Browsing by Author "Glass, JT"

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    A method to obtain a Ragone plot for evaluation of carbon nanotube supercapacitor electrodes
    (Journal of Materials Research, 2010-08-01) Raut, AS; Parker, CB; Glass, JT
    Electrochemical double layer capacitors, also referred to as supercapacitors, are a promising technology in the field of energy storage. Carbon nanotube (CNT)-based supercapacitors are particularly interesting because of CNTs' high surface area and conductivity. CNT supercapacitors can potentially be used in hybrid electric vehicles due to their higher power density. Comparing energy storage systems that store energy in different ways, such as batteries, fuel cells, supercapacitors, and flywheels, requires that an appropriate set of performance data be collected. A Ragone plot is a log-log plot of a device's energy density versus power density, giving insight into its operational range. A method to obtain Ragone plots for CNT-based supercapacitors in a three-terminal electrochemical cell was adapted from a technique to test commercial capacitors for electric vehicles. Ragone plots for different types of as-grown CNT electrodes in different electrolytes are presented, along with the procedural details of this new method to obtain electrode-specific energy and power densities. Additionally, a theoretical weight calculation for a carbon nanotube film was derived and validated with a direct weight measurement of a CNT film. This weight was used in the specific energy and power densities for the Ragone plot. © 2010 Materials Research Society.
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    Analysis of 3-panel and 4-panel microscale ionization sources
    (Journal of Applied Physics, 2010-06-15) Natarajan, S; Parker, CB; Piascik, JR; Gilchrist, KH; Stoner, BR; Glass, JT
    Two designs of a microscale electron ionization (EI) source are analyzed herein: a 3-panel design and a 4-panel design. Devices were fabricated using microelectromechanical systems technology. Field emission from carbon nanotube provided the electrons for the EI source. Ion currents were measured for helium, nitrogen, and xenon at pressures ranging from 10-4 to 0.1 Torr. A comparison of the performance of both designs is presented. The 4-panel microion source showed a 10× improvement in performance compared to the 3-panel device. An analysis of the various factors affecting the performance of the microion sources is also presented. SIMION, an electron and ion optics software, was coupled with experimental measurements to analyze the ion current results. The electron current contributing to ionization and the ion collection efficiency are believed to be the primary factors responsible for the higher efficiency of the 4-panel microion source. Other improvements in device design that could lead to higher ion source efficiency in the future are also discussed. These microscale ion sources are expected to find application as stand alone ion sources as well as in miniature mass spectrometers. © 2010 American Institute of Physics.
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    Atomic layer deposition for electrochemical energy generation and storage systems
    (Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, 2012-01-01) Peng, Q; Lewis, JS; Hoertz, PG; Glass, JT; Parsons, GN
    Clean renewable energy sources (e.g., solar, wind, and hydro) offers the most promising solution to energy and environmental sustainability. On the other hand, owing to the spatial and temporal variations of renewable energy sources, and transportation and mobility needs, high density energy storage and efficient energy distribution to points of use is also critical. Moreover, it is challenging to scale up those processes in a cost-effective way. Electrochemical processes, including photoelectrochemical devices, batteries, fuel cells, super capacitors, and others, have shown promise for addressing many of the abovementioned challenges. Materials with designer properties, especially the interfacial properties, play critical role for the performance of those devices. Atomic layer deposition is capable of precise engineering material properties on atomic scale. In this review, we focus on the current state of knowledge of the applications, perspective and challenges of atomic layer deposition process on the electrochemical energy generation and storage devices and processes. © 2012 American Vacuum Society.
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    Bias induced diamond nucleation studies on refractory metal substrates
    (Journal of Applied Physics, 1995-12-01) Wolter, SD; Glass, JT; Stoner, BR
    The carbide forming nature of the substrate appears to be an important property when performing bias-enhanced nucleation (BEN); therefore, various refractory metals were studied since they are known carbide formers. Nucleation densities approaching 1×1010/cm2 were observed on both hafnium and titanium. The nucleation density on tantalum, niobium, and tungsten was enhanced to a lesser extent in descending order of influence, respectively. An induction time prior to the onset of significant diamond nucleation was observed on the refractory metals as well as on silicon and may be reliant upon the formation of a critical carbide thickness. Shorter induction times were observed for silicon which may be explained since this material forms a carbide of typically only several nanometers in thickness as opposed to the refractory metals which may form carbides on the order of several microns in thickness. Also, a strong correlation was observed between the carbide heat of formation and the nucleation densities at 60 min of BEN. These findings verify the relevance of a carbide formation to diamond nucleation via BEN and also provides a clue as to the mechanism(s) by which diamond is nucleating. © 1995 American Institute of Physics.
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    Bias-enhanced nucleation of highly oriented diamond on titanium carbide (111) substrates
    (Applied Physics Letters, 1995) Wolter, SD; McClure, MT; Glass, JT; Stoner, BR
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    Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics
    (CHEM, 2018-10-11) Han, Q; Ding, J; Bai, Y; Li, T; Ma, JY; Chen, YX; Zhou, Y; Liu, J; Ge, QQ; Chen, J; Glass, JT; Therien, MJ; Liu, J; Mitzi, DB; Hu, JS
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    Effects of boron doping on the surface morphology and structural imperfections of diamond films
    (Diamond and Related Materials, 1992-05-01) Wang, XH; Ma, G-HM; Zhu, Wei; Glass, JT; Bergman, L; Turner, KF; Nemanich, RJ
    This paper reports the surface morphology and structural imperfection of boron-doped diamond films prepared by microwave plasma enhanced chemical vapor deposition. It was found that boron dopants improved the structural quality of diamond films. The surface morphology consisted mainly of the {111} facets. A significant enhancement of nucleation density and consequent decrease of grain size was observed with the addition of diborane in the gas phase. Raman spectroscopy indicated that, with the introduction of boron dopants, the integrated intensity of the diamond peak at 1332 cm-1 increased relative to the intensity of the non-diamond peak at about 1500 cm-1, and the full-width at half maximum of the 1332 cm-1 peak decreased. In addition, the 1.681 eV (738 nm) photoluminescence peak related to point defects was effectively reduced, or even eliminated by the boron dopants. Finally, transmission electron microscopy studies found that the densities of planar defects (mainly stacking faults and microtwins) also decreased with the boron addition. © 1992.
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    Electron microscopic characterization of diamond films grown on Si by bias-controlled chemical vapor deposition
    (Journal of Materials Research, 1990-01-01) Ma, GHM; Lee, YH; Glass, JT
    Diamond films grown by Bias-Controlled Hot Filament Chemical Vapor Deposition (BCCVD) on silicon (Si) substrates were characterized by Transmission Electron Microscopy (TEM). Both plan-view and cross-sectional TEM samples were made from diamond films grown under different biasing conditions. It was found that defect densities in the films were substantially reduced under zero and reverse bias (substrate negative relative to the filament) as compared to forward bias. Furthermore, the diamond/Si interface of the reverse and zero bias films consisted of a single thin interfacial layer whereas multiple interfacial layers existed at the diamond/Si interface of films grown under forward (positive) bias. Tungsten (W) contamination was also found in the interfacial layers of forward bias films. It is concluded that forward biasing in the present condition is not favorable for growing high quality, low defect density, diamond films. The possible mechanisms which induced the microstructural differences under different biasing conditions are discussed. © 1990, Materials Research Society. All rights reserved.