Kai-Siang Hsu

Bio: Kai-Siang Hsu is an academic researcher from National Cheng Kung University. The author has an hindex of 1, co-authored 1 publications receiving 49 citations.

On the Ammonia Gas Sensing Performance of a RF Sputtered NiO Thin-Film Sensor

Abstract: An interesting ammonia gas sensor based on a p-type NiO thin film, prepared by a radio frequency sputtering process, is studied and demonstrated. As compared with conventional n-type metal-oxide sensors, the studied device shows comparable and good sensing performance, including a high-sensing response ratio of 289%, a lower response time of 31 s, and a lower recovery time of 78 s, under an introduced 1000 ppm NH3/air gas at 250 °C and 350 °C, respectively. In addition, the studied sensor device exhibits a lower detection limit (<5 ppm NH3/air) at 250 °C. Consequently, based on these advantages and inherent benefits of low cost, chemical stability, and easy fabrication, etc., the studied NiO thin-film sensor shows the promise for high-performance ammonia gas sensing applications.

Semiconductor Gas Sensors: Materials, Technology, Design, and Application

Abstract: This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies.

Characteristics of a Pt/NiO thin film-based ammonia gas sensor

Abstract: The sensing characteristics of a Pt/NiO thin film-based resistor-type ammonia gas sensor are comprehensively studied and demonstrated. Experimentally, the studied Pt/NiO ammonia gas sensor exhibits improved performance, including a higher sensing response of ratio of 1278%, an extremely low detection limit of 10 ppb NH3/air, and fast speeds, at an optimal operating temperature of 300 °C. Based on the advantages indicated above and the benefits of its simple structure, relatively easy fabrication, and inherent p-type semiconductor properties, the studied device is promising for high-performance ammonia gas sensing and complementary metal oxide sensor (CMOS) array applications.

Wearable, Flexible Ethanol Gas Sensor Based on TiO2 Nanoparticles-Grafted 2D-Titanium Carbide Nanosheets

Abstract: Herein, we demonstrate a novel approach for development of TiO2 grafted 2D-TiC nanosheets (TiO2@2D-TiC) based room temperature operable, flexible ethanol gas sensor. The homogeneous distribution, unique composition, and crystalline microstructure of TiO2 nanoparticles grafted 2D-TiC nanosheets have been found to enhance the surface reactivity and efficiency of its transducer–receptor functions. The electron–hole recombination at the TiO2/2D-TiC interfaces offered superior sensor performance with fast response and recovery times. Moreover, TiO2@2D-TiC nanosheets based flexible sensor exhibited high selectivity toward trace-level ethanol gas (10 ppb–60 ppm) with extremely low noise-to-signal ratio and excellent stability. The results suggest that the development of low-cost flexible sensors based on TiO2@2D-TiC nanosheets could be applied for potential applications, such as printed/wearable electronics, biomedical sector and environmental monitoring.

Ppb-Level Xylene Gas Sensors Based on Co 3 O 4 Nanoparticle-Coated Reduced Graphene Oxide(rGO) Nanosheets Operating at Low Temperature

Abstract: Xylene is a toxic carcinogen, which may irritate eyes and respiratory tract, or damage the central nervous system. However, the traditional semiconductor gas sensor can only detect the ppm level of xylene gas, which cannot meet the building air quality monitoring requirements. Therefore, the development of low concentration gas detection of xylene gas sensor is necessary. In this article, a one-step hydrothermal method for the preparation of reduced graphene oxide (rGO)/Co3O4 nanocomposite was reported. Then, rGO/Co3O4 nanocomposites were characterized by various characterization methods. It was found that the structure of cobalt tetroxide (Co3O4) nanoparticle-coated rGO nanosheets was successfully synthesized. Specific internal morphology could be seen by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then the gas sensor made of rGO/Co3O4 nanocomposite material was tested for its gas sensitivity performance. A series of properties such as repeatability and stability of the material were tested. According to the test results, the sensitivity of 1rGO/Co3O4 (3.35 wt%) to xylene gas was better than that of 2rGO/Co3O4 (5.54 wt%) and pure Co3O4, and the optimal working temperature of rGO/Co3O4 to 50 ppm xylene was 175 °C, which was 50 °C lower than that of pure Co3O4. In addition, the rGO/Co3O4 gas sensor could also detect xylene gas with a minimum concentration of 1 ppb. Finally, the gas sensing mechanism of the gas sensor for xylene gas was analyzed.

New Insights Towards Electron Transport Mechanism of Highly Efficient p-Type CuO (111) Nanocuboids-Based H2S Gas Sensor

Abstract: Charge transport and adsorption kinetics of wet-chemically synthesized CuO nanocuboids have been explored. The growth direction of CuO nanocuboids was found to be (111) plane, which exhibited predominant surface catalytic activity toward the dissociation of H2S and O2. Temperature-dependent adsorption studies revealed the adsorption kinetics of (111) grown p-type CuO nanocuboids toward H2S gas. Adsorption of oxygen (O2) on the CuO (111) surface resulted in the formation of ionosorbed O2¯ species, which increased the hole density and enhanced the surface conductivity of CuO nanocuboids. H2S molecules were found to interact well with CuO (111) surface, donating electrons to the material and reducing the hole-accumulation layer width. Investigation of electrical characteristics of p-type CuO nanocuboids revealed absence of any structural phase transitions under H2S environment. The H2S sensing mechanism was found to be associated with local suppression/expansion of the hole-accumulation layer of p-CuO nanocu...