Fabrication of in2o3 nanowires for self heated gas sensor application

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER THESIS Fabrication of In2O3 nanowires for selfheated gas sensor application NGUYEN THANH DUONG Duong.NT202253M@sis.hust.edu.vn Specialized: Materials science (Electronic materials) Supervisor 1: Associate Professor Ph.D Nguyen Van Duy Unit: International Training Institute for Materials Science (ITIMS) Signature of supervisor Supervisor 2: Ph.D.Phùng Thị Hồng Vân Unit: Hanoi University of Natural Resources & Environment Signature of supervisor HANOI, 09/2022 i DECLARATION I hereby declare that this thesis represents my work which has been done after the registration for the degree of Master at the International Training Institute of Materials Science – Hanoi University of Science and Technology and has not been previously included in a thesis or dissertation submitted to this or any other institution for a degree, diploma or other qualifications Hanoi, 22th April, 2022 Nguyen Thanh Duong ii ACKNOWLEDGEMENT First of all, I am sincerely grateful to my thesis supervisor Assoc Prof Nguyen Van Duy and Prof Nguyen Duc Hoa - International Training Institute of Materials Science, for allowing me this opportunity to be their student; all of their advices, indication, and inspiration during the time I studied and carried out my Master thesis in ITIMS I am very proud to have their whole guidance, encouragement, and insight which have always been invaluable I would like to show my gratitude to all of teachers and staff not only in ITIMS but also in HUST to support me, I would like to send special thanks to Mr Dang Ngoc Son and Mr Lai Van Duy - ITIMS for sharing me the initial experiences and many useful suggestions relevant to my work Last but not the least, I would like to thank my family and my friends for their support and encouragement SUMMARY OF MASTER THESIS In this work, we focused on the fabrication and testing of the H2S gas sensing characteristic of the self-heated In2O3 nanowires sensor via a one-step CVD technique and drop-casting on the IDE electrode The self-heated In2O3 NWs gas sensor was measured at room temperature with different applied power toward H2S gas This performance was better than the state-of-the-art microheater gas sensor The sensor is a potential candidate for application related to H2S detection such as breath exhaled analysis and environmental monitoring Hanoi, 20th August, 2022 Master Student Nguyen Thanh Duong iii CONTENT DECLARATION ii ACKNOWLEDGEMENT iii ABBREVIATIONS vi LIST OF FIGURES .vii LIST OF TABLES x INTRODUCTION 1 Foundation of the thesis Aims of the thesis .2 Research object and scope of the thesis Research Methods New contributions of the thesis Structure of the thesis .3 CHAPTER OVERVIEW 1.1 Gas sensor .4 1.2 Self-heated gas sensor Error! Bookmark not defined.10 1.2.1 Self-heating effect .10 1.3 In2O3 materials in gas sensor .19 1.3.1 In2O3 materials .19 1.3.2 In2O3 nanowires in gas sensor .21 1.4 Hazardous properties of H2S gas 22 CHAPTER EXPERIMENTAL APPROACH 24 2.1 Synthesis of In2O3 nanowires 24 iv 2.1.1 Equipment and chemical .24 2.2 Fabrication of In2O3 nanowires 25 2.3 Fabrication of self-heated In2O3 gas sensor 27 CHAPTER RESULT AND DISCUSSION 30 3.1 Morphology of Indium Oxide (In2O3) synthesized by CVD method and In2O3 NWs based sensor fabricate by drop-casting 30 3.1.1 Effect of Sn proportion on the morphology of Indium Oxide (In2O3) materials .30 3.1.2 The distribution of In2O3 NWs in the various isopropanol solvent ratio 32 3.2 The microstructure characterization 33 3.3 Gas sensing properties .35 CONCLUSION AND RECOMMENDATIONS 48 REFERENCES 49 v ABBREVIATIONS Number Abbreviations and symbols Meaning ads Adsorption BET Brunauer- Emnet-Teller CVD Chemical Vapour Deposition EDS/EDX Energy-dispersive X-ray spectroscopy HRTEM High Resolution Transmission Electron Microscope IoT Internet of Things International Training Institute ITIMS Nanowires NWs ppb Parts per billion 10 ppm Parts per million 11 Ra Rair 12 Rg Rgas 13 S Sensitivity 14 SEM Scanning Electron Microscope 15 TEM Transition Electron Microscope 16 VOCs Volatile Organic Compounds for Materials Science vi 17 XRD X-ray Diffraction LIST OF FIGURES Figure 1.1 Detection methods of semiconductor gas sensing materials [1] Figure 1.2 Different material classes for gas sensing application [1] Figure 1.3 Sensing mechanism of metal oxide based gas sensor [1] Figure 1.4 Power consumption and temperature characterized of Hwang WJ’s microheater [8] .8 Figure 1.5 Sang Chung Gwiy, Jae-Min Young group’s micro heater [9] Figure 1.6 KMHP 100 commercial micro heater 10 Figure 1.7 Single SnO2 NW contacted with electron beam assisted platinum deposition in a four probes configuration before (a) and after (b) a few hours of operating in selfheating mode 19 Figure 1.8: In2O3 crystalline structure 20 Figure 1.9 The response of single oxide and composite sensors to ppm ethanol vapor at 100% RH [36] .22 Figure 2.1 CVD system - ITIMS .24 Figure 2.2 Precursor material (A), Aluminum oxide boat (B) 25 Figure 2.3 Thermal cycle of In2O3 nanowires fabrication process 26 Figure 2.4 FESEM microscope – HUST 27 Figure 2.5 Procedure of self-heated In2O3 NWs based gas sensor 28 Figure 2.6 Gas sensitive measuring system at ITIMS (A), Diagram of the gas measuring system by static measurement method (B) 29 Figure 3.1 Morphology and microstructure of three composite samples at (A),(B): %; (C),(D): 20 %; (E),(F): 50 %; (G),(H): 80 % mass ratio of Sn were observed by SEM scanning electron microscopy .30 vii Figure 3.2 Distribution of In2O3 NWs onto silicon substrate with (A)10 ml (B)20 ml and (C) 30ml of Isopropanol solvent 32 Figure 3.3 SEM image of In2O3 nanowires dispersion on the electrode with various ratio solvent .33 Figure 3.4 (a–d) XRD pattern of 0%, 20%, 50 and 80% SnO2/In2O3 NWs 34 Figure 3.5 EDX spectrum of (A) Pure In2O3 NWs and (B),(C) SnO2/In2O3 NWs .35 Figure 3.6 The response of self-heated In2O3 gas sensor versus time at different power of 600, 800, 1200, 1200 μW (a) and the function of response with concentration H2S gas (b) .36 Figure 3.7 The response of self-heated 20% wt SnO2/In2O3 NWs gas sensor versus time at different power of 300, 500 and 700 μW (RT) (a) and the function of response with concentration H2S gas (b) 38 Figure 3.8 The response of self-heated 50% wt SnO2/In2O3 NWs gas sensor versus time at different power of 300, 500 and 700 μW (RT) (a) and the function of response with concentration H2S gas (b) 39 Figure 3.9 The response of self-heated 80% wt SnO2/In2O3 NWs gas sensor versus time at different power of 300, 500 and 700 μW (RT) (a) and the function of response with concentration H2S gas (b) 40 Figure 3.10 Response and heating power graph of four fabricated sensors .41 Figure 3.11 The response of self-heated 80% wt SnO2/In2O3 NWs gas sensor versus time at different temperature of 200RC, 250 RC, 300 RC and 350 RC and the function of response with concentration H2S gas 42 Figure 3.12 Response characteristic of In2O3 – nanowires gas sensor toward ppm H2S at 250 oC and self-heating with a power consumption of 700 μW 43 Figure 3.13 Response characteristic of 80% SnO2/In2O3 NWs gas sensor toward ppm H2S at 250 RC and self-heating with a power consumption of 700 μW 43 viii Figure 3.14 Response to H2S of the 80% wt SnO2/In2O3 NWs sensor used self-heating effect (Orange line) and sensor using the external heater at 200 oC (Blue line) 44 Figure 3.15 Stability of sensor A External heater B Self-heated mode 45 Figure 3.16 Selectivity of In2O3 NWs gas sensor toward NH3, Ethanol and H2S gas under self-heating mode 46 Figure 3.17 In2O3 material H2S gas sensing mechanism 47 ix LIST OF TABLES Table 1.1 Summary of publication reporting quantitative information about self-heated devices based on nanomaterial 11 Table 1.2 Publications reported self- heating effects in gas sensor using metal oxide materials .12 Table 2.1 Precusor material in this experiment 26 Table 3.1: Comparison with previous study at ITIMS with same approach method .44 x Figure 3.8 The response of self-heated 50% wt SnO2/In2O3 NWs gas sensor versus time at different power of 300, 500 and 700 μW (RT) (a) and the function of response with concentration H2S gas (b) Similar trending was being witnessed with 50% wt SnO2/In2O3 NWs sensor as shown in Fig 3.8 Fig 3.8B showed that the highest response which is 1.7 at the power of 700 μW 39 Figure 3.9 The response of self-heated 80% wt SnO2/In2O3 NWs gas sensor versus time at different power of 300, 500 and 700 μW (RT) (a) and the function of response with concentration H2S gas (b) At almost all exposed concentrations of H2S gas, we could observe an increasing trend in gas response as the heating power goes up from 300 μW to 700 μW In details, gas response went from 1.25 to 1.55, 1.35 to 1.7 and 1.3 to 1.8 with 20% wt, 50% wt and 80% wt SnO2/In2O3 respectively with ppm H2S gas Gas response also increase with exposure higher H2S concentration even the same heating power 40 Figure 3.10 Response and heating power graph of four fabricated sensors From the comparison graph of response to H2S of four types of sensors, we see the highest response to H2S is 80% SnO2/In2O3 NWs with response of 1.8 with ppm H2S concentration We also see that composite oxide NWs of SnO2 and In2O3 based sensor consumed a dramatically smaller amount of power than pure In2O3 but exhibit a better performance in term of response with H2S gas Compare with self-heated gas sensor based on SnO2 NWs which was reported in [20], in which they used a high range of applied voltage (above 20V), these sensors only require V current to reach the highest heating power of 700 μW 41 80% SnO2/In2O3 NWs sensor gas sensing property has been tested with external heater in range of temperatue from 200 RC to 350 RC as result shown in Figure 3.11 Figure 3.11 The response of self-heated 80% wt SnO2/In2O3 NWs gas sensor versus time at different temperature of 200RC, 250 RC, 300 RC and 350 RC and the function of response with concentration H2S gas 42 80% wt SnO2/In2O3 NWs gas sensor response with H2S gas using external heater have an increasing trend in all temperature setting and reached the maximum value of 3.3 at 350 RC which all most twice larger than best self-heating performance (R = 1.8) In term of recovery and response time compared to the external thermal, the self-heated In2O3 sensor with an applied power of 800 μW exhibited a high-speed response to ppm H2S with the response and recovery time of 43 s and 236s Figure 3.12 Response characteristic of In2O3 – nanowires gas sensor toward ppm H2S at 250 oC and self-heating with a power consumption of 700 μW Figure 3.13 Response characteristic of 80% SnO2/In2O3 NWs gas sensor toward ppm H2S at 250 RC and self-heating with a power consumption of 700 μW 43 Figure 3.14 Response to H2S of the 80% wt SnO2/In2O3 NWs sensor used self-heating effect (Orange line) and sensor using the external heater at 200 oC (Blue line) Figure 3.14 shows that response line of 80% wt SnO2/In2O3 NWs sensor in self-heating mode @ 700 μW is almost similar with external heater at 200 oC response line Suppose that sensor was being heated up to 200 oC Calculate the Efficient Self-Heating coefficient (ESH) of this sample sensor: we have: ‫ ܪܵܧ‬ൌ οܶ ʹͲͲ െ ʹͷ ൌ ൌ ͲǤʹͷ ܲ ͹ͲͲ Table 3.1: Comparison with previous study at ITIMS with same approach method 44 To assess the stability of the sensors, we surveyed the repeatability of sensors after open/close cycles of ppm H2S gas compared to the background gas (no gas) at a working temperature of 300 ºC and self-heating mode at heating power of 300 μW as shown in Figure 3.15 Figure 3.15 Stability of sensor A External heater B Self-heated mode 45 Figure 3.16 Selectivity of In2O3 NWs gas sensor toward NH3, Ethanol and H2S gas under self-heating mode Selectivity of the sensor was also tested for the detection of Ethanol, NH3, and H2S under the heating power of 700 μW The sensor exhibited the best response to H2S among the tested gases, regarding to the test concentration of ppm The gas sensing mechanism is speculated as the resistance changes of the gas sensor before and after exposure to analytic gas For n-type semiconductor metal oxide-based gas sensors, the most widely accepted gas sensing mechanism is based on the change in resistance during the adsorption and desorption of gas molecules and chemical reactions on the surface of sensing materials [38] 46 Figure 3.17 In2O3 material H2S gas sensing mechanism As shown in Fig.3.17, when the sensor was exposed to ambient air, oxygen molecules adsorbed on the surface of the sensing material (Eq 3.3.1 and 3.3.2) captured electrons in the conduction band of In2O3 as well as SnO2/In2O3 NWs to form O2-, O-, O2- species then generated an electron depletion layer ି ܱଶሺ௚ሻ ൅  ݁ ି ՞  ܱଶሺ௔ௗ௦ሻ (3.3.1) ି ଶି ܱଶሺ௔ௗ௦ሻ ൅  ݁ ି ՞  ܱଶሺ௔ௗ௦ሻ (3.3.2) The chemisorbed oxygen species act as acceptors and capture electrons, and there is an increase in resistance of In2O3 nanowires When the In2O3 nanowires were exposed to H2S gas, the target molecules reacted with the previously adsorbed oxygen into SO2 and H2O, as following equations [39] ௫ି ՞ ʹ‫ܪ‬ଶ ܱ ൅ ʹܱܵଶሺ௚௔௦ሻ ൅ ͵‫( ି ݁ݔ‬3.3.3) ‫ܪ‬ଶ ܵ ൅ ͵ܱଶሺ௔ௗ௦ሻ The captured electron will be released back to the conduction band, hence there is a decrease in the resistance of the In2O3 nanowires The resistance of the sensor turns to initial baseline resistance after introducing fresh air 47 CONCLUSION AND RECOMMENDATIONS In this work, we focus on the fabrication and testing of the H2S gas characteristic of the self-heated In2O3 nanowires sensor via a one-step CVD technique and drop-casting on the IDE electrode The obtained In2O3 nanowires and SnO2/In2O3 nanowires were distributed randomly with a diameter of approximately 100 - 200 nm The XRD pattern shows that the crystalline structure of In2O3 indicates a cube phase without impurity of the peak The self-heated In2O3 gas sensor was measured at room temperature (~25 oC) with different applied power toward H2S gas The power consumption of sensor is significantly small compared with micro heater sensor The sensors response was 1.33 to ppm H2S at optimal power of 1200 μW with pure In2O3 NWs sensor and 1.5 to ppm H2S at optimal power of 700 μW which are sufficient to activate the reaction for the detection of reducing gas This performance was better than the state-of-the-art microheater gas sensor The sensor is a potential candidate for application related to H2S detection such as breath exhaled analysis and environmental monitoring However, this method also has some limitations The distribution of In2O3 NWs on the surface of IDE electrode is uncontrollable, leading to the accumulation effect Therefore, these reduce the sensing performance of 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Thermal cycle of In2O3 nanowires fabrication process 26 Figure 2.4 FESEM microscope – HUST 27 Figure 2.5 Procedure of self- heated In2O3 NWs based gas sensor 28 Figure 2.6 Gas sensitive