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Different models have been used to evaluate the interfacial Dzyaloshinskii–Moriya interaction (DMI) from the asymmetric bubble expansion method using magneto-optics. Here, we investigate the most promising candidates over a range of different magnetic multilayers with perpendicular anisotropy. Models based on the standard creep hypothesis are not able to reproduce the domain wall (DW) velocity profile when the DW roughness is high. Our results demonstrate that the DW roughness and the interface roughness of the sample layers are correlated. Furthermore, we give guidance on how to obtain reliable results for the DMI value with this popular method. A comparison of the results with Brillouin light scattering (BLS) measurements on the same samples shows that the BLS approach often results in higher measured values of DMI. [ABSTRACT FROM AUTHOR]

Recent investigations using polarimetric decomposition and numerical models have helped to improve the understanding of how radar signals interact with lake ice. However, further research is needed on how radar signals are impacted by varying lake ice properties. Radiative transfer (RT) models provide one method of improving this understanding. These are the first published experiments using the snow microwave RT (SMRT) model to investigate the response of different frequencies (L-, C-, and X-band) at horizontal-horizontal (HH) and vertical-vertical (VV) polarizations using various incidence angles (20°, 30°, and 40°) to changes in ice thickness, porosity, bubble radius, and ice–water interface roughness. This is also the first use of SMRT in combination with a thermodynamic lake ice model. Experiments were for a lake with tubular bubbles and one without tubular bubbles under difference scenarios. An analysis of the backscatter response to different properties indicates that increasing ice thickness and layer porosity have little impact on backscatter from lake ice. X-band backscatter shows increased response to surface ice layer bubble radius; however, this was limited to other frequencies except at shallower incidence angles (40°). All three frequencies display the largest response to increasing root mean square (rms) height at the ice–water interface, which supports surface scattering at the ice–water interface as being the dominant scattering mechanism. These results demonstrate that the SMRT is a valuable tool for understanding the response of backscatter to changes in freshwater lake ice properties and could be used in the development of inversion models. [ABSTRACT FROM AUTHOR]

A method is proposed to determine drain access resistance in saturation region of AlGaN/GaN heterostructure field-effect transistors (HFETs). The variation of drain access resistance is analyzed qualitatively and quantificationally. Comparing with source access resistance, the difference is attributed to the asymmetry of additional polarization charge distribution at AlGaN/GaN interface. Interaction strength between additional polarization charge and gate–drain channel electron is stronger than that of gate–source channel electron. The drain access resistance components corresponding to polarization Coulomb field (PCF) scattering, polar-optical-phonon (POP) scattering, piezoelectric (PE) scattering, and interface roughness (IFR) scattering are obtained quantificationally. POP scattering dominates drain access resistance with the increase of drain–source current, because of hot-electron and hot-POP effect. Moreover, PCF scattering also plays an important role, especially under low drain–source current, because of stronger PCF scattering potential and lower hot-POP temperature. [ABSTRACT FROM AUTHOR]

This article investigates the effect of different temperatures (30 °C, 50 °C, and 70 °C) on the interfacial and electrical insulation properties of 500 kV high voltage direct current (HVDC) cross-linked polyethylene (XLPE) cable factory joint having different roughness levels. The test samples with different interfacial roughness (#80, #400, #1000, #2000, and #0000) were prepared by surface polishing followed by an XLPE injection vulcanization process. At the interface, visible microporous defects were observed. The volume of pits on the sample surface and microporous defects at the interface can be reduced by a smooth interface. Moreover, the smoother interface facilitates space charge accumulation. The dc breakdown strength was nearly the same regardless roughness level at high temperatures. The results show that smooth interfaces help improving insulation properties of cable factory joints at low temperatures. However, the effect of interfacial roughness on insulating properties is weakened at elevated temperatures. [ABSTRACT FROM AUTHOR]

Pavement survey is one of the most important applications for ground penetrating radar (GPR) in civil engineering. In the case of centimeter scale of GPR waves, the influence of interface roughness cannot be neglected and should be taken into account in the radar data model. The objective of this article is to estimate the time-delay in the presence of interface roughness by GPR. Using the property of noncircular signals, we propose a modified orthogonal matching pursuit method to estimate the pavement parameters for both overlapped and nonoverlapped echoes. Compared with subspace-based methods in coherent scenarios, the proposed method can estimate the time delays of backscattered echoes without applying the cumbersome interpolation and spatial smoothing procedures, which are more practical in real applications. The performance of the proposed method is tested on both simulated and experimental data. The estimation results show the good performance of the proposed method. [ABSTRACT FROM AUTHOR]

This paper investigates a feasible nondestructive method for micron-sized kissing defects in the composite insulators, which are commonly utilized in ultra-high voltage (UHV) power grid. In this paper, cylindrical adhesive contact model was established to describe the obvious distortion of ultrasound propagation caused by kissing defects on the polymeric interface of composite insulators. The ultrasonic nonlinearity parameter was measured for each of the kissing defective and intact specimens. Moreover, the theoretical analysis has been proved by the test results on the kissing defective samples, which indicates that the 0.7 μm kissing defects existed in the composite insulators could be successfully recognized by the nonlinear ultrasonic methods and the nonlinearity is reduced by interface roughness. [ABSTRACT FROM AUTHOR]

This article reports the fabrication of a dual-ion beam sputtering (DIBS)-grown MgZnO/CdZnO (MCO)-based gateless heterostructure field-effect transistor (HFET). In addition, this article presents that by introducing a 30-nm yttria spacer layer, the crystallinity of the CdZnO buffer layer can be enhanced and the interface roughness at the heterojunction of the MCO heterostructure can be reduced. Furthermore, the source and drain metal contacts were optimized for the least specific contact resistivity (ρc) yielding metal combination and annealing conditions. The results suggest that the introduction of the yttria spacer layer improves the overall conductance [product of sheet carrier density (ns) and electron mobility (μ)] of MCO up to 3.5 × 11015 V−1 s−1 compared to 9 × 1014 V−1 s−1 in the non-yttria spacer-based MCO. In addition, the drain current (Id)–drain voltage (Vd) characteristic of the as-developed yttria spacer-based MCO HFET shows a high drain current value (~400 mA/mm). These results establish the DIBS-grown MCO heterostructure as a viable option for low-cost HFETs necessary for the fabrication of large-scale HFET-based power and sensor devices. [ABSTRACT FROM AUTHOR]

Co silicide on $\text{n}^{+}$ -Si substrate ($\text{N}_{\text {D}}= {8}\times {10}^{{{19}}}$ cm $^{{-{3}}}$) formed by atomic layer deposition (ALD) Co deposition and subsequent rapid thermal annealing (RTA) was proposed as the contact silicide for aggressively scaled contact technology. ALD-Co silicide formed by RTA of 750° C shows the best contact resistivity ($\rho _{text{c}}$) of ${1.0}\times {10}^{{-{8}}} \Omega $ -cm2 with crystallinity in CoSi2 phase, highly-oriented crystal structure and smooth surface. Compared to physical vapor deposition (PVD, sputter)-Co silicide, ALD-Co silicide shows greatly reduced $\rho _{\text {c}}$ by 76 %. The major difference between ALD- and PVD-Co silicide is the interface roughness between silicide and Si substrate which is 1.004 nm and 2.645 nm respectively. The much reduced interface roughness stems from the atomically smooth Co deposition by ALD and it is the much smoother interface that makes less pronounced roughness induced scattering effect and consequently a lower $\rho _{\text {c}}$. As the technology scales, contact silicide plays an essential role in determining parasitic resistance and ALD-Co silicide exhibits the great potential as the contact silicide beyond 5 nm technology node. [ABSTRACT FROM AUTHOR]

Horizontally stratified media are commonly used to represent naturally occurring and man-made structures, such as soils, roads, and pavements, when probed by ground-penetrating radar (GPR). Electromagnetic (EM) wave scattering from such multilayered media is dependent on the roughness of the interfaces. In this paper, we developed a closed-form asymptotic EM model considering random rough layers based on the scalar Kirchhoff-tangent plane approximation (SKA) model that we combined with planar multilayered media Green’s functions. In order to validate our extended SKA model, we conducted simulations using a numerical EM solver based on the finite-difference time-domain (FDTD) method. We modeled a medium with three layers—a base layer of perfect electric conductor (PEC) overlaid by two layers of different materials with rough interfaces. The reflections at the first and at the second interface were both well reproduced by the SKA model for each roughness condition. For the reflection at the PEC surface, the extended SKA model slightly overestimated the reflection, and this overestimation increased with the roughness amplitude. Good agreement was also obtained between the FDTD simulation input values and the inverted root mean square (rms) height estimates of the top interface, while the inverted rms heights of the second interface were slightly overestimated. The accuracy and the performances of our asymptotic forward model demonstrate the promising perspectives for simulating rough multilayered media and, hence, for the full waveform inversion of GPR data to noninvasively characterize soils and materials. [ABSTRACT FROM AUTHOR]

Normal-incidence echosounder signals are attractive for sediment characterization since they can be done easily and remotely over a large area. However, in addition to being sensitive to sediment type, these measurements are also sensitive to other factors such as layers, scattering, and gradients, which make sediment characterization much more difficult. In this study, a well-characterized set of normal-incidence bottom loss measurements are compared with a finite element model using measured environmental parameters such as sound speed, attenuation, and interface roughness. The acoustic measurements were taken in the midfrequency range (5–10 kHz) during the Target and Reverberation Experiment near the Florida panhandle in May 2013. To make the comparison, two sets of metrics were considered. The first was based on the statistical moments of the acoustic signal, a method commonly used for sediment characterization. The second set of metrics was based on features of the return identified by physical mechanisms. It was determined that the physically derived metrics were more robust for model-data comparison. The three physically derived metrics used were bottom loss, full-width-at-half-maximum (FWHM), and the ratio of the half-width-at-half-maximum (HWHM) before the peak to the HWHM after the peak (i.e., HWHM ratio). The finite-element model allowed for effects such as layering, gradients, and interface roughness to be disambiguated from the bulk sediment parameters, thus identifying the influence of these factors on the normal-incidence echo return. Considering all measured environmental and sediment properties, the model could not account for all of the bottom loss without a substantially lower value for the density than measured. Thus, the sediment was modeled using an effective density, a proxy for poroelastic effects. Although the low density model was consistent for most of the data for all three metrics, several areas of outliers in both FWHM and HWHM ratio indicated that other mechanisms such as volume scattering may be important in some areas. [ABSTRACT FROM AUTHOR]

A cavity is a typical defect in a solid insulator which may cause the appearance of partial discharge (PD) activity in power equipment [1–4]. It is mainly caused by imperfections in the manufacturing process as well as by the creep during equipment operation [5]. In epoxy resin insulators, the creep brings irreversible deformations that increase with time at elevated temperatures and external stress [6,7]. Once a cavity has been formed, the PD can lead to insulation failure. Many studies on PDs in void defects, a type of gas-filled cavity, have been performed by pasting together three epoxy laminates and demonstrated factors that affect their intensity, including void size, shape and interface roughness [8–12]. However, such a test void is quite different in its structure and composition from what we further consider in this article, i.e., cavities appearing during actual insulator operation. Moreover, the pressure in a real cavity is usually very low, because of air leakage and polymerization shrinkage, whereas the test void typically remains under atmospheric pressure. Considering the above mentioned differences, we prepared experimental model insulators, containing various low-pressure cavities. The insulators were manufactured by means of automatic pressure gelation (APG) technique by changing the pressure and temperature during the resin pouring process, which allowed for simulating a more realistic operating environment. [ABSTRACT FROM AUTHOR]

Insulations enhanced with multilayer dielectrics are widely used in many applications. However, the interfaces between the dielectric layers are the weakest regions. Interfacial breakdown occurs frequently at the XLPE/SiR interfaces of DC cable joints or terminations. In this paper, an interface contact model is proposed to analyze the morphology of the XLPE/SiR interface, and the relationship between the interfacial ramped DC breakdown voltage and interface morphology is studied. Based on the interface contact model, the densities of real contact asperities and the percentages of the real contact area of XLPE/SiR interfaces under different levels of roughness and different interface pressures were calculated. Moreover, the interface contact model was verified by the results of an interface contact experiment. Interfacial DC breakdown tests were performed under different levels of roughness and different interface pressures. The interfacial ramped DC breakdown voltage increased from 20.37 to 36.05 kV with the grit number of the sandpaper used to sand the XLPE samples, i.e., 60, 150, 240, and 400. As the interface pressure increased from 0.1 to 0.5 MPa, the interfacial ramped DC breakdown voltage increased from 22.34 to 46.84 kV. The mechanism dictating the relationship between the interfacial ramped DC breakdown voltage and interface morphology was analyzed. The real contact area was considerably smaller than the nominal contact area, and many micro voids were present at the interfaces. These micro voids could be the main channel of interfacial breakdown, and the contact asperities could inhibit breakdown. A higher density and larger average area of real contact asperities results in more obstacles the breakdown encounters and causes the interfacial ramped DC breakdown voltage to be higher. [ABSTRACT FROM AUTHOR]

In civil engineering, ground penetrating radar is a common technique for evaluating the structure and quality of road pavement. This paper focuses on the estimation of the time delay and interface roughness of civil engineering structure, like pavements. The influence of interface roughness is taken into account in the signal model. A modified estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm combined with an interpolated spatial smoothing technique is proposed. It allows us to jointly and efficiently estimate the time delay and interface roughness by ultrawideband radar (the upper frequency up to 8-10 GHz) with low computational complexity. The proposed algorithm is tested on both numerical and experimental data. Simulation and experimental results show the good performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

The sub-band formation in the triangular-like potential well in the channel of a tunnel field effect transistor (TFET) results in a delayed onset of the vertical band-to-band tunneling (BTBT) and in a reduction of the ON-current. Furthermore, the roughness of the oxide/semiconductor interface causes density-of-states (DOS) tails, i.e., a smoothing of the otherwise staircase-shaped 2D DOS in the TFET channel. The impact of interface roughness is modeled semi-classically using Ind’s perturbation approach. The developed model for the combined effect of the channel quantization and interface roughness on TFET performance has been implemented in a commercial device simulator. Simulations of a TFET with predominantly vertical BTBT show that the sharp onset of tunneling, which ideally originates from the 2D–3D DOS matching, is smoothed by the interface roughness. This leads to a degradation of the sub-threshold swing of the transistor with increasing amplitude and decreasing auto-correlation length of the roughness. [ABSTRACT FROM PUBLISHER]

AlGaN/GaN heterostructure FETs with the same gate length and different gate widths were fabricated, and the extrinsic transconductance was measured. The device with a wider gate width shows a lower peak value, but a slower drop of extrinsic transconductance. This phenomenon is attributed to the influence of polarization Coulomb field (PCF) scattering, which originates from the irregular distribution of the polarization charges at the AlGaN/GaN interface. PCF scattering influences the extrinsic transconductance by scattering the electrons in the gate–source channel, thus altering the source access resistance. Different gate widths are accompanied by different PCF scattering intensities, inducing different behaviors of extrinsic transconductance. It demonstrates the possibility to take advantage of PCF scattering to improve the characteristics of GaN devices. [ABSTRACT FROM PUBLISHER]

To achieve higher hard disk drive areal density, the head–disk clearance had been reduced to <2 nm recently. Head–disk interaction monitoring with high sensitivity and resolution is desired to monitor the intense interactions at near-contact and to prevent head–disk contact. In this paper, head–disk interaction monitoring based on the electrostatic force manipulation (EFM) principle is discussed. The mechanisms of the two setups to apply alternating electrostatic force ( F\mathrm {es} ) across the head–disk interface were investigated. It was shown that the distribution of the applied F\mathrm {es} was different for the two setups. This led to further studies of the effects of the F\mathrm {es} distribution on interactions monitoring. The results showed that when an alternating F\mathrm {es} was distributed at the pole region, the magnitude of the electrodynamically excited first-harmonic vibration increased significantly as the gap fly height was reduced. It was very sensitive to spacing change and useful for the head–disk interactions monitoring at the near-contact regime. The second harmonic was found sensitive to head–disk contact. When the alternating F\mathrm {es} was distributed at the slider body, the magnitudes of the first and second harmonics were larger due to larger effective surface area. However, the fly height of the slider body was mainly affected by the protrusion push-up effect, and hence the first and second harmonics showed a reverse trend as compared with the case where F\mathrm {es} was distributed at the pole region. In addition, slider pitch motion was also significantly affected. The effective EFM setup was constructed to demonstrate its effectiveness in head–disk interactions monitoring and contact detection. [ABSTRACT FROM AUTHOR]

This paper discusses the impact of the back-gate bias on the dc, low-frequency noise, and dynamic behavior characteristics of a p-GaN gate high-electron mobility transistor on silicon substrate. This paper is investigated to understand the physical mechanisms of the back-gate terminal modulation of normally OFF GaN power devices. When a negative back-gate bias VB voltage is applied, the 2-D electron gas channel will get closer to AlGaN/GaN heterointerface and interface scattering, such as interface roughness and alloy-disorder scattering will increases significantly, which may be responsible for the increased ON-state resistance ( R\mathrm{{\scriptstyle ON}} ). Meanwhile, the opportunity for the capture of carriers by deep-level traps is reduced and the low-frequency noise is thereby suppressed. Under positive VB bias, R\mathrm{{\scriptstyle ON}} can be reduced but, according to capacitance-voltage measurements and carrier fluctuations extracted from the low-frequency noise spectra, the transported carriers are obviously trapped by the deep-level. [ABSTRACT FROM AUTHOR]

The energy dependence of the interface states (Nss) and relaxation time (\tau) and capture cross section (\sigmap) of Nss in (Au/PVC+TCNQ/p\-Si) heterojunction were investigated using high–low frequency capacitance (CHF-CLF) and conductance method, which contains many capacitance/conductance [C/(G/\omega)-V] plots. The C value of the heterojunction increases with decreasing frequency as almost exponentially due to the existence of Nss between metal and semiconductor. The Nss and \tau values have been obtained in the (0.053-Ev)-(0.785-Ev)-eV energy range by considering the voltage-dependent surface potential obtained from the lowest measurable frequency C-V curve at 1 kHz. The magnitude of Nss ranges from 3.88\times 10^12~eV^-1cm^-2 to 3.24\times 10^12~eV^-1cm^-2. In the same energy range, the value of \tau ranges from 5.73\times 10^-5 to 1.58\times 10^-4~s and shows almost an exponential increase with increasing bias from the top of the valance band edge toward the midgap of semiconductor. The obtained Nss values from CHF{-}CLF and conductance methods are in good agreement with each other for the heterojunction. As a result, the mean value of Nss was found on the order of 10^12~eV^-1cm^-2 and this value is very suitable for an electronic device. [ABSTRACT FROM AUTHOR]

GeOx/Ge interfaces are fabricated by plasma postoxidation of Al2O3Ge (100) structures at 300^\circC and room temperature (RT). It is found that reduction of oxidation temperature results in a significant decrease of the GeOx/Ge interface roughness and a slight increase of the interface trap density. The Ge p- and n-channel MOSFETs with the GeOx/Ge interfaces oxidized at the RT provide 20% and 25% enhancement, respectively, of high field hole and electron mobilities than those of MOSFETs oxidized at 300^\circC. This mobility enhancement is attributable to the reduction of GeOx/Ge interface roughness, which has been proven by theoretical calculation of surface-roughness-limited mobility using the real MOS interface roughness directly extracted from transmission electron microscopy results. As a result, high hole and electron mobility of 179 and 378 cm^2/Vs, respectively, have been obtained at a Ns of 10^13~cm^-2 in MOSFETs fabricated by the RT plasma postoxidation. [ABSTRACT FROM AUTHOR]

One of the major efforts in reducing fly height (FH) in order to achieve higher recording areal density for hard disk drive, is to reduce slider-disk interfacial roughness. However, as roughness improves to the atomically smooth level, various interaction forces such as van der Waals force, electrostatic force, and intermittent contact force affect slider fly stability. In this paper, an electrostatic force manipulation methodology was employed to investigate roughness effect on slider-disk interactions at near-contact regime. In such methodology, an AC excitation with pre-determined frequency was applied across the slider-disk interface. First harmonic vibration response of the excitation was monitored. Such vibration response is sensitive to various interaction forces, as FH is reduced to near-contact regime. The phenomena observed were verified with static and dynamic simulations, using self-developed ABsolution simulation software. It was found that disk with higher roughness has larger adhesive force gradient and hence larger first harmonic vibration at near-contact. First harmonic vibration dip was observed near touchdown point. Simulation result suggests that the phenomenon is due to time-averaging effect of slider intermittently “snap” to the disk surface. It was found that magnitude of the vibration dip is surface roughness dependent. At contact regime, nonlinear contact stiffness-based contact detection is highly sensitive for smooth surface. Abrupt transition of low to high vibration state of smooth surface during contact is attributed to larger adhesion hysteresis effect. [ABSTRACT FROM PUBLISHER]

In order to obtain the average surface roughness R a of the long-term operating conductors in service, the features of 2-D surface morphologies were investigated based on the gray value matrix G. The neighborhood averaging method was utilized in obtaining G. In a wide range of R a, a linear relationship was discovered between the variance F and R a. Therefore, R a could be obtained based on the images from the camera and G without the need to dismantle the conductors in service, and it is more time saving and economical for the measurements. [ABSTRACT FROM AUTHOR]

We propose a low-temperature nickel silicidation with a dopant segregation approach to form shallow anode profiles in thin wafer insulated-gate bipolar transistors (IGBTs). The process provides an anode with a boron peak concentration of 3\times 10^19 /cm ^3 after annealing at 400 °C. The silicidation results in a NiSi phase with a strong interface roughness, independent of the polishing process after grinding. The devices exhibit characteristics comparable with the state-of-the-art IGBTs in terms of voltage drop ( $V_{{\rm {CE,{{\rm ON}}}}}$ ), which indicates that a higher anode activation was achieved at low temperature in comparison with the reference samples, since the anode is <27% of its initial thickness. Devices that underwent chemical mechanical planarization exhibit higher $V_{{\rm {CE,{{\rm ON}}}}}$ than those without, possibly due the increase of surface roughness. [ABSTRACT FROM AUTHOR]

The origin and the effect of topological coupling induced by interfacial roughness in spin valve type multilayers have been investigated. The upper bound of the coupling field, which is scale invariant, is predicted by a simplified model using a uniform magnetization approximation. Macroscopic sandwich structures ("macrosteps") of various complexity were fabricated to test these predictions. The coupling field was determined from the shift of the "free layer" B-H loop, or the difference in apparent coercivities. The dependence of the magnitude and the sign of the coupling on the characteristics of the roughness was measured. Implications for real spin valve films and devices are discussed, as well as the potential application of the "macrosteps", or artificial roughness, to provide desired coupling between films. [ABSTRACT FROM PUBLISHER]

The role of dislocation scattering in electron mobility in ZnMgO/ZnO heterostructures was studied. It was found that dislocation scattering was dominant in the low-electron concentration region. The total low-temperature mobility was calculated by considering dislocation scattering and interface-roughness scattering (IRS) together. The sheet density of dislocations was chosen as Ndis=1.5\times 10^8~\rm cm^-2 and the IRS parameters were \Delta=5.206 and \Lambda=30~\rm\AA. We obtained a good fit between our calculated results and experimental data reported in the works referenced. [ABSTRACT FROM AUTHOR]

The effect of structural imperfections such as interface roughness and layer strain on the sign and amplitude of the interlayer coupling between the two ferromagnetic layers of exchanged-biased NiFe/Cu/NiFe/FeMn spin valves is discussed. Two distinct regimes are found: when the NiFe-Cu interface is smooth, with a mean roughness smaller that 4 /spl Aring/, the interlayer coupling shows a distinct oscillatory behavior, with a period of /spl Lambda/=13.5 /spl Aring/, and can be well described by a RKKY-like exchange based mechanism. As the amplitude of the interface roughness increases the magnetostatic-type Neel's orange peel coupling becomes more important, and the ferromagnetic component of the coupling is enhanced. The higher than expected period of oscillation, observed in these spin valves, is explained in terms of a strain induced effect. [ABSTRACT FROM PUBLISHER]

In our original work [1], Table II of page 2300208–4 should be replaced by the following: [ABSTRACT FROM PUBLISHER]