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Achieving high material perfection in aluminum (Al) films and their associated Al/AlOx heterostructures is essential for enhancing the coherence time in superconducting quantum circuits. We grew Al films with thicknesses ranging from 3 to 30 nanometers (nm) epitaxially on sapphire substrates using molecular beam epitaxy (MBE). An integral aspect of our work involved electron-beam (e-beam) evaporation to directly deposit aluminum oxide (Al2O3) films on the freshly grown ultrathin epitaxial Al films in an ultra-high-vacuum (UHV) environment. This in situ oxide deposition is critical for preventing the oxidation of parts of the Al films, avoiding the formation of undesired native oxides, and thereby preserving the nm-thick Al films in their pristine conditions. The thicknesses of our Al films in the study were accurately determined; for example, coherence lengths of 3.0 and 20.2 nm were measured in the nominal 3.0 and 20 nm thick Al films, respectively. These Al films were epitaxially grown on sapphire substrates, showing an orientational relationship, denoted as Al (111) ⟨ 2 1 ¯ 1 ¯ ⟩ ∥ sapphire (0001) [ 2 1 ¯ 1 ¯ 0 ]. The Al/sapphire interface was atomically ordered without any interfacial layers, as confirmed by in situ reflection high-energy electron diffraction (RHEED) and cross-sectional scanning transmission electron microscopy (STEM). All sample surfaces exhibited smoothness with a roughness in the range of 0.1–0.2 nm. The Al films are superconducting with critical temperatures ranging from 1.23 to around 2 K, depending on the film thickness. [ABSTRACT FROM AUTHOR]

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices. [ABSTRACT FROM AUTHOR]

The effect of the GaAsP strain-compensating layer on type-II GaAs1−xSbx/InyGa1−yAs was investigated. GaAsSb/InGaAs multiple quantum wells (MQWs) without and with GaAsP strain-compensating layers were grown by molecular beam epitaxy. Increasing Sb or In compositions can extend photoluminescence (PL) emission at longer wavelength along with the highly induced compressive strain in the QWs. The power-dependent PL measured at low temperature reveals the type-II band characteristics of the GaAs1−xSbx/InyGa1−yAs system. A detailed analysis of the experimental data reveals that the GaAsP layers compensate the compressive strain of GaAsSb/InGaAs. The type-II QWs with GaAsP layers, (8 nm) GaAs0.84Sb0.16/(2.5 nm) In0.3Ga0.7As/(10 nm) GaAs0.85P0.15, emits PL at ∼1.1 μm, up to 210 K, while the PL of those strained sample without GaAsP vanishes at lower temperature. In view of the described sample, x-ray diffraction (XRD) analysis along with the simulation shows the validity of the procedure, resulting in nearly matched parameters of QW thicknesses and material compositions—(8.9 nm) GaAs0.835Sb0.165/(2.3 nm) In0.3Ga0.7As/(10.3 nm) GaAs0.85P0.15, with those of the designed QW. The thicknesses of QW from the TEM image, (8.6 nm) GaAsSb/(3.1 nm) InGaAs/(10.1 nm) GaAsP, agree well with the XRD results. [ABSTRACT FROM AUTHOR]

The discovery of graphene led to a burst in search for 2D materials originating from layered atomic crystals coupled by van der Waals force. While bulk bismuth crystals share this layered crystal structure, unlike other group V members of the periodic table, its interlayer bonds are stronger such that traditional mechanical cleavage and exfoliation techniques have shown to be inefficient. In this work, we present a novel mechanical cleavage method for exfoliating bismuth by utilizing the stress concentration effect induced by micro-trench SiO 2 structures. As a result, the exfoliated bismuth flakes can achieve thicknesses down to the sub-10 nm range, which are analyzed by atomic force microscopy and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The development of electrical insulators that are thermally conducting is critical for thermal management applications in many advanced electronics and electrical devices. Here, we synthesized polymer nanocomposite (PNC) films composed of polymers [polyethylenimine, poly(vinylamine), poly(acrylic acid), and poly(ethylene oxide)] and dielectric fillers (montmorillonite clay and hexagonal boron nitride) by layer-by-layer technique. The cross-plane thermal conductivity (k ⊥) of the film was measured by the 3ω method. The effect of various factors such as film growth, filler type, filler volume fraction, polymer chemical structures, and temperature on the thermal conductivity is reported. The k ⊥ of PNCs with thickness from 37 nm to 1.34 μm was found to be in the range of 0.11 to 0.21 ± 0.02 W m−1 K−1. The k ⊥ values were found to be lower than the constituent polymer matrix. The experimental result is compared with existing theoretical models of nanocomposite systems to get insight into heat transfer behavior in such layered films composed of dielectrics and polymers. [ABSTRACT FROM AUTHOR]

Electrically active defects in carbon-doped GaN layers were studied with a metal/carbon-doped GaN (GaN:C)/Si-doped GaN (GaN:Si) MIS structure. The GaN:C layers were grown with three different carbon doping concentrations (NC). A semi-vertical metal/semi-insulator/n-type semiconductor (MIS) device was fabricated to perform deep-level transient spectroscopy (DLTS) measurements. Two electron traps E1 and E2 with energy level at EC − (0.22–0.31) eV and EC − (0.45–0.49) eV were observed. E1 and E2 are associated with a nitrogen vacancy VN-related defect in the strain field of extended defects and a nitrogen antisite defect, respectively. By changing the reverse bias voltage of the DLTS measurement, the location and relative defect concentration of the E1 and E2 traps could be verified. A dominant electron trap E3 with an unusual capture cross section was only observed in devices with an NC = 2 × 1019 cm−3 GaN:C layer. This may charge carriers from a defect band and lead to the charge redistribution in the GaN:C layer when forward biased. A hole trap H1 with energy level at EV + 0.47 eV was found for the pulse bias in the forward ON-state. H1 is suggested to correspond with the CN induced 0/+ donor level. By analyzing the schematic band diagrams across the MIS structure, the carrier transport and defect charging mechanisms underlying the DLTS transient measurements are illustrated. The identification of the trap states in the carbon-doped GaN with different NC gives further understanding on the carbon doping impact on electric characteristics of GaN power devices made on Si substrates. [ABSTRACT FROM AUTHOR]

Epitaxial nanometer-thin indium nitride (InN) films are considered promising active layers in various device applications but remain challenging to deposit. We compare the morphological evolution and characterizations of InN films with various growth conditions in chemical vapor deposition (CVD) by both a plasma atomic layer deposition (ALD) approach and a conventional metalorganic CVD approach. Our results show that a time-resolved precursor supply is highly beneficial for deposition of smooth and continuous InN nanometer-thin films. The time for purging the reactor between the precursor pulses and low deposition temperature are key factors to achieve homogeneous InN. The gas exchange dynamics of the reactor is further studied using computational fluid dynamics. According to our study, 320 °C is found to be the upper temperature where the dynamics of the deposition chemistry can be controlled to involve only surface reactions with surface species. The results highlight the promising role of the ALD technique in realizing electronic devices based on nanometer-thin InN layers. [ABSTRACT FROM AUTHOR]

Recent studies have established that the anti-Stokes Raman signal from plasmonic metal nanostructures can be used to determine the two separate temperatures that characterize carriers inside the metal—the temperature of photoexcited "hot carriers" and carriers that are thermalized with the metal lattice. However, the related signal in the Stokes spectral region has historically impeded surface enhanced Raman spectroscopy, as the vibrational peaks of adsorbed molecules are always accompanied by the broad background of the metal substrate. The fundamental source of the metal signal, and hence its contribution to the spectrum, has been unclear. Here, we outline a unified theoretical model that describes both the temperature-dependent behavior and the broad spectral distribution. We suggest that the majority of the Raman signal is from inelastic scattering directly with carriers in a non-thermal energy distribution that have been excited via damping of surface plasmon. In addition, a significant spectral component (∼1%) is due to a sub-population of hot carriers with an energy distribution that is well approximated by an elevated temperature distribution, about 2000 K greater than the lattice temperature of the metal. We have performed temperature- and power-dependent Raman experiments to show how a simple fitting procedure reveals the plasmon dephasing time as well as the temperatures of the hot carriers and the metal lattice, in order to correlate these parameters with the quantitative Raman analysis of chemical species adsorbed on the metal surface. [ABSTRACT FROM AUTHOR]

We illuminate a gallium arsenide (GaAs) Gunn device and study the light-induced changes of Gunn oscillation properties. We observe that illumination leads to the modulation of the Gunn threshold voltage, the Gunn oscillation magnitude, and the coherency of Gunn oscillation, with the nature of the modulation being closely related to the position of illumination on the device. These effects are attributed to the generation of optically excited carriers, which results in the modulation of conductivity and the electric field profile along the device. The finite element method is used to simulate the change of the field profile of the Gunn device caused by illumination. We also report an unexpected phenomenon of Gunn oscillation property manipulation with an optical chopper. In addition, wavelength-dependent, power-dependent, and pulsed illumination measurements are performed to help with further understanding the observations. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW)-based acoustofluidic systems are emerging as an important tool for acoustophoresis. In this paper, we present a full cross-sectional model of standing SAW acoustofluidic devices for obtaining full-wave results. Our model involves a piezoelectric substrate with interdigitated electrodes and a rectangular water channel enclosed in a finite soft elastic solid. This model accounts for piezoelectric SAWs with electromechanical coupling, simultaneous transverse and longitudinal wave fields in the elastic solid from SAW radiation, and acoustic and streaming fields in the enclosed water channel in an integrated system by solving the elastodynamic and Navier–Stokes field equations. Accordingly, the acoustic radiation force and streaming-induced Stokes drag force are obtained to analyze the acoustophoretic motion of microparticles of different sizes. Using the full-wave results, we reveal the influences of the channel wall displacements and acoustic and flow fields in the water domain. The full-wave field also allows us to determine the effects of the channel dimensions and its location in the finite elastic solid on the force strengths. We demonstrate that the critical diameter of the microparticles can be reduced by an order of magnitude by changing the channel location, while maintaining the same acoustic frequency. We note that the results, mechanisms, and method presented in this study can be usefully applied to the rational design of standing SAW acoustofluidic devices and for developing innovative acoustophoretic systems involving complex structure–fluid interactions. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3 or BTO) is a perovskite structure material with interesting intrinsic properties, such as spontaneous ferroelectricity or electro-optical behavior, which strongly depend on thin film crystallinity. For such functional oxide systems, the pulsed-laser deposition (PLD) approach is one promising growth technique due to its precise stoichiometry control of the metals composing the perovskite crystal and higher oxygen environment compared to the classically used molecular beam epitaxy (MBE) approach. In this article, we demonstrate a BTO epitaxial layer by PLD onto an Si(001) substrate thanks to a thin pseudomorphic SrTiO3 buffer layer grown by MBE. In our study, the various investigated PLD parameters show strong impacts on the BTO polarization orientation. Hence, adjusting the growth conditions allows control of the polarization orientation, which is crucial for both electronic and optical applications. In addition, lattice parameter changes of BTO layers are investigated using x-ray diffraction and cross-sectional transmission electron microscopy, which evidenced a correlation between mismatch relaxation and oxygen growth pressure. Finally, with the analysis of BTO C–V curves, the polarization direction transition is demonstrated electrically. [ABSTRACT FROM AUTHOR]

We fabricate gallium arsenide-based devices with a wedge-shaped tapering region connected to a rectangular-shaped region and measure the threshold voltage required to trigger the Gunn effect. The threshold voltage reduction is attributed to the focusing of the electric field toward the narrower end of the device and is effective when the device has a steep enough tapering. We also model the electric field profile for the tapered devices using an intuitive graphical approach and the finite element method and provide estimates for the threshold voltages of tapered devices. Finally, we compare the estimates to the measured values and provide possible reasons for the discrepancies. We believe the capability of threshold voltage reduction with the wedge-shaped tapering design could be useful in device applications. [ABSTRACT FROM AUTHOR]

A direct current-pulse nitrogen atmospheric-pressure plasma jet (APPJ) is used to convert Pt-NiOx nanocompounds from liquid precursor films consisting of a mixture of chloroplatinic acid and nickel acetate. The Pt-NiOx nanoparticles are well-distributed on the fluorine-doped tin oxide (FTO) glass substrates. X-ray photoelectron spectroscopy results indicate that the reaction product mainly contains metallic Pt and oxidized Ni. Electrochemical impedance spectroscopy and Tafel experiments reveal an improvement in electrochemical catalytic effects. The APPJ-processed Pt-NiOx nanocompounds on FTO glass substrates are used as the counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). J − V curves indicate that DSSCs with 5-s APPJ-processed Pt-NiOx CEs showed significantly improved performance. The sample properties become stable after ∼45 s of APPJ calcination. Precursor solutions with three different mole ratios of chloroplatinic acid and nickel acetate are investigated. With the addition of an adequate amount of oxidized nickel, the transfer charge current density and electrochemical catalytic effects are enhanced. [ABSTRACT FROM AUTHOR]

Silicon-vacancy (SiV) centers were produced in single crystalline diamond (SCD) and ultrananocrystalline diamond (UNCD) nanostructures via Si ion implantation or in situ Si doping. SiV-embedded UNCD (SiV-UNCD) was fabricated by both top-down and bottom-up methods. The spectral properties of the SiV centers, including the zero phonon line (ZPL) width and decay time, were investigated in the SCD and UNCD nanostructures. All the SiV-UNCD nanostructures showed bright emission regardless of the preparation method. However, the decay time of the SiV centers was affected by the synthesis procedure. A SiV decay time of τ ∼ 0.19 ns was observed for UNCD nanostructures formed by in situ doping, whereas the SiV decay time was ∼0.43 ns for SiV-UNCD clusters prepared by Si ion implantation into UNCD deposited on Ti/sapphire substrates. The ultrasonication of UNCD clusters on Ti/sapphire pyramids produced bright SiV-UNCD nanoclusters with sizes of ∼50 nm, a ZPL width of 13.5 nm, and a decay time of 0.35 ns, suggesting promising potential in bioimaging applications. SiV-containing SCD (type Ia or type IIa) showed enhanced SiV spectral properties with a ZPL width of 6.08 nm and longer decay time of 1.3 ns. [ABSTRACT FROM AUTHOR]

Ion implantation is used to create nanodiamonds (NDs) with embedded magnetic ions for use in a wide range of biological and medical applications; however, the effectiveness of this process depends heavily on separating magnetic NDs from nonmagnetic ones. In this study, we use secondary ion mass spectrometry to verify the implantation of magnetic ions in NDs and the success of separation. When applied to a series of NDs with embedded iron or manganese ions, the sorting tool used in this study proved highly effective in selecting magnetic NDs. Besides, multienergy ion implantation and precise thickness control of NDs coating on the silicon wafer were suggested to improve this technology. [ABSTRACT FROM AUTHOR]

In this study, strong optomechanical (OM) coupling is proposed through the introduction of a slot in a dual-beam phoxonic crystal cavity structure. The structure can support a confined optical slot mode and localized phononic cavity modes to interact effectively through the slot surfaces. In addition to using conventional OM coupling rates for evaluating the coupling strength of photonic and phononic modes, we consider the optical forces induced by the optical slot mode to discuss the coupling between different mode pairs and the underlying mechanisms of the strong OM coupling. The optical field can induce radiation pressure and electrostrictive forces in the structure. We demonstrate that the radiation pressure dominates the coupling enhancement of photonic and phononic modes because of the slot, whereas the electrostrictive surface pressure plays a minor role and the electrostrictive body force has a negligible contribution. On the basis of the optical forces, we can then calculate the acoustic phonon spectrum through optical excitation. The spectrum indicates the appearance of strong OM coupling in the additional phononic cavity modes. The results suggest that the slot dual-beam cavity structure can be a promising choice for tailoring effective optical forces in micro- and nano-optomechanical systems for enhancing OM coupling. [ABSTRACT FROM AUTHOR]

Hybrid organic-inorganic lead halide perovskite materials show great promise in a number of optoelectronic applications, including solar cells, light emitting diodes, and photodetectors. Understanding their intrinsic material properties is critical to enhancing device performance and enabling innovative material and device designs. Here, we study lattice dynamics using far-infrared (FIR) reflectance and photogenerated carrier dynamics using surface photovoltage (SPV) measurements on high-quality methylammonium lead bromide (MAPbBr3) single crystals. FIR reflectance shows three coherent infrared-active phonon modes between 40 and 200 cm−1 that result in reststrahlen bands with much higher peak reflectance than has been previously reported. The phonon mode strength and damping are comparable to classical oxide perovskite single crystals. However, the effects of defects on photogenerated carrier recombination are still evident in SPV measurements. By performing SPV over different spectral ranges, we are able to separate the effects of surface and bulk defects on the recombination dynamics of photogenerated charge carriers. We further apply SPV measurements to obtain the minority carrier (electron) diffusion length for the MAPbBr3 crystal. This study demonstrates that both FIR reflectance and SPV measurements provide useful information on the electromagnetic response properties of halide perovskite single crystals. [ABSTRACT FROM AUTHOR]

Using light-emitting diodes (LEDs) for visible light communication has become an alternative choice of radio source due to channel crowding of the radio-frequency (RF) signal. The modulation bandwidth of LEDs is usually limited by the spontaneous carrier lifetime in multiple quantum wells. Here, sub-GHz modulation of GaN-based LED employing photonic crystal (PhC) nanostructure is demonstrated. The guided photonic modes of the LEDs are modulated by the RF signal. Both carrier lifetime of lower- and higher-order modes are studied in time-resolved photoluminescence (TRPL) at room temperature. The f-3dB-J curve of the PhC LED exhibits a higher bandwidth than the typical LED structure. At 11.41 kA/cm2, the optical –3-dB bandwidth (f-3dB) up to 234MHz of the PhC LED (PhCLED) is achieved. Our studies on TRPL at different wavelengths and frequency response at different injection current densities conclude that the higher operation speed is attributed to faster radiative carrier recombination of extracted guided modes from the PhC nanostructure. [ABSTRACT FROM AUTHOR]

A study reports about the room-temperature ultraviolet stimulated emission and lasing from optically pumped high-quality ZnO nanowires. Details of the characteristic cavity length that is determined by the Fourier transform of the lasing spectrum are discussed.

We study in this work the growth and fabrication of top-down highly doped n + InAs(Si)/p + GaSb(Si) Esaki tunneling diodes on (001) GaAs substrates. A careful investigation on the highly mismatched GaSb/GaAs growth is first conducted by means of Reflection High-Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and X-Ray Diffraction (XRD) analyses. These results are expected to pave the way to methods for III-Sb buffer layer's integration with low threading dislocation (TD) densities. A comparison between AFM, XRD, defect revealing by chemical etching and transmission electron microscopy (TEM) is then presented to calculate the precise TD density and its influence on the device structure. In the last part, we report on first operating sub-30 nm III-V vertical NW tunneling devices on (001) commercial GaAs substrates. [ABSTRACT FROM AUTHOR]

In0.53Ga0.47As p + n diodes with different densities of extended defects have been analyzed by detailed structural and electrical characterization. The defects have been introduced during Metal-Organic Vapor Phase Epitaxy (MOVPE) growth by using a lattice-mismatched layer on a semi-insulating InP or GaAs substrate. The residual strain and indium content in the n-type In0.53Ga0.47As layer have been determined by high-resolution X-ray diffraction, showing nearly zero strain and a fixed indium ratio of 0.53. The deep levels in the layer have been characterized by Deep Level Transient Spectroscopy. The mean value of electron traps at 0.17 ± 0.03 eV below the conduction band minimum EC is assigned to the "localized" states of α 60° misfit dislocations; another broad electron trap with mean activation energies between EC− 0.17 ± 0.01 and 0.39 ± 0.04 eV, is identified as threading dislocation segments with "band-like" states. A high variation of the pre-exponential factor KT by 7 orders of magnitude is found for the latter when changing the filling pulse time, which can be explained by the coexistence of acceptor-like and donor-like states in the core of split dislocations in III-V materials. Furthermore, two hole traps at EV+ 0.42 ± 0.01 and EV+ 0.26 ± 0.13 eV are related to the double acceptor of the Ga(In) vacancy (VGa/In3-/2-) and 60° β misfit dislocations, respectively. Finally, the dislocation climbing mechanism and the evolution of the antisite defects AsGa/In are discussed for n-type In0.53Ga0.47As. [ABSTRACT FROM AUTHOR]

The impact of intrinsic amorphous silicon bilayers in amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells is investigated. The microstructure factor R* of the interfacial a-Si:H layer, which is related to the Si-H bond microstructure and determined by infrared absorption spectroscopy, is controlled in a wide range by varying the growth pressure and the power density in plasma-enhanced chemical vapor deposition process. Surface passivation at the a-Si:H/c-Si interface is significantly improved by using an intrinsic a-Si:H bilayer, i.e., a stack of an interfacial layer with a large R* and an additional dense layer, particularly after the deposition of an overlying p-type a-Si:H layer. Consequently, the conversion efficiency of a-Si:H/c-Si heterojunction solar cells is markedly increased. However, it is also revealed that such an interfacial layer causes some negative effects including the increase in the series resistance and the current loss at the front side, depending on the growth condition. This result indicates that the interfacial layer has a significant impact on both the majority and the minority carrier transport. Thus, R* of the interfacial layer is an important parameter for obtaining good surface passivation at the a-Si/c-Si interface, but not the sole parameter determining the conversion efficiency of a-Si:H/c-Si heterojunction solar cells. [ABSTRACT FROM AUTHOR]

Read operation induced disturbance in SET-state in a tungsten oxide resistive switching memory is investigated. We observe that the reduction of oxygen vacancy density during read-disturb follows power-law dependence on cumulative read-disturb time. Our study shows that the SET-state readdisturb immunity progressively degrades by orders of magnitude as SET/RESET cycle number increases. To explore the cause of the read-disturb degradation, we perform a constant voltage stress to emulate high-field stress effects in SET/RESET cycling. We find that the read-disturb failure time degradation is attributed to high-field stress-generated oxide traps. Since the stressgenerated traps may substitute for some of oxygen vacancies in forming conductive percolation paths in a switching dielectric, a stressed cell has a reduced oxygen vacancy density in SET-state, which in turn results in a shorter read-disturb failure time. We develop an analytical read-disturb degradation model including both cycling induced oxide trap creation and read-disturb induced oxygen vacancy reduction. Our model can well reproduce the measured read-disturb failure time degradation in a cycled cell without using fitting parameters. [ABSTRACT FROM AUTHOR]

We present a numerical study on phononic band gaps and resonances occurring at the edge of a semi-infinite two-dimensional (2D) phononic crystal plate. The edge supports localized edge waves coupling to evanescent phononic plate modes that decay exponentially into the semi-infinite phononic crystal plate. The band-gap range and the number of edge-wave eigenmodes can be tailored by tuning the distance between the edge and the semi-infinite 2D phononic lattice. As a result, a phononic band gap for simultaneous edge waves and plate waves is created, and phononic cavities beside the edge can be built to support high-frequency edge resonances. We design an L3 edge cavity and analyze its resonance characteristics. Based on the band gap, high quality factor and strong confinement of resonant edge modes are achieved. The results enable enhanced control over acoustic energy flow in phononic crystal plates, which can be used in designing micro and nanoscale resonant devices and coupling of edge resonances to other types of phononic or photonic crystal cavities. [ABSTRACT FROM AUTHOR]

The near band-edge (NBE) luminescence properties of MgZnO powders produced by sol-gel method are comparatively analyzed with those of undoped ZnO powders by temperature-dependent photoluminescence. The increase of the exciton binding energy has resulted from a decrease of the exciton Bohr radius that is responsible for reducing the coupling strength of exciton-longitudinal optical phonon as increasing Mg content.

Piezoelectric force microscopy (PFM) is used to measure the crystal orientation and piezoelectric properties of solution grown ZnO nanorods on Ag films. The rod-to-rod variation is not due to sample topography, but it is speculated that conduction electrons arising from defects and impurities are responsible for the reduced piezoelectric responses in the nanorods.

The electronic properties of delta-doped In0.22Ga0.78As/GaAs quantum wells (QWs) are studied by van der Pauw Hall measurements and Shubnikov-de Haas measurements. From the temperature-dependent van der Pauw Hall measurements, two kinds of donors are observed, which have binding energies of 104 (plusmn) 7 and 9.6 (plusmn) 0.1 MeV.

An investigation on the luminescence characteristics of europium-ion activated Y3Al5O12 phosphors prepared through a sol-gel process is conducted in the vacuum ultraviolet (VUV) region using synchrotron radiation. The results imply that the excitation behavior of the sol-gel derived YAG:[Au.sup.3} phosphors could be tailored by controlling the calcinations temperature and the particle size.

A thin six-walled structure consisting of InGaN/GaN layers in the V defects using HAADF-STEM and field-emission gun scanning electron microscopy (FEG-SEM) imaging is observed. A formation mechanism for the V defects is proposed taking into account the growth kinetics of GaN and the segregation of In atoms in the strain field around the cores of the threading dislocations.

Interdigital electrodes are implemented in many commercial and novel liquid crystal devices to align molecules. Although many empirical principles and patents apply to electrode design, only a few numerical simulations of alignment have been conducted. Why and how the molecules align in an ordered manner has never been adequately explained. Hence, this investigation addresses the Fréedericksz transition of vertically aligned liquid crystal that is driven by fishbone electrodes, and thereafter identifies the mechanism of liquid crystal alignment. Theoretical calculations suggest that the periodic deformation that is caused by the fan-shaped fringe field minimizes the free energy in the liquid crystal cell, and the optimal alignment can be obtained when the cell parameters satisfy the relation p/2d = √k11/k33, where p is the spatial period of the strips of the electrode; d denotes the cell gap; and k11 and k33 are the splay and bend elastic constants of the liquid crystal, respectively. Polymer-stabilized vertical alignment test cells with various p values and spacings between the electrodes were fabricated, and the process of liquid crystal alignment was observed under an optical microscope. The degree of alignment was evaluated by measuring the transmittance of the test cell. The experimental results were consistent with the theoretical predictions. The principle of design, p/2d = √k11/k33, greatly improves the uniformity and stability of the aligned liquid crystal. The methods that are presented here can be further applied to cholesteric liquid crystal and other self-assembled soft materials. [ABSTRACT FROM AUTHOR]

The present work investigated the effect of in-situ Cu solubility on electromigration behavior in the current-stressed Cu/Sn/Cu microjoint. Firstly, we deduced that the in-situ Cu solubility in a current-stressed Cu/Sn/Cu microjoint can be determined by the magnitude relationship between the dissolution Cu flux and the electromigration Cu flux in the current-stressed Sn matrix. And, the in-situ Cu solubility in the current-stressed Sn solder matrix governs the electromigration-induced failure modes of the microCu/Sn/Cu solder joints. If the dissolution Cu flux is larger than the electromigration Cu flux, the equilibrium Cu solubility can be maintained in the Sn solder matrix, and the electromigration of the Sn host atoms can be retarded. Thus, no electromigration-induced voids could occur in the Sn solder matrix. Only electromigration-induced Cu-pad consumption could be observed at the cathode Sn/Cu interface under this condition. On the other hand, if the dissolution Cu flux is smaller than the electromigration Cu flux, the Cu solute in the Sn matrix phase is depleted by the electromigration Cu flux. Then, the Sn host atoms would electromigrate toward the anode side. Void formation occurs in the Sn matrix phase near the cathode interface.Using the magnitude relationship between the dissolution Cu flux and the electromigration Cu flux, the boundary parameters (critical temperatures and current densities) defining the electromigration-induced failure modes can be obtained. With the obtained boundary parameters, an electromigration-induced failure diagram is constructed, which can distinguish and predict the electromigration-induced failure modes (void formation and Cu-pad consumption) in the microCu/Sn/Cu solder joint. [ABSTRACT FROM AUTHOR]

A feasible "lightning-shaped" zigzag graphene nanoribbon (ZGNR) structure for planar interconnects is proposed. Based on the density functional theory and non-equilibrium Green's function, the electron transport properties are evaluated. The lightning-shaped structure increases significantly the conductance of the graphene interconnect with an odd number of zigzag chains. This proposed technique can effectively utilize the linear I-V characteristic of asymmetric ZGNRs for interconnect application. Variability study accounting for width/length variation and the edge effect is also included. The transmission spectra, transmission eigenstates, and transmission pathways are analyzed to gain the physical insights. This lightning-shaped ZGNR enables all 2D material-based devices and circuits on flexible and transparent substrates. [ABSTRACT FROM AUTHOR]

Quantum Well Infrared Photodetectors (QWIPs) with different structures were characterized for the study of surface plasmon wave coupling. Detailed comparisons between surface plasmon coupled and etched grating coupled devices were investigated. A bias dependence for the enhancement of the responsivity of surface plasmon coupled devices was found, especially for the samples with non-uniform quantum wells. The non-uniform QWIPs with surface plasmon coupling showed an asymmetric enhancement with respect to the bias directions. Stronger enhancements were shown under the biases when a higher effective electric field region is close to the collector. The change of the photocarrier escape probability due to the narrow coupling bandwidth of the surface plasmon wave is attributed to this unexpected bias dependence. [ABSTRACT FROM AUTHOR]

In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship h100iBTO(001)// 〈110〉Ge(001) with the substrate, describing a 45° lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I(001)/ I(002), I(101)/I(002), and I(111)/I(002) derived from ω-2θ scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response. [ABSTRACT FROM AUTHOR]

The influence of ruthenium addition at different doping concentrations on the optical properties and holographic behavior of Bi4Ge3O12 crystals is investigated. The diffraction efficiency increases with increasing of ruthenium content, especially after irradiation by ultraviolet light.

The plasma-enhanced chemical-vapor deposition (PECVD) a-SIN(sub x) films fabricated with different ammonia ratios X(sub g) are optimized to have a high optical gap and low permeability, to be exploited in top emission active matrix organic light-emitting diodes (AMOLEDs). The optimum ratio at a deposition temperature of 100 degree Celsius is SiH4:NH3:N2=10:3:197 standard cubic centimeter per minute (SCCM) and the optical gap is 3:1 eV.

Third-order susceptibility chi(super (3)) in disperse red 1 doped poly(methylmethacrylate) thin films was modulated by using near-resonant optical pumping, and an optically pumped degenerate four-wave mixing (DFWM) experiment was conducted to examine the photoreactive phase conjugation (PC) signals. The experimental results indicated a large anisotropy in PC signals arising from modulus of (chi(super (3))(sub 333))(super 2), and almost isotropic PC signals form modulus of (chi(super (3))(sub 333))(super 2) under s-polarized and p-polarized pump fields.

Raman measurements and photoluminescence (PL) were performed on the metal-organic chemical-vapor deposition epitaxially grown GaN before and after the implantation with Er and Er+O. The Raman peak is attributed to the O-implantation -induced detect complex.

The ability to plastically deform thin-film semiconductor structures on deformable substrate to spherical cap shapes without cracking the semiconductor layers is explored, through experiments and finite element analysis. The study shows strain on the device island after deformation is a function of the island structure, size, and substrate material properties.

The systematic examination of the crystal growth of a sillenite structure with a composition of Bi12(Si(sub 1-x)Ti(sub x))O20 and the corresponding optical characteristics shows that the cutoff wavelength increases and the optical activity decreases linearly depending upon the BTO content in the crystals. For the whole range of the x value, the incongruent melting material Bi12TiO20 (BTO) have been observed to form a solid solution with congruent melting materials Bi12SiO20 (BSO). The addition of BTO also modifies the photorefractive effect. The BTO content also increases the diffraction efficiency of the photorefractive grating.

Multiple component decays of photoluminescence (PL) in InGaN/GaN quantum wells are widely reported. Free exciton behaviors of the three samples at high temperatures are consistent with previously reported transmission electron microscopy results.

A polarization modulation (PM) technique is employed in combination with the near-field scanning optical microscope (NOSM) is used to map the anisotropic stress variations associated with features of a SiN membrane. A method is developed to remove the dichroic contribution from the measured retardance in order to determine the stress variation.

Optical intensity distribution in photonic crystals was mapped using near-field scanning optical microscopy.

A new study analyses the soft baking step of a photolithography process using a coordinates-transform technique.

A detailed description of the charge transfer process in AlGaN/GaN heterostructures is presented.

The photoluminescence (PL) properties and the ordering dependence of the carrier lifetimes of spontaneously ordered Ga0.52 In0.48 P/GaAs are investigated. The PL peak of the indirect transition is blueshifted with increasing excitation power, whereas the PL peak of the direct transition is not.

The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity. [ABSTRACT FROM AUTHOR]