Synthesis of 1T-Tantalum (IV) Sulfide and observation of charge density wave using scanning tunneling microscopy

Charge Density Wave;Transition Metal Dichalcogenides (TMDC);1T-Tantalum (IV) Sulfide (1T-TaS2);Tantalum Disulfide;Scanning Tunneling Microscope;Ultra-High Vacuum;2D Material;Chemical Vapor Transport

Rajarajan, Sundaravadivel

关键词: Charge Density Wave;    Transition Metal Dichalcogenides (TMDC);    1T-Tantalum (IV) Sulfide (1T-TaS2);    Tantalum Disulfide;    Scanning Tunneling Microscope;    Ultra-High Vacuum;    2D Material;    Chemical Vapor Transport;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/78417/RAJARAJAN-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Over the past decade, due to the increasing interest and urgency in finding an alternate material system for post-silicon logic and opto-electronic applications, staggering progress have been made in the study of low-dimensional materials. These low-dimensional materials not only help reduce transistor footprint and improve power and performance metrics, they also exhibit very peculiar electrical properties. A particular example is the existence of a charge density wave (CDW) in 1T-Tantalum (IV) Sulfide (1T-TaS2). A member of the transition metal dichalcogenide (TMDC) family, 1T-TaS2 exhibit a periodic modulation of electronic charge density. Unlike bulk semiconductor or metals, lattice distortion in this low-dimensional material creates non-uniform, wave-like electron densities.In this thesis, we have demonstrated two bulk material growth strategies for the synthesis of 1T-TaS2. We have successfully grown poly-crystalline 1T-TaS2 powder through a direct solid-solid reaction and single-crystals of 1T-TaS2 through Iodine-assisted chemical vapor transport (CVT). After a few growth setup revisions, the growth processes have given consistently high yields. Next, we performed an ultra-high vacuum scanning tunneling microscopy (UHV-STM) study of the grown poly-crystalline 1T-TaS2. The powder was deposited onto an atomically flat, H-passivated silicon substrate using dry contact transfer (DCT), an in-situ deposition technique developed by the Lyding group for clean, UHV-compatible transfer of nano-materials. We managed to directly observe room-temperature CDW on the deposited nano-flakes of 1T-TaS2. The periodicity of the CDW lat- tice correspond very closely to the expected sqrt(13) x sqrt(13) nearly commensurate room-temperature CDW phase.