Shaped nanocrystal particles and methods for making the same

1. A process of forming a nanocrystal particle, the process comprising:

(a) providing a core having a first crystal structure in a solution; and

(b) forming an arm extending from the core having a second crystal structure in the solution.

2. The process of claim 1 wherein the arm is a first arm, and wherein the process further comprises:

forming at least a second arm extending from the core in the solution, wherein the second arm has the second crystal structure.

3. The process of claim 1 wherein the arm is a first arm, and wherein the process further comprises:

forming at least a second arm extending from the core in the solution, wherein the second arm has the second crystal structure;

forming at least a third arm extending from the core in the solution, wherein the third arm has the second crystal structure; and

forming at least a fourth arm extending from the core in the solution, wherein the fourth arm has the second crystal structure.

4. The process of claim 3 wherein the first, second, third, and fourth arms are formed substantially simultaneously.

5. The process of claim 3 wherein the first, second, third, and fourth arms are formed at different times.

6. The process of claim 3 wherein the first, second, third, and fourth arms have substantially the same lengths.

7. The process of claim 3 wherein the first, second, third, and fourth arms have different lengths.

8. The process of claim 1 wherein the nanocrystal particle is a monopod.

9. The process of claim 1 wherein the first crystal structure is a cubic crystal structure, and the second crystal structure is a hexagonal crystal structure.

10. The process of claim 1 further comprising:

forming second, third and fourth arms extending from the core to form a tetrapod shaped nanocrystal particle.

11. The process of claim 1 wherein the arm is a first arm, and wherein the process further comprises:

forming a second arm extending from the core, wherein the second arm has the second crystal structure, and wherein the first and second arms are formed substantially simultaneously.

12. The process of claim 1 wherein the core and the arm comprise a Group III-V semiconductor, a Group II-VI semiconductor, a Group IV semiconductor, metal, or a material exhibiting polytypism.

13. The process of claim 1 wherein the core and the arm are formed using a mixture of surfactants.

14. The process of claim 1 wherein the core and the arm are formed using a mixture of surfactants, wherein the mixture of surfactants comprises at least two selected from the group consisting of a phosphonic acid, trioctylphosphine oxide, an amine, oleaic acid, and stearic acid.

15. The process of claim 1 wherein the core is a first core, and the arm is a first arm that includes a proximate end proximate to the first core and a distal end distal to the first core, and wherein the process further comprises:

(d) forming a second core at the distal end of the first arm; and

(e) forming additional arms extending from the second core.

16. The process of claim 1 wherein the core and the first arm are formed in a hot surfactant mixture wherein precursors used for forming the nanocrystal particle are injected sequentially into the hot surfactant mixture.

17. A process for forming semiconductor nanocrystal particles comprising:

introducing semiconductor nanocrystal particle precursors into a heated mixture of surfactants capable of promoting the growth of tetrapod shaped semiconductor nanocrystal particles; and

forming tetrapod shaped semiconductor nanocrystal particles.

18. The process of claim 17 wherein the semiconductor nanocrystal particles have shapes comprising branched tetrapod shapes.

19. The process of claim 17 wherein the precursors are introduced into the mixture at a temperature between about 20° C. to about 360° C.

20. The process of claim 17 wherein the precursors are introduced into the heated mixture of surfactants by injecting different precursors separately into the mixture of surfactants.

21. The process of claim 17 wherein the nanocrystal particles comprise a Group III-V or a Group II-VI semiconductor.

22. The process of claim 17 wherein the mixture comprises at least one selected from the group consisting of phosphinic acid, trioctylphosphine oxide, an amine, oleaic acid, and stearic acid.

23. A process for forming shaped nanocrystal particles comprising:

(a) mixing semiconductor precursors and a mixture of surfactants to form a solution; and

(b) forming nanocrystal particles in the solution,

wherein the nanocrystal particles are in the form of teardrops or arrows.

24. The process of claim 23 wherein the mixture of surfactants comprises a phosphine oxide and an alkylphosphonic acid, wherein the alkylphosphonic acid is greater than about 30 mol %, based on the total amount of surfactant.

25. The process of claim 24 wherein the alkylphosphonic acid is hexylphosphonic acid.

26. The process of claim 23 wherein (a) mixing comprises:

(a) introducing a first amount of the semiconductor precursors into the solution;

(b) waiting for a predetermined amount of time; and then

(c) introducing a second amount of the semiconductor precursors into the solution,

wherein the nanocrystal particles are in the form of teardrops.

27. The process of claim 23 wherein the nanocrystal particles are in the form of arrows.

28. The process of claim 23 wherein the semiconductor precursors comprise a Group II, Group III, Group IV, Group V, or a Group VI element.

29. The process of claim 23 wherein mixture of surfactants comprises a first surfactant comprising a phosphine oxide and a second surfactant.