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Investigation of Optical and Electronic Properties of Au Decorated MoS2

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Date Issued:
2015
Abstract/Description:
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.ivTo 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.
Title: Investigation of Optical and Electronic Properties of Au Decorated MoS2.
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Name(s): Bhanu, Udai, Author
Khondaker, Saiful, Committee Chair
Leuenberger, Michael, Committee Member
Zhai, Lei, Committee Member
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2015
Publisher: University of Central Florida
Language(s): English
Abstract/Description: 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.ivTo 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.
Identifier: CFE0006025 (IID), ucf:51013 (fedora)
Note(s): 2015-05-01
Ph.D.
Sciences, Physics
Doctoral
This record was generated from author submitted information.
Subject(s): MoS2 -- electron transport -- doping -- quenching -- photoluminescence
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0006025
Restrictions on Access: campus 2018-11-15
Host Institution: UCF

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