Yingai Li

Template-free synthesis of α-GaOOH hyperbranched nanoarchitectures via crystal splitting and their optical properties

In this paper, a facile, template-free, one-step solvothermal method to synthesize size- and shape-controllable α-GaOOH with hierarchical nanoarchitectures has been developed. Hyperbranched α-GaOOH nanocrystals with a sheaf-like morphology has been prepared via the alcoholysis process with GaCl3 and methanol as the reactants in the presence of benzene as solvent at 160 °C within an autoclave. For the formation of α-GaOOH hierarchical nanoarchitectures, the crystal splitting growth mechanism plays the dominant role, which has been evidenced by the characterization of the time-dependent morphologies of the prepared samples. The UV-vis absorption spectra recorded at room temperature reveal that the obtained nanostructured α-GaOOH is a direct band gap semiconductor and the band gap Eg is estimated to be about 5.24 eV. Furthermore, a broad PL emission band can be clearly observed in the 425 to 575 nm spectrum range for the synthesized hyperbranched sheaf-like α-GaOOH nanoarchitectures.

The solvothermal synthesis of γ-AlOOH nanoflakes and their compression behaviors under high pressures

Boehmite, γ-AlOOH, has attracted increasing research enthusiasm due to its scientific and technological importance. The compression behaviors of γ-AlOOH are of vital relevance to the insight into geophysical and geochemical processes in Earths mantle. In this work, free-standing γ-AlOOH nanoflakes with high purity and crystallinity have been synthesized via a template-free, one-step solvothermal alcoholysis strategy. The nanoflakes have high aspect ratio, with the lateral size ranging from 100 to 300 nm, and the thickness ranging from 20 to 45 nm. The band gap of the obtained γ-AlOOH nanoflakes is estimated to be 3.35 eV through UV-vis absorption spectra recorded at room temperature. A broad PL emission band can be observed in the 400 to 700 nm spectrum range, with the maximum at 480 nm. The compression behaviors of γ-AlOOH nanoflakes have been investigated by in situ high pressure synchrotron radiation angle dispersive X-ray diffraction up to 54.9 GPa and Raman scattering spectroscopy up to 22.4 GPa at room temperature. The compression is nearly linear and anisotropic, with b axis more compressible than a and c axes. The zero-pressure bulk modulus of γ-AlOOH nanoflakes is estimated to be 135.2 GPa, higher than the theoretical value of its bulk counterpart. The frequencies of the observed Al–O related Raman modes increase monotonously in a linear manner with increasing pressure. The mode Gruneisen coefficients are estimated, which may provide important information about the anharmonicity in the bonding nature of γ-AlOOH.

Multiphonon Raman scattering in ZnSe/Zn0.80Cd0.20Se superlattices

Abstract A study of the multiphonon (MP) Raman scattering in ZnSe Zn 0.80 Cd 0.20 Se superlattices has been performed for the first time. Two kinds of longitudinal optical phonon modes were observed under the excitation of the 457.9 nm (2.71 eV) and 488.0 nm (2.54 eV) lines of an Ar+ ion laser at room temperature. A systematic discussion to distinguish the MP Raman scattering from hot luminescence is presented.

Photoluminescence of ZnSe/Zn1 − xCdxSe strained superlattices under hydrostatic pressure

Abstract A study of the photoluminescence (PL) of ZnSe/Zn 1 − x Cd x Se strained superlattices under hydrostatic pressure (0–2.5 GPa) at room temperature has been performed for the first time. The small sublinear dependence of PL energy with pressure for the heavy-hole exciton of the well layers was observed. The pressure coefficients of the PL peak were obtained by least-squares fits to the experimental data. The linear pressure coefficient obtained by calculation is in good agreement with the experimental one.

The influence of defects on the transport properties of AgSbPb18Te20 prepared at high pressure and high temperature

We synthesized polycrystal AgSbPb18Te20 by using the method of high pressure and high temperature, and found that the defects produced by high pressure and high temperature caused the changes of transport properties. X-ray diffraction patterns showed that the cell parameters did not change obviously with synthesis at high pressure, apart from a small fluctuation. The electrical resistivity first increased, and then decreased to one quarter of the original value, as the synthesis pressure changed from low to high. The Seebeck coefficient decreased with the increase of synthesis pressure, and then changed from positive to negative. High pressure and high temperature could cause AgSbPb18Te20 to change from a p-type to n-type semiconductor, increase the carrier concentration at maximum by two orders of magnitude, and shift the infrared absorption edge to a higher energy range. All of these phenomena were regarded as showing that high pressure and high temperature favored the formation of certain defects which could change the band structure and thereby change the transport properties.