Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Salamo, Gregory J.

Committee Member

Churchill, Hugh O.H.

Second Committee Member

Yu, Shui-Qing "Fisher"

Third Committee Member

Naseem, Hameed A.

Fourth Committee Member

El-Ghazaly, Samir M.

Keywords

Electron Transport; Nanowire; Tellurium

Abstract

Since the experimental discovery of graphene, two dimensional materials have enjoyed more attention and emphasis in academic research than nanowires, but the latter are an important area of study for creating 1D materials, or single atom chains, the next generation materials for advancing electronic devices. Atomically thin layers can be generated from 2D materials with weak bonds in one direction, and by applying this concept to one dimensional weakly bonded materials, we hypothesize that single atom chains with atomic-scale diameters may be produced. Tellurium (Te) and selenium (Se) have lattices consisting of spiral chains oriented along the c-axis, and each chain weakly bonds with others to form a bulk crystal. Since Te exhibits higher mobility than Se, nanoscale Te was the primary focus of this work. Trigonal Te single crystals were exfoliated, without tape, on oxidized silicon substrates. Atomic force spectroscopy revealed that Te nanowires with heights of only 1–2 nm and widths less than 100 nm were successfully fabricated. Anisotropic Te flakes with a thickness of 15 nm showed ridges running along the length of the flake surfaces. A1 and E Raman modes of a 30 nm thick flake were consistent with those of bulk Te, but they showed a slight blueshift (4 cm-1). Polarized Raman spectroscopy was used to determine the crystal orientation of the flakes. Te and Se crystals were also grown on SiO2 substrates by physical vapor deposition. Te flakes and wires with heights of 60 nm and 30 nm were obtained; Se flakes with a height of 30–40 nm were also obtained. The synthesized Te wires were utilized in electron transport measurements. A four-terminal device showed a mobility of 51 cm2V-1s-1 at 2.8 K, a mobility lower than predicted due to the low quality of the Te wire. The contact resistance and resistivity of Te were estimated to be 9.4 kΩ and 9.4×10-4 Ω∙m by applying a correction factor of 0.6. Another successfully fabricated two-terminal device showed a mobility of 1032 cm2V-1s-1 at 10 K, which is a promising enough result to suggest that such a device could be used for quantum transport measurements.

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