ABSTRACT
The two-dimensional heterostructure nanobelts with a central CdSe region and lateral CdS structures are synthesized by a two-step physical vapor transport method. The large growth rate difference between lateral CdS structures on both +/- (0001) sides of the CdSe region is found. The growth anisotropy is discussed in terms of the polar nature of the side +/- (0001) surfaces of CdSe. High-resolution transmission electron microscopy reveals the CdSe central region covered with non-uniform CdS layer/islands. From micro-photoluminescence measurements, a systematic blueshift of emission energy from the central CdSe region in accordance with the increase of lateral CdS growth temperature is observed. This result indicates that the intermixing rate in the CdSe region with CdS increases with the increase of lateral CdS growth temperature. In conventional CdSSe ternary nanostructures, morphology and emission wavelength were correlated parameters. However, the morphology and emission wavelength are independently controllable in the CdS/CdSe lateral heterostructure nanobelts. This structure is attractive for applications in visible optoelectronic devices.
ABSTRACT
We have investigated the growth of ternary CdSSe nanostructures by physical vapor transport, specifically aiming at the synthesis of CdSSe nanosheets. CdSSe nanostructures with various S mole fractions are grown at growth temperatures less than 800 degrees C and photoluminescence from these nanostructures covers the entire visible spectral range. Morphological evolution from nanowires to nanosheets is observed as increasing growth temperatures due to the change of relative dominance in the growth mechanism from vapor-liquid-solid to vapor-solid. Nanosheets whose widths extend several tens of micrometers are successfully synthesized. However, nanosheets show a strong suppression effect of S incorporation when the growth is dominated by the vapor-solid mechanism. A micro-photoluminescence study shows high optical quality of individual CdSSe nanostructures with polarization anisotropy ratios rho ~ 0.1. In addition, lateral heterostructure CdS/CdSe nanosheets are successfully synthesized by two step growth. Strong red and green emissions are observed by selective laser excitations focusing at the center and edge parts of these heterostructure nanosheets, respectively. These heterostructure CdS/CdSe nanosheets may be useful for multicolor light emitting devices.
