Xuefei Li

Effects of (P, N) dual acceptor doping on band gap and p-type conduction behavior of ZnO films

A reproducible p-type P-N codoped ZnO [ZnO:(P, N)] film with high quality was achieved by magnetron sputtering and post-annealing techniques. It has room-temperature resistivity of 3.98 Ωcm, Hall mobility of 1.35 cm2/Vs, and carrier concentration of 1.16 × 1018 cm−3, which is better than electrical properties of the p-type N-doped ZnO (ZnO:N) and p-type P-doped ZnO (ZnO:P) films. Additionally, the p-ZnO:(P, N)/n-ZnO homojunction showed a clear p-n diode characteristic. The p-type conductivity of ZnO:(P, N) is attributed to the formation of an impurity band above the valance band maximum, resulting in a reduction in the band gap and a decrease in the ionization energy of the acceptor, as well as an improvement in the conductivity and stability of the p-type ZnO:(P, N).

The electrical transportation and carrier behavior of ZnSe under high pressure

With in situ electrical resistivity and Hall effect measurement, electrical transportation property and charge carrier behavior of ZnSe were investigated under high pressure using a diamond anvil cell (DAC). The electrical resistivity changed discontinuously at 7.7 and 11.9 GPa, corresponding to the phase transitions of ZnSe. In the pressure interval of 7.7–11.9 GPa, the electrical resistivity changed continuously, indicating the existence of the intermediate phase between the zinc blende and rock salt phases. The difference of carrier characteristic between the intermediate and rock salt phases can also suggest the existence of the intermediate phase. For the intermediate phase, the increase in electrical resistivity is from the decrease in mobility. While for the rock salt phase, the increase in charge carrier concentration leads to the decrease in electrical resistivity.

Mixed conduction in BaF2 nanocrystals under high pressure

The charge transport behavior of barium fluoride nanocrystals has been investigated by in situ impedance measurement up to 23 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in BaF2 nanocrystals include both F− ions and electrons. Pressure makes both the F− ions diffusion and electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the Fm3m and Pnma phases more difficult. The electron conduction plays a dominant role in the transport process. In the Fm3m and Pnma phases, the electron transference number increases with increasing pressure.

High pressure impedance spectroscopy of SrF2 nanocrystals

ABSTRACT The charge transport behavior of strontium fluoride nanocrystals has been investigated by in situ impedance measurement up to 41 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in SrF2 nanocrystals include both F− ions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the Fm3m and Pnma phases more difficult.

Effect of Tb-doped Concentration Variation on the Electrical and Dielectric Properties of CaF2 Nanoparticles

Calcium fluoride (CaF2) nanoparticles with various terbium (Tb) doping concentrations were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and alternating current (AC) impedance measurement. The original shape and structure of CaF2 nanoparticles were retained after doping. In all the samples, the dominant charge carriers were electrons, and the F− ion transference number increased with increasing Tb concentration. The defects in the grain region considerably contributed to the electron transportation process. When the Tb concentration was less than 3%, the effect of the ionic radius variation dominated and led to the diffusion of the F− ions and facilitated electron transportation. When the Tb concentration was greater than 3%, the increasing deformation potential scattering dominated, impeding F− ion diffusion and electron transportation. The substitution of Ca2+ by Tb3+ enables the electron and ion hopping in CaF2 nanocrystals, resulting in increased permittivity.

Photocatalytic properties of nano-structured carbon nitride: a comparison with bulk graphitic carbon nitride

Abstract We have synthesised two kinds of graphitic carbon nitride (g-C3N4) through a pyrolysis process involving urea and melamine. The obtained products were characterised by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflection spectroscopy, and nitrogen adsorption–desorption. The product derived from the urea shows a mesoporous honeycomb-like nanosheet structure (denoted by h-g-C3N4): compared with the bulk product obtained from melamine (denoted by b-g-C3N4), the h-g-C3N4 showed better adsorption and higher photo-activity for rhodamine B (RhB) reduction. The h-g-C3N4 also shows good reusability after cyclic adsorption–regeneration. The present results evinced an efficient design, an eco-friendly and convenient photocatalyst, and a tunable photo-reactivity for use in sustainable light-to-energy conversion.