Dan, Yaping
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Publication Chemical gas sensors based on nanowires(2008-01-01) Dan, YapingPublication Effect of Thermal Treatments on the Transduction Behaviors of Conductometric Hydrogen Gas Sensors Integrated with HCl-Doped Polyaniline Nanofibers(2008-01-01) Dan, Yaping; Somers, Luke A; Wang, Pen-Cheng; Johnson, A.T. Charlie; MacDiarmid, Alan GWe present the effect of thermal treatments on the transduction behaviors of HCl-doped polyaniline (PANI) nanofibers integrated in conductometric devices upon exposure to 1% H2 (carried by N2). After drying in N2 at 25ºC for 12 hours, devices showed a ~10% decrease in electrical resistance upon exposure to 1% H2. However, devices subject to 12-hour drying in N2 at 25ºC followed by further thermal treatments in N2 at 100ºC, 164ºC or 200ºC for 30 minutes showed different transduction behaviors. Specifically, devices subject to thermal treatments at 100ºC and 164ºC showed a decrease in electrical resistance by ~7% and <0.5%, respectively. More interestingly, the device subject to thermal treatment at 200ºC showed a transduction behavior with opposite polarity, i.e. a ~5% increase in electrical resistance upon exposure to 1% H2. SEM, FTIR and TGA were employed to investigate the effect of thermal treatments on the morphology and chemical characteristics of HCl-doped polyaniline nanofibers. The results indicated that the change in the devices? interesting transduction behaviors might be related to the thermal treatment effects on the HCl-doped PANI nanofibers in (i) removal of adsorbed water, and (ii) crosslinking and/or degradation of polymer backbones.Publication Dielectrophoretically assembled polymer nanowires for gas sensing(2007-07-16) Dan, Yaping; Cao, Yanyan; Mallouk, Tom E; Johnson, A. T. Charlie; Evoy, StephaneWe measured the electronic properties and gas sensing response of nanowires containing segments of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) that were synthesized using anodic aluminum oxide (AAO) membranes. The nanowires have a “striped” structure of gold-PEDOT/PSS-gold and are typically 8 μm long (1 μm-6 μm-1 μm for each section, respectively) and 220 nm in diameter. Dielectrophoretic assembly was used to position single nanowires on pre-fabricated gold electrodes. A polymer conductivity of 11.5 ± 0.7 S/cm and a contact resistance of 27.6 ± 4 kΩ were inferred from resistance measurements of nanowires of varying length and diameter. When used as gas sensors, the wires showed a resistance change of 10.5%, 9%, and 4% at the saturation vapor pressure of acetone, methanol and ethanol, respectively. Sensor response and recovery were rapid (seconds) with excellent reproducibility in time and across devices. “Striped” template-grown nanowires are thus intriguing candidates for use in electronic nose vapor sensing systems.Publication Gas sensing properties of single conducting polymer nanowires and the effect of temperature(2009-10-02) Dan, Yaping; Cao, Yanyan; Mallouk, Tom E; Johnson, A.T. Charlie; Evoy, StephaneWe measured the electronic properties and gas sensing responses of template-grown poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based nanowires. The nanowires had a 'striped' structure (gold–PEDOT/PSS–gold), and were typically 8 µm long (1 µm–6 µm–1 µm for the sections, respectively) and 220 nm in diameter. Single-nanowire devices were contacted with pre-fabricated gold electrodes using dielectrophoretic assembly. A polymer conductivity of 11.5 ± 0.7 S cm−1 and a contact resistance of 27.6 ± 4 kΩ were inferred from measurements on nanowires of varying length and diameter. The nanowire sensors detected a variety of odors, with rapid response and recovery (seconds). The response (ΔR/R) varied as a power law with analyte concentration. The power law exponent was found to increase with the molecular weight of the analyte and as a function of temperature. The detection limits are set by noise intrinsic to the device and are at the ppm level even for very volatile analytes.Publication Intrinsic Response of Graphene Vapor Sensors(2009-03-06) Dan, Yaping; Lu, Ye; Luo, Zhengtang; Johnson, A.T. Charlie; Kybert, Nicholas JGraphene is a two-dimensional material with extremely favorable chemical sensor properties. Conventional nanolithography typically leaves a resist residue on the graphene surface, whose impact on the sensor characteristics has not yet been determined. Here we show that the contamination layer chemically dopes the graphene, enhances carrier scattering, and acts as an absorbent layer that concentrates analyte molecules at the graphene surface, thereby enhancing the sensor response. We demonstrate a cleaning process that verifiably removes the contamination on the device structure and allows the intrinsic chemical responses of the graphene monolayer to be measured. These intrinsic responses are surprisingly small, even upon exposure to strong analytes such as ammonia vapor.