Narrow Results

White light-absorbing materials are in high demand for catalysis and energy harvesting. Due to the UV (ultraviolet) light absorption capacity of graphene and zinc oxide (ZnO) nanoparticles, the light harvesting of the whole range of visible and near-IR (infra-red) light by utilizing these materials is a significant barrier. In this study, a graphene-ZnO nanoparticle composite was prepared from graphene and ZnO powder through a simple and novel hot solvent process at low temperatures without a catalyst or expensive instrumentation. The fabricated composite was found to absorb light efficiently at an extended range of wavelengths (400–1665nm) with strong absorption intensity. Notably, the in situ graphene-ZnO showed a considerably low intensity of absorption in the visible to the near-IR range; however, when the graphene and ZnO powder were combined as a graphene-ZnO composite by ex situ hot solvent synthesis process, the light absorption intensity significantly increased within the whole range. The observation in this study is the first one that indicates that the ex situ hot solvent process tunes the light absorption properties at the extreme level of the visible- to the near-IR range. The prepared composite also showed excellent electrical conductivity. The graphene powder was also prepared through a straightforward self-developed solvothermal process with the help of the exfoliating agent.

Irregular rod-like bismuth sulphochloride (BiSCl) was synthesized by a high efficiency process in which BiCl₃ and Bi₂S₃ were fully ground and mixed in N₂ atmosphere followed by a sintering at 227^∘C for 9 h to achieve crimson BiSCl powder. The products were characterized by X-ray powder diffraction (XRD) and scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The BiSCl is an n-type semiconductor with a bandgap of 1.9 eV. In the temperature range of 300–500 K, thermal conductivity, electrical conductivity, Seebeck coefficient and thermoelectric figure of merit ZT of the BiSCl were tested and calculated. It is resulted that the BiSCl has a thermal conductivity of 0.45 Wm⁻¹K⁻¹ at 500 K and a Seebeck coefficient of −579 μVK⁻¹ at 400 K. This work will help inform future in-depth studies on possible applications of BiSCl in the fields of thermoelectricity, optoelectronics and photocatalyticity.

In the quantum system of nanolayer (NL) on silicon, the bandgap energy obviously increases with the decrease of NL thickness, where the quantum confinement (QC) effect plays the main role as the thickness of Si NL changes along with (100), (110) and (111) directions, respectively. And the simulation result demonstrated that the direct bandgap can be obtained as the NL with (001) direction is thinner than 10 nm on Si surface. However, it is discovered in the simulated calculation that the QC effect disappears as the NL thickness arrives at the size of the monoatomic layer, in which its bandgap sharply decreases, where the abrupt change effect in bandgap energy occurs near-ideal 2D-layer. In the experiment, we fabricated the Si NL structure by using electron beam irradiation and laser deposition methods, in which a novel way was used to control the NL thickness by modulating irradiation time of the electron beam. The new effect should have a good application on a photonic-electronic chip of silicon.

In this work, the structural, electronic and optical properties of Si-doped barium chalcogenide [barium sulfide (BaS)] with different Si concentrations ($0\le x\le 0.25$) are investigated by the first-principles calculations based on the density functional theory (DFT). The band structures, charge densities and complex dielectric functions of the pure as well as Si-doped BaS were presented and analyzed in detail using TB-mBJ approach by WIEN2k package. It is found that silicon concentration can control the bandgap by reducing it to values around 1.4eV and 1.6eV for 12.5% and 6.25% of Si-doped BaS, respectively. The electron charge density indicates the ionic bonding between silicon and sulfur atoms due to the high electronegativity between them. In fact, the results show that the absorption peaks of Si-doped BaS are enhanced compared with pure BaS. These results suggest that the Ba${}_{1-x}$Si_xS original structure displays excellent physical properties thereby revealing that it is a promising material in advanced optoelectronic and solar cell applications.

One avenue toward next-generation spintronic devices is to develop half-metallic ferromagnets with 100% spin polarization and Curie temperature above room temperature. Half-metallic ferromagnets have unique density of states, where the majority spins are metallic but the minority spins are semiconducting with the Fermi level lying within an energy gap. To date, the half-metallic bandgap has been predominantly estimated using Jullière’s formula in a magnetic tunnel junction or measured by the Andreev reflection at low temperature, both of which are very sensitive to the surface/interface spin polarization. Alternative optical methods such as photoemission have also been employed but with a complicated and expensive setup. In this study, we developed and optimized a new technique to directly measure the half-metallic bandgap by introducing circularly polarized infrared light to excite minority spins. The absorption of the light represents the bandgap under a magnetic field to saturate the magnetization of a sample. This technique can be used to provide simple evaluation of a half-metallic film.