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We report an updated isothermal equation of state (EoS) of molybdenum (Mo) obtained by compression in beveled and toroidal diamond-anvil cells (DACs). For an improved compression environment, we developed a copper (Cu) pressure-transmitting medium (PTM) for the toroidal diamond-anvil cell samples, as it is a soft metal compared to Mo with a well calibrated EoS. A Ne PTM was used for the conventional beveled DAC samples. The unit-cell volumes of Mo were measured to 336(1) GPa in the Cu PTM and 231.2(6) GPa in the Ne PTM at room temperature. We additionally calculated elastic stiffness and compliance constants and evaluated the uniaxial stress of Mo and Cu with pressure. A new EoS for Mo is presented from data collected in all sample environments and compared to our theoretical predictions as well as previous compression studies of Mo. The (200) lattice plane of Mo produced the lowest volumes across the pressure range of this study for all compression environments, suggesting that it is less affected by nonhydrostatic stresses in the DAC compared to the other observed diffraction planes. The presented Mo EoS is compatible with extrapolations of EoS fits of Mo in helium (He) within ∼1% at 330 GPa. Results from this work demonstrate that compressing a sample in a softer metal in the toroidal DAC can improve the compression environment and result in measured sample volumes comparable to those collected in noble-gas media at multi-megabar conditions. [ABSTRACT FROM AUTHOR]

Grazing incidence x-ray diffraction reveals that conventional post-deposition-annealed ZrO2 and in situ crystallized (by local epitaxy) ZrO2 thin films (<15 nm) have different internal strain states. A comparison between single- and two-step grown films enables the diverse strain components to be discretely identified. In particular, thickness-dependent intrinsic growth strain is unevenly distributed within the film according to the Volmer–Weber growth. Furthermore, extrinsic thermal strain, locally present in the annealed seed layer, does not spread over the in situ crystallized upper main layer of the two-step film. Post-deposition annealing of the two-step film renders the strain state identical to the single-step films by imposing thermal strain on the in situ crystallized main layer. Local strains created by diffused aluminum and yttrium dopants are also examined. Since each stress factor plays a vital role in the phase formation and electrical behaviors of ZrO2 and other fluorite-structure films, this method will pave the way for understanding the film's internal strain distribution and accompanying performance engineering. [ABSTRACT FROM AUTHOR]

Hyperdoped silicon is a promising material for near-infrared light detection, but to date, the device efficiency has been limited. To optimize photodetectors based on this material that operate at room temperature, we present a detailed study on the electrical nature of gold-hyperdoped silicon formed via ion implantation and pulsed-laser melting (PLM). After PLM processing, oxygen-rich and gold-rich surface layers were identified and a wet etch process was developed to remove them. Resistivity and Hall effect measurements were performed at various stages of device processing. The underlying gold-hyperdoped silicon was found to be semi-insulating, regardless of whether the surface gold was removed by etching or not. We propose a Fermi level pinning model to describe the band bending of the transformed surface layer and propose a promising device architecture for efficient Au-hyperdoped Si photodetectors. [ABSTRACT FROM AUTHOR]

As the channel lengths of electronic devices are scaled down to the nanometer range, the conventional methods to evaluate charge-carrier mobility approach a technical limit that is imposed by interfering effects of the electrode and forcing field. In this study, we demonstrate that electron spectroscopy provides additional (yet hidden) information on unipolar charge transport, which is free from conventional problems. We demonstrate that the estimated effective diffusion current through the target sample allows the measurement that is precise enough (10−4 cm2/V s) to obtain the mobility of electrons μelectron and holes μhole in nanolength organic channels. Using this method, we show how μelectron and μhole are correlated with the local structural order of poly(3-hexylthiophene) at the nanoscale. This method enables in situ charge-resolved observations of μelectron and μhole by eliminating the need for electrode and forcing field and will help to expand our understanding of charge conduction in nanoscale materials. [ABSTRACT FROM AUTHOR]

Germanium–tin (GeSn) alloys at sufficiently high Sn concentration, above several atomic percent, are the only group IV semiconductor exhibiting a direct bandgap and have generated much recent interest for optoelectronic applications into the mid-infrared region. Because the large lattice mismatch between GeSn and Si results in considerable strain for thin layers and a high defect density for thicker strain-relaxed layers, most reported GeSn growths incorporate a Ge buffer layer rather than depositing directly on Si substrates. Published reports of GeSn growth directly on Si utilize specialized precursors such as higher order germanes (Ge2H6, Ge3H8, or Ge4H10) or SnD4. In this paper, we report GeSn films with up to 10.6% Sn grown directly on Si substrates by remote plasma-enhanced chemical vapor deposition using GeH4 and SnCl4 precursors. These alloys have been characterized in detail using x-ray diffraction (XRD), transmission electron microscopy (TEM), and Rutherford backscattering spectrometry with channeling (RBS-C), as well as Raman spectroscopy (RS) and optical microscopy. The films studied are almost fully relaxed, with small residual strain observed, particularly in thinner films, and contain a high interface density of misfit dislocations that increases with Sn concentration. The defect density decreases toward the surface. Good agreement is found between the various characterization methods for the Sn content (XRD and RBS-C), lattice parameter measurement (XRD and TEM), and defect characterization (RBS-C, TEM, and RS). Such characterization of GeSn grown directly on Si substrates is essential to allow growth parameters to be optimized for the realization of the attractive optoelectronic properties of these alloys. [ABSTRACT FROM AUTHOR]

We study the W/Cu multilayers as a spin current source and the coherent spin–orbit torques in a Fe layer using the spin-torque ferromagnetic resonance (STFMR) technique. With increasing numbers of layers, the line shape of the STFMR signals changes from predominantly antisymmetric to predominantly symmetric. When using [W(0.5)/Cu(0.5)]5 as a spin current source, the symmetric amplitude increases by a factor of 5 compared to a single W layer. Simultaneously, the effective damping parameter also increases slightly due to enhanced spin pumping. Along with an increasing trend in the damping-like torque efficiency, this suggests that the extrinsic spin Hall effect is enhanced. Concurrently, the antisymmetric amplitude decreases significantly by a factor of 27, which indicates an increase in the field-like torque when multilayers are used as a spin current source. [ABSTRACT FROM AUTHOR]

Localized residual stress and elastic strain concentrations in microelectronic devices often affect the electronic performance, resistance to thermomechanical damage, and, likely, radiation tolerance. A primary challenge for the characterization of these concentrations is that they exist over sub- μ m length-scales, precluding their characterization by more traditional residual stress measurement techniques. Here, we demonstrate the use of synchrotron x-ray-based differential aperture x-ray microscopy (DAXM) as a viable, non-destructive means to characterize these stress and strain concentrations in a depth-resolved manner. DAXM is used to map two-dimensional strain fields between the source and the drain in a gallium nitride (GaN) layer within high electron mobility transistors (HEMTs) with sub- μ m spatial resolution. Strain fields at various positions in both pristine and irradiated HEMT specimens are presented in addition to a preliminary stress analysis to estimate the distribution of various stress components within the GaN layer. γ -irradiation is found to significantly reduce the lattice plane spacing in the GaN along the sample normal direction, which is attributed to radiation damage in transistor components bonded to the GaN during irradiation. [ABSTRACT FROM AUTHOR]

We investigate robust large-area elastic transverse wave propagation in an actively tunable membrane-type acoustic metamaterial. The waveguide with multiple degrees of freedom to control the width of the interface mode is realized by designing a heterostructure including three domains. One central domain is constructed by periodic unit cells in an ordinary state, where a Dirac cone can be observed in the band structure. The other two domains consist of periodic unit cells possessing opposite valley Chern numbers, respectively. By employing a finite element model, the topologically protected interface states with tunable degrees of freedom are exhibited. The energy of interface states distributes equally in the large-central region. Although a larger degree of freedom leads to lower amplitudes of interface states, larger total energy is demonstrated by defining a quality factor. Moreover, we design several waveguides with straight lines and sharp corners with different angles and denote three different notations to show clearly that the large-area transverse wave can propagate robustly through sharp corners. Finally, it is found that the large-area transverse wave transport shows immunity to disorders and defects in the propagation path. [ABSTRACT FROM AUTHOR]

We demonstrate that the thermal boundary conductivity (TBC) between graphene and GaN-based light-emitting diodes (LEDs) can be manipulated through thermal annealing, which is verified by measuring the acoustic phonons after reflection at the interface. Thermal annealing affects the interfacial morphology as evaluated by both the Raman spectra and the spatial profile of the graphene wrinkles in atomic force microscopy. By tracing the phase of ultrafast acoustic oscillations on the basis of the pump-probe scheme, we extract the phonon reflection coefficient at the interface as a function of annealing temperatures up to 400 ° C. Specifically, the phase shift of transient phononic oscillations at the graphene/LED interface conveys the photoelastic response during the phonon transfer process and can be used for extracting the interfacial coupling rate, which is strongly enhanced around ≈ 200 ° C. By incorporating the heat capacity and the interfacial coupling constants into TBC, along with analytical modeling based on the phonon reflection coefficients, we show that the TBC increases with the minimized surface roughness of graphene side at 200 ° C. This new comprehensive TBC extraction scheme could spark further discussion on improving the heat dissipation of LEDs. [ABSTRACT FROM AUTHOR]

We report the growth of large-scale, single-oriented zinc oxide (ZnO) nanowall networks on epitaxial hexagonal boron nitride (h-BN) films and their application to flexible inorganic ultraviolet (UV) light sensors. Using catalyst-free metal-organic vapor phase epitaxy, ZnO nanowall networks with good vertical alignment are grown on epitaxial h-BN films. The single-oriented crystal structure of the ZnO nanostructures on h-BN is investigated using x-ray diffraction (XRD) spectroscopy, and the heteroepitaxial relationship between ZnO and h-BN is revealed through synchrotron radiation XRD. Interestingly, when utilizing the grown ZnO nanostructure as a channel for UV sensors, better performance merits such as a high IUV/Idark ratio, faster recovery time, and low dark current are achieved if h-BN is employed as a growth template. As an example of inorganic flexible optoelectronic device applications, flexible UV sensors are fabricated using ZnO/h-BN heterostructures owing to the insulating and transferrable nature of h-BN substrates. The sensor maintained an excellent performance, even under highly bent conditions. [ABSTRACT FROM AUTHOR]

Achieving nitride-based device structures unaffected by polarization-induced electric fields can be realized with nonpolar GaN, although polarity plays a key role in the growth. (11 (2) over bar0) a-plane GaN films were grown on (1 (1) over bar 02) r-plane sapphire substrates and subsequently laterally overgrown using metalorganic chemical vapor deposition. Convergent beam electron diffraction analysis was used to determine the a-GaN polarity to explicitly define the film/substrate relationship, and subsequently to identify various growth features and surfaces observed throughout our studies of a-plane GaN. In particular, the effects of polarity on (1) lateral overgrowth from mask stripe openings aligned along [(1) over bar 100](GaN) and (2) pit formation in heteroepitaxial films grown under nonoptimized conditions were investigated. The fundamental differences between the polar surfaces are clearly observed; analysis of the lateral epitaxial overgrowth stripes revealed that (0001) surfaces grew faster than (000 (1) over bar) surfaces by approximately an order of magnitude, and these stable, slow-growing (000 (1) over bar) surfaces are a likely cause of pitting in a-GaN films. The growth features under investigation were imaged using scanning and transmission electron microscopy. (C) 2003 American Institute of Physics.

Topological phononic crystals and acoustic metamaterials have attracted enormous research attention in recent years due to the presence of robust and disorder-immune wave propagation. In this study, a sinusoidal lightweight elastic topological insulator with protected interface modes is investigated at a subwavelength frequency region. By a wave dispersion study, the dual Dirac cones are observed at a subwavelength frequency region due to the employment of two distinct cylinders connected with sinusoidal ligaments. Both cylindrical masses and sinusoidal ligaments are found responsible for opening low-frequency bandgaps that manipulate elastic wave wavelengths almost 30 times larger than the lattice size. Consequently, the subwavelength bandgap closing-and-reopening phenomenon with phase transitions is further captured and opposite signs of the valley Chern numbers are obtained for different structural parameters. A supercell structure is constructed based on the phase transition, and dual topologically protected interface modes (TPIMs) are captured with different quality factors. The comparison of topologically protected interface modes shows that TPIM I is in a higher and wider frequency range, while TPIM II is positioned in a comparatively narrow and extremely low-frequency range. Finally, the robust elastic wave propagation along various designated paths is demonstrated. The proposed lightweight topologically protected phononic lattice may spark future investigation of topological edge states in metadevices at a subwavelength frequency region. [ABSTRACT FROM AUTHOR]

The device and defect characteristics of amorphous indium–gallium–zinc oxide (In:Ga:Zn = 1:1:1 at.%) thin-film transistors (TFTs) as a function of the oxygen partial pressure were investigated. It was found that as the oxygen partial pressure increased, the field effect mobility decreased, the threshold voltage saw a positive shift, and this shift of threshold voltage increased under a negative gate bias stress. From our qualitative analysis of defect states below the conduction band, it was found that as the oxygen partial pressure increased, defect states in the shallow levels decreased, while defect states in the deep levels increased. A quantitative analysis of the defect states in the TFT structures was conducted using photoinduced current transient spectroscopy. It was found that as the oxygen partial pressure used during fabrication of the TFTs increased from 0% to 10% to 60%, the defect states in the shallow levels decreased from 2.74 × 1018 to 2.93 × 1017 to 3.55 × 1016 cm−3, while the defect states in the deep levels increased from non-availability to 1.86 × 1016 to 3.25 × 1016 cm−3. As the oxygen partial pressure increased, the decrease in shallow level defect density is strongly related to a decrease in carrier concentration; the increase in deep level defect density affects the mobility and causes device instability. [ABSTRACT FROM AUTHOR]

We report micromagnetic simulations of spin–orbit torque (SOT) induced magnetization switching of a ferromagnetic layer with perpendicular anisotropy in the absence of an external magnetic field. Field-free switching is achieved by antiferromagnetic interlayer exchange coupling (IEC) between two perpendicular ferromagnetic layers. At appropriate IEC values and an SOT current density exceeding the critical value (Jc), magnetization reversal can be achieved within sub-ns. The complete magnetization reversal of the synthetic antiferromagnetic free layer occurs upon removing the current pulse. Higher damping is preferred for the proposed switching scheme, as Jc decreases with the increase of damping. Remarkably, we also found that Jc has a parabolic dependence on the nanomagnet's diameter, with the vertex occurring at 90 nm. [ABSTRACT FROM AUTHOR]

Amorphous gallium/titanium (Ga,Ti) co-doped indium oxide (In2O3) (GTiIO) films present significant potential as transparent conducting electrodes for use in flexible electronic devices. Amorphous GTiIO films were grown on silicon and glass substrates using linear-facing target sputtering and various oxygen flow rates. Transmittance was as high as 80% in the visible range for O2 flow rates of 0.3, 0.7, and 1.0 SCCM. The lowest resistivity was obtained at f(O2) = 0.3 SCCM with 0.47 mΩ cm. Dielectric functions were determined, and optical gap energies were estimated as close to 3.4 eV using a Tauc formula. We show that Drude tail amplitude is proportional to the carrier density. An electronic transition was found at 2.7 eV from the optical spectra of the thin film at f(O2) = 0 SCCM; this transition was designated to be an inter-conduction band transition from the first to the second conduction band. Using Hall parameters and Drude tail amplitudes in dielectric functions, the effective mass of GTiIO films was determined as 0.398 m0 at f(O2) = 0.3 SCCM. [ABSTRACT FROM AUTHOR]

Following recent successful demonstrations of enhanced infrared absorption in Au-hyperdoped Si, there has been strong interest in fabricating other metal-hyperdoped Si systems as a highly attractive approach for Si-based infrared photodetection. In this work, we address the somewhat contentious issue in the literature as to whether it is possible, using ion implantation and nanosecond pulsed-laser melting, to achieve hyperdoping of Si with Ag and Ti at concentrations exceeding that required to form an intermediate impurity band within the Si bandgap (N IB ∼ 6 × 10 19 cm − 3 ). A wide range of characterization techniques were used to investigate these material systems, especially the quality of liquid-phase epitaxy, impurity concentration distribution both in depth and laterally, and impurity lattice location. Our results indicate that the high concentrations of opto-electrically active Ag or Ti in monocrystalline Si required to form an impurity band are not achieved. In particular, the usual behavior during rapid solidification is for near-complete surface segregation of the impurity, or for it to be trapped within a highly defective subsurface layer due to filamentary breakdown. Although our measurements showed that the maximum concentration of impurities outside metal-rich filaments is comparable to N IB for both Ag and Ti, there is no preferential Ag or Ti lattice location after pulsed-laser melting anywhere in the material. Thus, the concentration of opto-electrically active Ag and Ti that can be homogeneously incorporated into Si is expected to be well below N IB , leaving Au as the only viable impurity to date for achieving the required level of hyperdoping in Si. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM), a non-volatile memory technology, is considered the most promising candidate for storage class memory and neuro-inspired devices. It is generally fabricated based on GeTe–Sb2Te3 pseudo-binary alloys. However, natively, it has technical limitations, such as noise and drift in electrical resistance and high current in operation for real-world device applications. Recently, heterogeneously structured PCMs (HET-PCMs), where phase-change materials are hetero-assembled with functional (barrier) materials in a memory cell, have shown a dramatic enhancement in device performance by reducing such inherent limitations. In this Perspective, we introduce recent developments in HET-PCMs and relevant mechanisms of operation in comparison with those of conventional alloy-type PCMs. We also highlight corresponding device enhancements, particularly their thermal stability, endurance, RESET current density, SET speed, and resistance drift. Last, we provide an outlook on promising research directions for HET-PCMs including PCM-based neuromorphic computing. [ABSTRACT FROM AUTHOR]

In ternary semiconductors, both stacking disorder and cation disorder can cause the formation of polytypes and extended defects. We perform density functional theory calculations to investigate the stability of polytypes in six ternary sulfides, such as CuIn S 2 , CuGa S 2 , CuAl S 2 , AgIn S 2 , AgGa S 2 , and AgAl S 2 . The formation energy of polytypes generated by stacking disorders is used to generate the anisotropic next-nearest neighbor Ising models. The estimated stacking fault energy by the model is in good agreement with the calculated stacking fault energy. The incorporation of Ga and Ag tends to suppress and promote the formation of stacking faults, respectively. On the other hand, the electronic bandgap of the polytypes generated by cation disorder is negatively correlated with the formation energy, resulting in the trapping of charge carriers at antisite domain boundaries. The formation of antisite domain boundaries can be suppressed by the incorporation of Ag and Ga. [ABSTRACT FROM AUTHOR]

In previous studies of shock compression, pressure P , specific volume v , specific internal energy e , shock velocity U s , and particle velocity u p have typically been presented in a dimensional form. For different materials, the plots of P − v , P − u p , or U s − u p , often called Hugoniot curves, are different. Here, we predict the behavior of shock-compressed liquids through proper scaling of the Rankine–Hugoniot (RH) equations and dimensionless Hugoniot curves. The characteristic density and velocity scales are the density ρ 0 and bulk speed of sound c b 0 of the undisturbed liquid, respectively. Two dimensionless numbers arise from the scaled RH equations, one for the initial condition of pressure and the other for the initial condition of internal energy. Under normal conditions, these two numbers do not affect the solutions of the dimensionless RH equations. The dimensionless Hugoniot curves P / (ρ 0 c b 0 2) vs v ρ 0 , U s / c b 0 vs u p / c b 0 , and P / (ρ 0 c b 0 2) vs u p / c b 0 of different liquids merge reasonably well onto a single curve. The dimensionless Hugoniot curve v ρ 0 vs U s / c b 0 or v ρ 0 vs u p / c b 0 , often omitted in the previous work, is thus found to be useful in the understanding of shock compression. The v ρ 0 vs U s / c b 0 curve clearly shows that the dependence of the specific volume ratio v ρ 0 on U s / c b 0 is different for moderate and strong shocks. For a moderate strength shock (U s / c b 0 ≲ 10), a new approximation relation is proposed for shock velocity U s and particle velocity u p as (U s − u p) / c b 0 ≈ (U s / c b 0 ) n , where the exponent is determined empirically as n = 0.55 − 0.6. This new approximation relation is different from the commonly used linear relation between U s and u p and better predicts the behavior of shock-compressed liquids. Using the new approximation relation, the ratio v ρ 0 under moderate strength shocks can be approximated by a power law v ρ 0 ≈ (U s ∗) n − 1 . For stronger shocks, the decrease in the specific volume ratio is slower and is bounded. [ABSTRACT FROM AUTHOR]

The acoustic properties of tetragonal PbxBa1−xNb2O6 (PBN-x) single crystals with x = 0.5 were studied by Brillouin spectroscopy over a wide temperature range from room temperature to 600 °C. Anomalous changes in the Brillouin frequency shift and the half width of acoustic waves were observed at ∼350 °C that corresponds to the ferroelectric–paraelectric phase transition temperature of PBN-0.50. The longitudinal sound velocity and its associated elastic constant (C33) showed substantial softening in the paraelectric phase when the phonon propagated along the polar c axis, while their degree of softening for the phonon along the a axis was small, revealing clear acoustic anisotropy. It was associated with the strong polarization dependence of the quasi-elastic central peak. The relaxation time derived from the central peak seemed to follow the critical slowing-down behavior indicating order–disorder nature of the phase transition. Among C44 and C66, the former displayed substantial softening in the ferroelectric phase resembling the order parameter behavior. The longitudinal sound velocity and the related acoustic damping showed significant anomalies in the ferroelectric phase of unpoled PBN-0.5, which disappeared completely under poled condition. The possible origin for these unexpected acoustic anomalies was suggested. [ABSTRACT FROM AUTHOR]

We present site-dependent Sb-doping effects and optical phonon scattering-limited charge transport properties in a layered chalcogenide SnSe2. It was found that a group V element Sb acts as an electron acceptor at the cation site of Sn and as an electron donor at the anion site of Se in SnSe2 compounds. This phenomenon could be interpreted successfully by analyzing Bader atomic net charge, which is strongly affected by the difference of electronegativity between the elements. The charge transport mechanism in SnSe2, which had been controversial, was found to be optical phonon scattering with T−5/2-dependence, and the bandgap was measured to be ∼1.0 eV. [ABSTRACT FROM AUTHOR]

Understanding the magnetization switching dynamics induced by the spin–orbit torque (SOT) in a ferromagnetic layer is crucial to the design of the ultrafast and energy-saving spin–orbit torque magnetic random access memory. Here, we investigate the SOT switching dynamics of a ferromagnetic layer with in-plane anisotropy with various elliptic sizes in different easy-axis orientations using micro-magnetic simulations. The reliable and ultrafast magnetization switching can be realized by tilting the easy axis to an optimum angle with respect to the current injecting direction. The switching time, in general, decreases smoothly with an increasing current density, and the optimum tilting angle is determined for small device sizes with width smaller than 100 nm. This optimum angle is a small angle deviating from a case when the in-plane easy axis is orthogonal to the current direction. It depends on the size, the current density, and also the damping constant. However, with the device increasing to a certain size (e.g., 250 nm), especially at small tilting angles, we observe chaotic switching behavior where the switching times fluctuate locally with the current density. We attribute this size dependent chaotic switching phenomenon to the nucleation and formulation of complex multi-domains during switching. This chaotic phenomenon can be alleviated by enhancing the field-like torque in the device and thus decreasing the switching times. Consequently, the shape and size of the devices should be carefully taken into account while designing a practical fast switching and low power SOT device with in-plane anisotropy. [ABSTRACT FROM AUTHOR]

Using a multielement antenna, we have performed measurements of the angular dependence of propagating magnetostatic spin waves in a thin yttrium iron garnet film, both in-plane and out-of-plane, and compared the measurements with existing theoretical models. For most magnetic field directions, theory and experiments agree reasonably well. However, there is a range of magnetic field directions where differences between theory and experiment become large. [ABSTRACT FROM AUTHOR]

Hyperdoped Si formed by implantation followed by pulsed laser melting is a promising material for enhanced near-infrared photodetection. To realize the full potential of this material, it is crucial to understand the nature of defects arising from the fabrication process and how these may impact device operation. Here, we identify through deep level transient spectroscopy the presence of a range of defects in the substrate depletion layer that arise from interactions between high dose ion implantation and pulsed laser melting, and investigate their annealing behavior up to 650 ° C. In particular, the detection of a vacancy complex E 1 (0.35) with densities as high as 10 14 cm − 3 indicates that optical transitions between this level and the valence band may compete with the Au donor center, and hence could potentially contribute to the photocurrent in hyperdoped photodiodes. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we investigate the magnetic anisotropy energy (MAE) controlled by applying an external electric field in MgO/CoFe/capping structures. The capping materials include Ta, Hf, Ir, Nb, and Ru. We find that capping materials can tune the magnetic anisotropy via the capping-dependent distribution of d -electrons near the Fermi level and the competition between orbital-related spin–orbit coupling. Moreover, we find that the voltage control of magnetic anisotropy efficiency (VCMAE) (η) of MgO/CoFe/capping structures is also correlated with capping-dependent zero-field d -orbital configuration. Ta, Ir, Nb, and Hf cappings have the η value of − 179, − 149, − 119, and 387 fJ/V m, respectively. In addition, an η value as high as − 894 fJ/V m can be achieved with Ru capping. Our work suggests that capping materials play a key role in tuning MAE, and Ru capping could be used to enhance the VCMAE for voltage-controlled magnetic random access memory. [ABSTRACT FROM AUTHOR]

It is shown using classical molecular dynamics simulations that phonon scattering from disorder in the interatomic forces introduced by charge transfer and not from mass disorder is needed to explain the thermal conductivity reduction experimentally measured that accompanies the addition of a sixth cation to the entropy stabilized oxide J14 [(Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5]. The simulations were performed on five entropy-stabilized oxides, J14, and J14 plus Sc, Sn, Cr, or Ge in equi-molar cation proportions. Comparing the simulation results to predictions from the Bridgman equation using properties from the simulations suggests that despite phonon scattering from disorder in both atomic forces and mass, the thermal conductivity for these systems is still above an analytical limit for an amorphous structure. [ABSTRACT FROM AUTHOR]

We report experiments which characterize spin wave propagation in a thin (111) yttrium iron garnet film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film, we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eshbach mode; these arise from avoided crossings associated with the higher, exchange split, standing wave modes along the film normal, the positions of which correlate with the direct absorption measurements of their positions. This information allows a determination of the exchange parameter. Using this technique, we examine the nonreciprocity in spin wave propagation that results from an adjacent metal layer. [ABSTRACT FROM AUTHOR]

Tetramethylammonium (TMA) cadmium chloride (TMCC), (CH3)4NCdCl3, has four phases with first-order transition temperatures at 104 and 118 K. To investigate the proton dynamics, we performed 1H nuclear magnetic resonance spectroscopy on a single TMCC crystal and measured the spin–lattice relaxation rate 1/T1 and rotating frame relaxation rate 1/T1ρ in the range of 65−300 K at 206.4 MHz under ∼4.8 T. 1/T1 displays an abrupt increase at 111.5 K and 1/T1ρ exhibits a sudden jump between 110 and 120 K. The discontinuities of both 1/T1 and 1/T1ρ across the phase transitions are unique in TMCC and have not been observed in other TMA-based compounds. Above 118 K, the temperature dependence of both T1 and T1ρ is linear, which indicates Arrhenius behavior. Below 118 K, T1 has a single minimum, and both T1 and T1ρ are linear in the low temperature range. This behavior at 206.4 MHz is very different from the double minima observed in T1 at 14.7 MHz for powder TMCC samples and in both T1 and T1ρ for other TMA-based compounds. By fitting two different regimes to the Bloembergen-Purcell-Pound curves, we extract both E a and τ 0 above and below 118 K. By carefully analyzing the T1 and T1ρ data, we ascertain that the coexistence of CH3 and TMA motions displays the double minima, unlike the T1 and T1ρ data at 206.4 MHz. Therefore, we conclude that the only active proton dynamics of TMCC originate from the CH3 rotation, and there is no reorientation of TMA ions, unlike other TMA-based compounds. Both T1 and T1ρ data confirm that the proton dynamics of the CH3 groups suddenly switch from rapid rotation above 118 K to slow rotation below 118 K, with no TMA ion dynamics in TMCC. [ABSTRACT FROM AUTHOR]

A time-resolved optical study of the dynamics of carriers and phonons in Ga(sub 1-x)Mn(sub x)As layers for a series of Mn and hole concentrations. The direct observation on lattice vibrations in Ga(sub 1-x)Mn(sub x)As layers through the reflective electro-optic sampling technique.

The stoichiometry and work function of molybdenum oxide (MoOx) are of crucial importance for its performance as hole selective contact for crystalline silicon solar cells. Hydrogenated amorphous silicon (a-Si:H) is typically used as an interface passivation layer in combination with MoOx to reduce surface recombination. As the fabrication process of a solar cell typically contains subsequent high-temperature processes, the consideration of thermal stability of MoOx with and without a-Si:H becomes critical. In this work, in situ x-ray spectroscopy (XPS)/ultraviolet photoelectron spectroscopy and Fourier transform infrared spectroscopy in the temperature range from 300 K to 900 K are used to investigate the thermal stability of MoOx with and without a-Si:H. In addition, both the passivation and contact performance are studied by evaluating the surface saturation current density J0s, carrier lifetime τeff, and contact resistivity ρc. The XPS results reveal that the as-evaporated MoOx on top of both c-Si and a-Si:H is sub-stoichiometric, and the work function of both films is higher than 6 eV. While after in situ annealing, the evolution of MoOx phase on top of a-Si:H shows a different behavior compared to it on c-Si which is attributed to H diffusion from a-Si:H after 600 K, whereas the work function shows a similar trend as a function of the annealing temperature. The J0s of a p-type Si symmetrically passivated by MoOx is found to be 187 fA/cm2 and the ρc is ∼82.5 mΩ·cm2 in the as-evaporated state. With a-Si interface passivation layer, J0s is significantly lower at 5.39 fA/cm2. The J0s and the ρc increase after post-deposition annealing. The evolution of these functional properties can be attributed to the material properties. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate (KNN) is a lead free ceramic that can potentially replace PZT (Pb(ZrTi)O3). However, KNN suffers from a few major disadvantages. These include the presence of highly volatile alkaline elements and stoichiometry sensitive properties coupled with severe difficulties in controlling the composition. In this work, La doped sodium potassium niobate based perovskite (ABO3) ceramics, more specifically [{(1-x)(K0.5Na0.5)xLa}Nb(1–2x/5)O3] (0 < x < 0.1), have been developed. Among these, the material at 5 mol. % La doping appears with an unusually high density up to 99% of its theoretical value, while densities of the parent K0.5N0.5NbO3 (KNN) ceramics typically only reach ∼70% to 89% of the theoretical limit. The developed ceramics in their circular and rectangular disk form with thickness 0.8 mm show transparency and most importantly, this transparency is electrically tunable up to 52%. Additionally, the material shows sensitivity of its magnetic and optical properties to ultraviolet (UV) irradiation, i.e., these materials transform to a metastable and reversible state that exhibits graded color change from clear to deep blue and shows a considerable increase in magnetization under UV exposure. This feature makes the developed ceramics attractive for the fabrication of new generation devices; e.g., powerless UV detectors as well as protectors, since it absorbs UV completely. Based on first-principles calculations, we developed a model that attributes these observations to the occupancy of La fxyz orbitals induced by UV excitations. The model also indicates that UV induced absorption in the visible range and magnetism are related. [ABSTRACT FROM AUTHOR]

We evaluated the effect of strain on the diffusion process of amorphous alloys related to the strain mode in both as-cast and plastically deformed Zr-based bulk amorphous alloy. Experimental investigations of the diffusion process and the elemental distributions in the amorphous alloy were performed by secondary ion mass spectrometry after annealing at 523K following 30% plastic deformation by multiple cold rolling. Mathematical modeling analyses show an inhomogeneous sequence of the diffusion process by effective strain. The compressive strain near the surface of the deformed amorphous alloy retards ~13.7% of the diffusion process compared to the as-cast amorphous alloy. The combined experimental and mathematical analyses results reveal that the diffusion process of bulk amorphous alloys can be changed by strain variation and can be adjusted by controlling the effective strain during deformation. [ABSTRACT FROM AUTHOR]

Metal-free purely organic phosphorescent molecules are attractive alternatives to organometallic and inorganic counterparts because of their low cost and readily tunable optical properties through a wide chemical design window. However, their weak phosphorescent intensity due to inefficient spin-orbit coupling and, consequently, prevailing non-radiative decay processes limit their practical applicability. Here, we systematically studied phosphorescence emission enhancement of a purely organic phosphor system via plasmon resonance energy transfer. By precisely tuning the distance between purely organic phosphor crystals and plasmonic nanostructures using layer-by-layer assembled polyelectrolyte multilayers as a dielectric spacer, maximum 2.8 and 2.5 times enhancement in photoluminescence intensity was observed when the phosphor crystals were coupled with ~55 nm AuNPs and ~7 nm AgNPs, respectively, at the distance of 9.6 nm. When the distance is within the range of 3 nm, a dramatic decrease in phosphorescence intensity was observed, while at a larger distance, the plasmonic effect diminished rapidly. The distance-dependent plasmon-induced phosphorescence enhancement mechanism was further investigated by time-resolved photoluminescence measurements. Our results reveal the correlation between the amplification efficiency and plasmonic band, spatial factor, and spectral characteristics of the purely organic phosphor, which may provide an insightful picture to extend the utility of organic phosphors by using surface plasmon-induced emission enhancement scheme. [ABSTRACT FROM AUTHOR]

Highly controllable electronic properties (carrier mobility and conductivity) were obtained in the sophisticatedly devised, structure-controlled, boron-doped microcrystalline silicon structure. Variation of plasma parameters enabled fabrication of films with the structure ranging from a highly crystalline (89.8%) to semi-amorphous (45.4%) phase. Application of the innovative process based on custom-designed, optimized, remote inductively coupled plasma implied all advantages of the plasma-driven technique and simultaneously avoided plasma-intrinsic disadvantages associated with ion bombardment and overheating. The high degree of SiH4, H2 and B2H6 precursor dissociation ensured very high boron incorporation into the structure, thus causing intense carrier scattering. Moreover, the microcrystalline-to-amorphous phase transition triggered by the heavy incorporation of the boron dopant with increasing B2H6 flow was revealed, thus demonstrating a very high level of the structural control intrinsic to the process. Control over the electronic properties through variation of impurity incorporation enabled tailoring the carrier concentrations over two orders of magnitude (1018–1020 cm-3). These results could contribute to boosting the properties of solar cells by paving the way to a cheap and efficient industry-oriented technique, guaranteeing a new application niche for this new generation of nanomaterials. [ABSTRACT FROM AUTHOR]

Research describing the characteristics of metal oxide semiconductor capacitors is presented. In particular bulk charges, interface traps and gate oxide reliability are investigated.

Research was conducted to study the temperature and emission angle dependence of photoluminescence from an InGaAs/GaAs quantum well in a microcavity structure. The photoluminescence measurement allowed the spontaneous emission enhancement at the cavity mode to be clearly identified depending on the wavelength separation between the cavity resonance mode and the excitonic emission. Results revealed that the emission wavelength of the cavity mode changes to shorter wavelengths as the emission angle increases.

The effect of cell resolution change on the luminous efficacy of an alternating current plasma display panel with the three-dimensional plasma simulation is examined. The adoption of the geometrical parameters has caused the reduced plasma loss and hence the transport efficacy of visible light from phosphor through the front plate in a full high definition (HD) cell has resulted in increased improvement with the increase of Xe content.

Classical molecular dynamics simulations are used to examine the mechanical responses of several different carbon nanotube systems to applied torsional loading at various temperatures. The simulations have shown that the critical buckling moment can be modified by adjusting the system temperature and through chemical functionalization of the carbon nanotube walls.

The structural and electrical properties of [Bi.sub.2][Mg.sub.2/3][Nb.sub.4/3][O.sub.7] (BMN) pyrochlore thin films are examined for various film thicknesses. The thickness dependence of leakage current characteristics is attributed to the copper diffusion into the BMN films.

A homogeneous crystalline [Sm.sub.2][Ti.sub.2][O.sub.7] (ST) film is grown by radio frequency (rf) sputtering by using an ST ceramic target and their structural and electrical properties are investigated to evaluate their potential use for metal-insulator-metal (MIM) capacitors. The results have shown that the ST film can be used as a high performance MIM capacitor.

A study is done to elucidate the impact of multiple-pulsed laser irradiation on Ni silicide formation in Ni(Ti)/Si system. The empirical outcomes suggest the probability of gaining an optimum laser annealing condition in producing NiSi film using multiple-pulsed laser annealing.

A research of the dynamics of electro-optical switching processes in the biaxial nematic phase of an oxadizole-based bent-core liquid crystal (LC) is done. The results reveal that LC shows optical biaxiality in the lower temperature range of the nematic phase and optical uniaxiality in the higher temperature range.

The intracavity frequency doubling of a diode-pumped vertical-external-cavity surface-emitting lasers (VECSEL) has produced highly efficient blue lasers. The number of quantum wells (QWs) is increased and [Al.sub.0.3][Ga.sub.0.7]As carrier blocking layers are inserted in order to enhance recombination efficiency of the QW and the diamond heat spreader is directly bonded to VECSEL chip by using a capillary action for distilled water in order to solve the thermal problem.

The pentacene field effect transistor (FET) is examined as a Maxwell-Wagner effect element to better understand the details of organic field effect transistor (OFET) operations. Maxwell-Wagner effect causes carriers injected from source electrode to be accumulated at the interface between pentacence and Si[O.sub.2] gate insulator and it is also seen that the FET characteristic are classifiable into there regions depending on the electric field formed in the FET channel.

Thermal stability, frequency response, and refractive indices in a (001)-cut Pb(Zn1/3Nb2/3)0.90Ti0.10O3 (PZNT10%) crystal before and after an electric (E)-field poling, which are important for piezoelectric and optical uses is studied. The dielectric absorption reveals a broad dipolar relaxation in the region of 260-310 K in the unpoled sample.

The effects of the film thickness, average grain size, impurities and morphological defect on the resistivity increase of Cu films are evaluated in addition to the surface scattering of the Fuch-Sondheimer model and the grain boundary scattering of the Mayadas-Shatzkes model. The morphological defects such as a columnar structure with noticeable gaps in the Cu films deposited without the negative substrate bias voltage is shown to have a great influence on the resistivity increase even above the 100 nm thickness.

The effects of pulsed laser-induced annealing of TiN capped Co/Si bilayers with and without premorphized Si substrate are studied. A low fluence of 0.2J/sqcm gives a nostochiometric Co silicide with triple layer structure while highly textured CoSi(sub 2) grains are formed for a high fluence of 0.7J/sqcm and this highly textured layer is noncrystalline and fully coherent with the (111) plane of the Si substrate.

Detailed numerical analyses based on the conventional single-mode rate equations and a carrier heating model were performed to study the nonlinear behavior of a directly modulated 1.55 mum distributed feedback laser diode. The calculated results show the significant impact of band gap shrinkage on simulated results and also show that the carrier heating model is a self-consistent model that naturally describes the gain suppression phenomena in directly modulated laser diodes.