PHOTOLUMINESCENCE EMITTING PROPERTIES OF SINGLE ZnO NANOWIRE STUDIED BY SCANNING NEAR-FIELD OPTICAL MICROSCOPE

Scanning near-field optical microscope (SNOM) was employed to investigate the room temperature photoluminescence (PL) of single ZnO nanowires with different radii excited by 325 nm laser. Two-dimensional distribution of their PL intensity is provided for the analysis of intensity decay from emission source. It is found that the PL intensity at both ends of each ZnO nanowire (end emission) was much stronger than that at the sides of the wire (side emission). Further investigation indicates that the quality of end emission depends on the diameters of the wires. Some of the ZnO nanowires with special diameters emit stronger light, and the shape of the light is close to Gauss beam. In addition, the Gauss shape light can diffuse longer distance than what the side emission does, typically in the range of a few micrometers. It is a sign of the fact that special guided modes of the PL light are formed in the nanowires. The calculation results predicate that the special guiding mode strongly relies on the diameters of the ZnO nanowires. The good directional property and high intensity of the end emission have many potential applications, including optical switch and microanalysis. It has been shown that SNOM can provide direct evidence of light emission properties from single nanowires, and hence provide the clue of increasing light efficiency and the improvement of light-propagating mode.