Photo-induced tunability in charge carriers can be proven as a promising alternative approach to traditional electrostatic gating because of its flexibility to operate in noncontact mode. We have established a reversibly tunable optical gating technique on a few-layer black phosphorus (BP) flake by shining a laser beam, with variation in incident power and energy. The laser power-dependent evolution of Raman spectra of the BP flake is compared with the effect of conventional electrostatic gating. The comparison shows identical linear redshift in characteristic vibrational modes; thereby, a correlation between the laser power and induced charge carrier density is established. The transfer characteristics of BP field effect transistor (FET) under varying laser power validate the optical tunability of the gating effect and demonstrate identical variation in charge carrier density, found in conventional back-gated BP FET. KEYWORDS: photogating, electrostatic back gate, layered black phosphorus (BP), laser power, field effect transistor (FET)
Commanding charge carrier diffusion in semiconducting channels requires the precise and realistic experimental realization of electronic energy band alignments at the interfaces and within the channels. We have demonstrated a non-contact and direct way to accurately probe the energy band bending at nanoscale spatial precision on MoS2 flakes laid on gold electrodes by mapping the surface potential landscape at non-equilibrium conditions during carrier injection. By systematically varying the charge carrier injection, the contrast gradient in surface potential profiles is studied along the MoS2 channel. Corresponding interfacial parameters, such as surface electric field ([Formula: see text]), built-in potential ([Formula: see text]), and space charge density ([Formula: see text]), are experimentally determined.
2D van der Waals heterostructure paves a path towards next generation semiconductor junctions for nanoelectronics devices in the post silicon era. Probing the band alignment at a real condition of such 2D contacts and experimental determination of its junction parameters is necessary to comprehend the charge diffusion and transport through such 2D nano-junctions. Here, we demonstrate the formation of the p-n junction at the MoS2/Black phosphorene (BP) interface and conduct a nanoscale investigation to experimentally measure the band alignment at real conditions by means of measuring the spatial distribution of built-in potential, built-in electric field, and depletion width using the Kelvin probe force microscopy (KPFM) technique. We show that optimization of lift scan height is critical for defining the depletion region of MoS2/BP with nanoscale precision using the KPFM technique. The variations in the built-in potential and built-in electric field with varying thicknesses of MoS2 are revealed and calibrated.
Engineering catalytically active sites have been a challenge so far and often relies on optimization of synthesis routes, which can at most provide quantitative enhancement of active facets, however, cannot provide control over choosing orientation, geometry and spatial distribution of the active sites. Artificially sculpting catalytically active sites via laser‐etching technique can provide a new prospect in this field and offer a new species of nanocatalyst for achieving superior selectivity and attaining maximum yield via absolute control over defining their location and geometry of every active site at a nanoscale precision. In this work, a controlled protocol of artificial surface engineering is shown by focused laser irradiation on pristine MoS2 flakes, which are confirmed as catalytic sites by electrodeposition of AuNPs. The preferential Au deposited catalytic sites are found to be electrochemically active for nitrogen adsorption and its subsequent reduction due to the S‐vacancies rather than Mo‐vacancy, as advocated by DFT analysis. The catalytic performance of Au‐NR/MoS2 shows a high yield rate of ammonia (11.43 × 10−8 mol s−1 cm−2) at a potential as low as −0.1 V versus RHE and a notable Faradaic efficiency of 13.79% during the electrochemical nitrogen reduction in 0.1 m HCl.
In article number 2201320, Manpreet Kaur, Kiran S. Hazra, and colleagues report on electron beam based straightening of 2D materials, a step towards their practicality for next generation electronics. In-situ TEM monitoring demonstrates flattening of 2D layers is synchronous with the de-stressing of lattice under e-beam irradiation, and the declination-ridden lattice can be evolved into the uniformly spaced parallel lattice planes in a controlled manner.
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