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Environmental contaminants have become a major concern for human beings due to their adverse effects on drinking water quality. Heterogeneous photocatalysis has been extensively investigated as a potential strategy to minimize the consequences of as-related processes. Using a room-temperature ionic liquid-mediated co-precipitation method, Ag@AgCl nanoparticles were loaded onto tantalum pentoxide to make a plasmonic photocatalyst to remove Congo Red dye. The physicochemical properties of the photocatalysts were characterized by X-ray diffraction powder (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Diffuse Reflectance Spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM), photoluminescence (PL), and nitrogen adsorption–desorption isotherms. The results indicate that 96% of the dye was degraded within 20 min with a rate constant of 0.14 min−1. The key radicals involved in the photocatalysis, recognized as O2·– species, were identified by electron spin resonance (ESR) in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), as the spin trapping agent. Our findings and quenching experiments elucidates the mechanism of the charge carrier migration. The cytotoxicity activity of the nanostructures was also examined against human brain glioblastoma tumor cells for the first time. A precise analysis of the cell death pathway was conducted using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and caspase activity assays in combination with fluorescence microscopy images. The prepared nanomaterials were found to be promising candidates for treating the organic pollutants and biomedical waste effluents from academic and industrial activities. [ABSTRACT FROM AUTHOR]

The effect of different concentrations of urea on the morphology of iron oxide (Fe3O4) magnetic nanoparticles was studied. Fe3O4 magnetic nanoparticles were fabricated by the coprecipitation method. The morphology, crystallinity, compositional purity, and emission characteristics were tested by the techniques of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Raman characterization. The drop-casting technique was successfully used to fabricate a potentiometric urea biosensor producing initially isopropanol and chitosan solution, consisting of Fe3O4 nanoparticles, on a glass fiber filter. To measure the developed biosensor's voltage signal from the functionalized nanoparticles, a copper wire was utilized. The Fe3O4 nanoparticle surface functionalization was performed through the electrostatic immobilization of urease with the Fe3O4-chitosan (CH) nanobiocomposite. The presented urea biosensor measured a wide logarithmic range of urea concentration of 0.1–80 mM with a sensitivity of 42 mV/decade, and indicated a fast response time of approximately 12 s. The developed urea biosensor showed enhanced sensitivity, stability, reusability, and specificity. All experimental results demonstrate the application potential of the developed urea sensor for the monitoring of urea concentrations in human serum, drugs, and food industry-related samples. [ABSTRACT FROM AUTHOR]

This document is a retraction note from the journal Scientific Reports. The article titled "Empirical Modeling of Physiochemical Immune Response of Multilayer Zinc Oxide Nanomaterials under UV Exposure to Melanoma and Foreskin Fibroblasts" has been retracted by the editors due to concerns about the validity of the data and conclusions. The retraction is based on the discovery that several figures in the article appear to be identical to figures from other published articles. Some of the authors agree with the retraction, while others did not respond to the correspondence. The editors were unable to establish contact with one of the authors. [Extracted from the article]

Carcinogenesis is a complex molecular process starting with genetic and epigenetic alterations, mutation stimulation, and DNA modification, which leads to proteomic adaptation ending with an uncontrolled proliferation mechanism. The current research focused on the empirical modelling of the physiological response of human melanoma cells (FM55P) and human foreskin fibroblasts cells (AG01518) to the multilayer zinc oxide (ZnO) nanomaterials under UV-A exposure. To validate this experimental scheme, multilayer ZnO nanomaterials were grown on a femtotip silver capillary and conjugated with protoporphyrin IX (PpIX). Furthermore, PpIX-conjugated ZnO nanomaterials grown on the probe were inserted into human melanoma (FM55P) and foreskin fibroblasts cells (AG01518) under UV-A light exposure. Interestingly, significant cell necrosis was observed because of a loss in mitochondrial membrane potential just after insertion of the femtotip tool. Intense reactive oxygen species (ROS) fluorescence was observed after exposure to the ZnO NWs conjugated with PpIX femtotip model under UV exposure. Results were verified by applying several experimental techniques, e.g., ROS detection, MTT assay, and fluorescence spectroscopy. The present work reports experimental modelling of cell necrosis in normal human skin as well as a cancerous tissue. These obtained results pave the way for a more rational strategy for biomedical and clinical applications. [ABSTRACT FROM AUTHOR]

In this work, we design and fabricate a wireless system with the main operating device based on zinc oxide (ZnO) nanowires. The main operating device is based on piezoelectric nanogenerator (NG) achieved using ZnO nanowires grown hydrothermally on paper substrate. The fabricated NG is capable of harvesting ambient mechanical energy from various kinds of human motion, e.g., footsteps. The harvested electric output has been used to serve as a self-powered pressure sensor. Without any storage device, the signal from a single footstep has successfully triggered a wireless sensor node circuit. This study demonstrates the feasibility of using ZnO nanowire piezoelectric NG as a low-frequency self-powered sensor, with potential applications in wireless sensor networks. [ABSTRACT FROM AUTHOR]

In this study, a potentiometric urea biosensor has been fabricated on glass filter paper through the immobilization of urease enzyme onto chitosan/cobalt oxide (CS/CoO) nanocomposite. A copper wire with diameter of 500 µm is attached with nanoparticles to extract the voltage output signal. The shape and dimensions of CoO magnetic nanoparticles are investigated by scanning electron microscopy and the average diameter is approximately 80-100 nm. Structural quality of CoO nanoparticles is confirmed from X-ray powder diffraction measurements, while the Raman spectroscopy has been used to understand the chemical bonding between different atoms. The magnetic measurement has confirmed that CoO nanoparticles show ferromagnetic behavior, which could be attributed to the uncompensated surface spins and/or finite size effects. The ferromagnetic order of CoO nanoparticles is raised with increasing the decomposition temperature. A physical adsorption method is adopted to immobilize the surface of CS/CoO nanocomposite. Potentiometric sensitivity curve has been measured over the concentration range between 1 × 10 and 8 × 10 M of urea electrolyte solution revealing that the fabricated biosensor holds good sensing ability with a linear slope curve of ~45 mV/decade. In addition, the presented biosensor shows good reusability, selectivity, reproducibility and resistance against interferers along with the stable output response of ~12 s. [ABSTRACT FROM AUTHOR]

Cytotoxic effects of zinc oxide (ZnO) nanomaterials, individual and conjugated with a photosensitizer (protoporphyrin IX), were studied in the presence and absence of ultraviolet light exposure (240 nm of light wavelength for a very short time exposure) in cell cultures of human normal and cancerous skin models. Zinc Oxide nanowires (ZnO NWs) were grown on the capillary tip and conjugated with protoporphyrin IX (PpIX). This coated tip was used as tool/pointer for intracellular drug delivery protocol in suggested normal as well as carcinogenic cellular models. After true delivery of optimal drug, the labelled biological model was irradiated with UV-A, which led to a loss of mitochondrial membrane potential, as tested by neutral red assay (NRA). [ABSTRACT FROM AUTHOR]

We demonstrate the synthesis and investigate the electrical and optical characteristics of 'nanocorals' (NCs) composed of CuO/ZnO grown at low temperature through the hydrothermal approach. High-density CuO nanostructures (NSs) were selectively grown on ZnO nanorods (NRs). The synthesized NCs were used to fabricate p-n heterojunctions that were investigated by the current density-voltage ( J- V) and the capacitance-voltage ( C- V) techniques. It was found that the NC heterojunctions exhibit a well-defined diode behavior with a threshold voltage of about 1.52 V and relatively high rectification factor of ∼760. The detailed forward J- V characteristics revealed that the current transport is controlled by an ohmic behavior for V≤0.15 V, whereas at moderate voltages 1.46≤ V<1.5 the current follows a J α exp( βV) relationship. At higher voltages (≥1.5 V) the current follows the relation J α V, indicating that the space-charge-limited current mechanism is the dominant current transport. The C- V measurement indicated that the NC diode has an abrupt junction. The grown CuO/ZnO NCs exhibited a broad light absorption range that is covering the UV and the entire visible parts of the spectrum. [ABSTRACT FROM AUTHOR]

In this study, possibilities of scaling up the synthesis of zinc oxide (ZnO) nanorods (NRs) by the hydrothermal method have been explored. It was found that batches yielding several grams can easily be made using common and easily available materials. Further, a printable composition was fabricated by mixing the obtained ZnO NRs into a common solvent-based screen printable varnish. Scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, UV-vis spectroscopy analysis of the scaled up batch indicated that the ZnO nanostructures were of NRs shape, well crystalline and having less defects. Using the ZnO NRs-based printable composition a device fabrication on a flexible substrate was demonstrated, producing a flexible light-emitting device being highly tolerant to bending. [ABSTRACT FROM AUTHOR]

In this study, high density well aligned ZnO nanotubes were grown on glass via a two-step growth-then-etching by simple and template-free hydrothermal method. We used etching procedure to introduce additional zinc interstitial defects in the ZnO nanotubes. The optical properties of the ZnO nanotubes have been investigated by depth-resolved cathodluminescence spectroscopy (DRCLS) which provides information about the physical origin and growth dependence of optically active defects together with their spatial distribution. The DRCLS study gives clear evidence about the enhancement of zinc interstitial defects which are responsible for the violet and decrease of the DL emission in ZnO nanotubes when compared to the as grown ZnO nanorods. We observed a variation in the zinc interstitials along the nanotube depth. [ABSTRACT FROM AUTHOR]

We report white-light luminescence from ZnOorganic hybrid light emitting diodes grown on glass substrate by low temperature aqueous chemical growth. The configuration used for the hybrid white light emitting diodes (HWLEDs) consists of two-layers of polymers (PEDOT:PSS/PFO) on glass with top ZnO nanorods. Electroluminescence spectra of the HWLEDs demonstrate the combination of emission bands arising from the radiative recombination in polymer and ZnO nanorods. In order to distinguish emission bands we used a Gaussian function to simulate the experimental data. The emitted white light was found to be the superposition of a blue line at 454 nm, a green emission at 540 nm, orange line at 617 nm, and finally a red emission at 680 nm. The transitions causing these emissions are identified and discussed in terms of the energy band diagram of the hybrid junction. Color coordinates measurement of the WLED reveals that the emitted light has a white impression with 70 color rendering index and correlated color temperature 5500 K. Comparison between ITO and aluminum top contacts and its influence on the emitted intensity is also discussed. [ABSTRACT FROM AUTHOR]

Hybrid light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods and polymers (single and blended) were fabricated and characterized. The ZnO nanorods were grown by the chemical bath deposition method at 50°C. Three different LEDs, with blue emitting, orange-red emitting or their blended polymer together with ZnO nanorods, were fabricated and studied. The current-voltage characteristics show good diode behavior with an ideality factor in the range of 2.1 to 2.27 for all three devices. The electroluminescence spectrum (EL) of the blended device has an emission range from 450 nm to 750 nm, due to the intermixing of the blue emission generated by poly(9,9-dioctylfluorene) denoted as PFO with orange-red emission produced by poly(2-methoxy-5(20-ethyl-hexyloxy)-1,4-phenylenevinylene) 1,4-phenylenevinylene) symbolized as MEH PPV combined with the deep-band emission (DBE) of the ZnO nanorods, i.e. it covers the whole visible region and is manifested as white light. The CIE color coordinates showed bluish, orange-red and white emission from the PFO, MEH PPV and blended LEDs with ZnO nanorods, respectively. These results indicate that the choice of the polymer with proper concentration is critical to the emitted color in ZnO nanorods/p-organic polymer LEDs and careful design should be considered to obtain intrinsic white light sources. [ABSTRACT FROM AUTHOR]

ZnO nanorods (NRs) with high surface area to volume ratio and biocompatibility is used as an efficient photosensitizer carrier system and at the same time providing intrinsic white light needed to achieve cancer cell necrosis. In this letter, ZnO nanorods used for the treatment of breast cancer cell (T47D) are presented. To adjust the sample for intracellular experiments, we have grown the ZnO nanorods on the tip of borosilicate glass capillaries (0.5 μm diameter) by aqueous chemical growth technique. The grown ZnO nanorods were conjugated using protoporphyrin dimethyl ester (PPDME), which absorbs the light emitted by the ZnO nanorods. Mechanism of cytotoxicity appears to involve the generation of singlet oxygen inside the cell. The novel findings of cell-localized toxicity indicate a potential application of PPDME-conjugated ZnO NRs in the necrosis of breast cancer cell within few minutes. [ABSTRACT FROM AUTHOR]

Stable intrinsic white light–emitting diodes were fabricated from c-axially oriented ZnO nanorods (NRs) grown at 50°C via the chemical bath deposition on top of a multi-layered poly(9,9-dioctylfluorene-co– N-(4-butylpheneylamine)diphenylamine)/poly(9,9dioctyl-fluorene) deposited on PEDOT:PSS on highly flexible plastic substrate. The low growth temperature enables the use of a variety of flexible plastic substrates. The fabricated flexible white light–emitting diode (FWLED) demonstrated good electrical properties and a single broad white emission peak extending from 420 nm and up to 800 nm combining the blue light emission of the polyflourene (PFO) polymer layer with the deep level emission (DLEs) of ZnO NRs. The influence of the temperature variations on the FWLED white emissions characteristics was studied and the devices exhibited high operation stability. Our results are promising for the development of white lighting sources using existing lighting glass bulbs, tubes, and armature technologies. [ABSTRACT FROM AUTHOR]

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission. [ABSTRACT FROM AUTHOR]

We report the fabrication of heterostructure white light–emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet–blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour. [ABSTRACT FROM AUTHOR]

We report a demonstration of heterojunction light emitting diode (LED) based on a hybrid n-ZnO-nanorod/p-polymer layered structure. The ZnO was grown using the aqueous chemical growth (ACG) on top of the polymer(s) which were deposited on glass. The current–voltage (I–V) behavior of the heterojunctions showed good rectifying diode characteristics. Room-temperature electroluminescence (EL) spectra of the LEDs provided a broad emission band over a wide LED color range (430–650 nm), in which both zinc and oxygen vacancy peaks are clearly detected. We present here luminescent devices based on the use of ZnO-nanorods in combination with two different blended and multi-layered p-type polymers. Electroluminescence of the first batch of devices showed that white bluish strong emission for the presently used polymers is clearly observed. We obtained a turn-on voltage of 3 V and break-down voltage equal to −6 V for PVK-TFB blended device. The corresponding values for the NPD-PFO multilayer device were 4 V and −14 V, respectively. The rectification factors were equal to 3 and 10 for the two devices, respectively. The films and devices processed were characterized by scanning electron microscopy (SEM), DEKTAK 3ST Surface Profile, Semiconductor Parameter Analyzer, photoluminescence (PL), and electroluminescence (EL). [ABSTRACT FROM AUTHOR]

The Bose condensation of two-dimensional dipolar excitons in quantum wells is numerically studied by the diffusion Monte Carlo simulation method. The correlation, microscopic, thermodynamic, and spectral characteristics are calculated. It is shown that, in structures of coupled quantum wells, in which low-temperature features of exciton luminescence have presently been observed, dipolar excitons form a strongly correlated system. [ABSTRACT FROM AUTHOR]

Zinc oxide nanorods have been grown by vapor–liquid–solid (VLS) catalytic growth. The optical properties and structures properties of the grown ZnO nanostructures have been studied by photoluminescence, high resolution X-ray diffraction and scanning electron microscopy. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions and used substrates. It was found that oriented ZnO nanorods are grown more easily on a substrate with a similar crystalline structure as ZnO. By optimizing growth conditions, oriented-ZnO nanorods grown on Si(001) substrate with a diameter of around 300 nm and lengths of 20 to 35 μm have been achieved, and they show excellent optical properties. Laser action has been observed at room temperature by using optical pumping. [ABSTRACT FROM AUTHOR]

The Kosterlitz-Thouless phase transition in a system of exciton-polaritons in a microcavity is studied. The transition temperature to superfluid state was found as a function of exciton-photon detuning. A nonquadratic dispersion law was taken into account in the framework of the self-consistent harmonic approximation (SCHA). [ABSTRACT FROM AUTHOR]

In this paper, we will present our recent research on the growth and characterization of some Si-based heterostructures for optical and photonic devices. The heterostructures to be discussed are ZnO nanorods on Si, SiO2, and other substrates such as SiN and sapphire. We will also consider strained Si1-xGex/Si heterostructures for Si optoelectronics. The performance and functionality extension of Si technology for photonic applications due to the development of such heterostructures will be presented. We will focus on the results of structural and optical characterization in relation to device properties. The structural characterization includes x-ray diffraction for assessment of the crystallinity and stress in the films and secondary ion mass spectrometry for chemical analysis. The optical properties and electronic structure were investigated by using photoluminescence. The device application of these thin film structures includes detectors, lasers, and light emitting devices. Some of the Si-based heterostructures to be presented include devices emitting and detecting up to the blue-green and violet wave lengths. [ABSTRACT FROM AUTHOR]

p- and n-type InxGa1-xAs-InP quantum wells are suitable for multi-color infrared photodetector applications in atmospheric windows due to improved barrier quality and carrier-transport properties. We apply thek·pmethod to study the energy band structures and optical transition properties, which show that the peak response wavelengths of p- and n-type InxGa1-xAs-InP quantum well infrared photodetectors (QWIPs) are determined not only by the energy distance from the ground sublevels in the quantum well to the energy band edges of extended states, but also by the characteristics of the extended states. The optical phonon scattering process converts the broad absorption spectrum of the p-QWIP from 0 to 16 µm into a short-wavelength spectrum centered at 4.5 µm. The transport of electrons in the extended states of the n-QWIP is characterized by running wave boundary conditions, resulting in a theoretically optimal absorption rate by a 8-nm-thick In0.53Ga0.47As quantum well. Moreover, a conduction-band offset of 0.5 for an InxGa1-xAs-InP (x=0.53) heterostructure gives the best data fitting of theoretical and experimental response peaks, whereas 0.55 is generally recommended in the literature. [ABSTRACT FROM AUTHOR]

We have studied the dependence of the photoluminescence (PL) spectrum on the doping level and the film thickness of n-GaAs thin films, both experimentally and theoretically. It has been shown theoretically that modification of the PL spectrum of p-type material by p-type doping is very small due to the large valence-band hole effective mass. The PL spectrum of n-type material is affected by two factors: (1) the electron concentration which determines the Fermi level in the material; (2) the thickness of the film due to re-absorption of the PL signal. For the n-type GaAs thin films under current investigation, the doping level as well as the film thickness can be very well calibrated by the PL spectrum when the doping level is less than 2×1018 cm-3 and the film thickness is in the range of the penetration length of the PL excitation laser. [ABSTRACT FROM AUTHOR]

A two-dimensional mesoscopic Bose system of dipoles in a 2D trap is considered using computer simulation by the quantum path-integral Monte Carlo method. The model describes a rarefied system of spatially indirect excitons in a confining potential. Bose condensation in the system and its superfluid and structural properties are studied over a wide range of interparticle spatial correlations, from an almost ideal Bose gas to the regime of a strongly correlated system. It is found that, at strong interparticle spatial correlations, particles in the condensate form a crystal-like structure. In this case, the spatial correlations of particles in the condensate are less pronounced than the correlations of noncondensed particles. The effect of recurrent crystallization is observed in the regime of strong interparticle correlations. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Hot electron effects have been extensively studied in metal-oxide-semiconductor field-effect transistors (MOS-FETs). The importance of these effects when the dimensions are drastically reduced has so far not been thoroughly investigated. The scope of this paper is therefore to present a detailed study of the effective temperature of excess electrons in nanoscale MOS-FETs by solving coupled Schrödinger and Poisson equations. It is found that the increased doping levels and reduced junction depths lead to substantially higher local Fermi levels in the source and drain regions. As a result, the temperature difference between electrons injected into the drain and local electrons is reduced. The scaling of the gate oxide thickness, as well as the drain voltage furthermore reduces the electron temperature in the drain. The detrimental effects of hot electron injection are therefore expected to be decreased by scaling the MOSFET. [ABSTRACT FROM AUTHOR]

Many biosystems are complex mixtures of disparate biofluids. To study contact and transport phenomena in these mixtures, one has to apply much information on the biofluids which are components of the mixtures. A lot of the corresponding data can be extracted by means of experiments. However, it is not always easy to obtain experimental results on rather deep physical characteristics of biofluids, especially if the bioparticles are complicated systems and the fluid coexists in the mixture with a large number of other fluids. In these cases, the necessary data can, in principle, be extracted from those results which are easier to obtain experimentally. The present work proposes a method to evaluate the biofluid equilibrium pressure and electrochemical potential from common experimental values of the fluid concentration and absolute temperature as well as the fluid-particle mass, volume and spin. In so doing, the nonzero values of the particle volume are accounted for. The procedure is illustrated with a numerical example on the fluid of red blood cells (or erythrocytes) in human blood. The pressure values obtained are 49.1 and 38.8 micropascals for men and women respectively whereas the electrochemical-potential values are −2.124 and −2.130 electronvolts for men and women respectively. [ABSTRACT FROM AUTHOR]

Micro-photoluminescence (μ-PL) line scanning across a single V-groove, GaAs/AlGaAs quantum wire (QWR) has been performed at room temperature, revealing a clear spatial-dependence of the PL. After fitting each PL spectrum by multi-Gaussian line shapes, intensity profiles of each PL component from confined structures have been obtained as functions of the scanning position. The PL quenching of a side-wall quantum well (SQWL) has been recognized in a certain area in the vicinity of the QWR and is interpreted by carrier transfer into the QWR within effective transfer length. By simulating the carrier-transfer process from SQWL to QWR as a convolution of a step function for carrier distribution and a Gaussian function for exciting laser irradiance, the effective transfer length of about 1.8±0.3 µm has, therefore, been concluded. [ABSTRACT FROM AUTHOR]

We have studied theoretically the capacitance characteristics of a metal–insulator–semiconductor structure with an ultra-thin oxide layer by self-consistently solving Schrödinger and Poisson equations. It is demonstrated that a ‘diffused’ interface between Si and SiO[sub 2] results in a better agreement between the theoretical prediction of conduction current and experimental I–V data. The calculated steady-state capacitance, obtained both analytically and numerically, increases following the increase of the gate bias when the gate bias is small; it reaches a saturation value at intermediate gate bias. The capacitance decreases with increasing gate bias when the gate bias is rather large due to the depletion of the gate material. Simple analytical expressions for the gate capacitance are derived, based on quantum-mechanical considerations, for future device design. The steady-state capacitance of a metal–insulator–semiconductor structure with an oxide layer of 1.5–2.0 nm by state-of-the-art technology is 20 mF/m[sup 2] , while it is 40 mF/m[sup 2] when the practical limit of SiO[sub 2] layer thickness, i.e. 10–12 Å, is reached. [ABSTRACT FROM AUTHOR]

We have fabricated a GaAs/InGaAs/AlGaAs-based single-electron transistor (SET) formed by etched trenches and multiple gates. Clear Coulomb-blockade oscillations have been observed when the gate biases are scanned. By self-consistently solving three-dimensional Schrödinger and Poisson equations, we have studied the energy-band structure and the carrier distribution of our SET. General agreement between numerical simulation results and measurement data has been obtained, thus indicating the effectiveness of our SET-device design as well as the necessity of a complete three-dimensional quantum-mechanical simulation. [ABSTRACT FROM AUTHOR]

Electron spin relaxation by the D'yakonov-Perel' mechanism is investigated theoretically in asymmetrical III-V heterostructures. Spin relaxation anisotropy for all three dimensions is demonstrated for a wide range of structural parameters and temperatures. Dependences of spin relaxation rates are obtained both for a GaAs-based heterojunctions and triangular quantum wells. The calculations show a several-ordersof-magnitude difference between spin relaxation times for heterostructure parameters realized in experiments. [ABSTRACT FROM AUTHOR]

The dc electric conductance of isotropically conductive adhesive (ICA) was studied. Assuming completely random distribution of the metal fillers in the ICA, it was demonstrated that the percolation volume percentage of the metal fillers can be significantly reduced by adding nano-size fillers (nanofillers) into the system originally containing only micro-size fillers (microfillers). However experiments show that, due to the surface tensions, nanofillers tend to gather around microfillers as well as to form clusters themselves so the resistivity of the ICA increases following the increase of the nanofillers' volume percentage. In the present work, these cluster effects are investigated by simulating the detailed random walks of the nanofillers and microfillers in the system It is concluded that the cluster effects of the nanofillers deteriorate the electric conductivity of the ICA because the microfillers separate from each other so that it is more difficult to form the electrical conduction path in the ICA. [ABSTRACT FROM AUTHOR]

Abstract. We have studied the effect of the strain relaxation on the band-edge alignments in a Pt/p-Si[sub 1-x]Ge[sub x] Schottky junction with x = 0.14 by internal photoemission spectroscopy and current-voltage measurements. We have shown that the variations in the band-edge alignments can be observed directly by measuring the optical and electrical properties of a simple Schottky junction. The strain in the Si[sub 1-x]Ge[sub x] layer has been partially relaxed by thermal treatments at two different temperatures. The degree of relaxation and other structural changes have been determined by a high-resolution X-ray diffractometer. Both optical and electrical techniques have shown that the barrier height of the Pt/Si[sub 0.86]Geo[sub 14] junction increases with the amount of relaxation in the Si[sub 1-x]Ge[sub x] layer. This shows that the valence-band edge of the Si[sub 1-x]Ge[sub x] layer moves away from the Fermi level of the Pt/Si[sub 1-x]Ge[sub x] junction. The band-edge movement results from the increase in the band gap of the Si[sub 1-x]Ge[sub x] layer after the strain relaxation. This result agrees with the theoretical predictions for the strain-induced effects on the Si[sub 1-x]Ge[sub x] band structure. [ABSTRACT FROM AUTHOR]

Abstract. We investigate, both experimentally and theoretically, current and capacitance (I-V/C-V) characteristics and the device performance of Si/SiO[sub 2]/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO[sub 2] layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currants (about 5 x 10[sup -2] and 1.8 x 10[sup -2] mA/mm[sup 2]) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm[sup 2] for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm [sup 2] device area, 760-mu m modulation layer thickness and Is approximately equal to 10[sup 15-cm[sup -3] doping level), the estimated cut-off frequency is about 5 x 10[sup 7] Hz. With the physical parameters of the present existing III-V triplets, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. [ABSTRACT FROM AUTHOR]

Abstract. The effect of a random field caused by impurities, interface roughness and so on, on the optical properties and superfluidity of a quasi-two-dimensional system of excitons is studied. The influence of a random field on the density of the superfluid component of excitonic systems at low temperatures is investigated. For quasi-two-dimensional excitonic systems in a random field the Kosterlitz-Thouless temperature in the superfluid state is calculated. The superfluidity and Bose--Einstein condensation of indirect excitons in coupled quantum dots are studied. Magnetoexciton light absorption in the disordered quantum wells is considered. The two-particle problem of the magnetoexciton motion in the external field depending on the external magnetic field is reduced to the one-particle motion with effective magnetic mass in some effective field. The energy and optical absorption of the magnetoexciton in a single and coupled quantum dots are studied using the effective-magnetic-mass Hamiltonian. In the coherent potential approximation the coefficient of magnetoexciton optical absorption in single and coupled quantum wells is calculated. In the strong magnetic fields the exciton peak decreases with magnetic field increasing in accordance with the experimental data. The localization of direct and indirect magnetoexcitons is investigated. [ABSTRACT FROM AUTHOR]

The electron thermal flux and electron thermal conductivity of the interface between a normal metal and a high-temperature superconductor (HTSC) are calculated using quasiclassical equations. Calculations are made for various values of the interface transparency and various orientations of the axes of a HTSC crystal. It was shown that compared with an interface between a normal metal and an "ordinary" superconductor (s-type symmetry, isotropic order parameter), the thermal conductivity of an HTSC-normal-metal interface is substantially higher and has a nonactivation dependence. The thermal properties were calculated for various interface models, including mirror and diffuse, and also for various potential barrier profiles. An analysis is made of the possibility of using devices based on normal-metal-HTSC interfaces for bolometric and microrefrigerator applications. [ABSTRACT FROM AUTHOR]

Instability in a system of interacting quasi-two-dimensional excitons in a type II superlattice of a finite thickness due to attraction between oppositely-directed excitonic dipoles in neighboring layers has been discovered. A stable system is that of indirect quasi-two-dimensional biexcitons formed by indirect excitons with dipole moments oriented in opposite directions. The radius and binding energy of indirect biexcitons has been calculated. A collective spectrum of a system of such biexcitons with a weak quadrupole interaction between them has been studied. Feasibility of Bose condensation, the density n[sub s](T) of the superfluid component, and a phase transition to the superfliud state in a low-density system of indirect biexcitons have been analyzed. [ABSTRACT FROM AUTHOR]

This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal metal junction. At the measured thermal conductivity, G ≈ 6 × 10[sup -12] W/K, and a time constant of τ = 0.2 µs, and a temperature of 300 mK, the estimated noise-equivalent power NEP = 5 × 10[sup -18] W/Hz[sup ½], assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity drops to G ≈ 7 × 10[sup -14] W/K, which yields NEP = 2 × 10[sup -19] W/Hz[sup ½] at a time constant of τ = 5 µs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes. [ABSTRACT FROM AUTHOR]

A theory of degenerate four-wave mixing in a semiconductor optical cavity with quantum wells is constructed. The nonlinear response of a microcavity can be four to five orders of magnitude stronger than that of an isolated quantum well. For P2E- and P3-type nonlinearities the damped diffracted signal oscillates with a period determined by the Rabi splitting. For a biexcitonic mechanism of nonlinearity, the signal contains damped overtones of the Rabi splitting and the biexciton binding energy. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The frequency dependent capacitance of semiconductor-electrolyte junction and its relationship to the surface roughness of the semiconductor and the ions in the electrolyte are discussed. Due to very low mobility of the ions, the observed capacitance can be dominated by the Helmholtz double-layer of the electrolyte rather than the space charge layer of the semiconductor. The capacitance will also depend on the frequency. This, often observed power-law frequency dependence of capacitance is ascribed to the contribution of constant phase angle impedance. The power-law exponent can easily be related to the fractal dimension if the semiconductor surface can be described by fractal geometry. [ABSTRACT FROM AUTHOR]

3C-SiC/Si heterojunction diodes were prepared by reactive magnetron sputtering of pure Si in CH-Ar discharge on Si(111) substrates kept at temperatures (T) ranging from 800 to 1000°C. A good diode rectification process started for films grown at T≤900°C. Heterojunction diodes grown at T = 850°C showed the best performance with a saturation current density of 2.4 × 10 A cm. Diode reverse breakdown was obtained at a voltage of −110 V. The doping concentration (N) of the 3C-SiC films was calculated from 1/C vs V plot to be 3 × 10 cm. Band offset values obtained were −0.27 and 1.35 eV for the conduction and valence band, respectively. X-ray diffraction analysis revealed the film grown at T = 850°C to be single-phase 3C-SiC. The full width at half maximum of the 3C-SiC(111) peak was only 0.25 degree. Cross-sectional transmission electron microscopy showed the film to be highly (111)-oriented with an epitaxial columnar structure of double positioning domain boundaries. [ABSTRACT FROM AUTHOR]

The oxidation of 3C-SiC films deposited on off-oriented Si(001) substrates by reactive magnetron sputtering has been studied. The oxidation was carried out using dry conditions at a temperature of 1200°C. The composition of the oxide layer was investigated by Auger electron spectroscopy (AES). The oxide layer was found to contain no C except for the region very close to the interface, and the stoichiometry was found to be close to that of SiO. Cross-sectional transmis-sion electron microscopy (XTEM) showed the oxide layer to be completely amorphous, dense, and homogeneous with a uniform thickness. High-resolution XTEM imaging showed an atomically sharp SiO/SiC interface. [ABSTRACT FROM AUTHOR]

Current-voltage characteristics of metal contacts on 6H-SiC with a thin (5-20Å) oxide layer have been measured in the temperature range 300 to 1000K. The contacts were investigated in both H and O-atmospheres. As the SiC surface was nonideal due to pin holes and other defects generated during the growth process, it was necessary to treat the Schottky contacts as inhomogeneous contacts. The inhomogeneity explains the nonideal current-voltage behavior of the contacts such as ideality factors much larger than unity and voltage dependent ideality factors. It was found that some metals gave Schottky contacts in the entire temperature range, while other metals were ohmic at higher temperatures. Several different contact metals were investigated: Al, Ti, TaSi, and Pd were found to be ohmic at high temperatures, while Pt, Pt+Cr, Ni, Cr and another TaSi contact were found to behave like Schottky contacts in the entire temperature range. This is a preliminary investigation of the electrical characteristics of different metals that could be useful for high temperature gas sensor purposes. [ABSTRACT FROM AUTHOR]

We report a deductive method used in the incomplete far-infrared reflection spectrum analysis. The inherent restriction between the oscillator model and Kramers-Kronig relation is used to deduct the dielectric constant. In this way, one can analysis the incomplete far-infrared reflection spectrum of a crystal by combining both oscillator model and Kramers-Kronig relation. [ABSTRACT FROM AUTHOR]

Different Si homojunction and strained SiGe/Si heterojunction diodes and bipolar transistors have been fabricated by Si-MBE. The effect of annealing on Si homojunction diodes and transistors are studied. It is found that annealing generally improves the Si device performance, such as the ideality factor and breakdown characteristics. The influence ofCo γ irradiation on the SiGe/Si diode performances are investigated by studying the temperature dependence of their electrical characteristics, and the results are correlated with the quality of the MBE-films. γ irradiation causes a drop in material conductivity due to the generation of atom-displacement defects in the whole volume of the wafers and increases the defect density at hetero-interfaces. The forward I-V curves of SiGe/Si devices may shift towards lower or higher voltages, depending on the film quality and the irradiation dose. The increase of defect density in strained SiGe/Si films appears to occur easier for the films with lower quality. Electrical measurements and calculations show that the defect-associated tunneling process is important in current transport for these MBE grown Si homojunction and strained SiGe/Si heterojunction devices, which have initially medium film quality or have been treated by irradiation. [ABSTRACT FROM AUTHOR]

The Editor-in-Chief has retracted this article [1] because Figure 4 and Figure 5 appear to show cobalt oxide nanoparticles and not iron oxide nanoparticles as stated in the article. The data reported in this article are therefore unreliable. [ABSTRACT FROM AUTHOR]