PN heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current rectifiers, photodetectors, and photovoltaic devices. However, a direct or neardirect bandgap at the heterointerface that can significantly enhance optical generation, for high light absorbing few/multi-layer vdW materials, has not yet been shown. In this work, for the first time, few-layer group-6 transition metal dichalcogenide (TMD) WSe2 is shown to form a sizeable (0.7 eV) near-direct bandgap with type-II band alignment at its interface with the group-7 TMD ReS2 through density functional theory calculations. Further, the type-II alignment and photogeneration across the interlayer bandgap have been experimentally confirmed through micro-photoluminescence and IR 2 photodetection measurements, respectively. High optical absorption in few-layer flakes, large conduction and valence band offsets for efficient electron-hole separation and stacking of light facing, direct bandgap ReS2 on top of gate tunable WSe2 are shown to result in excellent and tunable photodetection as well as photovoltaic performance through flake thickness dependent optoelectronic measurements. Few-layer flakes demonstrate ultrafast response time (5 µs) at high responsivity (3 A/W) and large photocurrent generation and responsivity enhancement at the heterostructure overlap region (10-100×) for 532 nm laser illumination. Large open circuit voltage of 0.64 V and short circuit current of 2.6 µA enables high output electrical power. Finally, long term air-stability and a facile single contact metal fabrication process makes the multi-functional few-layer WSe2/ReS2 heterostructure diode technologically promising for next-generation optoelectronic applications.The semiconducting group-6 TMD WSe2, generally found in trigonal prismatic phase, 17 is an indirect bandgap material in its bulk form. 18,19 However, group-7 TMD e.g. 1T phase of ReS2 is distorted octahedral in structure 17,20 and exhibits direct (or, near-direct) bandgap at (or, close to) the Γ point of the Brillouin zone (BZ). Interestingly, unlike the group-6 TMDs, ReS2 exhibits a unique property owing to its distorted structure and weak interlayer coupling-the direct or near-direct nature of its bandgap remains unchanged from monolayer to bulk. [20][21][22] Closer examination of the bandstructure of group-7 TMDs reveals that the conduction band minimum of ReS2 remains at the Γ point, irrespective of the number of layers. 20,23 But for group-6 TMDs (such as WSe2) the valence band maximum relocates from K to Γ point of the BZ with increasing number of layers. 18,24 It is important to note that the valence band maximum at the Γ point differs in energy only slightly from that at the K point. 18 This gives rise to an increased probability of direct as well as indirect transitions from the Γ and the K valence maxima of WSe2 to the Γ conduction minimum of ReS2 respectively, for a predicted type-II band alignment. The possibility of a direct bandgap transition is not observed in a heter...

Negative Bias Temperature Instability (NBTI) is studied in p-MOSFETs having Decoupled Plasma Nitrided (DPN) gate oxides (EOT range of 12A O through 22A O ). Threshold voltage shift (∆V T ) is shown to be primarily due to interface trap generation (∆N IT ) and significant hole trapping (∆N OT ) has not been observed. ∆V T follows power-law time (t) dependence and Arrhenius temperature (T) activation. IntroductionNBTI is a serious reliability concern for p-MOSFETs [1]. Oxynitrides (required for suppressing boron penetration and gate leakage) show worse NBTI than control oxides and has attracted much attention [2][3][4][5]. It is important to correctly measure and extrapolate t evolution of ∆V T to accurately determine device lifetime. However, this extrapolation is complicated since (i) impact of delay time on measurement is not fully understood, (ii) ∆V T origin (∆N IT that predicts t

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For about the past eight decades, high concentrations of naturally occurring fluoride have been detected in groundwater in different parts of India. The chronic consumption of fluoride in high concentrations is recognized to cause dental and skeletal fluorosis. We have used the random forest machine-learning algorithm to model a data set of 12 600 groundwater fluoride concentrations from throughout India along with spatially continuous predictor variables of predominantly geology, climate, and soil parameters. Despite only surface parameters being available to describe a subsurface phenomenon, this has produced a highly accurate prediction map of fluoride concentrations exceeding 1.5 mg/L at 1 km resolution throughout the country. The most affected areas are the northwestern states/territories of Delhi, Gujarat, Haryana, Punjab, and Rajasthan and the southern states of Andhra Pradesh, Karnataka, Tamil Nadu, and Telangana. The total number of people at risk of fluorosis due to fluoride in groundwater is predicted to be around 120 million, or 9% of the population. This number is based on rural populations and accounts for average rates of groundwater consumption from nonmanaged sources. The new fluoride hazard and risk maps can be used by authorities in conjunction with detailed groundwater utilization information to prioritize areas in need of mitigation measures.

Pair distribution function analysis of in situ total scattering data recorded during formation of WO3 nanocrystals under hydrothermal conditions reveal that a complex precursor structure exists in solution. The WO6 polyhedra of the precursor cluster undergo reorientation before forming the nanocrystal. This reorientation is the critical element in the formation of different hexagonal polymporphs of WO3.

Platinum-based nanoparticles play a crucial role as catalysts, and solvothermal synthesis methods are attractive due to the excellent control of nanoparticle characteristics such as size, crystallinity, and morphology, which strongly affect the chemical and physical properties. Insight into the reaction mechanism leading to nanoparticle formation under solvothermal conditions generally remains elusive. This is mainly due to the experimental difficulties that lie in obtaining atomistic information on the nanoscale during the progression of the synthesis. Using in situ total X-ray scattering and pair distribution function (PDF) analysis with a time resolution of 1 s, we unravel the formation mechanisms of Pt and Pt 3 Gd nanoparticles under solvothermal conditions. We demonstrate that an octahedral Pt 4+ platinic acid precursor complex is reduced in two steps. Both Pt and Pt 3 Gd nanocrystal formation proceeds via conversion of a square-planar Pt 2+ complex to an unsaturated nanocluster (Pt 0 ), which subsequently grows by a combination of aggregation and ripening. In contrast to Rietveld analysis of powder X-ray diffraction data, the PDF method is able to uniquely establish that the structure of the Pt−Gd alloy is Pt 3 Gd rather than PtGd.

In this work, heterostructures formed with vertical stacking of two-dimensional (2D) layered materials are systematically studied. Considering near infrared (NIR)/short-wave-infrared (SWIR) photodetection, van der Waals (vdW) heterostructures with various possible combinations of group-6 and group-7 monolayer transition metal dichalcogenides (TMDs) are explored. Single-layer distorted 1T ReS2, being a dynamically stable semiconducting material, is adopted as the group-7 constituent. On the other hand, as group-6 constituents, five different semiconducting monolayer TMDs, viz., MoS2, WS2, MoSe2, WSe2, and MoTe2 have been chosen. A rational selection of group-6 TMDs based on intrinsic properties of individual materials as well as their heterointerfaces with single-layer ReS2 is demonstrated here to obtain type-II vdW heterostructures which can ensure efficient generation, separation, and collection of charge carriers resulting in significant improvement in photodetection metrics.