Jiyuan Guo

Exciton and electron-hole plasma lasing in ZnO dodecagonal whispering-gallery-mode microcavities at room temperature

Dodecagonal ZnO microrods were fabricated by vapor transport method. A dodecagonal ZnO microrod with diameter of 6.35 μm was employed as a whispering gallery mode microcavity, the low threshold exciton lasing was stimulated. In another smaller microrod, the electron-hole plasma lasing was observed under intense excitation as the carrier density was larger than the Mott transition density. The interference condition in the dodecagonal cavity was deduced, and the mode structures were investigated. Compared to the hexagonal microcavity with same diameter, the dodecagonal microcavity has higher lasing performance.

Welding of gold nanowires with different joining procedures

Welding of single-crystal metallic nanowires is likely to have an important role in the bottom-up fabrication of nanodevices. The welding effects of free ends of two single-crystal gold nanowires (Au–Au) were demonstrated by Monte Carlo simulations in this paper. The quantum corrected Sutton–Chen type many-body potential was used to model the metal–metal interactions. Metallic nanowires were first placed closely with head-to-head, head-to-side and side-to-side joining procedures. Two ends were successfully welded together to form a continuous nanowire by annealing at different temperatures. The welding effects of the different joining procedure with different temperatures were compared. Structures of the welded specimens were characterized by the common neighbor analysis technique. Variable atomic mobility, freedom and contacting angles may result in different bonding strengths in the three different configurations. The results showed that the joint structure welded at low temperature were similar to the cold welding without fusion meanwhile the molten phase was presented in the joint when processing at the high temperatures.

Multiphoton absorption-induced optical whispering-gallery modes in ZnO microcavities at room temperature

Ultralong ZnO microrods with a perfect hexagonal cross section were synthesized on a large scale by the vapour phase transport method and were employed as a whispering-gallery mode (WGM) cavity to realize optical resonance and lasing. An individual ZnO microrod was selected to investigate the multiphoton absorption-induced optical behaviours based on the enhancement of the nonlinear optical interaction in the WGM cavity. Three-photon absorption-induced UV lasing, second-harmonic generation and defect-related visible emission simultaneously present distinct WGMs under the excitation of femtosecond laser pulses at 1200 nm. When the pump laser was changed to 1240 nm, four-photon absorption-induced WGM lasing was observed. The characteristics and generation process of the above resonant signals were investigated in detail.

DEFECT-ORIGIN AND STABILITY OF VISIBLE EMISSION IN ZnO NANOPILLARS

ZnO nanopillars with the strong violet photoluminescence were fabricated via the vapor-phase transport method. The annealing effect on photoluminescence property was probed to indicate the defect-origins of visible emissions and their thermodynamic stabilities. Moreover, the electron structures of ZnO with zinc interstitial, oxygen vacancy and oxygen interstitial were calculated based on the density functional theory. Three important points were demonstrated: zinc interstitial as an instable donor determines the violet emission and the concentration of free carriers; oxygen vacancy as a steady donor is responsible for the green emission; and oxygen interstitial may induce the yellow-green emission and lead to the red-shift and asymmetry of photoluminescence spectra. These results are beneficial to understand the defect-origins of the visible emissions and their stabilities in ZnO nanostructures, and extending optical and electronic applications.