arXiv subjects

Paul R. Ohodnicki

Publications and source records attributed to Paul R. Ohodnicki.

5 recordsLinked to original sources

arXiv2020

In Situ characterization of the proton enhanced conductivity of 20nm TiO2 thin-films obtained on the surface of optical fiber

We report in situ characterized TiO2 thin-films deposited on optical fiber, having thicknesses in the 20-100nm range, and having enhanced conductivity values of 700S/cm upon interacting with hydrogen. This conductivity was achieved in pure hydrogen at 800-900C, having a measured activation energy of 0.26eV of the hopping type. Given the variability in the observed results, it is postulated that the highest conductivity achievable may be much greater than what is currently demonstrated. The conductivity is retained after cooling to ambient temperatures as confirmed by Hall measurements, and subsequent grazing-incidence x-ray diffraction and TEM measurements show the films to be in the rutile phase. The exceptional conductivity in these films is hypothesized to result from direct proton incorporation into the lattice populating the conduction band with excess electrons, or from altering the Titania lattice to form conductive Magneli phases. The films did not display any evidence of transformations, however formation of Magneli phases was confirmed for powders. These interesting results, observed by examining 20nm films on the surface of optical fiber in combination with the first impedance spectroscopy performed on films on optical fiber in high temperature Fuel Cell type environments, confirm hypotheses arrived at in prior publications where thin-films of Titania had optical properties which could only be explained by the current claim. Titania thin-films on optical-fiber are being explored for high temperature hydrogen derived energy generation, thermo-photonic energy conversion, and associated sensors due to their unique interactions with hydrogen.

cond-mat.mtrl-sci↗

arXiv2020

An 860 MHz Wireless Surface Acoustic Wave Sensor with a Metal-Organic Framework Sensing Layer for CO2 and CH4

Wireless and passive surface acoustic wave (SAW) devices with nanoporous metal-organic framework (MOF) sensing layers are attractive gas sensors for applications in many fields such as energy industries and air pollution control. Here, we report on enhancing the sensitivity and detection limit of zeolitic imidazolate framework-8 (ZIF-8) MOF-coated SAW reflective delay line mass sensors by increasing the operating frequency for sensitive detection of carbon dioxide (CO2) and methane (CH4) at ambient conditions. In particular, we show at least four times higher sensitivity of an 860 MHz (4-μm periodicity) SAW reflective delay line coated with a 240 nm thick ZIF-8 compared to the sensitivity of a 430 MHz (8-μm periodicity) otherwise identical sensor device to the targeted gases. The detection limits of the higher frequency wireless devices for CO2 and CH4 were estimated to be 0.91 vol-% and 7.01 vol-%, respectively. The enhanced sensitivity for higher frequency devices is explained in terms of the frequency dependent acoustic wave energy confinement.

physics.app-ph↗

arXiv2018

Near-Field Thermal Energy Conversion by Tunneling to a Waveguide

Energy is a vital resource and hence there is a continuous strive to improve upon existing technologies and to find new ones that address that basic need. The conversion of thermal energy is the primary method of generating electrical energy from a broad range of sources, for example fossil fuels, solar thermal, geothermal, and nuclear energy. A common need in all cases is the ability to efficiently extract the generated electromagnetic and thermal energy and to convert it to electricity. The current methods of thermal energy extraction are based on heat engines, thermoelectric and thermophotovoltaic conversion systems. In this report a method based on the direct extraction of Electromagnetic energy from the thermal near-field through tunneling and subsequent waveguiding, is presented.

cond-mat.mes-hall↗

arXiv2018

Zeolitic imidazolate framework-coated acoustic sensors for room temperature detection of carbon dioxide and methane

Integration of nanoporous materials such as metal organic frameworks (MOFs) with sensitive transducers can result robust sensing platforms for monitoring gases and chemical vapors for a range of applications. Here, we report on an integration of the zeolitic imidazolate framework-8 (ZIF-8) MOF with surface acoustic wave (SAW) and thickness shear mode quartz crystal microbalance (QCM) devices to monitor carbon dioxide(CO2)and methane (CH4) at ambient conditions. The MOF was directly coated on the custom fabricated Y-Z LiNbO3 SAW delay lines (operating frequency,f0 = 436 MHz)and AT-cut Quartz TSM resonators (resonant frequency, f0 = 9 MHz) and the devices were tested for various gases in N2 at ambient condition. The devices were able to detect the changes in CO2 or CH4 concentrations with relatively higher sensitivity to CO2, which was due to its higher adsorption potential and heavier molecular weight. The sensors showed full reversibility and repeatability which were attributed to the physisorption of the gases into the MOF and high stability of the devices. Both types of the sensors showed linear responses relative to changes in the binary gas compositions thereby allowing to construct calibration curves which correlated well with the expected mass changes in the sorbent layer based on mixed-gas gravimetric adsorption isotherms measured on bulk samples.For 200 nm thick films, the SAW sensitivity to CO2 and CH4 were 1.44x10^-6/vol-%, respectivel yagainst the QCM sensitivities 0.24x10^-6/vol-% and 1x10^-8/vol-%,respectively which were evaluated as the fractional change in the signal. The SAW sensors were also evaluated for 100 nm - 300 nm thick films, the sensitivities of which were found to increase with the thickness due to the increased number of pores for adsorption of larger amount of gases. Also, the SAW devices had a good wireless response for detecting gases remotely.

physics.app-ph↗

arXiv2017

Probing the Hydrogen Enhanced Near-Field Emission of ITO without a Vacuum-Gap

Thermal fluctuations of charged particles, fluctuations akin to Brownian motion, can excite optical surface-states leading to the concept of the thermal near-field, which is a highly localized, and, therefore, evanescent optical density of states that exist at distances much less than the thermal emission wavelength. By tunneling the surface charge emitted photons into nearby waveguides, the thermally excitable near-field optical density of states can be enhanced, engineered, and efficiently extracted to the far-field for observation. With this technique, the plasmonic thermal near-field of a 10nm thick ITO film, known to have plasmonic activity in the 1500nm wavelength region, was probed under external illumination and by thermal excitation at 873K. The results confirm that waveguides provide a large density of optical channels with spatial overlap and k-vector matching to facilitate plasmon de-excitation in the near-field through photon tunneling for extraction into the far-field. Furthermore, it is shown that the thermal near-field can be observed without the introduction of a vacuum-gap, a feature unique to this particular method.

cond-mat.mes-hall↗