Qiufeng Huang

Dye-sensitized solar cells based on nanoparticle-decorated ZnO/TiO2 core/shell nanorod arrays

Nanoparticles (NPs) decorated ZnO/TiO2 core/shell nanorod arrays were fabricated on transparent conductive glass substrates by sequential plasma deposition and post-annealing processes for dye-sensitized solar cells (DSSCs) applications. The NPs decorated ZnO/TiO2 nanorods were composed of single-crystalline ZnO nanorods, homogeneously coated thin TiO2 shells and entirely covered anatase TiO2 NPs. The photocurrent density of the composite electrode was largely enhanced due to the enlarged surface area, the dark current was suppressed and the open-circuit voltage was increased because of the energy barrier formed at the interface between the ZnO core and the TiO2 shell. The increased photocurrent and open-circuit voltage led to an improvement of twice the energy conversion efficiency.

The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell’s characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.

Physical properties and growth kinetics of co-sputtered indium-zinc oxide films

Indium-doped zinc oxide (IZO) films were fabricated by radio-frequency (RF) magnetron sputtering through co-deposition of zinc oxide (ZnO) and indium (In) at ambient temperature. Transparency of the IZO films is higher than 80% in the visible range while the optical band gap decreases with increasing In dopant concentration. The optimal measured resistivity, Hall mobility and carrier concentration of the film are 1.39 × 10−3 Ω cm, 10.11 cm2 V−1 s−1 and 5.35 × 1020 cm−3, respectively. The In dopant favors smoothing the film surface. The In dopant concentration in the film decreases vertically from the surface to the interface due to the surface segregation during the kinetic deposition process. The misfit strains of the films are gradually relaxed through dislocation.

Improved thermal stability of wet-oxidized AlAs

Lateral thermal wet oxidization of the AlAs layer in a GaAs/AlAs/GaAs sandwiched structure is studied by Raman spectroscopy and Nomarski microscopy. A significant improvement in thermal stability of the oxidized AlAs layer has been achieved by optimizing the oxidation conditions, which can be used to fabricate reliable devices. We show that the thermal stability is strongly related to the removal of volatile products, such as As and As2O3, as evidenced by the Raman spectroscopy measurement.

Diode-pumped tape casting planar waveguide YAG/Nd:YAG/YAG ceramic laser

We demonstrated the efficient guided laser action in a diode-pumped YAG/Nd:YAG/YAG ceramic planar waveguide produced by tape casting and vacuum sintering technology for the first time to the best of our knowledge. In the regime of continuous wave operation, a maximum output power of 840 mW corresponding to the slope efficiency of 65% was achieved. During passively Q-switched operation, by replacing the dichroic mirror with graphene-oxide based output coupler, we obtained the stable pulse trains with the shortest pulse duration of 179 ns at a pulse repetition rate of 930 kHz which resulted in the single pulse energy of 221 nJ.

Spectroscopic properties and energy transfers in Cr, Tm, Ho triple-doped Y 3 Al 5 O 12 transparent ceramics

Highly transparent Cr, Tm, Ho triple-doped Y3Al5O12 (YAG) ceramics were prepared using advanced ceramic technology and their spectroscopic properties were studied for infrared laser applications. 2.09 μm emission was observed by exciting at 430 nm, which indicated the realization of energy transition from Cr3+ to Ho3+ with Tm3+ acted as an intermediate media. The efficiency between the energy transfer (Tm3+) 3F4→ (Ho3+) 5I7 and its back-transfer process was 7.87, which was comparable to that of YAG single crystal and YLF. Studies on the optical gain and stimulated emission characteristics suggested that this triple-doped YAG ceramic could be an appropriate material for 2.09 μm laser application.

Low content indium-doped zinc oxide films with tunable work function fabricated through magnetron sputtering

Low content indium-doped zinc oxide (LC-IZO) films have been prepared through radio-frequency (RF) magnetron sputtering. The work functions of the LC-IZO films were successfully tuned up by modulating the deposited conditions, such as indium content, substrate temperature, bias voltage and film thickness. The work functions of the films may be modulated in a large range between 4.59 eV and 5.56 eV. The change of the work function may be the results induced by the change in the surface state. The results may be helpful for widening the application of LC-IZO films.

Growth kinetics of three-dimensional ZnO islands on various substrates

Growth kinetics of three-dimensional (3D) ZnO islands on silicon, sapphire, quartz glass and lime glass substrates, fabricated by radio-frequency magnetron sputtering, were investigated through physical–statistical analysis and the scaling behaviour method. These results show that the 3D islands nucleate with only one atom, and the scattered island size distribution indicates that the strain effect is significant for disturbing the atomic diffusion kinetic process. Gradual strain relaxation through dislocation is confirmed by the decreasing trend in the aspect ratio dependence on the lateral sizes for 3D islands. Additionally, surface roughening also works during strain relaxation.

Two-wave mixing in Stark geometry photorefractive quantum wells under a magnetic field

Using a modified method for measuring photorefractive two-wave mixing gain, we presented the experimental demonstration of nonreciprocal energy transfer during two-wave mixing under an external magnetic field. The nonreciprocal energy transfer is observed with mixing gain approaching 164u2002cm−1 and showed the characteristics of nonlinearity and saturation. A simple model of resonant tunneling and ultrafast carrier lifetime was proposed to explain these results.

Molecular beam epitaxial growth of Si/GeSi ridge structure

In this article, we review our recent studies on new rare-earth intermetallic compounds including the Ga, Si substituted 2:17-type compounds, their nitrides, carbides, and the Sm-3 (Fe,Ti)(29)N-5 compounds, Much of our recent work is focused on the Sm-2(Fe,Ga)(17)C-x alloys where we used melt spinning and subsequent annealing to obtain high coercivity, The highest coercivity obtained so far was in Sm2Fe14Ga3C2.5 with a value of 12.8 kOe at room temperature, The off-stoichiometric Sm2Fe14-xCoxSi2Ny nitrides maintain the Th2Zn17-type structure but with a unit-cell expansion Delta VV up to 5% compared to the host materials, The Sm2Fe14-xCoxSi2Cz, carbides maintain the Th2Zn17-type structure when z=1 and transform to the BaCd11-type structure when z = 2, A very large anisotropy field with an applied magnetic field (Ha) value of 227 kOe for Sm2Fe14Si2N2.6 and 276 kOe for Sm2Fe10Co4Si2N2.3 is observed at low temperature (1.5 K). The Sm-3(Fe,Ti)(29)N-5 compound and its nitrides show very interesting magnetic properties, Both of these compounds exhibit ferromagnetic ordering with Curie temperature (T-c) of 486 and 750 K, respectively, The room temperature saturation magnetization is 119 emu/g for the parent compounds and 145 emu/g for the nitrides, The easy magnetization direction changes from planar to uniaxial upon nitrogenation, The anisotropy field for the nitrides is 12 T at room temperature and 25 T at 4.2 K.