Gate modulation of the long-range magnetic order in a vanadium-doped WSe2 semiconductor

We demonstrate the gate-tunability of the long-range magnetic order in a p-type V-doped WSe2 monolayer 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, the short-range antiferromagnetic order is manifested at a high electron density by full compensation of the p-type V doping concentration. The hole-mediated long-range magnetic exchange is ~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 spintronics.Comment: 13 pages, 4 figures, 1 tabl

Charge transport in polycrystalline graphene : challenges and opportunities

Graphene has attracted significant interest both for exploring fundamental science and for a wide range of technological applications. Chemical vapor deposition (CVD) is currently the only working approach to grow graphene at wafer scale, which is required for industrial applications. Unfortunately, CVD graphene is intrinsically polycrystalline, with pristine graphene grains stitched together by disordered grain boundaries, which can be either a blessing or a curse. On the one hand, grain boundaries are expected to degrade the electrical and mechanical properties of polycrystalline graphene, rendering the material undesirable for many applications. On the other hand, they exhibit an increased chemical reactivity, suggesting their potential application to sensing or as templates for synthesis of one-dimensional materials. Therefore, it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries. Here, we review experimental progress on identification and electrical and chemical characterization of graphene grain boundaries. We use numerical simulations and transport measurements to demonstrate that electrical properties and chemical modification of graphene grain boundaries are strongly correlated. This not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electro-biochemical devices

Room-temperature ferromagnetism in monolayer WSe2 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, we report the room-temperature ferromagnetic domains with long-range order in semiconducting V-doped WSe2 monolayer synthesized by chemical vapor deposition. Ferromagnetic order is manifested using magnetic force microscopy up to 360K, while retaining high on/off current ratio of ~105 at 0.1% V-doping concentration. The V-substitution to W sites keep a V-V separation distance of 5 nm without V-V aggregation, scrutinized by high-resolution scanning transmission-electron microscopy, which implies the possibility of the Ruderman-Kittel-Kasuya-Yoshida interaction (or Zener model) by establishing the long-range ferromagnetic order in V-doped WSe2 monolayer through free hole carriers. More importantly, the ferromagnetic order is clearly modulated by applying a back gate. Our findings open new opportunities for using two-dimensional transition metal dichalcogenides for future spintronics.Comment: 16 pages, 4 figure

Incommensurate antiferromagnetic order in weakly frustrated two-dimensional van der Waals insulator CrPSe3_3

Although the magnetic order is suppressed by a strong magnetic frustration, it is maintained but appears in complex order forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetic-frustrated two-dimensional van der Waals material CrPSe$_3$. Polycrystalline CrPSe$_3$ was synthesized at an optimized temperature of 700$^\circ$C to avoid the formation of any secondary phases (e.g., Cr$_2$Se$_3$). The antiferromagnetic transition appeared at $T_N\sim 126$ K with a large Curie-Weiss temperature $T_{\rm CW} \sim -371$ via magnetic susceptibility measurements, indicating weak frustration in CrPSe$_3$ with a frustration factor $f (|T_{\rm CW}|/T_N) \sim 3$. Evidently, the formation of long-range incommensurate spin-density wave antiferromagnetic order with the propagation vector $k = (0, 0.04, 0)$ was revealed by neutron diffraction measurements at low temperatures (below 120K). The monoclinic crystal structure of C2/m symmetry is preserved over the studied temperature range down to 20K, as confirmed by Raman spectroscopy measurements. Our findings on the spin density wave antiferromagnetic order in two-dimensional (2D) magnetic materials, not previously observed in the MPX$_3$ family, are expected to enrich the physics of magnetism at the 2D limit, thereby opening opportunities for their practical applications in spintronics and quantum devices.Comment: 23 pages, 4 figures, 2 table

Effectiveness of perindopril/amlodipine fixed-dose combination in the treatment of hypertension: a systematic review

Background: Uncontrolled blood pressure is a major risk factor for cardiovascular diseases. Fixed-dose combination (FDC) therapy offers a promising approach to addressing this challenge by providing a convenient single-tablet solution that enhances the effectiveness of blood pressure control. In our systematic review, we assess the effectiveness of perindopril/amlodipine FDC in managing blood pressure.Methods: We conducted a comprehensive search across four primary electronic databases, namely, PubMed, Virtual Health Library (VHL), Global Health Library (GHL), and Google Scholar, as of 8 February 2022. Additionally, we performed a manual search to find relevant articles. The quality of the selected articles was evaluated using the Study Quality Assessment Tools (SQAT) checklist from the National Institute of Health and the ROB2 tool from Cochrane.Results: Our systematic review included 17 eligible articles. The findings show that the use of perindopril/amlodipine FDC significantly lowers blood pressure and enhances the quality of blood pressure control. Compared to the comparison group, the perindopril/amlodipine combination tablet resulted in a higher rate of blood pressure response and normalization. Importantly, perindopril/amlodipine FDC contributes to improved patient adherence with minimal side effects. However, studies conducted to date have not provided assessments of the cost-effectiveness of perindopril/amlodipine FDC.Conclusion: In summary, our analysis confirms the effectiveness of perindopril/amlodipine FDC in lowering blood pressure, with combination therapy outperforming monotherapy and placebo. Although mild adverse reactions were observed in a small subset of participants, cost-effectiveness assessments for this treatment remain lacking in the literature

V2Se: A novel antifluorite-type cubic phase with a metal-metal bonding

© 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

van der Waals Layered Materials: Opportunities and Challenges

Since 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

Efficient Photothermoelectric Conversion in Lateral Topological Insulator Heterojunctions

Tuning 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