Tungsten Ditelluride (wte2): An Atomic Layered Semimetal

Open Access
Author:
Lee, Chia Hui
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 02, 2015
Committee Members:
  • Joshua Alexander Robinson, Thesis Advisor
  • Thomas E Mallouk, Thesis Advisor
  • Mauricio Terrones Maldonado, Thesis Advisor
Keywords:
  • 2D materials; Layered Materials; WTe2; Tungsten Ditelluride; Td
Abstract:
Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We explored WTe2 synthesis via chemical vapor transport (CVT) method for bulk crystal, and chemical vapor deposition (CVD) routes for thin film material. We employed both experimental and theoretical techniques to investigate its structural, physical and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like behavior. Our findings confirmed the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. These findings confirm that, in its thermodynamically favored Td form. From our approach of developing WTe2 thin film materials via CVD processes, we have noticed that more reactive tungsten precursors could be the key to carry out WTe2 growth due to hydrogen reduction is the dominant reaction for tungsten trioxide (WO3) tellurization process. We successfully obtain Td-WTe2 thin film on various substrates from changing tungsten precursor to tungsten hexacarbonyl (W(CO)6). We verify the WTe2 film in Td structure by confirming Raman signature with synthesized WTe2 from CVT process. Further characterization and optimization of the growth process may be needed to understand WTe2 growth mechanism, substrate effects and growth conditions and achieve large area atomic layered growth of WTe2. All of these findings will help the utilization of WTe2 in electronic device architectures such as field effect transistors (FETs) may be reevaluated. More application should be explored for this special 2D layered WTe2 materials.