Shizheng Wang

Morphology-controlled synthesis and a comparative study of the physical properties of SnO2 nanostructures: from ultrathin nanowires to ultrawide nanobelts.

Controlled synthesis of one-dimensional materials, such as nanowires and nanobelts, is of vital importance for achieving the desired properties and fabricating functional devices. We report a systematic investigation of the vapor transport growth of one-dimensional SnO(2) nanostructures, aiming to achieve precise morphology control. SnO(2) nanowires are obtained when SnO(2) mixed with graphite is used as the source material; adding TiO(2) into the source reliably leads to the formation of nanobelts. Ti-induced modification of crystal surface energy is proposed to be the origin of the morphology change. In addition, control of the lateral dimensions of both SnO(2) nanowires (from approximately 15 to approximately 115 nm in diameter) and nanobelts (from approximately 30 nm to approximately 2 microm in width) is achieved by adjusting the growth conditions. The physical properties of SnO(2) nanowires and nanobelts are further characterized and compared using room temperature photoluminescence, resonant Raman scattering, and field emission measurements.

Ultraviolet light emission and excitonic fine structures in ultrathin single-crystalline indium oxide nanowires

We report the ultraviolet light emission from ultrathin indium oxide (In2O3) nanowires fabricated by the vapor-liquid-solid method. The high crystalline quality of the samples is confirmed by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Strong ultraviolet light emission is consistently observed in the temperature dependent photoluminescence measurements carried out between 10 and 300 K. Emissions related to free excitons and bound exciton complexes, donor-acceptor pair transition and its relevant longitudinal optical phonon replicas are identified and their temperature-dependent evolution is discussed in details.

Effect of oxygen stoichiometry on the insulator-metal phase transition in vanadium oxide thin films studied using optical pump-terahertz probe spectroscopy

Using optical pump-terahertz probe spectroscopy, we studied the dynamic behaviors of photoinduced insulator-metal phase transition in vanadium oxide thin films with different oxygen stoichiometry. We found that the insulator-metal phase transition of vanadium dioxide is very sensitive to oxygen stoichiometry: the increased oxygen content in vanadium oxide will reduce the magnitude of phase transition and change the dynamics of the phase transition. The transient complex photoconductivity of vanadium oxide thin films is investigated and analyzed with Drude-Smith model, supplying insight of the dynamic process of phase transition in vanadium oxide thin films.

Influence of thin metal nanolayers on the photodetective properties of ZnO thin films

We investigate the photoconductivity properties of ZnO thin films prepared by pulsed laser deposition with and without metals (Au or Pt) on the surface. The covering of nanostructured metals can largely enhance the photocurrent. Meanwhile, the dark currents have been increased significantly due to the increase in carrier concentration and mobility near the surface of ZnO thin film. Although plasmonic effect was observed by the photoluminescence enhancement, the main mechanism of the increase in the dark current and photoresponsivity for ZnO photoconductors has been interpreted by surface states, interface states, and persistent photoconductivity.

Surface-plasmon enhancement of band gap emission from ZnCdO thin films by gold particles

We present our study of the dependence of surface plasmon (SP) coupled band gap emission and defect emission on the sputtering time of gold particles on ZnCdO films. Eightfold enhancement of the band gap emission from ZnCdO thin films coated with Au particles is observed, while the defect emission is completely suppressed. The remarkable enhancement of the band gap emission is mainly attributed to the coupling between excitons in ZnCdO films and the SP of Au particles. While the suppression of the defect emission may be ascribed to a combined effect of the reduction in surface defects and the charge transfer from defect level to the Au Fermi level.

Surface plasmon induced exciton redistribution in ZnCdO/ZnO coaxial multiquantum-well nanowires

The authors present the surface plasmon effects of Au nanoparticles on the photoluminescence properties of ZnCdO/ZnO coaxial multiquantum-well nanowires fabricated using chemical vapor deposition and pulse laser deposition methods. The spontaneous emission rate from ZnCdO quantum wells was increased by surface plasmon coupling by 1.29 times. The strong plasmon coupling between ZnO barriers and Au nanoparticles provides an extra fast decay channel for excitons generated in ZnO barrier layer and leads to exciton redistribution in ZnCdO/ZnO coaxial quantum wells, which promotes radiative recombination in ZnO barriers but reduces the number of excitons relaxing into the ZnCdO quantum wells.

L1-optimized linear prediction for light field image compression

The advent of consumer-level plenoptic cameras has sparkled the interest towards the design of efficient compression techniques for light field images. State-of-the-art compression systems such as HEVC prove to be inefficient when directly applied on this type of data due to the inherent spatial discontinuities among neighboring microlens images. In this paper, a novel light field image compression system is proposed. The disk-shaped pixel clusters corresponding to each microlens in the light field image are efficiently predicted based on the neighboring disks. In this context, an optimized linear prediction design based on L1 minimization of the residuals is proposed. K-means clustering is employed on training data in order to determine the optimized set of predictors. The experimental results on an extensive set of light field images demonstrate that the proposed coding scheme yields an average of 2.93 dB and 3.22 dB gain in PSNR, and 52.67% and 57.27% average rate savings compared to HEVC and JPEG2000 respectively.

Multi-layer light field display characterisation

Light field 3D displays, where a hologram-like image is produced by using geometrical optical techniques as opposed to interference of light, require different measurement procedures to conventional stereoscopic displays for the measurement of certain parameters. This paper covers methods that are particularly applicable to multi-layer light field displays using two or more cascaded display layers where the images are produced by computationally-intensive algorithms. As the overall system performance is dependent on capture and computation as well as display hardware, we have developed methods that allow for all the components in the complete chain. In addition to describing these we also cover other selected measurement techniques here.

Two-layer optimized light field display using depth initialization

In this paper, we propose a method to optimize two-layer light field display using depth initialization. In contrast to existing trade-off work between performance and processing time, this paper firstly models the display principle of layered light field display, and then performs layered initialization with the prior known depth of 3D objects, and finally optimizes the layered images for light field display. Experiments demonstrate that the proposed initialization method can obviously save the iterations and related processing time for the existing online or offline algorithms to achieve the same reconstructed peak signal to noise ratio (PSNR) and present a better subjective reconstructed performance using the same computation resource.

Duality properties of light field capture and display on Lytro camera and multi-layer display

Light field capture and multi-layer light field displays are increasingly concerned topics for academia and industry. However, an integrated discussion connecting capture and display has been long neglected. Therefore, this paper proposes a duality analysis of capture and display to comprehensively analyze and define two basic attributes; depth range and angular resolution. The main contribution of this paper is to discuss the display properties based on the configurations of light field capture and its effect on displayed image quality rather than focusing on the display itself.