Three-dimensional (3D) topological insulators are known for their strong spin-orbit coupling (SOC) and the existence of spin-textured surface states that might be potentially exploited for "topological spintronics." Here, we use spin pumping and the inverse spin Hall effect to demonstrate successful spin injection at room temperature from a metallic ferromagnet (CoFeB) into the prototypical 3D topological insulator Bi2Se3. The spin pumping process, driven by the magnetization dynamics of the metallic ferromagnet, introduces a spin current into the topological insulator layer, resulting in a broadening of the ferromagnetic resonance (FMR) line width. Theoretical modeling of spin pumping through the surface of Bi2Se3, as well as of the measured angular dependence of spin-charge conversion signal, suggests that pumped spin current is first greatly enhanced by the surface SOC and then converted into a dc-voltage signal primarily by the inverse spin Hall effect due to SOC of the bulk of Bi2Se3. We find that the FMR line width broadens significantly (more than a factor of 5) and we deduce a spin Hall angle as large as 0.43 in the Bi2Se3 layer.

Localized surface plasmon resonances (LSPRs) enable tailoring of the optical response of nanomaterials through their free carrier concentration, morphology, and dielectric environment. Recent efforts to expand the spectral range of usable LSPR frequencies into the infrared successfully demonstrated LSPRs in doped semiconductor nanocrystals. Despite silicon's importance for electronic and photonic applications, no LSPRs have been reported for doped silicon nanocrystals. Here we demonstrate doped silicon nanocrystals synthesized via a nonthermal plasma technique that exhibits tunable LSPRs in the energy range of 0.07-0.3 eV or mid-infrared wavenumbers of 600-2500 cm(-1).

Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photo­emission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers.

Electronic structure, chemical bonding features, and electron charge density of the double-cubane single crystal [ Sb 7 S 8 Br 2 ] ( AlCl 4 ) 3 Appl. Phys. Lett. 98, 201903 (2011); 10.1063/1.3583674Structural characterization and electron-energy-loss spectroscopic study of pulsed laser deposited Li Nb O 3 films on a -sapphire Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO 3 or H 3 PO 3 during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.

Synthesis of semiconductor nanoparticles with uniform shapes, sizes, and compositions in series with a gradual size reduction has not been achieved for two-dimensional molecular sheets. We report a large-scale (>2.6 g) synthesis of 0.75-nm-thick diamond-shape lepidocrocite-type titanate molecular sheets with the sizes decreasing from (27.3, 19.1) to (7.7, 5.5), where the numbers in parentheses represent the long and short diagonal lengths, respectively, in nm. This is the first example of synthesizing semiconductor nanoparticles in series with the dimensionality reduction from two to zero, without coating the surfaces with surface-passivating ligands. The titanate molecular sheets showed three exciton-absorption bands in the 4.0-6.5 eV region, the absorption energies of which increased with decreasing the area. Contrary to the common belief, the per-unit cell oscillator strengths gradually increased with increasing area and the per-particle oscillator strengths increased in proportion to the area. The average reduced exciton masses along the two diagonal axes were 0.10 and 0.11 m e, respectively, which were much smaller than those of bulk titanates (by 60-130 times). The estimated average Bohr radii along the two-diagonal axes were 4.8 and 4.3 nm, respectively.