JPH06107493A - Formation of gold crystal - Google Patents

Abstract

PURPOSE:To provide a method for forming gold crystal suitable for production of a gold electrode optimal in the application to molecular electronic device with respect to the problems of conventional technic related to metallic electrode formed by the conventional method such as vacuum deposition method or sputtering method. CONSTITUTION:Gold crystal is deposited on a substrate by using high viscous solution in which gold is dissolved and reducing the solubility of gold in the solution or by proceding a process to reduce the solubility of gold in the solution and a proces to deposit gold crystal on the substrate in the gel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gold crystal used in a gold electrode most suitable for application to a molecular electronic device.

[0002]

2. Description of the Related Art Recently, the ordered structure of organic materials has attracted attention in connection with the development and improvement of electronic functions, and interest in molecular electronic devices for applying organic molecules to electronic devices has increased. A challenge for constructing a molecular electronic device is a technique for controlling the orientation of functional organic molecules. Therefore, recently, studies utilizing self-organization of organic molecules have been activated. In addition, research on the Langmuir Project film (hereinafter referred to as “LB” film), which is a technology for constructing an organic monomolecular film, has also progressed, and a sandwich structure element (which is narrowed from both sides with a conductive material such as metal) ( From that structure, a completely new switching phenomenon has been found in the electric conduction of the MIM structure or MIM element). On the other hand, how to exchange information between the molecular electronic device as described above and an external electric element manufactured by a conventional manufacturing method is also a big problem. In the past research on molecular electronic devices, electrodes have been formed using a vacuum deposition method or a sputtering method.

[0003]

However, since the metal thin film formed by these conventional methods becomes a polycrystalline film,
There is a problem that it is difficult to obtain smoothness in which the height difference of the irregularities on the surface of the thin film is 5 nm or less. When a molecular electronic device, for example, an MIM element using an LB film as an insulating layer is formed using such an electrode, the film thickness of the LB film is likely to be non-uniform. Therefore, there is a problem in that the characteristics of each element vary, and when the element, or particularly the thickness of the insulating film, is thin, element damage due to dielectric breakdown or the like is likely to occur from a portion to which a strong electric field is applied. In view of the above-mentioned problems of the conventional metal electrode prepared by a conventional method such as a vacuum deposition method or a sputtering method, an object of the present invention is to provide a gold electrode suitable for a method for producing a gold electrode most suitable for application to a molecular electronic device. It is to provide a method for producing a crystal.

[0004]

The above objects can be achieved by the present invention described below. That is, the present invention is a method for producing a gold crystal, which comprises using a highly viscous solution in which gold is dissolved, and decreasing the solubility of gold in the solution so that the gold crystal is extruded on a substrate in the solution. In the second invention of the present invention, a step of reducing the solubility of gold in the solution using a solution in which gold is dissolved and a step of protruding gold crystals on a substrate are carried out in a gel. This is a method for producing a gold crystal.

[0005]

In order to solve the above-mentioned problems of the prior art, the inventors of the present invention have earnestly studied about a method for producing a gold crystal, and as a result, the liquid phase growth of the gold crystal was performed in a highly viscous solution to obtain a large flat plate. The present invention has been accomplished by finding that it is possible to prepare a gold single crystal having a shape of a circle. Further, the inventors of the present invention have found that a large flat plate-shaped gold single crystal can be prepared by performing liquid phase growth of a gold crystal in a gel, and thus the present invention has been accomplished. Regarding the growth of gold crystals in the gel, P. Kratochvil and B. Sprusil
(J.Cryst.Growth, 3,4,360 (196
8)).

[0006]

EXAMPLES The present invention will be described in more detail with reference to examples. (First Invention) First Embodiment This embodiment will be described with reference to FIG. First, distilled water 400
1.5 g of gold dust is dissolved in a solution prepared by dissolving 32 g of potassium iodide and 4.8 g of iodine in cc (this solution was used as a stock solution). This undiluted solution, undiluted solution: distilled water = 1:
It was diluted with distilled water so that the ratio became 2, and this solution was used as a diluted solution. Furthermore, sucrose was diluted with this diluted solution 1
It was dissolved at a ratio of 2.5 g per cc to obtain a highly viscous solution for crystal growth. The gold in this highly viscous solution is
It is dissolved in a complex state of [AuI ₄ ] ^- . Next, FIG.
In a reaction vessel 1 as shown in Fig. 3, the Si substrate 3 is placed in the highly viscous solution 2 obtained as described above and heated so that the liquid temperature of the highly viscous solution is kept constant at 85 ° C. The temperature was controlled using the apparatus 4 (during which iodine was exhibited). After a while, a gold crystal grew on the Si substrate 3. When the gold crystal thus obtained was observed with an optical microscope, it had a triangular or hexagonal flat plate shape. When the crystal was observed with an electron microscope, the flat plate had an aspect ratio of 10 or more.
Further, it was confirmed from the result of X-ray diffraction measurement that the obtained gold crystal was a single crystal and the plane orientation of the flat plate was (111). Furthermore, when observing the flat surface of the gold crystal with a scanning tunneling microscope, the unevenness of the crystal surface was 1 μm × 1 μm.
It was 5 Å at m-square and was extremely smooth. As described above, a large flat plate-shaped gold single crystal having a size of about 1 mm could be obtained on the Si substrate.

Example 2 After preparing the same diluted solution as in Example 1, water glass was dissolved in the diluted solution at a ratio of water glass: diluted solution = 1: 3 to prepare a highly viscous solution for crystal growth. And Except for this condition, the same operation was performed under the same conditions as in Example 1, and the Si substrate 3
Gold crystals were grown on top. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 3 After preparing the same diluted solution as in Example 1, polyvinyl alcohol was dissolved in the diluted solution at a ratio of polyvinyl alcohol: diluted solution = 1: 3 to obtain a highly viscous solution for crystal growth. And Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 4 After preparing the same diluted solution as in Example 1, glycerin was dissolved in the diluted solution at a ratio of glycerin: diluted solution = 1: 8 to obtain a highly viscous solution for crystal growth. Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 5 After preparing the same diluted solution as in Example 1, ethylene glycol was dissolved in the diluted solution at a ratio of ethylene glycol: diluted solution = 1: 8 to prepare a highly viscous solution for crystal growth. And Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 6 First, about 6 × 1 of chloroauric acid (HAuCl ₄ .4H ₂ O)
A 0 ^-3 mol / l aqueous solution was prepared (this solution will also be referred to as a dilute solution). In this solution, gold is
It is dissolved in a complex state of [AuCl ₄ ] ^- . After dissolving sucrose in this dilution liquid in the same proportion as in Example 1,
Sodium sulfite was also dissolved to give a highly viscous solution for crystal growth. Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 7 After preparing the same diluted solution as in Example 6, 5 g of sucrose per 1 cc of the diluted solution was dissolved in the diluted solution, and potassium iodide was further dissolved therein to obtain a high viscosity for crystal growth. It was a solution. Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 8 Sucrose was dissolved in an aqueous solution of about 6 × 10 ^-3 mol / l of gold chloride (AuCl ₃ ) in an amount of 2.5 g per 1 cc of the aqueous solution, and then hydrochloric acid and oxalic acid were also dissolved to grow crystals. For use as a highly viscous solution. Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 9 After preparing the same diluted solution as in Example 1, 3 g of sucrose per 1 cc of the diluted solution was dissolved in the diluted solution, and further sodium sulfite was also dissolved in the diluted solution to obtain a highly viscous solution for crystal growth. And Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 10 After preparing the same diluted solution as in Example 1, the diluted solution 1c was prepared.
3 g of sucrose was dissolved per c, and oxalic acid was also dissolved to prepare a highly viscous solution for crystal growth. Except for this condition, the same operation as in Example 1 was performed to grow a gold crystal on the Si substrate 3. As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Example 11 In this example, selective growth of gold crystals was tried. Therefore, a seeded substrate as shown in FIG. 2 was prepared by photolithography. Reference numeral 5 is a Si substrate, and 6 is a thermal oxide film of Si. 7 is gold or platinum as a seed, and is formed in an island shape on the thermal oxide film 6. Reference numeral 8 is Cr used to improve the adhesion between the seed 7 and the oxide film 6.
The size of the seed is 1.5 μm × 1.5 μm square,
It is formed at intervals of 500 μm. With this substrate,
The same operation was performed under the same conditions as in Example 1 to grow a gold crystal on the position where the seed was formed on the Si substrate 3.
As a result, a large flat plate-shaped gold crystal having the same smoothness and size as in Example 1 was obtained.

Use Example 1 Next, a specific application example of the molecular electronic device will be described. A MIM structure element was manufactured using the gold electrode having a size of about 1 mm, which was manufactured by the method described in Example 1.
Specifically, first, the polyamic acid represented by the following formula (1) was dissolved in an N, N′-dimethylacetamide-benzene mixed solvent (1: 1 V / V) (concentration of monomer conversion 1 ×).
10 ^-3 M). Then, a 1 × 10 ⁻³ M solution of separately prepared N, N′-dimethyloctadecylamine in the same solvent was mixed at a ratio of 1: 2 (V / V) to give octadecyl polyamic acid represented by the following formula (2). An amine salt solution was prepared.

[0018]

[Chemical 1]

[0019]

[Chemical 2]

The solution prepared as described above is treated at a water temperature of 20
A monomolecular film was formed on the water surface by spreading on a water phase consisting of pure water at ℃. After removing the solvent by evaporation, the surface pressure was increased to 25 mN / m. Next, Example 1 was carried out while keeping the surface pressure constant.
5mm speed across the water surface of the substrate electrode prepared in
After gently immersing the film at 5 min / min, the film was gently pulled up at 5 mm / min to form a two-layer Y-type monomolecular cumulative film.
Repeat this operation a suitable number of times to make 12, 18, and 2
A four-layer, monomolecular cumulative film of three types of polyamic acid octadodecylamine salts was formed. Next, the substrate is depressurized (~
1 mmHg) at 200 ° C. for 30 minutes, the polyamic acid octadecylamine salt was imidized to obtain a polyimide monomolecular cumulative film of the following formula (3) on the gold electrode.

[0021]

[Chemical 3]

Next, an aluminum electrode was formed on the polyimide monomolecular cumulative film, and the cumulative film was narrowed together with the gold electrode.
In this way, a MIN structure element having an energization region of 500 μm □ was produced and its characteristics were evaluated. As a result, a switching characteristic having a memory property was observed, and 3
An ON / OFF ratio of the order of magnitude was obtained. Furthermore, an AC voltage was applied to continuously make a transition between both ON / OFF states for a long time, and a stable switching characteristic of ON / OFF transition was exhibited in each MIM structure element. In addition, element damage, which is considered to be caused by local electric field concentration, is less likely to occur, and the life is improved. In the organic MIM structure element manufactured by the present invention, very stable electric characteristics were observed as described above.

(Second Invention) Embodiment 12 This embodiment will be described with reference to FIG. First, the reaction container 11
After putting water glass in the solution, sodium sulfite is dissolved in the water glass. Next, hydrochloric acid is added to the water glass to gel the water glass (FIG. 3A). The Si substrate 13 is put into the water glass gel 12 thus obtained (FIG. 3B). Furthermore, a solution 14 in which gold is dissolved
Is placed in the reaction vessel 11, and the gel 12 and the solution 14 are brought into contact with each other (shown in FIG. 3C). The solution 14 used at this time was prepared as follows. First, 1.5 g of gold powder is dissolved in a solution prepared by dissolving 32 g of potassium iodide and 4.8 g of iodine in 400 cc of distilled water (this solution was used as a stock solution). This stock solution was diluted with a ratio of stock solution: distilled water = 1: 2 to obtain a solution 14. This solution, gold [Aul _4] ^- is dissolved in the complex state. After the solution 14 and the gel 12 are brought into contact with each other, the reaction container 11 is allowed to stand at room temperature for a while, and as shown in FIG.
A gold crystal 16 grew on the surface 15 of the Si substrate 13 in the vicinity of the interface 15 with the solution 14 and inside the gel 12. Gold crystals 17 were grown on other than the substrate surface. After crystal growth,
When the substrate 13 was taken out of the gel 12 and the gold crystal 16 grown on the surface was observed with an optical microscope, the crystal was in the form of a flat plate having a triangle or a hexagon. When the crystal was observed with an electron microscope, the flat plate had an aspect ratio of 10 or more. It was confirmed by X-ray diffraction that the crystal was a single crystal and the plane orientation of the flat plate was (111). Furthermore, when observing the flat surface of the gold crystal with a scanning tunneling microscope, it was found that the unevenness was 5Å
Met. As described above, the size is 1 on the Si substrate 13.
It was possible to obtain a large flat gold single crystal having a size of about mm.

Example 13 In this example, a gold crystal was grown on a Si substrate by performing the same operation as in Example 12 except that agar was used as the gel. As a result, a flat gold crystal having the same smoothness and size as in Example 12 was obtained.

Example 14 In this example, chloroauric acid (HAu) was used as the gold dissolving solution 14.
Cl ₄ .4H ₂ O) aqueous solution was used. The concentration of the solution is about 6 × 10 ⁻³ mol / l. Moreover, the gold in this solution [AuCl _4] ^- is dissolved in the complex state. Except this condition, the same operation was performed under the same conditions as in Example 12 to grow a gold crystal on the Si substrate. As a result, a flat gold crystal having the same smoothness and size as in Example 12 was obtained.

Example 15 In this example, after potassium iodide was dissolved in water glass, hydrochloric acid was added to gel the water glass. Except for this condition, the same operation as in Example 14 was performed, and S
Gold crystals were grown on the i substrate. As a result, Example 12
A flat gold crystal having a smoothness and a size similar to that of was obtained.

Embodiment 16 This embodiment will be described with reference to FIG. In this embodiment, after water glass is gelled with hydrochloric acid in the reaction vessel 11, S
The i-substrate 13 is put into the gel 18 as shown in FIG. Furthermore, a gold dissolving solution 1 having the same composition and concentration as in Example 12
4 is placed in the reactor 11 and brought into contact with the gel 18. The reaction container 11 was placed in a constant temperature bath (for example, an oil bath) in which the liquid temperature was set to 80 ° C. and left for a while to exhibit iodine. As a result, a flat gold crystal having the same smoothness and size as in Example 12 was obtained.

Embodiment 17 This embodiment will be described with reference to FIG. In this example, after AuCl ₃ was dissolved in the water glass in the reaction vessel 11, hydrochloric acid was added to the water glass to gel the water glass (FIG. 5).
(A) Illustration). The Si substrate 13 is put in the gel 20 of water glass. Next, as shown in FIG. 5C, an oxalic acid ((COOH) ₂ ) aqueous solution 21 is placed in the reaction vessel 11,
Contact with gel 20. Then, the reaction container 11 was left to stand at room temperature for a while. As a result, a flat gold crystal having the same smoothness and size as in Example 12 was obtained.

Example 18 In this example, selective growth of gold crystals was tried. Therefore, a seeded substrate as shown in FIG. 6 was prepared by photolithography. Reference numeral 22 is a Si substrate, and 23 is a thermal oxide film of Si. 25 is gold or platinum as a seed, and is formed in an island shape on the thermal oxide film 23. Incidentally, 24 is Cr used to improve the adhesion between the seed 25 and the oxide film 23. Seed size is 1.5μm × 1.5μ
It is an m-square and is formed at intervals of 500 μm. The same operation was performed under the same conditions as in Example 12 except that this substrate was used to grow a gold crystal on the substrate. As a result, a flat gold crystal having the same smoothness and size as in Example 12 was obtained.

Use Example 2 Next, a specific application example of the molecular electronic device will be described. A MIM structure element was manufactured using the gold electrode having a size of about 1 mm, which was manufactured by the method described in Example 12. Specifically, first, the polyamic acid represented by the following formula (1) was dissolved in a mixed solvent of N, N'-dimethylacetamide-benzene (1: 1 V / V) (concentration converted to monomer: 1 x 10). ^-3 M). Then, a 1 × 10 ⁻³ M solution of separately prepared N, N′-dimethyloctadecylamine in the same solvent was mixed at a ratio of 1: 2 (V / V) to give octadecyl polyamic acid represented by the following formula (2). An amine salt solution was prepared.

[0031]

[Chemical 4]

[0032]

[Chemical 5]

The solution prepared as described above was added at a water temperature of 20
A monomolecular film was formed on the water surface by spreading on a water phase consisting of pure water at ℃. After removing the solvent by evaporation, the surface pressure was increased to 25 mN / m. Next, Example 1 was carried out while keeping the surface pressure constant.
5mm speed across the water surface of the substrate electrode prepared in
After gently immersing the film at 5 min / min, the film was gently pulled up at 5 mm / min to form a two-layer Y-type monomolecular cumulative film.
Repeat this operation a suitable number of times to make 12, 18, and 2
A four-layer, monomolecular cumulative film of three types of polyamic acid octadodecylamine salts was formed. Next, the substrate is depressurized (~
1 mmHg) at 200 ° C. for 30 minutes, the polyamic acid octadecylamine salt was imidized to obtain a polyimide monomolecular cumulative film of the following formula (3) on the gold electrode.

[0034]

[Chemical 6]

Next, an aluminum electrode was formed on the polyimide monomolecular cumulative film, and the cumulative film was narrowed together with the gold electrode.
In this way, a MIN structure element having an energization region of 500 μm □ was produced and its characteristics were evaluated. As a result, a switching characteristic having a memory property was observed, and 3
An ON / OFF ratio of the order of magnitude was obtained. Furthermore, an AC voltage was applied to continuously make a transition between both ON / OFF states for a long time, and a stable switching characteristic of ON / OFF transition was exhibited in each MIM structure element. In addition, element damage, which is considered to be caused by local electric field concentration, is less likely to occur, and the life is improved. In the organic MIM structure element manufactured by the present invention, very stable electric characteristics were observed as described above.

[0036]

As described above, the present invention has the following effects. (1) A large gold single crystal can be grown in an environment near room temperature and pressure without using a large-scale device. (2) It is possible to form a smooth gold electrode having a surface roughness of 1 μm × 1 μm square and 5 Å. (3) The stability of the electrical characteristics of the MIM structure element using the LB film as an insulating layer could be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a crystal producing method used in Example 1.

FIG. 2 is a cross-sectional view of a substrate used for selective growth of a gold crystal of Example 11.

FIG. 3 is a schematic cross-sectional view of the crystal forming method used in Example 12.

FIG. 4 is a schematic cross-sectional view of the crystal forming method used in Example 16.

FIG. 5 is a schematic cross-sectional view of the crystal forming method used in Example 17.

FIG. 6 is a cross-sectional view of a substrate used for selective growth of gold crystals in Example 18.

FIG. 7 is an example of a method of immobilizing a substrate in gel.

[Explanation of sign]

 1, 11: Reaction container 2: Highly viscous solution 3, 13: Substrate 4: Heating device 5, 22: Si 6, 23: Si thermal oxide film 7, 25: Gold or platinum as a seed 8, 24: Cr 12, 18, 20, 26: Gel 14, 24: Solution to contact with gel 15: Near interface 16, 17: Gold crystal 19: Constant temperature bath

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Kasanuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Haruki Kawata 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non non corporation

Claims (31)

[Claims] 1. A method for producing a gold crystal, which comprises using a highly viscous solution in which gold is dissolved, and decreasing the solubility of gold in the solution so that the gold crystal is extruded on a substrate in the solution. 2. The method for producing a gold crystal according to claim 1, wherein the gold crystal has a flat plate shape. 3. The method for producing a gold crystal according to claim 1, wherein the highly viscous solution has a higher viscosity than water. 4. The method for producing a gold crystal according to claim 3, wherein the highly viscous solution in which gold is dissolved contains sucrose. 5. The method for producing a gold crystal according to claim 3, wherein the highly viscous solution in which gold is dissolved contains water glass. 6. The method for producing a gold crystal according to claim 3, wherein the highly viscous solution in which gold is dissolved contains polyvinyl alcohol. 7. The method for producing a gold crystal according to claim 3, wherein the highly viscous solution in which gold is dissolved contains glycerin. 8. The method for producing a gold crystal according to claim 3, wherein the highly viscous solution in which gold is dissolved contains ethylene glycol. 9. A highly viscous solution in which gold is dissolved is AuCl ₃
The method for producing a gold crystal according to claim 1, which is produced by using. 10. The method for producing a gold crystal according to claim 1, wherein gold in the highly viscous solution is dissolved in the solution in the form of a complex. 11. The method for producing a gold crystal according to claim 10, wherein the complex has at least [AuI ₄ ] ^- . 12. The method for producing a gold crystal according to claim 11, wherein the solubility of gold is reduced by volatilizing iodine from a highly viscous solution in which gold is dissolved. 13. The method for producing a gold crystal according to claim 10, wherein the complex has at least [AuCl ₄ ] ^- . 14. [AuCl _4] ^- a decrease in the solubility of the gold-containing solution, a method of creating gold crystal according to claim 13 carried out by reacting a solution of potassium iodide. 15. The method for producing a gold crystal according to claim 1, wherein the solubility of gold is reduced by reacting a highly viscous solution in which gold is dissolved with a reducing agent. 16. The method for producing a gold crystal according to claim 15, wherein the reducing agent is sodium sulfite. 17. The method for producing a gold crystal according to claim 15, wherein the reducing agent is oxalic acid. 18. The method for producing a gold crystal according to claim 1, wherein a gold or platinum seed is formed on the substrate. 19. A gold crystal comprising using a solution in which gold is dissolved, and performing a step of reducing the solubility of gold in the solution and a step of projecting a gold crystal on a substrate in a gel. How to create. 20. The method for producing a gold crystal according to claim 19, wherein the gold crystal has a flat plate shape. 21. The method for producing a gold crystal according to claim 19, wherein the gel is made of water glass. 22. The method for producing a gold crystal according to claim 19, wherein the gel is agar. 23. The method for producing a gold crystal according to claim 19, wherein the solution in which gold is dissolved is prepared using AuCl ₃ . 24. The gold in the solution is at least [AuI ₄ ] ^-
The method for producing a gold crystal according to claim 19, wherein the gold crystal is dissolved in the complex state. 25. The method for producing a gold crystal according to claim 20, wherein the solubility of gold is reduced by volatilizing iodine from a solution in which gold is dissolved. 26. The gold in the solution is at least [AuCl ₄ ].
^The method for producing a gold crystal according to claim 19, wherein the gold crystal is dissolved in the complex state of-. 27. [AuCl _4] ^- a decrease in the solubility of the gold-containing solution, a method of creating gold crystal according to claim 26 carried out by reacting a solution of potassium iodide. 28. The method for producing a gold crystal according to claim 19, wherein the solubility of gold is reduced by reacting a solution in which gold is dissolved with a reducing agent. 29. The method for producing a gold crystal according to claim 28, wherein the reducing agent is sodium sulfite. 30. The method for producing a gold crystal according to claim 28, wherein the reducing agent is oxalic acid. 31. The method for producing a gold crystal according to claim 19, wherein a seed of gold or platinum is formed on the substrate.