Systems and methods for forming thermoelectric devices

1. A method for forming a thermoelectric element, comprising:

(a) providing a substrate in a reaction space, wherein said substrate comprises a semiconductor material, wherein said substrate has a pattern of a metallic material adjacent to said substrate, which metallic material is configured to catalyze the oxidation of said substrate;

(b) exposing said metallic material to a vapor phase oxidizing agent and a vapor phase chemical etchant; and

(c) etching said substrate at an etch rate of at least about 0.01 micrometers/second to form holes in or wires from the substrate, thereby forming said thermoelectric element.

2. The method of claim 1 , wherein each of said holes or wires has an aspect ratio of at least about 20:1.

3. The method of claim 1 , wherein a ratio of oxidizing agent to chemical etchant in said gas is at least about 2:1.

4. The method of claim 1 , wherein said substrate is heated to a temperature between about −50° C. and 200° C.

5. The method of claim 1 , wherein (a) further comprises:

providing a mask adjacent to said substrate;

forming a pattern of holes in said mask, wherein an individual hole exposes an oxide layer adjacent to said substrate;

exposing said oxide layer to a vapor phase etchant to remove said oxide layer;

depositing said metallic material adjacent to said substrate; and

removing said mask.

6. The method of claim 1 , further comprising forming a passivation layer on an underside of said substrate prior to etching said substrate.

7. The method of claim 1 , further comprising applying an electric field across said substrate while etching said substrate.

8. The method of claim 1 , wherein said substrate is exposed to said vapor phase oxidizing agent and said vapor phase chemical etchant simultaneously.

9. The method of claim 1 , wherein said vapor phase oxidizing agent and said vapor phase chemical etchant are in the supercritical phase.

10. The method of claim 1 , wherein said thermoelectric element has a figure-of-merit of at least about 0.5.

11. A method for forming a thermoelectric element, comprising contacting a metallic material adjacent to a substrate with a vapor phase oxidizing agent and a vapor phase chemical etchant to form holes in or wires from the substrate at an etch rate of at least about 0.1 nanometer/second to form said thermoelectric element, wherein said holes or wires have an aspect ratio of at least about 20:1, and wherein surfaces of said substrate exposed by said holes or wires have a roughness between about 0.5 nanometers (nm) and 50 nm across said holes or wires as measured by transmission electron microscopy.

12. The method of claim 11 , wherein an individual hole or wire has a surface with a metal content of at least about 0.000001% as measured by x-ray photoelectron spectroscopy (XPS).

13. The method of claim 11 , wherein said substrate is simultaneously contacted with said vapor phase oxidizing agent and said vapor phase chemical etchant.

14. The method of claim 11 , wherein said thermoelectric element has a figure-of-merit of at least about 0.5.

15. A method for forming a thermoelectric device, comprising:

(a) providing particles of a metallic material adjacent to a substrate, wherein said particles of the metallic material each has an Euler Characteristic <2; and

(b) exposing said particles to an oxidizing agent and a chemical etchant in the gas phase to catalytically etch said substrate at an etch rate of at least about 0.01 micrometers/second to form holes in or wires from the substrate, thereby forming a thermoelectric element of said thermoelectric device.

16. The method of claim 15 , wherein (a) further comprises:

providing a mask adjacent to said substrate, the mask having an array of holes;

depositing a layer of said metallic material adjacent to said mask and exposed portions of said substrate; and

removing said mask to provide said particles of said metallic material adjacent to said substrate.

17. The method of claim 16 , wherein providing said mask further comprises:

forming said mask adjacent to said substrate, said mask having three-dimensional structures phase-separated in a polymer matrix; and

removing said three-dimensional structures, thereby providing said holes in said polymer matrix, which holes expose portions of said substrate.

18. The method of claim 15 , wherein said particles of said metallic material each has an Euler Characteristic equal to zero.

19. The method of claim 15 , wherein said thermoelectric element has a figure-of-merit of at least about 0.5.