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Light is recognized as an accurate and noninvasive tool for stimulating excitable cells. Here, we report on a non-genetic approach based on organic molecular phototransducers that allows wiring- and electrode-free tissue modulation. As a proof of concept, we show photostimulation of an in vitro cardiac microphysiological model mediated by an amphiphilic azobenzene compound that preferentially dwells in the cell membrane. Exploiting this optical based stimulation technology could be a disruptive approach for highly resolved cardiac tissue stimulation. [ABSTRACT FROM AUTHOR]

We propose one-dimensional hierarchical metamaterials (HMMs) that have simultaneously negative mass density and Young's modulus in the sense of effective properties. Frequency-dependent effective properties of the HMMs are evaluated by using a dynamic homogenization theory. By considering three necessary conditions for dynamic homogenizability, we verify that our proposed HMMs can have physically meaningful double negativity, whereas the conventional periodic structures cannot. In addition, HMMs yield the broader ranges of the frequency and the effective properties for double negativity due to the large number of geometrical parameters. By exploring all the possible effective properties of HMMs, we discuss whether we can design metamaterials with the opposite sign of material properties in nature, ultimately aiming at perfect impedance matching. [ABSTRACT FROM AUTHOR]

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter of A exciton deduced for the Ga (5×10[SUP5] dislocation cm[SUP-2] and N (1×10[SUP7] dislocation cm[SUP-2]) faces are 3 and 7 meV, respectively, indicating a lower defect concentration on the former face. The parameters that describe the temperature dependence of the interband transition energies of the A, B, and C excitons as well as the broadening function of the A and B features are evaluated. The results from an analysis of the temperature dependence of the broadening function of excitons A and B indicate that GaN exhibits a very large exciton-phonon coupling. [ABSTRACT FROM AUTHOR]

Presents information on a study that used picosecond ultrasonics techniques to examine the vibrations of several nanostructures composed of laterally patterned gold films on fused quartz substrates. Experimental procedure; Results and discussion on the study.

Molecular beam epitaxy (MBE) was employed to grow nanothick high κ HfO2 films on Si (100) as templates to suppress the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposited (ALD) HfO2 growth. A metal-oxide-semiconductor (MOS) diode with the ALD/MBE bilayer stack of an equivalent oxide thickness (EOT) of ∼1.1 nm has demonstrated markedly low electrical leakage of 8.3×10-3 A/cm2 at Vfb-1 V, a reduction by five order of magnitudes, comparing with those using SiO2 of the same EOT. The attainment of high dielectric constant and very small frequency dispersion in capacitance-voltage (C-V) curves suggests the absence of low κ capacitors in series near the oxide/Si interface. Furthermore, MOS field-effect transistors (MOSFETs) based on the ALD/MBE-HfO2 composites have been fabricated having excellent device performance, with a drain current (ID) of 240 mA/mm and transconductance (Gm) of 120 mS/mm. These are superior to those of the MOSFETs using either ALD (55 mA/mm, 60 mS/mm) or MBE (80 mA/mm, 35 mS/mm) gate dielectric. [ABSTRACT FROM AUTHOR]

The use of microwave plasma for sterilization is relatively new. The advantages of this method are the relatively low temperature, time-savings and its nontoxic nature, in contrast to traditional methods such as heat and gas treatment, and radiation. This study investigated the sterilization effects of microwave-induced argon plasma at atmospheric pressure on materials contaminated with various microorganisms, such as bacteria and fungi. A low-cost and reliable 2.45 GHz, waveguide-based applicator was designed to generate microwave plasma at atmospheric pressure. This system consisted of a 1 kW magnetron power supply, a WR-284 copper waveguide, an applicator including a tuning section, and a nozzle section. Six bacterial and fungal strains were used for the sterilization test. The results showed that regardless of the strain, all the bacteria used in this study were fully sterilized within 20 seconds and all the fungi were sterilized within 1 second. These results show that this sterilization method is easy to use, requires significantly less time than the other traditional methods and established plasma sterilization methods, and it is nontoxic. It can be used in the field of sterilization in medical and dental clinics as well as in laboratory settings. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A recent article [L. Pocivavsek et al., Soft Matter4, 2019 (2008)] by some of us pointed out difficulties in interpreting Wilhelmy plate measurements on elastic Langmuir monolayers that support anisotropic stress. Using a simplified geometry it showed conditions in which the Wilhelmy plate measures significantly different stress from the ambient stress. We correct a serious error in this analysis and strengthen its conclusion, showing that the Wilhelmy stress and the ambient stress can have opposite signs. [ABSTRACT FROM AUTHOR]

Spin-dependent transport is investigated in a Ni/Ge/AlGaAs junction with an electrodeposited Ni contact. Spin-polarized electrons are excited by optical spin orientation and are subsequently used to measure the spin dependent conductance at the Ni/Ge Schottky interface. We demonstrate electron spin transport and electrical extraction from the Ge layer at room temperature. [ABSTRACT FROM AUTHOR]

We have utilized polarized low temperature photoluminescence (PL) to probe the electronic states and structural symmetries of individual CdS nanosheets. High resolution transmission electron microscopy measurements indicate highly crystalline material with different nanosheets exhibiting significant variations of the direction of the c axis, which are consistent with polarization measurements of PL from single CdS nanosheets. The quality of the nanosheets is reflected in measurements of exciton lifetimes of ∼200 ps, a value significantly longer than observed for CdS nanowires whose diameter is the same as the thickness of these nanosheets, but shorter than that observed in bulk crystals. [ABSTRACT FROM AUTHOR]

Atomic-layer-deposited high κ dielectric HfO2 films on air-exposed In0.53Ga0.47As/InP (100), using Hf(NCH3C2H5)4 and H2O as the precursors, were found to have an atomically sharp interface free of arsenic oxides, an important aspect for Fermi level unpinning. A careful and thorough probing, using high-resolution angular-resolved x-ray photoelectron spectroscopy (XPS) with synchrotron radiation, however, observed the existence of Ga2O3, In2O3, and In(OH)3 at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide 7.8 nm thick follows the Fowler–Nordheim tunneling mechanism and shows a low leakage current density of ∼10-8 A/cm2 at VFB+1 V. Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of 2×1012 cm-2 eV-1 was derived. A conduction-band offset of 1.8±0.1 eV and a valence-band offset of 2.9±0.1 eV have been determined using the current transport data and XPS, respectively. [ABSTRACT FROM AUTHOR]

We have utilized spatially resolved low temperature photoluminescence to probe the electronic states and structural symmetries of individual single crystalline CdS nanosheets. Spatially resolved photoluminescence imaging of a single CdS nanosheet reveals a distinctive spectral variation across the nanosheet. We observe A-like exciton states which emit most strongly near the outer edges of the 5 μm wide nanosheet, while B-like exciton states emit most strongly along the center region of the 30 μm long axis of the nanosheet. [ABSTRACT FROM AUTHOR]

Inelastic electron tunneling spectroscopy (IETS) was applied to characterize the microstructure, interface, and trap-related states in silicon metal-oxide-semiconductor devices consisting of high-κ gate dielectrics HfO2, Y2O3, and stacked HfO2/Y2O3 bilayer by molecular beam epitaxy and atomic layer deposition under various heat treatments. Reproducible vibrational modes of monoclinic HfO2 and cubic Y2O3 were identified from IETS spectra, along with phonon modes related to interfacial structures for a given metal-oxide-semiconductor fabrication process. A simple modeling was employed to analyze the trap related features in IETS spectra of stacked HfO2/Y2O3 bilayers, and showed that most traps are located near the HfO2/Y2O3 interface due to dissimilar charge distributions of two ionic oxides of different cation valences, and the presence of interfacial strains of dissimilar structures. [ABSTRACT FROM AUTHOR]

The crystallization of thin silicon films at temperatures between 425 and 600 °C was investigated on glass substrates coated with Al-doped zinc oxide (ZnO:Al). Bare ZnO:Al layers degrade at the crystallization temperatures used. A silicon layer on top, however, efficiently prevents deterioration. The resistivity was even found to drop from 4.3×10-4 Ω cm for the as deposited ZnO:Al to 2.2×10-4 Ω cm in the case of aluminium induced crystallization and to 3.4×10-4 Ω cm for solid phase crystallization. The temperature-stable conductivity of ZnO:Al films coated with Si opens up appealing options for the production of polycrystalline silicon thin-film solar cells with transparent front contacts. [ABSTRACT FROM AUTHOR]

High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN/HfO2/GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8 nm were obtained, in terms of low electrical leakage current density (∼10-6A/cm2 at VFB+1 V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011 cm-2 eV-1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ∼1.8 nm thick, as probed using x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

An interfacial self-cleaning phenomenon was found in the atomic layer deposition of HfO2 on In0.15Ga0.85As/GaAs substrate using Hf(NCH3C2H5)4, i.e., TEMAH, and H2O as the precursors. The native oxides of InGaAs were all satisfactorily removed from the interface through ligand exchange (substitution) reactions with the TEMAH precursor. It relieves the Fermi-level pinning in the HfO2/InGaAs heterostructure, as verified by the clear transition from accumulation to depletion in high-frequency capacitance-voltage relations and inversion in quasistatic measurement. A very low leakage current was also found from the metal-oxide-semiconductor capacitors of Au/Ti/HfO2/InGaAs. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy (MBE) grown high κ dielectrics of Al2O3 and HfO2 are employed as templates to suppress effectively the oxide/Si interfacial layer formation during the subsequent atomic layer deposition (ALD) growth. The absence of the interfacial layer was confirmed using x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Two composite films consisting of ALD Al2O3(1.9 nm)/MBE Al2O3(1.4 nm) and ALD Al2O3(3.0 nm)/MBE HfO2(2.0 nm) showed overall κ values of 9.1 and 11.5, equivalent oxide thicknesses of 1.41 and 1.7 nm, Dit of 2.2×1011 and 2×1011 cm-2 eV-1, and leakage current densities of 2.4×10-2 A/cm2 at Vfb-1 V and 1.1×10-4 A/cm2 at Vfb+1 V, respectively. The attainment of high dielectric constant suggests that there is no low κ capacitor in series near the oxide/Si interface. [ABSTRACT FROM AUTHOR]

Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on TiN porous network templates formed by in situ thermal annealing of Ti in ammonia. The room-temperature decay times obtained from biexponential fits to time-resolved photoluminescence data are longer than ever reported for GaN. The carrier lifetime of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200 µm thick high-quality freestanding GaN. The linewidth of the asymmetric x-ray diffraction (XRD) (10...) peak decreases considerably with the use of TiN layer and with increasing in situ annealing time, indicating the reduction in threading dislocation density. However, no direct correlation is yet found between the decay times and the XRD linewidths, suggesting that point defect and impurity related nonradiative centers are the main parameters affecting the lifetime. [ABSTRACT FROM AUTHOR]

We report measurements of the Schottky barrier heights of Ni/Au contacts on Ga-polarity and N-polarity n-GaN under hydrostatic pressure and applied in-plane uniaxial stress. Under hydrostatic pressure the two different polarities of GaN yield significantly different rates of Schottky barrier height increase with increasing pressure. Uniaxial stress parallel to the surface affects the Schottky barrier height only minimally. The observed changes in barrier height under stress are attributed to a combination of band structure and piezoelectric effects. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]