The influence of interfacial tensile strain on the charge transport characteristics of MoS2-based vertical heterojunction devices

Pulsed Laser Phosphorus Doping and Nanocomposite Catalysts Deposition in Forming a-MoSx/NP-Mo//n+p-Si Photocathodes for Efficient Solar Hydrogen Production

Pulsed laser deposition of nanostructured molybdenum sulfide films creates specific nonequilibrium growth conditions, which improve the electrocatalytic properties of the films in a hydrogen evolution reaction (HER). The enhanced catalytic performance of the amorphous a-MoS_x (2 ≤ x ≤ 3) matrix is due to the synergistic effect of the Mo nanoparticles (Mo-NP) formed during the laser ablation of a MoS₂ target. This work looks at the possibility of employing a-MoS_x/NP-Mo films (4 and 20 nm thickness) to produce hydrogen by photo-stimulated HER using a p-Si cathode. A simple technique of pulsed laser p-Si doping with phosphorus was used to form an n⁺p-junction. Investigations of the energy band arrangement at the interface between a-MoS_x/NP-Mo and n⁺-Si showed that the photo-HER on an a-MoS_x/NP-Mo//n⁺p-Si photocathode with a 20 nm thick catalytic film proceeded according to a Z-scheme. The thickness of interfacial SiO_y(P) nanolayer varied little in photo-HER without interfering with the effective electric current across the interface. The a-MoS_x/NP-Mo//n⁺p-Si photocathode showed good long-term durability; its onset potential was 390 mV and photocurrent density was at 0 V was 28.7 mA/cm². The a-MoS_x/NP-Mo//n⁺p-Si photocathodes and their laser-based production technique offer a promising pathway toward sustainable solar hydrogen production.

Highly sensitive active pixel image sensor array driven by large-area bilayer MoS2 transistor circuitry

Various large-area growth methods for two-dimensional transition metal dichalcogenides have been developed recently for future electronic and photonic applications. However, they have not yet been employed for synthesizing active pixel image sensors. Here, we report on an active pixel image sensor array with a bilayer MoS2 film prepared via a two-step large-area growth method. The active pixel of image sensor is composed of 2D MoS2 switching transistors and 2D MoS2 phototransistors. The maximum photoresponsivity (Rph) of the bilayer MoS2 phototransistors in an 8 × 8 active pixel image sensor array is statistically measured as high as 119.16 A W-1. With the aid of computational modeling, we find that the main mechanism for the high Rph of the bilayer MoS2 phototransistor is a photo-gating effect by the holes trapped at subgap states. The image-sensing characteristics of the bilayer MoS2 active pixel image sensor array are successfully investigated using light stencil projection.

Ultra-flexible and rollable 2D-MoS2/Si heterojunction-based near-infrared photodetector via direct synthesis

Atomic two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for application in various optoelectronic devices such as image sensors, biomedical imaging systems, and consumer electronics and in diverse spectroscopic analyses. However, a complicated fabrication process, involving transfer and alignment of as-synthesized 2D layers onto flexible target substrates, hinders the development of flexible high-performance heterojunction-based photodetectors. Herein, an ultra-flexible 2D-MoS2/Si heterojunction-based photodetector is successfully fabricated through atmospheric-pressure plasma enhanced chemical vapor deposition, which enables the direct deposition of multi-layered MoS2 onto a flexible Si substrate at low temperature (<200 °C). The photodetector is responsive to near infrared light (λ = 850 nm), showing responsivity of 10.07 mA W-1 and specific detectivity (D*) of 4.53 × 1010 Jones. The measured photocurrent as a function of light intensity exhibits good linearity with a power law exponent of 0.84, indicating negligible trapping/de-trapping of photo-generated carriers at the heterojunction interface, which facilitates photocarrier collection. Furthermore, the photodetectors can be bent with a small bending radius (5 mm) and wrapped around a glass rod, showing excellent photoresponsivity under various bending radii. Hence, the device exhibits excellent flexibility, rollability, and durability under harsh bending conditions. This photodetector has significant potential for use in next-generation flexible and patchable optoelectronic devices.

Reconfigurable Dipole-Induced Resistive Switching of MoS2 Thin Layers on Nb:SrTiO3

The controllable band gap and charge-trapping capability of MoS₂ render it suitable for use in the fabrication of various electrical devices with high-k dielectric oxides. In this study, we investigated reconfigurable resistance states in a MoS₂/Nb:SrTiO₃ heterostructure by using conductive atomic force microscopy. Low-resistance and high-resistance states were observed in all MoS₂ because of barrier height modification resulting from redistribution of charge and oxygen vacancies in the vicinity of interfaces. In a thin layer of the MoS₂ film, the carrier density was high, and layer-dependent transport properties appeared because of the charge separation in MoS₂. The hysteresis and switching voltage of the MoS₂/Nb:SrTiO₃ heterostructure could be varied by controlling the number of layers of MoS₂.

Electronic Spectrum of Twisted Graphene Layers under Heterostrain

We demonstrate that stacking layered materials allows a strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of flat bands in twisted graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs, much more severely, the energy spectrum of TGLs than homostrain for which both layers are strained identically, a result which should apply to virtually all van der Waals structures opening exciting possibilities for straintronics with 2D materials.

A new method for fast statistical measurement of interfacial misfit strain around nano-scale semi-coherent particles

Nanoscale diffraction contrast reveals strain field distribution at a semi-coherent interface.