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

Rajarajan, Sundaravadivel

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Description

Title

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

Author(s)

Rajarajan, Sundaravadivel

Issue Date

2015-04-20

Department of Study

Electrical & Computer Engineering

Discipline

Electrical & Computer Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• 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

Abstract

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.

Graduation Semester

2015-5

Type of Resource

text

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Copyright 2015 Sundaravadivel Rajarajan

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