Title of Invention

"A PROCESS FOR PREPARATION OF ULTRATHIN NANOFILMS OF METALS"

Abstract A process has been developed for preparation of ultrathin nanofilm wherein two solutions are used, one containing a metal and other containing a chemical having reaction capabilities with metal component of first solution resulting in formation of metal particles. A thin metal film is form at the interface of two solution which may be compressed and deposited on a solid surface to get the nanofilm.
Full Text The present invention relates to a process for the preparation of ultrathin nanofilms of metals. The thickness of the films prepared by the process of the present invention is in the range of 30-500 A0. The films formed co.uld have various applications such as corrosion resistance coating, antireflection coating, surface passivation coating, non linear optics (NLO), catalysis, solar energy utilization etc.
The conventional methods employed for the formation of ultra-thin films of metals are :
(1) Vacuum Evaporation Technique (VE)
(2) Glow Dishcarge Technologies (Sputtering)
(3) Plasma processes
(4) Chemical Vapour Deposition (CVD)
(5) Electro plating
(6) Modified Langmuir Blodgett method
The above mentioned methods and their drawbacks are discussed below.
1. Vacuum Evaporative Technologies :- The substance of which a nanofilm 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 / dcpositc on substrate surface such as glass/ quartz plate, silicon wafer etc. This is a common technology for metal thin film deposition. 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. It is difficult to achieve nanoparticles in the resulting films prepared by this method.
Molecular beam epitaxy :- It is an improved technology over vacuum evaporation mainly used for growing single crystalline films (very ordered films) on single crystal substrates.
Drawback :- The cost and number of parameters are increased many folds. The operation is complex and throughput is very low.
a) Handbook of thin film deposition processes and techniques.
K. K. Schuegrat, Noyes Publication, Park Ridge, New Jersey USA (1988)
b) Thin film phenomenon
K. L. Chopra.
McGraw - Hill Book Co. New York USA (1969).
2. Glow discharge technologies (Sputtering):- The ejection of surface atoms
from an electrode surface by momentum tumsfer from bombarding ion is
called sputtering. In other words, during sputtering process,'source of
electrode material in vapour form 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. The films obtained by this method do not consist of nanosized particles.
a) Handbook of thin film deposition processes and techniques. K. K. Schuegrat, Noyes Publication, Park Ridge, New Jersey USA
(1988) b) Thin film phenomenon
K. L. Chopra.
McGraw - Hill Book Co. New York USA (1969).
3. Plasma processes :- Some chemical reactions are accelerated in presence
of bombarding reactive ions. Therefore, the electrode material (metal) in
presence of gases like O2, N2+H2, CH4 forming a glow discharge forms a
film of metal oxide, carbide, nitride on the substrate surface which on further processing can give metal films. 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 of compounds formed by this method need further processing to get metal films. Films with nano sized particle cannot be obtained.
a) Handbook of thin film deposition processes and techniques.
K. K. Schuegrat, Noyes Publication, Park Ridge, New Jersey USA (1988)
b) Thin film phenomenon
K. L. Chopra.
McGraw - Hill Book Co. New York USA (1969).
4. 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 available, CVD is versatile and flexible technique in producing variety of products in thin film form including metals, semiconductors, insulators.
Metal organics, inorganic compounds of metals having high vapour pressure like metal carbonyls are very convenient for CVD application as relatively low temperatures, can transform them in vapour phase. 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, thickness and material particle size control in the film is difficult.
a) Handbook of thin film deposition processes and techniques. K. K. Schuegrat, Noyes Publication, Park Ridge, New Jersey USA
(1988) b) Thin film phenomenon K. L. Chopra. McGraw - Hill Book Co. New York USA (1969).
5. 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. Films are not constitutaed with nanosized particles.
a) Handbook of thin film deposition processes and techniques.
K. K. Schuegrat, Noyes Publication, Park Ridge, New Jersey USA (1988)
b) Thin film phenomenon
K. L. Chopra.
McGraw - Hill Book Co. New York USA (1969).
6. Modified Langmuir Bloduett (LB) method
In a modification of LB method, ultra fine particles of a substance of which thin film is to be obtained, are given special chemical treatment so that particles get imcoagulative character. These particles are spread using suitable organic solvent on aqueous subphase as in the conventional LB
technique. The film formed at the interface is subsequently collected on the substrate.
In another modification the particles of the substance of which film is to be formed are obtained in a colloidal state. This colloidal solution is used as subphase over which fatty acid/ amine is spread using conventional LB technique. The particles in the colloidal state are bonded to the fatty acid/amine film formed at the interface which is collected on the substrate.
Drawbacks :A special chemical treatement is necessary to use conventional LB procedure for metal film formation. This increases the number of steps in film formation procedure.
a). T. Nakaya, Yu-Jun and K. Shibata
Preparation of ultrathin particle multilayers using the Lanbmuir-Blodgett
technique
J. Mat. Chem. 6(5), 1996, 691-97
b). A study of the influence of collidal subphase pH on the deposition of multilayer Langmuir Blodgett Films of gold clusters K. S. Mayya, V. Patil and M. Sastry J. Phys. Chem. (Accepted)
The principle by which the proccss of the present invention is developed is based on I) The formation of an aqueous solution of chemical species in the dilute concentration A, 2) Formation of a solution of another chemical species in organic solvent/mixture of organic solvents/mixture of organic solvent and water which spreads on aqueous surface e.g. carbon tetrachloride, chloroform, benzene, n-hexane, tetrahydrofuran (THF) etc., water and the mixture thereof etc. B, 3) Choosing the chemical species of A and B in 1 and 2 such that they can react with each other in solution form, generating a solid metal product or a precursor to metal 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 5) a suitable method for transferring the thin film formed on the aqueous surface to the substrate surface. 6) A suitable processing to convert precursor film to metal product when necessary.
The main object of the invention is to provide an improved and versatile method for preparation of nanofilms of metals. Another objective of the present invention is to provide an improved method for the prepaiation of ultrathin metal films.
Accordingly the present invention provides a process for the preparation of ultrathin nanofilms of metals which comprises:
a) preparing an aqueous solution containing chemical species of desired metals selected from Fe, Co, Ni, Cu, mo, Zn, Pd, Ag, Au, Pt such as the aqueous solution of silver nitrate, chloroplatinic acid, auric chloride, hexamine cobaltichloride, copper acetate, palladium chloride or other chemical species selected from hydrazene hydrate, sodium hydride, sodium borohydrite, lithium aluminium hydride which can react with a species containing metal component resulting in metal particles or precursor to metal, wherein solute concentration is in the range of 1CT6 to 10"3 M, at pH ranging 3 - 12 at a temperature ranging 10°C to 50°C
b) preparing another chemical solution in a volatile organic solvent such as herein described wherein chemical species used is selected from silver nitrate, chloroplatinic acid, auric acid, hexamine cobaltichloride, hydrazine hydrate, sodium hydride, sodium borohydride, lithium aluminum hydride, copper acetate, palladium chloride
c) spreading the solution prepared in step (b) on the aqueous solution prepared in step (a) to get a film at the interface of the aqueous solvent of step (a) and volatile organic solvent of step (b),
d) evaporating the volatile organic solvent of step ( c ) and compressing the obtained film with a lateral pressure in the range of 18.35 dyne/cm
e) dipping vertically a substrate such as herein described, in the solution obtained at step ( d ) followed by withdrawing at a uniform rate in the range of 0.5 to 1.5 cm/min to obtain a thin film on the substrate,
f) treating the thin film thus obtained on the surface of the substrate either chemically or physically to get the desired ultrathin nano-film.
In an embodiment of the present invention the solute concentration in step (a) may be in the range of 10"6 to 10"3 M.
In an embodiment of the present invention the solute concentration in step (a) may be in the range of 10"6 to 10"3 M.
In another embodiment the pH of the solution in step a) may be adjusted in the range of 3 to 12, if necessary.
In yet another embodiment the temperature of the solution in step a) is adjusted in the range of 10 to 50 °C, if necessary.
In yet another embodiment of the invention the solvent in step b) may be an organic solvent or a mixture of organic solvents or a mixture of organic solvent/s and water which also facilitates the spreading of the solution in step a) and is immiscible with the solvent used in a)
In yet another embodiment the solute concentration in step b) may be in the range of 10"6 to 10"3 M.
In still another embodiment the lateral pressure applied to the film formed may be in in the range of 18-35 dynes/cm.
In yet another embodiment the rate of vertically dipping and withdrawing the substrate may be a uniform rate in the range of 0.5 to 1.5 cm/min.
In yet another embodiment the metals used in the process of the invention may be selected from Fe, Co, Ni, Cu, Mo, Zn, Pd, Ag, Au, Pt in step a.
In yet another embodiment substrates may be selected from glass plates, quartz plates, single crystal wafers of Si, Ge, SrTiO3, BaTiO3 A12O3 plates, pellets of the compounds such as ZnO, plates of Z1O2, MgO etc.
In yet another embodiment the organic solvent used in step b) may be selected from carbon tetrachloride, chloroform, benzene, n-hexane, tetrahydrofuran, water, etc., and the mixtures thereof.
In yet another embodiment of the present invention the appropriate chemical species may be selected from silver nitrate, chloroplatinic acid, auric acid, hexaLmine cobaltichloride, hydrazene hydrate, sodium hydride, sodium borohydride , lithium aluminum hydride, copper acetate, palladium chloride, chloroplatinic acid etc.
In a feature of the invention the evaporation of the solvent may be effected by natural evaporation, IR heating etc.
The process of the present invention is described hereinbelow with reference to examples which are illustrative only and should not be construed to limit the scope of present invention in any manner.
Example -I
A solution of silver nitrate in a concentration of 1 x 10"4 M in double distilled water is prepared. The solution contained in a teflon trough of 45 cms times 15 cms times 2 cm size. The solution is labled as 'A'
A solution of hydrazene hydrate H2NNH2 .xH20 in carbon tetrachloride is prepared with a concentration of ~lx 10"5 mol. This solution is labled as 'B'
0.2 ml of solution 'B' is spread on solution 'A' to form a liquid film. The constituents in solutions A and B react to form a particulate film at the surface of aqueous solution. Carbon tetrachloride is evaporated. The film formed at the aqueous surface is compressed laterally with the help of oleic acid piston (pressure 30 dynes/cm). A quartz plate 1 cm X 1 cm X 0.25 cm was vertically dipped in the solution with the rate 0.5 cm/min. and lifted out with the same rate. During this process the dipped area is covered by the film. This operation is repeated fifty times for increasing the thickness.
A copper grid coated with collodion is also used as a substrate to deposit the film.
The film thus formed is charactarised by X ray diffraction (XR.D), Electron diffraction (ED) and Transmisson electron microscopy (TEM). The film is
characterised by XRD and ED as silver film. The particle size charactarisation by STM determined it to be in the range 1 - 20 nm.
Example -II
A. solution of hydrazene hydrate H2NNH2 .xH20 in a concentation of ~l x 10"4 M in double distilled water is prepared. A solution contained in teflon trough of 45 cm times 15 cm times 2 cm size is labled as 'A'
A solution of silver nitrate AgNC»3 in a concentration of lxlO"6 M in a mixture of water and carbon tetrachloride is labaled as 'B'
1 cc of B is spread over A to form a liquid film. The constituents in solution A and B react to form a particulate film at the surface of aqueous solution. Carbon tetrachloride is evaporated. The film formed at the aqueous surface is compressed laterally with the help of oleic acid piston (pressure 30 dynes/cm). The procedure of the deposition and characterisation of the film was followed as given in example 1.
Example -III
A solution of Auric chloride HAUCl4 4H20 in a concentation of 1 x 10"4 M in double distilled water is prepared. A solution contained in teflon trough of 45 cm times 15 cm times 2 cm size is labled as 'A'
A solution of lithium aluminum hydride in dry tetrahydrofuran (THF) in a concentration of 1 xlO"5 M is prepared. 0.2 cc of this solution is added to 3 cc dry carbon tetrachloride to form a miscible solution which is labled as 'B'.
0.5 cc of B is spread over A to form a liquid film. The constituents in solution A and B react to form a particulate film at the surface of aqueous solution. Carbon tetrachloride is evaporated. The particulate film formed at the aqueous surface is compressed laterally with the help of oleic acid piston (pressure 30 dynes/cm). The procedure of the deposition and characterisation of the film was followed as given in example I.
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. The method is useful to form a metal film with a particle size of metals in nano range.
9. Loss of precious chemicals is minimal.





We Claim:
1. A process for the preparation of ultrathin nanofilms of metals which comprises:
a) preparing an aqueous solution containing chemical species of desired metals selected from Fe, Co, Ni, Cu, mo, Zn, Pd, Ag, Au, Pt such as the aqueous solution of silver nitrate, chloroplatinic acid, auric chloride, hexamine cobaltichloride, copper acetate, palladium chloride or other chemical species selected from hydrazene hydrate, sodium hydride, sodium borohydrite, lithium aluminium hydride which can react with a species containing metal component resulting in metal particles or precursor to metal, wherein solute concentration is in the range of 10 -6 to 10"3 M, at pH ranging 3-12 at a temperature ranging 10°C to 50°C
b) preparing another chemical solution in a volatile organic solvent such as herein described wherein chemical species used is selected from silver nitrate, chloroplatinic acid, auric acid, hexamine cobaltichloride, hydrazine hydrate, sodium hydride, sodium borohydride, lithium aluminum hydride, copper acetate, palladium chloride
c) spreading the solution prepared in step (b) on the aqueous solution prepared in step (a) to get a film at the interface of the aqueous solvent of step (a) and volatile organic solvent of step (b),
d) evaporating the volatile organic solvent of step ( c ) and compressing the obtained film with a lateral pressure in the range of 18.35 dyne/cm
e) dipping vertically a substrate such as herein described, in the solution obtained at step ( d ) followed by withdrawing at a uniform rate in the range of 0.5 to 1.5 cm/min to obtain a thin film on the substrate
f) treating the thin film thus obtained on the surface of the substrate either chemically or physically to get the desired ultrathin nano-film.

2. A process as claimed in claim 1 wherein the substrates used is selected from glass plates, quartz plates, single crystal wafers of Si, Ge, SrTiO"3, BaTi03 AI2O3 plates, pellets of the compounds such as ZnO, plates of Zr02, MgO etc.
3. A process as claimed in claims 1 & 2 wherein the volatile organic solvent used in step (b) may be selected from carbon tetrachloride, chloroform, benzene, n-hexane, tetrahydrofuran and the mixtures thereof.
4. A process for the preparation of ultrathin nanofilms of metals substantially as herein described with reference to the examples.

Documents:

3513--del-1997-abstract.pdf

3513--del-1997-claims.pdf

3513--del-1997-correspondence-others.pdf

3513--del-1997-correspondence-po.pdf

3513--del-1997-description (complete).pdf

3513--del-1997-form-1.pdf

3513--del-1997-form-19.pdf

3513--del-1997-form-2.pdf

3513--del-1997-form-3.pdf


Patent Number 195172
Indian Patent Application Number 3513/DEL/1997
PG Journal Number 42/2008
Publication Date 17-Oct-2008
Grant Date 24-Nov-2006
Date of Filing 08-Dec-1997
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 SHIVARAM DATTATRAYA SATHAYE NATIONAL CHEMICAL LABORATORY, PUNE-411008, INDIA.
2 KASHINATH RANGU PATIL NATIONAL CHEMICAL LABORATORY, PUNE-411008,
3 DILIP VINAYAK PARANJAPE NATIONAL CHEMICAL LABORATORY, PUNE-411008,
PCT International Classification Number B82B 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA