Nontrivial Raman Characteristics in 2D Non-Van der Waals MoN.

Resonant Raman spectra of a two-dimensional (2D) non-van der Waals (vdW) material, molybdenum nitride (MoN), are measured across varying thicknesses, ranging from a few to tens of nanometers. Fifteen distinct Raman peaks are observed experimentally, and their assignments are made using first-principles calculations for the most stable AABB-stacking structure of MoN. The assignments are further supported by angular-dependent Raman measurements for all peaks, except the most intense one at 215 cm.

Universal Ensemble-Embedding Graph Neural Network for Direct Prediction of Optical Spectra from Crystal Structures.

Optical properties in solids, such as refractive index and absorption, hold vast applications ranging from solar panels to sensors, photodetectors, and transparent displays. However, first-principles computation of optical properties from crystal structures is a complex task due to the high convergence criteria and computational cost. Recent progress in machine learning shows promise in predicting material properties, yet predicting optical properties from crystal structures remains challenging due to the lack of efficient atomic embeddings.

Highly Efficient Photon Energy Conversion and Ultrasensitive Self-Powered Photodetection via a Monolithic p-3C-SiC Nanothin Film on p-Si/n-Si Double Junction.

The pursuit of increased efficiency of photoelectric energy conversion through optimized semiconductor structures remains highly competitive, with current results yet to align with broad expectations. In this study, we discover a significant enhancement in photocurrent performance of a p-3C-SiC nanothin film on p-Si/n-Si double junction (DJ) heterostructure that integrates p-3C-SiC/p-Si heterojunction and p-Si/n-Si homojunction. The vertical photocurrent (VPC) and vertical photoresponsivity exhibit a substantial enhancement in the DJ heterostructure, surpassing by a maximum of 43-fold compared to the p-3C-SiC/n-Si single junction (SJ) counterpart.

Field-free deterministic switching of all-van der Waals spin-orbit torque system above room temperature.

Two-dimensional van der Waals (vdW) magnetic materials hold promise for the development of high-density, energy-efficient spintronic devices for memory and computation. Recent breakthroughs in material discoveries and spin-orbit torque control of vdW ferromagnets have opened a path for integration of vdW magnets in commercial spintronic devices. However, a solution for field-free electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room temperatures, essential for building compact and thermally stable spintronic devices, is still missing.

Deep-Ultraviolet and Helicity-Dependent Raman Spectroscopy for Carbon Nanotubes and 2D Materials.

Recent progress of Raman spectroscopy on carbon nanotubes and 2D materials is reviewed as a topical review. The Raman tensor with complex values is related to the chiral 1D/2D materials without mirror symmetry for the mirror in the propagating direction of light, such as chiral carbon nanotube and black phosphorus. The phenomenon of complex Raman tensor is observed by the asymmetric polar plot of helicity-dependent Raman spectroscopy using incident circularly-polarized lights.

Interacting Phonons between Layers in Raman Spectra of Carbon Nanotubes inside Boron Nitride Nanotubes.

We present the resonant Raman spectra of a single-wall carbon nanotube inside a multiwall boron nitride nanotube (SWNT@BNNT). At = 1.58 eV, SWNT@BNNT exhibited resonant Raman spectra at 807 (ω) and 804 cm (ω).

Observing Axial Chirality of Chiral Single-Wall Carbon Nanotubes by Helicity-Dependent Raman Spectra.

Helicity-dependent Raman spectra of an isolated, chiral, single-wall carbon nanotube (SWNT) are reported using circularly polarized light. A polar plot of polarized Raman intensity for the radial breathing mode (RBM), which is excited by left-handed or right-handed circularly polarized light, shows asymmetric angle dependence relative to the nanotube axis direction, which reflects the axial chirality of a SWNT. The asymmetry in the polar plot of the RBM can be analyzed by a complex Raman tensor.

Nonlinear Optical Responses of Janus MoSSe/MoS Heterobilayers Optimized by Stacking Order and Strain.

Nonlinear optical responses in second harmonic generation (SHG) of van der Waals heterobilayers, Janus MoSSe/MoS, are theoretically optimized as a function of strain and stacking order by adopting an exchange-correlation hybrid functional and a real-time approach in first-principles calculation. We find that the calculated nonlinear susceptibility, χ, in AA stacking (550 pm/V) becomes three times as large as AB stacking (170 pm/V) due to the broken inversion symmetry in the AA stacking. The present theoretical prediction is compared with the observed SHG spectra of Janus MoSSe/MoS heterobilayers, in which the peak SHG intensity of AA stacking becomes four times as large as AB stacking.

Charge-Reduced Particles via Self-Propelled Electrohydrodynamic Atomization for Drug Delivery Applications.

Electrohydrodynamic atomization (EHDA) provides unparalleled control over the size and production rate of particles from solution. However, conventional methods produce highly charged particles that are not appropriate for inhalation drug delivery. We present a self-propelled EHDA system to address this challenge, a promising one-step platform for generating and delivering charge-reduced particles.

Vertical Piezo-Optoelectronic Coupling in a 3C-SiC/Si Heterostructure for Self-Powered and Highly Sensitive Mechanical Sensing.

This paper presents a novel self-powered mechanical sensing based on the vertical piezo-optoelectronic coupling in a 3C-SiC/Si heterojunction. The vertical piezo-optoelectronic coupling refers to the change of photogenerated voltage across the 3C-SiC/Si heterojunction upon application of mechanical stress or strain. The effect is elucidated under different photoexcitation conditions and under varying tensile and compressive strains.

Vapor-Phase Indium Intercalation in van der Waals Nanofibers of Atomically Thin WTe Wires.

One-dimensional (1D) conducting materials are of great interest as potential building blocks for integrated nanocircuits. Ternary 1D transition-metal chalcogenides, consisting of MX wires with intercalated A atoms (M = Mo or W; X = S, Se, or Te; A = alkali or rare metals, .), have attracted much attention due to their 1D metallic behavior, superconductivity, and mechanical flexibility.

Complex Raman Tensor in Helicity-Changing Raman Spectra of Black Phosphorus under Circularly Polarized Light.

In anisotropic two-dimensional materials, complex values of Raman tensors are necessary to explain the abnormal linearly polarized Raman spectra. In this work, we measured the helicity-changing Raman spectra of few-layer black phosphorus (BP) excited by circularly polarized light. We observed that the polarized Raman intensities of the modes show a deflection angle that depends on the sample orientation, thickness, and laser excitation energy.

Generation of a Charge Carrier Gradient in a 3C-SiC/Si Heterojunction with Asymmetric Configuration.

It is critical to investigate the charge carrier gradient generation in semiconductor junctions with an asymmetric configuration, which can open a new platform for developing lateral photovoltaic and self-powered devices. This paper reports the generation of a charge carrier gradient in a 3C-SiC/Si heterojunction with an asymmetric electrode configuration. 3C-SiC/Si heterojunction devices with different electrode widths were illuminated by laser beams (wavelengths of 405, 521, and 637 nm) and a halogen bulb.

COVID-19-related music-video-watching among the Vietnamese population: lessons on health education.

Background: Health education through music video plays a vital role in raising a person's knowledge, attitudes, and behaviors positively connected to health during COVID-19 pandemic.

Objective: This study aimed to estimate the prevalence of COVID-19-related music-video-watching and examine associated factors among the Vietnamese population.

Methods: A cross-sectional study in Vietnam was conducted in February 2021 via the Internet.

Selection rule for Raman spectra of two-dimensional materials using circularly-polarized vortex light.

Conservation of spin and orbital angular momenta of circularly-polarized vortex light is discussed for Raman spectra of two-dimensional materials. We first show the selection rule for optical absorption of two-dimensional materials as a function of the spin and orbital angular momentum of incident vortex light. In the case of two-dimensional materials, the Raman tensor for the incident vortex light does not change the symmetry of the phonon mode.

Anxiety among the Vietnamese Population during the COVID-19 Pandemic: Implications for Social Work Practice.

The COVID-19 pandemic is a global health crisis and threatening human lives, especially vulnerable groups. This study aimed to estimate the prevalence of self-reported anxiety and to examine associated factors among the Vietnamese population during the COVID-19 pandemic. A cross-sectional study in Vietnam was conducted in April 2020.

Charge-induced electromechanical actuation of two-dimensional hexagonal and pentagonal materials.

Using first-principles calculations, we investigate electromechanical properties of two-dimensional (2D) hexagonal and pentagonal materials as a function of electron and hole dopings, in which 2D materials including graphene, chair-like graphane, table-like graphane, penta-graphene (PG), hydrogenated penta-graphene (HPG), and penta-CN2 are considered. We find that the actuation responses such as actuation strain, stress generated, and work area-density per cycle of the 2D materials in the case of hole doping are substantially larger than those of electron doping. Moreover, the electromechanical properties of the 2D materials can be improved by hydrogenation.

Charge-induced electromechanical actuation of Mo- and W-dichalcogenide monolayers.

Using first-principle density functional calculations, we investigate electromechanical properties of two-dimensional MX (M = Mo, W; X = S, Se, Te) monolayers with the 1H and 1T structures as a function of charge doping for both electron and hole doping. We find that by increasing the atomic number, , of X atoms ( < < ), the work density per cycle of the MX monolayers are increased and decreased for the 1H and 1T structures, respectively. On the other hand, the work density per cycle of the WX monolayers are higher than that of the MoX monolayers for both the 1H and 1T structures.

Inversion domain boundaries in MoSe layers.

Structural defects, including point defects, dislocation and planar defects, significantly affect the physical and chemical properties of low-dimensional materials, such as layered compounds. In particular, inversion domain boundary is an intrinsic defect surrounded by a 60° grain boundary, which significantly influences electronic transport properties. We study atomic structures of the inversion domain grain boundaries (IDBs) in layered transition metal dichalcogenides (MoSe and MoS) obtained by an exfoliation method, based on the aberration-corrected scanning transmission electron microscopy observation and density functional theory (DFT) calculation.