition are comparatively slimmer and height smaller with typical width of 0.8 micron. However, the patterns of the lines followed those of the TEM grid metal lines as with the first layer. The relative orientation and position of the lines of the first and second layers are decided by the 12 relative orientation of the TEM grid at the time of the first layer deposition and that during the second layer. The details of the micrographs are shown in Figure 10. Example 7 The present example demonstrates generation of patterned structures of CdS quantum dots on a substrate surface by reaction. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. Aqueous solutions of 1.1 x 10-4 M of CdCI2 and 0.01 M Na2S is prepared in Milli-Q water. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully (using a pair of forceps) onto the drop such that the grid stays on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min using a pair of forceps such that the structures imprinted on the slide is minimally disturbed. Then, a drop (20 uL) of an aqueous solution of Na2S is placed on the patterned structures of CdCI2. CdS quantum dots are produced at the overlapping regions where reaction occurs between them. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 11. Example 8 This example demonstrates generation of patterned structures using two grids together. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. A droplet of an aqueous solution containing the colloidal particles (Au NPs or and any other solute/dispersed particles) is placed on the glass slide. Two TEM copper / nickel grids attached to each other such that their grid lines are at an angle, are then placed carefully onto the drop such that the grids hold their position on the drop. A schematic view of the method of pattern generation is similar to the one shown in Figure 2. The drop along with the two TEM grids is then left to evaporate at 300°C for 30 min. The grids are then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 12. 13 The main advantages of the present invention are: 1. The present invention is simplel in generating highly reproducible predetermined patterned deposits with the help of natural forces (capillary forces) only. The method does not require any additional physical force such as light (photolithography), pressure on the mold (soft lithography), high energy electrons (electron beam lithography), ions (ion beam lithography) etc. 2. It provides patterned deposits, of molecular, nanoscale and microscale materials, on a substrate surface with the resultant assembly of the precursor materials. 3. The patterns can be controlled by controlling the dimensions of the TEM grid. The sizes of the grid lines and holes and the nature of the patterns that makes up the grid guide the pattern that is deposited on the substrate surface. 4. The dimensions of the deposited patterns are scalable and thus the method has unique advantage. 5. The method allows layer-by-layer patterned depositions of materials, where the resulting depositions could be made of same or two different materials that allow combination of patterned depositions. 6. The method offers depositions of two reactive agents one after the other where the product of the reaction results in the formation of specific depositions at the intersections of the deposition in the case of two-layer depositions. 14 We claim 1. A method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising : i) providing solution/dispersion of said material in a volatile solvent on a flat surface; ii) placing at least one mask on droplet of said solution/dispersion; iii) exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask; iv) depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; v) removing the mask without disturbing the pattern formed along the mask. 2. The method as claimed in claim 1 wherein the mask is selected from metallic grids and plastic membrane. 3. The method as claimed in claim 2 wherein when the mask is metallic grid and the deposition of the material occurs along the pattern lines of the grid. 4. The method as claimed in claim 3 wherein the metallic grids used are TEM grids selected from copper and nickel grid. 5. The method as claimed in claim 3 wherein two metallic grids are simultaneously used being attached to one another at defined angle. 6. The method as claimed in claim 2 wherein when the mask is plastic membrane the deposition occurs along the pattern formed by the pores of the membrane. 7. The method as claimed in any preceding claim wherein the restricted evaporation is carried out at 300° C 15 8. The method as claimed in any preceding claims wherein the restriction evaporation occurs for 30 minutes. 9. The method as claimed in any preceding claim wherein the flat substrate is glass slide. 10. The method as claimed in any preceding claim wherein the material to be deposited which is provided in solution/dispersion is selected from molecular materials, nanoscale particles of metals, quantum dots, and inorganic materials. 11. The method a claimed in claim 9 wherein the molecular material is selected from Rhodamine B dye, Nile Red dye and the like. 12. The method a claimed in claim 9 wherein the nanoscale particles of metals are selected from Au NPs, Ag NPs, Cu NPs and other metal nano particles soluble in volatile solvent. 13. The method a claimed in claim 9 wherein the quantum dots are selected frm CdS, Mn2+ doped CdS, and other semiconductor nanoparticles dispersible in volatile solvent. 14. The method a claimed in claim 9 wherein the inorganic materials are selected from CdCI2, polyvenyl pyrrolidone and other polymers soluble in volatile solvent. 15. The method as claimed in any of claims 1 to 5 and 7 to 14 wherein the line widths of the deposits formed ranges from submicron to a few microns. 16. The method as claimed in any of claims 1 to 5 and 7 to 15 wherein the height of the line of deposits formed is around 0.4-0.6 micron. 17. The method as claimed in any of claims 1 to 5 and 7 to 16 wherein the patterns deposited on the substrate surface are selected from single line deposits, double line deposits and plate-like deposits depending on the evaporation process. 16 17 18. The method as claimed in claim 1 optionally comprising evaporation in presence of commercially available IR lamp to provide distinct pattern and thinner lines of deposition. 19. The method as claimed in any of claims 1 to 5 and 7 to 18 wherein two layers of patterned deposit comprising first and second material are deposited one above the other. 20. The method as claimed in claim 19 wherein the first and the second materials deposited are selected from the same material deposited twice, different materials, and two reagents which react chemically to produce a third product at the intersections of the grid-line-like deposits. 21. The method as claimed in any of claims 19 to 20 wherein the first layer and second layer are deposited at defined angle to each other. 22. The method as claimed in any of claim 1to 5 and 7 to 18 wherein overall dimensions of the total deposited patterns are scalable as per the dimensions of the metallic grid. Field of Invention The present invention relates to lithographic pattern formation upon evaporation of a liquid drop containing solute (molecules) or dispersed particles, referred herein as Evaporation Induced Lithography. More particularly the process of the present invention is entirely evaporation based producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. The process also includes formation of patterns of more than one layer including reaction of two species along the TEM grid lines Background and Prior Art Jumping Zhang, Yan Liu, Yonggang Ke, and Hao Yan Nano Letters,2006, teaches organization of periodic square-like gold nanoparticles arrays, templated by self assembled two dimension DNA nanogrids on a surface. Reference of lithographically patterned devices of nanocrystals can be found in Yi Cui, Mikael T. Bjork, J.Alexander Liddle, Carsten Sonnichsen, Benjamin Boussert, and A. Paul Alivisatos, Nano Letters, 2004. Further, Richard D. Piner, Jin Zhu, Feng Xu, Seunghun Hong,Chad A. Mirkin Science. 1999, teaches the development of a direct-write "dippen"nanolithography (DPN) to deliver molecules in a positive printing mode. An atomic force microscope (AFM) tip was used to write alkanethiols with 30-nanometer linewidth resolution on a gold thin film in a manner analogous to that of a dip-pen. Molecules are delivered from the AFM tip to a solid substrate of interest via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices. Site-specific fabrication of organic, inorganic, and hybrid solid-state nanostructures though a novel combination of electron beam lithography (eBL) and spin coating of liquid and sol-gel precursors, termed as soft eBL were discussed in Suresh Dontu, Zixiao Pan, Benjamin Myers, Gajendra Shekhawat, Nianqiang Wu, and Vinayak Dravid Nano Letters. 2005, Younan Xia, George M. Whitesides Angewandte Chemie. 1998, teaches the process of softlithography using elastomeric stamps and molds . Maria-Victoria Meli, Antonella Badia, Peter Grutter, and R. Bruce Lennox, Nano Letters 2002, discusses a methodology to create nanometer-scale patterns with a diblock copolymer mask with an intrinsic topological nanopattern. It is described in Bartosz A. Grzybowski, Kyle J. M. Bishop, Christopher J. Campbell, Marcin Fialkowski and Stoyan K. Smoukov Soft Matter. 2 2005, that an experimental method that allows precise control of reaction-diffusion processes at small scales based on two - dimensional microgeometries from which reactions are initiated; and provide a facile route to complex micro- and nano-structures. A review on colloidal lithography by Seung-Man Yang, Se Gyu Jang, Dae-Geun Choi, Sarah Kim, and Hyung Kyun Yu Small. 2006, where self-assembly of colloids and the spontaneous formation of well-ordered colloidal arrays is discussed. The review presents the versatility of the self assembled colloidal masks in fabricating novel nanopatterns such as nanocups, hollow shells, and multifaceted materials. US 7,018,944 describes a method for generating a mask: having a nanoscale pattern, the method comprises a suspension liquid (containing periodically arranged objects), being placed on top of a supporting liquid that is placed on a substrate surface. The periodic arrangement of the objects in the suspension liquid has to be maintained over a given area using the apparatus. These ordered objects in the suspension create a mask and deposit a material through interstices contained in the mask so as to create a pattern on the substrate. The deposition of the material is carried out by one of the processes like sputtering, evaporation and spraying of a colloidal solution. It does not have the rigidity of the grid in depositing patterns. Further, the primary aim of the above patent is to organize particles on a substrate by placing the original particles on a liquid, which upon drainage leads to arrangement of the particles on the substrate surface. In this way layer of particles are arranged on the substrate surface based on their natural separation depending on the diameters of the particles. In addition, depositions of materials in the interstices of the particles followed by removal of the particles generate patterns of the new materials. US 6,709,929 demonstrates a method of selective etching preferably using the etching template to produce nanoscale patterns. It describes a technique of forming selfassembled nanoporous anodic aluminum oxide thin films. Celio et al ("Patterned Assembly of Colloidal particles by Confined Dewetting Lithography" Langmuir: Vol. 22, No. 26: December 19, 2006, pp 11426- 11435) reports the assembly of colloidal particles into confined arrangements and patterns on various cleaned and chemically modified solid substrates using a method which the term 3 authors term as"confined dewetting lithography". It teaches use of functionalized substrate surfaces with positively charge materials so that negatively charge polystyrene spheres could be better deposited. This art teaches use of polystyrene spheres of micrometer sizes to deposit the same in patterned formats as per the pattern of the grid (which is a cell) on ITO/glass and Si/SiO2 surfaces. The drawbacks of the prior art methods of lithography is one or more of the following: (a) they are limited by the diffraction wavelength of light (photolithography); (b the pattern formation could be made on specific substrates and requires high vacuum conditions (electron and ion beam lithography or X-ray lithography); (c) the speed of writing any particular high-resolution large scale structure is very low (dip-pen lithography); (d) the structures obtained by the conventional method (soft lithography) have either low resolution or are not applicable to a large set of materials constituting the structure; (e) there is no systematic way of controlling the patterns of structures especially at the large scale and those that are not formed by reaction diffusion (pattern formation by reaction diffusion waves); (f) there is limited flexibility in terms of various pattern formation or systematic pattern generation (nanosphere lithography); (g) organized single-molecule patterns on substrates are either not possible or difficult to achieve, (h) does not have rigidity of the grids in depositing patterns. Thus there is need for a fast, efficient single method where colloidal particles or solute particles can be systematically patterned on substrate surfaces, and the nature of the patterns can be controlled by external parameters and also layer-by-layer deposition of patterned structures could be obtained. Objects of Invention Thus the main objective of the present invention is to generate scalable patterned assembly of colloidal particles and molecular materials deposited on a substrate surface such as glass slides by evaporating a liquid drop, containing the colloidal particles or molecular materials, onto which a metallic grid mask (TEM grid) is placed for guided pattern formation. 4 Summary of Invention According to main aspect of the present invention there is provided a method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising: i) providing solution/dispersion of said material in a volatile solvent on a flat surface; ii) placing at least one mask on droplet of said solution/dispersion; iii) exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask;, iv) depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; i) removing the mask without disturbing the pattern formed along the mask Detailed Description Of Invention Brief description of the accompanying drawings Figure 1a: Optical micrograph of a metallic (TEM) Grid (Copper). Figure 1b: Optical micrograph of a metallic (TEM) Grid (Nickel). Figure 2: Schematic of a drop evaporating in a restricted geometry used in the present method of pattern generation. Figure 3: Optical micrographs of (A) deposits of two-dimensional arrays of AuNPs (using Copper TEM grid) on glass slide. (B) An expanded view of (A). Figure 4: AFM image of the pattern of the two dimensional arrays of AuNPs (using Nickel TEM grid). Figure 5a: : Two dimensional arrays of of AuNPs (using Nickel TEM grid).). Figure 5b: EDX of the pattern of two dimensional arrays of AuNPs (using Nickel TEM grid). Figure 6: Two dimensional arrays of Rhodamine B dye generated using the present method with Copper TEM grid. 5 Figure 7: Two dimensional arrays of Nile Red dye deposited using the present method with Copper TEM grid. Figure 8: (A) Two dimensional arrays of CdCI2 deposited using the present method. (B) An expanded view of A. Figure 9: Two dimensional arrays of polyvinyl pyrrolidone (PVP) on glass deposited using the present method. (A) is deposited using a copper grid. (B) is deposited using a Nickel grid. Figure 10: Optical micrographs of layer-by-layer deposited three dimensional arrays AuNPs (using Nickel TEM grid) on glass slide. Here one layer was deposited over another by the method described in the text. (B) is an expanded view of (A). Figure 11: Optical micrographs of two-dimensional arrays of CdS quantum dots obtained by reaction between CdCI2 and Na2S. (B) is an expanded view of (A). Figure 12: Optical micrographs of two-dimensional cross patterns of arrays of AuNPs on glass generated using the present methods. (A) Two separate deposits were performed one afteranother. (B) Double-grid deposition was used for one-time deposition. Figure 13: Patterns by using a membrane with CdS quantum dots Unlike the prior art the present invention does not use any films. The grids used do not form cells and no charged particles of use of chemical charge for deposition is used. The rigidity of the grids used is also unlike that of prior art. More particularly the process of the present invention is entirely evaporation based and the sidewall of the glass slide on which the process is carried out is not even bounded and no supporting or suspension liquids are used unlike the prior art. Further the TEM grid is not pretreated before its usage. Moreover the application of present method for producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. Additionally the formation of patterns by reaction two species along the TEM grid lines (CdS nanoparticles by reaction between CdCI2 and Na2S) is demonstrated. 6 The method developed by the present inventors has the unique advantage of patterned deposition of molecular and colloidal particles on the substrate surface by evaporation at room temperature where the pattern is guided by the structure of the mask -metallic grid (TEM grid) and the structure is formed by assembly of the materials along the patterned lines. The mask could also be membrane and the deposition pattern in that case follows the porous structure of the membrane. It is a facile, versatile and a general method for the generation of micron and submicron scale patterns of molecular and nanoscale materials assembled on a substrate surface. The primary condition for generating patterns of any materials is that the substance, whose pattern is to be generated, should be soluble or dispersible in a volatile liquid like water and toluene. The substances, the patterns of which can be generated are nanoscale particles of metal such as gold (Au), silver (Ag) and copper (Cu) or other metal nanoparticles that are dispersible in a volatile solvent and semiconductors such as CdS, Mn2+ doped CdS and ZnS or other semiconductor nanoparticles that are dispersible in a volatile solvent, solutions of single molecules such as an organic dye (Rhodamine B, Nile Red), solution of inorganic materials such as CdCI2, solution/dispersion of polymers like polyvinyl pyrrolidone (PVP), or other polymers that are soluble or dispersible in a volatile solvent. The droplets of these solutions / dispersions, upon evaporation in the presence of a metallic grid mask such as a transmission electron microscope (TEM) grid, lead to the deposition of patterned assembly of molecular and nanoscale materials on the surface of glass slides (substrates) where the droplets were placed. The pattern of the assembly follow that of the TEM grid with dimensions of lines far reduced than those of the TEM grids. Smaller lines and arrays may be deposited using membrane as mask for deposition where the deposited pattern follows the pattern of the porous structure as shown in Figure 13 According to a preferred aspect the method produces layer-by-layer three-dimensional deposition of assembled materials on the substrate surface. The patterns of the second layer of deposition can be made at a chosen angle to that of the first layer patterns. 7 The materials of the second layer is same or different from that of the first layer. For example, when the first layer of patterned deposition is made of assembly of metal nanoparticles, the second layer is of semiconductor nanoparticles (quantum dots). If the first patterned layer is made of a reactant the second patterned layer is made of a second reactant, where the second reactant reacts with the first one at the overlapping regions and produces the product at the intersections, which constitute the reaction sites. Hence, present invention of patterns generation by restricted evaporation using a TEM grid or any other similar mask opens a new approach to the growth of organized multidimensional arrays of colloidal particles in general. The present invention reveals the versatility of the simple evaporation process for aligning nanometer-to-micrometer- sized objects. The striking simplicity of the present restricted evaporation process finds use in the fabrication of biological devices, semiconductors and other electronic devices. This facile method of arranging particles in two and three - dimensional arrays is considered as a general method of patterned deposition of particles of various sizes and nature. The method may be used as basis for higher hierarchical device structures and opens up the possibility of making large-scale electronic devices with individually addressable nanoscopic and or molecular components. The details of the method are mentioned below. The potential applications of this simple method range from optoelectronic devices to micro and nano arrays of DNA, proteins etc. The principle behind this new technique is to evaporate a droplet of the solution (dispersion) containing the materials, of which pattern is to be generated, placed on a substrate surface (flat) in the presence of a metallic grid mask placed on top of the droplet. The invention is now defined by way of following non-limiting illustrative examples: 8 Grids used in the examples Commercially available TEM grid is used as the metallic grid mask. TEM grids are used are made of copper or nickel metals. The grids made of copper had regular arrays of rectangular openings of 45 micron x 45 micron with the metallic arms of the rectangle having dimensions of 45 microns x 5 microns (Figure 1a). Overall, the grid is circular with a diameter of about 3 mm. On the other hand, the grids made of nickel has regular arrays of rectangular openings of 100 micron x100 micron with the metallic arms of the rectangle having dimensions of 100 microns x 10 microns (Figure 1b). Overall, the grid is circular with a diameter of about 3 mm. More than one such grids may be attached and used together. Example 1 The present example demonstrates generation of patterned structures of AuNPs on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then air-dried. A colloidal solution of Au nanoparticles is prepared by treating 5 mL aqueous HAuCI4 (0.1 mM) with 1 mM of NaBH4. A drop (20 uL) of an aqueous solution of the colloidal Au nanoparticles is then placed onto the glass slide. A TEM copper grid is then placed carefully onto the drop such that the grid stays on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide are minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy, atomic force microscopy, scanning electron microscopy etc. The details of the micrographs are shown in Figures 3, 4, 5a and 5b. These two dimensional arrays are 0.4-0.6 micron in height with a width of 4-6 micron. When the above evaporation is carried out in the presence of a commercially available IR light lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 2 micron instead of 4-6 micron) and the evaporation process is completed in 10 min instead of 30 min. 9 Example 2 The present example demonstrates generation of patterned structures of Rhodamine B dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then air-dried. An aqueous solution of Rhodamine B dye was prepared by dissolving 100 uL of 0.1 M dye in 10 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of the Rhodamine B dye was then placed onto the glass slide. A TEM copper / nickel grid was then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 6. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. Example 3 This example demonstrates generation of patterned structures of Nile Red dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. An aqueous solution of Nile Red dye is prepared by dissolving 0.1 mg of the dye in 5ml of toluene. A drop (20 uL) of an aqueous solution of the Nile Red dye is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed.The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 7. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines were thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. 10 Example 4 The present example demonstrates generation of patterned structures of CdCI2 on a substrate surface. A glass microscope slide of size 1 cm x 1 cm was first cleaned by ethanol solution and then dried. An aqueous solution of 1.1 x 10-4 M of CdCI2 is prepared. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min using such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 8. When the above evaporation was carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. Example 5 The present example demonstrates generation of patterned structures of PVP on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. An aqueous solution of PVP is prepared by dissolving 15 mg of PVP in 2 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of PVP is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid holds its position on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 9. When the above evaporation is carried out in the presence of a commercially available IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is completed in 10 min instead of 30 min. 11 The above methods provide two-dimensional micron line patterns, consisting of arrays of colloidal particles, on glass substrate surfaces. As can be seen from the figures there are three kinds of deposits as results of evaporation under the above conditions. They are as follows: (a) Single line deposits of materials along the TEM grid lines with thickness on the order of 6.01 microns. These lines have typical heights on the order of 0.45 microns on the substrate (glass) surface. (Figures 3A and 3B) (b) Double line deposits of materials (with a spacing of 20 micron) along the TEM grid lines with thickness on the order of 2 micron or less. These lines have typical heights on the order of 1 micron. (Figure 5a) (c) Plate -like continuous deposits of materials along the TEM grid lines with thickness on the order of 4 microns or less. These plates have typical heights on the order of 1 micron. (Figures8A, 8B.9A, 9B, 6) Example 6 The, deposition of two layers of patterned materials one on top of the other is demonstrated as follows. The first layer of material (Au nanoparticles) is deposited on a glass slide as mentioned above using a TEM grid on top of a drop of an aqueous solution of AuNPs. When the deposited material is completely dried in 30 min (after removal of the grid) another drop of the same solution is again placed at the place where the original drop was there (that led to the formation of first grid patterns). A TEM grid is likewise placed on top of this drop followed by evaporation of the same. The process finally led to the formation of double-layered patterns where one layer of patterned deposits is placed on top of a previous layer of patterned deposits. The deposition of the first patterned layer is same (similar) as those described earlier. The deposition of the second patterned layer is typically thinner than the first layer. In other words, the lines corresponding to the patterned deposition are comparatively slimmer and height smaller with typical width of 0.8 micron. However, the patterns of the lines followed those of the TEM grid metal lines as with the first layer. The relative orientation and position of the lines of the first and second layers are decided by the 12 relative orientation of the TEM grid at the time of the first layer deposition and that during the second layer. The details of the micrographs are shown in Figure 10. Example 7 The present example demonstrates generation of patterned structures of CdS quantum dots on a substrate surface by reaction. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. Aqueous solutions of 1.1 x 10-4 M of CdCI2 and 0.01 M Na2S is prepared in Milli-Q water. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully (using a pair of forceps) onto the drop such that the grid stays on the drop. A schematic view of the method of pattern generation is shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min using a pair of forceps such that the structures imprinted on the slide is minimally disturbed. Then, a drop (20 uL) of an aqueous solution of Na2S is placed on the patterned structures of CdCI2. CdS quantum dots are produced at the overlapping regions where reaction occurs between them. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 11. Example 8 This example demonstrates generation of patterned structures using two grids together. A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and then dried. A droplet of an aqueous solution containing the colloidal particles (Au NPs or and any other solute/dispersed particles) is placed on the glass slide. Two TEM copper / nickel grids attached to each other such that their grid lines are at an angle, are then placed carefully onto the drop such that the grids hold their position on the drop. A schematic view of the method of pattern generation is similar to the one shown in Figure 2. The drop along with the two TEM grids is then left to evaporate at 300°C for 30 min. The grids are then lifted after 30 min such that the structures imprinted on the slide is minimally disturbed. The structure imprinted on the slide is then investigated using optical microscopy. The details of the micrographs are shown in Figure 12. 13 The main advantages of the present invention are: 1. The present invention is simplel in generating highly reproducible predetermined patterned deposits with the help of natural forces (capillary forces) only. The method does not require any additional physical force such as light (photolithography), pressure on the mold (soft lithography), high energy electrons (electron beam lithography), ions (ion beam lithography) etc. 2. It provides patterned deposits, of molecular, nanoscale and microscale materials, on a substrate surface with the resultant assembly of the precursor materials. 3. The patterns can be controlled by controlling the dimensions of the TEM grid. The sizes of the grid lines and holes and the nature of the patterns that makes up the grid guide the pattern that is deposited on the substrate surface. 4. The dimensions of the deposited patterns are scalable and thus the method has unique advantage. 5. The method allows layer-by-layer patterned depositions of materials, where the resulting depositions could be made of same or two different materials that allow combination of patterned depositions. 6. The method offers depositions of two reactive agents one after the other where the product of the reaction results in the formation of specific depositions at the intersections of the deposition in the case of two-layer depositions. 14 We claim 1. A method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising : i) providing solution/dispersion of said material in a volatile solvent on a flat surface; ii) placing at least one mask on droplet of said solution/dispersion; iii) exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask; iv) depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; v) removing the mask without disturbing the pattern formed along the mask. 2. The method as claimed in claim 1 wherein the mask is selected from metallic grids and plastic membrane. 3. The method as claimed in claim 2 wherein when the mask is metallic grid and the deposition of the material occurs along the pattern lines of the grid. 4. The method as claimed in claim 3 wherein the metallic grids used are TEM grids selected from copper and nickel grid. 5. The method as claimed in claim 3 wherein two metallic grids are simultaneously used being attached to one another at defined angle. 6. The method as claimed in claim 2 wherein when the mask is plastic membrane the deposition occurs along the pattern formed by the pores of the membrane. 7. The method as claimed in any preceding claim wherein the restricted evaporation is carried out at 300° C 15 8. The method as claimed in any preceding claims wherein the restriction evaporation occurs for 30 minutes. 9. The method as claimed in any preceding claim wherein the flat substrate is glass slide. 10. The method as claimed in any preceding claim wherein the material to be deposited which is provided in solution/dispersion is selected from molecular materials, nanoscale particles of metals, quantum dots, and inorganic materials. 11. The method a claimed in claim 9 wherein the molecular material is selected from Rhodamine B dye, Nile Red dye and the like. 12. The method a claimed in claim 9 wherein the nanoscale particles of metals are selected from Au NPs, Ag NPs, Cu NPs and other metal nano particles soluble in volatile solvent. 13. The method a claimed in claim 9 wherein the quantum dots are selected frm CdS, Mn2+ doped CdS, and other semiconductor nanoparticles dispersible in volatile solvent. 14. The method a claimed in claim 9 wherein the inorganic materials are selected from CdCI2, polyvenyl pyrrolidone and other polymers soluble in volatile solvent. 15. The method as claimed in any of claims 1 to 5 and 7 to 14 wherein the line widths of the deposits formed ranges from submicron to a few microns. 16. The method as claimed in any of claims 1 to 5 and 7 to 15 wherein the height of the line of deposits formed is around 0.4-0.6 micron. 17. The method as claimed in any of claims 1 to 5 and 7 to 16 wherein the patterns deposited on the substrate surface are selected from single line deposits, double line deposits and plate-like deposits depending on the evaporation process. 16 17 18. The method as claimed in claim 1 optionally comprising evaporation in presence of commercially available IR lamp to provide distinct pattern and thinner lines of deposition. 19. The method as claimed in any of claims 1 to 5 and 7 to 18 wherein two layers of patterned deposit comprising first and second material are deposited one above the other. 20. The method as claimed in claim 19 wherein the first and the second materials deposited are selected from the same material deposited twice, different materials, and two reagents which react chemically to produce a third product at the intersections of the grid-line-like deposits. 21. The method as claimed in any of claims 19 to 20 wherein the first layer and second layer are deposited at defined angle to each other. 22. The method as claimed in any of claim 1to 5 and 7 to 18 wherein overall dimensions of the total deposited patterns are scalable as per the dimensions of the metallic grid. A method of formation of lithographic pattern of micron and submicron scale of molecular and nanoscale materials assembled on a flat substrate surface, said method comprising providing solution/dispersion of said material in a volatile solvent on a flat surface;placing at least one mask on droplet of said solution/dispersion;exposing to restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in presence of the mask;depositing at least one layer of patterned assembly of molecular and nanoscale material on the substrate along position of the mask; removing the mask without disturbing the pattern formed along the mask. The process is entirely evaporation based producing patterns of colloidal particles ranging from nanoparticles, quantum dots, single molecules to polymers in aqueous and organic solvents. The process also includes formation of patterns of more than one layer including reaction of two species along the TEM grid lines (mask).

Full Text

Field of Invention
The present invention relates to lithographic pattern formation upon evaporation of a
liquid drop containing solute (molecules) or dispersed particles, referred herein as
Evaporation Induced Lithography. More particularly the process of the present invention
is entirely evaporation based producing patterns of colloidal particles ranging from
nanoparticles, quantum dots, single molecules to polymers in aqueous and organic
solvents. The process also includes formation of patterns of more than one layer
including reaction of two species along the TEM grid lines
Background and Prior Art
Jumping Zhang, Yan Liu, Yonggang Ke, and Hao Yan Nano Letters,2006, teaches
organization of periodic square-like gold nanoparticles arrays, templated by self
assembled two dimension DNA nanogrids on a surface. Reference of lithographically
patterned devices of nanocrystals can be found in Yi Cui, Mikael T. Bjork, J.Alexander
Liddle, Carsten Sonnichsen, Benjamin Boussert, and A. Paul Alivisatos, Nano
Letters, 2004. Further, Richard D. Piner, Jin Zhu, Feng Xu, Seunghun Hong,Chad A.
Mirkin Science. 1999, teaches the development of a direct-write "dippen"nanolithography
(DPN) to deliver molecules in a positive printing mode. An atomic force microscope
(AFM) tip was used to write alkanethiols with 30-nanometer linewidth resolution on a
gold thin film in a manner analogous to that of a dip-pen. Molecules are delivered from
the AFM tip to a solid substrate of interest via capillary transport, making DPN a
potentially useful tool for creating and functionalizing nanoscale devices.
Site-specific fabrication of organic, inorganic, and hybrid solid-state nanostructures
though a novel combination of electron beam lithography (eBL) and spin coating of liquid
and sol-gel precursors, termed as soft eBL were discussed in Suresh Dontu, Zixiao Pan,
Benjamin Myers, Gajendra Shekhawat, Nianqiang Wu, and Vinayak Dravid Nano
Letters. 2005, Younan Xia, George M. Whitesides Angewandte Chemie. 1998, teaches
the process of softlithography using elastomeric stamps and molds . Maria-Victoria Meli,
Antonella Badia, Peter Grutter, and R. Bruce Lennox, Nano Letters 2002, discusses a
methodology to create nanometer-scale patterns with a diblock copolymer mask with an
intrinsic topological nanopattern. It is described in Bartosz A. Grzybowski, Kyle J. M.
Bishop, Christopher J. Campbell, Marcin Fialkowski and Stoyan K. Smoukov Soft Matter.
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2005, that an experimental method that allows precise control of reaction-diffusion
processes at small scales based on two - dimensional microgeometries from which
reactions are initiated; and provide a facile route to complex micro- and nano-structures.
A review on colloidal lithography by Seung-Man Yang, Se Gyu Jang, Dae-Geun Choi,
Sarah Kim, and Hyung Kyun Yu Small. 2006, where self-assembly of colloids and the
spontaneous formation of well-ordered colloidal arrays is discussed. The review
presents the versatility of the self assembled colloidal masks in fabricating novel
nanopatterns such as nanocups, hollow shells, and multifaceted materials.
US 7,018,944 describes a method for generating a mask: having a nanoscale pattern,
the method comprises a suspension liquid (containing periodically arranged objects),
being placed on top of a supporting liquid that is placed on a substrate surface. The
periodic arrangement of the objects in the suspension liquid has to be maintained over a
given area using the apparatus. These ordered objects in the suspension create a mask
and deposit a material through interstices contained in the mask so as to create a
pattern on the substrate. The deposition of the material is carried out by one of the
processes like sputtering, evaporation and spraying of a colloidal solution. It does not
have the rigidity of the grid in depositing patterns.
Further, the primary aim of the above patent is to organize particles on a substrate by
placing the original particles on a liquid, which upon drainage leads to arrangement of
the particles on the substrate surface. In this way layer of particles are arranged on the
substrate surface based on their natural separation depending on the diameters of the
particles. In addition, depositions of materials in the interstices of the particles followed
by removal of the particles generate patterns of the new materials.
US 6,709,929 demonstrates a method of selective etching preferably using the
etching template to produce nanoscale patterns. It describes a technique of forming
selfassembled nanoporous anodic aluminum oxide thin films.
Celio et al ("Patterned Assembly of Colloidal particles by Confined Dewetting
Lithography" Langmuir: Vol. 22, No. 26: December 19, 2006, pp 11426- 11435) reports
the assembly of colloidal particles into confined arrangements and patterns on various
cleaned and chemically modified solid substrates using a method which the term
3

authors term as"confined dewetting lithography". It teaches use of functionalized
substrate surfaces with positively charge materials so that negatively charge polystyrene
spheres could be better deposited. This art teaches use of polystyrene spheres of
micrometer sizes to deposit the same in patterned formats as per the pattern of the grid
(which is a cell) on ITO/glass and Si/SiO2 surfaces.
The drawbacks of the prior art methods of lithography is one or more of the following: (a)
they are limited by the diffraction wavelength of light (photolithography); (b the pattern
formation could be made on specific substrates and requires high vacuum conditions
(electron and ion beam lithography or X-ray lithography); (c) the speed of writing any
particular high-resolution large scale structure is very low (dip-pen lithography); (d) the
structures obtained by the conventional method (soft lithography) have either low
resolution or are not applicable to a large set of materials constituting the structure; (e)
there is no systematic way of controlling the patterns of structures especially at the large
scale and those that are not formed by reaction diffusion (pattern formation by reaction
diffusion waves); (f) there is limited flexibility in terms of various pattern formation or
systematic pattern generation (nanosphere lithography); (g) organized single-molecule
patterns on substrates are either not possible or difficult to achieve, (h) does not have
rigidity of the grids in depositing patterns.
Thus there is need for a fast, efficient single method where colloidal particles or solute
particles can be systematically patterned on substrate surfaces, and the nature of the
patterns can be controlled by external parameters and also layer-by-layer deposition of
patterned structures could be obtained.
Objects of Invention
Thus the main objective of the present invention is to generate scalable patterned
assembly of colloidal particles and molecular materials deposited on a substrate surface
such as glass slides by evaporating a liquid drop, containing the colloidal particles or
molecular materials, onto which a metallic grid mask (TEM grid) is placed for guided
pattern formation.
4

Summary of Invention
According to main aspect of the present invention there is provided a method of
formation of lithographic pattern of micron and submicron scale of molecular and
nanoscale materials assembled on a flat substrate surface, said method comprising:
i) providing solution/dispersion of said material in a volatile solvent on a flat
surface;
ii) placing at least one mask on droplet of said solution/dispersion;
iii) exposing to restricted evaporation at temperature of 30°C of droplet of said
solution/dispersion in presence of the mask;,
iv) depositing at least one layer of patterned assembly of molecular and
nanoscale material on the substrate along position of the mask;
i) removing the mask without disturbing the pattern formed along the mask
Detailed Description Of Invention
Brief description of the accompanying drawings
Figure 1a: Optical micrograph of a metallic (TEM) Grid (Copper).
Figure 1b: Optical micrograph of a metallic (TEM) Grid (Nickel).
Figure 2: Schematic of a drop evaporating in a restricted geometry used in the present
method of pattern generation.
Figure 3: Optical micrographs of (A) deposits of two-dimensional arrays of AuNPs (using
Copper TEM grid) on glass slide. (B) An expanded view of (A).
Figure 4: AFM image of the pattern of the two dimensional arrays of AuNPs (using
Nickel TEM grid).
Figure 5a: : Two dimensional arrays of of AuNPs (using Nickel TEM grid).).
Figure 5b: EDX of the pattern of two dimensional arrays of AuNPs (using Nickel TEM
grid).
Figure 6: Two dimensional arrays of Rhodamine B dye generated using the present
method with Copper TEM grid.
5

Figure 7: Two dimensional arrays of Nile Red dye deposited using the present method
with Copper TEM grid.
Figure 8: (A) Two dimensional arrays of CdCI2 deposited using the present method.
(B) An expanded view of A.
Figure 9: Two dimensional arrays of polyvinyl pyrrolidone (PVP) on glass deposited
using the present method.
(A) is deposited using a copper grid.
(B) is deposited using a Nickel grid.
Figure 10: Optical micrographs of layer-by-layer deposited three dimensional arrays
AuNPs (using Nickel TEM grid) on glass slide. Here one layer was deposited over
another by the method described in the text. (B) is an expanded view of (A).
Figure 11: Optical micrographs of two-dimensional arrays of CdS quantum dots obtained
by reaction between CdCI2 and Na2S. (B) is an expanded view of (A).
Figure 12: Optical micrographs of two-dimensional cross patterns of arrays of AuNPs on
glass generated using the present methods. (A) Two separate deposits were performed
one afteranother. (B) Double-grid deposition was used for one-time deposition.
Figure 13: Patterns by using a membrane with CdS quantum dots
Unlike the prior art the present invention does not use any films. The grids used do not
form cells and no charged particles of use of chemical charge for deposition is used. The
rigidity of the grids used is also unlike that of prior art. More particularly the process of
the present invention is entirely evaporation based and the sidewall of the glass slide on
which the process is carried out is not even bounded and no supporting or suspension
liquids are used unlike the prior art. Further the TEM grid is not pretreated before its
usage. Moreover the application of present method for producing patterns of colloidal
particles ranging from nanoparticles, quantum dots, single molecules to polymers in
aqueous and organic solvents. Additionally the formation of patterns by reaction two
species along the TEM grid lines (CdS nanoparticles by reaction between CdCI2 and
Na2S) is demonstrated.
6

The method developed by the present inventors has the unique advantage of patterned
deposition of molecular and colloidal particles on the substrate surface by evaporation at
room temperature where the pattern is guided by the structure of the mask -metallic grid
(TEM grid) and the structure is formed by assembly of the materials along the patterned
lines. The mask could also be membrane and the deposition pattern in that case follows
the porous structure of the membrane.
It is a facile, versatile and a general method for the generation of micron and submicron
scale patterns of molecular and nanoscale materials assembled on a substrate surface.
The primary condition for generating patterns of any materials is that the substance,
whose pattern is to be generated, should be soluble or dispersible in a volatile liquid like
water and toluene. The substances, the patterns of which can be generated are
nanoscale particles of metal such as gold (Au), silver (Ag) and copper (Cu) or other
metal nanoparticles that are dispersible in a volatile solvent and semiconductors such as
CdS, Mn2+ doped CdS and ZnS or other semiconductor nanoparticles that are
dispersible in a volatile solvent, solutions of single molecules such as an organic dye
(Rhodamine B, Nile Red), solution of inorganic materials such as
CdCI2, solution/dispersion of polymers like polyvinyl pyrrolidone (PVP), or other polymers
that are soluble or dispersible in a volatile solvent.
The droplets of these solutions / dispersions, upon evaporation in the presence of a
metallic grid mask such as a transmission electron microscope (TEM) grid, lead to
the deposition of patterned assembly of molecular and nanoscale materials on the
surface of glass slides (substrates) where the droplets were placed. The pattern of the
assembly follow that of the TEM grid with dimensions of lines far reduced than those of
the TEM grids.
Smaller lines and arrays may be deposited using membrane as mask for deposition
where the deposited pattern follows the pattern of the porous structure as shown in
Figure 13
According to a preferred aspect the method produces layer-by-layer three-dimensional
deposition of assembled materials on the substrate surface. The patterns of the second
layer of deposition can be made at a chosen angle to that of the first layer patterns.
7

The materials of the second layer is same or different from that of the first layer. For
example, when the first layer of patterned deposition is made of assembly of metal
nanoparticles, the second layer is of semiconductor nanoparticles (quantum dots).
If the first patterned layer is made of a reactant the second patterned layer is made of a
second reactant, where the second reactant reacts with the first one at the overlapping
regions and produces the product at the intersections, which constitute the reaction
sites.
Hence, present invention of patterns generation by restricted evaporation using a TEM
grid or any other similar mask opens a new approach to the growth of organized
multidimensional arrays of colloidal particles in general. The present invention reveals
the versatility of the simple evaporation process for aligning nanometer-to-micrometer-
sized objects.
The striking simplicity of the present restricted evaporation process finds use in the
fabrication of biological devices, semiconductors and other electronic devices. This facile
method of arranging particles in two and three - dimensional arrays is considered as a
general method of patterned deposition of particles of various sizes and nature. The
method may be used as basis for higher hierarchical device structures and opens up the
possibility of making large-scale electronic devices with individually addressable
nanoscopic and or molecular components.
The details of the method are mentioned below. The potential applications of this
simple method range from optoelectronic devices to micro and nano arrays of DNA,
proteins etc.
The principle behind this new technique is to evaporate a droplet of the solution
(dispersion) containing the materials, of which pattern is to be generated, placed on a
substrate surface (flat) in the presence of a metallic grid mask placed on top of the
droplet.
The invention is now defined by way of following non-limiting illustrative examples:
8

Grids used in the examples
Commercially available TEM grid is used as the metallic grid mask. TEM grids are used
are made of copper or nickel metals. The grids made of copper had regular arrays of
rectangular openings of 45 micron x 45 micron with the metallic arms of the rectangle
having dimensions of 45 microns x 5 microns (Figure 1a). Overall, the grid is circular
with a diameter of about 3 mm.
On the other hand, the grids made of nickel has regular arrays of rectangular openings
of 100 micron x100 micron with the metallic arms of the rectangle having dimensions of
100 microns x 10 microns (Figure 1b). Overall, the grid is circular with a diameter of
about 3 mm.
More than one such grids may be attached and used together.
Example 1
The present example demonstrates generation of patterned structures of AuNPs on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then air-dried. A colloidal solution of Au nanoparticles is prepared
by treating 5 mL aqueous HAuCI4 (0.1 mM) with 1 mM of NaBH4. A drop (20 uL) of an
aqueous solution of the colloidal Au nanoparticles is then placed onto the glass slide. A
TEM copper grid is then placed carefully onto the drop such that the grid stays on the
drop. A schematic view of the method of pattern generation is shown in Figure 2. The
drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is
then lifted after 30 min such that the structures imprinted on the slide are minimally
disturbed. The structure imprinted on the slide is then investigated using optical
microscopy, atomic force microscopy, scanning electron microscopy etc. The details of
the micrographs are shown in Figures 3, 4, 5a and 5b. These two dimensional arrays are
0.4-0.6 micron in height with a width of 4-6 micron. When the above evaporation is
carried out in the presence of a commercially available IR light lamp (commercial 150
watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line
width of 2 micron instead of 4-6 micron) and the evaporation process is completed in 10
min instead of 30 min.
9

Example 2
The present example demonstrates generation of patterned structures of Rhodamine B
dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned
by ethanol solution and then air-dried. An aqueous solution of Rhodamine B dye was
prepared by dissolving 100 uL of 0.1 M dye in 10 mL of Milli-Q water. A drop (20 uL) of
an aqueous solution of the Rhodamine B dye was then placed onto the glass slide. A
TEM copper / nickel grid was then placed carefully onto the drop such that the grid holds
its position on the drop. A schematic view of the method of pattern generation is shown
in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30
min. The grid is then lifted after 30 min such that the structures imprinted on the slide is
minimally disturbed. The structure imprinted on the slide is then investigated using
optical microscopy. The details of the micrographs are shown in Figure 6. When the
above evaporation is carried out in the presence of a commercially available IR lamp
(commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are
thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is
completed in 10 min instead of 30 min.
Example 3
This example demonstrates generation of patterned structures of Nile Red dye on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then dried. An aqueous solution of Nile Red dye is prepared by
dissolving 0.1 mg of the dye in 5ml of toluene. A drop (20 uL) of an aqueous solution of
the Nile Red dye is then placed onto the glass slide. A TEM copper / nickel grid is then
placed carefully onto the drop such that the grid holds its position on the drop. A
schematic view of the method of pattern generation is shown in Figure 2. The drop along
with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted
after 30 min such that the structures imprinted on the slide is minimally disturbed.The
structure imprinted on the slide is then investigated using optical microscopy. The details
of the micrographs are shown in Figure 7.
When the above evaporation is carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines were thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
10

Example 4
The present example demonstrates generation of patterned structures of CdCI2 on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm was first cleaned by
ethanol solution and then dried. An aqueous solution of 1.1 x 10-4 M of CdCI2 is
prepared. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass
slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid
holds its position on the drop. A schematic view of the method of pattern generation is
shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C
for 30 min. The grid is then lifted after 30 min using such that the structures imprinted on
the slide is minimally disturbed. The structure imprinted on the slide is then investigated
using optical microscopy. The details of the micrographs are shown in Figure 8.
When the above evaporation was carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
Example 5
The present example demonstrates generation of patterned structures of PVP on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then dried. An aqueous solution of PVP is prepared by dissolving
15 mg of PVP in 2 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of PVP is
then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto
the drop such that the grid holds its position on the drop. A schematic view of the
method of pattern generation is shown in Figure 2. The drop along with the TEM grid is
then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that
the structures imprinted on the slide is minimally disturbed. The structure imprinted on
the slide is then investigated using optical microscopy. The details of the micrographs
are shown in Figure 9.
When the above evaporation is carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
11

The above methods provide two-dimensional micron line patterns, consisting of arrays of
colloidal particles, on glass substrate surfaces. As can be seen from the figures there
are three kinds of deposits as results of evaporation under the above conditions. They
are as follows:
(a) Single line deposits of materials along the TEM grid lines with thickness on the
order of 6.01 microns. These lines have typical heights on the order of 0.45
microns on the substrate (glass) surface. (Figures 3A and 3B)
(b) Double line deposits of materials (with a spacing of 20 micron) along the TEM
grid lines with thickness on the order of 2 micron or less. These lines have typical
heights on the order of 1 micron. (Figure 5a)
(c) Plate -like continuous deposits of materials along the TEM grid lines with
thickness on the order of 4 microns or less. These plates have typical heights on
the order of 1 micron. (Figures8A, 8B.9A, 9B, 6)
Example 6
The, deposition of two layers of patterned materials one on top of the other is
demonstrated as follows.
The first layer of material (Au nanoparticles) is deposited on a glass slide as mentioned
above using a TEM grid on top of a drop of an aqueous solution of AuNPs. When the
deposited material is completely dried in 30 min (after removal of the grid) another drop
of the same solution is again placed at the place where the original drop was there (that
led to the formation of first grid patterns). A TEM grid is likewise placed on top of this
drop followed by evaporation of the same. The process finally led to the formation of
double-layered patterns where one layer of patterned deposits is placed on top of a
previous layer of patterned deposits. The deposition of the first patterned layer is same
(similar) as those described earlier.
The deposition of the second patterned layer is typically thinner than the first layer. In
other words, the lines corresponding to the patterned deposition are comparatively
slimmer and height smaller with typical width of 0.8 micron. However, the patterns of the
lines followed those of the TEM grid metal lines as with the first layer. The relative
orientation and position of the lines of the first and second layers are decided by the
12

relative orientation of the TEM grid at the time of the first layer deposition and that during
the second layer. The details of the micrographs are shown in Figure 10.
Example 7
The present example demonstrates generation of patterned structures of CdS quantum
dots on a substrate surface by reaction. A glass microscope slide of size 1 cm x 1 cm is
first cleaned by ethanol solution and then dried. Aqueous solutions of 1.1 x 10-4 M of
CdCI2 and 0.01 M Na2S is prepared in Milli-Q water. A drop (20 uL) of an aqueous
solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then
placed carefully (using a pair of forceps) onto the drop such that the grid stays on the
drop. A schematic view of the method of pattern generation is shown in Figure 2. The
drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is
then lifted after 30 min using a pair of forceps such that the structures imprinted on the
slide is minimally disturbed. Then, a drop (20 uL) of an aqueous solution of Na2S is
placed on the patterned structures of CdCI2. CdS quantum dots are produced at the
overlapping regions where reaction occurs between them. The structure imprinted on the
slide is then investigated using optical microscopy. The details of the micrographs are
shown in Figure 11.
Example 8
This example demonstrates generation of patterned structures using two grids together.
A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and
then dried. A droplet of an aqueous solution containing the colloidal particles (Au NPs or
and any other solute/dispersed particles) is placed on the glass slide. Two TEM copper /
nickel grids attached to each other such that their grid lines are at an angle, are then
placed carefully onto the drop such that the grids hold their position on the drop. A
schematic view of the method of pattern generation is similar to the one shown in Figure
2. The drop along with the two TEM grids is then left to evaporate at 300°C for 30 min.
The grids are then lifted after 30 min such that the structures imprinted on the slide is
minimally disturbed. The structure imprinted on the slide is then investigated using
optical microscopy. The details of the micrographs are shown in Figure 12.
13

The main advantages of the present invention are:
1. The present invention is simplel in generating highly reproducible predetermined
patterned deposits with the help of natural forces (capillary forces) only. The method
does not require any additional physical force such as light (photolithography), pressure
on the mold (soft lithography), high energy electrons (electron beam lithography), ions
(ion beam lithography) etc.
2. It provides patterned deposits, of molecular, nanoscale and microscale materials, on a
substrate surface with the resultant assembly of the precursor materials.
3. The patterns can be controlled by controlling the dimensions of the TEM grid. The
sizes of the grid lines and holes and the nature of the patterns that makes up the grid
guide the pattern that is deposited on the substrate surface.
4. The dimensions of the deposited patterns are scalable and thus the method has
unique advantage.
5. The method allows layer-by-layer patterned depositions of materials, where the
resulting depositions could be made of same or two different materials that allow
combination of patterned depositions.
6. The method offers depositions of two reactive agents one after the other where the
product of the reaction results in the formation of specific depositions at the intersections
of the deposition in the case of two-layer depositions.
14

We claim
1. A method of formation of lithographic pattern of micron and submicron scale of
molecular and nanoscale materials assembled on a flat substrate surface, said method
comprising :
i) providing solution/dispersion of said material in a volatile solvent on a flat
surface;
ii) placing at least one mask on droplet of said solution/dispersion;
iii) exposing to restricted evaporation at temperature of 30°C of droplet of said
solution/dispersion in presence of the mask;
iv) depositing at least one layer of patterned assembly of molecular and
nanoscale material on the substrate along position of the mask;
v) removing the mask without disturbing the pattern formed along the mask.
2. The method as claimed in claim 1 wherein the mask is selected from metallic grids
and plastic membrane.
3. The method as claimed in claim 2 wherein when the mask is metallic grid and the
deposition of the material occurs along the pattern lines of the grid.
4. The method as claimed in claim 3 wherein the metallic grids used are TEM grids
selected from copper and nickel grid.
5. The method as claimed in claim 3 wherein two metallic grids are simultaneously
used being attached to one another at defined angle.
6. The method as claimed in claim 2 wherein when the mask is plastic membrane the
deposition occurs along the pattern formed by the pores of the membrane.
7. The method as claimed in any preceding claim wherein the restricted evaporation is
carried out at 300° C
15

8. The method as claimed in any preceding claims wherein the restriction evaporation
occurs for 30 minutes.
9. The method as claimed in any preceding claim wherein the flat substrate is glass
slide.
10. The method as claimed in any preceding claim wherein the material to be deposited
which is provided in solution/dispersion is selected from molecular materials,
nanoscale particles of metals, quantum dots, and inorganic materials.
11. The method a claimed in claim 9 wherein the molecular material is selected from
Rhodamine B dye, Nile Red dye and the like.
12. The method a claimed in claim 9 wherein the nanoscale particles of metals are
selected from Au NPs, Ag NPs, Cu NPs and other metal nano particles soluble in
volatile solvent.
13. The method a claimed in claim 9 wherein the quantum dots are selected frm CdS,
Mn2+ doped CdS, and other semiconductor nanoparticles dispersible in volatile
solvent.
14. The method a claimed in claim 9 wherein the inorganic materials are selected from
CdCI2, polyvenyl pyrrolidone and other polymers soluble in volatile solvent.
15. The method as claimed in any of claims 1 to 5 and 7 to 14 wherein the line widths of
the deposits formed ranges from submicron to a few microns.
16. The method as claimed in any of claims 1 to 5 and 7 to 15 wherein the height of the
line of deposits formed is around 0.4-0.6 micron.
17. The method as claimed in any of claims 1 to 5 and 7 to 16 wherein the patterns
deposited on the substrate surface are selected from single line deposits, double line
deposits and plate-like deposits depending on the evaporation process.
16

17
18. The method as claimed in claim 1 optionally comprising evaporation in presence of
commercially available IR lamp to provide distinct pattern and thinner lines of
deposition.
19. The method as claimed in any of claims 1 to 5 and 7 to 18 wherein two layers of
patterned deposit comprising first and second material are deposited one above the
other.
20. The method as claimed in claim 19 wherein the first and the second materials
deposited are selected from the same material deposited twice, different materials,
and two reagents which react chemically to produce a third product at the
intersections of the grid-line-like deposits.
21. The method as claimed in any of claims 19 to 20 wherein the first layer and second
layer are deposited at defined angle to each other.
22. The method as claimed in any of claim 1to 5 and 7 to 18 wherein overall dimensions
of the total deposited patterns are scalable as per the dimensions of the metallic grid.

Field of Invention
The present invention relates to lithographic pattern formation upon evaporation of a
liquid drop containing solute (molecules) or dispersed particles, referred herein as
Evaporation Induced Lithography. More particularly the process of the present invention
is entirely evaporation based producing patterns of colloidal particles ranging from
nanoparticles, quantum dots, single molecules to polymers in aqueous and organic
solvents. The process also includes formation of patterns of more than one layer
including reaction of two species along the TEM grid lines
Background and Prior Art
Jumping Zhang, Yan Liu, Yonggang Ke, and Hao Yan Nano Letters,2006, teaches
organization of periodic square-like gold nanoparticles arrays, templated by self
assembled two dimension DNA nanogrids on a surface. Reference of lithographically
patterned devices of nanocrystals can be found in Yi Cui, Mikael T. Bjork, J.Alexander
Liddle, Carsten Sonnichsen, Benjamin Boussert, and A. Paul Alivisatos, Nano
Letters, 2004. Further, Richard D. Piner, Jin Zhu, Feng Xu, Seunghun Hong,Chad A.
Mirkin Science. 1999, teaches the development of a direct-write "dippen"nanolithography
(DPN) to deliver molecules in a positive printing mode. An atomic force microscope
(AFM) tip was used to write alkanethiols with 30-nanometer linewidth resolution on a
gold thin film in a manner analogous to that of a dip-pen. Molecules are delivered from
the AFM tip to a solid substrate of interest via capillary transport, making DPN a
potentially useful tool for creating and functionalizing nanoscale devices.
Site-specific fabrication of organic, inorganic, and hybrid solid-state nanostructures
though a novel combination of electron beam lithography (eBL) and spin coating of liquid
and sol-gel precursors, termed as soft eBL were discussed in Suresh Dontu, Zixiao Pan,
Benjamin Myers, Gajendra Shekhawat, Nianqiang Wu, and Vinayak Dravid Nano
Letters. 2005, Younan Xia, George M. Whitesides Angewandte Chemie. 1998, teaches
the process of softlithography using elastomeric stamps and molds . Maria-Victoria Meli,
Antonella Badia, Peter Grutter, and R. Bruce Lennox, Nano Letters 2002, discusses a
methodology to create nanometer-scale patterns with a diblock copolymer mask with an
intrinsic topological nanopattern. It is described in Bartosz A. Grzybowski, Kyle J. M.
Bishop, Christopher J. Campbell, Marcin Fialkowski and Stoyan K. Smoukov Soft Matter.
2

2005, that an experimental method that allows precise control of reaction-diffusion
processes at small scales based on two - dimensional microgeometries from which
reactions are initiated; and provide a facile route to complex micro- and nano-structures.
A review on colloidal lithography by Seung-Man Yang, Se Gyu Jang, Dae-Geun Choi,
Sarah Kim, and Hyung Kyun Yu Small. 2006, where self-assembly of colloids and the
spontaneous formation of well-ordered colloidal arrays is discussed. The review
presents the versatility of the self assembled colloidal masks in fabricating novel
nanopatterns such as nanocups, hollow shells, and multifaceted materials.
US 7,018,944 describes a method for generating a mask: having a nanoscale pattern,
the method comprises a suspension liquid (containing periodically arranged objects),
being placed on top of a supporting liquid that is placed on a substrate surface. The
periodic arrangement of the objects in the suspension liquid has to be maintained over a
given area using the apparatus. These ordered objects in the suspension create a mask
and deposit a material through interstices contained in the mask so as to create a
pattern on the substrate. The deposition of the material is carried out by one of the
processes like sputtering, evaporation and spraying of a colloidal solution. It does not
have the rigidity of the grid in depositing patterns.
Further, the primary aim of the above patent is to organize particles on a substrate by
placing the original particles on a liquid, which upon drainage leads to arrangement of
the particles on the substrate surface. In this way layer of particles are arranged on the
substrate surface based on their natural separation depending on the diameters of the
particles. In addition, depositions of materials in the interstices of the particles followed
by removal of the particles generate patterns of the new materials.
US 6,709,929 demonstrates a method of selective etching preferably using the
etching template to produce nanoscale patterns. It describes a technique of forming
selfassembled nanoporous anodic aluminum oxide thin films.
Celio et al ("Patterned Assembly of Colloidal particles by Confined Dewetting
Lithography" Langmuir: Vol. 22, No. 26: December 19, 2006, pp 11426- 11435) reports
the assembly of colloidal particles into confined arrangements and patterns on various
cleaned and chemically modified solid substrates using a method which the term
3

authors term as"confined dewetting lithography". It teaches use of functionalized
substrate surfaces with positively charge materials so that negatively charge polystyrene
spheres could be better deposited. This art teaches use of polystyrene spheres of
micrometer sizes to deposit the same in patterned formats as per the pattern of the grid
(which is a cell) on ITO/glass and Si/SiO2 surfaces.
The drawbacks of the prior art methods of lithography is one or more of the following: (a)
they are limited by the diffraction wavelength of light (photolithography); (b the pattern
formation could be made on specific substrates and requires high vacuum conditions
(electron and ion beam lithography or X-ray lithography); (c) the speed of writing any
particular high-resolution large scale structure is very low (dip-pen lithography); (d) the
structures obtained by the conventional method (soft lithography) have either low
resolution or are not applicable to a large set of materials constituting the structure; (e)
there is no systematic way of controlling the patterns of structures especially at the large
scale and those that are not formed by reaction diffusion (pattern formation by reaction
diffusion waves); (f) there is limited flexibility in terms of various pattern formation or
systematic pattern generation (nanosphere lithography); (g) organized single-molecule
patterns on substrates are either not possible or difficult to achieve, (h) does not have
rigidity of the grids in depositing patterns.
Thus there is need for a fast, efficient single method where colloidal particles or solute
particles can be systematically patterned on substrate surfaces, and the nature of the
patterns can be controlled by external parameters and also layer-by-layer deposition of
patterned structures could be obtained.
Objects of Invention
Thus the main objective of the present invention is to generate scalable patterned
assembly of colloidal particles and molecular materials deposited on a substrate surface
such as glass slides by evaporating a liquid drop, containing the colloidal particles or
molecular materials, onto which a metallic grid mask (TEM grid) is placed for guided
pattern formation.
4

Summary of Invention
According to main aspect of the present invention there is provided a method of
formation of lithographic pattern of micron and submicron scale of molecular and
nanoscale materials assembled on a flat substrate surface, said method comprising:
i) providing solution/dispersion of said material in a volatile solvent on a flat
surface;
ii) placing at least one mask on droplet of said solution/dispersion;
iii) exposing to restricted evaporation at temperature of 30°C of droplet of said
solution/dispersion in presence of the mask;,
iv) depositing at least one layer of patterned assembly of molecular and
nanoscale material on the substrate along position of the mask;
i) removing the mask without disturbing the pattern formed along the mask
Detailed Description Of Invention
Brief description of the accompanying drawings
Figure 1a: Optical micrograph of a metallic (TEM) Grid (Copper).
Figure 1b: Optical micrograph of a metallic (TEM) Grid (Nickel).
Figure 2: Schematic of a drop evaporating in a restricted geometry used in the present
method of pattern generation.
Figure 3: Optical micrographs of (A) deposits of two-dimensional arrays of AuNPs (using
Copper TEM grid) on glass slide. (B) An expanded view of (A).
Figure 4: AFM image of the pattern of the two dimensional arrays of AuNPs (using
Nickel TEM grid).
Figure 5a: : Two dimensional arrays of of AuNPs (using Nickel TEM grid).).
Figure 5b: EDX of the pattern of two dimensional arrays of AuNPs (using Nickel TEM
grid).
Figure 6: Two dimensional arrays of Rhodamine B dye generated using the present
method with Copper TEM grid.
5

Figure 7: Two dimensional arrays of Nile Red dye deposited using the present method
with Copper TEM grid.
Figure 8: (A) Two dimensional arrays of CdCI2 deposited using the present method.
(B) An expanded view of A.
Figure 9: Two dimensional arrays of polyvinyl pyrrolidone (PVP) on glass deposited
using the present method.
(A) is deposited using a copper grid.
(B) is deposited using a Nickel grid.
Figure 10: Optical micrographs of layer-by-layer deposited three dimensional arrays
AuNPs (using Nickel TEM grid) on glass slide. Here one layer was deposited over
another by the method described in the text. (B) is an expanded view of (A).
Figure 11: Optical micrographs of two-dimensional arrays of CdS quantum dots obtained
by reaction between CdCI2 and Na2S. (B) is an expanded view of (A).
Figure 12: Optical micrographs of two-dimensional cross patterns of arrays of AuNPs on
glass generated using the present methods. (A) Two separate deposits were performed
one afteranother. (B) Double-grid deposition was used for one-time deposition.
Figure 13: Patterns by using a membrane with CdS quantum dots
Unlike the prior art the present invention does not use any films. The grids used do not
form cells and no charged particles of use of chemical charge for deposition is used. The
rigidity of the grids used is also unlike that of prior art. More particularly the process of
the present invention is entirely evaporation based and the sidewall of the glass slide on
which the process is carried out is not even bounded and no supporting or suspension
liquids are used unlike the prior art. Further the TEM grid is not pretreated before its
usage. Moreover the application of present method for producing patterns of colloidal
particles ranging from nanoparticles, quantum dots, single molecules to polymers in
aqueous and organic solvents. Additionally the formation of patterns by reaction two
species along the TEM grid lines (CdS nanoparticles by reaction between CdCI2 and
Na2S) is demonstrated.
6

The method developed by the present inventors has the unique advantage of patterned
deposition of molecular and colloidal particles on the substrate surface by evaporation at
room temperature where the pattern is guided by the structure of the mask -metallic grid
(TEM grid) and the structure is formed by assembly of the materials along the patterned
lines. The mask could also be membrane and the deposition pattern in that case follows
the porous structure of the membrane.
It is a facile, versatile and a general method for the generation of micron and submicron
scale patterns of molecular and nanoscale materials assembled on a substrate surface.
The primary condition for generating patterns of any materials is that the substance,
whose pattern is to be generated, should be soluble or dispersible in a volatile liquid like
water and toluene. The substances, the patterns of which can be generated are
nanoscale particles of metal such as gold (Au), silver (Ag) and copper (Cu) or other
metal nanoparticles that are dispersible in a volatile solvent and semiconductors such as
CdS, Mn2+ doped CdS and ZnS or other semiconductor nanoparticles that are
dispersible in a volatile solvent, solutions of single molecules such as an organic dye
(Rhodamine B, Nile Red), solution of inorganic materials such as
CdCI2, solution/dispersion of polymers like polyvinyl pyrrolidone (PVP), or other polymers
that are soluble or dispersible in a volatile solvent.
The droplets of these solutions / dispersions, upon evaporation in the presence of a
metallic grid mask such as a transmission electron microscope (TEM) grid, lead to
the deposition of patterned assembly of molecular and nanoscale materials on the
surface of glass slides (substrates) where the droplets were placed. The pattern of the
assembly follow that of the TEM grid with dimensions of lines far reduced than those of
the TEM grids.
Smaller lines and arrays may be deposited using membrane as mask for deposition
where the deposited pattern follows the pattern of the porous structure as shown in
Figure 13
According to a preferred aspect the method produces layer-by-layer three-dimensional
deposition of assembled materials on the substrate surface. The patterns of the second
layer of deposition can be made at a chosen angle to that of the first layer patterns.
7

The materials of the second layer is same or different from that of the first layer. For
example, when the first layer of patterned deposition is made of assembly of metal
nanoparticles, the second layer is of semiconductor nanoparticles (quantum dots).
If the first patterned layer is made of a reactant the second patterned layer is made of a
second reactant, where the second reactant reacts with the first one at the overlapping
regions and produces the product at the intersections, which constitute the reaction
sites.
Hence, present invention of patterns generation by restricted evaporation using a TEM
grid or any other similar mask opens a new approach to the growth of organized
multidimensional arrays of colloidal particles in general. The present invention reveals
the versatility of the simple evaporation process for aligning nanometer-to-micrometer-
sized objects.
The striking simplicity of the present restricted evaporation process finds use in the
fabrication of biological devices, semiconductors and other electronic devices. This facile
method of arranging particles in two and three - dimensional arrays is considered as a
general method of patterned deposition of particles of various sizes and nature. The
method may be used as basis for higher hierarchical device structures and opens up the
possibility of making large-scale electronic devices with individually addressable
nanoscopic and or molecular components.
The details of the method are mentioned below. The potential applications of this
simple method range from optoelectronic devices to micro and nano arrays of DNA,
proteins etc.
The principle behind this new technique is to evaporate a droplet of the solution
(dispersion) containing the materials, of which pattern is to be generated, placed on a
substrate surface (flat) in the presence of a metallic grid mask placed on top of the
droplet.
The invention is now defined by way of following non-limiting illustrative examples:
8

Grids used in the examples
Commercially available TEM grid is used as the metallic grid mask. TEM grids are used
are made of copper or nickel metals. The grids made of copper had regular arrays of
rectangular openings of 45 micron x 45 micron with the metallic arms of the rectangle
having dimensions of 45 microns x 5 microns (Figure 1a). Overall, the grid is circular
with a diameter of about 3 mm.
On the other hand, the grids made of nickel has regular arrays of rectangular openings
of 100 micron x100 micron with the metallic arms of the rectangle having dimensions of
100 microns x 10 microns (Figure 1b). Overall, the grid is circular with a diameter of
about 3 mm.
More than one such grids may be attached and used together.
Example 1
The present example demonstrates generation of patterned structures of AuNPs on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then air-dried. A colloidal solution of Au nanoparticles is prepared
by treating 5 mL aqueous HAuCI4 (0.1 mM) with 1 mM of NaBH4. A drop (20 uL) of an
aqueous solution of the colloidal Au nanoparticles is then placed onto the glass slide. A
TEM copper grid is then placed carefully onto the drop such that the grid stays on the
drop. A schematic view of the method of pattern generation is shown in Figure 2. The
drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is
then lifted after 30 min such that the structures imprinted on the slide are minimally
disturbed. The structure imprinted on the slide is then investigated using optical
microscopy, atomic force microscopy, scanning electron microscopy etc. The details of
the micrographs are shown in Figures 3, 4, 5a and 5b. These two dimensional arrays are
0.4-0.6 micron in height with a width of 4-6 micron. When the above evaporation is
carried out in the presence of a commercially available IR light lamp (commercial 150
watts IR lamp, Brite Lamps) the patterns are more distinct, lines are thinner (typical line
width of 2 micron instead of 4-6 micron) and the evaporation process is completed in 10
min instead of 30 min.
9

Example 2
The present example demonstrates generation of patterned structures of Rhodamine B
dye on a substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned
by ethanol solution and then air-dried. An aqueous solution of Rhodamine B dye was
prepared by dissolving 100 uL of 0.1 M dye in 10 mL of Milli-Q water. A drop (20 uL) of
an aqueous solution of the Rhodamine B dye was then placed onto the glass slide. A
TEM copper / nickel grid was then placed carefully onto the drop such that the grid holds
its position on the drop. A schematic view of the method of pattern generation is shown
in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C for 30
min. The grid is then lifted after 30 min such that the structures imprinted on the slide is
minimally disturbed. The structure imprinted on the slide is then investigated using
optical microscopy. The details of the micrographs are shown in Figure 6. When the
above evaporation is carried out in the presence of a commercially available IR lamp
(commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct, lines are
thinner (typical line width of 1 micron instead of 3 micron) and the evaporation process is
completed in 10 min instead of 30 min.
Example 3
This example demonstrates generation of patterned structures of Nile Red dye on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then dried. An aqueous solution of Nile Red dye is prepared by
dissolving 0.1 mg of the dye in 5ml of toluene. A drop (20 uL) of an aqueous solution of
the Nile Red dye is then placed onto the glass slide. A TEM copper / nickel grid is then
placed carefully onto the drop such that the grid holds its position on the drop. A
schematic view of the method of pattern generation is shown in Figure 2. The drop along
with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is then lifted
after 30 min such that the structures imprinted on the slide is minimally disturbed.The
structure imprinted on the slide is then investigated using optical microscopy. The details
of the micrographs are shown in Figure 7.
When the above evaporation is carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines were thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
10

Example 4
The present example demonstrates generation of patterned structures of CdCI2 on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm was first cleaned by
ethanol solution and then dried. An aqueous solution of 1.1 x 10-4 M of CdCI2 is
prepared. A drop (20 uL) of an aqueous solution of CdCI2 is then placed onto the glass
slide. A TEM copper / nickel grid is then placed carefully onto the drop such that the grid
holds its position on the drop. A schematic view of the method of pattern generation is
shown in Figure 2. The drop along with the TEM grid is then left to evaporate at 300°C
for 30 min. The grid is then lifted after 30 min using such that the structures imprinted on
the slide is minimally disturbed. The structure imprinted on the slide is then investigated
using optical microscopy. The details of the micrographs are shown in Figure 8.
When the above evaporation was carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
Example 5
The present example demonstrates generation of patterned structures of PVP on a
substrate surface. A glass microscope slide of size 1 cm x 1 cm is first cleaned by
ethanol solution and then dried. An aqueous solution of PVP is prepared by dissolving
15 mg of PVP in 2 mL of Milli-Q water. A drop (20 uL) of an aqueous solution of PVP is
then placed onto the glass slide. A TEM copper / nickel grid is then placed carefully onto
the drop such that the grid holds its position on the drop. A schematic view of the
method of pattern generation is shown in Figure 2. The drop along with the TEM grid is
then left to evaporate at 300°C for 30 min. The grid is then lifted after 30 min such that
the structures imprinted on the slide is minimally disturbed. The structure imprinted on
the slide is then investigated using optical microscopy. The details of the micrographs
are shown in Figure 9.
When the above evaporation is carried out in the presence of a commercially available
IR lamp (commercial 150 watts IR lamp, Brite Lamps) the patterns are more distinct,
lines are thinner (typical line width of 1 micron instead of 3 micron) and the evaporation
process is completed in 10 min instead of 30 min.
11

The above methods provide two-dimensional micron line patterns, consisting of arrays of
colloidal particles, on glass substrate surfaces. As can be seen from the figures there
are three kinds of deposits as results of evaporation under the above conditions. They
are as follows:
(a) Single line deposits of materials along the TEM grid lines with thickness on the
order of 6.01 microns. These lines have typical heights on the order of 0.45
microns on the substrate (glass) surface. (Figures 3A and 3B)
(b) Double line deposits of materials (with a spacing of 20 micron) along the TEM
grid lines with thickness on the order of 2 micron or less. These lines have typical
heights on the order of 1 micron. (Figure 5a)
(c) Plate -like continuous deposits of materials along the TEM grid lines with
thickness on the order of 4 microns or less. These plates have typical heights on
the order of 1 micron. (Figures8A, 8B.9A, 9B, 6)
Example 6
The, deposition of two layers of patterned materials one on top of the other is
demonstrated as follows.
The first layer of material (Au nanoparticles) is deposited on a glass slide as mentioned
above using a TEM grid on top of a drop of an aqueous solution of AuNPs. When the
deposited material is completely dried in 30 min (after removal of the grid) another drop
of the same solution is again placed at the place where the original drop was there (that
led to the formation of first grid patterns). A TEM grid is likewise placed on top of this
drop followed by evaporation of the same. The process finally led to the formation of
double-layered patterns where one layer of patterned deposits is placed on top of a
previous layer of patterned deposits. The deposition of the first patterned layer is same
(similar) as those described earlier.
The deposition of the second patterned layer is typically thinner than the first layer. In
other words, the lines corresponding to the patterned deposition are comparatively
slimmer and height smaller with typical width of 0.8 micron. However, the patterns of the
lines followed those of the TEM grid metal lines as with the first layer. The relative
orientation and position of the lines of the first and second layers are decided by the
12

relative orientation of the TEM grid at the time of the first layer deposition and that during
the second layer. The details of the micrographs are shown in Figure 10.
Example 7
The present example demonstrates generation of patterned structures of CdS quantum
dots on a substrate surface by reaction. A glass microscope slide of size 1 cm x 1 cm is
first cleaned by ethanol solution and then dried. Aqueous solutions of 1.1 x 10-4 M of
CdCI2 and 0.01 M Na2S is prepared in Milli-Q water. A drop (20 uL) of an aqueous
solution of CdCI2 is then placed onto the glass slide. A TEM copper / nickel grid is then
placed carefully (using a pair of forceps) onto the drop such that the grid stays on the
drop. A schematic view of the method of pattern generation is shown in Figure 2. The
drop along with the TEM grid is then left to evaporate at 300°C for 30 min. The grid is
then lifted after 30 min using a pair of forceps such that the structures imprinted on the
slide is minimally disturbed. Then, a drop (20 uL) of an aqueous solution of Na2S is
placed on the patterned structures of CdCI2. CdS quantum dots are produced at the
overlapping regions where reaction occurs between them. The structure imprinted on the
slide is then investigated using optical microscopy. The details of the micrographs are
shown in Figure 11.
Example 8
This example demonstrates generation of patterned structures using two grids together.
A glass microscope slide of size 1 cm x 1 cm is first cleaned by ethanol solution and
then dried. A droplet of an aqueous solution containing the colloidal particles (Au NPs or
and any other solute/dispersed particles) is placed on the glass slide. Two TEM copper /
nickel grids attached to each other such that their grid lines are at an angle, are then
placed carefully onto the drop such that the grids hold their position on the drop. A
schematic view of the method of pattern generation is similar to the one shown in Figure
2. The drop along with the two TEM grids is then left to evaporate at 300°C for 30 min.
The grids are then lifted after 30 min such that the structures imprinted on the slide is
minimally disturbed. The structure imprinted on the slide is then investigated using
optical microscopy. The details of the micrographs are shown in Figure 12.
13

The main advantages of the present invention are:
1. The present invention is simplel in generating highly reproducible predetermined
patterned deposits with the help of natural forces (capillary forces) only. The method
does not require any additional physical force such as light (photolithography), pressure
on the mold (soft lithography), high energy electrons (electron beam lithography), ions
(ion beam lithography) etc.
2. It provides patterned deposits, of molecular, nanoscale and microscale materials, on a
substrate surface with the resultant assembly of the precursor materials.
3. The patterns can be controlled by controlling the dimensions of the TEM grid. The
sizes of the grid lines and holes and the nature of the patterns that makes up the grid
guide the pattern that is deposited on the substrate surface.
4. The dimensions of the deposited patterns are scalable and thus the method has
unique advantage.
5. The method allows layer-by-layer patterned depositions of materials, where the
resulting depositions could be made of same or two different materials that allow
combination of patterned depositions.
6. The method offers depositions of two reactive agents one after the other where the
product of the reaction results in the formation of specific depositions at the intersections
of the deposition in the case of two-layer depositions.
14

We claim
1. A method of formation of lithographic pattern of micron and submicron scale of
molecular and nanoscale materials assembled on a flat substrate surface, said method
comprising :
i) providing solution/dispersion of said material in a volatile solvent on a flat
surface;
ii) placing at least one mask on droplet of said solution/dispersion;
iii) exposing to restricted evaporation at temperature of 30°C of droplet of said
solution/dispersion in presence of the mask;
iv) depositing at least one layer of patterned assembly of molecular and
nanoscale material on the substrate along position of the mask;
v) removing the mask without disturbing the pattern formed along the mask.
2. The method as claimed in claim 1 wherein the mask is selected from metallic grids
and plastic membrane.
3. The method as claimed in claim 2 wherein when the mask is metallic grid and the
deposition of the material occurs along the pattern lines of the grid.
4. The method as claimed in claim 3 wherein the metallic grids used are TEM grids
selected from copper and nickel grid.
5. The method as claimed in claim 3 wherein two metallic grids are simultaneously
used being attached to one another at defined angle.
6. The method as claimed in claim 2 wherein when the mask is plastic membrane the
deposition occurs along the pattern formed by the pores of the membrane.
7. The method as claimed in any preceding claim wherein the restricted evaporation is
carried out at 300° C
15

8. The method as claimed in any preceding claims wherein the restriction evaporation
occurs for 30 minutes.
9. The method as claimed in any preceding claim wherein the flat substrate is glass
slide.
10. The method as claimed in any preceding claim wherein the material to be deposited
which is provided in solution/dispersion is selected from molecular materials,
nanoscale particles of metals, quantum dots, and inorganic materials.
11. The method a claimed in claim 9 wherein the molecular material is selected from
Rhodamine B dye, Nile Red dye and the like.
12. The method a claimed in claim 9 wherein the nanoscale particles of metals are
selected from Au NPs, Ag NPs, Cu NPs and other metal nano particles soluble in
volatile solvent.
13. The method a claimed in claim 9 wherein the quantum dots are selected frm CdS,
Mn2+ doped CdS, and other semiconductor nanoparticles dispersible in volatile
solvent.
14. The method a claimed in claim 9 wherein the inorganic materials are selected from
CdCI2, polyvenyl pyrrolidone and other polymers soluble in volatile solvent.
15. The method as claimed in any of claims 1 to 5 and 7 to 14 wherein the line widths of
the deposits formed ranges from submicron to a few microns.
16. The method as claimed in any of claims 1 to 5 and 7 to 15 wherein the height of the
line of deposits formed is around 0.4-0.6 micron.
17. The method as claimed in any of claims 1 to 5 and 7 to 16 wherein the patterns
deposited on the substrate surface are selected from single line deposits, double line
deposits and plate-like deposits depending on the evaporation process.
16

17
18. The method as claimed in claim 1 optionally comprising evaporation in presence of
commercially available IR lamp to provide distinct pattern and thinner lines of
deposition.
19. The method as claimed in any of claims 1 to 5 and 7 to 18 wherein two layers of
patterned deposit comprising first and second material are deposited one above the
other.
20. The method as claimed in claim 19 wherein the first and the second materials
deposited are selected from the same material deposited twice, different materials,
and two reagents which react chemically to produce a third product at the
intersections of the grid-line-like deposits.
21. The method as claimed in any of claims 19 to 20 wherein the first layer and second
layer are deposited at defined angle to each other.
22. The method as claimed in any of claim 1to 5 and 7 to 18 wherein overall dimensions
of the total deposited patterns are scalable as per the dimensions of the metallic grid.

A method of formation of lithographic pattern of micron and submicron scale of
molecular and nanoscale materials assembled on a flat substrate surface, said method
comprising providing solution/dispersion of said material in a volatile solvent on a flat
surface;placing at least one mask on droplet of said solution/dispersion;exposing to
restricted evaporation at temperature of 30°C of droplet of said solution/dispersion in
presence of the mask;depositing at least one layer of patterned assembly of molecular
and nanoscale material on the substrate along position of the mask; removing the mask
without disturbing the pattern formed along the mask. The process is entirely
evaporation based producing patterns of colloidal particles ranging from nanoparticles,
quantum dots, single molecules to polymers in aqueous and organic solvents. The
process also includes formation of patterns of more than one layer including reaction of
two species along the TEM grid lines (mask).

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=sLt4MUQJTcS8M7GLsA+VRQ==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

279359

Indian Patent Application Number

1537/KOL/2007

PG Journal Number

03/2017

Publication Date

20-Jan-2017

Grant Date

19-Jan-2017

Date of Filing

07-Nov-2007

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY

Applicant Address

NORTH GUWAHATI, GUWAHATI, ASSAM

Inventors:

#	Inventor's Name	Inventor's Address
1	SINGH, ANUGRAH	INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI, DEPARTMENT OF CHEMICAL ENGINEERING, NORTH GUWAHATI, GUWAHATI (ASSAM), PIN 781039
2	CHATTOPADHYAY, ARUN	INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI, CENTRE FOR NANOTECHNOLOGY AND DEPARTMENT OF CHEMISTRY, NORTH GUWAHATI, GUWAHATI (ASSAM), PIN 781039
3	PINJALA, NAGARAJU, RAO	INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI, DEPARTMENT OF CHEMICAL ENGINEERING, NORTH GUWAHATI, GUWAHATI (ASSAM), PIN 781039

PCT International Classification Number

B 41F

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA