Xueqiong Su

Random Laser Based on Waveguided Plasmonic Gain Channels

A waveguide-plasmonic scheme is constructed by coating the matrix of randomly distributed gold nanoisland structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser. Excellent overlap of the plasmonic resonance of the gold nanoislands with the photoluminescence spectrum of the dye molecules and the strong confinement mechanism provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. This kind of feedback configuration potentially enables directional output from such random lasers. The flexible solution-processable fabrication of the plasmonic gold nanostructures not only enables easy realization of such a random laser but also provides mechanisms for the tuning and multicolor operation of the laser emission.

Soft plasmons with stretchable spectroscopic response based on thermally patterned gold nanoparticles

Flexible photonic crystals are attractive devices owing to their multifold tunable parameters additionally introduced by soft substrates or by nanostructured, nano-doped, or nano-embedded soft matters. This not only extends significantly the intrinsic functions of photonic crystals, but also facilitates easy integration of the photonic crystal device into various optoelectronic and sensing systems. So far, flexible metallic photonic structures have been constructed on micrometer scales with complex fabrication procedures. Much simpler and more reproducible methods are expected to achieve such metamaterials in large scales and at low costs. In address to these challenges, we developed a straightforward approach to create soft plasmonic photonic crystals consisting of gold nanolines arranged on stretchable substrates with nanoscale periods, centimeter-scale areas, and high reproducibility using annealed gold nanoparticle colloids.

InGaZnO semiconductor thin film fabricated using pulsed laser deposition

The InGaZnO thin films are fabricated on the quartz glass using pulsed laser deposition (PLD), where the target is prepared by mixing the Ga(2)O(3), In(2)O(3), and ZnO powders at a mol ratio of 1:1:8 before the solid-state reactions in a tube furnace at the atmospheric pressure. The product thin films were characterized comprehensively by X-ray diffraction, atomic force microscopy, Hall-effect investigation, and X-ray photoelectron spectroscopy. Thus, we demonstrate semiconductor thin-film materials with high smoothness, high transmittance in visible region, and excellent electrical properties.

Role of cobalt in ZnO : Co thin films

We prepared a series of Co-doped thin films using the pulsed laser deposition method at deposition temperatures from 400 to 800??C under oxygen pressures from 10?4 to 15?Pa. We found that the ferromagnetic signals in ZnO?:?Co thin films only appear simultaneously with the detectable Co 2p spectra from incompletely oxidized Co metal. Therefore, we concluded that the ferromagnetism in ZnO?:?Co thin films is not an inherent magnetism in the material. On the other hand, we proposed that the inhomogeneous distribution of Co in the films could improve the link of the grains and increase the carrier concentration of the films, leading to positive Hall signals although the film is n-type. Therefore, the coexistence of ferromagnetism and p-type conductivity in ZnO?:?Co thin films need to be re-examined carefully.

Sensitivity enhancement through overlapping simultaneously excited Fano resonance modes of metallic-photonic-crystal sensors

We investigated enhancement of sensitivity of sensors based on metallic photonic crystals through tuning the thickness of the waveguide layer by pulsed laser deposition. Thicker waveguides made of InGaZnO allow double resonance of Fano coupling modes due to plasmonic-photonic interactions. Tuning the angle of incidence enables overlap between these doubly resonant modes, which induces much enlarged and spectrally narrowed sensor signals, leading to significantly enhanced sensitivity of the sensor device. The thickness of the waveguide layer is found to be a crucial structural parameter to improve sensitivity of the MPC sensors.

Pulsed laser deposited cobalt-doped ZnO thin film

To realize the room-temperature ferromagnetism (RTFM) in diluted magnetic semiconductors (DMS), we prepared a series of Cobalt-doped ZnO thin films using pulsed laser deposition (PLD) at deposition temperatures 500°C under oxygen pressure from 2.5×10-4 Pa to 15 Pa. To elucidate the physical origin of RTFM, Co 2p spectra of cobalt-doped ZnO thin films was measured by X-ray photoelectron spectroscopy (XPS). The magnetic properties of films were measured by an alternating gradient magnetometer (AGM), and the electrical properties were detected by a Hall Effect instrument using the Van der Pauw method. XPS analysis shows that the Co2+ exists and Co clusters and elemental content change greatly in samples under various deposition oxygen pressures. Not only the valence state and elemental content but also the electrical and magnetic properties were changed. In the case of oxygen pressure 10 Pa, an improvement of saturation magnetic moment about one order of magnitude over other oxygen pressure experiments, and the film exhibits ferromagnetism with a curie temperature above room temperature. It was found that the value of carrier concentration in the Co-doped ZnO film under oxygen pressure 10Pa increases about one order of magnitude than the values of other samples under different oxygen pressure. Combining XPS with AGM measurements, we found that the ferromagnetic signals in cobalt-doped ZnO thin film deposited at 500 °C under oxygen pressure 10 Pa only appear with the detectable Co2+ spectra from incompletely oxidized Co metal or Co cluster. So oxygen pressure 10 Pa can be thought the best condition to obtain room-temperature dilute magnetic semiconductor about cobalt-doped ZnO thin films.

Ferromagnetism in transparent thin film of Co-doped ZnO

Transparent thin films are manufactured by PLD (pulsed laser deposition) in different oxygen pressure. The various property of samples is measured by Atomic Force Microscope (AFM), X-ray diffraction (XRD) and optical transmission spectrum. All samples retain the original structure in wurtzite lattice by XRD, there is not being of metallic cobalt or other impurity phase with the limit detection. The surface morphology of the films observes the smoother than that in undoped ZnO thin film. The transparency of thin films has altered greatly with the different oxygen pressure or not by PLD, which is shown that the oxygen pressure has impacted on the transparency of the film and surface morphology. And UV-visible spectra fully have been demonstrated the presence of Co2+ to substitute for Zn2+ in the films with the different oxygen pressure.

Analysis of properties of ZnCoO bulks by solid state reaction

Zn0.9Co0.1O bulks were prepared by solid state reaction at various fritting temperatures in order to investigate the structural and optical properties of the bulks. The valence electron and doping concentration in bulk was measured by Xray photoelectron spectroscopy (XPS) instrument. Some basic properties of the bulk material in powder were examined to enhance the comprehension of magnetism in these semiconductors. The corresponding magnetic properties were evaluated by field-cooling and zero-field-cooling magnetization measurements, while the optical properties were tested by Fourier transformed infrared spectrum (FTIR). It is indcated that Co ions are well inserted in the ZnO structure and surrounded by four oxygen. It means that a series of Co have substituted Zn and the sample all the same maintains original wurtzite structure in lattice with a sintered temperature of 1200 °C, then it leads to chemical bond formation of Co-O. Furthermore, the fritting temperature do not play a crucial role in the determination of Co content.

Substrate temperature influence on the properties of InGaZnO thin films grown by PLD technique

In this paper, the effects of substrate temperature during film growth at relative high temperature have been reported. The IGZO thin films were fabricated by means of pulse laser deposition (PLD) with the InGaZnO (In2O3: Ga2O3: ZnO=1: 1: 8 mol %) target. The substrate temperature altered from room temperature (RT) to 800 °C. The product thin films were characterized rigorously by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-VIS spectrometer, Halleffect investigation and X-ray photoelectron spectroscopy (XPS). The IGZO films was with smooth surface, high transmission in the visible spectral range (about 75-92 %), carrier mobility > 8.0 cm2/(V·s) and carrier concentration at about 1018 cm-3. Finally, the character changes influenced by temperature were obtained from analysis results. This task may benefit to a flat panel display in the process of thin film transistors(TFT) fabrications and improvements.