The functional convergence of the Internet with radio-frequency identification and sensors has led to the era of the Internet of Things (IoT), which is a computing concept in which everyday objects are online and communicate via the Internet. In particular, the IoT is effective and appropriate for monitoring and controlling objects in hazardous environments to enable people to access them. In order to apply gas sensors to the IoT, operation at room temperature (low power consumption), a high efficiency (sensitivity, response/recovery time, and stability), low-cost fabrication, miniaturization, and easy integration with circuits are essential because these factors enhance the feasibility of utilizing a gas sensor, thereby enabling the collection, processing, analysis, and dissemination of valuable information gathered from a variety of environments. Among various types of gas sensors, semiconducting gas sensors based on various metal oxides are considered to be the strongest candidate for the application in IoT owing to their small size, simplicity in operation, low cost, and compatibility with integrated circuits. A wide variety of nanostructured metal oxides, including nanowire, nanobelt, nanorods, nanosheets, nanospheres, and nanotubes has been exploited for semiconductor gas sensors during the past decade. Despite these efforts, achieving a reproducible fabrication, easy integration with other circuits, and compatibility with well-established semiconductor production processes that are related to mass production have remained challenges for the utilization of the semiconducting sensors in the IoT.

 In the presentation, we show our research efforts to synthesize well-ordered metal-oxide nanostructures such as nanorods, nanohemispheres, nanospheres and nanowells using physical vapor deposition (PVD) methods for the high performance chemoresistive gas sensors.