Rational construction of Z-scheme photocatalysts and exploration of the Z-scheme charge transfer mechanism have drawn much attention in the field of CO2 reduction because of its great potential to alleviate energy crisis and environmental problems. In this study, a series of Z-scheme CdS/BiOI composites were constructed by depositing CdS nanoparticles on the surface of BiOI nanosheets. The synthesized materials were characterized comprehensively, and their photoreduction CO2 activities were evaluated. The results show that the composites exhibit higher photoreduction CO2 activity under visible light irradiation (λ > 400 nm) than pure CdS and BiOI. The yields of CO and CH4 for the optimal composite after 3 h irradiation are 3.32 and 0.54 μmol/g, respectively. The improved photocatalytic activity is attributed to Z-scheme transfer mode of the photogenerated charges in the composites. The mechanism of CO2 reduction is proposed and verified experimentally.

The growth of high-quality indium (In)-rich InXGa1−XN alloys is technologically important for applications to attain highly efficient green light-emitting diodes and solar cells. However, phase separation and composition modulation in In-rich InXGa1−XN alloys are inevitable phenomena that degrade the crystal quality of In-rich InXGa1−XN layers. Composition modulations were observed in the In-rich InXGa1−XN layers with various In compositions. The In composition modulation in the InXGa1−XN alloys formed in samples with In compositions exceeding 47%. The misfit strain between the InGaN layer and the GaN buffer retarded the composition modulation, which resulted in the formation of modulated regions 100 nm above the In0.67Ga0.33N/GaN interface. The composition modulations were formed on the specific crystallographic planes of both the {0001} and {0114} planes of InGaN.

Nitrogen and tellurium co-doped ZnO (ZnO:[N+Te]) films have been grown on (0001) ZnO substrate by plasma-assisted molecular beam epitaxy. The electron concentration of tellurium doped ZnO (ZnO:Te) gradually increases, compared that of undoped ZnO (u-ZnO). On the other hand, conductivity of ZnO:[N+Te] changes from n-type to p-type characteristic with a hole concentration of 4×1016 cm-3. However, nitrogen doped ZnO film (ZnO:N) still remain as n-type conductivity with a electron concentration of 2.5×1017 cm-3. Secondary ion mass spectroscopy reveals that nitrogen concentration ([N]) of ZnO:[N+Te] film (2×1021 cm-3) is relatively higher than that of ZnO:N film (3×1020 cm-3). 10 K photoluminescence spectra shows that considerable improvement of emission properties of ZnO:[N+Te] with an emergence of narrow acceptor bound exciton (A°X, 3.359 eV) and donor-acceptor pair (DAP, 3.217 eV), compared with those of u-ZnO. Consequently, high quality p-type ZnO with high N concentration is realized by using Te and N co-doping technique due to reduction of Madelung energy.

We report that the nonlinear optical response of polarity controlled ZnO films grown by selective growth technique of Zn-polar and O-polar ZnO layers on sapphire substrate using Cr-compound buffer layers. ZnO layers grown on CrN/sapphire show Zn polar, while those grown on Cr2O3/sapphire result in O-polar ZnO films. In order to verify the origin of nonlinear optical response of ZnO, the polarity-controlled ZnO thin films grown on different buffer layers were investigated as nonlinear optical materials for second harmonic generation (SHG). The effective nonlinear optical coefficient (deff) of ZnO grown on Cr-compound buffer layers showed a higher value than that of ZnO grown on MgO buffer layers. Finally, by combining suggested in-situ polarity control technique with photolithography technique, we have fabricated 1D and 2D periodically-polarity-inverted (PPI) hetro-structures with periodicity ranging from 60 μm to 2 μm. The lateral polarity inversion is confirmed by piezo response microscopy. Such PPI ZnO heterostructures show the enhancement of SHG intensity comparing with the ZnO films.

Composite amorphous powder core made by field-annealing with new insulations could improve the high frequency AC magnetic and mechanical properties. All of the amorphous ribbons with composition Fe78B16Si5C and Fe40Ni38Mo4B17Si were annealed at temperature higher than their embrittlement temperature but lower than the crystallization temperature. After the ribbons become brittle, they were mechanically crushed and milled to produce powders with size about 50 ∼ 250μm. To make a core, the amorphous powders combined with insulation binder were put into an evacuted toroidal followed by hot mechanical compaction. The weight percentages of binder were about 3 wt%, 5 wt% and 10 wt%. Field-annealings were carried out for different conditions in an Ar (or N2) atmosphere chamber at elevated temperature with applied field about 10 Oe. The initial magnetization curve and saturation magnetization were measured by vibrating sample magnetometer (O≤H≤10 KOe). DC and AC magnetic properties such as permeability, coercive force, core loss, etc. were tested by B-H loop tracer. It shows the AC properties can be improved by increasing the particle size of the amorphous powder and by increasing the interparticle contacts at high frequency.