Chemical vapor transport growth of two-dimensional transition-metal dichalcogenides
A two-dimensional transition-metal dichalcogenide layer is grown by reacting a non- or low-volatile source material with a volatilized halogen or halide compound to produce a volatilized composition comprising at least one reaction product. The volatilized composition is flowed through an open chamber of a tube furnace with a temperature gradient, wherein the temperature changes along a path through which the volatilized composition flows through the open chamber of the tube furnace. Where the temperature along the path in the open chamber is in a reaction-temperature range, the volatilized composition is deposited as a two-dimensional crystalline transition-metal dichalcogenide layer.
1. A method for growing a two-dimensional transition-metal dichalcogenide layer, comprising:
reacting a non- or low-volatile source material comprising a transition-metal dichalcogenide with a volatilized halogen or halide compound to produce a volatilized composition comprising at least one reaction product;
flowing the volatilized composition through an open chamber of an open-chamber tube furnace with a temperature gradient, wherein the temperature changes along a path through which the volatilized composition flows through the open chamber of the tube furnace; and
where the temperature along the path in the open chamber is in a reaction-temperature range, depositing the volatilized composition as a two-dimensional crystalline layer of the transition-metal dichalcogenide.
2. The method of claim 1 , further comprising providing a vacuum pump at one end of the open chamber, wherein the vacuum pump reduces contamination and controls pressure in the open chamber and draws the flow of the volatilized composition through the open chamber.
3. The method of claim 2 , further comprising maintaining a vapor pressure in a range from 50 mTorr to 20 Torr in the open chamber.
4. The method of claim 1 , further comprising vaporizing the halogen or halide compound from a solid salt in the tube furnace.
5. The method of claim 4 , wherein the halogen is selected from chlorine, bromine, and iodine.
6. The method of claim 5 , wherein the halogen is chlorine.
7. The method of claim 6 , wherein the chlorine is volatilized from sodium chloride.
8. The method of claim 1 , wherein the crystalline transition-metal dichalcogenide has the formula MX 2 , wherein M is a transition metal selected from Ti, Zr, Hf, V, Ta, Nb, Cr, Mo, W, Tc, Re, Pt, and Pd, and wherein X is a chalcogen selected from S, Se, and Te.
9. The method of claim 8 , wherein the crystalline transition-metal dichalcogenide is selected from WS 2 and WSe 2 .
10. The method of claim 1 , wherein the deposited two-dimensional crystalline transition-metal dichalcogenide layer is a monolayer.
11. The method of claim 1 , wherein the reaction of the transition-metal dichalcogenide with the volatized halogen or halide compound replaces the chalcogen of the transition-metal dichalcogenide with the halogen.
12. The method of claim 11 , wherein the chalcogen replaces the halogen when the crystalline two-dimensional transition-metal dichalcogenide layer is deposited.
13. The method of claim 1 , wherein the chalcogen of the transition-metal dichalcogenide is selected from sulfur, selenium, and tellurium.
14. The method of claim 1 , further comprising entraining the volatilized composition in a flowing gas mixture comprising argon and hydrogen through the open chamber of the tube furnace.
15. The method of claim 14 , wherein WS s , is deposited, and wherein the flow rate of the volatilized composition and gas mixture is in a range from 100 sccm to 150 sccm.
16. The method of claim 1 , wherein the temperature decreases along the flow path of the volatilized composition, wherein the volatilized composition reacts where the temperature drops below a reaction temperature.
17. The method of claim 1 , wherein the volatilized composition comprises at least two reaction products, and wherein the reaction products react with each other to produce the deposited two-dimensional crystalline transition-metal dichalcogenide layer.