Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF ULTATHIN/THIN FILMS OF METALLIC COMPOUNDS"
Abstract	The present invention provides an improved process for the preparation of ultrathin/ thin films of metallic compounds comprising of preparing an aqueous solution containing cation/anion or species of corresponding elements in a concentration ranging 10~5 to 10-3M leading to the formation of metal oxides, chalcogenides or halides of which the thin film is desired; adjusting the pH of the solution; preparing a solution of the cation or anion in a volatile organic solvent or a mixture of organic solvents and water leading to formation of metal oxides, chalcogenides, and halides on reacting only in solution form ; spreading the solution on the aqueous solution to form a film at the interface of the aqueous and solvent solutions, evaporating the solvent, compressing the film formed at the interface laterally with a constant compression pressure; dipping a substrate in the solution and withdrawing it from the solution at a uniform rate in the range of 0.5 to 1.5 m/min at a temperature range of 10-50°C;heating thin films formed for crystallization at a temperature ranging between 500 to 800°C to obtain the product.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF ULTATHIN/THIN FILMS OF METALLIC COMPOUNDS"

Abstract

The present invention provides an improved process for the preparation of ultrathin/ thin films of metallic compounds comprising of preparing an aqueous solution containing cation/anion or species of corresponding elements in a concentration ranging 10~5 to 10-3M leading to the formation of metal oxides, chalcogenides or halides of which the thin film is desired; adjusting the pH of the solution; preparing a solution of the cation or anion in a volatile organic solvent or a mixture of organic solvents and water leading to formation of metal oxides, chalcogenides, and halides on reacting only in solution form ; spreading the solution on the aqueous solution to form a film at the interface of the aqueous and solvent solutions, evaporating the solvent, compressing the film formed at the interface laterally with a constant compression pressure; dipping a substrate in the solution and withdrawing it from the solution at a uniform rate in the range of 0.5 to 1.5 m/min at a temperature range of 10-50°C;heating thin films formed for crystallization at a temperature ranging between 500 to 800°C to obtain the product.

Full Text	The present invention relates to an. improved process for the preparation of ultrathin/ thin films of metallic compounds. Particularly the process relates to the preparation of film of metal in the form of oxides, halides, chalcogenides ( i.e. sulphides, selenides, Tellurides). The thickness of the films prepared by the process of the present invention is in the range of 30 to 500 A. The films formed are useful in molecular electronics. The various applications of such films could be as electric capacitors, electrochromic films, corrosion resistant coatings, antireflection coatings, surface passivation coatings etc. The conventional methods employed for the formation of thin/ultrathin films are: (1) Sol-gelation method (sol-gel) (2) Vapour Evaporation Technique (VE) (3) Glow Dishcarge Technologies (Sputtering) (4) Plasma processes (5) Chemical Vapour Deposition (CVD) (6) Electro plating (7) Spray Pyrolysis (8) Spin on method (9) Langmuir Blodgett Method (LB) (10) Liquid liquid interface reaction technique (LLIRT) The above mentioned methods and their drawbacks are discussed below. (1) Sol-gel Method: Molecular or atomic conglomerates when stabilize in a suspended state in an aqueous liquid is called sol. These conglomerates or suspensions can be destabilized to aggregated particles or homogeneous gel by changing the conditions of solvation or suspension in sols. If the said molecular or atomic conglomerates are desired to be deposited in the form of uniform films during gelation, a substrate, glass plate or quartz plate or the like is dipped in a sol and drawn out. A thin coating of gel is formed. The substrate is then dried. The heat treatment of substrate leads to oxide coating. Drawbacks: The conditions of sol stabilization and gelation are very critical. Also, thickness control is difficult. During the drying of gel and post deposition heat treatment, large volume changes bring about cracks in gel material and therefore it is difficult to get homogeneous, uncracked films. Reference: Journal of non-crystalline solids, vol 100, Proceedings of the Forth International Workshop on Glasses and Glass Ceramics from Gels, section 7, Pages. 479-542, 1988. (2) Vacuum Evaporative Technologies: The substance of which a thin / ultrathin film is to be deposited is generated in vapour state by boiling, sublimating or vapourizing by giving sufficient energy by heating, electron beam bombardment, lasers or any other energy source.' In the second step vapour is transported to substrate without any chemical change occuring in the substance and in the last step, the substance is allowed to condense / deposite on substrate surface such as glass/ quartz plate, silicon wafer etc. Drawbacks: High vacuum is required. Some chemical changes in substance composition is quite common such as nonstoichiometry or contamination from source container. For the uniform and adherent films to be obtained, the number of parameters are large and therefore process monitoring and control is needed. Molecular beam epitaxy which is an improved technology over vacuum evaporation is mainly used for growing single crystalline films (very ordered films) on single crystal substrates. The cost and number of parameters are increased many folds. The operation* is complex and throughput is very low. Reference: Handbook of thin film deposition processes and techniques. K. K. Schuegrat Noyes Publication, Park Ridge, New Jersey USA (1988) Thin film phenomenon K. L. Chopra. McGraw -Hill Book Co. New York USA (1969). (3) Glow discharge technologies (Sputtering): The ejection of surface atoms from an electrode surface by momentum transfer from bombarding ion is called sputtering. In other words during sputtering process source of electrode material in vapour state is made available, which is used for thin film formation as in vacuum evaporation. There are various ways in which basic process is modified. AC sputtering, bias sputtering, magnetron sputtering are often used modifications. Drawback : The main drawback is contamination problem. Also, the equipment is sophisticated and very costly. Reference Handbook of thin film deposition processes and techniques. K. K. Schuegrat Noyes Publication, Park Ridge, New Jersey USA (1988) Thin film phenomenon K. L. Chopra. McGraw - Hill Book Co. New York USA (1969). (4) Plasma processes: Some chemical reactions are accelerated in presence of bombarding reactive ions. Therefore, the electrode material (metal) in presence of gases like 02 , N2+H2, CH4 forming a glow discharge forms a film of metal oxide, carbide, nitride on the substrate surface. The plasma can be generated by means of discharge in vacuum, electron bumbardment, cyclotron resonance etc. Drawback: The drawbacks of this process is again high cost equipment. Also limited number of reactions can be carried out and thin films formed by this method. Reference: Handbook of thin film deposition processes and techniques. K. K. Schuegrat Noyes Publication, Park Ridge, New Jersey USA (1988) Thin film phenomenon K. L. Chopra. McGraw Hill Book Co. New York USA (1969). (5) Chemical vapour deposition: In this method the constituents of vapour phase are made to react near or on the substrate surface where the solid product is obtained in thin film form. Since large number of reactions are avail¬able, CVD is versatile and flexible technique in producing variety of products (oxides, sulphides, selenides etc.) in thin film form including metals, semiconductors, insulators. Metal organics are very convenient for CVD application as relatively low temperatures, can transform them in vapour phase, compared to pure inorganic compounds. This, therefore has become a main modification of CVD called MOCVD. As a modification of CVD, other energy sources assistance is taken to carry out reactions by increasing the reaction rates. The lasers, photons (light) are utilized for this purpose. > Drawback : Although the chemistry part of CVD appears to be simple, the monitoring of many parameters is needed to achieve films of good quality. The process, therefore, becomes technically complicated and critical. Also, thick¬ness control of the film is difficult. Reference Handbook of thin film deposition processes and techniques. K. K. Schuegrat Noyes Publication, Park Ridge, New Jersey USA (1988) Thin film phenomenon K. L. Chopra. McGraw -Hill Book Co. New York USA (1969). (6) Electroplating: When a current is passed through a conducting solution (electrolyte) and suitable reactions are taking place at either cathode i.e. negative electrode or anode i.e. positive electrode, it is possible to employ this method in depositing thin films on conducting substrates. By controlling the pH, current density (current / area of electrode ), temperature, composition of electrolyte it is possible to get uniform films of metals.some metal oxides, chalcogenides etc. Drawbacks: Films are obtained only on the conducting substrates. Also, the contamination is a common problem as many reactions can take place simultaneously. Reference Handbook of thin film deposition processes and techniques. K. K. Schuegrat Noyes Publication, Park Ridge, New Jersey USA (1988) Thin film phenomenon K. L. Chopra. McGraw A Hill Book Co. New York USA (1969). (7) Spry pyrolysis: The "atomised" droplets of the solution are spread on hot substrate where pyrolysis takes place, leading to a film on the substrate surface. Although versatile, this method is not useful for making ultra-thin films. Reference Chemical spray deposition process for inorganic films. R. R. Chamberlin and J. S. Skarman. J. Electrochem Soc. 113(1) 86, (1966). J. E. Hill and R. R. Chamberlin. U. S. Patent 3,148.084 (1964). (8) Spin on method: In "spin on" method of depositing thin films a drop of solution or sol is placed on rotating substate. By centrifugal force the solution /sol is spread on the surface of the substrate where geletion reaction takes place as explained in the sol -gel technique. Further heating the substrate, converts the gel film in ,to oxide film. Drawbacks: The method can be used only for specific applications. Also, very thin film in submicron range cannot be deposited by this method with uniformity and continuity. Reference: Schroeder H. Physics of thin films, Vol.5, Page 87- Editor G. Mass and R.E.Thun Acad. Press. New York, 1969. (9) Langmuir Blodgett method: In this method a known quantity (1x10"5 tolxlO^M) of a solution of film forming materials such as fatty acids C PH 2n+i COOH or amines C nH 2n+i NH 2 dissolved in volatile solvent such as benzene, chloroform, carbon tetrachloride etc. is delivered on a known area of clean water surface held in Langmuir trough (rectangular or circular) fitted with film pressure balance. These materials form monomolecular films at air- water interface, on lateral compression of the film with help of barrier or oil piston (such as oleic acid), condensed phase is obtained. If the soluble metal salts are added in aqueous subphase the cations/or(anions) get attached to the acid/(or amine) groups at the surface. The deposition of a monolayer on to a solid substrate such as glass plate quartz plate silicon wafer etc. is effected by introducing the substrate inside the aqueous subphase. For every withdrawal or dipping of the substrate one monolayer is deposited. Usually the dipping or withdrawal is effected under constant surface pressure (15 to 35 dynes/cm.).The nature and the amount of the species deposited from the aqueous subphase depends on deposition condition such as concentration, pH, rate of dipping and withdrawal, deposition pressure etc. By varying the deposition parameters the optimal condition for the deposition of metal ion is obtained. The deposited films are then thermally decomposed (500-900° C) to get stable ultrathin oxide films. The thickness of the film can be controlled by the number of monolayer deposited. Drawbacks: Only limited number of cation or anions could be brought in the film to react and to give desired product. Also, in the post deposition treatment, the long chain carbon containing part is to be removed mainly by burning. This leaves some chances of 'C'(carbon) contamination in the films. Also, the chemical reduction of the film material by carbon during heat treatment is possible. Reference: T.Nakaya, Yu Jun, K. Shibata Preparation of ultrathin particle multilayers using the Langmuir-Blogette technique. J. Mat. Chem. 6(5), 1996, 691-697. (10) Liquid liquid interface reaction technique (LLIRT): In this process two immiscible, an aqueous and organic solvent- solutions, containing spacies which react at the interface and form a solid product of desired material or a precursor to it, in a particulate film form. This film is pressurised laterally which facilitates its transfer on desired substrate when the substrate is vertically dipped and withdrawn from the solution with a conveninent rate. Drawback: One of the solutions use oraganic solvent which limits the scope of this method. The spacies which are insoluble in organic solvent and soluble in aqueous solvent only, could not be used via spreading over aqueous phase. Reference: S.D.Sathaye, K.R.Patil, D.V.Paranjape U.S.Patent no.5549931 dated 27th Sept. 1996. The main object of the invention is to provide an improved and versatile method for preparation of ultrathin/thin films. Another object of the present invention is to provide an improved process for preparation of ultra thin films. The principle by which the process of the present invention is developed is based on 1) The formation of an aqueous salt solution in the dilute concentration, 2) Formation of a solution of another salt in organic solvent or a mixture of organic solvents or a mixture of organic solvents and water which spreads on aqueous surface e.g. carbon tetrachloride, chloroform, benzene, n-hexane etc. 3) Choosing the salts in 1 and 2 such that they can react with each other in solution state and form a solid product. 4) Since the reaction takes place only on the surface of the aqueous phase, the solid product obtained can be in the form of a thin film and finally 5) A suitable method for transferring the thin film formed on the aqueous surface to the substrate surface. Accordingly, the present invention provides an improved process for the preparation of ultrathin/ thin films of metallic compounds comprising of a) preparing an aqueous solution containing cation/anion or species of corresponding elements in a concentration ranging 10"" to 10-"M leading to the formation of metal oxides, chalcogenides or halides of which the thin film is desired; b) adjusting the pH of the solution in the range of 3 to 12; c) preparing a solution of the cation or anion or species of the another salt in a concentration ranging 10° to 10-JM and the said salt being immiscible and reacting interfacially with the salt prepared in step (a), in a volatile organic solvent or a mixture of organic solvents and water leading to formation of metal oxides, chalcogenides, and halides on reacting only hi solution form with the solution prepared in step (a); d) spreading the solution as prepared in step (c) on the aqueous solution prepared in step (a) so as to form a film at the interface of the aqueous and solvent solutions, evaporating the solvent, compressing the film formed at the interface laterally with a constant compression pressure in the range of 18-35 dynes/cm; e) dipping a substrate in the solution formed in step d) to have a thin film on the surface of the said substrate and withdrawing it from the solution at a uniform rate in the range of 0.5 to 1.5 m/min at a temperature range of 10-50°C; f) heating thin films so formed as in step e) for crystallization at a temperature ranging between 500 to 800°C. In an embodiment of the present invention the elements used for preparing aqueous solution are selected from Si, Ti, Al, V, Cr, Min, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo. Pd, Sn, In, Sb, Ba, Sr, La, Ta, W, Pb, Ce and their solid solutions. In another embodiment of the present invention elements used for preparing chaleogenides form in solvent solution are selected from Cu, Fe, Ni, Ga, In, Sn. Sb, Cd, Hg and their solid solutions and in halide forms are selected from Ag. Hg, Cu and their solid solutions. The organic solvents used in the process of invention may be selected from carbon tetrachloride, chlroform, benzene, n-hexane, tetrahydrofuran, carbon disulphide, water and mixtures thereof. The evaporation of the solvent may be effected by natural evaporation, IR heating etc. The substrates may be selected from glass plates, quartz plates, single crystal wafers of Si, Ge, SrTiOS, BaTiOS AI203 plates, pellets of the compounds such as ZnO, Zr02, MgO, plates of Zr02, MgO etc. The invention is illustrated by the examples given below which should not be construed to the limit of the scope of present invention. Example I A solution of sodium hydroxide in a concentration of 1x 10~3 M in double distilled water is prepared. The solution is contained in a teflon trough 45 times 15 times 2 cms size. The solution is marked as 'A'. A solution of potassium titanyl oxalate in a concentration of 1 x 10'3 M in a mixture of carbon tetrachloride and water is prepared. This solution is marked as 'B'. 0.5 ml. of solution 'B' is spread on solution 'A1. The film formed at the interface of aqueous phase and spreading solution is compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.), after evaporating the spreading solvent. A quartz plate 1 times 1 cm. was vertically dipped and withdrawn from the solution with a rate 1cm./min. transfering the film on the substrate. This operation is repeated fifty times, for increasing the thickness. A film thus formed is heated to high temperature 800°C for 24 hours. The film is characterized by X-ray diffraction and was determined to be TiO2 Example II A solution of potassium iodide in the concentration of 3 x 10"* M. in double distilled water was prepared. The solution is ontained in a teflon trough of 45x15x2 cm. size. This solution is marked, as 'A'. A solution of AgN03 in undried chloroform is prepared with the concentration of 1 x 10~5 M. This solution is marked as solution 'B'. 0.2 ml. of 'B' was spread on 'A' to form a film of silver iodide on the surface of aqueous solution. After evaporating chloroform the film was compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.) and transferred on glass substrate of 1x1x0.25 cm. size, by dipping it into the solutions for 100 times to form the thin layer of film on the substrate. The film thus formed is charactrised by low angled XRD and was found to be of Silver iodide. Example III A solution of sodium hydroxide in a concentration of 1 x 10"3 M in double distilled water is prepared. The solution is contained in teflon trough of the size 45x15x2 cm. The solution is marked as 'A'. A solution of zinc chloride in a concentration of 1 x 10~3 M in water is prepared. o.2 ml of this solution is added to 5 ml of dry carbon tetrachloride. This solution is marked as 'B1. 0.5ml. of 'B1 is spread over 'A'. The film forms at interface. The spread solution / is allowed to evaporate. The film on the aqueous surface is compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.). A quartz substrate is vertically dipped and withdrawn from the solutions with a fix rate of 0.5 cm/min. This operation is repeated 100 times. The film is transfered on quartz substrate during this process. The film is thus obtained is heated at 600° C and characharised by XRD as zinc oxide phase. The main advantages of the present invention. 1. The method does not require any sophisticated equipment. 2. The method is low cost. 3. The method is very simple and the parameters can easily be monitored. 4. The thickness of the film prepared can be controlled. 5. Uniformity and adherence of the film prepared is good. 6. Large area deposition is possible. 7. The method is useful to deposit ultrathin films. 8. Inorganic spacies insoluble in pure organic solvents also could be spread by using suitable mixture of organic solvents and water. 9. Saving of chemicals. We Claim: 1. An improved process for the preparation of ultrathin/ thin films of metallic compounds a) preparing an aqueous solution containing cation/anion or species of corresponding elements in a concentration ranging 10"5 to 10-3M leading to the formation of metal oxides, chalcogenides or halides of which the thin film is desired; b) adjusting the pH of the solution in the range of 3 to 12; c) preparing a solution of the cation or anion or species of the another salt in a concentration ranging 10~5 to 10-3M and the said salt being immiscible and reacting interfacially with the salt prepared in step (a), in a volatile organic solvent or a mixture of organic solvents and water leading to formation of metal oxides, chalcogenides, and halides on reacting only in solution form with the solution prepared in step (a); d) spreading the solution as prepared in step (c) on the aqueous solution prepared in step (a) so as to fofm a film at the interface of the aqueous and solvent solutions, evaporating the solvent, compressing the film formed at the interface laterally with a constant compression pressure in the range of 18-35 dynes/cm; e) dipping a substrate in the solution formed in step d) to have a thin film on the surface of the said substrate and withdrawing it from the solution at a uniform rate in the range of 0.5 to 1.5 m/min at a temperature range of 10-50°C; f) heating thin films so formed as in step e) for crystallization at a temperature ranging between 500 to 800°C. 2. A process as claimed in claim 1, wherein the elements used for preparing films in oxide form in aqueous solution are selected from Si, Ti, Al, V, Cr, Min, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Pd, Sn, In, Sb, Ba, Sr, La, Ta, W, Pb, Ce and their solid solutions. 3. A process as claimed in claims 1 and 2, wherein elements used for preparing chaleogenides form in solvent solution are selected from Cu, Fe, Ni, Ga, In, Sn, Sb, Cd, Hg and their solid solutions and in halide forms are selected from Ag, Hg, Cu and their solid solutions. 4. A process as claimed in claims 1 to 3, wherein the substrates which can be used for deposition of the films are selected from the group of materials, glass, quartz, polymer silicon or other organic and inorganic solid flats. 5. A process as claimed in claims 1 to 4, wherein solvents used in step c) are selected from carbon tetrachloride, chloroform, hexane, benzene, tetrahydrofuran, water and the mixtures thereof 6. An improved process for the preparation of ultrathin/ thin films of metallic compounds substantially as hereinbefore described with reference to the examples.

Full Text

The present invention relates to an. improved process for the preparation of ultrathin/ thin films of metallic compounds. Particularly the process relates to the preparation of film of metal in the form of oxides, halides, chalcogenides ( i.e. sulphides, selenides, Tellurides). The thickness of the films prepared by the process of the present invention is in the range of 30 to 500 A. The films formed are useful in molecular electronics. The various applications of such films could be as electric capacitors, electrochromic films, corrosion resistant coatings, antireflection coatings, surface passivation coatings etc.
The conventional methods employed for the formation of thin/ultrathin films are:
(1) Sol-gelation method (sol-gel)
(2) Vapour Evaporation Technique (VE)
(3) Glow Dishcarge Technologies (Sputtering)
(4) Plasma processes
(5) Chemical Vapour Deposition (CVD)
(6) Electro plating
(7) Spray Pyrolysis
(8) Spin on method
(9) Langmuir Blodgett Method (LB)
(10) Liquid liquid interface reaction technique (LLIRT)
The above mentioned methods and their drawbacks are discussed below.
(1) Sol-gel Method: Molecular or atomic conglomerates when stabilize in a suspended state in an aqueous liquid is called sol. These conglomerates or suspensions can be destabilized to aggregated particles or homogeneous gel by changing the conditions of solvation or suspension in sols. If the said molecular or atomic conglomerates are desired to be deposited in the form of uniform films during gelation, a substrate, glass plate or quartz plate or the like is dipped in a sol and drawn out. A thin coating of gel is formed. The substrate is then dried. The heat treatment of substrate leads to oxide coating.

Drawbacks: The conditions of sol stabilization and gelation are very critical. Also, thickness control is difficult. During the drying of gel and post deposition heat treatment, large volume changes bring about cracks in gel material and therefore it is difficult to get homogeneous, uncracked films.
Reference:
Journal of non-crystalline solids, vol 100, Proceedings of the Forth International Workshop on Glasses and Glass Ceramics from Gels, section 7, Pages. 479-542, 1988.
(2) Vacuum Evaporative Technologies: The substance of which a thin / ultrathin film is to be deposited is generated in vapour state by boiling, sublimating or vapourizing by giving sufficient energy by heating, electron beam bombardment, lasers or any other energy source.' In the second step vapour is transported to substrate without any chemical change occuring in the substance and in the last step, the substance is allowed to condense / deposite on substrate surface such as glass/ quartz plate, silicon wafer etc.
Drawbacks: High vacuum is required. Some chemical changes in substance composition is quite common such as nonstoichiometry or contamination from source container. For the uniform and adherent films to be obtained, the number of parameters are large and therefore process monitoring and control is needed. Molecular beam epitaxy which is an improved technology over vacuum evaporation is mainly used for growing single crystalline films (very ordered films) on single crystal substrates. The cost and number of parameters are increased many folds. The operation* is complex and throughput is very low.
Reference:
Handbook of thin film deposition processes and techniques.
K. K. Schuegrat
Noyes Publication, Park Ridge, New Jersey USA (1988)

Thin film phenomenon
K. L. Chopra.
McGraw -Hill Book Co. New York USA (1969).
(3) Glow discharge technologies (Sputtering): The ejection of surface
atoms from an electrode surface by momentum transfer from bombarding ion
is called sputtering. In other words during sputtering process source of
electrode material in vapour state is made available, which is used for thin film
formation as in vacuum evaporation.
There are various ways in which basic process is modified. AC sputtering, bias sputtering, magnetron sputtering are often used modifications.
Drawback : The main drawback is contamination problem. Also, the equipment is sophisticated and very costly.
Reference
Handbook of thin film deposition processes and techniques.
K. K. Schuegrat
Noyes Publication, Park Ridge, New Jersey USA (1988)
Thin film phenomenon
K. L. Chopra.
McGraw - Hill Book Co. New York USA (1969).
(4) Plasma processes: Some chemical reactions are accelerated in
presence of bombarding reactive ions. Therefore, the electrode material
(metal) in presence of gases like 02 , N2+H2, CH4 forming a glow discharge
forms a film of metal oxide, carbide, nitride on the substrate surface. The
plasma can be generated by means of discharge in vacuum, electron
bumbardment, cyclotron resonance etc.

Drawback: The drawbacks of this process is again high cost equipment. Also limited number of reactions can be carried out and thin films formed by this method.
Reference:
Handbook of thin film deposition processes and techniques.
K. K. Schuegrat
Noyes Publication, Park Ridge, New Jersey USA (1988)
Thin film phenomenon K. L. Chopra. McGraw Hill Book Co. New York USA (1969).
(5) Chemical vapour deposition: In this method the constituents of vapour phase are made to react near or on the substrate surface where the solid product is obtained in thin film form. Since large number of reactions are avail¬able, CVD is versatile and flexible technique in producing variety of products (oxides, sulphides, selenides etc.) in thin film form including metals, semiconductors, insulators.
Metal organics are very convenient for CVD application as relatively low temperatures, can transform them in vapour phase, compared to pure inorganic compounds. This, therefore has become a main modification of CVD called MOCVD.
As a modification of CVD, other energy sources assistance is taken to
carry out reactions by increasing the reaction rates. The lasers, photons (light)
are utilized for this purpose. >
Drawback : Although the chemistry part of CVD appears to be simple, the monitoring of many parameters is needed to achieve films of good quality. The process, therefore, becomes technically complicated and critical. Also, thick¬ness control of the film is difficult.

Reference
Handbook of thin film deposition processes and techniques.
K. K. Schuegrat
Noyes Publication, Park Ridge, New Jersey USA (1988)
Thin film phenomenon
K. L. Chopra.
McGraw -Hill Book Co. New York USA (1969).
(6) Electroplating: When a current is passed through a conducting solution
(electrolyte) and suitable reactions are taking place at either cathode i.e.
negative electrode or anode i.e. positive electrode, it is possible to employ this
method in depositing thin films on conducting substrates. By controlling the
pH, current density (current / area of electrode ), temperature, composition of
electrolyte it is possible to get uniform films of metals.some metal oxides,
chalcogenides etc.
Drawbacks: Films are obtained only on the conducting substrates. Also, the contamination is a common problem as many reactions can take place simultaneously.
Reference
Handbook of thin film deposition processes and techniques.
K. K. Schuegrat
Noyes Publication, Park Ridge, New Jersey USA (1988)
Thin film phenomenon K. L. Chopra. McGraw A Hill Book Co. New York USA (1969).
(7) Spry pyrolysis: The "atomised" droplets of the solution are spread
on hot substrate where pyrolysis takes place, leading to a film on the

substrate surface. Although versatile, this method is not useful for making ultra-thin films.
Reference
Chemical spray deposition process for inorganic films.
R. R. Chamberlin and J. S. Skarman.
J. Electrochem Soc. 113(1) 86, (1966).
J. E. Hill and R. R. Chamberlin. U. S. Patent 3,148.084 (1964).
(8) Spin on method: In "spin on" method of depositing thin films a drop
of solution or sol is placed on rotating substate. By centrifugal force the
solution /sol is spread on the surface of the substrate where geletion
reaction takes place as explained in the sol -gel technique. Further
heating the substrate, converts the gel film in ,to oxide film.
Drawbacks: The method can be used only for specific applications. Also, very thin film in submicron range cannot be deposited by this method with uniformity and continuity.
Reference:
Schroeder H.
Physics of thin films, Vol.5, Page 87-
Editor G. Mass and R.E.Thun
Acad. Press. New York, 1969.
(9) Langmuir Blodgett method: In this method a known quantity (1x10"5
tolxlO^M) of a solution of film forming materials such as fatty acids C PH 2n+i
COOH or amines C nH 2n+i NH 2 dissolved in volatile solvent such as benzene,
chloroform, carbon tetrachloride etc. is delivered on a known area of clean

water surface held in Langmuir trough (rectangular or circular) fitted with film pressure balance.
These materials form monomolecular films at air- water interface, on lateral compression of the film with help of barrier or oil piston (such as oleic acid), condensed phase is obtained. If the soluble metal salts are added in aqueous subphase the cations/or(anions) get attached to the acid/(or amine) groups at the surface. The deposition of a monolayer on to a solid substrate such as glass plate quartz plate silicon wafer etc. is effected by introducing the substrate inside the aqueous subphase. For every withdrawal or dipping of the substrate one monolayer is deposited. Usually the dipping or withdrawal is effected under constant surface pressure (15 to 35 dynes/cm.).The nature and the amount of the species deposited from the aqueous subphase depends on deposition condition such as concentration, pH, rate of dipping and withdrawal, deposition pressure etc. By varying the deposition parameters the optimal condition for the deposition of metal ion is obtained. The deposited films are then thermally decomposed (500-900° C) to get stable ultrathin oxide films. The thickness of the film can be controlled by the number of monolayer deposited.
Drawbacks: Only limited number of cation or anions could be brought in the film to react and to give desired product. Also, in the post deposition treatment, the long chain carbon containing part is to be removed mainly by burning. This leaves some chances of 'C'(carbon) contamination in the films. Also, the chemical reduction of the film material by carbon during heat
treatment is possible.
Reference:
T.Nakaya, Yu Jun, K. Shibata
Preparation of ultrathin particle multilayers using the Langmuir-Blogette
technique.
J. Mat. Chem. 6(5), 1996, 691-697.

(10) Liquid liquid interface reaction technique (LLIRT): In this process two immiscible, an aqueous and organic solvent- solutions, containing spacies which react at the interface and form a solid product of desired material or a precursor to it, in a particulate film form. This film is pressurised laterally which facilitates its transfer on desired substrate when the substrate is vertically dipped and withdrawn from the solution with a conveninent rate.
Drawback: One of the solutions use oraganic solvent which limits the scope of this method. The spacies which are insoluble in organic solvent and soluble in aqueous solvent only, could not be used via spreading over aqueous phase.
Reference:
S.D.Sathaye, K.R.Patil, D.V.Paranjape
U.S.Patent no.5549931 dated 27th Sept. 1996.
The main object of the invention is to provide an improved and versatile method for preparation of ultrathin/thin films. Another object of the present invention is to provide an improved process for preparation of ultra thin films.
The principle by which the process of the present invention is developed is based on 1) The formation of an aqueous salt solution in the dilute concentration, 2) Formation of a solution of another salt in organic solvent or a mixture of organic solvents or a mixture of organic solvents and water which spreads on aqueous surface e.g. carbon tetrachloride, chloroform, benzene, n-hexane etc. 3) Choosing the salts in 1 and 2 such that they can react with each other in solution state and form a solid product. 4) Since the reaction takes place only on the surface of the aqueous phase, the solid product obtained can be in the form of a thin film and finally 5) A suitable method for transferring the thin film formed on the aqueous surface to the substrate surface.

Accordingly, the present invention provides an improved process for the preparation of
ultrathin/ thin films of metallic compounds comprising of
a) preparing an aqueous solution containing cation/anion or species of corresponding elements in a concentration ranging 10"" to 10-"M leading to the formation of metal oxides, chalcogenides or halides of which the thin film is desired;
b) adjusting the pH of the solution in the range of 3 to 12;
c) preparing a solution of the cation or anion or species of the another salt in a
concentration ranging 10° to 10-JM and the said salt being immiscible and
reacting interfacially with the salt prepared in step (a), in a volatile organic
solvent or a mixture of organic solvents and water leading to formation of metal
oxides, chalcogenides, and halides on reacting only hi solution form with the
solution prepared in step (a);
d) spreading the solution as prepared in step (c) on the aqueous solution prepared in step (a) so as to form a film at the interface of the aqueous and solvent solutions, evaporating the solvent, compressing the film formed at the interface laterally with a constant compression pressure in the range of 18-35 dynes/cm;
e) dipping a substrate in the solution formed in step d) to have a thin film on the
surface of the said substrate and withdrawing it from the solution at a uniform rate in the range of 0.5 to 1.5 m/min at a temperature range of 10-50°C;
f) heating thin films so formed as in step e) for crystallization at a temperature
ranging between 500 to 800°C.
In an embodiment of the present invention the elements used for preparing aqueous solution are selected from Si, Ti, Al, V, Cr, Min, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo. Pd, Sn, In, Sb, Ba, Sr, La, Ta, W, Pb, Ce and their solid solutions.
In another embodiment of the present invention elements used for preparing chaleogenides form in solvent solution are selected from Cu, Fe, Ni, Ga, In, Sn. Sb, Cd, Hg and their solid solutions and in halide forms are selected from Ag. Hg, Cu and their solid solutions.
The organic solvents used in the process of invention may be selected from carbon tetrachloride, chlroform, benzene, n-hexane, tetrahydrofuran, carbon disulphide, water and mixtures thereof.
The evaporation of the solvent may be effected by natural evaporation, IR heating etc.
The substrates may be selected from glass plates, quartz plates, single crystal wafers of Si, Ge, SrTiOS, BaTiOS AI203 plates, pellets of the compounds such as ZnO, Zr02, MgO, plates of Zr02, MgO etc.
The invention is illustrated by the examples given below which should not be construed to the limit of the scope of present invention.
Example I
A solution of sodium hydroxide in a concentration of 1x 10~3 M in double distilled water is prepared. The solution is contained in a teflon trough 45 times 15 times 2 cms size. The solution is marked as 'A'.
A solution of potassium titanyl oxalate in a concentration of 1 x 10'3 M in a mixture of carbon tetrachloride and water is prepared. This solution is marked as 'B'. 0.5 ml. of solution 'B' is spread on solution 'A1. The film formed at the interface of aqueous phase and spreading solution is compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.), after evaporating the spreading solvent. A quartz plate 1 times 1 cm. was vertically dipped and withdrawn from the solution with a rate 1cm./min. transfering the film on the substrate. This operation is repeated fifty times, for increasing the thickness. A film thus formed is heated to high temperature 800°C for 24 hours. The film is characterized by X-ray diffraction and was determined to be TiO2
Example II
A solution of potassium iodide in the concentration of 3 x 10"* M. in double distilled water was prepared. The solution is ontained in a teflon trough of 45x15x2 cm. size. This solution is marked, as 'A'. A solution of AgN03 in undried chloroform is prepared with the concentration of 1 x 10~5 M.
This solution is marked as solution 'B'. 0.2 ml. of 'B' was spread on 'A' to form a film of silver iodide on the surface of aqueous solution. After evaporating chloroform the film was compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.) and transferred on glass substrate of 1x1x0.25 cm. size, by dipping it into the solutions for 100 times to form the thin layer of film on the substrate. The film thus formed is charactrised by low angled XRD and was found to be of Silver iodide.
Example III
A solution of sodium hydroxide in a concentration of 1 x 10"3 M in double distilled water is prepared. The solution is contained in teflon trough of the size 45x15x2 cm. The solution is marked as 'A'. A solution of zinc chloride in a concentration of 1 x 10~3 M in water is prepared. o.2 ml of this solution is added to 5 ml of dry carbon tetrachloride. This solution is marked as 'B1. 0.5ml. of 'B1 is spread over 'A'. The film forms at interface. The spread solution
/
is allowed to evaporate. The film on the aqueous surface is compressed laterally with the help of oleic acid piston ( pressure 30 dynes/cm.). A quartz substrate is vertically dipped and withdrawn from the solutions with a fix rate of 0.5 cm/min. This operation is repeated 100 times. The film is transfered on quartz substrate during this process.
The film is thus obtained is heated at 600° C and characharised by XRD as zinc oxide phase.
The main advantages of the present invention.
1. The method does not require any sophisticated equipment.
2. The method is low cost.
3. The method is very simple and the parameters can easily be monitored.
4. The thickness of the film prepared can be controlled.
5. Uniformity and adherence of the film prepared is good.
6. Large area deposition is possible.
7. The method is useful to deposit ultrathin films.

8. Inorganic spacies insoluble in pure organic solvents also could be
spread by using suitable mixture of organic solvents and water.
9. Saving of chemicals.

We Claim:
1. An improved process for the preparation of ultrathin/ thin films of metallic compounds
a) preparing an aqueous solution containing cation/anion or species of
corresponding elements in a concentration ranging 10"5 to 10-3M
leading to the formation of metal oxides, chalcogenides or halides of
which the thin film is desired;
b) adjusting the pH of the solution in the range of 3 to 12;
c) preparing a solution of the cation or anion or species of the another
salt in a concentration ranging 10~5 to 10-3M and the said salt being
immiscible and reacting interfacially with the salt prepared in step (a),
in a volatile organic solvent or a mixture of organic solvents and water
leading to formation of metal oxides, chalcogenides, and halides on
reacting only in solution form with the solution prepared in step (a);
d) spreading the solution as prepared in step (c) on the aqueous solution
prepared in step (a) so as to fofm a film at the interface of the
aqueous and solvent solutions, evaporating the solvent, compressing
the film formed at the interface laterally with a constant compression
pressure in the range of 18-35 dynes/cm;
e) dipping a substrate in the solution formed in step d) to have a thin
film on the surface of the said substrate and withdrawing it from the
solution at a uniform rate in the range of 0.5 to 1.5 m/min at a
temperature range of 10-50°C;
f) heating thin films so formed as in step e) for crystallization at a
temperature ranging between 500 to 800°C.
2. A process as claimed in claim 1, wherein the elements used for
preparing films in oxide form in aqueous solution are selected
from Si, Ti, Al, V, Cr, Min, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo,
Pd, Sn, In, Sb, Ba, Sr, La, Ta, W, Pb, Ce and their solid
solutions.
3. A process as claimed in claims 1 and 2, wherein elements used for
preparing chaleogenides form in solvent solution are selected from
Cu, Fe, Ni, Ga, In, Sn, Sb, Cd, Hg and their solid solutions and
in halide forms are selected from Ag, Hg, Cu and their solid
solutions.
4. A process as claimed in claims 1 to 3, wherein the substrates which
can be used for deposition of the films are selected from the
group of materials, glass, quartz, polymer silicon or other
organic and inorganic solid flats.
5. A process as claimed in claims 1 to 4, wherein solvents used in step c) are
selected from carbon tetrachloride, chloroform, hexane, benzene,
tetrahydrofuran, water and the mixtures thereof
6. An improved process for the preparation of ultrathin/ thin films of
metallic compounds substantially as hereinbefore described with
reference to the examples.

Documents:

2372-del-1998-abstract.pdf

2372-del-1998-claims.pdf

2372-del-1998-correspondence-others.pdf

2372-del-1998-correspondence-po.pdf

2372-del-1998-description (complete).pdf

2372-del-1998-form-1.pdf

2372-del-1998-form-19.pdf

2372-del-1998-form-2.pdf

« Previous Patent

Next Patent »

Patent Number

215039

Indian Patent Application Number

2372/DEL/1998

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

20-Feb-2008

Date of Filing

13-Aug-1998

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	PATIL RASHINATH RANGU,	NATIONAL CHEMICAL LABORATORY, PUNE 411008, MAHARASHTRA, INDIA.
2	PARANJAPE DILIP VINAYAK	NATIONAL CHEMICAL LABORATORY, PUNE 411008, MAHARASHTRA, INDIA.
3	SATHAYE SHIVARAM DATTATRAYA,	NATIONAL CHEMICAL LABORATORY, PUNE 411008, MAHARASHTRA, INDIA.

PCT International Classification Number

H01F 10/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA