Title of Invention	"A PROCESS FOR GENERATING MICRO AND SUB-MICRO PATTERNS ON THE SURFACES OR LAYERS OF POLYMERS"
Abstract	The invention describes a process for generating micron and sub-micron sized physical relief patterns by direct solid state imprinting on soft solid surface layers, at room temperature, without the application of any external pressure, using a patterned flexible foil as the stamp. The pattern transfer takes place primarily due to elastic deformations at the surface, due to the adhesive interaction between the patterned stamp and soft solid surface. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of curved soft solid surface layers. The other novel feature of the invention relates to the possible use of the flexible patterned foils, obtained from commercially available optical data storage discs, like CDs, DVDs etc. We also demonstrate that it is possible to create complex structures (array of pits and pillars) on the foils of the data disks by programming and subsequent laser burning of specific data onto such disks. When such a foil is used for patterning, it is possible to create complex structures like array of beakers etc. on the soft solid surface layers. The invented method is versatile and is capable of creating variety of structures, which include one dimensional (parallel lines), two dimensional (cross patterns) or complex (arrays of pillars or holes) patterns, from a simple one dimensional stripe patterned stamp on soft solid surface layers.

Title of Invention

"A PROCESS FOR GENERATING MICRO AND SUB-MICRO PATTERNS ON THE SURFACES OR LAYERS OF POLYMERS"

Abstract

The invention describes a process for generating micron and sub-micron sized physical relief patterns by direct solid state imprinting on soft solid surface layers, at room temperature, without the application of any external pressure, using a patterned flexible foil as the stamp. The pattern transfer takes place primarily due to elastic deformations at the surface, due to the adhesive interaction between the patterned stamp and soft solid surface. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of curved soft solid surface layers. The other novel feature of the invention relates to the possible use of the flexible patterned foils, obtained from commercially available optical data storage discs, like CDs, DVDs etc. We also demonstrate that it is possible to create complex structures (array of pits and pillars) on the foils of the data disks by programming and subsequent laser burning of specific data onto such disks. When such a foil is used for patterning, it is possible to create complex structures like array of beakers etc. on the soft solid surface layers. The invented method is versatile and is capable of creating variety of structures, which include one dimensional (parallel lines), two dimensional (cross patterns) or complex (arrays of pillars or holes) patterns, from a simple one dimensional stripe patterned stamp on soft solid surface layers.

Full Text	FIELD OF INVENTION The present invention relates to creation of micro and sub-micron sized physical relief patterns on soft solid surface layers, for example, surfaces of soft polymeric materials, by a pressure less room temperature patterning process, using a flexible patterned foil as the stamp or master for patterning. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer and also allows patterning of non planar soft solid surface layers. This invented process is the first Nano Imprinting method that does not require the application of any external uniform pressure for pattern transfer. In this method, the pattern transfer takes place directly in the solid state. Two dimensional patterns by using a one dimensional stamp can be created by multiple imprinting using the same or different stamps during patterning. The simple technique invented here is suitable for fabrication of low cost, large area polymer templates for various bulk-nano applications, for example in areas like molecular electronics, optical elements, organic light emitting materials, structured optical coatings, patterned "smart" adhesives, confined chemistry applications, carbon-MEMS and microbattery, controlled dewetting on patterned surfaces, surfaces for nano-biotechnology applications like biochemical sensors, drug delivery, tissue engineering, single molecule enzymology, pnoteomic or genomic arrays, photodiode arrays for sub retinal implant and patterned substrates for probing of cell behavior etc. BACKGROUND OF THE INVENTION Patterning of substrates on micro- or nano- meter scales is of great technological importance in the fabrication of semiconductors, integrated circuits, optical devices like display devices, anti-reflective surface coatings, MEMS/NEMS, chemical or biological sensors, DNA enrichment and other biological applications, lab-on-a-chip diagnostic devices, micro-fluidics, super hydrophobia surfaces etc. Lithography, which has several major variants, is the key process to create patterns on thin films or surfaces, hard or soft. The pattern created can be physical (relief patterns) or can be chemical (different wettability domains or different type of doping) in nature. Of all the lithographic methods, photolithography is the most well established and popular method (see, for example, reference Xia, Y. and Whitesides, G. M. Angew. Chem. Int. Ed. 1998, 37, 550,). A typical photolithography process involves placing a mask on a resist layer (a photosensitive polymer) and exposing it with an optical source. In most cases, upon exposing the resist layer to the source light, the chemical structure of the exposed area (areas not covered by the mask) of the film changes, so that when immersed in a developer, either the exposed area or the unexposed area of the resist (depending on whether the resist used is positive or negative) gets removed to recreate the patterns. The lithography resolution is limited by the wavelength of the optical source and proper alignment of the mask with respect to the surface. Photolithography requires dedicated setup and can pattern only a photosensitive polymer layer. Numerous technologies have been developed which aims at obtaining as small feature size as possible, overcoming the optical resolution limit of photolithography. Electron beam lithography has demonstrated 10 nm lithography resolutions, (see references Broers, A. N., Harper J. M. and Molzen, W. W. Appl. Phys. Lett. 1978, 33, 392, Fischer, P. B. and Chou, S. Y. Appl. Phys. Lett. 1993, 62, 2989). But using it for mass production of sub-50 nm structures is economically impractical due to inherent low throughput in a serial processing tool. X-ray lithography, which can have a high throughput, has demonstrated 50 nm lithography resolutions, (see reference K. Early, M. L. Schattenburg, and H. I. Smith, Microelectronic Engineering 1990, 11, 317). But e-beam and X-ray lithography tools are expensive and its ability for mass producing submicron structures is yet to be realised. While these methods aim at producing smallest feature size (~20 nm), none of them are suitable for large area patterning, due to the inherent serial nature of the processes. The applications of patterned surfaces is not only limited to semiconductor or electronics industry only and thus, there is need for processes that are able to rapidly produce micron and submicron sized surface patterns at affordable costs, without using very sophisticated instruments and will be able to pattern "soft" surfaces like those of polymers. That is the reason for the alternative, "soft" lithographic processes (see, for example, reference Xia, Y. and Whitesides, G. M. Angew. Chem. Int. Ed. 1998, 37, 550) like micro contact printing;, micro molding in capillaries, replica molding, Nano Imprint Lithography etc. becoming preferred and popular tools for patterning soft surfaces over large areas. In the context of patterning of polymeric surfaces and creation of physical relief structures at submicron dimensions, Nano imprint lithography (NIL) (U. S. Patent No. 5,772,905 and references Chou, S. Y., Krauss, P. R. and Renstrom, P. J. Appl. Phys. Lett. 1995, 67, 3114 and Science 1996, 272, 85) has been successfully demonstrated as a method to create relief pattern of sub 25 nm feature size on polymer surfaces, over large areas. In a typical imprinting process, a polymer surface layer or film is heated above its glass transition temperature. A hard mold or master or stamp is then pressed against this softened polymer layer, which is subsequently quenched with the mold in place. Once cooled, the stamp is taken off, leaving an exact negative replica of the stamp on the polymer surface. The critical issues associated with the process are heating of the polymer layer (which might lead to thermal degradation of the polymer), pressing the mold against the softened polymer by applying uniform pressure (typically 4-13 MPa) and chances of damage to the created patterns during withdrawal of the stamp. U. S. Patent No. 6,818,139 describes a method in which a polymer thin film is deposited on the substrate. A rigid mold having the desired shape and pattern is pressed into the polymer film at room temperature by high pressure compression techniques. The polymer undergoes irreversible plastic deformation and flow at high pressures to replicate the pattern in the mold. The polymer is made to undergo glass transition and thus made liquid- like at room temperature by absorbing a solvent. The solvent is evaporated after which the moid is removed leaving behind a more permanent negative replica of the mold in the surface layer. A major improvement over the existing method of Nano Imprint Lithography is the room temperature high pressure nano imprint lithography (RTNIL) (see reference Khang, D-Y., Yoon, H. and Lee, H. H. Adv. Mater. 2001, 13, 749), where the step involving heating of the polymer is eliminated and the pattern transfer is achieved by plastic deformation of the polymer layer at room temperature itself. However, the advantage originating from the elimination of the thermal cycle is more than offset by the need of high pressure (~50 MPa). This method uses a hard stamp to apply high pressures. U. S. Patent No. 6,833,162 describes a method for generating colored nanolithography patterns of parallel lines or cross pattern lines on a glass or plastic substrate, said process consisting the steps of pressing a polycarbonate or aluminum mold obtained from a compact disk on a glass or plastic surface inked with a permanent marker ink for one or more times to create lithographic patterns of parallel colored lines or cross pattern lines. However, this invention does not mention any method of creating relief patterns on soft polymeric surfaces. Even after substantial development in the area of physical patterning of surfaces at sub micron and nano scales (primarily based on different variants of Nano Imprint Lithography), several key issues still need to be addressed. Still not a single method exists for creating physical patterns on soft solid surfaces at micron and sub micron scales that does not require application of external pressure. Other disadvantages include the use of rigid stamps or masters for patterning, which are fabricated by some other lithographic process, application of thermal cycle and high pressure, chances of damage of the created patterns during removal of the stamp, limitations in obtaining large area patterns, critical control of uniformity of the applied pressure, ensuring perfectly parallel configuration between the stamp and the surface to be patterned etc. Therefore, there is a great need to develop low-cost technologies (better, if no specialized and dedicated setup is needed) for bulk fabrication sub micron structures over large areas on soft solid surface layers. Such a technology will definitely have an enormous impact in many areas of engineering and science, apart from the semiconductor industry. Such a method can particularly be useful for scientific work that is not directly related to surface patterning but require patterned surfaces routinely as templates (for example, confined chemistry applications, cellular biology applications etc.). Important criteria for any such a process would be the ability to pattern surfaces that are non specific nature (for example, direct photolithographic patterning is possible only for a special class of photosensitive polymers), surfaces having any arbitrary shape, that is the method should be equally effective for patterning planar as well as non planar curved surfaces. The present invention originates from the need of having a sub micron scale patterning method, which is cost effective, does not require any specialized tools and equipment, can be practiced in any laboratory (even with no setup for lithography) and patterning can be achieved without the application of temperature or external pressure. The pattern transfer takes place primarily due to elastic deformations at the surface, due to the adhesive interaction between the patterned stamp and soft polymer surface. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of non planar soft solid surface layers. The possible use of commercially available optical data storage disc, as a source of patterned foil is the other novel concept associated with the proposed method. Using foils available from these optical discs makes the process extremely cost effective. Additionally, laser burning of optical disks have also been used to create more complex patterns on these foils for subsequent usage as a stamp. The usage of a flexible foil, instead of a rigid stamp provides several key advantages like conformal contact between surface and stamp, ease of stamp removal without any damage to the created patterns and most importantly, patterning of curved surfaces. SUMMARY OF THE INVENTION The invention relates to a method for creating micron and submicron sized physical relief patterns on soft solid surface layers at room temperature by pressure-less imprint method, where the deformation on the soft solid surface is predominantly elastic in nature. The stamp used for patterning is a patterned flexible foil. The method can be used to pattern surfaces of various types of soft solid materials, like soft elastomeric polymers (for example, cross linked PDMS (polydimethylsiloxane)) and various types of soft gels (for example, PAA (polyacrylamide) based hydrogels, gelatin etc.). The invention relates to patterning of soft solids having planar as well as curved surfaces. The invention also enables it possible to create two dimensional ordered structures by using a simple one dimensional stamp, by repeated imprinting. The use of patterned foils obtained from optical data storage discs like CD and DVD is another novel aspect of the invention. These foils can be procured at a very low cost and can be subsequently used for patterning. Their use also provides a major advantage in the way that, when some data (or files) are stored (or "burnt") on these data storage discs, it results in surface patterns in the form of array of pillars or pits can be generated on the metal foil, which actually correspond to the laser writing or "burning" marks. Use of the foil from such a disc (which has some data or files written on it) for patterning, results in the formation of array of holes along channels, instead of using a foil from a "blank" (that is, containing no data or files written on it) optical disk, where the pattern will only be stripes of parallel lines. The inventors further demonstrate that by programming the data to be stored, the number density of the said features (pillars or pits) can be controlled. The present invention provides a process for generating micro and sub-micro patterns on soft solid surface layers by elastic deformations at room temperature and without application of any external pressure, comprising the step of using a patterned flexible foil as the stamp. The method invented is novel in the following ways: 1. Direct patterning in the solid state. 2. Deformation of the soft solid surface layer in conformal contact with the stamp, leading to the pattern transfer is predominantly elastic in nature. 3. Use of a flexible patterned foil as the stamp for patterning, allowing excellent pressure less conformal contact and high fidelity pattern transfer. 4. No heating necessary for the polymer film or layer to be patterned. 5. No application of uniform external pressure for pattern transfer. 6. Large area submicron patterning of wide range of soft surfaces without using any specially designed tool or equipment. 7. Can pattern soft solid layers having planar as well as curved surfaces. 8. Possible to generate patterns which have lateral dimension smaller than that of the stamp dimension. 9. Possible to generate patterns having periodicity (pitch) smaller than that of the stamp periodicity (pitch). 10. Possible to generate two dimensional ordered patterns by multiple imprinting. 11. Creation of complex surfaces by programming the data stored in an optical disc and by subsequent use of the patterned foil portion of such a disc as the stamp for patterning. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Figure 1: Schematic of the room temperature pressure less adhesive force assisted patterning method for creation of relief patterns on flat soft solid surface layers, using patterned flexible foils as stamps, as claimed in claim 1. Figure 2: Schematic of the room temperature pressure less adhesive force assisted patterning method for creation of relief patterns on non planar soft solid surface layers, using patterned flexible foils as stamps, as claimed in claim 1. Figure 3: 3-D AFM images of various patterned flexible foils used as stamp. (A) Patterned flexible aluminum foil having stripe width 750 nm, stripe height 130 nm and periodicity 1.5 urn. (B) Patterned flexible aluminum foil having stripe width 400 nm, stripe height 70 nm and periodicity 800 nm. (C) Patterned PVA (polyvinyl alcohol) foil having stripe width 750 nm, stripe height 130 nm and periodicity 1.5 urn. Figure 4: (A) 2-D AFM image of the flexible metal foil portion (with cross sectional details) of a CD on which an unformatted file containing only "...LLLLLLLL..." is stored, as in claim 15. (B) 2-D AFM image of the flexible metal foil portion (with cross sectional details) of a CD on which an unformatted file containing only "...00000000..." is stored, as in claim 15. Figgure 5: (A) 3-D AFM image of the stripe pattern obtained on a 1.63 urn thick soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on quartz substrate by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(A) as the stamp. A perfect negative replica of the stamp is achieved. (B) 3-D AFM image of the stripe pattern obtained on a 1.43 urn thick on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on quartz substrate by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(B) as the stamp. A perfect negative replica of the stamp is achieved. (C) 3-D AFM image of the pattern obtained on a 1.98 urn thick on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on quartz substrate by pressure less room temperature imprinting using a flexible patterned metal foil obtained from a CD having data stored in it as the stamp (figure 4(A)), foil of a CD in which data was stored. The elongated holes along the trenches correspond to the laser burn marks on the metal foil due to storage of data. Figure 6: (A) Schematic illustration of the imprinting process that leads to the formation of "split" patterns, when the thickness of the polymer film (H) is less than a critical thickness (Hc), as per claims 11 and 12. (B) 3-D AFM image of a typical "under split' pattern in a 231 nm thick on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer when imprinted using a patterned aluminum foil shown in figure 3(A) as per claims 11 and 12. (C) 3-D AFM image of a "perfect split"pattern obtained in a 92 nm thick on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer when imprinted using a patterned aluminum foil shown in figure 3(B), as per claims 11 and 12. Figure 7: 3-D AFM images of two dimensional cross patterns obtained by multiple imprinting on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layers coated on quartz substrates. (A) 700 nm x 700 nm square pillars obtained using a patterned aluminum foil shown in figure 3(A). The second imprint is at right angles to the direction of the first imprint. (B) 350 nm x 350 nm square pillars obtained using a using a patterned aluminum foil shown in figure 3(B). The second imprint is at right angles to the direction of the first imprint. (C) 700 nm x 350 nm rectangular pillars obtained by imprinting with a patterned aluminum foil shown in figure 3(A) first and subsequently with another patterned aluminum foil shown in figure 3(B), at right angles to the direction of the stripes obtained after the first imprinting. (D) Rhombic columns obtained by imprinting twice with a patterned aluminum foil as shown in figure 3(B), by making the second imprint at an angle of 45° relative to the direction of the first imprint. Figure8: (A) Digicam image of a 6.0 urn thick patterned crosslinked PDMS (polydimethylsiloxane) surface layer on a cylindrical glass tube having diameter 1.8 cm. The length of the patterned zone is 4.0 cm. Patterning is achieved by room temperature imprinting followed by UV irradiation to make the patterns permanent. Flexible patterned PVA foil, as shown in figure 3(C) was used as the stamp. (B) Optical micrograph of the patterned PDMS (polydimethylsiloxane) film shown in figure 9(A). (C) Optical micrograph of the surface of a patterned 3.8 um thick crosslinked PDMS (polydimethylsiloxane) surface layer coated on a cylindrical glass rod having diameter 1.2 cm using the flexible patterned PVA foil having 800 nm periodicity as stamp. (D) Optical micrograph of 2-D cross patterns obtained by multiple imprinting on a 4.6 um thick cross linked PDMS (polydimethylsiloxane) surface layer coated on a cylindrical glass tube having diameter 2.2 cm. Flexible patterned PVA foil, as shown in figure 3(C) was used for both the imprints. Figure 9: (A) Digicam image of a 3 cm x 2 cm (x 1.8 mm thick) block of crosslinked PDMS (polydimethylsiloxane), imprinted with the patterned metal foil as stamp, as shown in figure 3(A). The patterns are made permanent by UV irradiation. (B) 3-D AFM image of the surface of the patterned PDMS (polydimethylsiloxane) block shown in figure 9(A). (C) 2-D AFM image of the surface of a patterned block crosslinked PDMS (polydimethylsiloxane) block using the foil potion of a CD having data stored on it, as shown in figure 4(A). Figure 10: (A) 3-D AFM image of the stripe pattern obtained on a 4.92 um thick soft PAA (polyacrylamide) based hydrogel surface layer, cast on a glass lide by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(A) as the stamp. A perfect negative replica of the stamp is achieved. (B) 3-D AFM image of the stripe pattern obtained on a 6.2 pm thick soft PAA (polyacrylamide) based hydrogel surface layer, cast on a glass lide by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(B) as the stamp. A perfect negative replica of the stamp is achieved. DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS The present invention relates to creation of micro and sub-micron sized physical relief patterns on soft solid surface layers, for example, surfaces of soft polymeric materials, by a pressure less room temperature patterning process, using a flexible patterned foil as the stamp or master for patterning. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of non planar soft solid surface layers. The generated physical patterns can be parallel lines or cross patterns on surface of various polymers. The schematic of the proposed method is shown in figure 1. In the invented method, unlike the NIL based methods, patterning can be achieved at room-temperature, without the application of external uniform pressures and without critically maintaining a parallel alignment of the stamp with the surface to be patterned. This bench-top method can thus be easily implemented without any expensive or specialized equipment in any laboratory. Unlike the emerging NIL based methods, the proposed method differs in three key aspects-a flexible foil rather than a rigid stamp is used for facilitating a pressureless uniform and conformal contact with the film. Secondly, the conformal contact of flexible foil is facilitated by adhesive forces rather than by the application of external pressure. Finally, the most important aspect is that the pattern transfer of imprinting takes place directly in the solid state. The method is not specific to any special class of polymer, and can be easily applied for patterning completely different classes of materials which are "soft" at room temperature, like polyacrylamaide (PAA) based hydrogels, or cross linked elastomers like Polydimethylsiloxane (PDMS). In the context of present invention, "soft" surfaces mean the shear modulus of the material should be less than 100 MPa, more preferably less than 10 MPa. The other novel feature of the method, as already mentioned is the use of a flexible stamp, instead of a rigid stamp. A flexible stamp comes into closer conformal contact with a surface, compared to a rigid stamp, even if there are minor localized defects on the surface to be patterned. The use of a flexible patterned stamp, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. Additionally, a foil can be wrapped around any regularly or arbitrarily curved surface, thereby making the method versatile for patterning non planar surfaces too. Not too many methods are readily available for patterning films or layers of materials that have non planar surfaces (figure 2). The pattern transfer takes place on the surface of the soft solid material, primarily by elastic deformations, due to the adhesive interaction between the patterned stamp and soft polymer surface. Withdrawal of the stamp from contact proximity to the film will lead the soft surface relaxing back to its original fiat state and the patterns disappear. Depending on the type of soft solid surface layer to be patterned, different strategies have been adopted to make the patterns permanent. For patterning of PAA (polyacrylamide) based hydrogel films, controlled drying, with the stamp in conformal contact with the surface was adopted. For soft patterning soft surface layers of crosslinked elastomeric PDMS (polydimethylsiloxane), the patterns were made permanent by UV-ozone treatment. UV irradiation at 185 nm produces ozone from atmospheric oxygen, which further gets dissociated to atomic oxygen at 254 nm irradiation. This atomic species reacts with the siloxane group, releasing volatile products and leaving behind a stiff surface layer consisting of oxides of silicon (see references Ouyang, M.; Muisener, R. J.; Boulares, A.; Koberstein, J.T. Journal of Membrane Sci. 2000, 177, 177. Ouyang, M.; Yuan, C; Muisener, R. 1; Boulares, A.; Koberstein, J. T. Chem. Mater. 2000, 12, 1591.). The higher modulus of the surface layer prevents the relaxation of the film and preserves the relief patterns imprinted on the soft surface by the foil. Figure 1 and 2 shows schematically the various patterning options in the invention for patterning planar and curved surfaces respectively. Figure 3 shows various types of flexible metal as well as polymeric foils that have been used as stamps in this process. One of the possible sources of the flexible patterned foils, which can be used as the stamp for the patterning, can be easily and readily obtained from the commercially available optical data storage discs like CD-R, DVD etc., which allow patterning capabilities in any laboratory, at an extremely low cost and eliminates the step of fabrication of the stamp or the master pattern by any other specialized lithographic method. And more interestingly, when a commercial optical data storage disc is used, instead of always using a blank media, a disc containing some data of files stored ("burnt") on it can also be used. The laser burning process creates array of small (~30 nm high) pillars along the tracks (Refer to figure 4) of the channels on the foils and by using such a foil for patterning, more complex structures can be created. It is also possible, to some extant, to control the number density of these structures by programming the data that is stored on the disc. Writing of any data (in the form of a file) on an optical disk by a "write laser" etches pits along the tracks on the polycarbonate disk and matching "burn marks" in the form of raised pillars on the adjoining metal foil. Briefly, it may be noted that the data is saved on the disc in a binary format; the flat portions of the etched track represent "0" while any change of the height along the track represents a binary "1". More details are available in Example 1. Figure 5(A) and 5(B) shows the patterns formed on a soft PDMS (polydimethylsiloxane) surface layer, coated on a quartz substrate by imprinting with patterned flexible aluminum foils shown in figures 3(A) and 3(B) respectively. The patterns obtained on a cross linked PDMS film using the foil obtained from a compact disk (CD) which has some specific data (a data file containing "...LLLLLL..", corresponding ASCII code of 076 and binary string of 01001100) written on to it (figure 4A) is shown in figure 5(C). Figure 6 shows the images of patterns obtained where the periodicity of the patterns obtained is more than the periodicity of the stamp as well as the lateral dimension of the features is less than the lateral dimension of the features on the stamp (claims 11 and 12). Figure 7 shows examples of obtaining 2-D patterns using 1-D patterned flexible stamps by the invented method, by multiple imprinting of the surface, with the same stamp or different stamps being used for consecutive imprints. Both isotropic and anisotropic as features can be generated using this method. Figure 8 demonstrates that a soft cross-linked elastomeric PDMS (polydimethylsiloxane) film coated on a non planar curved substrate can be patterned by this method. As shown in figure 2, for patterning of non planar curved surfaces, the flexible patterned stamp is wrapped around the film. In this case, it should be noted that a patterned metal foils, which are not transparent to UV irradiation, can't be used. If such a foil is wrapped around a curved surface, UV irradiation cant reach the surface of the PDMS (polydimethylsiloxane) film and therefore the surface reaction leading to the breakage of the siloxane group and formation of the hard surface layer gets hindered. In order to overcome this problem, specifically for these cases, a patterned PVA foil has been used as the stamp, as PVA (polyvinyl alcohol) is transparent to UV. Figure 9 shows that the method is not only applicable for soft solid surface layers coated on planar substrates, but is equally applicable for pre-cast self standing layers and blocks of soft solids, like cross linked PDMS (polydimethylsiloxane). Here we demonstrate that the surface of a cross linked PDMS (polydimethylsiloxane) block can also be patterned in the same way, as shown in figure 1. In this case, similar to the case of patterning a PDMS (polydimethylsiloxane) filmscoated on a curved surfaces, in order to ensure transparency to UV irradiation, a flexible patterned PVA (polyvinyl alcohol) stamp has been used and subsequent UV hardening of the PDMS (polydimethylsiloxane) surface is done to make the patterns permanent. Figures 10 shows the patterns obtained on PAA (polyacrylamide) based hydrogel films using patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The flexible stamp results in close conformal contact with hydrogel film surface, thereby ensuring the formation of a perfect negative replica of the stamp pattern. The critical stage while patterning hydrogel films by this method was found to be the gelation time, which was a function of the initial volume of the reaction mixture added to cast the film. Another critical parameter was the drying of the film while in contact with the stamp. The main advantages of the present invention are: 1. In the present method, patterning is achieved directly in the solid phase. 2. Patterning is achieved at gentle processing conditions, with the application of no external pressure or temperature. 3. The use of a flexible patterned foil as a stamp ensures total and conformal contact with the surface to be patterned, thereby ensuring large area uniform pattern transfer (~ cm2), without the need of maintaining a parallel configuration between the stamp and the surface to be patterned, as is necessary while using a rigid stamp. 4. The use of a flexible patterned foil as a stamp also reduces the chances of pattern damage during stamp withdrawal. 5. By using components of commercially available optical data storage disks containing data as stamp, it is possible to create complex patterns (for example, array of beakers in channels). 6. No need for any specialized tools, instruments or facilities. 7. Possible to generate patterns which have lateral dimension smaller than that of the stamp dimension. 8. Possible to generate patterns having periodicity (pitch) smaller than that of the stamp periodicity (pitch). 9. Possible to generate two dimensional ordered patterns by multiple imprinting. 10. Creation of complex surfaces by programming the data stored in an optical disc and by subsequent use of the patterned foil portion of such a disc as the stamp for patterning. Probable areas of application of the patterned surfaces using the present invention: In general, the innovation will be useful for all the areas that are related to bulk nanotechnology applications involving polymers and other soft materials. Some of the specific target areas could be: • Areas related to molecular electronics, for example patterning of indium tin oxide thin films for organic light-emitting diode, fabrication of thin-film transistor (TFT) arrays, patterned PMMA composite as an optical diffuser in a liquid crystal display for backlighting unit (BLU), control on thermo-physical and optical properties of a diffuser using patterned polymer in LCD backlights units. Micro patterning of polymer surfaces for Electronic and Biornaterials applications. Surfaces for nano-biotechnology applications like biochemical sensors, drug delivery, tissue engineering, single molecule enzymology, proteomic or genomic arrays, photodiode arrays for sub retinal implant and patterned substrates for probing of cell behavior etc. MEMS-Based Micro-Fuel Cell Systems for portable power applications. Large-area micro patterning of polymers to facilitate light management in transflective displays. Fabrication of diffraction gratings/optical wave guides. Confined chemistry applications. Application in the areas of microfluidics, for example for fabrication of large number of parallel micro channels. Creating of surfaces with structural colors. Fabrication of patterned "smart" adhesives and super adhesive surfaces with possible "clean" peeling options. Templates for the fabrication of ordered polymer structures by controlled dewetting on patterned surfaces. EXAMPLES EXAMPLE 1 Method for generating complex micro patterned surfaces by data storage As mentioned already, one of the possible sources of patterned flexible foils to be used as stamps is the commercially available optical data storage disc like CD-R, DVD etc. More complex patterns are created simply by storing unformatted data in optical storage disks, like CD-R or DVD-R etc., as listed in claim 12. It is known from information in open domain that any character is stored in a binary form in a computer memory (see for example, reference http://computer.howstuffworks.com/cd-burner4.htm). Eight bits represent one character and each bit can hold a value of either "0" or "1". Each character has its own binary map, which can be obtained in "ASCII Table" (For example, "A" in 8 bit form is 00110001, while "B" is 00110010 etc.). When any data is stored or "written" in an optical disk a "write laser" etches some pits along this track on the polycarbonate disk and matching "bum marks" in the form of raised pillars are created on the adjoining metal foil. It is also known that the flat portion of the etched track represents "0" while any change of height along the track represents "1". This way, laser etching by the "write laser" itself is creating a patterned surface. The laser beam irradiates the polymeric track, so as to elevate the temperature of that region to a predetermined level where polymer gets "burnt" to form the pits, which now physically represent "0"s and "l"s, corresponding to the sequence of data to be stored. For the sake of completion, it should be mentioned that these topographical features, is decoded by the "read laser", as it picks up the variation of reflected optical intensity of the incident laser beam when it scans the structured topography of storage medium. The "read laser" does not change the surface topography of the track. Based on the understanding of the mapping of the actual physical topography created on the optical data storage disk (by laser burning) corresponding to each character it was possible to program the data to be stored and generate any specific pattern. By modulating the data to be stored, it was, for example possible to control the number density of the features created on the tracks of the flexible metal foil or the patterned polymer part of a digital data storage disk. The features in this context relate to the array of raised pillars along the tracks in case of the flexible metal foil part or array of holes along the trenches of the patterned polymer (polycarbonate) part of the disks. For example, by saving a data file, containing the character "L" only (....LLLLLL ) in a format free text file and subsequently burning it to a CD, the features obtained on the flexible foil part of a CD is shown in figure 4(A). The number density of the pillars is ~ 0.30 ± 0.023 per urn2 area, with length of each pillar ~ 1.45 ± 0.22 urn and the height of the pillars is ~ 35 nm. The size of the file was ~ 700 MB, so that it spreads over the entire storage area of the CD, ensuring the formation of the features all over the CD. Similarly, by creating another file which contained the character "o* only, the number density of the features obtained was ~ 0.18 ± 0.027 per pm2 area for the pits and the average length of each pillar ~ 2.85 ± 0.57 urn (figure 2(B)). EXAMPLE 2: Room temperature pressure less adhesive force assisted imprinting of soft elastomeric films coated on planar surfaces using flexible patterned foil: Experiments were performed on crosslinked polydimethylsiloxane (PDMS) films (surface layers) of thickness range varying from about 0.2 to about 15 urn, deposited on quartz substrate. The shear modulus of the surface layer was varied from about 0.01 MPa to 2.0 MPa by varying the concentration of the crosslinker between 5 % and 15 % (Sylgard 184, a two part thermally curable elastomer from Dow Chemicals) in the casting solution. The PDMS (polydimethylsiloxane) surface layer was spin coated from solution in hexane and then cured at 130° C for 12 hours to crosslink the PDMS (polydimethylsiloxane) and yield a dominantly elastic surface layer. The invented method allows formation of sub micron features on soft elastic polymeric material surface by imprinting with the flexible patterned foils as stamps. A schematic view of the present method of imprinting patterns on soft surfaces layers is shown in figure 3. The patterned foils were cleaned and placed upside down on a flat glass plate, with the patterns facing upwards. The cross linked PDMS (polydimethylsiloxane) surface layers were gently placed on the patterned foils (as shown in figure 1). As the slides were placed on the foil pieces, the only compressive force the PDMS (polydimethylsiloxane) films were subjected to was due to the weight of the quartr slides themselves. The adhesive between the films and the foils were strong enough to cause deformation of the low shear modulus PDMS (polydimethylsiloxane) surface layer together with a conformal bending of the foils resulting in a perfect negative replica. This imprinting on the surface layer is engendered by elastic deformation in the cross linked PDMS (polydimethylsiloxane) layer, as evidenced by a rapid disappearance of the imprint upon removal of the foils form the surface of the PDMS (polydimethylsiloxane) layer. The patterns were made permanent by UV-ozone treatment for 30 minutes of the PDMS (polydimethylsiloxane) layer in contact with the flexible foil stamp. UV irradiation at 185 nm produces ozone from atmospheric oxygen, which further gets dissociated to atomic oxygen at 254 nm irradiation. This atomic species reacts with the siloxane group, releasing volatile products and leaving behind a stiff surface layer consisting of oxides of silicon (see references Ouyang, M.; Muisener, R. J.; Boulares, A.; Koberstein, J. T. Journal of Membrane Sci. 2000, 177, 177. Ouyang, M.; Yuan, C.; Muisener, R. J.; Boulares, A.; Koberstein, J. T. Chem. Mater. 2000, 12, 1591.). The higher modulus of the surface layer prevents the relaxation of the film and preserves the relief patterns imprinted on the soft surface by the foil. The novelty of the method lies in the fact that no pressure was applied externally to imprint the patterns on the PDMS (polydimethylsiloxane) surface layer. Figures 5(A) and 5(B) show the patterns obtained on 1.63 urn and 1.43 urn thick cross linked PDMS (polydimethylsiloxane) surface layer coated on quartz substrates using a the patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The width, height and the periodicity of the stripes obtained using a CD mold were 743 nm (± 30 nm), 108 nm (± 15 nm) and 1.55 urn (± 0.092 um), respectively. The same parameters obtained using a DVD were 260 nm (± 25 nm), 66 nm (± 9.1 nm) and 773 nm (± 43 nm), respectively (figure 4B). In case of figure 5(C), the foil of a CD having data written on it (file containing " ..LLLLLL.", figure 4(A)) was used to pattern a crosslinked PDMS (polydimethylsiloxane) film having thickness 1.98 um. The imprinted pattern had array of elongated holes along the trenches, apart from having parallel stripes, having periodicity 1.50 um and height of 125 nm. The average length and depth of the holes were 1.68 um (± 0.19 um) and 27 nm (± 4.0 nm) respectively. Imprinting very thin surface layers, with the same stamps as shown in figure 3(A) and 3(B), it was no longer possible to obtain perfect negative replica of the stamp below a critical film thickness (Hc). Instead, a doubly-periodic structure with stripes split in the middle was obtained as shown in figure 6. The critical thickness was found to be a function of the periodicity of the pattern on the stamp only. The splitting of the stripes result from the fact that as the film gets thinner, the material deformed is not adequate to fill up the space between the adjacent protrusions of the master completely, as shown schematically in figure 6(A). For film thickness slightly lower than Hc. the depth of the line that splits a stripe is less than the depth of the "valley" between the two adjacent stripes, which is termed as the"partially split' configuration. Example of this is shown in the pattern of figure 6(B). In case of figure 6(B), a 231 nm film was imprinted with an aluminum foil shown in figure 3(A). In this case, while the height of the stripes is ~ 77 nm, the depth of the spilt is ~ 36 nm. With progressive reduction of the film thickness the asymmetric split patterns obtained tend to become more symmetric in nature as another critical thickness, Hchalf is reached. At this thickness, the cross sectional profiles of the line splitting a stripe and that of the valley between the two "original" adjacent stripes becomes identical, which is termed as the "perfect split" (schematic in figure 6(A)) configuration. For example, by imprinting a 92 nm thick surface layer of cross-linked PDMS (polydimethylsiloxane) with an aluminum foil shown in figure 3(B) as stamp, "perfect split' patterns having 35 (± 3.8) nm high stripes with periodicity of 379 nm (± 11.3) were obtained (Figure 6(C)). Interestingly, this pattern now appears as if it is a perfect replica of a mold of 400 nm periodicity, even though the mold used is of 800 nm period! In essence, the imprinted pattern now has half the periodicity of the master. Thus it is possible to obtain patterns having lateral dimension less than that of the original stamp as well pattern periodicity (pitch) less than the periodicity (pitch) of the stamp, as claimed in claims 11 and 12. Two dimensional crossed patterns can also be generated on the surface layer by using a stamp with one dimensional feature by a two step process. The top surface of the PDMS (polydimethylsiloxane) film, in presence of the patterned flexible stamp was first partially hardened by the UV irradiation for a short duration (~ 5 minutes) to prevent its immediate relaxation. The stamp was then withdrawn, rotated and brought back into contact with the film at an angle to the initial patterns and subsequently cured with UV-ozone for another 25 minutes. The isotropic array of square pillars thus obtained using aluminum foils as shown in figures 3(A) and 3(B) respectively as stamp, with 90° rotations of the molds are shown in figures 7(A) and 7(B), respectively. To create the anisotropic pattern shown in figure 7(C), the PDMS (polydimethylsiloxane) film was first imprinted with a patterned aluminum foil shown in figure 3(A) and subsequently with another patterned aluminum foil shown in figure 3(B), at right angles to the direction of the stripes obtained after the first imprinting. This resulted in an array of rectangular pillars, having roof dimensions of about 750 nm x 370 nm. The second imprint at an angle of 45° to the direction of the first imprint using aluminum foil shown in figure 3(B) as stamp, resulted in the pattern shown in figure 7(D), where an array of rhombic columns on the surface is obtained. Thus, by using a combination of multiple 1-D masters and varying the angles between the successive imprints, one can engineer a large variety of complex 2-D patterns. It may be noted that no external pressure was needed even for the second imprinting stage too. EXAMPLE 3: Room temperature pressure less adhesive force assisted imprinting of soft elastomeric films coated on non-planar (curved) surfaces using flexible patterned foil: Similar to patterning of soft crosslinked PDMS (polydimethylsiloxane) films coated on planar surfaces (as discussed in Example 2), this method can be used for making permanent relief patterns on the surfaces of such (crosslinked PDMS (polydimethylsiloxane) films) coated on non planar, curved surfaces. However, as discussed already, a patterned metal foil can't be used in this case as a stamp, as it is not transparent to UV and therefore, patterned PVA foils, which are transparent to UV irradiation was used as the stamp to in order to successfully make the patterns permanent. Figure 8(A) shows a digicam picture of a ~ 6.0 urn thick patterned crosslinked PDMS (polydimethylsiloxane) film on a cylindrical glass tube having diameter 1.8 cm. For this case, a PVA foil having 1.5 urn periodicity (750 nm stripe width) was used. The length of the patterned zone is ~ 4.0 cm. Figure 8(B) shows the corresponding optical micrograph of the patterned PDMS (polydimethylsiloxane) film. Figure 8 (C) shows the Optical micrograph of the surface patterns achieved on a 3.8 urn thick crosslinked PDMS (polydimethylsiloxane) film coated on a cylindrical glass rod having diameter 1.2 cm using the flexible patterned PVA foil having 800 nm periodicity as stamp. Even 2-D cross patterns, as have been discussed in details in the context of figure 7, have been successfully obtained on the surface of a 4.6 urn thick crosslinked PDMS (polydimethylsiloxane) film, coated on a 2.2 cm diameter metal tube, as shown in the optical micrograph figure 8(D). EXAMPLE 4: Room temperature pressure less adhesive force assisted imprinting of soft etastomeric pre-cast blocks and layers fusing flexible patterned foil: Figure 9 shows that the method is not only applicable for soft solid surface layers coated on planar substrates, but is equally applicable for pre-cast block of soft solid. Here we demonstrate that the surface of a block of cross linked PDMS (polydimethylsiloxane) block can also be patterned in the same way, as shown in figure 1. Similar to the case of patterning a crosslinked PDMS (polydimethylsiloxane) film coated on a curved surface, here too, a flexible patterned PVA stamp has been used and subsequent UV hardening of the PDMS (polydimethylsiloxane) surface is done to make the patterns permanent. EXAMPLE 7 Room temperature imprinting of Hydrogel films using flexible patterned stamps: Figures 14(A) and 14(B) show the patterns obtained on ~ 5.0 urn thick PAA (polyacrylamide) based hydrogel films using patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The width, height and the periodicity of the stripes obtained using a the stamp shown in figure 3(A) were 781 nm (± 17 nm), 121 nm (± 11 nm) and 1.49 urn (± 0.105 urn), respectively. The same parameters obtained using the stamp shown in figure 3(B) were 291 nm (± 18 nm), 69 nm (± 4.3 nm) and 804 nm (± 31 nm), respectively. The flexible stamp results in close conformal contact with hydrogel film surface, thereby ensuring the formation of a perfect negative replica of the stamp pattern. The critical staqe while patterning hydrogel films by this method was found to be the gelation time, which was a function of the initial volume of the reaction mixture added to cast the film. Another critical parameter was the drying of the film while in contact with the stamp. For thicker hydrogel films, the drying was associated with buckling of the film, which resulted in peeling of the film from the substrate (glass slide). Thinner films ( 1. A process for generating micro and sub-micro patterns on soft solid surface layers by elastic deformations at room temperature and without application of any external pressure, comprising the step of using a patterned flexible foil as the stamp. 2. The method as claimed in claim 1, wherein the process of forming patterns by pressure less room temperature patterning on soft solid surface layers by elastic deformation, comprises the steps of: i. using the flexible patterned foil as the stamp for patterning; ii. placing the stamp in a conformal contact with the soft surface layer; iii. allowing an adhesive force assisted imprint to form on the soft surface layer, by a conformal adhesive contact with the stamp, leading to elastic deformation of the soft surface; iv. rendering the resultant patterns on the soft solid surface layer permanent; and v. repeating the steps of using the flexible patterned foil as the stamp and rendering the pattern on the soft surface layer permanent in a desired sequence, by withdrawing the stamp compared to its previous position, and re-engage it to create a new pattern on the soft solid surface by elastic deformation each cycle. 3. The method as claimed in claim 1, wherein the shear modulus of the soft solid surface layers in steps (i)-(v) of claim 2 is less than 100 MPa, more preferably less than 10 MPa. 4. The method as claimed in claim 1, wherein the soft solid surface layer patterned is planar or curved. 5. The method as claimed in claim 1, wherein the patterning of the soft solid surface layer is achieved directly in the solid state. 6. The method as claimed in claim 1, wherein the soft solid surface layer is at room temperature during steps (i)-(v) of claim 2. 7. The method as claimed in claim 1, wherein no external pressure is applied during steps (i)-(v) of claim 2, either on the stamp or on the soft solid surface layer. 8. The method as claimed in claim 1, wherein said soft solid surface layer patterned can be polymers like cross-linked polydimethylsiloxane (PDMS), polyacrylamide (PAA) based hydrogels, gelatin etc. 9. The method as claimed in claim 1, wherein rendering the resultant pattern permanent involves surface curing by chemical or physical process. The possible surface curing steps can be ultra-violet radiation, controlled drying, chemical reactions on the surface etc. 10. The method as claimed in claim 1, wherein the patterns are comprised channels, array of pits within the channels, array pillars having rectangular, square or rhombic cross sections, or a combination of these structures. 11. The method as claimed in claim 1, wherein the periodicity (pitch) of the patterns created on the soft solid surface layer are identical to or less than the periodicity (pitch) of the patterns on the stamp. 12. The method as claimed in claim 1, wherein the lateral dimensions of the patterns created on the soft solid surface layer are identical or smaller than the lateral dimensions of the patterns on the stamp. 13. The method as claimed in claim 1, wherein the patterned flexible foil used as the stamp is a patterned metal foil or a patterned polymer foil. 14. The method as claimed in claim 1, where the patterned flexible foil used as the stamp can be obtained from a commercially available optical data storage disk, wherein the optical data storage disk is a data storage medium like a CD-R, a CD- RW, a DVD-R, a DVD-RW, a Blue Ray Disk or a Digital Multilayer Disk. 15. The method as claimed in claim 15, wherein said optical data storage disk from which patterned flexible foil is used for patterning is either blank (no data is written on the disk) or said disk contains some data written or stored therein. 16. The method as claimed in claim 16, wherein distinct topological features like arrays of pits and protrusions or pillars on the disk foil can be created by writing of data on the disk. 17. A process for generating a micro and sub-micro patterns on the surfaces or layers of different of polymers, substantially as herein described and illustrated in the accompanying drawings.

Full Text

FIELD OF INVENTION
The present invention relates to creation of micro and sub-micron sized physical relief patterns on soft solid surface layers, for example, surfaces of soft polymeric materials, by a pressure less room temperature patterning process, using a flexible patterned foil as the stamp or master for patterning. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer and also allows patterning of non planar soft solid surface layers. This invented process is the first Nano Imprinting method that does not require the application of any external uniform pressure for pattern transfer. In this method, the pattern transfer takes place directly in the solid state. Two dimensional patterns by using a one dimensional stamp can be created by multiple imprinting using the same or different stamps during patterning.
The simple technique invented here is suitable for fabrication of low cost, large area polymer templates for various bulk-nano applications, for example in areas like molecular electronics, optical elements, organic light emitting materials, structured optical coatings, patterned "smart" adhesives, confined chemistry applications, carbon-MEMS and microbattery, controlled dewetting on patterned surfaces, surfaces for nano-biotechnology applications like biochemical sensors, drug delivery, tissue engineering, single molecule enzymology, pnoteomic or genomic arrays, photodiode arrays for sub retinal implant and patterned substrates for probing of cell behavior etc. BACKGROUND OF THE INVENTION
Patterning of substrates on micro- or nano- meter scales is of great technological importance in the fabrication of semiconductors, integrated circuits, optical devices like display devices, anti-reflective surface coatings, MEMS/NEMS, chemical or biological sensors,

DNA enrichment and other biological applications, lab-on-a-chip diagnostic devices, micro-fluidics, super hydrophobia surfaces etc. Lithography, which has several major variants, is the key process to create patterns on thin films or surfaces, hard or soft. The pattern created can be physical (relief patterns) or can be chemical (different wettability domains or different type of doping) in nature.
Of all the lithographic methods, photolithography is the most well established and popular method (see, for example, reference Xia, Y. and Whitesides, G. M. Angew. Chem. Int. Ed. 1998, 37, 550,). A typical photolithography process involves placing a mask on a resist layer (a photosensitive polymer) and exposing it with an optical source. In most cases, upon exposing the resist layer to the source light, the chemical structure of the exposed area (areas not covered by the mask) of the film changes, so that when immersed in a developer, either the exposed area or the unexposed area of the resist (depending on whether the resist used is positive or negative) gets removed to recreate the patterns. The lithography resolution is limited by the wavelength of the optical source and proper alignment of the mask with respect to the surface. Photolithography requires dedicated setup and can pattern only a photosensitive polymer layer.
Numerous technologies have been developed which aims at obtaining as small feature size as possible, overcoming the optical resolution limit of photolithography. Electron beam lithography has demonstrated 10 nm lithography resolutions, (see references Broers, A. N., Harper J. M. and Molzen, W. W. Appl. Phys. Lett. 1978, 33, 392, Fischer, P. B. and Chou, S. Y. Appl. Phys. Lett. 1993, 62, 2989). But using it for mass production of sub-50 nm structures is economically impractical due to inherent low throughput in a serial processing tool. X-ray lithography, which can have a high throughput, has demonstrated 50 nm lithography resolutions, (see reference K. Early, M. L. Schattenburg, and H. I. Smith,

Microelectronic Engineering 1990, 11, 317). But e-beam and X-ray lithography tools are expensive and its ability for mass producing submicron structures is yet to be realised. While these methods aim at producing smallest feature size (~20 nm), none of them are suitable for large area patterning, due to the inherent serial nature of the processes.
The applications of patterned surfaces is not only limited to semiconductor or electronics industry only and thus, there is need for processes that are able to rapidly produce micron and submicron sized surface patterns at affordable costs, without using very sophisticated instruments and will be able to pattern "soft" surfaces like those of polymers. That is the reason for the alternative, "soft" lithographic processes (see, for example, reference Xia, Y. and Whitesides, G. M. Angew. Chem. Int. Ed. 1998, 37, 550) like micro contact printing;, micro molding in capillaries, replica molding, Nano Imprint Lithography etc. becoming preferred and popular tools for patterning soft surfaces over large areas.
In the context of patterning of polymeric surfaces and creation of physical relief structures at submicron dimensions, Nano imprint lithography (NIL) (U. S. Patent No. 5,772,905 and references Chou, S. Y., Krauss, P. R. and Renstrom, P. J. Appl. Phys. Lett. 1995, 67, 3114 and Science 1996, 272, 85) has been successfully demonstrated as a method to create relief pattern of sub 25 nm feature size on polymer surfaces, over large areas. In a typical imprinting process, a polymer surface layer or film is heated above its glass transition temperature. A hard mold or master or stamp is then pressed against this softened polymer layer, which is subsequently quenched with the mold in place. Once cooled, the stamp is taken off, leaving an exact negative replica of the stamp on the polymer surface. The critical issues associated with the process are heating of the polymer layer (which might lead to thermal degradation of the polymer), pressing the mold against the softened polymer by applying uniform pressure (typically 4-13 MPa) and chances of

damage to the created patterns during withdrawal of the stamp.
U. S. Patent No. 6,818,139 describes a method in which a polymer thin film is deposited on the substrate. A rigid mold having the desired shape and pattern is pressed into the polymer film at room temperature by high pressure compression techniques. The polymer undergoes irreversible plastic deformation and flow at high pressures to replicate the pattern in the mold. The polymer is made to undergo glass transition and thus made liquid- like at room temperature by absorbing a solvent. The solvent is evaporated after which the moid is removed leaving behind a more permanent negative replica of the mold in the surface layer.
A major improvement over the existing method of Nano Imprint Lithography is the room temperature high pressure nano imprint lithography (RTNIL) (see reference Khang, D-Y., Yoon, H. and Lee, H. H. Adv. Mater. 2001, 13, 749), where the step involving heating of the polymer is eliminated and the pattern transfer is achieved by plastic deformation of the polymer layer at room temperature itself. However, the advantage originating from the elimination of the thermal cycle is more than offset by the need of high pressure (~50 MPa). This method uses a hard stamp to apply high pressures.
U. S. Patent No. 6,833,162 describes a method for generating colored nanolithography patterns of parallel lines or cross pattern lines on a glass or plastic substrate, said process consisting the steps of pressing a polycarbonate or aluminum mold obtained from a compact disk on a glass or plastic surface inked with a permanent marker ink for one or more times to create lithographic patterns of parallel colored lines or cross pattern lines. However, this invention does not mention any method of creating relief patterns on soft polymeric surfaces.

Even after substantial development in the area of physical patterning of surfaces at sub micron and nano scales (primarily based on different variants of Nano Imprint Lithography), several key issues still need to be addressed. Still not a single method exists for creating physical patterns on soft solid surfaces at micron and sub micron scales that does not require application of external pressure. Other disadvantages include the use of rigid stamps or masters for patterning, which are fabricated by some other lithographic process, application of thermal cycle and high pressure, chances of damage of the created patterns during removal of the stamp, limitations in obtaining large area patterns, critical control of uniformity of the applied pressure, ensuring perfectly parallel configuration between the stamp and the surface to be patterned etc.
Therefore, there is a great need to develop low-cost technologies (better, if no specialized and dedicated setup is needed) for bulk fabrication sub micron structures over large areas on soft solid surface layers. Such a technology will definitely have an enormous impact in many areas of engineering and science, apart from the semiconductor industry. Such a method can particularly be useful for scientific work that is not directly related to surface patterning but require patterned surfaces routinely as templates (for example, confined chemistry applications, cellular biology applications etc.). Important criteria for any such a process would be the ability to pattern surfaces that are non specific nature (for example, direct photolithographic patterning is possible only for a special class of photosensitive polymers), surfaces having any arbitrary shape, that is the method should be equally effective for patterning planar as well as non planar curved surfaces.
The present invention originates from the need of having a sub micron scale patterning method, which is cost effective, does not require any specialized tools and equipment, can be practiced in any laboratory (even with no setup for lithography) and

patterning can be achieved without the application of temperature or external pressure. The pattern transfer takes place primarily due to elastic deformations at the surface, due to the adhesive interaction between the patterned stamp and soft polymer surface. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of non planar soft solid surface layers. The possible use of commercially available optical data storage disc, as a source of patterned foil is the other novel concept associated with the proposed method. Using foils available from these optical discs makes the process extremely cost effective. Additionally, laser burning of optical disks have also been used to create more complex patterns on these foils for subsequent usage as a stamp. The usage of a flexible foil, instead of a rigid stamp provides several key advantages like conformal contact between surface and stamp, ease of stamp removal without any damage to the created patterns and most importantly, patterning of curved surfaces. SUMMARY OF THE INVENTION
The invention relates to a method for creating micron and submicron sized physical relief patterns on soft solid surface layers at room temperature by pressure-less imprint method, where the deformation on the soft solid surface is predominantly elastic in nature. The stamp used for patterning is a patterned flexible foil. The method can be used to pattern surfaces of various types of soft solid materials, like soft elastomeric polymers (for example, cross linked PDMS (polydimethylsiloxane)) and various types of soft gels (for example, PAA (polyacrylamide) based hydrogels, gelatin etc.). The invention relates to patterning of soft solids having planar as well as curved surfaces. The invention also enables it possible to create two dimensional ordered structures by using a simple one dimensional

stamp, by repeated imprinting.
The use of patterned foils obtained from optical data storage discs like CD and DVD is another novel aspect of the invention. These foils can be procured at a very low cost and can be subsequently used for patterning. Their use also provides a major advantage in the way that, when some data (or files) are stored (or "burnt") on these data storage discs, it results in surface patterns in the form of array of pillars or pits can be generated on the metal foil, which actually correspond to the laser writing or "burning" marks. Use of the foil from such a disc (which has some data or files written on it) for patterning, results in the formation of array of holes along channels, instead of using a foil from a "blank" (that is, containing no data or files written on it) optical disk, where the pattern will only be stripes of parallel lines. The inventors further demonstrate that by programming the data to be stored, the number density of the said features (pillars or pits) can be controlled.
The present invention provides a process for generating micro and sub-micro patterns on soft solid surface layers by elastic deformations at room temperature and without application of any external pressure, comprising the step of using a patterned flexible foil as the stamp.
The method invented is novel in the following ways:
1. Direct patterning in the solid state.
2. Deformation of the soft solid surface layer in conformal contact with the stamp,
leading to the pattern transfer is predominantly elastic in nature.
3. Use of a flexible patterned foil as the stamp for patterning, allowing excellent
pressure less conformal contact and high fidelity pattern transfer.
4. No heating necessary for the polymer film or layer to be patterned.
5. No application of uniform external pressure for pattern transfer.

6. Large area submicron patterning of wide range of soft surfaces without using any
specially designed tool or equipment.
7. Can pattern soft solid layers having planar as well as curved surfaces.
8. Possible to generate patterns which have lateral dimension smaller than that of the
stamp dimension.
9. Possible to generate patterns having periodicity (pitch) smaller than that of the
stamp periodicity (pitch).
10. Possible to generate two dimensional ordered patterns by multiple imprinting.
11. Creation of complex surfaces by programming the data stored in an optical disc
and by subsequent use of the patterned foil portion of such a disc as the stamp for
patterning.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1: Schematic of the room temperature pressure less adhesive force assisted patterning method for creation of relief patterns on flat soft solid surface layers, using patterned flexible foils as stamps, as claimed in claim 1.
Figure 2: Schematic of the room temperature pressure less adhesive force assisted patterning method for creation of relief patterns on non planar soft solid surface layers, using patterned flexible foils as stamps, as claimed in claim 1.
Figure 3: 3-D AFM images of various patterned flexible foils used as stamp.
(A) Patterned flexible aluminum foil having stripe width 750 nm, stripe height
130 nm and periodicity 1.5 urn.
(B) Patterned flexible aluminum foil having stripe width 400 nm, stripe height
70 nm and periodicity 800 nm.
(C) Patterned PVA (polyvinyl alcohol) foil having stripe width 750 nm, stripe
height 130 nm and periodicity 1.5 urn.
Figure 4: (A) 2-D AFM image of the flexible metal foil portion (with cross sectional details) of a CD on which an unformatted file containing only "...LLLLLLLL..." is stored, as in claim 15.
(B) 2-D AFM image of the flexible metal foil portion (with cross sectional details) of a CD on which an unformatted file containing only "...00000000..." is stored, as in claim 15.
Figgure 5: (A) 3-D AFM image of the stripe pattern obtained on a 1.63 urn thick soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on quartz substrate by pressure less room temperature imprinting using a
flexible patterned aluminum foil shown in figure 3(A) as the stamp. A perfect negative replica of the stamp is achieved.
(B) 3-D AFM image of the stripe pattern obtained on a 1.43 urn thick on soft
elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on
quartz substrate by pressure less room temperature imprinting using a
flexible patterned aluminum foil shown in figure 3(B) as the stamp. A perfect
negative replica of the stamp is achieved.
(C) 3-D AFM image of the pattern obtained on a 1.98 urn thick on soft
elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer coated on
quartz substrate by pressure less room temperature imprinting using a
flexible patterned metal foil obtained from a CD having data stored in it as
the stamp (figure 4(A)), foil of a CD in which data was stored. The elongated
holes along the trenches correspond to the laser burn marks on the metal foil
due to storage of data.
Figure 6: (A) Schematic illustration of the imprinting process that leads to the formation of "split" patterns, when the thickness of the polymer film (H) is less than a critical thickness (Hc), as per claims 11 and 12.
(B) 3-D AFM image of a typical "under split' pattern in a 231 nm thick on soft
elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer when
imprinted using a patterned aluminum foil shown in figure 3(A) as per claims
11 and 12.
(C) 3-D AFM image of a "perfect split"pattern obtained in a 92 nm thick on
soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layer when imprinted using a patterned aluminum foil shown in figure 3(B), as per claims 11 and 12.
Figure 7: 3-D AFM images of two dimensional cross patterns obtained by multiple imprinting on soft elastomeric crosslinked PDMS (polydimethylsiloxane) surface layers coated on quartz substrates.
(A) 700 nm x 700 nm square pillars obtained using a patterned aluminum foil
shown in figure 3(A). The second imprint is at right angles to the direction of
the first imprint.
(B) 350 nm x 350 nm square pillars obtained using a using a patterned
aluminum foil shown in figure 3(B). The second imprint is at right angles to
the direction of the first imprint.
(C) 700 nm x 350 nm rectangular pillars obtained by imprinting with a
patterned aluminum foil shown in figure 3(A) first and subsequently with
another patterned aluminum foil shown in figure 3(B), at right angles to the
direction of the stripes obtained after the first imprinting.
(D) Rhombic columns obtained by imprinting twice with a patterned
aluminum foil as shown in figure 3(B), by making the second imprint at an
angle of 45° relative to the direction of the first imprint.
Figure8: (A) Digicam image of a 6.0 urn thick patterned crosslinked PDMS (polydimethylsiloxane) surface layer on a cylindrical glass tube having diameter 1.8 cm. The length of the patterned zone is 4.0 cm. Patterning is achieved by room temperature imprinting followed by UV irradiation to make the patterns permanent. Flexible patterned PVA foil, as shown in figure 3(C) was used as the stamp.
(B) Optical micrograph of the patterned PDMS (polydimethylsiloxane) film
shown in figure 9(A).
(C) Optical micrograph of the surface of a patterned 3.8 um thick crosslinked
PDMS (polydimethylsiloxane) surface layer coated on a cylindrical glass rod
having diameter 1.2 cm using the flexible patterned PVA foil having 800 nm
periodicity as stamp.
(D) Optical micrograph of 2-D cross patterns obtained by multiple imprinting
on a 4.6 um thick cross linked PDMS (polydimethylsiloxane) surface layer
coated on a cylindrical glass tube having diameter 2.2 cm. Flexible patterned
PVA foil, as shown in figure 3(C) was used for both the imprints.
Figure 9: (A) Digicam image of a 3 cm x 2 cm (x 1.8 mm thick) block of crosslinked PDMS (polydimethylsiloxane), imprinted with the patterned metal foil as stamp, as shown in figure 3(A). The patterns are made permanent by UV irradiation.
(B) 3-D AFM image of the surface of the patterned PDMS
(polydimethylsiloxane) block shown in figure 9(A).
(C) 2-D AFM image of the surface of a patterned block crosslinked PDMS
(polydimethylsiloxane) block using the foil potion of a CD having data stored
on it, as shown in figure 4(A).
Figure 10: (A) 3-D AFM image of the stripe pattern obtained on a 4.92 um thick soft PAA (polyacrylamide) based hydrogel surface layer, cast on a glass lide by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(A) as the stamp. A perfect negative replica of the stamp is achieved.
(B) 3-D AFM image of the stripe pattern obtained on a 6.2 pm thick soft PAA (polyacrylamide) based hydrogel surface layer, cast on a glass lide by pressure less room temperature imprinting using a flexible patterned aluminum foil shown in figure 3(B) as the stamp. A perfect negative replica of the stamp is achieved.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS
The present invention relates to creation of micro and sub-micron sized physical relief patterns on soft solid surface layers, for example, surfaces of soft polymeric materials, by a pressure less room temperature patterning process, using a flexible patterned foil as the stamp or master for patterning. The use of a flexible patterned stamp, instead of a rigid one, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. The use of a flexible foil stamp also allows patterning of non planar soft solid surface layers. The generated physical patterns can be parallel lines or cross patterns on surface of various polymers. The schematic of the proposed method is shown in figure 1.
In the invented method, unlike the NIL based methods, patterning can be achieved at room-temperature, without the application of external uniform pressures and without critically maintaining a parallel alignment of the stamp with the surface to be patterned. This bench-top method can thus be easily implemented without any expensive or specialized equipment in any laboratory. Unlike the emerging NIL based methods, the proposed method differs in three key aspects-a flexible foil rather than a rigid stamp is used for facilitating a pressureless uniform and conformal contact with the film. Secondly, the conformal contact of flexible foil is facilitated by adhesive forces rather than by the application of external pressure. Finally, the most important aspect is that the pattern transfer of imprinting takes place directly in the solid state. The method is not specific to any special class of polymer, and can be easily applied for patterning completely different classes of materials which are "soft" at room temperature, like polyacrylamaide (PAA) based hydrogels, or cross linked elastomers like Polydimethylsiloxane (PDMS). In the context of
present invention, "soft" surfaces mean the shear modulus of the material should be less than 100 MPa, more preferably less than 10 MPa.
The other novel feature of the method, as already mentioned is the use of a flexible stamp, instead of a rigid stamp. A flexible stamp comes into closer conformal contact with a surface, compared to a rigid stamp, even if there are minor localized defects on the surface to be patterned. The use of a flexible patterned stamp, results in deformations of both the stamp and the soft surface to make a spontaneous conformal contact allowing high fidelity pattern transfer. Additionally, a foil can be wrapped around any regularly or arbitrarily curved surface, thereby making the method versatile for patterning non planar surfaces too. Not too many methods are readily available for patterning films or layers of materials that have non planar surfaces (figure 2).
The pattern transfer takes place on the surface of the soft solid material, primarily by elastic deformations, due to the adhesive interaction between the patterned stamp and soft polymer surface. Withdrawal of the stamp from contact proximity to the film will lead the soft surface relaxing back to its original fiat state and the patterns disappear. Depending on the type of soft solid surface layer to be patterned, different strategies have been adopted to make the patterns permanent. For patterning of PAA (polyacrylamide) based hydrogel films, controlled drying, with the stamp in conformal contact with the surface was adopted. For soft patterning soft surface layers of crosslinked elastomeric PDMS (polydimethylsiloxane), the patterns were made permanent by UV-ozone treatment. UV irradiation at 185 nm produces ozone from atmospheric oxygen, which further gets dissociated to atomic oxygen at 254 nm irradiation. This atomic species reacts with the siloxane group, releasing volatile products and leaving behind a stiff surface layer consisting of oxides of silicon (see references Ouyang, M.; Muisener, R. J.; Boulares, A.; Koberstein, J.T. Journal of Membrane Sci. 2000, 177, 177. Ouyang, M.; Yuan, C; Muisener, R. 1; Boulares, A.; Koberstein, J. T. Chem. Mater. 2000, 12, 1591.). The higher modulus of the surface layer prevents the relaxation of the film and preserves the relief patterns imprinted on the soft surface by the foil. Figure 1 and 2 shows schematically the various patterning options in the invention for patterning planar and curved surfaces respectively. Figure 3 shows various types of flexible metal as well as polymeric foils that have been used as stamps in this process.
One of the possible sources of the flexible patterned foils, which can be used as the stamp for the patterning, can be easily and readily obtained from the commercially available optical data storage discs like CD-R, DVD etc., which allow patterning capabilities in any laboratory, at an extremely low cost and eliminates the step of fabrication of the stamp or the master pattern by any other specialized lithographic method. And more interestingly, when a commercial optical data storage disc is used, instead of always using a blank media, a disc containing some data of files stored ("burnt") on it can also be used. The laser burning process creates array of small (~30 nm high) pillars along the tracks (Refer to figure 4) of the channels on the foils and by using such a foil for patterning, more complex structures can be created. It is also possible, to some extant, to control the number density of these structures by programming the data that is stored on the disc. Writing of any data (in the form of a file) on an optical disk by a "write laser" etches pits along the tracks on the polycarbonate disk and matching "burn marks" in the form of raised pillars on the adjoining metal foil. Briefly, it may be noted that the data is saved on the disc in a binary format; the flat portions of the etched track represent "0" while any change of the height along the track represents a binary "1". More details are available in Example 1.
Figure 5(A) and 5(B) shows the patterns formed on a soft PDMS (polydimethylsiloxane) surface layer, coated on a quartz substrate by imprinting with patterned flexible aluminum foils shown in figures 3(A) and 3(B) respectively. The patterns obtained on a cross linked PDMS film using the foil obtained from a compact disk (CD) which has some specific data (a data file containing "...LLLLLL..", corresponding ASCII code of 076 and binary string of 01001100) written on to it (figure 4A) is shown in figure 5(C).
Figure 6 shows the images of patterns obtained where the periodicity of the patterns obtained is more than the periodicity of the stamp as well as the lateral dimension of the features is less than the lateral dimension of the features on the stamp (claims 11 and 12).
Figure 7 shows examples of obtaining 2-D patterns using 1-D patterned flexible stamps by the invented method, by multiple imprinting of the surface, with the same stamp or different stamps being used for consecutive imprints. Both isotropic and anisotropic as features can be generated using this method.
Figure 8 demonstrates that a soft cross-linked elastomeric PDMS (polydimethylsiloxane) film coated on a non planar curved substrate can be patterned by this method. As shown in figure 2, for patterning of non planar curved surfaces, the flexible patterned stamp is wrapped around the film. In this case, it should be noted that a patterned metal foils, which are not transparent to UV irradiation, can't be used. If such a foil is wrapped around a curved surface, UV irradiation cant reach the surface of the PDMS (polydimethylsiloxane) film and therefore the surface reaction leading to the breakage of the siloxane group and formation of the hard surface layer gets hindered. In order to overcome this problem, specifically for these cases, a patterned PVA foil has been used as the stamp, as PVA (polyvinyl alcohol) is transparent to UV.

Figure 9 shows that the method is not only applicable for soft solid surface layers coated on planar substrates, but is equally applicable for pre-cast self standing layers and blocks of soft solids, like cross linked PDMS (polydimethylsiloxane). Here we demonstrate that the surface of a cross linked PDMS (polydimethylsiloxane) block can also be patterned in the same way, as shown in figure 1. In this case, similar to the case of patterning a PDMS (polydimethylsiloxane) filmscoated on a curved surfaces, in order to ensure transparency to UV irradiation, a flexible patterned PVA (polyvinyl alcohol) stamp has been used and subsequent UV hardening of the PDMS (polydimethylsiloxane) surface is done to make the patterns permanent.
Figures 10 shows the patterns obtained on PAA (polyacrylamide) based hydrogel films using patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The flexible stamp results in close conformal contact with hydrogel film surface, thereby ensuring the formation of a perfect negative replica of the stamp pattern. The critical stage while patterning hydrogel films by this method was found to be the gelation time, which was a function of the initial volume of the reaction mixture added to cast the film. Another critical parameter was the drying of the film while in contact with the stamp.
The main advantages of the present invention are:
1. In the present method, patterning is achieved directly in the solid phase.
2. Patterning is achieved at gentle processing conditions, with the application of no
external pressure or temperature.
3. The use of a flexible patterned foil as a stamp ensures total and conformal contact with
the surface to be patterned, thereby ensuring large area uniform pattern transfer (~

cm2), without the need of maintaining a parallel configuration between the stamp and the surface to be patterned, as is necessary while using a rigid stamp.
4. The use of a flexible patterned foil as a stamp also reduces the chances of pattern
damage during stamp withdrawal.
5. By using components of commercially available optical data storage disks containing
data as stamp, it is possible to create complex patterns (for example, array of beakers in
channels).
6. No need for any specialized tools, instruments or facilities.
7. Possible to generate patterns which have lateral dimension smaller than that of the
stamp dimension.
8. Possible to generate patterns having periodicity (pitch) smaller than that of the stamp
periodicity (pitch).
9. Possible to generate two dimensional ordered patterns by multiple imprinting.
10. Creation of complex surfaces by programming the data stored in an optical disc and by
subsequent use of the patterned foil portion of such a disc as the stamp for patterning.
Probable areas of application of the patterned surfaces using the present invention:
In general, the innovation will be useful for all the areas that are related to bulk nanotechnology applications involving polymers and other soft materials. Some of the specific target areas could be:
• Areas related to molecular electronics, for example patterning of indium tin oxide thin films for organic light-emitting diode, fabrication of thin-film transistor (TFT) arrays, patterned PMMA composite as an optical diffuser in a liquid crystal display for

backlighting unit (BLU), control on thermo-physical and optical properties of a diffuser
using patterned polymer in LCD backlights units.
Micro patterning of polymer surfaces for Electronic and Biornaterials applications.
Surfaces for nano-biotechnology applications like biochemical sensors, drug delivery,
tissue engineering, single molecule enzymology, proteomic or genomic arrays,
photodiode arrays for sub retinal implant and patterned substrates for probing of cell
behavior etc.
MEMS-Based Micro-Fuel Cell Systems for portable power applications.
Large-area micro patterning of polymers to facilitate light management in transflective
displays.
Fabrication of diffraction gratings/optical wave guides.
Confined chemistry applications.
Application in the areas of microfluidics, for example for fabrication of large number of
parallel micro channels.
Creating of surfaces with structural colors.
Fabrication of patterned "smart" adhesives and super adhesive surfaces with possible
"clean" peeling options.
Templates for the fabrication of ordered polymer structures by controlled dewetting on
patterned surfaces. EXAMPLES
EXAMPLE 1
Method for generating complex micro patterned surfaces by data storage
As mentioned already, one of the possible sources of patterned flexible foils to be used as stamps is the commercially available optical data storage disc like CD-R, DVD etc. More complex patterns are created simply by storing unformatted data in optical storage disks, like CD-R or DVD-R etc., as listed in claim 12. It is known from information in open domain that any character is stored in a binary form in a computer memory (see for example, reference http://computer.howstuffworks.com/cd-burner4.htm). Eight bits represent one character and each bit can hold a value of either "0" or "1". Each character has its own binary map, which can be obtained in "ASCII Table" (For example, "A" in 8 bit form is 00110001, while "B" is 00110010 etc.). When any data is stored or "written" in an optical disk a "write laser" etches some pits along this track on the polycarbonate disk and matching "bum marks" in the form of raised pillars are created on the adjoining metal foil. It is also known that the flat portion of the etched track represents "0" while any change of height along the track represents "1".
This way, laser etching by the "write laser" itself is creating a patterned surface. The laser beam irradiates the polymeric track, so as to elevate the temperature of that region to a predetermined level where polymer gets "burnt" to form the pits, which now physically represent "0"s and "l"s, corresponding to the sequence of data to be stored. For the sake of completion, it should be mentioned that these topographical features, is decoded by the "read laser", as it picks up the variation of reflected optical intensity of the incident laser beam when it scans the structured topography of storage medium. The "read laser" does not change the surface topography of the track.
Based on the understanding of the mapping of the actual physical topography created on the optical data storage disk (by laser burning) corresponding to each character it was possible to program the data to be stored and generate any specific pattern. By modulating the data to be stored, it was, for example possible to control the number density of the features created on the tracks of the flexible metal foil or the patterned polymer part of a digital data storage disk. The features in this context relate to the array of raised pillars along the tracks in case of the flexible metal foil part or array of holes along the trenches of the patterned polymer (polycarbonate) part of the disks. For example, by saving a data file,
containing the character "L" only (....LLLLLL ) in a format free text file and subsequently
burning it to a CD, the features obtained on the flexible foil part of a CD is shown in figure 4(A). The number density of the pillars is ~ 0.30 ± 0.023 per urn2 area, with length of each pillar ~ 1.45 ± 0.22 urn and the height of the pillars is ~ 35 nm. The size of the file was ~ 700 MB, so that it spreads over the entire storage area of the CD, ensuring the formation of the features all over the CD. Similarly, by creating another file which contained the character "o* only, the number density of the features obtained was ~ 0.18 ± 0.027 per pm2 area for the pits and the average length of each pillar ~ 2.85 ± 0.57 urn (figure 2(B)). EXAMPLE 2:
Room temperature pressure less adhesive force assisted imprinting of soft elastomeric films coated on planar surfaces using flexible patterned foil:
Experiments were performed on crosslinked polydimethylsiloxane (PDMS) films (surface layers) of thickness range varying from about 0.2 to about 15 urn, deposited on quartz substrate. The shear modulus of the surface layer was varied from about 0.01 MPa to 2.0 MPa by varying the concentration of the crosslinker between 5 % and 15 % (Sylgard 184, a two part thermally curable elastomer from Dow Chemicals) in the casting solution.
The PDMS (polydimethylsiloxane) surface layer was spin coated from solution in hexane and then cured at 130° C for 12 hours to crosslink the PDMS (polydimethylsiloxane) and yield a dominantly elastic surface layer.
The invented method allows formation of sub micron features on soft elastic polymeric material surface by imprinting with the flexible patterned foils as stamps.
A schematic view of the present method of imprinting patterns on soft surfaces layers is shown in figure 3. The patterned foils were cleaned and placed upside down on a flat glass plate, with the patterns facing upwards. The cross linked PDMS (polydimethylsiloxane) surface layers were gently placed on the patterned foils (as shown in figure 1). As the slides were placed on the foil pieces, the only compressive force the PDMS (polydimethylsiloxane) films were subjected to was due to the weight of the quartr slides themselves. The adhesive between the films and the foils were strong enough to cause deformation of the low shear modulus PDMS (polydimethylsiloxane) surface layer together with a conformal bending of the foils resulting in a perfect negative replica. This imprinting on the surface layer is engendered by elastic deformation in the cross linked PDMS (polydimethylsiloxane) layer, as evidenced by a rapid disappearance of the imprint upon removal of the foils form the surface of the PDMS (polydimethylsiloxane) layer. The patterns were made permanent by UV-ozone treatment for 30 minutes of the PDMS (polydimethylsiloxane) layer in contact with the flexible foil stamp. UV irradiation at 185 nm produces ozone from atmospheric oxygen, which further gets dissociated to atomic oxygen at 254 nm irradiation. This atomic species reacts with the siloxane group, releasing volatile products and leaving behind a stiff surface layer consisting of oxides of silicon (see references Ouyang, M.; Muisener, R. J.; Boulares, A.; Koberstein, J. T. Journal of Membrane Sci. 2000, 177, 177. Ouyang, M.; Yuan, C.; Muisener, R. J.; Boulares, A.; Koberstein, J. T.
Chem. Mater. 2000, 12, 1591.). The higher modulus of the surface layer prevents the relaxation of the film and preserves the relief patterns imprinted on the soft surface by the foil. The novelty of the method lies in the fact that no pressure was applied externally to imprint the patterns on the PDMS (polydimethylsiloxane) surface layer.
Figures 5(A) and 5(B) show the patterns obtained on 1.63 urn and 1.43 urn thick cross linked PDMS (polydimethylsiloxane) surface layer coated on quartz substrates using a the patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The width, height and the periodicity of the stripes obtained using a CD mold were 743 nm (± 30 nm), 108 nm (± 15 nm) and 1.55 urn (± 0.092 um), respectively. The same parameters obtained using a DVD were 260 nm (± 25 nm), 66 nm (± 9.1 nm) and 773 nm (± 43 nm), respectively (figure 4B). In case of figure 5(C), the foil of a CD having data written on it (file containing " ..LLLLLL.", figure 4(A)) was used to pattern a crosslinked PDMS (polydimethylsiloxane) film having thickness 1.98 um. The imprinted pattern had array of elongated holes along the trenches, apart from having parallel stripes, having periodicity 1.50 um and height of 125 nm. The average length and depth of the holes were 1.68 um (± 0.19 um) and 27 nm (± 4.0 nm) respectively.
Imprinting very thin surface layers, with the same stamps as shown in figure 3(A) and 3(B), it was no longer possible to obtain perfect negative replica of the stamp below a critical film thickness (Hc). Instead, a doubly-periodic structure with stripes split in the middle was obtained as shown in figure 6. The critical thickness was found to be a function of the periodicity of the pattern on the stamp only. The splitting of the stripes result from the fact that as the film gets thinner, the material deformed is not adequate to fill up the space between the adjacent protrusions of the master completely, as shown schematically in figure 6(A). For film thickness slightly lower than Hc. the depth of the line that splits a
stripe is less than the depth of the "valley" between the two adjacent stripes, which is termed as the"partially split' configuration. Example of this is shown in the pattern of figure 6(B). In case of figure 6(B), a 231 nm film was imprinted with an aluminum foil shown in figure 3(A). In this case, while the height of the stripes is ~ 77 nm, the depth of the spilt is ~ 36 nm. With progressive reduction of the film thickness the asymmetric split patterns obtained tend to become more symmetric in nature as another critical thickness, Hchalf is reached. At this thickness, the cross sectional profiles of the line splitting a stripe and that of the valley between the two "original" adjacent stripes becomes identical, which is termed as the "perfect split" (schematic in figure 6(A)) configuration. For example, by imprinting a 92 nm thick surface layer of cross-linked PDMS (polydimethylsiloxane) with an aluminum foil shown in figure 3(B) as stamp, "perfect split' patterns having 35 (± 3.8) nm high stripes with periodicity of 379 nm (± 11.3) were obtained (Figure 6(C)). Interestingly, this pattern now appears as if it is a perfect replica of a mold of 400 nm periodicity, even though the mold used is of 800 nm period! In essence, the imprinted pattern now has half the periodicity of the master. Thus it is possible to obtain patterns having lateral dimension less than that of the original stamp as well pattern periodicity (pitch) less than the periodicity (pitch) of the stamp, as claimed in claims 11 and 12.
Two dimensional crossed patterns can also be generated on the surface layer by using a stamp with one dimensional feature by a two step process. The top surface of the PDMS (polydimethylsiloxane) film, in presence of the patterned flexible stamp was first partially hardened by the UV irradiation for a short duration (~ 5 minutes) to prevent its immediate relaxation. The stamp was then withdrawn, rotated and brought back into contact with the film at an angle to the initial patterns and subsequently cured with UV-ozone for another 25 minutes. The isotropic array of square pillars thus obtained using
aluminum foils as shown in figures 3(A) and 3(B) respectively as stamp, with 90° rotations of the molds are shown in figures 7(A) and 7(B), respectively. To create the anisotropic pattern shown in figure 7(C), the PDMS (polydimethylsiloxane) film was first imprinted with a patterned aluminum foil shown in figure 3(A) and subsequently with another patterned aluminum foil shown in figure 3(B), at right angles to the direction of the stripes obtained after the first imprinting. This resulted in an array of rectangular pillars, having roof dimensions of about 750 nm x 370 nm. The second imprint at an angle of 45° to the direction of the first imprint using aluminum foil shown in figure 3(B) as stamp, resulted in the pattern shown in figure 7(D), where an array of rhombic columns on the surface is obtained. Thus, by using a combination of multiple 1-D masters and varying the angles between the successive imprints, one can engineer a large variety of complex 2-D patterns. It may be noted that no external pressure was needed even for the second imprinting stage too.
EXAMPLE 3:
Room temperature pressure less adhesive force assisted imprinting of soft elastomeric films coated on non-planar (curved) surfaces using flexible patterned foil:
Similar to patterning of soft crosslinked PDMS (polydimethylsiloxane) films coated on planar surfaces (as discussed in Example 2), this method can be used for making permanent relief patterns on the surfaces of such (crosslinked PDMS (polydimethylsiloxane) films) coated on non planar, curved surfaces. However, as discussed already, a patterned metal foil can't be used in this case as a stamp, as it is not transparent to UV and therefore, patterned PVA foils, which are transparent to UV irradiation was used as the stamp to in order to successfully make the patterns permanent. Figure 8(A) shows a digicam picture of
a ~ 6.0 urn thick patterned crosslinked PDMS (polydimethylsiloxane) film on a cylindrical glass tube having diameter 1.8 cm. For this case, a PVA foil having 1.5 urn periodicity (750 nm stripe width) was used. The length of the patterned zone is ~ 4.0 cm. Figure 8(B) shows the corresponding optical micrograph of the patterned PDMS (polydimethylsiloxane) film. Figure 8 (C) shows the Optical micrograph of the surface patterns achieved on a 3.8 urn thick crosslinked PDMS (polydimethylsiloxane) film coated on a cylindrical glass rod having diameter 1.2 cm using the flexible patterned PVA foil having 800 nm periodicity as stamp. Even 2-D cross patterns, as have been discussed in details in the context of figure 7, have been successfully obtained on the surface of a 4.6 urn thick crosslinked PDMS (polydimethylsiloxane) film, coated on a 2.2 cm diameter metal tube, as shown in the optical micrograph figure 8(D). EXAMPLE 4:
Room temperature pressure less adhesive force assisted imprinting of soft etastomeric pre-cast blocks and layers fusing flexible patterned foil:
Figure 9 shows that the method is not only applicable for soft solid surface layers coated on planar substrates, but is equally applicable for pre-cast block of soft solid. Here we demonstrate that the surface of a block of cross linked PDMS (polydimethylsiloxane) block can also be patterned in the same way, as shown in figure 1. Similar to the case of patterning a crosslinked PDMS (polydimethylsiloxane) film coated on a curved surface, here too, a flexible patterned PVA stamp has been used and subsequent UV hardening of the PDMS (polydimethylsiloxane) surface is done to make the patterns permanent. EXAMPLE 7
Room temperature imprinting of Hydrogel films using flexible patterned stamps: Figures 14(A) and 14(B) show the patterns obtained on ~ 5.0 urn thick PAA
(polyacrylamide) based hydrogel films using patterned flexible aluminum foils as shown in figure 3(A) and 3(B) respectively. The width, height and the periodicity of the stripes obtained using a the stamp shown in figure 3(A) were 781 nm (± 17 nm), 121 nm (± 11 nm) and 1.49 urn (± 0.105 urn), respectively. The same parameters obtained using the stamp shown in figure 3(B) were 291 nm (± 18 nm), 69 nm (± 4.3 nm) and 804 nm (± 31 nm), respectively. The flexible stamp results in close conformal contact with hydrogel film surface, thereby ensuring the formation of a perfect negative replica of the stamp pattern. The critical staqe while patterning hydrogel films by this method was found to be the gelation time, which was a function of the initial volume of the reaction mixture added to cast the film. Another critical parameter was the drying of the film while in contact with the stamp. For thicker hydrogel films, the drying was associated with buckling of the film, which resulted in peeling of the film from the substrate (glass slide). Thinner films (

1. A process for generating micro and sub-micro patterns on soft solid surface layers by
elastic deformations at room temperature and without application of any external
pressure, comprising the step of using a patterned flexible foil as the stamp.
2. The method as claimed in claim 1, wherein the process of forming patterns by
pressure less room temperature patterning on soft solid surface layers by elastic
deformation, comprises the steps of:
i. using the flexible patterned foil as the stamp for patterning;
ii. placing the stamp in a conformal contact with the soft surface layer;
iii. allowing an adhesive force assisted imprint to form on the soft surface
layer, by a conformal adhesive contact with the stamp, leading to elastic
deformation of the soft surface; iv. rendering the resultant patterns on the soft solid surface layer permanent;
and v. repeating the steps of using the flexible patterned foil as the stamp and
rendering the pattern on the soft surface layer permanent in a desired
sequence, by withdrawing the stamp compared to its previous position, and
re-engage it to create a new pattern on the soft solid surface by elastic
deformation each cycle.
3. The method as claimed in claim 1, wherein the shear modulus of the soft solid
surface layers in steps (i)-(v) of claim 2 is less than 100 MPa, more preferably less
than 10 MPa.
4. The method as claimed in claim 1, wherein the soft solid surface layer patterned is
planar or curved.

5. The method as claimed in claim 1, wherein the patterning of the soft solid surface
layer is achieved directly in the solid state.
6. The method as claimed in claim 1, wherein the soft solid surface layer is at room
temperature during steps (i)-(v) of claim 2.
7. The method as claimed in claim 1, wherein no external pressure is applied during
steps (i)-(v) of claim 2, either on the stamp or on the soft solid surface layer.
8. The method as claimed in claim 1, wherein said soft solid surface layer patterned
can be polymers like cross-linked polydimethylsiloxane (PDMS), polyacrylamide
(PAA) based hydrogels, gelatin etc.
9. The method as claimed in claim 1, wherein rendering the resultant pattern
permanent involves surface curing by chemical or physical process. The possible
surface curing steps can be ultra-violet radiation, controlled drying, chemical
reactions on the surface etc.
10. The method as claimed in claim 1, wherein the patterns are comprised channels,
array of pits within the channels, array pillars having rectangular, square or rhombic
cross sections, or a combination of these structures.
11. The method as claimed in claim 1, wherein the periodicity (pitch) of the patterns
created on the soft solid surface layer are identical to or less than the periodicity
(pitch) of the patterns on the stamp.
12. The method as claimed in claim 1, wherein the lateral dimensions of the patterns
created on the soft solid surface layer are identical or smaller than the lateral
dimensions of the patterns on the stamp.
13. The method as claimed in claim 1, wherein the patterned flexible foil used as the
stamp is a patterned metal foil or a patterned polymer foil.
14. The method as claimed in claim 1, where the patterned flexible foil used as the
stamp can be obtained from a commercially available optical data storage disk,
wherein the optical data storage disk is a data storage medium like a CD-R, a CD-
RW, a DVD-R, a DVD-RW, a Blue Ray Disk or a Digital Multilayer Disk.
15. The method as claimed in claim 15, wherein said optical data storage disk from
which patterned flexible foil is used for patterning is either blank (no data is written
on the disk) or said disk contains some data written or stored therein.
16. The method as claimed in claim 16, wherein distinct topological features like arrays
of pits and protrusions or pillars on the disk foil can be created by writing of data on
the disk.
17. A process for generating a micro and sub-micro patterns on the surfaces or layers of
different of polymers, substantially as herein described and illustrated in the
accompanying drawings.

Documents:

1519-del-2006-Abstract-(05-06-2014).pdf

1519-del-2006-abstract.pdf

1519-del-2006-Claims-(05-06-2014).pdf

1519-del-2006-claims.pdf

1519-del-2006-correspondenc-other.pdf

1519-del-2006-Correspondence Others-(05-06-2014).pdf

1519-del-2006-Correspondence Others-(16-10-2014).pdf

1519-del-2006-Correspondence-Others-(12-02-2008).pdf

1519-del-2006-description (complete).pdf

1519-del-2006-drawings.pdf

1519-del-2006-form-1.pdf

1519-del-2006-Form-18-(12-02-2008).pdf

1519-del-2006-form-2.pdf

1519-del-2006-form-26.pdf

1519-del-2006-form-3.pdf

1519-del-2006-GPA-(16-10-2014).pdf

« Previous Patent

Next Patent »

Patent Number

263318

Indian Patent Application Number

1519/DEL/2006

PG Journal Number

43/2014

Publication Date

24-Oct-2014

Grant Date

20-Oct-2014

Date of Filing

28-Jun-2006

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY

Applicant Address

KANPUR U.P., INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	SHARMA ASHUTOSH	INDIAN INSTITUTE OF TECHNOLOGY, KANPUR U.P., INDIA.
2	FARUQUI DANISH	INDIAN INSTITUTE OF TECHNOLOGY, KANPUR, U.P. INDIA.
3	MUKHERJEE RABIBRATA	INDIAN INSTITUTE OF TECHNOLOGY, KANPUR, U.P. INDIA
4	PATIL, GANESH	INDIAN INSTITUTE OF TECHNOLOGY, KANPUR, U.P. INDIA
5	FARUQUI DANISH	INDIAN INSTITUTE OF TECHNOLOGY, KANPUR, U.P. INDIA

PCT International Classification Number

G03F 9/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA