Electrolytic preparation of tin, other metals, alloys and compounds

• US 5,215,631 A
• Filed: 10/11/1991
• Issued: 06/01/1993
• Est. Priority Date: 06/25/1982
• Status: Expired due to Fees

• Current Assignee: CEL Systems Coporation
• Original Assignee: CEL Systems Coporation
• Inventors: Westfall, Richard M.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): BOLAM, BRIAN
• Application Number:
  US07/775,270
• Time in Patent Office: 599 Days
• Field of Search: 156/600, 204/64 R, 205/111, 205/112, 205/157, 205/230
• US Class Current: 205/351
• CPC Class Codes: C30B 29/02 Elements
• CPC Class Codes: C30B 7/00 Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions from molten solvents C30B9/00; by normal or gradient freezing C30B11/00; under a protective fluid C30B27/00
• CPC Class Codes: C30B 7/005 Epitaxial layer growth
• CPC Class Codes: C30B 7/12 by electrolysis
• CPC Class Codes: H01L 21/02562 Tellurides
• CPC Class Codes: H01L 21/02573 Conductivity type
• CPC Class Codes: H01L 21/02628 using solutions
• CPC Class Codes: H01L 31/028 including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/073 comprising only AIIBVI compound semiconductors, e.g. CdS/CdTe solar cells
• CPC Class Codes: H01L 31/1032 the devices comprising active layers formed only by AIIBVI compounds, e.g. HgCdTe IR photodiodes
• CPC Class Codes: H01L 31/1828 the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
• CPC Class Codes: H01L 31/184 the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
• CPC Class Codes: Y02E 10/543 Solar cells from Group II-VI materials
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y10S 117/902 Specified orientation, shape, crystallography, or size of seed or substrate

Abstract

Electrolytic processes for the growth of crystalline tin or other elemental crystals, with or without the use of a substrate. Exemplified cubic forms of alpha-tin and tetragonal forms of beta-tin are grown using a shaped anode and a pointed cathode to provide electrical geometric fields within an electrodeposition system to enhance the growth of the desired crystalline tin.

Claims

1. A process for electrolytically producing elemental free-standing single crystals and free-standing dendritic crystalline materials chosen from the group consisting of:

beryllium, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, actinium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, boron, aluminum, indium, thallium, carbon, tin, lead, arsenic, antimony, bismuth, selenium and tellurium, by performing the steps of;

forming a solvent molten salt bath such as a single alkali halide salt or a eutectic metal halide mixture capable of supporting high solubilities for cations of the to-be-deposited material with molten salt bath melting point less than the melting point of the material to be produced as a single crystal;

purifying the solvent eutectic metal halide molten salt bath with appropriate oxygen removal and purification treatments such as;

electropurification, addition of free metal, and bubbling of gases such as HF, HCl, HBr, HI, and H2 under vacuum;

dissolving a metal halide salt composed of the to-be-deposited metal and appropriate halide ion(s) as the solute in the molten salt bath in order to provide sufficient bulk-replenishing concentration (activity) of the cations of the material to be deposited as a crystal upon passage of electrical current;

purifying the electrolytic bath containing the to-be-deposited cations through electropurification where current is passed from a high purity sacrificial anode of the material to be deposited to a cathode operated at potentials slightly more negative than the cathodic surface potential used in production of the to-be-produced material;

immersing a cathode and an anode into said bath, said cathode being shaped in a manner to be capable of providing for nucleation of the cations on the tip of the pointed cathode, and said anode shaped to substantially replicate the crystallographic morphology desired;

application of an electrical voltage between the anode and the cathode, with applied cathodic potentials more negative than the reduction potential of the cations of the to-be-produced material, yet above the critical overpotential (cathode driving negative) for the composition of the bath; and

reduction of the cations of the material to be deposited at the cathode by the passage of said electrical current to thereby form a crystalline metal deposit at the cathode.

3. The invention as defined in claim 1 wherein the material is one or more of the following group:

beryllium, magnesium calcium, strontium, barium, boron, and carbon, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs) and the halides of group VIIA (F, Cl, Br, I) in mixtures such as baths;

1, 4, 6, 7, 9, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45, 46, 48, 51, 53-56, 61, 62, 67-69, 71, 74, 77, 78, 86-88, 90-92, 97-105 in the case of beryllium or baths;

39, 41-43, 45, 46, 48, 51, 54, 61, 66-69, 71, 74, 75, 77, 80, 81, 86, 88, 90-92, 95, 98, 99, 101 in the case of magnesium or baths;

7, 10, 11, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45-48, 51, 54, 57, 60, 61, 67-71, 74, 77, 86, 88, 90-92, 98, 99, 101 in the case of calcium or baths;

15, 19, 22, 28=30, 34, 35, 39-41, 42, 45, 46, 48, 51, 52, 54, 61, 67-69, 71, 74, 77, 86, 88, 90-92, 98, 99, 101 in the case of strontium or baths;

22, 28-30, 35, 39, 41, 42, 44-46, 48, 51, 53-56, 59, 61, 62, 67-69, 71, 74, 77, 78, 86-88, 90-92, 97-105 in the case of barium or baths;

1, 4, 6, 7, 9, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45, 46, 48, 51, 53-56, 61, 62, 67-69, 71, 74, 77, 78, 84, 86-88, 90-92, 97-105, 140 in the case of boron or baths;

1, 4, 6, 7, 9, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45, 46, 48, 51, 53-56, 61, 62, 67-69, 71, 74, 77, 78, 86-88, 90-92, 97-105 in the case of carbon, or in other proportions.

5. The invention as defined in claim 1, wherein the material is one or more of the following group:

scandium, yttrium, lanthanum, actinium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs), group IIA elements (Be, Mg, Ca, Sr, Ba), and the halides or group VIIA (F, Cl, Br, I) in mixtures such as baths;

1-48, 51-57, 59-62, 64, 66-71, 74, 75, 77, 78, 80, 81, 86-88, 90-92, 95, 97-105, and baths;

3-48, 51-57, 59-62, 64, 66-71, 74, 75, 77, 78, 80, 81, 86-88, 90-92, 95, 97-105 in the case of lanthanum or in other proportions.

6. The invention as defined in claim 1, wherein the material is one or more of the following group:

zirconium and zinc, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs), group IIA elements (Be, Mg, Ca, Br, Ba), zirconium (Zr), and the halides or group VIIA (F, Cl, Br, I) in mixtures such as baths;

1-48, 51-57, 59-62, 64-83, 86-92, 94, 95, 97-105 in the case of zirconium or baths;

78-83, 86-92, 94, 95, 97-105 in the case of zinc or in other proportions.

7. The invention as defined in claim 1, wherein the material is one or more of the following group:

rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, aluminum, arsenic, antimony, and tellurium, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs), group IIA elements (Be, Mg, Ca, Sr, Ba), zirconium (Zr), group IIIA element aluminum (Al), and the halides or group VIIA (F, Cl, Br, I) in mixtures such as baths;

1-146 or baths;

3-146 in the case of silver or baths;

36-146 in the case of aluminum or baths;

7-146 in the case of arsenic or baths;

44-146 in the case of antimony or baths;

68-146 in the case of tellurium or in other proportions.

8. The invention as defined in claim 1, wherein the material is one or more of the following group:

cadmium, thallium, and lead, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs), group IIA element (Be), group IIIA element aluminum (Al) (aluminum must be excluded from cadmium baths containing iodide and from thallium baths containing bromide and(or) iodide), and the halides or group VIIA (F, Cl, Br, I) in mixtures such as baths;

100-107, 112-115, 118-120, 122, 124, 125, 127, 128, 30-139, 141, and mixtures of 119 and 141 in the case of cadmium or baths;

103-105, 107, 114, 118-120, 122, 124, 125, 127, 134, 135, 138, 139, 141 and mixtures of 119 and 141 in the case of thallium or baths;

98-120, 122-141, and mixtures of 119 and 141 in the case of lead or in other proportions.

9. The invention as defined in claim 1, wherein the material is one or more of the following group:

indium, tin, bismuth, and selenium, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs), group IIIA element aluminum (Al), and the halides or group VIIA (F, Cl, Br, I) in mixtures such as baths;

118-120, 122-141, and mixtures of 119 and 141 in the case of indium or baths;

110-146 in the case of tin or baths;

107-120, 122-141, and mixtures of 119 and 141 in the case of bismuth or baths;

111-120, 122-141, and mixtures of 119 and 141 in the case of selenium or in other proportions.

10. The invention as defined in claims 1 or 2, wherein the bath is substantially saturated with cations of the material to be electrolytically produced.

11. The invention as defined in claims 1 or 2, wherein the anode is constructed of the material to be electrolytically produced.

12. The invention as defined in claim 1 or 2, wherein the anode has a larger surface area than that of the cathode.

13. The invention as defined in claim 1 or 2, wherein an electric potential is applied between the anode and th cathode, with applied cathodic potentials slightly more negative than the cathodic surface potential used to produce the desired crystalline materials of the to-be-produced material, inducing a current flow between the anode to the cathode through the bath to remove cation impurities from the bath.

14. The invention as defined in claim 1 or 2, wherein a portion of the anode is V-shaped and the cathode is immersed in the bath substantially intermediate the legs of said V-shaped portion of said anode.

15. The invention as defined in claims 1 or 2 or 14, wherein the V-shaped portion of the anode forms an angle which coincides substantially with the crysta lographic angle of the material to be electrolytically produced to provide a shaped electric field between the anode and cathode which enhances or reinforces desired crystalline growth.

16. The invention as defined in claim 1 or 2, wherein a portion of the anode is shaped (cubic, tetragonal, pyramidal, octahedral, hexagonal, rhombohedral, trigonal, orthorhombic, and pentagonal) in such a way as to substantially replicate the morphological shape or habit of the desired crystalline material to be produced and the cathode is immersed in the bath such that the tip of the cathode is substantially positioned at a central location within the shaped field of the anode.

17. The invention as defined in claims 1 or 2 or 16, wherein the shaped (cubic, tetragonal, pyramidal, octahedral, hexagonal, rhombohedral, trigonal, orthorhombic, and pentagonal) portion of the anode coincides substantially with the crystallographic morphological shape of the material to be electrolytically produced to provide a shaped electric field between the anode and cathode which enhances or reinforces desired crystalline growth.

2. A process for electrolytically producing elemental free-standing single crystals and free-standing dendritic crystalline materials chosen from the group consisting of silicon and germanium by performing the steps of:

forming a solvent molten salt bath, a eutectic metal halide mixture capable of supporting high solubilities for cations of the to-be-deposited material and a molten salt bath melting point less than the melting point of the material to be produced as a single crystal;

purifying the solvent eutectic metal halide molten salt bath with appropriate electropurification, addition of free metal, and bubbling of gases such as HF, HCl, HBr, HI, and H2 under vacuum;

dissolving a metal halide salt composed of the to-be-deposited metal and appropriate halide ion(s) as the solute in the molten salt bath in order to provide sufficient bulk-replenishing concentration (activity) of the cations of the material to be deposited as a crystal upon passage of eleotrical current;

purifying the electrolytic bath containing the to-be-deposited cations through electropurification where current is passed from a high purity sacrificial anode of the material to-be-deposited to a cathode operated at potentials slightly more negative than the cathodic surface potential used in production of the to-beproduced material;

immersing a cathode and an anode into said bath, said cathode being shaped in a manner to be capable of providing for nucleation of the cations on the tip of the pointed cathode and said anode shaped to substantially replicate the crystallographic morphology desired;

application of an electrical voltage between the anode and the cathode, with applied cathodic potentials more negative than the reduction potential of the cations of the to-be-produced material, yet above the critical overpotential (cathode driving negative) for the composition of the bath; and

reduction of the cations of the material to be deposited at the cathode by the passage of said electrical current to thereby form a crystalline metal deposit at the cathode.

4. The invention as defined in claim 2 wherein the material is one or more of the following group:

silicon and germanium, and wherein the molten salt bath is composed of group IA elements (Li, Na, K, Rb, Cs) and the halides or group VIIA (CI, Br, I) in mixtures such as baths;

1, 4, 6, 7, 9, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45, 46, 48, 51, 53-56, 62, 67-69, 71, 74, 77, 78, 86-88, 90-92, 97-105, and baths;

4, 6, 7, 9, 12, 13, 15, 19, 22, 28-30, 35, 39, 41, 42, 45, 46, 48, 51, 53-56, 62, 67-69, 71, 74, 77, 78, 86-88, 90-92, 97-105 in the case of germanium.