We have investigated the optical transitions in Ga1−yInyNxAs1−x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Qc, electron effective mass me*, and band gap energy Eg were estimated. It was found that the Qc is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0–1)%. The me* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the me* and Eg of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states.

The formation of oxygen vacancies is one of the most critical factors that can improve the electronic and catalytic properties of metal oxides, in which an important challenge is to lower the formation energy of oxygen vacancies at the interface structure. Here we show that clay surfaces rich with hydroxyl groups can induce the formation of oxygen vacancies in metal oxide catalysts. Based on density functional theory calculations, kaolinite is shown to hinder the surface dehydration process of Co 3 O 4 nanoparticles, and enhances the charge transfer process at the interface by the highly diffusible protons. Experimental results confirm that vacancy-rich Co 3 O 4 is easily produced by a reduction method and kaolinite enhances the formation of oxygen vacancies and divalent cobalt on the nanoparticle surface. As expected, the defective Co 3 O 4 /kaolinite exhibits enhanced catalytic and electrocatalytic performances. This finding provides an improved way to design efficient clay-based catalysts.

No abstract

We investigate the origin of yellow luminescence in n-type GaN. It is found that the relative intensity of yellow luminescence increases as the full width at half maximum of the x-ray diffraction rocking curve at the (102) plane increases. This indicates that the yellow luminescence is related to the edge dislocation density. In addition, the relative intensity of yellow luminescence is confirmed to increase with increasing Si doping for the high quality GaN we have obtained. We propose that the yellow luminescence is effectively enhanced by the transition from donor impurities such as Si to acceptors around the edge dislocations in n-type GaN.

The surface plasmon resonance (SPR) and Schottky effects are important photocatalytic activity boosters in metallic cocatalyst/photocatalyst systems, but it is difficult to differentiate them. In this report, we design a simple method to distinguish the two effects by utilizing a distance-tunable self-assembled monolayer (SAM) in a gold (Au)-Cu2O composite in conjunction with UV and visible-light sources, by which we had only the SPR or Schottky effect identified in the visible or UV light, respectively. Cysteine (cys) and mercaptoundecanoic acid (MUA) SAMs as linkers were used respectively for making Au-cys-Cu2O and Au-MUA-Cu2O composites. Au-citrate-Cu2O as a mild linker was also synthesized. Under UV-light irradiation, Au-Cu2O showed only the Schottky effect, while Au-MUA-Cu2O and Au-cys-Cu2O showed neither of the two effects. Under visible-light irradiation, Au-MUA-Cu2O and Au-cys-Cu2O showed clearly only the localized SPR (LSPR) effect, while Au-Cu2O demonstrated the coexistence of the two effects, which was further confirmed by their LSPR enhancement factor.

We have investigated the interband electron transitions in a GaNAs/GaAs single quantum well (QW) by photoluminescence and absorption spectra. The experimental results show that the dominant photoluminescence at low temperature and high excitation intensity originates from transitions within the GaNAs layer. The interband transition energy for QWs with different well widths can be well fitted if a type-II band line up of GaNAs/GaAs QWs is assumed.

Using spatially resolved cathodoluminescence spectroscopy, we investigate the spatial luminescence distribution in a fully strained ͑In,Ga͒N layer, in particular, its correlation with the distribution of threading dislocations ͑TDs͒. Regarding the impact of TDs on the luminescence properties, we can clearly distinguish between pure edge-type TDs and TDs with screw component. At the positions of both types of TDs, we establish nonradiative recombination sinks. The radius for carrier capture is at least four times larger for TDs with screw component as for pure edge-type TDs. The large capture radius of the former is due to a spiral-like growth mode resulting in an increase in the In content in the center of the spiral domains in comparison to their periphery.

No abstract