Keywords

Mos2, electron transport, doping, quenching, photoluminescence

Abstract

Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate optical and electronic properties due to charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, catalysis, and biosensing. Here in this dissertation, we study the charge transfer interaction between Au nanoparticals and MoS2 flakes and its effect on Photoluminescence and electronic transport properties. The MoS2 was mechanically exfoliated from bulk single crystal. Number of layers in the flake was identified with the help of AFM and Raman Spectra. Au was deposited by physical vapor deposition method (PVD) in multiple steps to decorate MoS2 flakes. We first study the photoluminescence of pristine and Au decorated MoS2 and shows that in the presence of Au, the photoluminescence of MoS2 quenches significantly. We infer that the PL quenching can be attributed to a change in the electronic structure of the MoS2-Au system. The difference in Fermi level of a of MoS2 and Au results in a 0.4 eV energy level offset, which causes a band bending in the MoS2-Au hybrid. Upon illumination, the electrons in the excited state of MoS2 transfer to Au, leaving a hole behind, thus cause p-doping in MoS2. As electrons from MoS2 are transferred to Au, they do not decay back to their initial ground state, leading to PL quenching in the hybrid system. To study the effect of Au deposition on electronic properties of ultra-thin and multilayers MoS2 flakes, we have fabricated MoS2 FETs from (1) ultra-thin sample (2-4 MoS2 layers) and (2) multilayers samples (more than 20 layers). After each deposition of Au, we measured the electrical characteristics of FET at room temperature. We show that the threshold voltage shifts towards the positive gate voltage as we increase the thickness of Au. This shift in threshold voltage is indicative of p doping of the MoS2. We further show that the field effect mobility of MoS2 FET decrease with Au thickness. We have quantitatively estimated the charge transferring from MoS2 to Au.

Notes

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Graduation Date

2015

Semester

Spring

Advisor

Khondaker, Saiful

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Physics

Degree Program

Physics

Format

application/pdf

Identifier

CFE0006025

URL

http://purl.fcla.edu/fcla/etd/CFE0006025

Language

English

Release Date

November 2018

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Campus-only Access)

Subjects

Dissertations, Academic -- Sciences; Sciences -- Dissertations, Academic

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