Solar thermoplasmonic nanofurnaces and method for making and using same
Titanium nitride (TiN) nanofurnaces are fabricated in a method that involves anodization of a titanium (Ti) foil to form TiO 2 nanocavities. After anodization, the TiO 2 nanocavities are converted to TiN at 600° C. under ammonia flow. The resulting structure is an array of refractory (high-temperature stable) subwavelength TiN cylindrical cavities that operate as plasmonic nanofurnaces capable of reaching temperatures above 600° C. under moderate concentrated solar irradiation. The nanofurnaces show near-unity solar absorption in the visible and near infrared spectral ranges and a maximum thermoplasmonic solar-to-heat conversion efficiency of 68 percent.
1. A method of fabricating a device, comprising:
(a) anodizing titanium (Ti) foil to form titanium dioxide (TiO 2 ) nanocavities; and
(b) perform nitridization of the titanium dioxide nanocavities in ammonia atmosphere to form a plurality of titanium nitride (TiN) nanocavities.
2. The method of claim 1 , wherein the titanium foil has a thickness in the range of 0.1 mm to 1 mm.
3. The method of claim 1 , further comprising, before the anodization step (a), cleaning the titanium foil in acetone, ethanol and deionized water solutions under sonication.
4. The method of claim 1 wherein the anodization step (a) comprises:
(a1) employing the titanium foil as the working electrode;
(a2) employing a platinum foil as a counter electrode;
(a3) applying a voltage across the working electrode and the counter electrode.
5. The method of claim 4 , further comprising disposing the working electrode and counter electrode in an electrolyte composed of a mixture of hydrofluoric acid (HF) and phosphoric acid (H 3 PO 4 ) during the anodization step (a).
6. The method of claim 5 , wherein the hydrofluoric acid is provided in a predetermined concentration in the phosphoric acid to produce a predetermined diameter of the TiO 2 nanocavities.
7. The method of claim 6 , wherein the hydrofluoric acid is provided in a concentration of 3 molarity (3M).
8. The method of claim 7 , wherein the TiN nanocavities have a diameter of about 80 nm.
9. The method of claim 6 , wherein the hydrofluoric acid is provided in a concentration of 1-2M.
10. The method of claim 9 , wherein the TiN nanocavities have a diameter greater than 80 nm.
11. The method of claim 6 , wherein the hydrofluoric acid is provided in a concentration of 4-5M.
12. The method of claim 9 , wherein the TiN nanocavities have a diameter less than 80 nm.
13. The method of claim 4 , wherein step (a3) further comprises applying a DC voltage of between 10 volts and 30 volts to produce a predetermined diameter of the TiO 2 nanocavities.
14. The method of claim 13 , wherein step (a3) further comprises applying the DC voltage for a time period of one hour to three hours.
15. The method of claim 14 , wherein step (a3) further comprises applying a DC voltage of 15 volts for about two hours.
16. The method of claim 1 , wherein the nitridization step (b) is performed at 500-700° C.
17. The method of claim 9 , wherein the nitridization step (b) is performed at 500-600° C. for 25 minutes.
18. The method of claim 1 , wherein the nitridization step (b) is performed at an ammonia flow of 5-10 mL/minute.
19. The method of claim 1 , wherein the plurality of TiN nanocavities have an average diameter of 80 nm, average length of 180 nm, average wall thickness of about 20 nm and an average center-to-center distance of 100 nm, to define nanocontainers with a volume of about 750 zeptoliter.
20. The method of claim 1 , wherein at least a first of the TiN nanocavities comprises a titanium nitride nanofurnace disposed on a titanium film, the titanium nitride nanofurnace having an open top, a titanium nitride bottom, and a titanium nitride tubular middle portion extending from the open top to the titanium nitride bottom, and
wherein the method further comprises:
flowing a molecular gas in at least the titanium nitride nanofurnace;
applying light to the titanium nitride nanofurnace; and
using the titanium nitride nanofurnace to heat the molecular gas therein to bring about a chemical transformation in the first molecular gas.