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The hydrogen gas-sensing properties have been investigated of two types of thermochemical hydrogen (TCH) sensors composed of thermoelectric layers based on chalcogenide nanowire arrays and anodic aluminum oxide (AAO) templates. The monomorphic-type TCH sensor, which had only Bi2Te3 nanowire arrays, showed an output signal of 23.7 μV in response to 5 vol% hydrogen gas at room temperature, whereas an output signal of 215 μV was obtained from an n-p junction-type TCH sensor made of connected Bi2Te3 and Sb2Te3 nanowire arrays in an AAO template. Despite its small deposition area, the output signal of the n-p sensor was more than nine times that of the monomorphic sensor. This observation can be explained by the difference in electrical connections (parallel and serial conversions) in the TCH sensor between each type of nanowire array. Also, our n-p sensor had a wide detection range for hydrogen gas (from 400 ppm to 45 vol%) and a fast response time of 1.3 s at room temperature without requiring external power.

Metal-assisted chemical etching (MACE) using a nanosphere lithography (NSL) technique is regarded as a general fabrication method for silicon nanowire (SINW) arrays. However, morphology control of SiNWs using this method has not been reported. In this study, silicon nanowire (SINW) and silicon nanocone (SINC) arrays were fabricated by MACE using a NSL. Depending on the concentration of etchants in the etching solution, the morphology of the wires and etching rate were systemically changed. At high concentrations, the wires were etched cylindrically and at low concentrations, tapered (cone-like) wires were obtained. To quantify the degree of tapering, the volume ratio of the etched part was calculated from their morphology. The degree of tapering increased as the concentrations of etchants decreased. We suggest that the mechanism of the formation of nanocone is related to the degree of hole diffusion under the metal layer, which was supported by field emission scanning electron microscope (FE-SEM) images.