Determination of the influence of SnO2 nanowires on resistive-type gas sensors

This project involved the study of metal-oxide nanowires as resistive-type gas sensors and how the fabrication method impacted the sensor’s performance. The goals were to develop a method of growing ZnO nanowires and determine the optimal number of nanowires for a sensor. The growth of ZnO nanowires involved a vapor-liquid-solid technique where source material was placed in the center of a tube furnace with a gold-coated Si growth substrate downstream. ZnO nanowire growth was observed using a graphite and ZnO source powder, a temperature gradient of 750oC, an upright growth substrate, Ar gas flow and a pressure of 50 torr. Further research into the parameters for longer and more numerous NW growth is needed. Ethanol, Methanol, DI water, and Dimethylformamide (DMF) were tested as solutions for transferring the nanowires to a substrate with electrodes, with the conclusion that DMF was the most adequate solution for testing. Solution with suspended SnO2 nanowires were dropped onto the sensor substrate, which consisted of Pt electrodes on an alumina substrate. Sensors were tested in a sealed probe station with Au probes to measure resistance. At a temperature of 350oC, a series of gases were introduced to the electrode. N2 flowed for one hour, then 21% O2 for another hour, then back to N2. The change in resistance with atmosphere determined the sensors response value. Determination of optimum number of nanowires for a sensor involved testing the sensor after every 5 drops of solution. This method for testing amounts showed that adding successive drops did not guarantee more material on the sensor, meaning the amount of material was random after the drops. The problem was approached again, testing a sensor with high material coverage versus one with lower coverage. No trend of NW amount on gas sensing properties was determined, but the data suggested that more material on the sensor meant lower resistance and larger response values. More data would determine if there is indeed a trend.The College of EngineeringNational Science Foundation grant 1609142Academic Major: Materials Science and Engineerin

Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared

Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in visible and near infrared (NIR), associated with two different intrinsic defects. As these defects can potentially be generated at a low or even single defect level, our approach can be used to realize electrically driven single photon source for quantum telecommunication and information processing

Trend tests for the evaluation of exposure-response relationships in epidemiological exposure studies

One possibility for the statistical evaluation of trends in epidemiological exposure studies is the use of a trend test for data organized in a 2 × k contingency table. Commonly, the exposure data are naturally grouped or continuous exposure data are appropriately categorized. The trend test should be sensitive to any shape of the exposure-response relationship. Commonly, a global trend test only determines whether there is a trend or not. Once a trend is seen it is important to identify the likely shape of the exposure-response relationship. This paper introduces a best contrast approach and an alternative approach based on order-restricted information criteria for the model selection of a particular exposure-response relationship. For the simple change point alternative H1 : 1 =.= q <q+1 =. = k an appropriate approach for the identification of a global trend as well as for the most likely shape of that exposure-response relationship is characterized by simulation and demonstrated for real data examples. Power and simultaneous confidence intervals can be estimated as well. If the conditions are fulfilled to transform the exposure-response data into a 2 × k table, a simple approach for identification of a global trend and its elementary shape is available for epidemiologists

Mortality in infants of obese mothers: is risk modified by mode of delivery?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90196/1/j.1600-0412.2011.01331.x.pd

Nanotransfer Printing of Organic and Carbon Nanotube Thin-Film Transistors on Plastic Substrates

A printing process for high-resolution transfer of all components for organic electronic devices on plastic substrates has been developed and demonstrated for pentacene (Pn), poly (3-hexylthiophene) and carbon nanotube (CNT) thin-film transistors (TFTs). The nanotransfer printing process allows fabrication of an entire device without exposing any component to incompatible processes and with reduced need for special chemical preparation of transfer or device substrates. Devices on plastic substrates include a Pn TFT with a saturation, field-effect mobility of 0.09 cm^2 (Vs)^-1 and on/off ratio approximately 10^4 and a CNT TFT which exhibits ambipolar behavior and no hysteresis.Comment: to appear in Applied Physics Letter

Broad-band properties of the hard X-ray cataclysmic variables IGR J00234+6141 and 1RXS J213344.1+510725

A significant number of cataclysmic variables were detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type. We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class. Timing and spectral analysis of IGR J00234+6141 are based on a XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725 we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data. We determine a spin period of 561.64 +/- 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to about 2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 +/- 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of about 50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of about 100 eV. This latter adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars. (abridged)Comment: 12 pages, 8 figures, 5 tables. Accepted for publication in A&