Gnade, Bruce E.

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Dr. Gnade is Professor of materials science and engineering and holds the Distinguished Chair in Microelectronics. He also serves as UTD's Vice President for Research. Learn more about Dr. Gnade's research on his Research Explorer page.


Recent Submissions

Now showing 1 - 8 of 8
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    The Effect of Poling Conditions on the Performance of Piezoelectric Energy Harvesters Fabricated by Wet Chemistry
    (Royal Soc Chemistry) Fuentes-Fernandez, Erika M. A.; Gnade, Bruce E.; Quevedo-Lopez, Manuel A.; Shah, Pradeep; Alshareef, H. N.; 00049719‏ (Gnade, BE); 6602171886 (Quevedo-Lopez, MA); Fuentes-Fernandez, Erika M. A.; Gnade, Bruce E.; Quevedo-Lopez, Manuel A.
    The effect of poling conditions on the power output of piezoelectric energy harvesters using sol-gel based Pb(Zr{0.53}, Ti{0.47})O{3}3-Pb(Zn{1/3}, Nb{2/3})O{3} piezoelectric thin-films has been investigated. A strong correlation was established between the poling efficiency and harvester output. A method based on simple capacitance-voltage measurements is shown to be an effective approach to estimate the power output of harvesters poled under different conditions. The poling process was found to be thermally activated with an activation energy of 0.12 eV, and the optimum poling conditions were identified (200 kV cm⁻¹, 250 ⁰C for 50 min). The voltage output and power density obtained under optimum poling conditions were measured to be 558 V cm⁻² and 325 μW cm⁻², respectively.
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    Thin Film Cadmium Telluride Charged Particle Sensors for Large Area Neutron Detectors
    (Amer Inst Physics) Murphy, John W.; Smith, Lindsey; Calkins, J.; Mejia, Israel; Cantley, Kurtis D.; Chapman, Richard A.; Quevedo-Lopez, Manuel A.; Gnade, Bruce E.; 0000 0003 8371 1336‏ (Gnade, BE); 00049719‏ (Gnade, BE); C-2327-2008‏ (Gnade, BE)
    Thin film semiconductor neutron detectors are an attractive candidate to replace ³He neutron detectors, due to the possibility of low cost manufacturing and the potential for large areas. Polycrystalline CdTe is found to be an excellent material for thin film charged particle detectors−an integral component of a thin film neutron detector. The devices presented here are characterized in terms of their response to alpha and gamma radiation. Individual alpha particles are detected with an intrinsic efficiency of >80%, while the devices are largely insensitive to gamma rays, which is desirable so that the detector does not give false positive counts from gamma rays. The capacitance-voltage behavior of the devices is studied and correlated to the response due to alpha radiation. When coupled with a boron-based neutron converting material, the CdTe detectors are capable of detecting thermal neutrons.
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    Using Interlayer Step-Wise Triplet Transfer to Achieve an Efficient White Organic Light-Emitting Diode with High Color-Stability
    (American Institute of Physics) Wang, Qi; Ma, Dongge; Leo, Karl; Ding, Junqiao; Wang, Lixiang; Qiao, Qiquan; Jia, Huiping; Gnade, Bruce E.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE)
    An efficient phosphorescent white organic light emitting-diode with a red-green-blue 3tri-emitting-layer structure is reported. The host of the red dopant possesses a lower triplet-energy than the green dye. An interlayer step-wise triplet transfer via blue dye -> green dye -> red host -> red dye is achieved. This mechanism allows an efficient triplet harvesting by the three dopants, thus maintaining a balanced white light and reducing energy loss. Moreover, the color stability of the device is improved significantly. The white device not only achieves a peak external quantum efficiency of 21.1 +/- 0.8% and power efficiency of 37.5 +/- 1.4 lm/W but shows no color shift over a wide range of voltages.
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    Benzodithiophene Homopolymers Synthesized by Grignard Metathesis (GRIM) and Stille Coupling Polymerizations
    (Royal Soc Chemistry, 2014-04-16) Magurudeniya, Harsha D.; Kularatne, Ruvini S.; Rainbolt, Elizabeth A.; Bhatt, Mahesh P.; Murphy, John W.; Sheina, Elena E.; Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE); 55039821 (Stefan, MC); Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.
    Poly{4,8-bis(95-dodecylthiophene-2-yl) benzo[1,2-b: 4,5-b'] dithiophene} has been synthesized by both Grignard metathesis (P1) and Stille coupling polymerizations (P2). Polymers P1 and P2 were characterized and their optoelectronic properties, charge carrier mobilities, and photovoltaic properties were compared. The field-effect mobilities of the polymers were measured on both untreated and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FS) treated organic field effect transistor (OFET) devices. The polymers were also evaluated in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor.
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    Structural Variation of Donor-Acceptor Copolymers Containing Benzodithiophene with Bithienyl Substituents to Achieve High Open Circuit Voltage in Bulk Heterojunction Solar Cells
    (Royal Soc Chemistry, 2013-11-06) Kularatne, Ruvini S.; Taenzler, Ferdinand J.; Magurudeniya, Harsha D.; Du, Jia; Murphy, John W.; Sheina, E. E.; Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE); 55039821 (Stefan, MC); Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.
    Three new donor-acceptor copolymers P1, P2, and P3 were synthesized with benzodithiophene with bithienyl substituents as the donor and 5,6-difluorobenzo[c][1,2,5]thiadiazole, 4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole, and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole as the acceptors, respectively. The insertion of thiophene spacer between the donor and the acceptor broadened the absorption of the polymers P2 and P3 and resulted in a red shift of ~30 nm as compared to that of the polymer P1. However, the inclusion of fluorine atoms on the polymer had detrimental effects on the photovoltaic properties of the polymers. The synthesized donor-acceptor polymers were tested in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) acceptor. Polymer P2 gave a PCE of 3.52% with PC71BM in which the active layer was prepared in chloroform with 3% v/v 1,8-diiodooctane (DIO) additive. The effect of fluorine substitution and thiophene group insertion on the UV/Vis absorbance, photovoltaic performances, morphology, and charge carrier mobilities for the polymers are discussed.
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    Performance and Stability of Solution-Based Cadmium Sulfide Thin Film Transistors: Role of CdS Cluster Size and Film Composition
    Salas-Villasenor, A. L.; Mejia, I.; Sotelo-Lerma, M.; Gnade, Bruce E.; Quevedo-Lopez, Manuel A.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE)
    Improved carrier mobility and threshold voltage (VT) stability in cadmium sulfide (CdS) thin film transistors (TFTs) were studied and attributed to larger grain clusters in thicker CdS films rather than individual crystallite size. Non-zero VT shifts (∼200 mV) in thicker films are attributed to the presence of cadmium hydroxide [Cd(OH)2] at the dielectric/CdS interface resulting from the chemical bath deposition process used to deposit the CdS films. VT and mobility analyses indicate that clusters of CdS grains have a larger impact on TFT performance and stability than the presence of impurities in the bulk of the CdS. TFTs using this fabrication method achieved mobilities of ∼22 cm2/Vs with V T of 7 V and ΔVT of <200 mV after testing. The maximum processing temperature is 100°C which makes this process compatible with flexible substrates.
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    Evaluation of CdS Interfacial Layers in ZnO Nanowire/Poly(3-Hexylthiophene) Solar Cells
    Murphy, John Winter; Mejia, Israel; Gnade, Bruce E.; Quevedo-Lopez, Manuel A.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE)
    We prepare ZnO:poly(3-hexylthiophene) (P3HT) thin-film solar cells and ZnO nanowire:P3HT nanostructured solar cells and evaluate the effect of adding an interfacial layer between the ZnO and P3HT as a function of the nanowire height. We evaluate several different interlayers of CdS deposited, using two different chemical bath deposition (CBD) recipes. The height of the nanowire array is varied from a bilayer device with no nanowires up to arrays with a height of 2 mu m. We find that achieving a conformal coating of the ZnO with the interfacial layer is critical to improve device performance and that CBD can be used to grow conformal films on nonuniform surfaces.
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    Optimizing Diode Thickness for Thin-Film Solid State Thermal Neutron Detectors
    (American Institute of Physics, 2012-10-04) Murphy, John W.; Mejia, Israel; Quevedo-López, Manuel A.; Gnade, Bruce E.; 0000 0003 8371 1336 (Gnade, BE); 00049719‏ (Gnade, BE); Erik Jonsson School of Engineering and Computer Science
    In this work, we investigate the optimal thickness of a semiconductor diode for thin-film solid state thermal neutron detectors. We evaluate several diode materials, Si, CdTe, GaAs, C (diamond), and ZnO, and two neutron converter materials, 10B and 6LiF. Investigating a coplanar diode/converter geometry, we determine the minimum semiconductor thickness needed to achieve maximum neutron detection efficiency. By keeping the semiconductor thickness to a minimum, gamma rejection is kept as high as possible. In this way, we optimize detector performance for different thin-film semiconductor materials.