Ultrafast and Broad-Band Graphene Heterojunction Photodetectors with High Gain.

Graphene possesses an exotic band structure that spans a wide range of important technological wavelength regimes for photodetection, all within a single material. Conventional methods aimed at enhancing detection efficiency often suffer from an extended response time when the light is switched off. The task of achieving ultrafast broad-band photodetection with a high gain remains challenging.

Gamma-Ray Irradiation Induced Ultrahigh Room-Temperature Ferromagnetism in MoS Sputtered Few-Layered Thin Films.

Defect engineering is of great interest to the two-dimensional (2D) materials community. If nonmagnetic transition-metal dichalcogenides can possess room-temperature ferromagnetism (RTFM) induced by defects, then they will be ideal for application as spintronic materials and also for studying the relation between electronic and magnetic properties of quantum-confined structures. Thus, in this work, we aimed to study gamma-ray irradiation effects on MoS, which is diamagnetic in nature.

Structural and Superconducting Proximity Effect of SnPb Bimetallic Nanoalloys.

We report the superconducting properties between a conventional strong-coupled Pb and weak-coupled Sn superconductor. A series of SnPb nanoalloys with various compositions r were synthesized, and their superconducting properties were measured using superconducting quantum interference devices (SQUIDs) magnetometer. Our results reveal a superconducting proximity effect (SPE) between immiscible Sn and Pb granules in the range of r = 0.

Precise Sn-Doping Modulation for Optimizing CdWO Nanorod Photoluminescence.

The cadmium tungstate rods have been given much attention due to their potential for usage in numerous luminescent applications. We have prepared single crystalline Sn-doped CdSnWO (where x = 0, 1, 3, and 5%) nanorods (NRDs) and characterized them using refined X-ray diffraction and TEM analysis, revealing a monoclinic phase and a crystallite size that decreased from 62 to 38 nm as Sn concentration increased. Precise Sn doping modulation in CdWO NRDs causes surface recombination of electrons and holes, which causes the PL intensity to decrease as the Sn content rises.

One-pot hydrothermal preparation and defect-enhanced photocatalytic activity of Bi-doped CdWO nanostructures.

In the field of photocatalysis, the suppression of electron-hole recombination through various defects has been an emerging trend to enhance photocatalytic activity. The separation efficiency of electron-hole recombination of well-explored wolframite structured monoclinic CdWO, prepared using the one-pot hydrothermal method, was further improved by Bi doping in CdWO. Studies using the partial density of states illustrated that Bi 6s and 6p orbitals altered the electronic band structure to the extent of lowering the band gap, resulting in more photon absorption.

WSe/WS Heterobilayer Nonvolatile Memory Device with Boosted Charge Retention.

A two-dimensional (2D) nonvolatile memory device architecture to improve the long-term charge retention with the minimum charge loss without compromising storage capacity and the extinction ratio for practical applications has been an imminent demand. To address the current issue, we adopted a novel type-II band-aligned heterobilayer channel comprising vertically stacked monolayer WSe nanodots on monolayer WS. The band offset modulation leads to electron doping from WSe nanodots into the WS channel without any external driving electric field.

Room Temperature Magnetic Memory Effect in Nanodiamond/γ-FeO Composites.

We report a room temperature magnetic memory effect (RT-MME) from magnetic nanodiamond (MND) (ND)/γ-FeO nanocomposites. The detailed crystal structural analysis of the diluted MND was performed by synchrotron radiation X-ray diffraction, revealing the composite nature of MND having 99 and 1% weight fraction ND and γ-FeO phases, respectively. The magnetic measurements carried out using a DC SQUID magnetometer show the non-interacting superparamagnetic nature of γ-FeO nanoparticles in MND have a wide distribution in the blocking temperature.

Phase transformation and room temperature stabilization of various BiO nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species.

We report the grain growth from the nanoscale to microscale and a transformation sequence from Bi →β-BiO→γ-BiO→α-BiO with the increase of annealing temperature. The room temperature (RT) stabilization of β-BiO nanoparticles (NPs) was attributed to the effect of reduced surface energy due to adsorbed carbon species, and oxygen vacancy defects may have played a significant role in the RT stabilization of γ-BiO NPs. An enhanced red emission band was evident from all the samples attributed to oxygen-vacancy defects formed during the growth process in contrast with the observed white emission band from the air annealed Bi ingots.

Structural and Enhanced Optical Properties of Stabilized γ‒BiO Nanoparticles: Effect of Oxygen Ion Vacancies.

We report the synthesis of room temperature (RT) stabilized γ-BiO nanoparticles (NPs) at the expense of metallic Bi NPs through annealing in an ambient atmosphere. RT stability of the metastable γ-BiO NPs is confirmed using synchrotron radiation powder X-ray diffraction and Raman spectroscopy. γ-BiO NPs exhibited a strong red-band emission peaking at ~701 nm, covering 81% integrated intensity of photoluminescence spectra.

Role of cobalt cations in short range antiferromagnetic CoO nanoparticles: a thermal treatment approach to affecting phonon and magnetic properties.

We report the phonon and magnetic properties of various well-stabilized CoO nanoparticles. The net valence in cobalt (II)/(III) cation can be obtained by subtracting the Co ions in tetrahedral interstices and Co ions in the octahedral interstices, respectively, which will possess spatial inhomogeneity of its magnetic moment via Co in tetrahedra and Co in octahedral configurations in the normal spinel structure. Furthermore, the distribution of Co/Co governed by various external (magnetic field and temperature) and internal (particle size and slightly distorted CoO octahedra) sources, have led to phenomena such as a large redshift of phonon-phonon interaction and short-range magnetic correlation in the inverse spinel structure.

Routes to probe Bismuth induced strong-coupling superconductivity in bimetallic BiIn alloys.

We report the observation of strong electron-phonon coupling in intergranular linked BiIn superconductors over an infinite range mediated by low-lying phonons. An enhanced superconducting transition temperature was observed from the magnetization, revealing a main diamagnetic Meissner state below T(0) = 5.86(1) K and a critical field H(0) = 1355(15) Oe with an InBi phase of the composite sample.

Strong Deep-Level-Emission Photoluminescence in NiO Nanoparticles.

Nickel oxide is one of the highly promising semiconducting materials, but its large band gap (3.7 to 4 eV) limits its use in practical applications. Here we report the effect of nickel/oxygen vacancies and interstitial defects on the near-band-edge (NBE) and deep-level-emission (DLE) in various sizes of nickel oxide (NiO) nanoparticles.

Magnetic resonance study of exchange-biased Ni/NiO nanoparticles.

Finite sized Ni/NiO nanoparticles (NPs) are prepared by oxidizing pure Ni-NPs in an ambient atmosphere with varying annealing time (t ). A synchrotron radiation x-ray diffraction technique was used to estimate the grain size, weight fraction and lattice parameters of Ni and NiO. The temperature (T) dependencies of effective g-factor and line-width of ferromagnetic resonance (FMR) spectra for a series of Ni/NiO NPs are determined.

Magnetocrystalline two-fold symmetry in CaFeO single crystal.

Understanding of magnetocrystalline anisotropy in CaFeO is a matter of importance for its future applications. A high quality single crystal CaFeO sample is studied by using synchrotron x-ray diffraction, a magnetometer and the electron spin resonance (ESR) technique. A broad feature of the susceptibility curve around room temperature is observed, indicating the development of 1D spin interactions above the on-set of antiferromagnetic transition.

Strong Pinned-Spin-Mediated Memory Effect in NiO Nanoparticles.

After a decade of effort, a large number of magnetic memory nanoparticles with different sizes and core/shell compositions have been developed. While the field-cooling memory effect is often attributed to particle size and distribution effects, other magnetic coupling parameters such as inter- and intra-coupling strength, exchange bias, interfacial pinned spins, and the crystallinity of the nanoparticles also have a significant influence on magnetization properties and mechanisms. In this study, we used the analysis of static- and dynamic-magnetization measurements to investigate NiO nanoparticles with different sizes and discussed how these field-cooling strengths affect their memory properties.