Degree

Doctor of Philosophy (PhD)

Department

Electrical Engineering

Document Type

Dissertation

Abstract

This work presents both a feasibility study and an investigation into the voltage-controlled spray deposition of different nanoparticles, namely, carbon nanotubes (CNTs), as well as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) from the transition metal dichalcogenides (TMDCs) family of materials. The study considers five different types of substrates as per their potential application to next-generation device electronics. The substrates selected for this research were: 1) aluminum as a conducting substrate, 2) silicon as a semiconducting substrate, 3) glass, silicon dioxide (SiO2), and syndiotactic poly methyl methacrylate (syndiotactic PMMA) as insulating substrates.

Since the 1990’s, carbon nanotubes have been the subject of intense research due to their extraordinary properties of conductivity, strength, and thermal stability. To utilize CNTs to their full potential, it is important to analyze their characteristics with respect to their amenability to deposition onto different substrate species, as future device technologies may demand. However, prior to the actual deposition, the natural tendency of CNTs to agglomerate must be taken into account. Thus, in this study the two commonly used methods of acid refluxing and surfactant treatment were used for dispersing the CNTs. Although CNTs were successfully dispersed in preparation for the form of voltage-controlled deposition developed for this research, a deeper investigation elucidated materials processing challenges stemming from the use of acid refluxing and surfactant-based methods. Thus, alternatively, a new method of dispersing CNTs, using isopropyl alcohol (IPA) and an anionic (positively charged) surfactant has been devised for this study. This, in conjunction with the five types of substrates, provided the testbed needed to investigate the feasibility of voltage-controlled spray deposition as a means for producing the uniform coatings of CNTs, the latter having application to device processing.

On the other hand, TMDCs are garnering the attention of researchers due the extraordinary electronic, catalytic, and optical properties of these materials. The two particular TMDCs chosen for this work, MoS2 and WS2, are considered to be alternatives to, if not potential replacements for, the zero band gap conductor graphene. Both MoS2 and WS2 act as direct band gap semiconductors in single layer form and as indirect band gap semiconductors in multi-layer formation. This property makes these TMDCs promising as the basis for applications in solar cells, flexible electronics, sensors, and supercapacitors. However, systematic characterization and analysis are necessary to assess the suitability of any promising electronic material. Therefore, as with the aforementioned CNTs, in this study MoS2 and WS2 are dispersed in solvent, followed by deposition and characterization. Here again, the above-mentioned five different substrates are used as the template onto which these selected TMDCs are deposited via the method of voltage controlled spray deposition.

The results of spectroscopic analysis, microstructural imaging, and characterization of the morphology of the nanoparticles and films deposited for this study will be presented. The effectiveness of the voltage-controlled spraying in light of these results will be discussed.

Finally, a forward-looking study into the use of WS2 in surface enhanced Raman spectroscopy (SERS) has been undertaken in support of future work. This TMDC was used in conjunction with platinum to fabricate a WS2 based SERS substrate.

Date

5-16-2018

Committee Chair

Daniels-Race, Theda

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