In order to easily locate the excitation area for pumping each individual ZnO microcavity, a 200-mesh transmission electron microscopy grid was fixed on the sample. To measure the photoluminescence, a micro-photoluminescence (μ-PL) system was used to analyze the optical properties of the individual ZnO microcavities under the excitation of a 325-nm HeCd laser or a 266-nm Nd: YAG pulsed laser. The sample was placed on a sample holder that was mounted on a three-axis translational stage. A camera was used

to distinguish the signals emitted from individual ZnO microcavities. All of the optical measurements were performed at room temperature. Results and discussion Figure 1 shows the typical XRD patterns of the products synthesized in HDAC inhibitor the first and second steps. For the products that were obtained before the oxidation process, all of the peaks were identified as Zn with a hexagonal structure (JCPDS No. 87-0713); no obvious diffraction peaks of ZnO were identified Selleckchem C188-9 because there was no diffraction pattern attributed to the impurities. After the oxidation process, almost all of the

diffraction peaks could be readily indexed as the hexagonal wurtzite ZnO phase (JCPDS No. 36-1451), except for the Zn peak at 43.36°. These results indicated that the Zn crystals were oxidized. The Zn could have originated from the inner core of the first products, where the Zn had yet to be transformed fully into the ZnO structures. Figure 1 XRD patterns of the Zn microcrystal (bottom branch) and the annealed sample (upper branch). The circles denote peaks corresponding to Zn and the squares to ZnO. Figure 2a shows a representative SEM image of the morphology

of the product fabricated during the first step. The figure shows hexagonal Zn/ZnO microcrystals with six-faceted side walls. The diameter and height of the Zn/ZnO microcrystals were 4.5 and 1.5 μm, respectively. A low-magnification SEM image of a large area (not shown) showed that these microcrystals had diameters that ranged from 3 to 16 μm. After the oxidation process in step 2, urchin-like ZnO microstructures with multilayer sheets and multiple nanowires were observed, as shown in Figure 2b. Figure 2c shows an enlarged image of the typical nanowire with a tapered structure. The diameters Urocanase and lengths of the tapered nanowires had ranges of 70 to 300 nm and 0.5 to 10 μm, respectively. Figure 2 SEM images of individual ZnO microcrystal, magnification image of tapered nanowire, and the oxidation process. SEM images of an individual ZnO microcrystal (a) before and (b) after oxidation at 500°C. (c) The magnification image of the tapered nanowire. (d) Illustration images of the metallic Zn transformed into ZnO microcavity during the oxidation process. The growth mechanism of these urchin-like structures was proposed to be self-catalyzed growth resulting from the oxidation of metallic Zn. Figure 2d shows the proposed mechanism by which these urchin-like ZnO microstructures were formed.