Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Physics & Astronomy

First Advisor

Marija Drndic

Abstract

We report how the presence of sulfur vacancies affects first-order Raman modes and correlate the effects with the evolution of the two-terminal conductivity of monolayer MoS2 . We show that irradiation causes partial removal of sulfur and correlate the dependence of the Raman peak shifts with S vacancy density (a few %). This allows us to quantitatively correlate the frequency shifts with vacancy concentration. In situ device current measurements show an exponential decrease in channel current upon irradiation. Our analysis demonstrates that the observed frequency shifts are intrinsic properties of the defective systems and that Raman spectroscopy can be used as a quantitative diagnostic tool to characterize MoS2-based transport channels.

The combination of a nanopore with a local field-effect transistor, like a nanoribbon, nanotube, or nanowire, in order to sense single molecules translocating through the pore is promising for DNA sequencing at megahertz bandwidths. Previously, it was experimentally determined that the detection mechanism was due to local potential fluctuations that arise when an analyte enters a nanopore and constricts ion flow through it, rather than the theoretically proposed mechanism of direct charge coupling between the DNA and nanowire. However, there has been little discussion on the experimentally observed detection mechanism and its relation to the operation of real devices. We model the intrinsic signal and noise in such an FET-nanopore device. At bandwidths dominated by thermal noise, the signal-to-noise ratio in FET-nanopore devices is lower than in the ionic current signal. At high frequencies, where noise due to parasitic capacitances in the amplifier and chip is the dominant source of noise in ionic current measurements, high-transconductance FET-nanopore devices can outperform ionic current measurements.

Large-area growth of monolayer transition metal dichalcogenides is of interest due to their exciting electrical and optical properties. 1T’ monolayers have been predicted to be large-gap quantum spin Hall insulators. We use aberration-corrected scanning electron microscopy to characterize the structure novel 1T’-TMDs grown by chemical vapor depostion.

Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS