Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoTe offers tremendous opportunities in various device applications. However, most of the existing methods so far only address the small-area local phase change or the growth of certain kinds of phases of MoTe film by laser irradiation, mechanical strain, or procursor type. Obtaining facile, tunable, reversible, and continuous-phase transition and evolution between different phases in direct growth of large-area, few-layer MoTe still remains challenging. Here, we develop a facile method to achieve phase control and transition and report a highly tunable, tellurization velocity-dependent metallic-semiconducting-metallic phase evolution in chemical vapor deposition (CVD) growth of large-area, few-layer MoTe. We found four different phase stages, including two different types of coexistence phases of both 2H and 1 T' phases, 100% 2H phase, and 100% 1T' phase, would emerge, relying on the adopted tellurization velocity. Importantly, the tellurization velocity should be extremely controlled to obtain 100% 2H phase MoTe, while 100% 1T' phase requires a fast tellurization velocity. We further found that such metallic-semiconducting-metallic phase evolution took place with a homogeneous spatial distribution and differs from previous reports in which obvious phase separations are usually found during the phase transition. The resulting MoTe shows high quality with room-temperature mobility comparable with mechanically exfoliated materials. The results might impact large-scale phase engineering of TMDs and other 2D materials for Weyl semimetal topological physics and potential 2D semiconductor device applications.

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WTe 2 shows unique properties different from sulfides and selenides. Large-area, uniform few-layer 1T′ phase WTe 2 and long-term stability are essential for fundamental studies and applications of WTe 2 . Here, centimeter-scale, large-area, uniform few-layer 1T′-WTe 2 films are prepared by a facile, low-temperature, chemical vapor deposition (CVD) method and the long-term stability of such CVD-grown 1T′-WTe 2 up to 30 days in ambient condition is studied for the first time. Raman spectroscopy and transmission electron microscopy reveal the high quality of WTe 2 . The thickness of few-layer WTe 2 can be well tuned, and thickness-dependent Raman spectra are observed. The electrical and quantum electronic transport properties are found to be highly influenced by air exposure with different exposure times under ambient condition. The conductivity decreases by about 10 times with exposure, whereas weak antilocation behavior is observed in both pristine and air-exposed samples for 30 days. Surface-oxidization-induced magnetoresistance enhancement up to 30% is discovered unexpectedly.

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Emerging polymer memory devices with resistive switching are promising alternatives to existing conventional random access memory technology due to their ability of information storage and process. [1-4] An effective strategy to realize resistive switching for memory effect is organicinorganic hybrid design in polymer device, with the merits of tailorable components, tunable properties, solution process and low-cost manufacturing. [5-8] In the organicinorganic hybrid systems, insulating or semiconducting polymers are widely used as active matrix, low dimensional inorganic materials including zero dimensional (0D) nanodots, [9,10] 1D nanotubes [11,12] and 2D nanosheets [13,14] are introduced into polymer matrix as charge trapping to trigger the resistive switching. Among these nanomaterials, quantum dots (QDs) have attracted much attention because of outstanding quantum confinement for charge trapping and well dispersion in matrix for high reproducibility as well as operation stability. Recently, a series of novel QDs derived from 2D materials have been successfully synthesized and applied into polymer memories, such as graphene QDs, [15,16] black phosphorus QDs, [17,18] and transition-metal dichalcogenide (TMD) QDs, [19] with the function of nonvolatile write once read many times (WORM) and Flash memory effect. [20,21] More recently, MXene nanosheets, referring to a new class of 2D materials, [22,23] have aroused extensive attention owing to their metallic conductivity, abundant active sites, and hydrophilic surface. Compared to intrinsic 2D MXene nanosheets, the smallsized MXene with a diameter of less than 10 nm, referred as MXene quantum dots (MQDs), [24,25] shows stronger quantum confinement, edge effect, and hydrophilic properties, making them very promising to disperse in water soluble polymer and act as charge trapping center. [26,27] Therefore, constructing MQDs-polymer hybrid architecture will provide the feasibility of memory achievement for data storage and extend their application in information fields. [28] Herein, for the first time, we report the controllable resistive switching and nonvolatile memory behaviors in MQDs and PVP hybrid composite films. By modulating MQDs doping

The Weyl semimetal WTe2 and MoTe2 show great potential in generating large spin currents since they possess topologically protected spin‐polarized states and can carry a very large current density. In addition, the intrinsic non‐centrosymmetry of WTe2 and MoTe2 endows with a unique property of crystal symmetry‐controlled spin–orbit torques. An important question to be answered for developing spintronic devices is how spins relax in WTe2 and MoTe2. Here, a room‐temperature spin relaxation time of 1.2 ns (0.4 ns) in WTe2 (MoTe2) thin film using the time‐resolved Kerr rotation (TRKR) is reported. Based on ab initio calculation, a mechanism of long‐lived spin polarization resulting from a large spin splitting around the bottom of the conduction band, low electron–hole recombination rate, and suppression of backscattering required by time‐reversal and lattice symmetry operation is identified. In addition, it is found that the spin polarization is firmly pinned along the strong internal out‐of‐plane magnetic field induced by large spin splitting. This work provides an insight into the physical origin of long‐lived spin polarization in Weyl semimetals, which could be useful to manipulate spins for a long time at room temperature.

Borna disease virus (BDV) is a neurotropic virus that produces neuropsychiatric dysfunction in a wide range of warm-blooded species. Several studies have associated BDV with human psychiatric illness, but the findings remain controversial. Although oligodendrocytes are a major glial component of brain white matter and play a pivotal role in neuronal cell function, BDV's effects on human oligodendrocytes have not been clarified. Here, the effects of two BDV strains, Hu-H1 (isolated from a bipolar patient) and Strain V (a laboratory strain), on the proliferation and apoptosis of human oligodendrocytes were investigated. Three experimental cell lines were constructed: Hu-H1-infected oligodendroglioma (Hu-H1) cells, Strain V-infected oligodendroglioma (Strain V) cells, and non-infected oligodendroglioma (control) cells. BDV infection was assayed by BDV nucleoprotein (p40) immunofluorescence, cell proliferation was assayed by Cell Counting Kit-8 (CCK8), and cell cycle phases and apoptosis were assayed by flow cytometry. Expressions of the apoptosis-related proteins Bax and Bcl-2 were measured by Western blotting. p40 expression was confirmed in Hu-H1 and Strain V on and after day three post-infection. Strain V cells showed significantly greater cellular proliferation than Hu-H1 cells on and after day three post-infection. In Hu-H1 cells, Bax and Bcl-2 expression were significantly increased and decreased, respectively, on and after day three post-infection. In contrast, in Strain V cells, Bax and Bcl-2 expression were significantly decreased and increased, respectively, on and after day three post-infection. In conclusion, Hu-H1 inhibits cellular proliferation and promotes apoptosis in human oligodendrocytes via Bax upregulation and Bcl-2 downregulation. In contrast, Strain V promotes cellular proliferation and inhibits apoptosis in human oligodendrocytes via Bax downregulation and Bcl-2 upregulation. The effects of the Hu-H1 strain (isolated from a bipolar patient) are opposite from those of Strain V (a laboratory strain), thereby providing a proof of authenticity for both.

We study the temperature dependent magnetic susceptibility of a strained graphene quantum dot using the determinant quantum Monte Carlo method. Within the Hubbard model on a honeycomb lattice, our unbiased numerical results show that a relative small interaction U may lead to a edge ferromagnetic-like behavior in the strained graphene quantum dot. Around half filling, the ferromagnetic fluctuations at the zigzag edge are strengthened both by the on-site Coulomb interaction and the strain, especially in low temperature region.