Double-etch nanowire process
In an aspect of this disclosure, a method is provided comprising the steps of: (a) providing a silicon-containing substrate, (b) depositing a first metal on the substrate, (c) etching the substrate produced by step (b) using a first etch, and (d) etching the substrate produced by step (c) using a second etch, wherein the second etch is more aggressive towards the deposited metal than the first etch, wherein the result of step (d) comprises silicon nanowires. The method may further comprise, for example, steps (b1) subjecting the first metal to a treatment which causes it to agglomerate and (b2) depositing a second metal.
1. A method comprising the steps of: (a) providing a silicon-containing substrate, (b) depositing a first metal on the substrate, (c) etching the substrate produced by step (b) using a first etch comprising immersion in a solution comprising HF and a first oxidizer, and (d) etching the substrate produced by step (c) using a second etch comprising immersion in a solution comprising HF and a second oxidizer, wherein the second etch is more aggressive towards the deposited metal than the first etch, wherein the result of step (c) comprises silicon nanowires and the result of the step (d) comprises silicon nanowires.
2. The method of claim 1 , further comprising steps (b1) of subjecting the first metal to a treatment which causes it to agglomerate and (b2) depositing a second metal.
3. The method of claim 2 , wherein the treatment which causes the first metal to agglomerate comprises heating.
4. The method of claim 2 , wherein the second metal deposited has a thickness of at least about 10 nm.
5. The method of claim 3 , wherein the heating of the first metal involves subjecting the substrate to temperatures in a range between about 200° C. and about 400° C.
6. The method of claim 2 , wherein the heating of the first metal involves subjecting the substrate to temperatures in the range for a time between about 2 and about 20 minutes.
7. The method of claim 1 , wherein the first metal deposited comprises silver.
8. The method of claim 1 , wherein the first oxidizer comprises O 2 .
9. The method of claim 8 , wherein the O 2 is bubbled through a dilute solution of HF.
10. The method of claim 1 , wherein the silicon nanowires are predominantly parallel to each other.
11. The method of claim 1 , wherein the silicon nanowires are approximately round.
12. The method of claim 1 , wherein the substrate comprises polycrystalline silicon.
13. The method of claim 1 , wherein the silicon nanowires predominantly have their long directions at an angle between 0 and about 45 degrees to a line perpendicular to a surface of the substrate.
14. The method of claim 1 , wherein the silicon nanowires predominantly have a long dimension in excess of about 30 μm.
15. The method of claim 1 , wherein the silicon nanowires predominantly have cross sections in a plane perpendicular to their long direction which are no more than about 200 nm in diameter.
16. The method of claim 1 , wherein the diameter of the silicon nanowires over a final 10% of their length is less than about 10 nm.
17. The method of claim 1 , further comprising the step of employing the silicon nanowires resulting from step (d) in a lithium ion battery anode.
18. The method of claim 1 , further comprising the step of employing the silicon nanowires resulting from step (d) in a thermoelectric generator.
19. The method of claim 1 , wherein the first metal deposited has a thickness of at least about 10 nm.