Nanoparticle synthesis
A noble metal nanoparticle can be grown on a semiconductor substrate by contacting a predetermined region of the substrate with a solution including noble metal ions. The predetermined region of the semiconductor substrate can be exposed by applying a polymeric layer over the substrate selectively removing a portion of the polymeric layer. The nanoparticles can be prepared in a predetermined pattern. The nanoparticle can be formed with a barrier separating it from another nanoparticle on the substrate; for example, nanoparticle can be located in a pit etched in the substrate. The size and location of the nanoparticle can be stable at elevated temperatures.
1. A method of growing a nanoparticle on a substrate comprising contacting a predetermined region of a semiconductor substrate with a solution including noble metal ions,
wherein contacting a predetermined region of a semiconductor substrate with a solution including noble metal ions comprises forming a nanoparticle on the semiconductor substrate, the nanoparticle being laterally separated from other nanoparticles in predetermined positions on the semiconductor substrate by a barrier; and the barrier is a portion of the semiconductor substrate that is raised relative to the region of the semiconductor substrate upon which the nanoparticle is positioned
wherein the nanoparticle is positioned in a pit in a surface of the semiconductor substrate, the pits having sidewalls that form in the surface of the semiconductor substrate.
2. The method of claim 1 , further comprising exposing the predetermined region of the semiconductor substrate, wherein exposing includes applying a polymeric layer over the semiconductor substrate; and
selectively removing a portion of the polymeric layer.
3. The method of claim 1 , wherein the substrate includes GaAs.
4. The method of claim 2 , wherein the polymeric layer includes PMMA.
5. The method of claim 1 , wherein the noble metal is Au.
6. The method of claim 1 , wherein the nanoparticle is a nanocrystal.
7. The method of claim 1 , wherein contacting a predetermined region of a semiconductor substrate with a solution including noble metal ions includes selecting conditions for a galvanic reaction between the semiconductor substrate and the noble metal ions.
8. The method of claim 1 , wherein exposing a portion of the substrate through the polymeric layer comprises e-beam lithography.
9. The method of claim 1 , wherein the nanoparticle is a member of a nanoparticle population having an average diameter of 25 nm or smaller, or of 10 nm or smaller.
10. The method of claim 1 , wherein the nanoparticle is positioned in a pit on the substrate.
11. The method of claim 2 , wherein selectively removing a portion of the polymeric layer comprises forming a pattern.
12. The method of claim 11 , wherein the pattern is an array of openings.
13. The method of claim 12 , wherein the openings in the array have a dimension of 1 nm or less, 5 nm or less, 10 nm or less, 25 nm or less, or a larger dimension.
14. The method of claim 1 , wherein the average diameter of the nanoparticle is 25 nm or smaller.
15. The method of claim 1 , wherein the average diameter of the nanoparticle is 10 nm or smaller.
16. The method of claim 10 , further comprising etching a portion of the semiconductor substrate to form the pit.