Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Subject "Ionic Liquid"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Continuos Doping of La2CuO4+x Thin Films
    (2015-09) Kinney, Joseph
    Finding more efficient ways of exploring the doping phase diagrams of high temperature superconductors as well as probing the fundamental properties of these materials are essential ingredients for driving the discovery of new materials. We use a doping technique involving gating with ionic liquids to systematically and continuously tune the Tc of superconducting La2CuO4+x thin films. We probe both the transport properties and the penetration depth of these samples and find that Homes scaling, lambda^-2 ~ sigma*Tc, is obeyed, consistent with these materials being in the dirty limit. This result is independent of the precise mechanism for the gating process as all of the parameters of the scaling relationship are determined by direct measurements on the films.
  • Thumbnail Image
    Item
    Hopping Conduction and Metallic behavior in 2D Silicon Surface States induced by an Ionic Liquid
    (2015-06) Nelson, JJ
    Ionic liquids (ILs) are essentially molten salts with a melting point below room temperature. When used as the gate dielectric of a transistor, carrier densities on the order of $10^{15}\text{ cm}^{-2}$ can be achieved. These record high carrier densities are significantly higher than the maximum carrier density achievable with oxide dielectrics. The physical mechanism for inducing carriers to such a high carrier density is not well understood. Some groups have reported that the induced carriers are a result of electrostatic and electrochemical processes. Other groups have suggested that carriers induced with an IL may be entirely due to electrochemical reactions. Here we report on IL gated Si at carrier densities from $10^{11}\text{ cm}^{-2}$ to $10^{13}\text{ cm}^{-2}$. The experiment was designed to preferentially induce electrostatic carriers over electrochemical reactions. At low carrier densities, sample surface conductivity follows nearest neighbor hopping conduction. This form of conduction has also been observed in experiments where surface conductivity was induced by implanting $\text{Na}^{+}$ near the oxide surface interface. A surprising result of this work was that in some samples a 2D metallic state could be created on the surface of Si. The transition to metallic behavior occurred just below $10^{13}\text{ cm}^{-2}$. High quality Si transistors with oxide dielectric materials observe critical carrier densities around $10^{11}\text{ cm}^{-2}$. The critical carrier density observed in IL gated Si is the highest density reported to date. At carrier densities higher than $10^{13}\text{ cm}^{-2}$ it was observed that the sample conductivity decreased with increasing carrier density. The behavior was unexpected and not fully understood. Both metallic and non metallic samples show a similar reduction in conductivity that is not thought to be due to sample degradation by the IL. The reduction in the sample conductivity at high carrier densities is thought to be due to surface roughness scattering. Similar behavior has been observed in other IL gated experiments on different materials.
  • Thumbnail Image
    Item
    Polymer-Based Ion Gels as a Versatile Platform of Solid Electrolytes
    (2018-07) Tang, Boxin
    Ion gels are a versatile class of functional materials. Combining the excellent electrical properties such as high ionic conductivity and capacitance of the ionic liquid (IL) and the mechanical integrity of the polymer, the composite materials have led to a variety of applications such as electrolyte-gated transistors (EGTs), electroluminescent, and electrochromic soft materials. This thesis is built up from previous research on the electrical and mechanical properties of the ABA triblock polymer-based ion gels and continues to improve properties of the materials for electrochemical device applications. In the first part of the thesis work, the objective is to improve the existing ABA triblock polymer systems with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) as the IL-solvating midblock by combining the merit of the low Tg from PEO and hydrophobicity from PMMA into one system. As a result, poly(styrene-b-ethyl acrylate-b-styrene) (SEAS) triblock polymer was developed. The ion gels made with SEAS demonstrate similarly high ionic conductivity as the PEO-based ion gels, which are significantly improved from those of the PMMA-based ion gels. By shortening the midblock size of the triblock polymer, a synergistic improvement of both the ionic conductivity and the modulus can be achieved. Additionally, the EGTs made by SEAS-based ion gels demonstrate superior stability under humidity compared with EGTs made by SOS-based ion gels. In the following two projects of the thesis work, the polymer platform changes from petroleum-based polymers with hydrocarbon backbones to renewable aliphatic polyesters with the potential aim of EGTs in biocompatible applications. To achieve the ion gels, both physical and chemical crosslinked-systems have been explored. The physically crosslinked ABA aliphatic polyester triblock ion gels demonstrate good mechanical integrity and can be successfully printed under similar conditions as the previous systems, and demonstrate improved ionic conductivity from the PMMA-based ion gels. In addition, the resulting ion gels also demonstrate efficient hydrolytic degradation under basic condition. In a different approach, chemically crosslinked poly(lactide) (PLA)-based ion gels can be synthesized from a facile one-pot method. Owing to a smaller volume fraction in ion-insulating domain, the ion gel demonstrates an excellent ionic conductivity at low polymer concentration. Meanwhile, the ion gel also possesses a high toughness owing to the chemical crosslinks. The thin chemically crosslinked PLA-ion gels can be laminated onto EGTs via a cut-and-stick method. On the other hand, the bulk ion gel demonstrates a good electromechanical response with high electromechanical sensitivity with the applied strain and a low hysteresis between stretching and unstretching.