1,721,038 research outputs found
V2Se: A novel antifluorite-type cubic phase with a metal-metal bonding
No full text© 2019 The Royal Society of Chemistry.A new antifluorite-type (Li2O-type) cubic compound, V2Se, has been synthesized for the first time by changing the amount of selenium in chemical vapor transport. The vanadium-based cubic phase studied here reveals a metal-metal bonding feature in the electronic band structure. This compound is the first example of an antifluorite-type cubic structure in a V-Se system11sci
Efficient Photothermoelectric Conversion in Lateral Topological Insulator Heterojunctions
No full textTuning the electron and phonon transport properties of thermoelectric materials by nanostructuring has enabled improving their thermopower figure of merit. Three-dimensional topological insulators, including many bismuth chalcogenides, attract increasing attention for this purpose, as their topologically protected surface states are promising to further enhance the thermoelectric performance. While individual bismuth chalcogenide nanostructures have been studied with respect to their photothermoelectric properties, nanostructured p-n junctions of these compounds have not yet been explored. Here, we experimentally investigate the room temperature thermoelectric conversion capability of lateral heterostructures consisting of two different three-dimensional topological insulators, namely, the n-type doped Bi2Te2Se and the p-type doped Sb2Te3. Scanning photocurrent microscopy of the nanoplatelets reveals efficient thermoelectric conversion at the p-n heterojunction, exploiting hot carriers of opposite sign in the two materials. From the photocurrent data, a Seebeck coefficient difference of Delta S = 200 mu V/K was extracted, in accordance with the best values reported for the corresponding bulk materials. Furthermore, it is in very good agreement with the value of Delta S = 185 mu V/K obtained by DFT calculation taking into account the specific doping levels of the two nanostructured components. © 2016 American Chemical Society7
Gate modulation of the long-range magnetic order in a vanadium-doped WSe2 semiconductor
No full text© Author(s) 2020 Generation of spin-charge coupling by doping semiconductors with magnetic dopants is a promising approach for gate-tunable spintronic devices without applying an external magnetic field. Here, we demonstrate that the magnetic orders in V-doped WSe2 can be modulated by tuning carrier densities using ab initio calculations. We found that at a low V-doping concentration limit, the long-range ferromagnetic order is enhanced by increasing the hole density. In contrast, this long-range ferromagnetic order is suppressed at high electron density by compensating the p-type V dopant, originating from the strong localized antiferromagnetic coupling between V and W atoms and between V and Se atoms. The hole-mediated long-range magnetic exchange is similar to 70 meV, thus strongly suggesting the ferromagnetism in V-doped WSe2 at room temperature. Our findings on strong coupling between charge and spin order in V-doped WSe2 provide plenty of room for multifunctional gate-tunable spintronics11Nsciescopu
van der Waals Layered Materials: Opportunities and Challenges
No full textSince graphene became available by a scotch tape technique, a vast class of two-dimensional (2D) van der Waals (vdW) layered materials has been researched intensively. What is more intriguing is that the well-known physics and chemistry of three-dimensional (3D) bulk materials are often irrelevant, revealing exotic phenomena in 2D vdW materials. By further constructing heterostructures of these materials in the planar and vertical directions, which can be easily achieved via simple exfoliation techniques, numerous quantum mechanical devices have been demonstrated for fundamental research and technological applications. It is, therefore, necessary to review the special features in 2D vdW materials and to discuss the remaining issues and challenges. Here, we review the vdW materials library, technology relevance, and specialties of vdW materials covering the vdW interaction, strong Coulomb interaction, layer dependence, dielectric screening engineering, work function modulation, phase engineering, heterostructures, stability, growth issues, and the remaining challenges. © 2017 American Chemical Society192
Probing Multiphased Transition in Bulk MoS2 by Direct Electron Injection
Full text link© 2019 American Chemical Society.Structural phase transitions in layered two-dimensional (2D) materials are of significant interest owing to their ability to exist in multiple metastable states with distinctive properties. However, phase transition in bulk MoS2 by nondestructive electron infusion has not yet been realized. In this study, we report the 2H to 1T′ phase transition and in-between intermediates in bulk MoS2 using MoS2/[Ca2N]+·e- heterostructures, in which kinetic free electrons were directly injected into MoS2. We observed various phases in MoS2 ranging from heavily doped 2H to a distorted lattice state and then on to a complete 1T′ state. Snapshots of the multiphase transition were captured by extraordinary Raman shift and bandgap reduction and were further elucidated by theoretical calculations. We also observed a weakening in interlayer coupling in the vicinity of the metallic regime, which led to an unusually strong photoluminescence emission, suggesting light-efficient bulk MoS2. Our results thus suggest the optoelectronic applications that can fully utilize the multiphase transition of bulk 2D materials11sciescopu
Oxidize Graphene by UV-Ozone Treatment in Vacuum Chamber
No full textAs changing graphene properties is vital to promote it as electronic device, we developed graphene modified method with epoxy group by two simple methods: ultraviolet irradiation with various partial oxygen pressures and ultraviolet irradiation under rich oxygen condition with various temperatures. By Hall measurement, the electric mobility in graphene was decreased with increasing temperature during UV-ozone treatment at 50 °C, 80 °C, 100 °C and 120 °C. At low partial oxygen pressure (less than 160 Torr) the oxidation degree is not significant. Additionally, Raman spectroscopy showed the disrupted π-π structure in graphene. Based on the above identification we supposed that epoxy group might establish on graphene surface. © 2016 American Scientific Publishers. All rights reserved2211sciescopu
Light-emitting Ti2N (MXene) quantum dots: synthesis, characterization and theoretical calculations
No full text© The Royal Society of Chemistry 2022. MXene-based quantum dots (MQDs), which are obtained by fragmenting MXenes into a nanometer scale, can display photoluminescence (PL), suggesting light-emitting applications for bandgap-less MXenes. However, despite the diverse possible formations of MXene components, only carbide MXene-based MQDs have been reported to emit light. In this study, we synthesized water-soluble MQDs with an average diameter of 3.14 nm using the titanium nitride (Ti2N) MXene. Ti2N MQDs exhibited efficient PL, with a maximum quantum yield of 7.5%, upon light absorption over the deep UV wavelength range of 400-230 nm. The density functional theory calculations and PL excitation measurements identified a bandgap of 3.8 eV and the existence of an unfulfilled band (E-1) between the occupied low-energy (E-0) and unoccupied high-energy (E-2) bands, which induces strong absorption in deep UV energy originating from the E-0-E-2 transition. Light-emitting nitride MQDs expand and facilitate the UV optoelectronic applications of MQDs.11Nsciescopu
Proximity Engineering of the van der Waals Interaction in Multilayered Graphene
Full text linkThe van der Waals (vdW) interaction in two-dimensional (2D)-layered materials affects key characteristics of electronic devices, such as the contact resistance, with a vertical heterostructure geometry. While various functionalizations to manipulate the properties of 2D materials have shown issues such as defect generation or have a limited spatial range for the methods, engineering the vdW interaction in nondestructive ways for device applications has not been tried or properly achieved yet. Here, we introduce the proximity engineering of the vdW interaction in multilayered graphene, which is observed as modified interlayer distances and deviated stacking orders by Raman spectroscopy. A 2D electride, [Ca2N](+)center dot e(-), possessing a low-work function of 2.6 eV, was used to trigger an avalanche of electrons over tens of graphene layers, exceeding the conventional spatial-range limit (similar to 1 nm) by screening with a carrier density of 10(14) cm(-2). Our proximity engineering reduces the vdW interaction in a nondestructive way and achieves a promising graphene-metal contact resistance of 500 Omega.mu m without using complicated edge contacts, which demonstrates a way to use moderately decoupled graphene layers for device applications. © 2019 American Chemical Society11sciescopu
Graphene/ferroelectrics/graphene hybrid structure: Asymmetric doping of graphene layers
Full text linkWe report graphene/ferroelectric/graphene hybrid structure to demonstrate an asymmetrical doping in two graphene layers, one side with electrons and another side with holes. Two ferroelectrics, a poly(vinylidenefluoride) (PVDF) and a hydrofluorinated graphene, were used to demonstrate the concept with density functional calculations, revealing the Fermi level shift of 0.35 and 0.75 eV, respectively. This concept was confirmed by Raman spectroscopy using graphene/poly(vinylidenefluoride-co-trifluoroethylene)(P(VDF-TrFE))/graphene hybrid, which can easily form beta-phase close to our simulation model. G-band peak position was downshifted for electron doping and upshifted for hole doping. This hybrid structure opens an opportunity to study bilayer graphene system with a controllable thickness for a wide range of high carrier concentration. (C) 2015 AIP Publishing LLC1771sciescopu
Long-range ferromagnetic ordering in vanadium-doped WSe2 semiconductor
Full text link© 2019 Author(s).We report long-range ferromagnetic ordering in a vanadium-doped monolayer WSe2 semiconductor using spin-polarized density functional calculations. We found that the vanadium dopant is located in the fully occupied state inside the valence band, inherent from spin-orbit coupling, leading to the presence of free holes in the valence band. As a consequence, the spin-polarized hole carriers are delocalized not only in the vanadium site but also persistently in the tungsten sites distant from vanadium to facilitate the long-range ferromagnetic ordering in the vanadium-doped monolayer WSe2. Our findings of this study pave the way for the future exploration of carrier-mediated room-temperature two-dimensional ferromagnetic semiconductors via magnetic dopants11sciescopu
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