Electric-field induced abrupt and multi-step insulator-metal transitions in vanadium dioxide nanobeams

Both abrupt and multi-step Insulator-metal transitions triggered by applied voltage (electric field) were observed in VO2 nanobeams. The multi-step transition occurs due to nucleation and subsequent expansion of multiple insulating and metallic domains across the nanobeam whereas the abrupt transition results from the propagation of a parallel metallic domain across the nanobeam. A simple power dissipation based model was also used to study the local temperature evolution during these transitions in the nanobeam. Both types of transitions are suitable for prospective application in resistive memory and switches.clos

Unimer-Assisted Exfoliation for Highly Concentrated Aqueous Dispersion Solutions of Single- and Few-Layered van der Waals Materials

We suggest a unimer-assisted exfoliation method for the exfoliation of van der Waals two-dimensional (2D) materials such as graphene, MoS₂, and h-BN and show that the micellar size is a critical parameter for enhancing the exfoliation efficiency. To explain the effectiveness of the unimers in the exfoliation, the influence of the micellar size of a biocompatible block copolymer, Pluronic F-68, is evaluated in view of the yield and thickness of exfoliated 2D flakes. By the addition of water-soluble alcohols, the surfactants exist in the form of a unimer, which facilitates the intercalation into the layered materials and their exfoliation. The results showed that the high exfoliation efficiency could be achieved by controlling the micellar size mostly to be unimers; the average yield rate of MoS₂ exfoliation was 4.51% per hour, and the very high concentration of 1.45 mg/mL was obtained by sonication for 3 h. We also suggested the dielectrophoresis technique as a method for forming a film composed of 2D flakes for diverse applications requiring electrical signals. The unimer-assisted exfoliation method will be substantially utilized to achieve highly concentrated aqueous dispersion solutions of 2D materials

Gate-Tunable Hole and Electron Carrier Transport in Atomically Thin Dual-Channel WSe2/MoS2 Heterostructure for Ambipolar Field-Effect Transistors

An ambipolar dual-channel field-effect transistor (FET) with a WSe2/MoS2 heterostructure formed by separately controlled individual channel layers is demonstrated. The FET shows a switchable ambipolar behavior with independent carrier transport of electrons and holes in the individual layers of MoS2 and WSe2, respectively. Moreover, the photo-response is studied at the heterointerface of the WSe2/MoS2 dual-channel FET © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim8

Tunable Electrical and Optical Characteristics in Monolayer Graphene and Few-Layer MoS₂ Heterostructure Devices

Lateral and vertical two-dimensional heterostructure devices, in particular graphene–MoS₂, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene–MoS₂ heterostructure. The few-layer MoS₂ devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS₂ on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS₂ overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS₂ FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS₂ FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene–MoS₂ heterostructure

Conductance Control in VO2 Nanowires by Surface Doping with Gold Nanoparticles

The material properties of semiconductor nanowires are greatly affected by electrical, optical, and chemical processes occurring at their surfaces because of the very large surface-to-volume ratio. Precise control over doping as well as the surface charge properties has been demonstrated in thin films and nanowires for fundamental physics and application-oriented research. However, surface doping behavior is expected to differ markedly from bulk doping in conventional semiconductor materials. Here, we show that placing gold nanoparticles, in controlled manner, on the surface of an insulating vanadium dioxide nanowire introduces local charge carriers in the nanowire, and one could, in principle, completely and continuously alter the material properties of the nanowire and obtain any intermediate level of conductivity. The current in the nanowire increased by nearly 3 times when gold nanoparticles of 10(11) cm(-2) order of density were controllably placed on the nanowire surface. A strong quadratic space-charge limited (SCL) transport behavior was also observed from the conductance curve suggesting the formation of two-dimensional (2D) electron-gas-like confined layer in the nanowire with adsorbed Au NPs. In addition to stimulating scientific interest, such unusual surface doping phenomena may lead to new applications of vanadium dioxide-based electronic, optical, and chemical sensing nanodevices.close