Simple fabrication process for 2D ZnO nanowalls and their potential application as a methane sensor.

Two-dimensional (2D) ZnO nanowalls were prepared on a glass substrate by a low-temperature thermal evaporation method, in which the fabrication process did not use a metal catalyst or the pre-deposition of a ZnO seed layer on the substrate. The nanowalls were characterized for their surface morphology, and the structural and optical properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL). The fabricated ZnO nanowalls have many advantages, such as low growth temperature and good crystal quality, while being fast, low cost, and easy to fabricate. Methane sensor measurements of the ZnO nanowalls show a high sensitivity to methane gas, and rapid response and recovery times. These unique characteristics are attributed to the high surface-to-volume ratio of the ZnO nanowalls. Thus, the ZnO nanowall methane sensor is a potential gas sensor candidate owing to its good performance.

Deep and alignment free patterned etching of GaN surface using an atomic force microscope.

Successful deep and alignment-free patterned etching on GaN using atomic force microscope (AFM) local oxidation followed by in-situ chemical etching is demonstrated. Oxide ridges are grown on GaN on an AFM by applying positive sample bias at 80% humidity, with the oxidation reaction expedited by UV light. The oxide ridges are then etched by HCl solution, leaving troughs in the GaN surface. A dripping strategy for the in-situ chemical etching is recommended that allows deep, alignment-free multiple AFM oxidation/etching works on the GaN surface without any need of substrate removal from the AFM platform. Repeated etching followed by AFM oxidation on a spot on a GaN surface resulting in a hole as deep as 800 nm was also demonstrated. Further, a preliminary evaluation of the porosity of the AFM-grown oxide indicates that the oxide ridges grown on GaN at an AFM cantilever moving speed of 300 nm/s are porous in structure, with an estimated porosity of 86%, which porosity could be reduced if longer resident time of the AFM cantilever on the target oxidation region was used.

Direct patterning of zinc oxide with control of reflected color through nano-oxidation using an atomic force microscope.

Atomic force microscope oxidation on Zn creating amorphous ZnO (a-ZnO) with the a-ZnO showing multiple colors under white light at different oxidation voltages was successfully demonstrated. Simulation of reflected colors at different thicknesses of a-ZnO was also conducted. The presented technique can not only be applied to near diffraction limit multilevel optical data storage, but also makes it possible to represent the color spectra observed in nature at near diffraction limits. It can also be used for device fabrication in situations exploiting the semiconductor nature of ZnO.