Y.P. Leung

Synthesis of wurtzite ZnSe nanorings by thermal evaporation

In this study, free standing crystalline ZnSe nanorings and nanowires have been fabricated on Au coated Si substrates by simple thermal evaporation of ZnSe powders. Ring- or wirelike morphology can be achieved in a controllable manner by using different reactor pressures during growth, while all the other conditions remain the same. Our results show that the ZnSe nanorings are wurtzite phase instead of the zinc-blende phase, observed in typical one-dimensional ZnSe nanostructures. The growth mechanism of the nanorings has been discussed, and the cathodoluminescence of the nanorings has been described.

Synthesis and analysis of abnormal wurtzite ZnSe nanowheels

An abnormal structure of the ZnSe nanowheels composed of teethlike extended patterns on nanoring bases has been successfully synthesized by thermal evaporation method. It is interesting to note that the as-synthesized ZnSe nanowheels are metastable wurtzite phase with the dominant exposed surfaces of ±(21¯1¯0) while the stable ZnSe is typically zinc blende phase. A full picture of the growth mechanism of the metastable wurtzite phase ZnSe nanostructures will be proposed from the thermodynamic point of view. Meanwhile, the formation of the nanowheels is also explained by a two-stage mechanism. In the first stage, the base of the nanowheel begins to form by vapor-solid mechanism, while in the second stage, the teethlike extended structures grow through the self-catalyzed growth process. The cathodoluminescence spectrum of ZnSe nanowheel exhibited a band edge transition at about 460nm and a strong self-activated luminescence at 610nm. It is important to note that the discussions of the nanostructure thermody...

Largely extended light-emission shift of ZnSe nanostructures with temperature.

ZnSe nanowires and nanobelts with zinc blende structure have been synthesized. The morphology and the growth mechanisms of the ZnSe nanostructures will be discussed. From the photoluminescence (PL) of the ZnSe nanostructures, it is interesting to note that red color emission with only a single peak at the photon energy of 2 eV at room temperature is obtained while the typical bandgap transition energy of ZnSe is 2.7 eV. When the temperature is reduced to 150 K, the peak wavelength shifts to 2.3 eV with yellowish emission and then blue emission with the peak at 2.7 eV at temperature less than 50 K. The overall wavelength shift of 700 meV is obtained as compared to the conventional ZnSe of about 100 meV (i.e., sevenfold extension). The ZnSe nanostructures with enhanced wavelength shift can potentially function as visible light temperature-indicator. The color change from red to yellowish and then to blue is large enough for the nanostructures to be used for temperature-sensing applications. The details of PL spectra of ZnSe at various temperatures are studied from (i) the spectral profile, (ii) the half-width half-maximum, and (iii) the peak photon energy of each of the emission centers. The results show that the simplified configuration coordinate model can be used to describe the emission spectra, and the frequency of the local vibrational mode of the emission centers is determined.

CVD grown zinc based nanostructures on zinc selenide microscale grains

With a suitable growth condition using CVD method, single crystal ZnO nanorods grow on the well-defined bounded facets of the random shape ZnSe grains using Zn and Se powders without any metal catalyst. To our best knowledge, there is no report in growing ZnO nanostructures on in-situ synthesized ZnSe. The growth direction of ZnSe nanorods on a facet of a ZnSe grain is quiet uniform. The growth mechanism of the nanostructure will be discussed. Meanwhile, the photoluminescence of the nanostructures will be investigated.

ZnSe nanorings and its cathodoluminescence

In this paper, we report free-stand wurtzite phase ZnSe nanorings and zinc blende phase nanowires fabricated on Au coated Si substrates through the thermal evaporation of pristine ZnSe powders. The Ring-or wire-like nanstructures can be achieved in a controllable manner by using different reactor pressures during growth, while all the other conditions remain the same. To our knowledge, the wurtzite phase ZnSe rings have not been reported to date. The growth mechanism of the nanorings has been discussed and the cathodoluminescence of the nanorings has been described.

Wavelength Tunable Light Emitting Nanostructures and Devices

In this paper, we report our recent progress in wavelength tunable organic light emitting diodes (OLEDs) and nanostructures. For OLEDs, a considerable color tunability by changing the applied voltage is demonstrated and the mechanisms of the tunability are discussed. For the nanostructures, the tunable emission of ZnSe nanobelts by modifying the operation temperature is reported. The origins of the emission light will be discussed.