InGaN/GaN quantum dots (QD) in nanowires exhibit excellent optical properties and are promising candidates for nanoscale optoelectronic devices. However, a large amount of surface states would cause low quantum efficiency more severely than bulk materials, through not only nonradiative recombination centers but also upward band bending. Therefore, it is necessary to control the band bending effect in order to improve the quantum efficiency of QDs. In this work, quantitative measurements are carried out by ultraviolet photoelectron spectroscopy (UPS) to describe the band bending effect in InGaN/GaN QD in nanowires coated with three different dielectric layers including SiN x , Al2O3, and SiO2. Furthermore, their passivation mechanisms are investigated by photoluminescence (PL), time-resolved PL. Contrary to SiO2 passivation, the SiN x and Al2O3 passivation nanowires demonstrate notable improvements in emission intensity. Most essentially, all experimental findings are consilience with the physical model that the deposition of dielectric layers effectively alter the surface states of nanowires resulting a weakening or strengthen in band bending near the surface. Our systematic studies on passivation of nanowires can provide strategies for optimizing the performance of nanowire-based optoelectronic applications.

In quantum structures and nanomaterials, surface conditions have significant influence on the material’s optical and electrical properties; hence, surface modification is an inevitable and critical step during the fabrication process of optoelectronic devices. A comprehensive understanding on how surface conditions impact on the performance is a key issue; however, it is difficult to apply experimental techniques to study the surface physics in the atomic scale. In this paper, the photoluminescence properties of InGaN/GaN quantum dots in nanopillar samples were carefully investigated and compared after applying various surface manipulation techniques. Spectroscopic results show that the localization features including recombination energy level and peak shift with temperature are extremely sensitive to surface treatment. Based on the localized state ensemble model, a quantitative analysis is performed taking into account of thermal activation and density of states distribution function of localization. The correlation between optical properties and the physical mechanism of surface modification is established. This spectroscopic technique along with the analytical method provides physical insights and reliable basis for nanoscale device evaluation and optimization.

The liquid flow during the process of liquid explosion dissemination is a typical complex high-speed unsteady motion with multi-scale in space and time. The motion of liquid flow may be partitioned to several stages. The first is initial liquid expansion by the action of shock wave and explosive gaseous products. The second is breakup of liquid annulus and turbulent mixing, which is called near-field flow. The third is two-phase mixing flow of gas and liquid drops, which is called far-field flow. To first stage, a compressible inviscid liquid model was used, while an elastic and plastic model was used to depict-the expansion of solid shell. Numerical study in two dimensional has been made by using the Arbitrary Euler-Lagrange (ALE) methods. In near-field, the unstable flow of liquid annulus is dominated by many factors. (1) The shock action of gaseous expansive products. (2) The geometric structure of wave system in liquid. (3) The local bubble and cavitating flow in annulus, induce much of local unstable interface, tear up interfaces, and enhance the instability and breakup of liquid annulus. In this paper, some postulations are proposed that the cavitations in liquid annulus are induced by shock wave and the flow of liquid annulus is a two phase flow (liquid and a discrete bubble groups). Some experimental results will be presented that the breakup of interface and turbulent mixing is visualized qualitatively and measured quantitatively by using shadow photography method. The primary results are some flow patten of interfaces and some transient flow parameters by which the nonlinear character will be obtained, and provide an experiential support for modeling to unstable interface flow and turbulent mixing. The two-phase mixing flow between liquid drops and gas in far-field can be studied by numerical methods where the turbulent motion of gas phase is represented with k-r model in Euler system, the motion of particle phase is represented with particle stochastic trajectory in Lagrange system, and the behavior of drops are calculated with breakup, coalescence, and evaporation models.