Article and process for selective etching

1. A process for etching, the process comprising:

disposing an activating catalyst on a substrate;

providing a vapor composition comprising an etchant oxidizer and an activatable etchant;

contacting the activating catalyst with the etchant oxidizer;

contacting the substrate with the activatable etchant;

performing an oxidation-reduction reaction between the substrate, the activatable etchant, and the etchant oxidizer in a presence of the activating catalyst and the vapor composition;

forming an etchant product comprising a plurality of atoms from the substrate; and removing the etchant product from the substrate to etch the substrate.

2. The process of claim 1 , further comprising adjusting a position of the activating catalyst in the substrate.

3. The process of claim 2 , further comprising forming an etch void in the substrate as a result of removing the etchant product from the substrate,

wherein a shape of the etch void corresponds to a cumulative position of the activating catalyst in the substrate.

4. The process of claim 3 , wherein the etch void is a one-dimensional etch void in the substrate as a result of adjusting a position of the activating catalyst in the substrate.

5. The process of claim 3 , wherein the substrate comprises a plurality of the etch voids formed in the substrate, and

the substrate has a gradient in a density of a volume of the substrate due to a presence of the plurality of the etch voids.

6. The process of claim 3 , wherein the substrate comprises a plurality of the etch voids formed in the substrate, and

the substrate has a uniform density of a volume of the substrate due to a presence of the plurality of the etch voids.

7. The process of claim 1 , further comprising controlling a rate of forming the etch product.

8. The process of claim 7 , wherein controlling the rate comprises isolating the activating catalyst from the etchant oxidizer, the substrate from the activatable etchant, or a combination comprising at least one of the foregoing.

9. The process of claim 8 , wherein isolating is conducted intermittently.

10. The process of claim 7 , wherein controlling the rate comprises changing a rate of formation of the etch product.

11. The process of claim 1 , further comprising forming a dendritic vein in the substrate to form the coating, the dendritic vein being anisotropically disposed in the coating.

12. The process of claim 1 , wherein disposing the activating catalyst on the substrate comprises disposing the activating catalyst in a selected pattern on the substrate.

13. The process of claim 1 , further comprising producing the etchant oxidizer in the vapor composition from a liquid phase.

14. The process of claim 1 , further comprising producing the activatable etchant in the vapor composition from a liquid phase.

15. The process of claim 1 , wherein the substrate is a semiconductor material comprising an element from group III, group IV, group V of the periodic table, or a combination comprising at least one of the foregoing elements.

16. The process of claim 1 , wherein the activating catalyst comprises a plurality of metal catalysts.

17. The process of claim 16 , wherein the plurality of metal catalysts comprises different metal catalysts.

18. The process of claim 16 , wherein the plurality of metal catalysts comprises a plurality of different shapes, different sizes, or combination comprising at least one of the foregoing shapes or sizes.

19. The process of claim 16 , where in the plurality of metal catalysts comprises gold, platinum, palladium, tungsten, silver, or commission comprising at least one of the foregoing.

20. The process of claim 1 , wherein the etchant oxidizer comprises an oxidant that is reduced by the activating catalyst, and the activatable etchant comprises a reducing compound that is oxidized by the substrate.