Chunqian Zhang

Enhanced photoluminescence from porous silicon nanowire arrays

The enhanced room-temperature photoluminescence of porous Si nanowire arrays and its mechanism are investigated. Over 4 orders of magnitude enhancement of light intensity is observed by tuning their nanostructures and surface modification. It is concluded that the localized states related to Si-O bonds and self-trapped excitations in the nanoporous structures are attributed to the strong light emission.

A binder-free Si-based anode for Li-ion batteries

A binder-free anode for lithium ion batteries consisting of micro-sized silicon particles and polyacrylonitrile (PAN) was prepared. By optimizing the size of the Si particles and the ratio of Si particles to PAN, the performance of the anode was greatly enhanced. Although its columbic efficiency in the first cycle is comparatively lower than that made by traditional methods, it increases to 99% in the 8th cycle, and remains above 99.5% for up to 190+ cycles. Due to its adhesivity and conductance, pyrolyzed PAN (PPAN) can be used both as a binder and the conductive agent at the same time.

Interface effect on emission properties of Er-doped Si nanoclusters embedded in SiO2 prepared by magnetron sputtering

Er-doped Si nanoclusters embedded in SiO2 (NCSO) films were prepared by radio frequency magnetron sputtering on either silicon or quartz substrates. A 1.16 mu m (1.08 eV) photoluminescence (PL) peak was observed from an Er-doped NCSO film deposited on a Si substrate. This 1.16 mu m peak is attributed to misfit dislocations at the NCSO/Si interface. The emission properties of the 1.16 mu m peak and its correlation with the Er3+ emission (1.54 mu m) have been studied in detail. The observed behavior suggests that the excitation mechanism of the 1.16 mu m PL is in a fashion similar to that shown for Er-doped Si nanoclusters embedded in a SiO2 matrix

Mechanism of texture formation during heat‐treatment process in Ag‐sheathed Bi‐2223 tapes

The texture formation and development of Bi‐based superconducting phases during the heat‐treatment process are carefully investigated. With increasing anneal time, the (001) texture of both 2212 and 2223 phases is enhanced. The reduction of the interfacial energy due to a Bi2O2 layer in the cell is the main factor contributing to the texture formation. The texture of the parent phase and the interface parallel to the (001) plane are beneficial factors. The effects of sheathed Ag, second phases, and voids on the texture formation are studied.

Impact of ammonia on the electrical properties of p-type Si nanowire arrays

The electrical properties of vertically upstanding p-type silicon nanowires arrays in the ambience of NH3 are studied. It is found that, the introducing of ammonia lowers their conductivity. By investigating the absorption and desorption processes of ammonia on nanowires (NW) surfaces, the current modulations of Si NWAs are interpreted in terms of band bending at the NW edge due to injections of negative carriers from ammonia.

A generalization of the Drude-Smith formula for magneto-optical conductivities in Faraday geometry

In this study, we generalize the impulse response approach and Poisson statistics proposed by Smith [Phys. Rev. B 64, 155106 (2001)] to evaluate the longitudinal and transverse magneto-optical conductivities in an electron gas system in Faraday geometry. Comparing with the standard Drude model, the coefficients an are introduced in the Drude-Smith formula to describe the backscattering or localization effect for the nth electronic scattering event. Such a formula can also be applied to study the elements of the dielectric function matrix in the presence of magnetic and radiation fields in electron gas systems. This theoretical work is primely motivated by recent experimental activities in measuring the real and imaginary parts of longitudinal and transverse magneto-optical conductivities in condensed matter materials and electronic devices using terahertz time-domain spectroscopy. We believe that the results obtained from this study can provide an appropriate theoretical tool in reproducing the experimental findings and in fitting with experimental data to determine the important sample and material parameters.

Hedgehog-like polycrystalline Si as anode material for high performance Li-ion battery

A hedgehog-like Si nanomaterial has been prepared by metal assisted chemical etching method with polycrystalline Si powder as raw material and used as anode for lithium-ion batteries. The cycle stability and impedance are greatly enhanced compared with pristine silicon powder, and the Columbic efficiency (CE) keeps above 99.5% for up to 200+ cycles. The improved electrochemical characteristics are attributed to its volume buffering and effective conductance due to the unique structure, which combines nanowires on the surface and a core inside. The additives in electrolyte and suitable conductive materials help to stabilise the anode as well.