@article{blumenschein_slomski_paskov_kaess_breckenridge_muth_paskova_2018, title={Thermal conductivity of bulk and thin film beta-Ga2O3 measured by the 3 omega technique}, volume={10533}, ISSN={["1996-756X"]}, DOI={10.1117/12.2288267}, abstractNote={Thermal conductivity of undoped and Sn-doped β-Ga2O3 bulk and single-crystalline thin films have been measured by the 3ω technique. The bulk samples were grown by edge-defined film-field growth (EFG) method, while the thin films were grown on c-plane sapphire by pulsed-laser deposition (PLD). All samples were with (-201) surface orientation. Thermal conductivity of bulk samples was calculated along the in-plane and cross-plane crystallographic directions, yielding a maximum value of ~ 29 W/m-K in the [010] direction at room temperature. A slight thermal conductivity decrease was observed in the Sn-doped bulk samples, which was attributed to enhanced phonon-impurity scattering. The differential 3ω method was used for β-Ga2O3 thin film samples due to the small film thickness. Results show that both undoped and Sndoped films have a much lower thermal conductivity than that of the bulk samples, which is consistent with previous reports in the literature showing a linear relationship between thermal conductivity and film thickness. Similarly to bulk samples, Sn-doped thin films have exhibited a thermal conductivity decrease. However, this decrease was found to be much greater in thin film samples, and increased with Sn doping concentration. A correlation between thermal conductivity and defect/dislocation density was made for the undoped thin films.}, journal={OXIDE-BASED MATERIALS AND DEVICES IX}, author={Blumenschein, N. and Slomski, M. and Paskov, P. P. and Kaess, F. and Breckenridge, M. H. and Muth, J. F. and Paskova, T.}, year={2018} }
 @article{paskov_slomski_leach_muth_paskova_2017, title={Effect of Si doping on the thermal conductivity of bulk GaN at elevated temperatures - theory and experiment}, volume={7}, ISSN={["2158-3226"]}, DOI={10.1063/1.4989626}, abstractNote={The effect of Si doping on the thermal conductivity of bulk GaN was studied both theoretically and experimentally. The thermal conductivity of samples grown by Hydride Phase Vapor Epitaxy (HVPE) with Si concentration ranging from 1.6×1016 to 7×1018 cm-3 was measured at room temperature and above using the 3ω method. The room temperature thermal conductivity was found to decrease with increasing Si concentration. The highest value of 245±5 W/m.K measured for the undoped sample was consistent with the previously reported data for free-standing HVPE grown GaN. In all samples, the thermal conductivity decreased with increasing temperature. In our previous study, we found that the slope of the temperature dependence of the thermal conductivity gradually decreased with increasing Si doping. Additionally, at temperatures above 350 K the thermal conductivity in the highest doped sample (7×1018 cm-3) was higher than that of lower doped samples. In this work, a modified Callaway model adopted for n-type GaN at high temperatures was developed in order to explain such unusual behavior. The experimental data was analyzed with examination of the contributions of all relevant phonon scattering processes. A reasonable match between the measured and theoretically predicted thermal conductivity was obtained. It was found that in n-type GaN with low dislocation densities the phonon-free-electron scattering becomes an important resistive process at higher temperatures. At the highest free electron concentrations, the electronic thermal conductivity was suggested to play a role in addition to the lattice thermal conductivity and compete with the effect of the phonon-point-defect and phonon-free-electron scattering.}, number={9}, journal={AIP ADVANCES}, author={Paskov, P. P. and Slomski, M. and Leach, J. H. and Muth, J. F. and Paskova, T.}, year={2017}, month={Sep} }
 @article{slomski_paskov_leach_muth_paskova_2017, title={Thermal conductivity of bulk GaN grown by HVPE: Effect of Si doping}, volume={254}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.201600713}, abstractNote={The thermal conductivity of bulk GaN grown by Hydride Phase Vapor Epitaxy with intentional Si doping was measured using the 3ω method. The effect of Si concentration ranging from 1.6 × 1016 to 7 × 1018 cm−3 on the thermal conductivity was studied over the temperature range of 295–470 K. The room temperature thermal conductivity was found to decrease with increasing Si doping from 245 to 210 W/m · K. Also, for each Si doped sample the thermal conductivity decreases with increasing temperature. The experimental data were analysed by a modified Callaway model and the contribution of different resistive phonon scattering process was examined. It was found that in n‐type GaN the phonon‐free‐electron scattering became an important resistive process that leads to a reduction of the thermal conductivity at high temperatures. At the highest free electron concentrations, electronic thermal conduction was found to play a role in addition to lattice thermal conduction and compete with the effects of phonon‐free‐electron scattering.}, number={8}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Slomski, Michael and Paskov, Plamen P. and Leach, Jacob H. and Muth, John F. and Paskova, Tania}, year={2017}, month={Aug} }
 @article{wilkins_slomski_paskova_weyher_ivanisevic_2015, title={Modulated optical sensitivity with nanostructured gallium nitride}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4918739}, abstractNote={Surface functionalization via etching of high aspect ratio gallium nitride (GaN) nanostructures provides a way to modulate the optical properties in addition to properties gained from unique topographical formations. In this study, planar layered (heteroepitaxy) and bulk free-standing gallium nitride were modified via a phosphonic acid (1H,1H,2H,2H-perfluorooctanephosphonic acid) assisted phosphoric acid etch in conjunction with an aqueous KOH + K2S2O8 formed gallium nitride nanostructured surface. Despite the high defect concentrations in the thin planar and nanostructured GaN layer, the nanostructured GaN sample produced improved photoluminescence intensities versus the high quality bulk free-standing gallium nitride. Subsequent treatments with additive and additive-free phosphoric etches provided a means of additional optical manipulation in the form of red-shifting the near-band-edge (NBE) emission of the nanostructured GaN sample and increasing the maximum NBE photoluminescence intensity.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Wilkins, S. J. and Slomski, M. J. and Paskova, T. and Weyher, J. L. and Ivanisevic, A.}, year={2015}, month={Apr} }
 @article{ishmael_slomski_luo_white_hunt_mandzy_muth_nesbit_paskova_straka_et al._2014, title={Thermal conductivity and dielectric properties of a TiO2-based electrical insulator for use with high temperature superconductor-based magnets}, volume={27}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/27/9/095018}, abstractNote={Quench protection is a remaining challenge impeding the implementation of high temperature superconductor (HTS)-based magnet applications. This is due primarily to the slow normal zone propagation velocity (NZPV) observed in Bi2Sr2CaCu2OX (Bi2212) and (RE)Ba2Cu3O7 − x (REBCO) systems. Recent computational and experimental findings reveal significant improvements in turn-to-turn NZPV, resulting in a magnet that is more stable and easier to protect through three-dimensional normal zone growth (Phillips M 2009; Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). These improvements are achieved by replacing conventional insulation materials, such as Kapton and mullite braid, with a thin, thermally conducting, electrically-insulating ceramic oxide coating. This paper reports on the temperature-dependent thermal properties, electrical breakdown limits and microstructural characteristics of a titanium oxide (TiO2) insulation and a doped-TiO2-based proprietary insulation (doped-TiO2) shown previously to enhance quench behavior (Ishmael S et al 2013 IEEE Trans. Appl. Supercond. 23 7201311). Breakdown voltages at 77 K ranging from ∼1.5 kV to over 5 kV are reported. At 4.2 K, the TiO2 increases the thermal conductivity of polyimide by about a factor of 10. With the addition of a dopant, thermal conductivity is increased by an additional 13%, and a high temperature heat treatment increases it by nearly an additional 100%. Similar increases are observed at 77 K and room temperature. These results are understood in the context of the various microstructures observed.}, number={9}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Ishmael, S. A. and Slomski, M. and Luo, H. and White, M. and Hunt, A. and Mandzy, N. and Muth, J. F. and Nesbit, R. and Paskova, T. and Straka, W. and et al.}, year={2014}, month={Sep} }