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1. Two-dimensional Dirac spin-gapless semiconductors with tunable perpendicular magnetic anisotropy and a robust quantum anomalous Hall effect

   https://doi.org/10.1039/d0mh00396d  

   Sun, Qilong ; Ma, Yandong ; Kioussis, Nicholas ( August 2020 , Materials Horizons)

   A major recent breakthrough in materials science is the emergence of intrinsic magnetism in two-dimensional (2D) crystals, which opens the door to more cutting-edge fields in the 2D family and could eventually lead to novel data-storage and information devices with further miniaturization. Herein we propose an experimentally feasible 2D material, Fe 2 I 2 , which is an intrinsic room-temperature ferromagnet exhibiting perpendicular magnetic anisotropy (PMA). Using first-principles calculations, we demonstrate that single-layer (SL) Fe 2 I 2 is a spin-gapless semiconductor with a spin-polarized Dirac cone and linear energy dispersion in one spin channel, exhibiting promising dissipation-less transport properties with a Fermi velocity up to 6.39 × 10 5 m s −1 . Our results reveal that both strain and ferroelectric polarization switching could induce an out-of- to in-plane spin reorientation in the 2D Fe 2 I 2 layer, revealing its advantage in assembling spintronic devices. In addition, spin–orbit coupling (SOC) triggers a topologically nontrivial band gap of 301 meV with a nonzero Chern number (| C | = 2), giving rise to a robust quantum anomalous Hall (QAH) state. The 2D crystal also exhibits high carrier mobilites of 0.452 × 10 3 and 0.201 × 10 3 cmmore »2 V −1 s −1 for the electrons and holes, respectively. The combination of these unique properties renders the 2D Fe 2 I 2 ferromagnet a promising platform for high efficiency multi-functional spintronic applications.« less
2. Toward understanding the phase-selective growth mechanism of films and geometrically-shaped flakes of 2D MoTe ₂

   https://doi.org/10.1039/d1ra07787b  

   Limbu, Tej B. ; Adhikari, Bikram ; Song, Seung Keun ; Chitara, Basant ; Tang, Yongan ; Parsons, Gregory N. ; Yan, Fei ( November 2021 , RSC Advances)

   Two-dimensional (2D) molybdenum ditelluride (MoTe 2 ) is an interesting material for fundamental study and applications, due to its ability to exist in different polymorphs of 2H, 1T, and 1T′, their phase change behavior, and unique electronic properties. Although much progress has been made in the growth of high-quality flakes and films of 2H and 1T′-MoTe 2 phases, phase-selective growth of all three phases remains a huge challenge, due to the lack of enough information on their growth mechanism. Herein, we present a novel approach to growing films and geometrical-shaped few-layer flakes of 2D 2H-, 1T-, and 1T′-MoTe 2 by atmospheric-pressure chemical vapor deposition (APCVD) and present a thorough understanding of the phase-selective growth mechanism by employing the concept of thermodynamics and chemical kinetics involved in the growth processes. Our approach involves optimization of growth parameters and understanding using thermodynamical software, HSC Chemistry. A lattice strain-mediated mechanism has been proposed to explain the phase selective growth of 2D MoTe 2 , and different chemical kinetics-guided strategies have been developed to grow MoTe 2 flakes and films.
3. Raman study of silicon telluride nanoplates and their degradation

   https://doi.org/10.1088/1361-6528/ac5c13  

   Hathaway, Evan ; Chen, Jiyang ; Gonzalez-Rodriguez, Roberto ; Lin, Yuankun ; Cui, Jingbiao ( April 2022 , Nanotechnology)

   Abstract Silicon telluride (Si 2 Te 3 ) has emerged as one of the many contenders for 2D materials ideal for the fabrication of atomically thin devices. Despite the progress which has been made in the electric and optical properties of silicon telluride, much work is still needed to better understand this material. We report here on the Raman study of Si 2 Te 3 degradation under both annealing and in situ heating with a laser. Both processes caused pristine Si 2 Te 3 to degrade into tellurium and silicon oxide in air in the absence of a protective coating. A previously unreported Raman peak at ∼140 cm −1 was observed from the degraded samples and is found to be associated with pure tellurium. This peak was previously unresolved with the peak at 144 cm −1 for pristine Si 2 Te 3 in the literature and has been erroneously assigned as a signature Raman peak of pure Si 2 Te 3 , which has caused incorrect interpretations of experimental data. Our study has led to a fundamental understanding of the Raman peaks in Si 2 Te 3 , and helps resolve the inconsistent issues in the literature. This study ismore »not only important for fundamental understanding but also vital for material characterization and applications.« less
4. A review of the growth, doping, and applications of Beta-Ga2O3 thin films

   https://doi.org/10.1117/12.2302471  

   Teherani, Ferechteh H. ; Khodaparast, Giti A. ; Xu, Yaobin V. ; Wu, Jinsong ; Dravid, Vinayak P. ; Pavlidis, Dimitris ; Razeghi, Manijeh ; McClintock, Ryan ; Rogers, David J. ; Park, Ji-Hyeon ; et al ( March 2018 , Proc. SPIE 10533, Oxide-based Materials and Devices IX)

   β-Ga2O3 is emerging as an interesting wide band gap semiconductor for solar blind photo detectors (SBPD) and high power field effect transistors (FET) because of its outstanding material properties including an extremely wide bandgap (Eg ~4.9eV) and a high breakdown field (8 MV/cm). This review summarizes recent trends and progress in the growth/doping of β-Ga2O3 thin films and then offers an overview of the state-of-the-art in SBPD and FET devices. The present challenges for β-Ga2O3 devices to penetrate the market in real-world applications are also considered, along with paths for future work.
5. Two-dimensional halide perovskites featuring semiconducting organic building blocks

   https://doi.org/10.1039/d0qm00233j  

   Gao, Yao ; Wei, Zitang ; Hsu, Sheng-Ning ; Boudouris, Bryan W. ; Dou, Letian ( January 2020 , Materials Chemistry Frontiers)

   Two-dimensional (2D) organic–inorganic hybrid halide perovskites exhibit unique properties, such as long charge carrier lifetimes, high photoluminescence quantum efficiencies, and great tolerance to defects. Over the last several decades tremendous progress has occurred in the development of 2D layered halide perovskite semiconductor materials and devices. Chemical functionalization of 2D halide perovskites is an effective approach for tuning their electronic properties. A large amount of effort has been made in compositional engineering of the cations and anions in the perovskite lattice. However, few efforts have incorporated rationally designed semiconducting organic moieties into these systems to alter the overall chemical and optoelectronic properties of 2D perovskites. In fact, incorporation of large conjugated organic groups in the spatially confined inorganic perovskite matrix was found to be challenging, and this synthetic challenge hinders a deeper understanding of the materials’ structure–property relationships. Recently, exciting progress has been made regarding the molecular design, optical characterization, and device fabrication of novel 2D halide perovskite materials that incorporate functional organic semiconducting building blocks. In this article, we provide a timely review regarding this recent progress. Moreover, we discuss successes and current challenges regarding the synthesis, characterization, and device applications of such hybrid materials and provide a perspective onmore »the true future promise of these advanced nanomaterials.« less