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The W/Cu thin film structure is deposited by magnetron sputtering to form the infrared reflector for the TiNxOy based selective solar absorber (SSA) that can be used in the low- and middle-temperature applications. The structural, chemical, and optical properties of the SSA layers that experienced thermal annealing at different temperatures for various durations have been investigated with the characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, spectroscopic ellipsometry, and spectrophotometry. Without a W layer, the reflectance in both visible and infrared ranges of the SSA increases as a result of the crystallization of the Cu layer at elevated temperatures. With a W layer with appropriate film thickness, the increase of the reflectance in the visible range can be suppressed to maintain a high solar absorptance, whereas a high infrared reflectance can be maintained to achieve a low thermal emittance. It is shown that for the SiO2-TiNxOy-W-Cu-Glass SSA with a 15 nm W thin film, thermal annealing can significantly reduce the thermal emittance to a low value (e.g., 4.4% at the temperature of 400 °C for annealing at 400 °C for 6 h), whereas the solar absorptance can be maintained at a high value (e.g., 92.2% for the annealing at 400 °C for 6 h). [ABSTRACT FROM AUTHOR]

Ion beam irradiation is a powerful method to fabricate and tailor the nanostructured surface of materials. Nanorods on the surface of single crystal rutile TiO2 were formed by N+ ion irradiation. The dependence of nanorod morphology on ion fluence and energy was elaborated. With increasing ion fluence, nanopores grow in one direction perpendicular to the surface and burst finally to form nanorods. The length of nanorods increases with increasing ion energy under same fluence. The development of the nanorod structure is originated from the formation of the nanopores while N2 bubbles and aggregation of vacancies were responsible for the formation of nanopores and nanorods. Combining C+ ion irradiation and post-irradiation annealing experiments, two qualitative models are proposed to explain the formation mechanism of these nanorods. [ABSTRACT FROM AUTHOR]

The bandgap and optical properties (dielectric functions and optical constants) of dome-shaped Ge nanocrystals (nc-Ge) with average sizes of ∼6 nm in height and ∼13 nm in diameter have been investigated using spectroscopic ellipsometry based on the Forouhi-Bloomer optical dispersion model. As compared to bulk crystalline Ge, the nc-Ge exhibited a bandgap expansion of ∼0.2 eV and a significant reduction in the dielectric function. The bandgap expansion and dielectric suppression are discussed in terms of the quantum confinement effect as well as the bond contraction model. [ABSTRACT FROM AUTHOR]

The band gap and optical properties (dielectric functions and optical constants) of Ge thin films with various thicknesses below 50 nm, which were synthesized with electron beam evaporation technique, have been determined using spectroscopic ellipsometry and UV-visible spectrophotometry. The optical properties are well described with the Forouhi–Bloomer model. Both the band gap and optical properties show a strong dependence on the film thickness. For film thickness smaller than ∼10 nm, a band gap expansion is observed as compared to bulk crystalline Ge, which is attributed to the one-dimensional quantum confinement effect. However, a band gap reduction was observed for thickness larger than ∼10 nm, which is explained in terms of the amorphous effect in the Ge layers. [ABSTRACT FROM AUTHOR]

High Mg-content, wurtzite MgZnO films were grown on sapphire (0001) substrates by pulsed laser deposition. It was found that the compositions, defect states, optical, and electrical properties of MgZnO films depend critically on the substrate temperature and oxygen pressure. As the substrate temperature increases, Mg content in single-phase wurtzite MgZnO films increases significantly from 27 close to 46 at. %, and corresponding band gap is widened from 3.49 to 3.88 eV. X-ray photoelectron spectroscopy studies show that plenty of Zn interstitials are present in MgZnO films grown at lower oxygen pressures, which lead to the lattice expansion and the high electron concentration as native donor defects; while the films grown at higher oxygen pressure exhibit high resistivity with indeterminate conductivity type and the relatively wide band gap. [ABSTRACT FROM AUTHOR]

Highly dispersed ZnO quantum dots (QDs) in polyvinylpyrrolidone (PVP) nanotubes have been prepared by a single capillary electrospinning. The structure and optical properties characterizations were performed by x-ray diffraction, scanning and transmission electron microscopy, absorption, photoluminescence, and resonant Raman spectra. In the composites, PVP molecules passivate the surface defects of ZnO QDs and prevent the aggregations of ZnO QDs. As a result, the composites exhibit narrower band edge emissions and less laser thermal effects. Blueshifted band gap, enlarged exciton energy, and less exciton-longitudinal optical (LO) phonon interaction due to the quantum confinement effect have also been observed. [ABSTRACT FROM AUTHOR]

The recombination mechanisms of nitrogen-related emissions in p-type ZnO films were investigated by photoluminescence (PL) measurements. The enhanced peak at 3.260 eV was confirmed as a donor-acceptor pair (DAP) transition and the emission around 3.310 eV was assigned to the free electron to acceptor (FA) recombination by studying the temperature evolution of DAP and FA luminescence, calculating the energy level of the corresponding nitrogen acceptor, and measuring the decay time of DAP transition. By comparing the PL spectra of the samples with various hole concentrations, it can be found that as the hole concentration increases, the DAP peak significantly dominates the spectra. In addition, the acceptor binding energy is estimated to be about 120 meV from the FA transition, which is in good agreement with the value calculated by a hydrogenic acceptor model. [ABSTRACT FROM AUTHOR]

Si nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix have been synthesized with various recipes of Si ion implantation. The influence of nanocrystal size on optical properties, including dielectric functions and optical constants, of the nc-Si has been investigated with spectroscopic ellipsometry. The optical properties of the nc-Si are found to be well described by the four-term Forouhi-Bloomer model. A strong dependence of the dielectric functions and optical constants on the nc-Si size is observed. For the imaginary part of the dielectric functions, the magnitude of the main peaks at the transition energies E1 and E2 exhibits a large reduction and a significant redshift in E2 depending on the nc-Si size. A band gap expansion is observed when the nc-Si size is reduced. The band gap expansion with the reduction of nc-Si size is in good agreement with the prediction of first-principles calculations based on quantum confinement. [ABSTRACT FROM AUTHOR]

The Zn1-xMnxO (x=0, 0.16, and 0.25) thin films were grown on fused quartz substrates by reactive magnetron cosputtering. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. As Mn concentration increased in the Zn1-xMnxO films, the c-axis lattice constant and band-gap energy increased gradually. In Raman-scattering studies, an additional Mn-related vibration mode appeared at 520 cm-1. E2H phonon line of Zn1-xMnxO alloy was broadened asymmetrically and redshifted as a result of microscopic structural disorder induced by Mn2+ random substitution. The Zn0.84Mn0.16O film exhibited a ferromagnetic characteristic with a Curie temperature of ∼62 K. However, with increasing Mn concentration to 25 at. %, ferromagnetism disappeared due to the enhanced antiferromagnetic superexchange interactions between neighboring Mn2+ ions. [ABSTRACT FROM AUTHOR]

Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples. [ABSTRACT FROM AUTHOR]

ZnO particles embedded in SiO2 thin films were prepared by a radio-frequency magnetron sputtering technique. X-ray diffraction (XRD) and optical-absorption spectra showed that ZnO particles with hexagonal wurtzite structure had been embedded in the SiO2 matrix, and the size of ZnO particles increased with increasing annealing temperature from 773 to 973 K. Raman-scattering and Fourier transform infrared (FTIR) spectrum measurements also confirmed the presence of ZnO particles. When the annealing temperature was lower than 973 K, room-temperature photoluminescence (PL) spectra showed dominative deep-level emissions in the visible region and very weak ultraviolet emissions. As the annealing temperature increased to 973 K, an emission band in the ultraviolet region besides the emissions from free and bound excitons recombination was observed in the low-temperature PL spectra. The origin of the ultraviolet emission bands was discussed with the help of temperature-dependent PL spectra. When the annealing temperature was higher than 973 K, Zn2SiO4 particles were formed, as shown by XRD and FTIR results. [ABSTRACT FROM AUTHOR]

This article presents information on the optical properties of ZnO hexagonal prisms grown from poly (vinylpyrrolidone)-assisted electrochemical assembly onto Si (111) substrate. ZnO has attracted considerable research attention recently because it is a suitable candidate for blue or ultraviolet light-emitting devices and photodetectors. ZnO is a direct wide-band-gap s3.37 eVd semiconductor with a high exciton binding energy of 60 meV. The morphology, size, and orientation of ZnO are crucial to the application of this material.

In this article, we observe the optically pumped lasing from the high-quality nanocrystalline ZnO thin films obtained by thermal oxidation of ZnS thin films, which were grown on SiO[sub 2] substrates by low-pressure-metalorganic chemical vapor deposition technique. The x-ray diffraction (XRD) patterns indicate that high-quality ZnS films possess a preferred (111) orientation. ZnS has a transformation to ZnO at an annealing temperature (T[sub a]) of 500°C, and fully transforms into ZnO at T[sub a] ≥ 700°C from the XRD patterns. The obtained ZnO films possess a polycrystalline hexagonal wurtzite structure. The fifth-order Raman scattering is observed in the films, which indicates that a large deformation energy exists in the lattice. In photoluminescence (PL), spectra, for all the samples with different annealing temperatures, the near-band-edge (NBE) PL peak has a pronounced blueshift with increasing annealing temperature, while the full width at half maximum (FWHM) decreases gradually. We think that emissions of the bound excitons play an important role in NBE PL. A strong PL with a FWHM of 62 meV at 3.30 eV from NBE has been obtained at room temperature for the samples annealed at 900°C. The PL intensity ratio of the ultraviolet emission to the deep-level emission is as high as 98 at room temperature, indicating the high-quality of the nanocrystalline ZnO films. [ABSTRACT FROM AUTHOR]

High quality ZnO thin films have been grown on a Si(100) substrate by plasma enhanced chemical vapor deposition using a zinc organic source [Zn(C[sub 2]H[sub 5])[sub 2]] and carbon dioxide (CO[sub 2]) gas mixtures at the low temperature of 180 °C. The dependence of ZnO thin film quality on the gas flow rate ratio of Zn(C[sub 2]H[sub 5])[sub 2] to CO[sub 2] (GFRRZC) is studied by using x-ray diffraction (XRD), optical absorption (OA) spectra, and cathodoluminescence (CL) spectra. High quality ZnO thin films with a c-axis-oriented wurtzite structure are obtained when the GFRRZC is 0.33. XRD shows that the full width at half maximum of (0002) ZnO located at 34.42° is about 0.2°. At room temperature, a pronounced free exciton absorption peak around 365 nm is clearly observed. Also, a strong free exciton emission without deep level defect emission is observed around 385 nm, and its temperature dependence is studied from the photoluminescence spectra. These observations indicate the formation of a high quality ZnO film. Additionally, nitridation of the Si surface caused by releasing NH[sub 3] plasma into the deposition chamber is an effective way to improve film quality. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which explored the growth of ultrathin silicon dioxide films by silicon irradiation with oxygen electron cyclotron resonance microwave plasma at low temperatures. Experimental details; Results and discussion; Conclusions.

Deals with a study that characterized platinum (Pt)-silicon (Si) interface by spectroscopic ellipsometry. Determination of optical response of Pt-Si interface by ellipsometry; Ellipsometric measurements performed; Effective-medium theory simulation to the complex dielectric constant of the interface layer.

Studies a method of combining preoxidation and subsequent sputter deposition for fabricating thin silicon oxide films by using a sputter-type electron cyclotron resonance plasma system. Structural properties of silicon oxide; Thermal annealing in argon ambient; Effects of the preoxide on the structural and electrical properties of deposited oxide films.

Photoluminescence (PL) spectra of single-crystal ZnO bulk under hydrostatic pressure are studied using the diamond-anvil-cell technique at room temperature. The PL spectrum of ZnO single crystal taken at atmospheric pressure was dominated by a strong near-band-edge exciton emission. The emission line was found to shift towards higher energy with increasing applied pressure. By examining the pressure-dependent PL spectral features, the pressure coefficient of the direct Γ band gap of the wurtzite ZnO was determined. The hydrostatic deformation potential of the band gap has also been deduced from the experimental results. [ABSTRACT FROM AUTHOR]

Photoluminescence and Raman spectra of ZnO single-crystal nanosheets have been studied as a function of applied hydrostatic pressure using the diamond-anvil-cell technique at room temperature. The ZnO nanosheets synthesized via a vapor transport process have uniform plane surfaces with lateral dimensions up to several microns and thickness of ∼100 nm. In terms of Raman results, the ZnO nanosheets underwent a transition from wurtzite to rock-salt structure with an increase of pressure, and the phase-transition pressure was measured to be about 11.2 GPa. However, a strong near-band-edge UV emission of ZnO nanosheets was observed with the applied pressure up to 20.0 GPa. Simultaneously, the emission peak shifted to higher-energy side with increasing pressure. By examining the dependence of the near-band-edge emission peak on the applied pressure, the pressure coefficient of the direct Γ band gap in the wurtzite ZnO nanosheets was determined. [ABSTRACT FROM AUTHOR]

Resistive-switching memory with ultralow-power consumption is very promising technology for next-generation data storage and high-energy-efficiency neurosynaptic chips. Herein, Ta2O5-xbased multilevel memories with ultralow-power consumption and good data retention were achieved by simple Gd-doping. The introduction of a Gd ion, as an oxygen trapper, not only suppresses the generation of oxygen vacancy defects and greatly increases the Ta2O5-x resistance but also increases the oxygen-ion migration barrier. As a result, the memory cells can operate at an ultralow current of 1 μA with the extrapolated retention time of >10 years at 85 °C and the high switching speeds of 10 ns/40 ns for SET/RESET processes. The energy consumption of the device is as low as 60 fJ/bit, which is comparable to emerging ultralow-energy consumption (<100 fJ/bit) memory devices. [ABSTRACT FROM AUTHOR]

We demonstrated transferable and flexible resistive switching (RS) memory devices using a nondestructive water-dissolution method. To satisfy future demands, the free-standing Al/Fe3O4-PMMA/Al devices were transferred onto various nonconventional substrates to demonstrate various features, such as flexibility, 3-D conformality, and biocompatibility. Thanks to the strong van der Waals interaction, the devices can easily conform to these substrates and normally display RS behavior even after undergoing bending tests. In particular, the memory devices with the PET substrate present excellent memory performance as well as high flexibility, including fast switching speed (<50 ns), large ROFF/RON ratio (~4 x 105), and long retention time (>104 s). No performance degradation occurs after bending the device to different angles and up to 104 times. The RS mechanism can be attributed to the trapping/de-trapping of electrons at the sites of Fe3O4 nanoparticles. This result provides a feasible approach to achieve transferable RS memory device for future conformal and flexible electronics. [ABSTRACT FROM AUTHOR]

In this work, flexible and energy-efficient transparent heaters based on graphene and aligned silver nanowire (G-ASNW) hybrid structures are fabricated by thermal evaporation of silver on the aligned electrospun nanofiber templates and subsequent transfer of monolayer graphene onto the ASNWs. The G-ASNW films exhibit few wire-wire junctions and low resistance along the aligned direction, which are favorable for low-voltage transparent heater applications. Coating the ASNW network with monolayer graphene increases the saturated temperature of the hybrid heater due to the high thermal conductivity and low convective heat-transfer coefficient of graphene. Meanwhile, G-ASNW films show excellent electromechanical stability under cyclic bending because the graphene anchoring on the top surface of ASNWs could share tensile stress and serve as local conducting pathways at break-points even if small cracks were generated. The G-ASNW hybrid structures present a perspective on wearable transparent heaters. [ABSTRACT FROM AUTHOR]

Shows that the photovoltage and the internal photoemission techniques can be used for studying metal/semi-insulating (SI) semiconductor contacts. Description of gallium arsenide (GaAs) sample preparation; Reason that photocurrent may be generated when monochromatic light is incident upon the nickel (Ni) film; Reversed current voltage characteristics of the Ni/SIGaAs contact at room temperature.

Presents a study which examined the influence of annealing on Fermi-level pinning and current transport at gold-silicon and gold-gallium arsenide semiconductor interfaces. Measurement of the Schottky barrier height and its temperature dependence; Experimental details; Results.

Focuses on the synthesis of the barium-titanium-oxygen ferroelectric films of quality suitable for applying as dielectrics dynamic random access memory. Use of laser ablation technique; Crystal structure and microstructure of the films; Value of the leakage current density.

Single crystal ferromagnetic Fe3Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe3Si/GaAs(111) yielded a saturation moment of 990 emu/cm³ with a small coercive field ≤1 Oe at room temperature. [ABSTRACT FROM AUTHOR]

A high-quality high-σ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high j dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angleresolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5Å to 1Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high j dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (Dit) reveal the improved high-σ/Ge interface using the Ge epi-layer approach. [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron (EMIC) waves can lead to the rapid decay (on a timescale of hours) of the terrestrial ring current. Such decay process is usually investigated in the framework of quasi-linear theory. Here, both theoretical analysis and test-particle simulation are performed to understand the nonlinear interaction between ring current ions and EMIC waves. In particular, the dependence of the nonlinear wave-particle interaction processes on the ion initial latitude is investigated in detail. These nonlinear processes are classified into the phase trapping and phase bunching, and the phase bunching is further divided into the channel and cluster effects. Compared to the prediction of the quasi-linear theory, the ring current decay rate can be reduced by the phase trapping, increased by the channel effect phase bunching, but non-deterministically influenced by the cluster effect phase bunching. The ion initial latitude changes the occurrence of the phase trapping, modulates the transport direction and strength of the cluster effect phase bunching, and only slightly affects the channel effect phase bunching. The current results suggest that the latitudinal dependence of these nonlinear processes should be considered in the evaluation of the ring current decay induced by EMIC waves. [ABSTRACT FROM AUTHOR]

Resistive-switching (RS) memories with good performance and flexibility are demonstrated in p-type amorphous CuAlOx. The nature of conducting filaments (CFs) is studied via the dependence of RS behaviors on the oxygen concentration of CuAlOx. It is observed that with increasing oxygen concentration, (1) both resistance-states and switching-voltages reduce, showing an opposite trend to popular n-type oxide devices; and (2) a transition from non-degenerate to degenerate states occurs in CFs. These observations indicate that the CFs are composed of Cu-vacancy shallow acceptors. The oxygen-concentration dependence of CFs' resistance results from the change of Cu-vacancy content, rather than CFs' size or number. [ABSTRACT FROM AUTHOR]

Localized surface plasmon (LSP)-enhanced ultraviolet light-emitting diodes were manufactured by introducing Ag nanoparticles and MgO spacer layer into n-ZnO/i-ZnO/p-GaN heterostructures. By optimizing the MgO thickness, which can suppress the undesired charge transfer and nonradiative Förster resonant energy transfer between Ag and ZnO, a 7-fold electroluminescence enhancement was achieved. Time-resolved and temperature-dependent photoluminescence measurements reveal that both spontaneous emission rate and internal quantum efficiency are increased as a result of coupling between ZnO excitons and Ag LSPs, and simple calculations, based on experimental data, also indicate that most of LSP's energy can be converted into the photon energy. [ABSTRACT FROM AUTHOR]

Ultraviolet light-emitting diodes using MgZnO-coated and bare ZnO nanorod arrays as active layers were manufactured. Both types were exposed to ambient air over a 1-yr period to assess their stability. By monitoring the electroluminescence evolution with air-exposure time and comparing the changes of electroluminescence and x-ray photoelectron spectra before and after vacuum desorption, it is concluded that surface-adsorbed O2 and OH- species, as acceptor and donor surface states, quench ultraviolet electroluminescence, and favor undesirable surface-mediated nonradiative and deep-level recombination. The MgZnO coating prevents surface adsorption, and so the coated nanorod device shows higher efficiency and stability than the uncoated one. [ABSTRACT FROM AUTHOR]

Quantum transport properties of two-dimensional electron gas (2DEG) in undoped MgxZn1-xO/ZnO heterostructures grown by metal organic vapor phase epitaxy have been investigated. A large zero-field spin-splitting energy more than 15 meV in the 2DEG is determined at 1.6 K. Meanwhile, ferromagnetism is observed in the heterostructures. The findings reveal that the 2DEG is spin polarized at zero magnetic fields. It is believed that the exchange interaction between the itinerant electrons in the two-dimensional channel and the magnetic polarons in the MgxZn1-xO barrier around the interface results in the spin polarization of the 2DEG. [ABSTRACT FROM AUTHOR]

Ti–Si–N–O nanocomposite coatings with different contents of oxygen were deposited by a combined dc/rf reactive unbalanced magnetron sputtering process in an Ar+N2+O2 mixture atmosphere. The composition, structure, mechanical, and tribological properties of the as-deposited coatings were analyzed by energy dispersive analysis of x-rays, x-ray diffraction (XRD), nanoindentation, and pin-on-disk tribometer experiments, respectively. It was found that in the range of lower oxygen content with atomic ratio of O/N<=0.72, the tribological properties of the Ti–Si–N–O coatings are evidently improved, in comparison with the coating without oxygen incorporation. At O/N=0.72, the friction coefficient and wear rate of the as-deposited coatings are reduced to 20% and 45%, respectively. Meanwhile, however, their hardness was not reduced, but, on the contrary, slightly increased. With increasing oxygen content further to O/N>=0.72, coating hardness decreased significantly. The friction coefficient of the as-deposited coatings decreased monotonously with the increase of oxygen content in the whole composition range investigated. The wear rate of the coatings exhibited a minimum value at around O/N=0.72. In the lower range of O/N, wear rate decreased significantly due to the lubricant effect of oxygen incorporation, while in the higher range of O/N, wear rate increased gradually due to the weakening of coating hardness. XRD patterns revealed that the as-deposited coatings were mainly crystallized in cubic TiN phase, accompanied with minority of rutile structure titania in the case of higher oxygen incorporation. [ABSTRACT FROM AUTHOR]