Zinc oxide nanomaterials with a wurtzite structure are used for various applications including catalysis [1]. ZnO nanowires are of interest due to its high surface-to-volume ratio and thermodynamic stability of non-polar { } surfaces. Metal particles have been deposited onto the prismatic planes of ZnO nanowires for sensing and photocatalytic applications [2]. The interfacial structure between ZnO { } surfaces and various metals have been investigated [3]. Kra evec et al. reported that an oriented overgrowth of the spinel layers was observed between ZnO surfaces and a thin Sb-rich film [4]. Uniform antimony coating onto the surfaces of ZnO nanowires may provide new functions for applications in sensing, catalysis, energy conversion or nanoelectronics. We report here our recent study of the adsorption of Sb onto the { } facets of ZnO nanowires.The Sb/ZnO nanowires were synthesized in a high temperature tube furnace by a standard vapor phase transport process. Mixed ZnO and carbon powders were heated to about 1100°C and powders were placed down the stream of the tube furnace and were heated to generate Sb vapor inside the furnace. ZnO nanowires, formed in the high temperature zone, were carried to the low temperature zone where Sb atoms adsorbed onto the surfaces of the ZnO nanowires. By controlling the Sb partial vapor pressure we can control the thickness of the deposited Sb layers. The JEOL JEM-ARM200F aberrationcorrected scanning transmission electron microscope (STEM), with a nominal image resolution of 0.08 nm in the high-angle annular dark-field (HAADF) imaging mode, was used to investigate the atomic structure of the deposited Sb and its relationship with the facets of the ZnO nanowires. Figure 1a shows a HAADF image of an as-synthesized Sb/ZnO nanowire. The ZnO nanowire is atomically smooth with a diameter of about 20 nm. Analyses of HAADF images revealed that the ZnO nanowire grew along the [0001] axis and was enclosed by the six { } surfaces. Detailed examination of the HAADF images revealed that the surface atoms of the ZnO nanowire ( Fig. 1a and 1b) yielded a brighter image contrast. Furthermore, the brighter atoms only decorated on every other column of the surface Zn atoms. Since such brighter surface atoms have not been observed in ZnO nanowires that have been synthesized without the addition of Sb, we assigned these brighter dots to columns of antimony atoms adsorbed onto the { } surfaces of the ZnO nanowire. It should be noted that Fig. 1a shows both the ( ) and ( ) surfaces of the ZnO nanowire and that Sb only adsorbs { } surfaces.The proposed structure of the Sb-ZnO ( ) surface is shown in Fig 2. Fig 2a was constructed according to the HAADF image (Fig 1b): Sb atoms occupy the positions of the Zn1 atoms on the ( ) surface. The slightly larger spacing from the next Zn layer may be due to the larger size of Sb and modification of its bonding with the oxygen atoms. Four different Zn and four different O are labeled as 1, 2, 3 and 4. The coordination number of the inner oxygen atoms (e.g. O2) is 4...

Semiconducting ZnO is a promising material for various optical and electrical applications. Due to the ultraviolet light-emitting characteristics of ZnO nanowires, their luminescence properties are an attractive subject of investigation [1]. While Photoluminescence (PL) refers to emission from materials excited by photons, cathodoluminescence (CL) measures the degree of luminescence originated from the decay of electron-hole pairs caused by high energy electron bombardment [2]. CL can be used as a valuable tool to evaluate material properties and high resolution CL imaging can provide spatial information on the electronic properties of nanostructures. Here we report our recent investigation of CL imaging of ZnO, Sb/ZnO and Bi/ZnO nanostructures.ZnO nanowires were fabricated via a vapor deposition process inside a horizontal quartz tube furnace. Bi/ZnO and Sb/ZnO nanostructures were prepared by introducing metal vapor and deposit them on ZnO nanostructures via the vapor phase transport process. JEOL JXA-8530F hyper probe, consisting of a field-emission scanning electron microscope equipped with five wavelength dispersive spectrometers and a CL detector of panchromatic type, collecting signals in the wavelength range of 200 nm to 900 nm. This instrument can provide a spatial resolution of 3 nm in the secondary electron and backscattered electron imaging mode. Fig.1 shows high magnification backscattered electron image (a) and the corresponding CL image (b) of ZnO nanowires. Analyses of many CL images showed that when the diameter of ZnO nanowires is below about 30 nm the CL signals were hardly detectable. Preliminary investigation suggests that the signal reduction may not just originate from the smaller emission volume. Further study of this phenomenon is under way. Fig. 2 (a) is a BSE image of the synthesized Bi/ZnO nanostructure; the brighter contrast represents the bismuth oxide phase. Fig. 2 (b) is the corresponding CL image, revealing that the two oxides provide a similar integrated CL signal. Figures 2(c) and 2(d) show a BSE image and a CL image of the Sb/ZnO nanostructures, respectively. The relatively low CL intensity of the antimony oxide microwires (compared to ZnO nanowires) suggests that CL imaging can be used to investigate the CL emission properties of mixed (Sb)ZnO nanoscale structures. Detailed analyses of the local CL emission from various nanostructures will be discussed [3].