Degree

Doctor of Engineering (DEng)

Department

Electrical and Computer Engineering

Document Type

Dissertation

Abstract

The electrical characteristics of 2D materials such as high electron mobility and current density are of great interest to various fields from optoelectronics to renewable energy. Researchers have focused their efforts on transition metal dichalcogenides (TMDCs) due to their direct energy band gap. One such TMDC that has garnered much attention is molybdenum disulfide (MoS2). MoS2 has electrical properties comparable to graphene and is a TMDC with characteristics amenable to applications such as solar cells and sensors. Commonly deposited through time-consuming and complex deposition methods such as chemical vapor deposition (CVD), the viability of MoS2 as an electronic material will require improvement in the speed of its deposition, reproducibility, and scalability, and in production. In this research we focus on developing a recipe for the formation of MoS2 thin films through electrophoretic deposition (EPD). EPD has become a popular technique in recent years for the deposition of many electronic materials including TMDCs as it is an economical, room temperature, suspension based wet coating technique that can control film thickness and deposition onto arbitrary substrates. The research explained in this dissertation details our investigation into the feasibility of using EPD to deposit MoS2 thin films for applications in semiconductor research. The initial testing of EPD for MoS2 film formation pursued in this work produced spotty particle deposition. To improve the MoS2 depositions on silicon substrates, we functionalized the silicon surface with 3-aminopropyl-triethoxysilane (APTES) which is an organosilane. The organosilane treated silicon surface assists the formation of the MoS2 films through the Coulombic force of attraction between the positively charged NH2 APTES surface groups and the negatively charged sulfur molecules located on the edge plane of MoS2 flakes. Through functionalizing the silicon, we produced depositions of MoS2 superior in comparison to MoS2 on non-functionalized silicon. Raman spectroscopy was used to confirm material composition. Optical microscopy in combination with ImageJ software was used to examine coverage and uniformity with respect to non-functionalized silicon. The organosilane assisted EPD increases the yield of MoS2 particles that are deposited onto the silicon substrate. Further research to improve the quality of the MoS2 thin films involves testing the addition of sodium dodecyl sulfate (SDS) in the EPD suspension to increase the zeta potential. SDS will be added to the MoS2 suspensions at various ratios to test the extent of the effect that SDS has on MoS2 EPD thin films. Microscope images of the samples on different substrates were taken to examine surface characteristics and the coffee ring effect. Weight, temperature, and deposition current measurements are used to determine characteristics of the deposition rate. Raman spectroscopy was used to determine any change in the material quality of MoS2 due to the different ratios of SDS. The I – V curve of the samples were measured to analyze the I – V characteristics as a precursor to the PN – junction characteristics of the thin films. The adhesion property of the MoS2 to the substrate surface was also studied using the Scotch tape test.

Date

11-1-2023

Committee Chair

Daniels-Race, Theda

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