Synthesis and gas sensing properties of tio2 nanowires

PHAM HONG TRANG MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF TECHNOLOGY AND SCIENCE - PHAM HONG TRANG MATERIAL SCIENCE SYNTHESIS AND GAS-SENSING PROPERTIES OF TIO2 NANOWIRES MASTER THESIS OF SCIENCE MATERIAL SCIENCE 2009-2011 Hanoi – 2011 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF TECHNOLOGY AND SCIENCE PHAM HONG TRANG SYNTHESIS AND GAS-SENSING PROPERTIES OF TIO2 NANOWIRES MASTER THESIS OF SCIENCE MATERIAL SCIENCE SUPERVISOR : ASS.PROF NGUYEN VAN HIEU Hanoi – 2011 ABSTRACT INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE BATCH ITIMS 2009-2011 Title: Synthesis and gas-sensing properties of TiO2 nanowires Author: Pham Hong Trang Batch: 2009-2011 Supervisor: Asso Prof Dr Nguyen Van Hieu  Abstract: One-dimensional (1-D) TiO2 nanostructures have recently attractedsignificant attention in gas-sensor applications because of their good chemical stability, nontoxicity, and favorable electrical and optical properties Moreover, the fabrication and understanding of the growth mechanism of 1-D TiO2 nanostructures can be a building block to be realized In this study, we report the gas sensing properties of the TiO2 nanowire prepared by reactive sputtering technique and subsequently grown self-catalytically without the use of any other catalyst metals on Si(100) at a moderate growth range of temperature of (~650 to 850°C)using thermal oxidation process The oxygen source for the growing process is ethanol The shape of the TiO2 nanowires are wires which represents the tetragonal lattice structure of anatase and/or rutile TiO2 The lengths, diameters of the nanowires are ~ (80-300)nm and ~ (1.22.5)nm respectively TiO2 thin films are extensively studied for application in gas sensor devices The films were first annealed at 5000C, 7000C, 9000C and exposed to different concentration of H2 gas at 100, 250, 500ppm Their gas sensing properties was obtained by measuring their resistance and were strongly dependent on synthesize technique, annealing temperature, wires size This result was compared with the sensing properties of TiO2nanopowder synthesized by hydrothermal at the same range of H2 concentration TÓM TẮT LUẬN VĂN THẠC SĨ VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU Khóa ITIMS 2009-2011 Đềtài: Nghiên cứu chế tạo tính chất nhạy khí dây nano TiO2 Tácgiả: PhạmHồngTrang Khóa: 2009-2011 Ngườihướngdẫn: PGS.TS NguyễnVănHiếu Nội dung tóm tắt: Trong năm gần vật liệu cấu trúc nano TiO2 chiều thu hút ý đáng kể ứng dụng cảm biến tính chất bền hóa khơng độc hại Hơn nữa, việc tìm hiểu chế tạo vật liệu cấu trúc nano TiO2 được tiến hành Trong nghiên cứu này, đưa phương pháp nghiên cứu khả nhạy khí vật liệu TiO2, đề tài thực với hai nhiệm vụ : - Nghiên cứu quy trình chế tạo dây TiO2 - Khảo sát tính chất nhạy khí dây nano TiO2 Đế vật liệu chuẩn bị kỹ thuật phún xạ sau tiến hành q trình tổng hợp tự xúc tác không sử dụng kim loại làm chất xúc tác Si (100) khoảng nhiệt độ (~650-8500C) cách sử dụng q trình ơxy hóa nhiệt Nguồn ôxy cho trình phát triển ethanol Các dây nano TiO2 có cấu trúc mạng tứ diện anatase / TiO2 Rutile Độ dài, đường kính dây nano TiO2 (8-30) nm ~ (1,2-2,5) nm Màng mỏng TiO2 nghiên cứu rộng rãi cho ứng dụng thiết bị cảm biến khí Các sensor sau chế tạo ủ 5000C, 7000C, 9000C kiểm tra tính nhạy khí với nồng độ H2 100, 250, 500 ppm Các đặc tính nhậy khí thu cách đo điện trở sensor phụ thuộc nhiều kỹ thuật tổng hợp, nhiệt độ ủ, kích thước dây Kết so sánh với thuộc tính cảm ứng bột TiO2 chế tạo phương pháp thủy nhiệt khoảng nồng độ H2 Qua so sánh nhận thấy sensor vật liệu TiO2 chế tạo phương pháp vật lý có độ nhạy không thua so với sensor chế tạo vật liệu bột TiO2 phương pháp hóa học ASSURANCE I hereby declare that the thesis named “Synthesis and Characterization of One Dimensional TiO2 Nanowires” is the individual study that actually based on theoretical studies and experimental work at Gas Sensor group under the supervise of Ass.Prof Nguyen Van Hieu and the results and data presented in this thesis are true, and have never been published in other previous works I would confirm that this assurance istrue Hanoi, October 2011 LỜI CAM ĐOAN Tôi xin cam đoan luận văn “ Nghiên cứu chế tạo tính chất nhạy khí dây nano TiO2” cơng trình nghiên cứu thực cá nhân sở nghiên cứu lý thuyết tiến hành thực nghiệm nhóm Cảm biến khí hướng dẫn PGS TS Nguyễn Văn Hiếu Các số liệu kết trình bày luận văn trung thực chưa cơng bố cơng trình khác trước Tôi xin khảng định lời cam đoan thật Hà Nội, tháng 10 năm 2011 Tácgiả Phạm Hồng Trang Acknowledgments Firstly, I am deeply grateful to my advisor Professor Nguyen Van Hieu for his direct guidance and advising me during my Master course He has believed and encouraged me by creating all the best conditions and opportunities possible for my research I would like to express my gratitude to all the members of Gas Sensor group for their availability and willingness to share their knowledge and materials, especially their skill of doing experiments and using devices It would be difficult for me to reach this final without their helps I also thank to Hanoi Institute of Hygiene Epidemiology - Center for Electron Microscopy, for their help in SEM, X-ray measurement I would like to thank the committee members for their valuable comments and suggestions on my thesis I thank all the members in the laboratory and staffs from ITIMS for their help in my life and my work Whenever I needed their support, they were pleased to help me Finally but not least, I would like to thank family for their endless support and encouragement during all studies starting from day one Hanoi, October 2011 Author Pham Hong Trang Contents ABSTRACT ASSURANCE Acknowledgments .4 List of tables .5 List of Figures Preface 13 Chapter I Error! Bookmark not defined Introduction to TiO2 – based material Error! Bookmark not defined 1.1 Preview on TiO2 nano structure Error! Bookmark not defined 1.1.1 Crystal structure and chemical bonding Error! Bookmark not defined 1.1.2 Synthesis methods for 1-D TiO2nanostructures 20 1.2 Synthesis mechanism for 1-D TiO2 nanostructures Error! Bookmark not defined 1.2.1 Vapor – Liquid – Solid (VLS) Mechanism Error! Bookmark not defined 1.2.2 Vapor –Solid (VS) Mechanism Error! Bookmark not defined 1.2.3 Solution - Liquid –Solid (SLS) Mechanism Error! Bookmark not defined 1.3 Characterization techniques for 1-D TiO2 nanostructures Error! Bookmark not defined 1.3.1 Scanning electron microscopy Error! Bookmark not defined 1.3.2 Transmission electron microscopy Error! Bookmark not defined 1.3.3 Raman spectroscopy 30 1.3.4 X-Ray photoelectron spectroscopy (XPS) .30 1.4 Gas sensing application 31 1.4.1 Introduction to gas sensor 31 1.4.2 The characteristics of gas sensors Error! Bookmark not defined 1.4.3 Responsibility and Influencing Factors Error! Bookmark not defined Chapter II Error! Bookmark not defined Experimental Techniques Error! Bookmark not defined 2.1 Synthesis of 1-D TiO2 nanostructures by thermal oxidationError! Bookmark not defined 2.1.1 Specimens and tools preparation Error! Bookmark not defined 2.1.2 Synthesis of 1-D TiO2 nanostructures of TiO2 thin film Error! Bookmark not defined 2.2 Synthesis of 1-D TiO2 nanostructures by hydrothermal Error! Bookmark not defined 2.2.1 Source materials and preparation methods Error! Bookmark not defined 2.2.2 Synthesis of 1-D TiO2 nanostructures of TiO2 nano powder Error! Bookmark not defined 2.3 Sensor fabrication 50 Chapter III Error! Bookmark not defined Results and Discussion Error! Bookmark not defined 3.1 Surface morphological analysisof 1-D TiO2 nanostructure Error! Bookmark not defined 3.1.1 Analysis of TiO2 sputtering layer Error! Bookmark not defined 3.1.2 Morphological analysis of TiO2 nanowire using thermal oxidation Error! Bookmark not defined.   3.1.3 Morphological analysis of TiO2 nanopowder using hydro thermal…….73  3.2 X-ray diffraction analysis Error! Bookmark not defined 3.2.1 X-ray diffraction analysis of TiO2 nanowires Error! Bookmark not defined 3.2.2 X-ray diffraction analysis of TiO2 nanopowder Error! Bookmark not defined 3.3 Gas sensing properties analysis Error! Bookmark not defined 3.3.1 Gas sensing properties analysis of TiO2 nanowires Error! Bookmark not defined 3.3.2 Gas sensing properties analysis of TiO2 nanopowder .82 3.3.3 Gas sensing property comparison Error! Bookmark not defined Conclusions Error! Bookmark not defined References Error! Bookmark not defined.    List of Tables Page Table 1.1 TiO2 phases and their lattice constants 20 Table 2.1 The experimental modes and the numbers of experiments taken in each mode 47 Table 2.2 The experimental modes which have stable repetition 48 Table 3.1 H2 (0.5%) gas concentrations 52 (b) (c) Figure 3.24 Gas sensing characteristic of TiO2 nanowires with annealing temp: 700°C /gas concentration : (a)100- (b)250- (c)500ppm 128 O r i g i n P r o 700 E va lu a Annealing Ct i o n O rig in P ro E va lu a tio n Response (Rg/Ra)% 126 O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n 124 122 120 118 116 114 112 100 200 300 400 500 Time (s) Figure 3.25 Gas sensing characteristic comparison of TiO2 nanowires with annealing temp: 700°C/gas concentration : 100- 250-500ppm 79 At operating temperature 4500C, as the gas concentration increased, the response properties show the change varied from approximately 114 – 128%, 10% above the response properties of the sensor annealed in 5000C This may be explained that at higher annealed temperature, the nanowire bond tightly together and make the sensor more contacted, so it has the better interaction between sensitive film and adsorbed gas Sensor resistance was 31MΩ Gas sensing analysis of TiO2 nanowires annealed at 9000C (a) (b) (c) Figure 3.26 Gas sensing characteristic of TiO2 nanowires with annealing temp: 900°C /gas concentration : (a) 100- (b) 250- (c) 500ppm 80 140 Response (Rg/Ra)% 138 136 o O r i g i n P r o E900 v a l u aC tio n Annealing O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n O rig in P ro E va lu a tio n O rig in P ro E va lu atio n 134 132 130 128 126 100 200 300 400 500 Time (s) Figure 3.27 Gas sensing characteristic comparison of TiO2 nanowires with annealing temp: 900°C/gas concentration : 100- 250-500ppm As the gas concentration increased, the response properties show the change varied from approximately 128 – 140%, 14% above the response properties of the sensor annealed in 7000C Sensor resistance was 32MΩ In comparison of gas sensing properties of TiO2 nanowires gas sensor, it is worth pointing out that the difference in gas sensitive to H2 under identical experimental conditions should be attributed to the different interactions between sensitive film and adsorbed gas The annealing temperature affect the bonding in nanowire layer, making the resistance and responsibly of gas sensor increased as increasing annealing temperature Fig 3.29 give us the evident that at higher annealing temperature, the response characteristic of TiO2 nanowire-based sensor increases Moreover, at the same gas concentration, the response characteristic increased at the higher annealing temperature In such a way, this resultsshows the importance of layer bonding on gas sensor responsibility 81 140 Response (Rg/Ra)% 135 Annealing 500 C Annealing 700 C OriginP r o E v a l u a t i900 on Annealing C Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n OriginPro Evaluation Orig in P ro E valu atio n 130 125 120 115 110 100 200 300 400 500 Time (s) Figure 3.28 Gas sensing characteristic comparison of TiO2 nanowires gas sensor with annealing temperature varied from 5000C, 7000C, 9000C 3.3.2 Gas sensing properties analysis of TiO2 nanopowder Gas sensor based on TiO2 nanopowder was annealed at 7000C to make electrical contact between the sensor and powder layer It response behavior was measure as follow (a) 82 (b) (c) Figure 3.29 Gas sensing characteristic of TiO2 nanowires with annealing temp: 700°C /gas concentration : (a)100- (b)250- (c)500ppm 128 TiO2 nanopowder O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n O rig in P ro E valu atio n 126 Response (Ra/Rg)% 124 122 120 118 116 114 112 110 108 100 200 300 400 500 Test gas concentration (ppm) Figure 3.30 Gas sensing characteristic comparison of TiO2 nanopowder with annealing temp: 700°C /gas concentration : 100- 250-500ppm 83 The response characteristic of TiO2 nanopowder –based gas sensor is beyond the rule of the response characteristic of TiO2 nanowire –based gas sensor Gas sensor increased its response from 110 – 126% while increasing the H2 concentration But its resistance is much higher than TiO2 nanowires, it is about 96MΩ 3.3.3 Gas sensing property comparison 140 Response (Rg/Ra)% 135 Thin8 filmAnnealing 500 E va lu a tio n O r i g iC n P ro Thin filmAnnealing 700 C 900 O r i g i n Thin P r o filmAnnealing E va lu a tio n O r i g iC n P ro TiO2 nanopowder O rig in P ro E va lu a tio n E va lu a tio n 130 O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n 125 O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n 120 O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n 115 O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n O rig in P ro E va lu a tio n 110 100 200 300 400 500 Time (s) Figure 3.31 Gas sensing characteristic comparison of TiO2 nanowire and nanopowder In order to compare with TiO2nanowire sensor, the TiO2nanopowder sensor was also prepared, and its response behavior was measured It is evident shown on Fig 3.32 that response characteristic of two kind of sensor are similar The response line of TiO2nanopowder sensor was found staying between the response line of TiO2nanowire sensor annealed at 5000C and 7000C The synthesis and characteristic of TiO2nanopowder sensor was redone several time but its response behavior stayed almost the same 84 Conclusions In a period of time studying the thesis “Synthesis and Characterization of One-Dimensional TiO2 Nanowires “ in Gas sensor Group – International Training Institute for Material science (ITIMS), the study was posed the research purposes as follow: - Synthesized and stabilized process for TiO2 nanowires - Gas sensing characteristic of gas sensor based on TiO2 nanowires - Compare gas sensing characteristic of gas sensor based on TiO2 nanowires and nanopowder synthesized by two methods The results this thesis received are as follow: - Synthesized and stabilized process for TiO2 nanowires by oxidation method at temperature of 650 – 8500C, at pressure (1-2)10-1Torr Source materials used was Ti thin layer sputtered on Si (100)substrate, the Ti layer was 1.87 – 1.96 µm thick The SEM image show the morphology of TiO2 nanowires with wire’s diameter was between (0.8-2)µm and the length was (1.02.5)µm The best result was received at 7500C and ethanol concentration of 15 sccm The SEM also provided the effect of ethanol concentration and annealing temperature on the length and diameter of TiO2 nanowires XRD pattern also indicated that TiO2 nanowires was in rutile face - Synthesized TiO2 nanopowder as preparation specimen by hydrothermal - Fabricated sensor based on TiO2 nanowires with different annealing temperature 5000C, 7000C, 9000C andsensor based on TiO2 nanopowder which were H2 sensing characterized at concentration of 100-250-500ppm 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Bookmark not defined 3.3 Gas sensing properties analysis Error! Bookmark not defined 3.3.1 Gas sensing properties analysis of TiO2 nanowires Error!... (b)250-(c)500ppm 80 Gas sensing characteristic comparison of TiO2 nanowires Figure 3.27 with annealing temp: 900°C /gas concentration : 100- 250- 81 500ppm Gas sensing characteristic comparison of TiO2 nanowires