In this letter, we report an in-situ predeposition plasma nitridation process, which is adopted to remove the GaN surface oxygen-related bonds and reduce surface dangling bonds by forming Ga-N bonds prior to the low-pressure chemical vapor deposition (LPCVD)Si ₃ N ₄ deposition. It demonstrates that the Vth hysteresis and current collapse of the device were dramatically improved due to high-quality LPCVD-Si ₃ N ₄ /GaN interface. The MIS-HEMTs using this in-situ pre-deposition plasma nitridation exhibit a very-low Vth hysteresis of 186 mV at VG-sweep = (-30 V, +24 V), a high breakdown voltage of 881 V with the substrate grounded. Meanwhile, the MIS-HEMT dynamic RON is only 18% larger than the static RON after OFF-state VDS stress of 600 V (the OFF to ON switching time interval is set to 200 μs).

Background: Over the last decade safety concerns have arisen about the use of metal-based nanoparticles in the cosmetics field. Metal-based nanoparticles have been linked to both environmental and animal toxicity in a variety of studies. Perhaps the greatest concern involves the large amounts of TiO₂ nanoparticles that are used in commercial sunscreens. As an alternative to using these potentially hazardous metal-based nanoparticles, we have isolated organic nanoparticles from English ivy (Hedera helix). In this study, ivy nanoparticles were evaluated for their potential use in sunscreens based on four criteria: 1) ability to absorb and scatter ultraviolet light, 2) toxicity to mammalian cells, 3) biodegradability, and 4) potential for diffusion through skin. Results: Purified ivy nanoparticles were first tested for their UV protective effects using a standard spectrophotometric assay. Next the cell toxicity of the ivy nanoparticles was compared to TiO₂ nanoparticles using HeLa cells. The biodegradability of these nanoparticles was also determined through several digestion techniques. Finally, a mathematical model was developed to determine the potential for ivy nanoparticles to penetrate through human skin. The results indicated that the ivy nanoparticles were more efficient in blocking UV light, less toxic to mammalian cells, easily biodegradable, and had a limited potential to penetrate through human skin. When compared to TiO₂ nanoparticles, the ivy nanoparticles showed decreased cell toxicity, and were easily degradable, indicating that they provided a safer alternative to these nanoparticles. Conclusions: With the data collected from this study, we have demonstrated the great potential of ivy nanoparticles as a sunscreen protective agent, and their increased safety over commonly used metal oxide nanoparticles.

Bonding and anti-bonding modes of plasmon coupling effects are numerically investigated in TiO₂-Ag core-shell nano dimers. First, splitting phenomena of the coupled anti-bonding modes are observed under the longitudinal polarization when the distance between the monomers decreases to a certain level. Second, one of the split resonance modes is identified to be formed by the dipole anti-bonding mode of the monomers from charge density distribution patterns. Those split modes have similar redshift behaviors as the coupled dipole bonding modes in the same situations. Furthermore, the intensities of those anti-bonding modes weaken with decreasing distance between the monomers, because of the interaction of the induced dipole moment in the monomers and the charge distribution variation on the facing surfaces of the gap by the coulomb attraction. Other split bands are the higher-order mode (octupole-like or triakontadipole-like), which do not have obvious peak-shift behavior and the intensities have very little attenuation with decreasing distance. Finally, the coupling of the bonding and anti-bonding modes under the longitudinal polarization is symmetric (bonding).

We report the direct measurements of methyl radicals (CH₃) in methane/air flames at atmospheric pressure by using coherent microwave Rayleigh scattering (Radar) from Resonance Enhanced Multi-Photon Ionization (REMPI), also known as the Radar REMPI technique. A tunable dye laser was used to selectively induce the (2 + 1) REMPI ionization of methyl radicals (CH₃, $3p^2{A}_2^{\text{'}\text{'}}{0}_0^0$ band) in a near adiabatic and premixed laminar methane/air flame, generated by a Hencken burner. In situ measurements of the REMPI electrons were made by non-intrusively using a microwave homodyne transceiver detection system. The REMPI spectrum of the CH₃ radical was obtained and a spatial distribution of the radicals limited by focused laser beam geometry, approximately 20 µm normal to the flame front and 2.4 mm parallel to the flame, was determined. The measured CH₃ was in good agreement with numerical simulations performed using the detailed kinetic mechanism of GRI-3.0. To the authors’ knowledge, these experiments represent the first directly-measured spatially-resolved CH₃ in a flame at atmospheric pressure.

Here we report nonintrusive local rotational temperature measurements of molecular oxygen, based on coherent microwave scattering (radar) from resonance-enhanced multiphoton ionization (REMPI) in room air and hydrogen/air flames. Analyses of the rotational line strengths of the two-photon molecular oxygen $C^3\mathrm{\Pi }(v=2)\leftarrow X^3\mathrm{\Sigma }(v^{\prime }=0)$ transition have been used to determine the hyperfine rotational state distribution of the ground $X^3\mathrm{\Sigma }(v^{\prime }=0)$ state. Rotationally resolved $2+1$ REMPI spectra of the molecular oxygen $C^3\mathrm{\Pi }(v=2)\leftarrow X^3\mathrm{\Sigma }(v^{\prime }=0)$ transition at different temperatures were obtained experimentally by radar REMPI. Rotational temperatures have been determined from the resulting Boltzmann plots. The measurements in general had an accuracy of $\sim \pm 60\mathrm{K}$ in the hydrogen/air flames at various equivalence ratios. Discussions about the decreased accuracy for the temperature measurement at elevated temperatures have been presented.