| Titre : | Elaboration and characterization of nanostructuring NiO thin films for gas sensing applications |
| Auteurs : | Mebrouk Ghougali, Auteur ; Okba Belahssen, Directeur de thèse |
| Type de document : | Thése doctorat |
| Editeur : | Biskra [Algérie] : Faculté des Sciences Exactes et des Sciences de la Nature et de la Vie, Université Mohamed Khider, 2019 |
| Format : | 1 vol. (179 p.) / 30 cm |
| Langues: | Anglais |
| Mots-clés: | Spray Pyrolysis Technique (SPT) ; NiO Thin Films ; Metal Oxide Semiconductors (MOS) ; Gas Sensor ; Sensing Mechanism in (MOS). |
| Résumé : |
This work has been based on the chemical spray pyrolysis technique, it is a very attractive method, that for its ease and low cost on the one hand and the quality of the films prepared by it on the other hand, it is used to produce thin films for different applications including the most important (MOS)-based gas sensors, Such as (NiO)-based gas sensors. At first, a comprehensive study is presented on the effect of deposition parameters on the structural, optical and electrical properties of undoped and Co and Cu-doped (NiO) thin films; the finest samples obtained are then used in the sensor to study their sensing performance for some Volatile organic gases such as ethanol, acetone and methanol. In the following we summarize the most important results obtained: The XRD patterns showed that the structure of the undoped and doped NiO films is polycrystalline structure with the preferred direction (111) also showed that there was no significant shift in the direction of diffraction peaks after doping with cobalt or copper. The crystalline size (D) is increased by thermal annealing and decreases by increasing the doping in the (NiO) samples. From the transmittance spectra, for all samples it was observed that the optical transparency values were moderate to relatively weak, it decrease by thermal annealing, by increasing the molar concentration of the precursor solution, or by increasing the percentage of doping with cobalt or copper. Cobalt or copper doping was also found to be decreasing the band gap energy for the above mentioned reasons, and its values ranged from 3.86 to 3.64 eV for undoped NiO films. For doped films, it ranged between 3.61 and 3.48 eV to cobalt doped films and between 3.60 and 3.43 eV to copper doped films. It was observed that the electrical conductivity of all samples is good and it is the P-type and it has been shown to increase by thermal annealing or by increasing the proportion of doping with cobalt or copper in general, and its value exceeded (0.29 Ω-1.cm-1) when doped By 12 at.% of Copper. Five samples were selected from the prepared samples to study their sensing performance towards ethanol, acetone and methanol vapors, where all films had high ohmic resistance. Optimum operating temperatures, sensitivity, selectivity and detection limits were determined to the gas-based sensor. |
| Sommaire : |
Acknowledgements Dedication Contents I List of figures VII List of tables XIV General introduction 1 Chapter 1: Thin films deposition and characterization methods 1.1 Introduction 9 1.2 Definition of the thin film (layer) 10 1.3 Thin film Deposition Methods 10 1.4 Chemical Spray Pyrolysis Technique (SPT) 11 1.4.1 Processing steps of spray pyrolysis technique 13 1.4.1.1 Precursor atomization 13 1.4.1.2 Aerosol transport of droplets 14 1.4.1.3 Precursor decomposition 15 1.4.2 Influence of the some main SPT parameters on the quality of the deposited films 1.4.2.1 Influence of the temperature 16 1.4.2.2 Influence of precursor solution 17 1.4.2.3 Influence of atomizer (nozzle)-to-substrate distance 17 1.4.3 Growth kinetics of thin films 18 1.5 Films characterization techniques 20 1.5.1 Weight difference method 21 1.5.2 X-Ray diffraction technique (XRD) 21 1.5.2.1 Information obtained from the X-ray diffractogram 22 1.5.3 Scanning Electron Microscopy (SEM) 25 1.5.4 Spectroscopy UV- visible 27 1.5.4.1 Information obtained from the UV-Visible transmittance spectra 28 1.5.6 Method of four probes 33 1.6 Nickel Oxide (NiO) thin film 34 1.6.1 Crystallographic and structural properties 35 1.6.2 Electronic and electrical properties 37 1.6.3 Optical properties 40 1.6.4 Doping types in the NiO film 40 1.6.4.1 Extrinsic doping (substitutional) 41 1.6.4.2 Intrinsic doping 42 1.6.5 Review of nickel oxide prepared by SPT 42 1.7 Conclusion 44 Chapter 2: Chemical gas sensors based on (MOS) thin films 2.1 Introduction 46 2.2 Definition of chemical gas sensor 47 2.2.1 Sensing element of the chemical gas sensor 47 2.2.2 The transducer of the chemical gas sensor 48 2.3 Classification of chemical gas sensors 50 2.4 The main parameters of gas sensor 50 2.4.1 Sensitivity 51 2.4.2 Operating temperature 53 2.4.3 Selectivity 54 2.4.4 Stability 55 2.4.5 Response time 55 2.4.6 Recovery time 56 2.4.7 Reproducibility or repeatability 56 2.4.8 Linearity 57 2.4.9 Sensitivity limit or detection limit 57 2.5 Gas sensing mechanism in(MOS) gas sensors 59 2.5.1 Principles of primary physical interaction 59 2.5.2 Basic phenomena of sensing 59 2.5.3 Working principle 59 2.5.4 Parameters influencing the conductive properties of the sensor 65 2.5.4.1 Influence the morphology and porosity of the sensitive layer 65 2.5.4.2 Influence of grain size 66 2.5.4.3 Influence of the temperature 67 2.5.4.4 Influence of doping 68 2.5.4.5 Influence of film thickness 69 2.6 Role of nanostructures in gas sensors 69 2.7 Review researches of nickel oxide gas sensor 70 2.8 Applications and implications of gas sensors 71 2.8.1 Applications of gas sensors 71 2.8.2 Implications of gas sensors 72 2.9 Conclusion 72 Chapter 3: Elaboration and characterizations of NiO thin films 3.1 Introduction 74 3.2 Elaboration of NiO thin films 74 3.2.1 Experimental montage of a homemade SPT system 74 3.2.2 Thin film deposition parameters 76 3.2.3 Experimental procedure 76 3.2.3.1 Preparation of substrates 76 3.2.3.2 Preparation method of the precursor solution 77 3.2.3.2 Deposition steps of the NiO thin films 78 3.3 Characterizations of prepared NiO thin films 79 3.3.1 Effect of precursor molarity on properties of NiO thin films 79 3.3.1.1 Preparation of samples 79 3.3.1.2 Devices and measurements 80 3.3.1.3 Results and discussions 80 3.3.1.3.a Structural properties 80 3.3.1.3.b Optical properties 82 3.3.1.3.c Electrical properties 86 3.3.2 Effect of annealing on physical properties of NiO thin films 87 3.3.2.1 Preparation of samples 87 3.3.2.2 Devices and measurements 88 3.3.2.3 Results and discussions 88 3.3.2.3.a Structural properties 88 3.3.2.3.b Optical properties 89 3.3.2.3.c Electrical properties 92 3.3.3 Effect of cobalt doping on physical properties of NiO thin films 93 3.3.2.1 Preparation of samples 93 3.3.3.2 Devices and measurements 94 3.3.3.3 Results and discussions 95 3.3.3.3.a Structural and surface morphological properties 95 3.3.3.3.b Optical properties 101 3.3.3.3.c Electrical properties 104 3.3.4 Effect of copper doping on physical properties of NiO thin films 105 3.3.4.1 Preparation of samples 105 3.3.4.2 Devices and measurements 107 3.3.4.3 Results and discussions 107 3.3.4.3.a Structural and surface morphological properties 107 3.3.4.3.b Optical properties 114 3.3.4.3.c Electrical properties 119 3.4 Conclusion 120 Chapter 4: Gas sensing performance of NiO thin films 4.1 Introduction 122 4.2 Fabrication of gas sensor 123 4.3 Gas sensing measurement 124 4.4 Principle and mechanism of gas sensor 126 4.5 Gas sensing performance 128 4.5.1 Gas sensing performance of undoped NiO thin films 128 4.5.1.1 Operating temperature 128 4.5.1.2 Selectivity 129 4.5.1.3 Sensitivity 130 4.5.1.4 Response and recovery times 131 4.5.1.5 Detection limit 131 4.5.1.6 Stability 132 4.5.2 Gas sensing performance of Co-doped NiO thin films 133 4.5.2.1 Operating temperature 133 4.5.2.2 Selectivity 133 4.5.2.3 Sensitivity 134 4.5.2.4 Response and recovery times 135 4.5.2.5 Detection limit 136 4.5.2.6 Stability 137 4.5.3 Gas sensing performance of Cu-doped NiO thin films 138 4.5.3.1 Operating temperature 138 4.5.3.2 Sensitivity 139 4.5.3.3 Selectivity 141 4.5.3.4 Response and recovery times 141 4.5.3.5 Detection limit 141 4.5.2.6 Stability 143 4.6 Comparative study 144 4.6.1 Resistance 144 4.6.2 Response and recovery times 144 4.6.3 Operation temperature 146 4.6.4 Sensitivity 146 4.6.5 Stability 147 4.6.6 General comparison between our results and results of other works 147 4.7 Conclusion 148 General conclusion and Future Works 1 5 1 Appendix 157 References 164 |
| En ligne : | http://thesis.univ-biskra.dz/id/eprint/4617 |
Disponibilité (1)
| Cote | Support | Localisation | Statut |
|---|---|---|---|
| TPHY/92 | Théses de doctorat | bibliothèque sciences exactes | Consultable |
