Browsing by Author "Gnade, Bruce E."
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Item 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.Item 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.Item Evaluation of CdS Interfacial Layers in ZnO Nanowire/Poly(3-Hexylthiophene) Solar CellsMurphy, 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.Item Fabrication and Characterization of Thermoelectric Materials and Their Stable Contacts at Elevated Temperatures(2017-12) Zhang, Bo; Gnade, Bruce E.Contact resistance plays an important role in maintaining high device performance in thermoelectric (TE) generators and coolers. In order to achieve 95% device efficiency, the contact resistance needs to be < 10% of the total leg resistance. Therefore, stable contact electrodes with low contact resistivity are necessary to ensure good device efficiency. In this dissertation, various contact materials (Hf, Ni, Ti and Au) were evaluated as potential contact metals to Mg2Si used for moderate temperature applications. The data indicate that Ni is the best candidate among the four: it can be stable up to 400°C. The contact failure analysis showed that Ni diffuses into Mg2Si after annealing at 450°C for as short as two hours. The TaAlN ternary thin film system was evaluated as a contact material to SiGe to be used at high temperature. The thermal stability study indicates that TaAlN films are stable and conductive after at least 106 hr post-deposition annealing, without showing signs of cracking or delamination. The contact resistance of TaAlN-SiGe contacts remains stable at approximately 10-6 Ω-cm after annealing for 106 hr. Furthermore, experimental data showed a sharp interface between TaAlN and SiGe, indicating no inter-diffusion occurs after post-deposition annealing. The excellent thermal stability, good conductivity and low contact resistance to SiGe makes thin TaAlN films a promising candidate for contact electrodes to high-temperature SiGe based thermoelectric devices.Item Incorporating Novel Functionality on In Vitro Microelectrode Arrays(2018-05) Hammack, Audrey Sue; 0000-0001-5620-1993 (Hammack, AS); Gnade, Bruce E.; Pantano, Paul; Sherry, A. Dean; Zheng, JieThe microelectrode array (MEA) is an inexpensive, high throughput platform for measuring and recording extracellular electrical potentials from a culture of electrogenic tissues. However, this technology is not without drawbacks, which this work seeks to address. On conventional MEAs, stimulation of a culture is achieved via electrical stimulation through the electrodes, which may introduce recording artifacts. Optogenetics is a molecular biology technique that can be used to decouple the recording and stimulation functions of the MEA electrode, but hardware required to utilize optogenetics in combination with an MEA is a barrier that prevents utilization of this technique. One project presented here seeks to integrate an MEA with an array of organic light-emitting diodes (OLEDs) driven by thin film transistors (TFTs), to create a multifunctional MEA with optical stimulating capabilities, in order to streamline the hardware required for an in vitro optogenetics recording experiment. Discreet functional components are demonstrated and a proof of concept integrated substrate is presented. Another project presented in this dissertation seeks to insulate the MEA electrodes with polystyrene. The vast set of organic and inorganic materials used to insulate MEA electrodes present challenges to users who must modify cell culture protocols for cell adhesion to the surface of the MEAs. An MEA that features a patterned film of polystyrene, a material that is far more common to cell culture work, as electrode insulation is presented. Viable cell culture on this MEA and recordings that are comparable to other MEA substrates are demonstrated.Item Nano-biothiol Interactions of Engineered Nanoparticles(December 2021) Zhou, Qinhan; Zheng, Jie; Kesden, Michael; Gnade, Bruce E.; Nielsen, Steven O.; Meloni, Gabriele; D'Arcy, SheenaNanomedicines have been extensively studied in the past decades at the fundamental level because they could potentially make a paradigm shift in human healthcare. Nano-bio interactions play a central role in the precise control of the benefit and hazards of nanomedicines, but current studies mainly focus on how nanoparticles are taken up by cells and interact with different receptors. There is still not enough investigation of how the physiological environment transforms engineered nanoparticles through a variety of biochemical reactions. This dissertation aims to fundamentally understand the nanoparticle-biochemical interactions and the in vivo transport of engineered nanoparticles modulated by these interactions. In Chapter 1 of this dissertation, an overall review is given on the current understanding of nanobio interactions at the molecular and chemical levels, particularly. In Chapter 2, we systematically investigated how the nanoparticle size, the thiols species, and the protein binding affect the interactions between the nanoparticles and thiols at the in vitro level. In Chapter 3, we focused on unraveling the relation between the nanoparticle-biothiol interactions in vitro and the nanoparticle-biothiol interactions in vivo. In Chapter 4, we explored the nanoparticle-biothiol interactions in the diseased mice model and illustrated the application of nanoparticle-biothiol interactions in disease diagnosis. Finally, in Chapter 5, we present the summary and outlook. These new understanding on nano-biochemical interactions at both in vitro and in vivo levels will help further advance physiology at the nanoscale as well as open new pathways to early disease diagnosis and treatment.Item 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 ScienceIn 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.Item Performance and Stability of Solution-Based Cadmium Sulfide Thin Film Transistors: Role of CdS Cluster Size and Film CompositionSalas-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.Item Solid-state Devices for Ionizing Radiation Detection(December 2023) Shamsi, Zeshaan Hussain 1995-; Quevedo-Lopez, Manuel; Rodrigues, Danieli; Gnade, Bruce E.; Young, Chadwin D.; McCall, KyleDetection of ionizing radiation is an increasingly important topic. As technology advances in renewable fission/fusion energy, medical imaging, and the ever-increasing threat to national security from foreign threats, radiation detection must be at the forefront to provide real-time responses to safety concerns. Improvements in materials, synthesis, fabrication, and device engineering with intrinsic benefits are required to outperform current state-of-the-art detection mechanisms. In this regard, solid-state detectors can provide highly efficient detection modes and enable a portable and low-power solution. Examples include efficient detection of ionizing radiation from neutrons, and high energy photons (X-rays) are highly desired as they pose health effects if not considered. Biological interactions with neutrons may cause mutations in DNA due to ionization, while long X-ray exposure can induce burns and cancer at high dosages. This research focuses on the fabrication and scalability of highly efficient microstructured thermal neutron detectors (MSNDs) based on PIN-structured Si wafers and highly sensitive inorganic perovskite X-ray detectors. Presented with novel deposition techniques that include a solvent-free material synthesis and device fabrication process, thin and thick-film inorganic lead- halide perovskite X-ray detectors which exceed performances of the commonly used materials, such as amorphous Selenium and cadmium-zinc-telluride (CZT), are achieved. Lastly, a path to technology integration with commonly used signal processing units is discussed.Item 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.Item 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.Item 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.