The electronic structure of a strongly bound sandwich MoS2-WS2 heterobilayer.

First of all, we show that two kinds of sandwich bilayers (BLs) are dynamically, thermally, and mechanically stable, which are degenerate p-type materials with intercalated Ca atoms, i.e., Nb-doped MoS2 homobilayers (HoBLs) and Nb-doped WS2-MoS2 heterobilayers (HtBLs) with 25% Nb content. Specifically, their interlayer bindings are five times stronger than van der Waals interactions in their pristine counterparts. Both of them are semiconductors with indirect band gaps in the visible region within the HSE06 exchange-correlation functional. Depending upon the presence and absence of centrosymmetry, they display interesting spin-valley coupling effects in such a way that opposite hidden spin polarization or opposite spin splitting is observed at opposite k-points. They can be easily engineered into direct gap materials under compressive (>2%) strain along the zigzag direction even with an explicit consideration of giant spin splitting. Under strain, they satisfy thermodynamic conditions for bifunctional catalysis in photocatalytic water splitting. In addition, the photoholes of the BLs can be subjected to lower overpotentials than those of pristine BLs for the oxygen evolution reaction. Electrons and holes in the sandwich HtBL can be separated into different layers under photon irradiation, allowing it to be more efficient than the corresponding HoBL in solar energy harvesting.

Polymorphic Ga2S3 nanowires: phase-controlled growth and crystal structure calculations.

The polymorphism of nanostructures is of paramount importance for many promising applications in high-performance nanodevices. We report the chemical vapor deposition synthesis of Ga2S3 nanowires (NWs) that show the consecutive phase transitions of monoclinic (M) → hexagonal (H) → wurtzite (W) → zinc blende (C) when lowering the growth temperature from 850 to 600 °C. At the highest temperature, single-crystalline NWs were grown in the thermodynamically stable M phase. Two types of H phase exhibited 1.8 nm periodic superlattice structures owing to the distinctively ordered Ga sites. They consisted of three rotational variants of the M phase along the growth direction ([001]M = [0001]H/W) but with different sequences in the variants. The phases shared the same crystallographic axis within the NWs, producing novel core-shell structures to illustrate the phase evolution. The relative stabilities of these phases were predicted using density functional theory calculations, and the results support the successive phase evolution. Photodetector devices based on the p-type M and H phase Ga2S3 NWs showed excellent UV photoresponse performance.

Effect of heat treatment on the photocatalytic activity of α-Fe2O3 nanoparticles: towards diclofenac elimination.

α-Fe2O3 nanoparticles were synthesized via a straightforward method. XRD, FTIR, SEM, ESR, and DRS techniques investigated the influence of various calcination temperatures on the crystal structure, optical, and photocatalytic properties of the samples. The obtained results demonstrated that the average crystallite size increased with the increase in the calcination temperature. Measured and computed optical properties were in accordance and the bandgap energy decreased with the increase in the calcination temperature. The highest photocatalytic degradation efficiency for diclofenac (DCF) was obtained with the sample calcinated at 300 °C (96%). The photocatalytic process occurs because of the presence of OH• radicals. The addition of H2O2 led to the inhibition of OH• radicals that H2O2 scavenged.