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Description
Transition metal dichalcogenides (TMDs) are a family of layered crystals with the chemical formula MX2 (M = W, Nb, Mo, Ta and X = S, Se, Te). These TMDs exhibit many fascinating optical and electronic properties making them strong candidates for high-end electronics, optoelectronic application, and spintronics. The layered structure of TMDs allows the crystal to be mechanically exfoliated to a monolayer limit, where bulk-scale properties no longer apply and quantum effects arise, including an indirect-to-direct bandgap transition. Controllably tuning the electronic properties of TMDs like WSe2 is therefore a highly attractive prospect achieved by substitutionally doping the metal atoms to enable n- and p-type doping at various concentrations, which can ultimately lead to more effective electronic devices due to increased charge carriers, faster transmission times and possibly new electronic and optical properties to be probed. WSe2 is expected to exhibit the largest spin splitting size and spin-orbit coupling, which leads to exciting potential applications in spintronics over its similar TMD counterparts, which can be controlled through electrical doping. Unfortunately, the well-established doping technique of ion implantation is unable to preserve the crystal quality leading to a major roadblock for the electronics applications of tungsten diselenide. Synthesizing WSe2 via chemical vapor transport (CVT) and flux method have been previously established, but controllable p-type (niobium) doping WSe2 in low concentrations ranges (<1 at %) by CVT methods requires further experimentation and study. This work studies the chemical vapor transport synthesis of doped-TMD W1-xNbxSe2 through characterization techniques of X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, and X-ray Photoelectron Spectroscopy techniques. In this work, it is observed that excess selenium transport does not enhance the controllability of niobium doping in WSe2, and that tellurium tetrachloride (TeCl4) transport has several barriers in successfully incorporating niobium into WSe2.
ContributorsRuddick, Hayley (Author) / Tongay, Sefaattin (Thesis director) / Jiao, Yang (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2024-05
ContributorsAnderson, Kristian (Performer) / ASU Library. Music Library (Publisher)
Created1998-04-25
Description
Additive manufacturing (AM) gathers increasing attention for its customization and sustainability benefits, including material efficiency, lightweighting, and energy conservation. This dissertation explores innovative strategies for 3D printing elastomers using vat photopolymerization (VP) and direct ink writing (DIW). The first study introduces a strategy for incorporating high molecular weight isoprene rubber latexes into VP to address the challenges of processing elastomers. The addition of water-soluble monomers and crosslinkers to the latex aqueous phase yielded a photocurable, low-viscosity precursor suitable for VP. Photopolymerization in the aqueous phase created a hydrogel scaffold surrounding the polymeric particles, solidifying the latex into a green body. Post-processing removed water, driving the coalescence of isoprene rubber particles and resulting in a semi-interpenetrating polymepost-processing) with exceptional elongation at break up to 600%. Expanding on this, VP of sulfonated ethylene-propylene-diene monomer (sEPDM) latex demonstrated the 3D printing of olefinic elastomers. The sEPDM formed a physically crosslinked network due to ionic aggregation, leading to an interpenetrating polymer network (IPN) with tunable mechanical properties after sEPDM particles coalesced throughout the scaffold network during the post processing of printed green body. The introduction of polymerizable counterions for sulfonate groups at the sEPDM particle interfaces created a novel photocuring mechanism for latexes. The copolymerization of monomer added in the aqueous phase and 2-(Dimethylamino)ethyl methacrylate (DMAEMA) at the sEPDM particles generated a physically crosslinked hydrogel network through the ionic association on the latex particle interfaces. The absence of covalent crosslinked network highlighted the potential of 3D printing reprocessable materials. The last two projects utilized hybrid colloids composed of inorganic nanoparticles and styrene-butadiene rubber (SBR) particles for the 3D printing of polymer composites. The mixture of silica nanoparticle colloid and SBR latex demonstrated shear yield-stress behavior, enabling DIW. The modification of silica nanoparticle surface functionalities tuned the interaction between the silica and the polymer matrix, influencing the material mechanical properties. Electrically conductive fillers, single-wall carbon nanotubes (SWCNTs), were applied in SBR hybrid colloids to demonstrate VP of SWCNT-SBR composites. The results revealed enhanced electrical conductivity of the composites with increased SWCNT content, demonstrating the potential application of 3D printing elastomeric conductive materials.
ContributorsWen, Jianheng (Author) / Long, Timothy E (Thesis advisor) / Jin, Kailong (Committee member) / Sample, Caitlin S (Committee member) / Arizona State University (Publisher)
Created2024