Biomass-Derived Activated Carbon Supported Fe₃O₄ Nanoparticles as Recyclable Catalysts for Reduction of Nitroarenes

Highly porous beetroot-derived activated carbons incorporated with well-dispered magnetite nanoparticles (Fe₃O₄ NPs; average size <i>ca</i>. 3.8 ± 0.5 nm) were fabricated via a microwave-assisted synthesis route. The magnetic Fe₃O₄@BRAC catalysts so-fabricated were characterized by a variety of diffent physicochemical teniques, viz. XRD, FE-TEM, VSM, gas physisorption/chemisorption, TGA, XPS, Raman, ICP-AES, and FT-IR spectroscopy. The as-prepared catalysts were exploited for heterogeneous-phase reduction of a series of nitroaromatics (RNO₂; R = H, OH, NH₂, CH₃, and COOH) under KOH as a base, isopropyl alcohol acting as a hydrogen donor as well as solvent and also tested with other solvents. The reaction system not only exhibits excellent activity with high anilines yield but also represents a green and durable catalytic process, which facilitates facile operation, easy separation, and catalyst recycle

Growth of the Bi₂Se₃ Surface Oxide for Metal–Semiconductor–Metal Device Applications

The effect of the surface structure of Bi₂Se₃ on its interior properties has been well studied recently, but the interfacial structure and electrical properties of the oxidized Bi₂Se₃ surface are little known. In contrast to the self-limited formation of native oxide on Bi₂Se₃, the degree of oxidation on the Bi₂Se₃ surface in oxygen plasma is enhanced. Results of transmission electron microscopy and X-ray photoelectron spectroscopy show that the surface of the oxidized Bi₂Se₃ is composed of a layer of amorphous bismuth oxide (BiO_<i>x</i>), and the thickness of the BiO_<i>x</i> layer can be controlled by the length of the plasma process. Electrical measurements of this structure present the Schottky-type transport property at the interface between the oxidized layer and the bulk Bi₂Se₃ crystal, and the turn-on voltage depends on the thickness of the surface BiO_<i>x</i> layer. This study of the structure, formation mechanism, and electrical properties of the surface oxide of Bi₂Se₃ formed in oxygen plasma provides useful information for future development of electronic devices based on bismuth chalcogenides

Organic Monolayer Protected Topological Surface State

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)/Bi₂Se₃ and Fe/PTCDA/Bi₂Se₃ heterointerfaces are investigated using scanning tunneling microscopy and spectroscopy. The close-packed self-assembled PTCDA monolayer possesses big molecular band gap and weak molecule–substrate interactions, which leaves the Bi₂Se₃ topological surface state intact under PTCDA. Formation of Fe-PTCDA hybrids removes interactions between the Fe dopant and the Bi₂Se₃ surface, such as doping effects and Coulomb scattering. Our findings reveal the functionality of PTCDA to prevent dopant disturbances in the TSS and provide an effective alternative for interface designs of realistic TI devices

Tuning Rashba Spin–Orbit Coupling in Gated Multilayer InSe

Manipulating the electron spin with the aid of spin–orbit coupling (SOC) is an indispensable element of spintronics. Electrostatically gating a material with strong SOC results in an effective magnetic field which can in turn be used to govern the electron spin. In this work, we report the existence and electrostatic tunability of Rashba SOC in multilayer InSe. We observed a gate-voltage-tuned crossover from weak localization (WL) to weak antilocalization (WAL) effect in quantum transport studies of InSe, which suggests an increasing SOC strength. Quantitative analyses of magneto-transport studies and energy band diagram calculations provide strong evidence for the predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we attribute the tendency of the SOC strength to saturate at high gate voltages to the increased electronic density of states-induced saturation of the electric field experienced by the electrons in the InSe layer. This explanation of nonlinear gate voltage control of Rashba SOC can be generalized to other electrostatically gated semiconductor nanomaterials in which a similar tendency of spin–orbit length saturation was observed (e.g., nanowire field effect transistors), and is thus of broad implications in spintronics. Identifying and controlling the Rashba SOC in InSe may serve pivotally in devising III–VI semiconductor-based spintronic devices in the future

Intrinsic Electron Mobility Exceeding 10³ cm²/(V s) in Multilayer InSe FETs

Graphene-like two-dimensional (2D) materials not only are interesting for their exotic electronic structure and fundamental electronic transport or optical properties but also hold promises for device miniaturization down to atomic thickness. As one material belonging to this category, InSe, a III–VI semiconductor, not only is a promising candidate for optoelectronic devices but also has potential for ultrathin field effect transistor (FET) with high mobility transport. In this work, various substrates such as PMMA, bare silicon oxide, passivated silicon oxide, and silicon nitride were used to fabricate multilayer InSe FET devices. Through back gating and Hall measurement in four-probe configuration, the device’s field effect mobility and intrinsic Hall mobility were extracted at various temperatures to study the material’s intrinsic transport behavior and the effect of dielectric substrate. The sample’s field effect and Hall mobilities over the range of 20–300 K fall in the range of 0.1–2.0 × 10³ cm²/(V s), which are comparable or better than the state of the art FETs made of widely studied 2D transition metal dichalcogenides

Tunable Photoinduced Carrier Transport of a Black Phosphorus Transistor with Extended Stability Using a Light-Sensitized Encapsulated Layer

In this article, we propose a novel approach to demonstrate tunable photoinduced carrier transport of a few-layered black phosphorus (BP) field-effect transistor (FET) with extended air stability using a “light-sensitized ultrathin encapsulated layer”. Titanium suboxide (TiO_x) ultrathin film (approximately 3 nm), which is an amorphous phase of crystalline TiO₂ and can be solution processed, simultaneously exhibits the unique dual functions of passivation and photoinduced doping on a BP FET. The photoinduced electron transfer at TiO_x/BP interfaces provides tunable n-type doping on BP through light illumination. Accordingly, the intrinsic hole-dominated transport of BP can be gradually tuned to the electron-dominated transport at a TiO_x/BP FET using light modulation, with enhanced electron mobility and extended air stability of the device. The novel device structure consisting of a light-sensitized encapsulated layer with controllable and reversible doping through light illumination on BP exhibits great potential for the future development of stable BP-based semiconductor logic devices or optoelectronic devices

Topological Type-II Dirac Fermions Approaching the Fermi Level in a Transition Metal Dichalcogenide NiTe₂

Type-II Dirac/Weyl semimetals are characterized by strongly tilted Dirac cones such that the Dirac/Weyl node emerges at the boundary of electron and hole pockets as a new state of quantum matter, distinct from the standard Dirac/Weyl points with a point-like Fermi surface which are referred to as type-I nodes. The type-II Dirac fermions were recently predicted by theory and have since been confirmed in experiments in the PtSe₂-class of transition metal dichalcogenides. However, the Dirac nodes observed in PtSe₂, PdTe₂, and PtTe₂ candidates are quite far away from the Fermi level, making the signature of topological fermions obscure as the physical properties are still dominated by the non-Dirac quasiparticles. Here, we report the synthesis of a new type-II Dirac semimetal NiTe₂ in which a pair of type-II Dirac nodes are located very close to the Fermi level. The quantum oscillations in this material reveal a nontrivial Berry’s phase associated with these Dirac fermions. Our first-principles calculations further unveil a topological Dirac cone in its surface states. Therefore, NiTe₂ may not only represent an improved system to formulate the theoretical understanding of the exotic consequences of type-II Dirac fermions, it also facilitates possible applications based on these topological carriers

Quasiparticle Scattering in the Rashba Semiconductor BiTeBr: The Roles of Spin and Defect Lattice Site

Observations of quasiparticle interference have been used in recent years to examine exotic carrier behavior at the surfaces of emergent materials, connecting carrier dispersion and scattering dynamics to real-space features with atomic resolution. We observe quasiparticle interference in the strongly Rashba split 2DEG-like surface band found at the tellurium termination of BiTeBr and examine two mechanisms governing quasiparticle scattering: We confirm the suppression of spin-flip scattering by comparing measured quasiparticle interference with a spin-dependent elastic scattering model applied to the calculated spectral function. We also use atomically resolved STM maps to identify point defect lattice sites and spectro-microscopy imaging to discern their varying scattering strengths, which we understand in terms of the calculated orbital characteristics of the surface band. Defects on the Bi sublattice cause the strongest scattering of the predominantly Bi 6p derived surface band, with other defects causing nearly no scattering near the conduction band minimum

Low-Threshold Lasing from 2D Homologous Organic–Inorganic Hybrid Ruddlesden–Popper Perovskite Single Crystals

Organic–inorganic hybrid two-dimensional (2D) perovskites have recently attracted great attention in optical and optoelectronic applications due to their inherent natural quantum-well structure. We report the growth of high-quality millimeter-sized single crystals belonging to homologous two-dimensional (2D) hybrid organic–inorganic Ruddelsden–Popper perovskites (RPPs) of (BA)₂(MA)_{<i><i>n</i></i>−1}Pb_{<i><i>n</i></i>}I_{3<i><i>n</i></i>+1} (<i>n</i> = 1, 2, and 3) by a slow evaporation at a constant-temperature (SECT) solution-growth strategy. The as-grown 2D hybrid perovskite single crystals exhibit excellent crystallinity, phase purity, and spectral uniformity. Low-threshold lasing behaviors with different emission wavelengths at room temperature have been observed from the homologous 2D hybrid RPP single crystals. Our result demonstrates that solution-growth homologous organic–inorganic hybrid 2D perovskite single crystals open up a new window as a promising candidate for optical gain media

One-Dimensional Oxygen Diffusion Mechanism in Sr₂ScGaO₅ Electrolyte Explored by Neutron and Synchrotron Diffraction, ¹⁷O NMR, and Density Functional Theory Calculations

We investigated moderate-temperature oxygen diffusion mechanisms in Sr₂ScGaO₅ with Brownmillerite structure type. From oxygen isotope ¹⁸O–¹⁶O exchange experiments we determined that oxygen mobility sets in above 550 °C. Temperature-dependent neutron and X-ray (synchrotron) diffraction experiments allowed us to correlate the oxygen mobility with a subtle phase transition of the orthorhombic room-temperature structure with <i>I</i>2<i>mb</i> space group toward <i>Imma</i>, going along with a disorder of the (GaO₄)_∞-tetrahedral chains. From lattice dynamical simulations we could clearly evidence that dynamic switching of the (GaO₄)_∞-tetrahedral chains from its R to L configuration sets in at 600 °C, thus correlating oxygen diffusion with the dynamic disorder. Oxygen ion diffusion pathways are thus constrained along the one-dimensional oxygen vacancy channels, which is a different diffusion mechanism compared to that of the isostructural CaFeO_2.5, where diffusion of the apical oxygen atoms into the vacant lattice sites are equally involved in the diffusion pathway. The proposed ordered room-temperature structure in <i>I</i>2<i>mb</i> is strongly supported by ¹⁷O, ⁴⁵Sc, and ⁷¹Ga NMR measurements, which indicate the presence of crystallographically unique sites and the absence of local disordering effects below the phase transition. The electric field gradient tensor components measured at the nuclear sites are found to be in excellent agreement with calculated values using the WIEN2k program. The oxygen site assignment has been independently confirmed by ¹⁷O­{⁴⁵Sc} transfer of adiabatic populations double-resonance experiments