No description available.

Yang, Li. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 67-72). / Abstract also in Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background and Motivation --- p.1 / Chapter 1.2 --- Objectives --- p.2 / Chapter 1.3 --- Contributions --- p.2 / Chapter 1.4 --- Organization of the Dissertation --- p.3 / Chapter 2 --- Carbon Nanotubes as Sensing Elements --- p.4 / Chapter 2.1 --- Introduction --- p.4 / Chapter 2.2 --- Introduction to Carbon Nanotubes --- p.4 / Chapter 2.3 --- Chemical Sensor Applications --- p.6 / Chapter 2.3.1 --- Semiconducting Sensors --- p.7 / Chapter 2.3.2 --- Dielectric Sensors --- p.8 / Chapter 2.3.3 --- Adsorption Based Sensors --- p.9 / Chapter 2.4 --- Dielectrophoresis of CNTs --- p.9 / Chapter 2.4.1 --- Theory and Methodology --- p.10 / Chapter 2.4.2 --- Basic CNTs Sensor Fabrication Process Using DEP Force --- p.13 / Chapter 2.4.3 --- Electronic-Grade Carbon Nanotubes --- p.13 / Chapter 2.4.4 --- Simulation --- p.14 / Chapter 2.5 --- Photodesorption Phenomenon --- p.16 / Chapter 2.5.1 --- Chemical Desorption Process Induced by UV Illumination --- p.16 / Chapter 2.6 --- Summary --- p.19 / Chapter 3 --- Design of NaOCl Sensors Based on EG-CNTs in Microfluidic System --- p.20 / Chapter 3.1 --- Introduction --- p.20 / Chapter 3.2 --- Chemical --- p.20 / Chapter 3.2.1 --- Introduction to Chemical Properties and Reactions --- p.21 / Chapter 3.2.2 --- Reagents --- p.23 / Chapter 3.3 --- Methods for Chemical Detection --- p.23 / Chapter 3.3.1 --- Hypochlorite Detection --- p.23 / Chapter 3.3.2 --- Chlorine Gas Detection --- p.24 / Chapter 3.4 --- Design and Fabrication --- p.26 / Chapter 3.4.1 --- Sodium Hypochlorite Sensor Using Microfluidic System --- p.26 / Chapter 3.4.2 --- Modified Design For Indirect Detection to Chlorine Gas --- p.29 / Chapter 3.5 --- Equipments --- p.30 / Chapter 3.5.1 --- Source Meter --- p.30 / Chapter 3.5.2 --- Pneumatic Pump --- p.31 / Chapter 3.5.3 --- UV Illumination Devices --- p.31 / Chapter 3.5.4 --- Experimental Setup --- p.32 / Chapter 3.6 --- Summary --- p.34 / Chapter 4 --- Results --- p.35 / Chapter 4.1 --- Introduction --- p.35 / Chapter 4.2 --- Processes of the Experiments --- p.35 / Chapter 4.2.1 --- Response to Static Solution --- p.35 / Chapter 4.2.2 --- Response to Fluid Flow --- p.36 / Chapter 4.2.3 --- Response to Gas --- p.36 / Chapter 4.3 --- Noise and Accuracy --- p.37 / Chapter 4.4 --- I-V Characteristics --- p.38 / Chapter 4.4.1 --- EG-CNTs Sensor --- p.38 / Chapter 4.4.2 --- Variation Under UV Illumination --- p.39 / Chapter 4.5 --- Responses to Sodium Hypochlorite Solution --- p.41 / Chapter 4.5.1 --- Typical Responses --- p.41 / Chapter 4.5.2 --- Selectivity --- p.44 / Chapter 4.5.3 --- Sensitivity --- p.45 / Chapter 4.5.4 --- Effect of Injection Flow Rate on Sensor Performance --- p.50 / Chapter 4.5.5 --- Effect of Volume on Sensor Performance --- p.51 / Chapter 4.5.6 --- Continuous Detection --- p.54 / Chapter 4.5.7 --- Operating Power Limit --- p.57 / Chapter 4.6 --- Response to Chlorine Gas by Modified Design --- p.59 / Chapter 4.7 --- Desorption Induced by UV Illumination --- p.60 / Chapter 4.8 --- Summary --- p.63 / Chapter 5 --- Conclusion --- p.64 / Chapter 5.1 --- Future Work --- p.65 / Chapter 5.1.1 --- Selectivity --- p.65 / Chapter 5.1.2 --- Gaseous Chlorine Detection --- p.66 / Chapter 5.1.3 --- UV-LED Induced Desorption --- p.66 / Chapter 5.2 --- Concluding Remarks --- p.66 / Bibliography --- p.67

Ouyang, Mengxing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 83-88). / Abstracts in English and Chinese. / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Background and Motivation --- p.1 / Chapter 1.2 --- Objectives --- p.2 / Chapter 1.3 --- Contributions --- p.3 / Chapter 1.4 --- Organization of the Dissertation --- p.3 / Chapter 2. --- CNTs and Their Application as Sensors --- p.5 / Chapter 2.1 --- Introduction to CNTs --- p.5 / Chapter 2.2 --- CNTs Based Sensors --- p.8 / Chapter 3. --- F-CNTs Based Ethanol Sensors --- p.10 / Chapter 3.1 --- Introduction --- p.10 / Chapter 3.1.1 --- Carbon Nanotube Alcohol Sensors --- p.11 / Chapter 3.1.2 --- CNTs Sensor Configuration --- p.12 / Chapter 3.1.3 --- Activation of CNTs Sensor --- p.13 / Chapter 3.1.4 --- Functionalization of CNTs --- p.14 / Chapter 3.2 --- Fabrication of F-CNTs Based Ethanol Sensors --- p.16 / Chapter 3.2.1. --- Fabrication of f-CNTs --- p.16 / Chapter 3.2.2. --- Fabrication of Sensing Elements by DEP Manipulation --- p.17 / Chapter 3.2.3. --- Experimental Setup --- p.19 / Chapter 3.2.4. --- Mechanism of Ethanol Sensor --- p.20 / Chapter 3.3 --- Characterization of F-CNTs Based Ethanol Sensors --- p.21 / Chapter 3.3.1. --- I-V Characteristics --- p.21 / Chapter 3.3.2. --- Thermal Sensitivity --- p.22 / Chapter 3.3.3. --- Stability --- p.23 / Chapter 3.3.4. --- FFT and Spectral Analysis --- p.23 / Chapter 3.4 --- Performance of F-CNTs Based Ethanol Sensors --- p.26 / Chapter 3.4.1. --- Typical Response --- p.26 / Chapter 3.4.2. --- Selectivity --- p.27 / Chapter 3.4.3. --- Towards Low Concentration --- p.28 / Chapter 3.4.4. --- Towards Realistic application --- p.29 / Chapter 3.5 --- Constant Power Configuration --- p.32 / Chapter 3.5.1. --- Constant Power Circuit for Ethanol Detection --- p.32 / Chapter 3.5.2. --- Sensor Response versus Power --- p.35 / Chapter 3.5.3. --- Responsivity --- p.37 / Chapter 3.5.4. --- Noise --- p.38 / Chapter 3.5.5. --- Sensitivity --- p.39 / Chapter 3.5.6. --- Dynamic Response --- p.41 / Chapter 3.6 --- Comparison between F-MWNTs and MWNTs --- p.43 / Chapter 3.6.1. --- I-V Characteristics --- p.43 / Chapter 3.6.2. --- Cycling Response --- p.44 / Chapter 3.6.3. --- Dynamic Response --- p.46 / Chapter 3.6.4. --- Sensor Performance under Different Power --- p.48 / Chapter 3.7 --- Summary --- p.53 / Chapter 4. --- EG-CNTs Based Flow Sensors --- p.55 / Chapter 4.1 --- Introduction to CNTs Flow Sensors --- p.55 / Chapter 4.2 --- EG-CNTs and Their Applications --- p.56 / Chapter 4.2.1 --- Intro to EG-CNTs Sensor --- p.56 / Chapter 4.2.2 --- Fabrication of EG-CNTs Sensor --- p.57 / Chapter 4.2.3 --- Experimental Characterization --- p.59 / Chapter 4.2.3.1. --- I-V Characteristics --- p.59 / Chapter 4.2.3.2. --- Thermal Sensitivity --- p.61 / Chapter 4.2.3.3. --- Humidity responsivity --- p.63 / Chapter 4.2.3.4. --- Stability --- p.65 / Chapter 4.2.3.5. --- Hysteresis --- p.66 / Chapter 4.2.4 --- Summary --- p.68 / Chapter 4.3 --- Fabrication of EG-CNTs Flow Sensor --- p.70 / Chapter 4.3.1. --- Fabrication Procedure --- p.70 / Chapter 4.3.2 --- Experimental Setup --- p.73 / Chapter 4.4 --- Characterization of EG-CNTs Flow Sensor --- p.74 / Chapter 4.4.1. --- Typical Response --- p.74 / Chapter 4.4.2. --- Power Consumption --- p.75 / Chapter 4.4.3. --- Repeatability --- p.77 / Chapter 4.4.4. --- Flow Sensitivity --- p.78 / Chapter 4.5 --- Summary --- p.79 / Chapter 5. --- Conclusion --- p.80 / Chapter 6. --- Bibliography --- p.83

Triethanolamine (TEA) is a semiconducting polymer which exhibits a resistance change when exposed to various gases. The polymer also exhibits a number of reactions with nitrogen dioxide, with the reaction products being heavily dependent on the presence or absence of water vapor. Previous studies have attempted the incorporation of a TEA-carbon nanoparticle composite as the active sensing layer in a chemresistive sensor for detection of NO₂. The incorporation of carbon nanoparticles in the polymer nanocomposite was thought to amplify the sensor's response. There are a number of chemical reactions that can occur between TEA and NO₂, with the reaction products being heavily dependent on the presence and amount of water vapor in the environment. Because of this influence, it becomes necessary to know to what degree the presence of water vapor interferes with the sensing response. In this work we show that the sensor exhibits a reversible resistance change as background humidity changes. This sensitivity to humidity changes is so large that it renders undetectable any resistance change that could be caused by the reaction of TEA with NO₂. Furthermore, we show that the presence of low levels of NO₂ do not interfere with adsorption of water vapor. The detection mechanism is based on measuring resistance changes in the TEA film due to the adsorption/desorption of water vapor. The sensing response can be described by Langmuir adsorption by using a site-based model for the polymer film resistance. Breakdown of the polymer film over time due to continuous adsorption of water vapor, as well as photodegradation of the polymer film, will be discussed. SEM images will also be presented showing growth of crystallites on the electrode walls, as well as experimental results demonstrating degradation of the sensing film during sensor operation.

A sensor is described which utilizes the phenomenon of surface plasmon resonance to detect changes in refractive index of chemical or biochemical samples applied to a surface modified optical fiber. The sensor is constructed by polishing a short section of the lateral surface of an optical fiber to its evanescent field surrounding the fiber core. One or more thin films are applied to the polished section of the fiber to produce the sensing element. One of the films is the metal silver, which acts as the support for the surface plasmon. Under the proper conditions, TM polarized energy propagating in the fiber can be coupled to a surface plasmon electromagnetic mode on the metal film. This coupling depends on the wavelength, the nature of the fiber, the refractive index and thickness of the thin films applied to the fiber, and the refractive index of a chemical sample in contact with the modified surface. The fiber to plasmon coupling is seen as a large attenuation of the light reaching the distal terminus of the fiber. / Ph. D.

Polarimetry, as applied to chemical analysis, deals with the determination of the extent and direction that an optically active chemical species will rotate incident linearly polarized light. Although well developed for physical sensing, the technique of fiber optic polarimetry for chemical sensing remains in its infancy. This thesis is concerned with the design and development of an optical fiber polarimeter which measures the optical rotation of linearly polarized light that occurs in a sensing region between two multi-mode optical fibers. Over short distances, the polarization preserving capabilities of large-core multi-mode optical fibers were investigated. Polarimetric analyses were performed using sucrose and quinine hydrochloride. The instrument has a resolution of 0.08·, and is an excellent platform for an LC or FIA detector. Its more intriguing future lies in evanescent field sensor applications and studies of chiroptical surface interactions. / Master of Science

Portable mass spectrometers provide a unique opportunity to obtain in situ measurements. This minimizes need for sample collection or in laboratory analysis. Membrane Inlet Mass Spectrometry (MIMS) utilizing a semi permeable membrane for selective rapid introduction for analysis. Polydimethylsiloxane membranes have been proven to be robust in selecting for aromatic chemistries. Advances in front end design have allowed for increased sensitivity, rapid sample analysis, and on line measurements. Applications of the membrane inlet technique have been applied to environmental detection of clandestine drug chemistries and pollutants. Emplacement of a mass spectrometer unit in a vehicle has allowed for large areas to be mapped, obtaining a rapid snapshot of the various concentrations and types of environmental pollutants present. Further refinements and miniaturization have allowed for a backpackable system for analysis in remote harsh environments. Inclusion of atmospheric dispersion modeling has yielded an analytical method of approximating upwind source locations, which has law enforcement, military, and environmental applications. The atmospheric dispersion theories have further been applied to an earth based separation, whereby chemical properties are used to approximate atmospheric mobility, and chemistries are further identified has a portable mass spectrometer is traversed closer to a point source.