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Suematsu Koichi Last modified date:2023.10.17

Associate Professor / Functional and Structual Materials Science
Department of Advanced Materials Science and Engineering
Faculty of Engineering Sciences

Graduate School
Undergraduate School

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 Reseacher Profiling Tool Kyushu University Pure
Academic Degree
Dr. Engineering
Field of Specialization
Functional inorganic materials
Research Interests
  • Design of dielectric thin films using Organic/Inorganic composite nanoparticles
    keyword : BaTiO3 nano-particles, highly dispersed sol
  • Materials design and advantages of semiconductor gas sensors
    keyword : semiconductor nano-particle, micro structure, gas diffusion
Academic Activities
1. Koichi Suematsu, Yuki Hiroyama, Ken Watanabe, Kengo Shimanoe, Amplifying the Receptor Function on Ba0.9La0.1FeO3-SnO2 Composite Particle Surface for High Sensitivity Toward Ethanol Gas Sensing, Sensors and Actuator B Chemical, 10.1016/j.snb.2021.131256, 354, 131256, 2021.12, Composite particles of Ba0.9La0.1FeO3 (BLF) and SnO2 have been designed to amplify the receptor function of semiconductor gas sensor and achieve high sensitivity toward volatile organic compound gases. During operation, the sensor was driven under double-pulse mode (DP-mode) that includes high-temperature preheating. According to the temperature programmed desorption measurement, oxygen desorption from the BLF-SnO2 composite occurred at lower temperatures than that from SnO2, and the amount of oxygen desorption was also larger. Under the DP-mode, the electrical resistance of BLF-SnO2 was significantly higher than that of SnO2, because BLF acted as an oxygen supplier to increase effective oxygen concentration in the sensing layer. In addition, temperature programmed reaction measurement revealed that ethanol desorbed from BLF, and that the total amount of ethanol desorption and combustion on BLF-SnO2 was larger than that on SnO2. Thus, the sensor response to ethanol based on ethanol combustion reaction was enhanced when using BLF-SnO2 under the DP-mode, especially the sensor response to 1 ppm ethanol showed 143 at the preheating and measurement temperatures of 400 °C and 250 °C, respectively. This enhanced response was attributed to the condensation of oxygen and ethanol under the DP-mode, with BLF playing the role of oxygen and ethanol provider. Thus, compositing BLF with SnO2 significantly amplified the receptor function of the sensing material, and such materials design could lead to improved sensitivity..
2. Koichi Suematsu, Wataru Harano, Shigeto Yamasaki, Ken Watanabe, Kengo Shimanoe , One-Trillionth Level Toluene Detection Using Dual-Designed Semiconductor Gas Sensor: Materials and Sensor Driven Designs, ACS Applied Electronic Materials, 10.1021/acsaelm.0c00902, 2020.12, Lowering the volatile organic compound (VOC) gas detection limit toward the ppt level on a resistive-type semiconductor gas sensor was achieved by combining the material and sensor-driven designs. We fabricated Pd-SnO2 clustered nanoparticles, a material that is highly sensitive to VOC gas, on a microsensor device with a double-pulse-driven mode. This mode was involved in switching the heater-on periods at high-temperature preheating and measurement phases and the rest phase during a heater-off period between preheating and measurement phases. The electrical resistance in synthetic air and the sensor response to toluene increased as preheating temperatures increased because of an increase in the amount of O2– adsorbed on the particle surface. In addition, extending the rest time between the preheating and measurement phases significantly improved the sensor response to toluene. According to the relationship between the sensor response and toluene concentration, we improved the lower detection limit for toluene gas to below 10 ppt, with preheating and measurement temperatures at 400 and 250 °C, respectively, and rest time at 100 s. Therefore, the combination of the material and sensor-driven designs may play a key role in improving the sensor performance..
3. Koichi Suematsu, Tokiharu Oyama, Wataru Mizukami, Yuki HIroyama, Ken Watanabe, Kengo Shimanoe, Selective Detection of Toluene Using Pulse-Driven SnO2 Micro Gas Sensors, ACS Applied Electronic Materials, 2, 2913-2920, 2020.08, Improvement of gas selectivity, especially among volatile organic compound (VOC) gases, was attempted by introducing pulse-driven modes in semiconductor gas sensors. The SnO2 microsensor was fabricated on a miniature sensor device constructed with a microheater and electrode. The gas-sensing properties were evaluated under a pulse-driven mode by switching the heater on and off. According to density functional theory calculations and temperature-programmed reaction measurements, toluene molecule, which is one of the VOC gases, was adsorbed on the SnO2 surface by van der Waals forces. The conventional sensor response, Se, defined as the change in the electrical resistance in air and target gas atmosphere, to toluene was four and eight times greater than that to CO and H2, respectively. Moreover, the newly proposed sensor response, Sp, defined as the change in the electrical resistance of the device in the target gas atmosphere during the heater-on period, to toluene was 33 and 29 times greater than that to CO and H2, respectively. This significant difference in the Sp to toluene was caused by the combustion reaction of condensed toluene within the sensing layer. Accordingly, the pulse-driven mode of the semiconductor gas sensor can be exploited to improve the gas selectivity of VOC gases based on these newly defined sensor response measures..
4. Koichi Suematsu, Ken Watanabe, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Effect of Ambient Oxygen Partial Pressure on the Hydrogen Response of SnO2 Semiconductor Gas Sensors, Journal of the Electrochemical Society, 10.1149/2.1391906jes, 166, B618-B622, 2019.04, In this study, the influence of the oxygen partial pressures (PO2) on the sensor response to H2 of SnO2 resistive-type gas sensors was evaluated under various humid atmospheres. SnO2 nanoparticles of 8–15 nm in diameter were synthesized using a hydrothermal technique followed by calcination at 600°C. Additionally, a large amount of pores with diameters greater than 10 nm was confirmed in the nanoparticles. The electrical resistance at 350°C was decreased with decreasing the PO2, and the electrical resistance in the presence of 10 ppm H2 was much smaller than that in the absence of H2 in both dry and humid atmospheres regardless of the PO2. Furthermore, the sensor response to 10 ppm H2 at 350°C increased with decreasing PO2 in both dry and humid atmospheres. Thus, decreasing the amount of oxygen adsorption enhanced the effect of rooted hydroxyl formation on the SnO2 surface through a combustion reaction between H2 and adsorbed oxygen and improved the sensor response to H2. These results are important for understanding the fundamental mechanisms of gas detection and for the material surface design of highly sensitive resistive-type semiconductor gas sensors..
5. Koichi Suematsu, Wataru Harano, Tokiharu Oyama, Yuka Shin, Ken Watanabe, Kengo Shimanoe, Pulse-Driven Semiconductor Gas Sensors Toward ppt Level Toluene Detection, Analytical Chemistry, 2018.08, Improvements in the responses of semiconductor gas sensors and reductions in their detection limits toward volatile organic compounds (VOCs) are required in order to facilitate the simple detection of diseases, such as cancer, through human-breath analysis. In this study, we introduce a heater-switching, pulse-driven, micro gas sensor composed of a microheater and a sensor electrode fabricated with Pd-SnO2-clustered nanoparticles as the sensing material. The sensor was repeatedly heated and allowed to cool by the application of voltage to the microheater; the VOC gases penetrate into the interior of the sensing layer during its unheated state. Consequently, the utility factor of the pulse-driven sensor was greater than that of a conventional, continuously heated sensor. As a result, the response of the sensor to toluene was enhanced; indeed, the sensor responded to toluene at levels of 1 ppb. In addition, according to the relationship between its response and concentration of toluene, the pulse-driven sensor in this report can detect toluene at concentrations of 200 ppt and even lower. Therefore, the combination of a pulse-driven microheater and a suitable material designed to detect toluene resulted in improved sensor response, and facilitated ppt-level toluene detection. This sensor may play a key role in the development of medical diagnoses based on human breath..
6. Koichi Suematsu, Masashi Arimura, Naoyuki Uchiyama, Shingo Saita, Transparent BaTiO3/PMMA Nanocomposite Films for Display Technologies: Facile Surface Modification Approach for BaTiO3 Nanoparticles, ACS Applied Nano Materials, 1, 2430-2437, 2018.04, Fabrication of a transparent film composed of a barium titanate (BaTiO3) and poly(methyl methacrylate) (PMMA) matrix is reported to expand the application field for composite films such as displays and touch panel screens. BaTiO3 nanoparticles are synthesized by sol–gel route with dispersion carried out in 2-methoxyethanol. The synthesized nanoparticles are 10 nm in size and are highly dispersed in the solvent. The surfaces of the obtained nanoparticles are modified by treatment with titanium isopropoxide and by using two silane coupling agents: n-decyltrimethoxysilane and 3-(triethoxysilyl)propyl methacrylate. The surface-modified BaTiO3 nanoparticles were then added to a sample of methyl methacrylate to obtain a transparent BaTiO3 dispersion. Transparent BaTiO3/PMMA nanocomposite films (sheet type, thickness of 150 μm) are obtained by the polymerization of the BaTiO3/MMA dispersion via heat treatment and by using a polymerization initiator. The visual transparency of the BaTiO3/PMMA film is comparable to that of the original PMMA film. Additionally, no difference in the transparency of the BaTiO3/PMMA films is observed when the BaTiO3 weight ratio is varied between 5% and 33%. The dielectric constant of the nanocomposite film improved from 4.6 (PMMA only) to 7.1 by incorporating 10 wt % of BaTiO3. Such improvement in the dielectric properties, while maintaining the transparency, flexibility, and workability of PMMA films, allows the expansion of the fields of functional ceramics and polymers..
7. Koichi Suematsu, Nan Ma, Ken Watanabe, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Effect of humid Aging on the Oxygen Adsorption in SnO2 Gas Sensors, Sensors, 18, 254, 2018.01.
8. Koichi Suematsu, Kosuke Watanabe, Akihiro Tou, Yonjiao Sun, Kengo Shimanoe, Ultraselective Toluene Gas Sensor: Nanosized Gold Loaded on Zinc Oxide Nanoparticles, Analytical Chemistry, 90, 1959-1966, 2018.01, Selectivity is an important parameter of resistivetype gas sensors that use metal oxides. In this study, a highly selective toluene sensor is prepared using highly dispersed goldnanoparticle-loaded zinc oxide nanoparticles (Au-ZnO NPs). Au-ZnO NPs are synthesized by coprecipitation and calcination at 400 °C with Au loadings of 0.15, 0.5, and 1.5 mol %. The Au NPs on ZnO are about 2−4 nm in size, and exist in a metallic state. Porous gas-sensing layers are fabricated by screen printing. The responses of the sensor to 200 ppm hydrogen, 200 ppm carbon monoxide, 100 ppm ethanol, 100 ppm acetaldehyde, 100 ppm acetone, and 100 ppm toluene are evaluated at 377 °C in a dry atmosphere. The sensor response of 0.15 mol % Au-ZnO NPs to toluene is about 92, whereas its sensor responses to other combustible gases are less than 7. Such selective toluene detection is probably caused by the utilization efficiency of the gas-sensing layer. Gas diffusivity into the sensing layer of Au-ZnO NPs is lowered by the catalytic oxidation of combustible gases during their diffusion through the layer. The present approach is an effective way to improve the selectivity of resistive-type gas sensors..
9. Koichi Suematsu, Kiyomi Yamada, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Evaluation of Oxygen Adsorption Based on the Electric Properties of SnO2 Semiconductor Gas Sensors, Sensors and Materials, 28, 1211-1217, 2016.08.
10. Koichi Suematsu, Masashi Arimura, Naoyuki Uchiyama, Shingo Saita, Teruhisa Makino, Synthesis and Design of BaTiO3/Polymer Composite Ink to Improve the Dielectric Properties of Thin Films, Composites Part B: Engineering, 10.1016/j.compositesb.2016.08.011, 104, 80-86, 2016.08.
11. Koichi Suematsu, Miyuki Sasaki, Nan Ma, Masayoshi Yuasa, Kengo Shimanoe, Antimony-doped tin dioxide gas sensors exhibiting high stability of the sensitivity to humidity changes, ACS Sensors, 10.1021/acssensors.6b00323, 1, 913-920, 2016.06, The type and amounts of oxygen adsorption species at various atmospheric humidity levels are important factors in improving the sensitivity to combustible gases and stability to humidity changes of SnO2-based resistive-type gas sensors. We investigated the effect of antimony (Sb) doping of SnO2 nanoparticles on the stability of the sensitivity to humidity changes and oxygen adsorption species under humid atmosphere. No significant degradation of the sensitivity to hydrogen of Sb-SnO2 sensors was observed between 16 and 96 RH%, while an undoped SnO2 sensor showed gradually ecreasing responses with increasing humidity. An evaluation of oxygen adsorption species under humid atmosphere showed a transition from O2− to O− with increasing humidity from 16 to 96 RH%. However, the O2− adsorption sites were maintained on the surfaces of the Sb- SnO2, even as the humidity increased. Moreover, the extent of oxygen adsorption on the Sb-SnO2 was not obviously changed with increasing humidity. These results indicate that Sb atoms function as hydroxyl absorbers and also generate O2− adsorption sites in their vicinity. Additionally, Pd loading on the Sb-SnO2 further enhanced the sensor response under humid atmosphere, while maintaining the stability to humidity changes. Therefore, we successfully imparted stability to the sensitivity of SnO2 nanoparticles during humidity changes, representing an important improvement with applications to the development of high performance, practical, resistive-type gas sensors..
12. Koichi Suematsu, Nan Ma, Kazuya Kodama, Masayoshi Yuasa, tetsuya Kida, Kengo Shimanoe, Vanadium oxide loading on tin dioxide nanoparticles for improving gas detection in a humid atmosphere, Materials Letters, 10.1016/j.matlet.2016.05.083, 179, 214-216, 2016.05.
13. Koichi Suematsu, Masashi Arimura, Naoyuki Uchiyama, Shingo Saita, Teruhisa Makino, High-performance dielectric thin film nanocomposites of barium titanate and cyanoethyl pullulan: controlling the barium titanate nanoparticle size using a sol-gel method, RSC Advances, 10.1039/C5RA27644F, 6, 20807-20813, 2016.02.
14. Koichi Suematsu, Kazuya Kodama, Nan Ma, Masayoshi Yuasa, tetsuya Kida, Kengo Shimanoe, Role of vanadium oxide and palladium multiple loading on the sensitvity and recovery kinetics of tin dioxide based gas sensors, RSC Advances, 10.1039/C5RA20994C, 6, 5169-5176, 2015.12.
15. Koichi Suematsu, Nan Ma, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Surface-modification of SnO2 nanoparticles by incorporation of Al for the detection of combustible gases in humid atmosphere, RSC Advances, 10.1039/C5RA17556A, 5, 86347-86354, 2015.10.
16. Koichi Suematsu, Yuka Shin, Nan Ma, Tokiharu Oyama, Miyuki Sasaki, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Pulse-Driven Micro Gas Sensor Fitted with Clustered Pd/SnO2 Nanoparticles, Analytical Chemistry, 10.1021/acs.analchem.5b01767, 87, 8407-8415, 2015.07.
17. Nan Ma, Koichi Suematsu, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Effect of Water Vapor on Pd-Loaded SnO2 Nanoparticles Gas Sensor, ACS Applied Materials and Interfaces, 10.1021/am509082w, 7, 5863-5869, 2015.03.
18. Koichi Suematsu, Masayoshi Yuasa, Tetsuya Kida, Noboru Yamazoe, Kengo Shimanoe, Determination of Oxygen Adsorption Species on SnO2: Exact Analysis of Gas Sensing Properties Using a Sample Gas Pretreatment System, Journal of Electrochemical Society, 10.1149/2.004406jes, 161, B123-B128, 2014.04.
19. Koichi Suematsu, Yuka Shin, Zhongqiu Hua, Kohei Yoshida, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Nanoparticle Cluster Gas Sensor: Controlled Clustering of SnO2 Nanoparticles for Highly Sensitive Toluene Detection, ACS Applied Materials and Interfaces, 10.1021/am500944a, 6, 5319-5326, 2014.03.
20. Tetsuya Kida, Shuhei Fujiyama, Koichi Suematsu, Masayoshi Yuasa, Kengo Shimanoe, Pore and Particle Size Control of Gas Sensing Films Using SnO2 Nanoparticles Synthesized by Seed-Mediated Growth: Design of Highly Sensitive Gas Sensors, Journal of Physical Chemistry C, 10.1021/jp4045226, 117, 17574-17582, 2013.07.
21. Koichi Suematsu, Masayoshi Yuasa, Tetsuya Kida, Noboru Yamazoe, Kengo Shimanoe, Effects of crystallite size and donor density on the sensor response of SnO2 nano-particles in the state of volume depletion, Journal of Electrochemical Society, 10.1149/2.107204jes, 159, J136-J141, 2012.02.
1. Koichi Suematsu, Ultra-high sensitive (ppt) gas sensor based on the pulse heating using MEMS technique, 8th GOSPEL Workshop, 2019.06, High sensitivity and low limit of detection to volatile organic compounds (VOCs) gases are typical properties on the resistive-type semiconductor gas sensors using SnO2-based materials. In this few decades, semiconductor gas sensors were improved on the point of not only the sensitivity but also both compact and low power consumption by using the micro gas sensors equipped with the microheater and microelectrode using the MEMS (Micro Electronic Mechanical System) technique. Recently, we proposed the micro gas sensor driven in repeating mode of instantaneous heating and cooling (pulse-driving) [1,2]. According to the pulse-driving mode, VOCs gases can introduce into the sensing layer during cooling period, and it improves the utilize efficiency of the sensing layer. Thus, in this study, we aimed to improve the sensor response in low concentration of VOCs gases, SnO2 based gas sensor was driven under pulse-driving mode with monotonic and two-step heating..
2. Koichi Suematsu, Wataru Harano, Tokiharu Oyama, Nan Ma, Ken Watanabe, Kengo Shimanoe, ULTRA-HIGH SENSITIVE GAS DETECTION USING PULSE-DRIVEN MEMS SENSOR BASED ON TIN DIOXIDE, 18th International Symposium on Olfaction and Electronic Nose (ISOEN), 2019.05.
3. Koichi Suematsu, Sun Yongjiao, Ken Watanabe, Maiko Nishibori, Kengo Shimanoea, Analysis of Oxygen Adsorption on Surface of Metal Oxide to Understand Sensing Mechanism of Semiconductor Gas Sensors, 12th Asian Conference on Chemical Sensors, 2017.11.
4. Koichi Suematsu, Nano-Scale Particles Design of Metal Oxide Semiconductor Gas sensors for Environmental Protection, The 18th International Symposium on Eco-materials Processing and Design (ISEPD 2017), 2017.02, To detect the harmful gases in atmosphere using gas sensors is important for environment protection. Recently, the building gas sensors with high performance such as high gas sensitivity, rapid response and recovery, gas selectivity, and humidity resistance are strongly required. Resistive-type semiconductor gas sensors, especially SnO2-based gas sensors, are attracting the most attention because of their high potentiality. So far, we have reported that the introduction of three key factors, receptor function, transducer function and utility factor, to material design of sensors gives ultrahigh sensitivity in ppb level. However, the decrease in electric resistance by water vapor poisoning is most fundamental problem for practical use, because atmospheric environment includes water vapor and also the amount is different in each time and place. Recently, we tried to overcome such weak-point on SnO2-based gas sensors from viewpoint of materials design. For example, the decrease in electric resistance by water vapor poisoning can be improved by surface Sb substitution. Such materials design can raise the sensor performances and allow the practical use for environmental protection..