Band Alignment Transition and Enhanced Performance in Vertical SnS/MoS van der Waals Photodetectors.

The strong light-matter interaction and naturally passivated surfaces of van der Waals materials make heterojunctions of such materials ideal candidates for high-performance photodetectors. In this study, we fabricated SnS/MoS van der Waals heterojunctions and investigated their photoelectric properties. Using an applied gate voltage, we can effectively alter the band arrangement and achieve a transition in type II and type I junctions.

Enhanced NO Sensitivity of Vertically Stacked van der Waals Heterostructure Gas Sensor and Its Remarkable Electric and Mechanical Tunability.

Nanodevices based on van der Waals heterostructures have been predicted, and shown, to have unprecedented operational principles and functionalities that hold promise for highly sensitive and selective gas sensors with rapid response times and minimal power consumption. In this study, we fabricated gas sensors based on vertical MoS/WS van der Waals heterostructures and investigated their gas sensing capabilities. Compared with individual MoS or WS gas sensors, the MoS/WS van der Waals heterostructure gas sensors are shown to have enhanced sensitivity, faster response times, rapid recovery, and a notable selectivity, especially toward NO.

Miniaturized spectrometer with intrinsic long-term image memory.

Miniaturized spectrometers have great potential for use in portable optoelectronics and wearable sensors. However, current strategies for miniaturization rely on von Neumann architectures, which separate the spectral sensing, storage, and processing modules spatially, resulting in high energy consumption and limited processing speeds due to the storage-wall problem. Here, we present a miniaturized spectrometer that utilizes a single SnS/ReSe van der Waals heterostructure, providing photodetection, spectrum reconstruction, spectral imaging, long-term image memory, and signal processing capabilities.

Field Effect Transistor Gas Sensors Based on Mechanically Exfoliated Van der Waals Materials.

The high surface-to-volume ratio and flatness of mechanically exfoliated van der Waals (vdW) layered materials make them an ideal platform to investigate the Langmuir absorption model. In this work, we fabricated field effect transistor gas sensors, based on a variety of mechanically exfoliated vdW materials, and investigated their electrical field-dependent gas sensing properties. The good agreement between the experimentally extracted intrinsic parameters, such as equilibrium constant and adsorption energy, and theoretically predicted values suggests validity of the Langmuir absorption model for vdW materials.

Light-Tunable Polarity and Erasable Physisorption-Induced Memory Effect in Vertically Stacked InSe/SnS Self-Powered Photodetector.

van der Waals heterojunctions with tunable polarity are being actively explored for more Moore and more-than-Moore device applications, as they can greatly simplify circuit design. However, inadequate control over the multifunctional operational states is still a challenge in their development. Here, we show that a vertically stacked InSe/SnS van der Waals heterojunction exhibits type-II band alignment, and its polarity can be tuned by an external electric field and by the wavelength and intensity of an illuminated light source.

Efficient Suppression of Charge Recombination in Self-Powered Photodetectors with Band-Aligned Transferred van der Waals Metal Electrodes.

Recombination of photogenerated electron-hole pairs dominates the photocarrier lifetime and then influences the performance of photodetectors and solar cells. In this work, we report the design and fabrication of band-aligned van der Waals-contacted photodetectors with atomically sharp and flat metal-semiconductor interfaces through transferred metal integration. A unity factor α is achieved, which is essentially independent of the wavelength of the light, from ultraviolet to near-infrared, indicating effective suppression of charge recombination by the device.

Graphene/SnS van der Waals Photodetector with High Photoresponsivity and High Photodetectivity for Broadband 365-2240 nm Detection.

The fabrication of graphene/SnS van der Waals photodetectors and their photoelectrical properties are systematically investigated. It was found that a dry transferred graphene/SnS van der Waals heterostructure had a broadband sensing range from ultraviolet (365 nm) to near-infrared (2.24 μm) and respective improved responsivities and photodetectivities of 7.

Phase analysis on the error scaling of entangled qubits in a 53-qubit system.

We have studied carefully the behaviors of entangled qubits on the IBM Rochester with various connectivities and under a "noisy" environment. A phase trajectory analysis based on our measurements of the GHZ-like states is performed. Our results point to an important fact that entangled qubits are "protected" against environmental noise by a scaling property that impacts only the weighting of their amplitudes.

Giant gauge factor of Van der Waals material based strain sensors.

There is an emergent demand for high-flexibility, high-sensitivity and low-power strain gauges capable of sensing small deformations and vibrations in extreme conditions. Enhancing the gauge factor remains one of the greatest challenges for strain sensors. This is typically limited to below 300 and set when the sensor is fabricated.

Frequency-induced negative magnetic susceptibility in epoxy/magnetite nanocomposites.

The epoxy/magnetite nanocomposites express superparamagnetism under a static or low-frequency electromagnetic field. At the microwave frequency, said the X-band, the nanocomposites reveal an unexpected diamagnetism. To explain the intriguing phenomenon, we revisit the Debye relaxation law with the memory effect.

Enhanced Sensitivity of CO on Two-Dimensional, Strained, and Defective GaSe.

The toxic gas carbon monoxide (CO) is fatal to human beings and it is hard to detect because of its colorless and odorless properties. Fortunately, the high surface-to-volume ratio of the gas makes two-dimensional (2D) materials good candidates for gas sensing. This article investigates CO sensing efficiency with a two-dimensional monolayer of gallium selenide (GaSe) via the vacancy defect and strain effect.

Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS.

Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron-electron and electron-phonon inter-actions, can lead to a new type of electronic band structure. Bulk 2H-TaS is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS and the transition temperature can reach 140 K, which is much higher than that in the bulk.

Photoelectrical properties of graphene/doped GeSn vertical heterostructures.

GeSn is a group IV alloy material with a narrow bandgap, making it favorable for applications in sensing and imaging. However, strong surface carrier recombination is a limiting factor. To overcome this, we investigate the broadband photoelectrical properties of graphene integrated with doped GeSn, from the visible to the near infrared.

STT-DPSA: Digital PUF-Based Secure AuthenticationUsing STT-MRAM for the Internet of Things.

Physical unclonable function (PUF), a hardware-efficient approach, has drawn a lot ofattention in the security research community for exploiting the inevitable manufacturing variabilityof integrated circuits (IC) as the unique fingerprint of each IC. However, analog PUF is notrobust and resistant to environmental conditions. In this paper, we propose a digital PUF-basedsecure authentication model using the emergent spin-transfer torque magnetic random-accessmemory (STT-MRAM) PUF (called STT-DPSA for short).

Enhanced NO Sensitivity in Schottky-Contacted n-Type SnS Gas Sensors.

Layered materials are highly attractive in gas sensor research due to their extraordinary electronic and physicochemical properties. The development of cheaper and faster room-temperature detectors with high sensitivities especially in the parts per billion level is the main challenge in this rapidly developing field. Here, we show that sensitivity to NO () can be greatly improved by at least two orders of magnitude using an n-type electrode metal.

Electrical Contact Barriers between a Three-Dimensional Metal and Layered SnS.

Field-effect transistors derived from traditional 3D semiconductors are rapidly approaching their fundamental limits. Layered semiconducting materials have emerged as promising candidates to replace restrictive 3D semiconductor materials. However, contacts between metals and layered materials deviate from Schottky-Mott behavior when determined by transport methods, while X-ray photoelectron spectroscopy measurements suggest that the contacts should be at the Schottky limit.

Photon-assisted spin transport in blue phosphorene nanotubes.

We have investigated photon-assisted spin injection into blue phosphorene nanotubes (PNTs) with ferromagnetic cobalt electrodes by nonequilibrium Green's function combined with light-matter interaction based on the first-order Born approximation. The results show the photo-induced spin current. The spin up and spin down photocurrents flow in opposite directions for zigzag blue nanotubes (ZPNTs) with anti-parallel magnetic configuration of the electrodes.

Enhanced NO Sensing at Room Temperature with Graphene via Monodisperse Polystyrene Bead Decoration.

Graphene is a single layer of carbon atoms with a large surface-to-volume ratio, providing a large capacity gas molecule adsorption and a strong surface sensitivity. Chemical vapor deposition-grown graphene-based NO gas sensors typically have detection limits from 100 parts per billion (ppb) to a few parts per million (ppm), with response times over 1000 s. Numerous methods have been proposed to enhance the NO sensing ability of graphenes.

High Selectivity Gas Sensing and Charge Transfer of SnSe.

SnSe is an anisotropic binary-layered material with rich physics, which could see it used for a variety of potential applications. Here, we investigate the gas-sensing properties of SnSe using first-principles calculations and verify predictions using a gas sensor made of few-layer SnSe grown by chemical vapor deposition. Theoretical simulations indicate that electrons transfer from SnSe to NO, whereas the direction of charge transfer is the opposite for NH.

Dielectric relaxation of the double perovskite oxide BaPrRuO.

Samples of BaPrRuO were prepared by the solid state reaction method and the structure was characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and dielectric measurements were performed in order to investigate the morphology and electric properties of the ceramics. X-ray diffraction data reveal that the BaPrRuO samples are of the cubic crystal structure with the space group 3̄ at room temperature.

Strategy for Fabricating Wafer-Scale Platinum Disulfide.

PtS is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films.

Photo-enhanced gas sensing of SnS with nanoscale defects.

Recently a SnS based NO gas sensor with a 30 ppb detection limit was demonstrated but this required high operation temperatures. Concurrently, SnS grown by chemical vapor deposition is known to naturally contain nanoscale defects, which could be exploited. Here, we significantly enhance the performance of a NO gas sensor based on SnS with nanoscale defects by photon illumination, and a detection limit of 2.

Curvature induced quantum phase transitions in an electron-hole system.

In this work, we study the effect of introducing a periodic curvature on nanostructures, and demonstrate that the curvature can lead to a transition from a topologically trivial state to a non-trivial state. We first present the Hamiltonian for an arbitrarily curved nanostructure, and introduce a numerical scheme for calculating the bandstructure of a periodically curved nanostructure. Using this scheme, we calculate the bandstructure for a sinusoidally curved two-dimensional electron gas.

Inherent orbital spin textures in Rashba effect and their implications in spin-orbitronics.

The Rashba effect gives rise to the key feature of chiral spin texture. Recently it was demonstrated that the orbital angular momentum (OAM) texture forms the underlying basis for Rashba spin texture. Here we solve a model Hamiltonian of a generic p-orbital system in the presence of crystal field, internal spin-orbit coupling (SOC) and inversion symmetry breaking (ISB), and demonstrate, in addition to OAM and spin texture, the existence of orbital projection (OP) of the spin texture in a general Rashba system.

Debye formulas for a relaxing system with memory.

Rate (master) equations are ubiquitous in statistical physics, yet, to the best of our knowledge, a rate equation with memory has previously never been considered. We write down an integro-differential rate equation for the evolution of a thermally relaxing system with memory. For concreteness we adopt as a model a single-domain magnetic particle driven by a small ac field and derive the modified Debye formulas.