The length of single crystalline nanowires (NWs) offers a perfect pathway for electron transfer, while the small diameter of the NWs hampers thermal losses to tje environment, substrate, and metal electrodes. Therefore, Joule self-heating effect is nearly ideal for operating NW gas sensors at ultralow power consumption, without additional heaters. The realization of the self-heated NW sensors using the "pick and place" approach is complex, hardly reproducible, low yield, and not applicable for mass production. Here, we present the sensing capability of the self-heated networked SnO NWs effectively prepared by on-chip growth. Our developed self-heated sensors exhibit a good response of 25.6 to 2.5 ppm NO gas, while the response to 500 ppm H, 100 ppm NH, 100 ppm HS, and 500 ppm CHOH is very low, indicating the good selectivity of the sensors to NO gas. Furthermore, the detection limit is very low, down to 82 parts-per-trillion. As-obtained sensing performance under self-heating mode is nearly identical to that under external heating mode. While the power consumption under self-heating mode is extremely low, around hundreds of microwatts, as scaled-down the size of the electrode is below 10 μm. The selectivity of the sensors can be controlled simply by tuning the loading power that enables simple detection of NO in mixed gases. Remarkable performance together with a significantly facile fabrication process of the present sensors enhances the potential application of NW sensors in next generation technologies such as electronic noses, the Internet of Things, and smartphone sensing.

The effectiveness of rear-flow-controlled mist chemical vapor deposition (mist CVD) for the growth of 2-inch α-Ga2O3 epilayers was studied. The numerical simulation indicated that the low velocity of the flow is appropriate for inducing an upward flow on the growth front without a vortex. Under the flow velocity of 0.08 m/s, α-Ga2O3 the epilayers were successfully grown on c-plane sapphire substrates. The epilayers were high-quality with full widths at half maximum of 42 arcsec and 1993 arcsec for the (0006) and (104) plane reflections, respectively. The rear-flow-controlled mist CVD was demonstrated to be effective for long-time growth. The thickness was adequately increased with increasing growth time. At the same time, corundum α-phase crystal features were distinguished. The suggested mist CVD system not only provides a cost-saving solution for Ga2O3 epilayers’ growth but is also effective for retaining the uniformity of the Ga2O3 epilayers over a large area.

α–Ga2O3 thin films were grown on a c–plane sapphire substrate by mist chemical vapor deposition in a horizontal furnace. The microstructure of the α–Ga2O3 grown layers was confirmed by X-ray diffraction. The effects of the temperature distribution and velocity field of the mist flow at the surface of the substrate on the uniformity of the epitaxy layers were revealed by numerical simulations and experimental measurements. The thickness uniformity of the thin film was found to be dependent on the position of the inlet and on the flow rate. The suggested configuration for obtaining highly uniform Ga2O3 epilayers is a low flow rate of less than 0.1 m/s and the flow directed from the bottom of the substrate to the top surface of the substrate.