Then, Zn vapor was generated through the carbothermal reduction of ZnO powder at high temperature. The Zn vapor was carried to a low-temperature region by the flow of Ar gas, and the result was the condensation of Zn microcrystals onto the Si substrate located downstream.

The zinc microcrystals had AICAR nmr the morphology of hexagonally shaped platelets. Second, in the O2 environment that existed during the oxidation process, the as-grown Zn microcrystals were transformed into sheets with side faces that were flat [14]. The oxidation of Zn was caused by the increased surface mobility of the nanosized, liquid Zn droplets and oxygen atoms, which induced the nucleation and growth of ZnO crystals into nanowires. The side face of each flat plane was covered with armlike nanowire structures, hence the name ‘urchin-like’ microstructures. Figure 3 shows the μ-PL spectra of the Zn/ZnO microcrystals (solid line) and urchin-like ZnO microstructures (dashed line). The PL spectrum of the urchin-like ZnO microstructures shows an excitonic UV emission centered at 382 nm and a relatively weak emission associated with defects located at 522 nm. The intensity of the UV emission is five times greater than that of the as-grown selleck screening library sample. The appearance of

the UV emission from these microcrystals indicates that the Zn, which can be oxidized quickly, has been partially oxidized to form a thin ZnO layer on the surface. A blue shift in the UV band can be interpreted by the quantum confined effect to indicate that the thickness of the native oxide on the surface is just a few nanometers. Figure 3 Micro-PL Megestrol Acetate spectra of the sample before and after oxidation by cw-laser excitation. Next, we concentrated on the selleck chemical lasing characteristics of the individual urchin-like ZnO microstructures. Figure 4a shows a typical excitation-dependent μ-PL measurement of a ZnO microstructure with a size of 6.15 μm. The broad emission centered at 381 nm had no remarkable features at low excitation densities. As the excitation density increased, sharp peaks were observed at 379.5, 380.8, 382.5, and 383.8 nm. Furthermore, the peak intensities increased

rapidly with further increases in the excitation density. The sharp PL emissions and nonlinear increase in the PL intensities with the excitation density indicated that lasing action was occurring, and the lasing threshold density was approximately 0.94 MW/cm2, as shown in the inset of Figure 4a. The width of the spectral line of the lasing peak was less than 0.15 nm. Therefore, the cavity mode had an intrinsically high quality (Q) factor, which was estimated to be 2,500 using the equation Q = λ/δλ, where λ is the peak wavelength. This Q factor was higher than those of other ZnO nano/microstructures [25, 26]. The quality factor (Q) of the lasing spectra was estimated to be approximately 2,500, which was higher than that of our expectation.