Helicity-multiplexed metasurfaces based on symmetric spin–orbit interactions (SOIs) have practical limits because they cannot provide central-symmetric holographic imaging. Asymmetric SOIs can effectively address such limitations, with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices. Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently. In this paper, we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon (a-Si:H) nanoresonators. The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness. Two on-axis, distinct wavefronts are produced with high transmission efficiencies, demonstrating the concept of asymmetric wavefront generation in two antiparallel directions. Additionally, the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride (GaN) and titanium dioxide (TiO2) for visible light. The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency, multifunctional, and chip-integrated demonstration of various phenomena.

The MoS2 photodetector on different substrates stacked via van der Waals force has been explored extensively because of its great potential in optoelectronics. Here, we integrate multilayer MoS2 on monocrystalline SiC substrate though direct chemical vapor deposition. The MoS2 film on SiC substrate shows high quality and thermal stability, in which the full width at half-maximum and first-order temperature coefficient for the $E_{2g}^1$ Raman mode are 4.6 cm−1 and −0.01382 cm−1/K, respectively. The fabricated photodetector exhibits excellent performance in the UV and visible regions, including an extremely low dark current of ~1 nA at a bias of 20 V and a low noise equivalent of 10−13–10−15 W/Hz1/2. The maximum responsivity of the MoS2/SiC photodetector is 5.7 A/W with the incident light power of 4.35 μW at 365 nm (UV light). Furthermore, the maximum photoconductive gain, noise equivalent power, and normalized detectivity for the fabricated detector under 365 nm illumination are 79.8, 7.08 × 10−15 W/Hz1/2, and 3.07 × 1010 Jonesat, respectively. We thus demonstrate the possibility for integrating high-performance photodetectors array based on MoS2/SiC via direct chemical vapor growth.

Abstract-Wavelength conversion by difference frequency generation is demonstrated in domain-disordered quasi-phase matched waveguides. The waveguide structure consisted of a GaAs/AlGaAs superlattice core that was periodically intermixed by ion-implantation. For quasi-phase matching periods of 3.0-3.8 µm, degeneracy pump wavelengths were found by secondharmonic generation experiments for fundamental wavelengths between 1520-1620 nm in both type-I and type-II configurations. In the difference frequency generation experiments, output powers up to 8.7 nW were generated for the type-I phase matching interaction, and 1.9 nW for the type-II interaction. The conversion bandwidth was measured to be over 100 nm covering the C, L, and U optical communications bands, which agrees with predictions.

No abstract

As a representative wide bandgap semiconductor material, gallium nitride (GaN) has attracted increasing attention because of its superior material properties (e.g., high electron mobility, high electron saturation velocity, and critical electric field). Vertical GaN devices have been investigated, are regarded as one of the most promising candidates for power electronics application, and are characterized by the capacity for high voltage, high current, and high breakdown voltage. Among those devices, vertical GaN-based PN junction diode (PND) has been considerably investigated and shows great performance progress on the basis of high epitaxy quality and device structure design. However, its device epitaxy quality requires further improvement. In terms of device electric performance, the electrical field crowding effect at the device edge is an urgent issue, which results in premature breakdown and limits the releasing superiorities of the GaN material, but is currently alleviated by edge termination. This review emphasizes the advances in material epitaxial growth and edge terminal techniques, followed by the exploration of the current GaN developments and potential advantages over silicon carbon (SiC) for materials and devices, the differences between GaN Schottky barrier diodes (SBDs) and PNDs as regards mechanisms and features, and the advantages of vertical devices over their lateral counterparts. Then, the review provides an outlook and reveals the design trend of vertical GaN PND utilized for a power system, including with an inchoate vertical GaN PND.

No abstract

A theoretical framework to investigate the accuracy limit of phonon-limited carrier mobility in intrinsic n-type SnSe2 has been developed by solving the Boltzmann transport equation based on ab initio calculated electron-phonon interactions. The electron-phonon coupling matrix elements have been computed using maximally localized Wannier functions and density functional perturbation theory. The intrinsic electron mobility of ∼8.75 cm 2 V −1 s −1 has been achieved at 300 K, incorporating spin-orbit coupling, many-body quasiparticle corrections, and iterative solution of the Boltzmann transport equation using dense sampling of the Brillouin zone. The calculated intrinsic mobility is in close agreement with the experimental values. Furthermore, the electron mean-free path, electrical conductivity, and Seebeck coefficient have been calculated for SnSe2 under varying temperatures. The maximum mean-free path of 20 nm has been achieved for electrons at 300 K. This contribution provides a comprehensive method to investigate the transport properties and presents a framework towards the accuracy limit of prototypical SnSe2.

Background. Work-related musculoskeletal disorders (WMSDs) have a negative impact on quality of life, and dentists are at risk of WMSDs due to the nature of work being static, repetitious, and for a long duration. The study was aimed at measuring the prevalence and distribution of work-related musculoskeletal disorders and determining the risk factors associated with affliction among Pakistani dentists. Methods. An online cross-sectional survey was conducted using a validated questionnaire consisting of four sections. The first section had questions related to sociodemographic information, the second section had questions that assessed the intensity and frequency of musculoskeletal pain (MSP), third section questions were concerned with the effect of MSP on the respondents’ daily life, while the last section contained questions on whether they perceived their work in the dental clinic as a cause of their pain. Chi-square and one-way ANOVA tests were used for the analysis of the data in SPSS-23. Results. A total of 600 completely filled questionnaires were received with a response rate of 76.4%, and about 87% of the dental practitioners had some sort of MSD. The intensity and frequency of WMSDs were statistically significant ( p < 0.05 ) in association with all the sociodemographic characteristics. The lower back area was the most reported site of WMSD pain (51.3%) followed by the neck/upper back (21.3%) and shoulder (17.6%). The site of pain was statistically significant ( p < 0.05 ) in association with all the sociodemographic characteristics except gender ( p = 0.11 ). A majority of participants (95.4%) had sought medical treatment and taken sick leaves (70%) due to WMSDs pain during their life. Participants attributed a number of working years and working posture as the two main reasons behind WMSDs. Conclusion. Considering the high prevalence of WMSDs among dentists, preventive strategies that minimize the occurrence of WMSDs should be adopted by dental professionals. The impact of WMSDs can be reduced by maintaining good posture, taking breaks and rest in between work, doing regular exercise, and improving the work environment.