Tuning Optical and Electrical Properties of Vanadium Oxide with Topochemical Reduction and Substitutional Tin.

Vanadium oxides are widely tunable materials, with many thermodynamically stable phases suitable for applications spanning catalysis to neuromorphic computing. The stability of vanadium in a range of oxidation states enables mixed-valence polymorphs of kinetically accessible metastable materials. Low-temperature synthetic routes to, and the properties of, these metastable materials are poorly understood and may unlock new optoelectronic and magnetic functionalities for expanded applications.

Highly Efficient Van Der Waals Heterojunction on Graphdiyne toward the High-Performance Photodetector.

Graphdiyne (GDY), a new 2D material, has recently proven excellent performance in photodetector applications due to its direct bandgap and high mobility. Different from the zero-gap of graphene, these preeminent properties made GDY emerge as a rising star for solving the bottleneck of graphene-based inefficient heterojunction. Herein, a highly effective graphdiyne/molybdenum (GDY/MoS ) type-II heterojunction in a charge separation is reported toward a high-performance photodetector.

CNT-molecule-CNT (1D-0D-1D) van der Waals integration ferroelectric memory with 1-nm junction area.

The device's integration of molecular electronics is limited regarding the large-scale fabrication of gap electrodes on a molecular scale. The van der Waals integration (vdWI) of a vertically aligned molecular layer (0D) with 2D or 3D electrodes indicates the possibility of device's integration; however, the active junction area of 0D-2D and 0D-3D vdWIs remains at a microscale size. Here, we introduce the robust fabrication of a vertical 1D-0D-1D vdWI device with the ultra-small junction area of 1 nm achieved by cross-stacking top carbon nanotubes (CNTs) on molecularly assembled bottom CNTs.

Synthesis of a Selectively Nb-Doped WS-MoS Lateral Heterostructure for a High-Detectivity PN Photodiode.

In this study, selective Nb doping (-type) at the WS layer in a WS-MoS lateral heterostructure a chemical vapor deposition (CVD) method using a solution-phase precursor containing W, Mo, and Nb atoms is proposed. The different chemical activity reactivity (MoO > WO > NbO) enable the separation of the growth temperature of intrinsic MoS to 700 °C (first grown inner layer) and Nb-doped WS to 800 °C (second grown outer layer). By controlling the Nb/(W+Nb) molar ratio in the solution precursor, the hole carrier density in the -type WS layer is selectively controlled from approximately 1.

One-Step Synthesis of NbSe/Nb-Doped-WSe Metal/Doped-Semiconductor van der Waals Heterostructures for Doping Controlled Ohmic Contact.

van der Waals heterostructures (vdWHs) of metallic (m-) and semiconducting (s-) transition-metal dichalcogenides (TMDs) exhibit an ideal metal/semiconductor (M/S) contact in a field-effect transistor. However, in the current two-step chemical vapor deposition process, the synthesis of m-TMD on pregrown s-TMD contaminates the van der Waals (vdW) interface and hinders the doping of s-TMD. Here, NbSe/Nb-doped-WSe metal-doped-semiconductor (M/d-S) vdWHs are created via a one-step synthesis approach using a niobium molar ratio-controlled solution-phase precursor.

Selective Pattern Growth of Atomically Thin MoSe Films via a Surface-Mediated Liquid-Phase Promoter.

Two-dimensional transition metal dichalcogenides (TMDs) offer numerous advantages over silicon-based application in terms of atomically thin geometry, excellent opto-electrical properties, layer-number dependence, band gap variability, and lack of dangling bonds. The production of high-quality and large-scale TMD films is required with consideration of practical technology. However, the performance of scalable devices is affected by problems such as contamination and patterning arising from device processing; this is followed by an etching step, which normally damages the TMD film.

Ferromagnetic Order at Room Temperature in Monolayer WSe Semiconductor via Vanadium Dopant.

Diluted magnetic semiconductors including Mn-doped GaAs are attractive for gate-controlled spintronics but Curie transition at room temperature with long-range ferromagnetic order is still debatable to date. Here, the room-temperature ferromagnetic domains with long-range order in semiconducting V-doped WSe monolayer synthesized by chemical vapor deposition are reported. Ferromagnetic order is manifested using magnetic force microscopy up to 360 K, while retaining high on/off current ratio of ≈10 at 0.

CVD-Grown Carbon Nanotube Branches on Black Silicon Stems for Ultrahigh Absorbance in Wide Wavelength Range.

We report a black silicon-carbon nanotube (bSi-CNT) hybrid structure for ultrahigh absorbance at wide spectral range of wavelength (300-1200 nm). CNTs are densely grown on entire bSi stems by chemical vapor deposition (CVD) through uniformly coating Fe catalyst. The bSi-CNT not only increases the surface roughness for enhancing the light suppression, but also allows the absorption of light in a wide wavelength range over the Si band gap (>1000 nm owing to 1.

Unveiling the Hot Carrier Distribution in Vertical Graphene/h-BN/Au van der Waals Heterostructures for High-Performance Photodetector.

Graphene is one of the most promising materials for photodetectors due to its ability to convert photons into hot carriers within approximately 50 fs and generate long-lived thermalized states with lifetimes longer than 1 ps. In this study, we demonstrate a wide range of vertical photodetectors having a graphene/h-BN/Au heterostructure in which an hexagonal boron nitride (h-BN) insulating layer is inserted between an Au electrode and graphene photoabsorber. The photocarriers effectively tunnel through the small hole barrier (1.

Efficient Gate Modulation in a Screening-Engineered MoS/Single-Walled Carbon Nanotube Network Heterojunction Vertical Field-Effect Transistor.

In this report, a screening-engineered carbon nanotube (CNT) network/MoS/metal heterojunction vertical field effect transistor (CNT-VFET) is fabricated for an efficient gate modulation independent of the drain voltage. The gate field in the CNT-VFET transports through the empty space of the CNT network without any screening layer and directly modulates the MoS semiconductor energy band, while the gate field from the Si back gate is mostly screened by the graphene layer. Consequently, the on/off ratio of CNT-VFET maintained 10 in overall drain voltages, which is 10 times and 1000 times higher than that of the graphene (Gr) VFET at = 0.

Tunable Negative Differential Resistance in van der Waals Heterostructures at Room Temperature by Tailoring the Interface.

Vertically stacked two-dimensional van der Waals (vdW) heterostructures, used to obtain homogeneity and band steepness at interfaces, exhibit promising performance for band-to-band tunneling (BTBT) devices. Esaki tunnel diodes based on vdW heterostructures, however, yield poor current density and peak-to-valley ratio, inferior to those of three-dimensional materials. Here, we report the negative differential resistance (NDR) behavior in a WSe/SnSe heterostructure system at room temperature and demonstrate that heterointerface control is one of the keys to achieving high device performance by constructing WSe/SnSe heterostructures in inert gas environments.