D. Gao

Plasma-chemical synthesis, structure and photoluminescence properties of hybrid graphene nanoflake–BNCO nanowall systems

We describe a simple, efficient plasma-chemical technique for the synthesis of hybrid structures formed by vertically oriented BNCO nanowalls and vertically oriented graphene nanoflakes (BNCONW/GNFs), as well as their structure and photoluminescence properties. The BNCONW/GNF hybrid structures were fabricated by the synthesis of vertically oriented BNCO nanowalls in N2–H2 plasma using the plasma-enhanced hot filament chemical vapour deposition technique, followed by the direct synthesis of vertically oriented graphene nanoflakes on the BNCO nanowalls in a methane environment using a hot filament chemical vapour deposition method, where the B4C compound was used as the boron and carbon source. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectrometry measurements indicated that the BNCONW/GNF hybrid structures were composed of vertically oriented BNCO nanowalls and vertically oriented graphene nanoflakes. The photoluminescence studies of the vertically oriented BNCONW/GNF hybrid structures using a Ramalog system equipped with a 325 nm He–Cd laser demonstrated the possibility to efficiently tune the photoluminescence properties of the BNCONW/GNF structures by growing the graphene nanoflakes on the vertically oriented BNCONWs. Our findings can contribute to the designing of complex hybrid graphene–semiconductor structures suitable for applications in advanced next-generation optoelectronic nanodevices.

Preparation and characterization of Co and Ga2O3-codoped ZnS and ZnSe bulk ceramics

The bulk ceramics (Co)x(Ga2O3)0.6−x(ZnS/Se)0.4 (x = 0.1, 0.3 and 0.5) were fabricated via a solid state reaction in a high temperature pipe boiler at temperatures ranging from 1000 to 1400 °C. The structure, optical, valence and morphological properties were determined by XRD, XPS, Raman spectroscopy, SEM, UV-vis spectroscopy and IR absorption spectroscopy. The impressive effect of the sintering temperature on the doping elements was investigated, and the optimum sintering temperature in the range 1000–1200 °C was revealed, by analysis of the mass loss, molar ratio and shrinkage rate of (Co)x(Ga2O3)0.6−x(ZnS/Se)0.4. The zinc-blende structure of the bulk ceramic, and optimum doping ratio of (Co)0.5(Ga2O3)0.1(ZnS/Se)0.4, was confirmed by XRD and Raman spectroscopy. A broad and continuous absorption band from visible to infrared wavelengths was demonstrated for (Co)0.5(Ga2O3)0.1(ZnS/Se)0.4. The +2 and +3 valences of Co and Ga in the materials was proved by XPS. The surface morphology of the films was visualised by SEM and exhibited excellence when sintering temperatures were in the range 1000–1200 °C. The bulk ceramics (Co)x(Ga2O3)0.6−x(ZnS/Se)0.4 show a promising potential for future applications.

Investigation into Co and Ga2O3 co-doped ZnSe chalcogenide composite semiconductor thin films fabricated using PLD

(Ga2O3)0.1(Co)0.5(ZnSe)0.4 thin films were fabricated via PLD at different pressures and substrate temperatures. The influence of different preparation conditions on the thin films was deeply explored through investigating the structural, optical and electromagnetic properties, and surface morphologies. The thicknesses of the thin films were greatly affected by the preparation conditions. The poor light transmittance of the thin films under conditions of 4 Pa and 600 °C was revealed through refractive index measurements. The stable amorphous structure was confirmed via XRD. The optimum preparation conditions, room temperature, 800 °C and 10 Pa, were reflected in the transmission spectra. Greater energy transfer between each of the energy levels and more activity under the temperature conditions used were indicated through PL spectra. The lower resistivity and higher carrier concentration in the quartz substrate were shown in the results of Hall effect measurements. The significant impact of high temperature preparation conditions on the thin films was visualised using AFM. All of the results indicated that the properties of the thin films are significantly influenced by the preparation conditions. Furthermore, a semiconductor chalcogenide material with excellent optical and electromagnetic properties was proposed in this investigation.

Structural and optoelectronic properties of ZnGaO thin film by pulsed laser deposition

ZnO has attracted much attention because of its high-energy gap and exciton binding energy at room temperature. Compared to ZnO thin films, ZnGaO thin films are more resistive to oxidation and have smaller deformation of lattice. In this study, the high purity ZnSe and Ga2O3 powders were weighted at a molar ratio of 18:1. Se was oxidized to Se2O3 and separated from the mixture powders by using conventional solid state reaction method in air, and the ZnGaO ceramic target was prepared. We fabricated the ZnGaO films on silica glass by pulsed laser deposition (PLD) method under different oxygen pressure at room temperature. The as-grown films were tested by X-ray diffraction and atomic force microscope (AFM) to diagnose the crystal structure and surface morphology. Moreover, we obtained the optical transmittance of ZnGaO film and found that the electrical conductivity capacity varied with the increase of oxygen pressure.

ZnS:Co film grown by pulsed laser deposition and optical properties analysis

The modification of ZnS by doping method is one of the important directions in the research of ZnS nano materials. Doping of transition metal ions in the ZnS matrix has attracted much attention in recent years. Doping transition metal ions can modulate the emission region of ZnS, and improve the efficiency of fluorescence. The doping concentration in ZnS has determined the distribution, absorption, excitation, emission, and structural properties of particles. Due to ZnS:Co crystal materials have the best characteristics: the stability of the mechanical properties, high emission cross section and wide bandgap tuning at room temperature. So the ZnS:Co film is grown by pulsed laser deposition and the near infrared spectrum properties have analyzed that have researched in theory and experiment. We change the pressure in the vacuum chamber by controlling the pressure of the argon gas to fabricated the ZnS:Co film by PLD, at the same time, we chose three kinds of materials as the substrate of the thin film, and compared the characteristics of the thin films. This method has the advantages of short fabrication time and material saving, so it is good for to detect and research the optical properties of the films of ZnS:Co. A variety of film detection of X-ray diffraction, laser particle size analyzer, UV-Vis spectrophotometer, fluorescence spectrophotometer, morphology, the particle size and optical properties of the samples have tested. From the results, the infrared transmittance of the Co doped ZnS is almost above 90%, and the transmission capacity increases with the increase of pressure. The film thickness decreases with the increase of pressure and there is a sharp peak in absorption spectrum, this point has important significance for studying photoluminescence of the near infrared spectrum.