Optical Coherence Tomography (OCT) is a novel optical imaging technique that has assumed significant importance in bio-medical imaging in the last two decades because it is non-invasive and provides accurate, high resolution images of three dimensional cross-sections of body tissue, exceeding the capabilities of the current predominant imaging technique –ultrasound. In this thesis, high resolution OCT is investigated for in vivo detection of abnormal skin pathology for the early diagnosis of cancer. The technology presented is based on a dynamic focusing microscopic imaging probe conceived for skin imaging and the detection of abnormalities in the epithelium. A novel method for dynamic focusing in the biological sample using liquid crystal (LC) lens technology to obtain three dimensional images with invariant resolution throughout the cross-section and depth of the sample is presented and discussed. Two different skin probe configurations that incorporate dynamic focusing with LC lenses, one involving a reflective microscope objective sub-system, and the other involving an all-refractive immersion microscope objective sub-system are investigated. In order to ensure high resolution imaging, a low coherence broadband source, namely a femtosecond mode-locked Ti: sapphire laser centered at a wavelength of approximately 800nm is used to illuminate the sample. An in-depth description and analysis of the optical design and predicted performance of the two microscope objectives designed for dynamic three dimensional imaging at 5ìm resolution for the chosen broadband spectrum is presented.

Yes / A confocal microscope provides a sequence of images of the corneal layers and structures at different depths from which medical clinicians can extract clinical information on the state of health of the patient’s cornea. Hybrid model based on snake and particle swarm optimisation (S-PSO) is proposed in this paper to analyse the confocal endothelium images. The proposed system is able to pre-process (quality enhancement, noise reduction), detect the cells, measure the cell density and identify abnormalities in the analysed data sets. Three normal corneal data sets acquired using confocal microscope, and two abnormal endothelium images associated with diseases have been investigated in the proposed system. Promising results are achieved and the performance of this system are compared with the performance of two morphological based approaches. The developed system can be deployed as clinical tool to underpin the expertise of ophthalmologists in analysing confocal corneal images.

Yes / A confocal microscope provides a sequence of images of the various corneal layers and structures at different depths from which medical clinicians can extract clinical information on the state of health of the patient’s cornea. Preprocessing the confocal corneal images to make them suitable for analysis is very challenging due the nature of these images and the amount of the noise present in them. This paper presents an efficient preprocessing approach for confocal corneal images consisting of three main steps including enhancement, binarisation and refinement. Improved visualisation, cell counts and measurements of cell properties have been achieved through this system and an interactive graphical user interface has been developed.

Two-dimensional (2D) layered hexagonal boron nitride (h-BN) has become a very popular material in nanoelectronics in recent years because of its extraordinary chemical stability and thermal conductivity [1]. Recently, h-BN is also commonly used as a dielectric material [2], and research in this area is still in its early stages. The commonly used methods for fabricating h-BN include mechanical exfoliation and chemical vapor deposition (CVD). CVD is a recognized industry-compatible method for producing large-area h-BN. However, studies have shown that multilayer h-BN grown by CVD is polycrystalline and contains multiple local defects [3]. These defects and inhomogeneity cannot be avoided and lead to small amounts of atom-wide amorphous regions that have weak dielectric strength [3]. Although the general characteristics of h-BN prepared by these two fabrication methods can be learned from different works in the literature, it is difficult to study the quality of h-BN without systematically comparing the differences between the two growth methods under the same experimental conditions and with large number of samples. This also makes it difficult for researchers to choose the best-quality h-BN. In this work, the morphological characteristics and electrical properties of mechanically exfoliated h-BN and CVD-grown h-BN from different sources have been compared under different conditions. Commercially available h-BN flakes mechanically exfoliated from NIMS h-BN bulk crystal show no leakage current at electrical fields up to 25.9 MV/cm, and above this applied electrical force, the size of the conductive spots is extremely small (1.99 ± 1.81 nm2). On the contrary, “monolayer” CVD-grown h-BN samples from Graphene Supermarket were shown to be amorphous in ~20% of their area, which makes them appear discontinuous from an electrical point of view, plus they contain large thickness fluctuations up to 6 layers. Moreover, in nanoelectronic measurements collected with a conductive atomic force microscope (CAFM) working in vacuum, mechanically exfoliated h-BN showed better electrical homogeneity and presented later dielectric breakdown compared to the h-BN samples fabricated by the CVD method.

No description available.

An atomic force microscope (AFM) has been used to conduct force measurements to better understand the role of hydrophobic forces in flotation. The force measurements were conducted between a flat mineral substrate and a hydrophobic glass sphere in aqueous solutions. It is assumed that the hydrophobic glass sphere may simulate the behavior of air bubbles during flotation. The results may provide information relevant to the bubble-particle interactions occurring during flotation. The glass sphere was hydrophobized by octadecyltrichlorosilane so that its water contact angle was 109 degrees. The mineral systems studied include covellite (CuS), sphalerite (ZnS) and hornblende (Ca₂(Mg, Fe)₅(Si₈O₂₂)(OH,F)₂). The collector used for all the mineral systems studied was potassium ethyl xanthate (KEX). For the covellite-xanthate system, a biopotentiostat was used in conjunction with the AFM to control the potential of the mineral surface during force measurements. This was necessary since the adsorption of xanthate is strongly dependent on the electrochemical potential (Eₕ) across the solid/liquid interface. The results show the presence of strong hydrophobic forces not accounted for by the DLVO (named after Derjaguin, Landau, Verwey and Overbeek) theory. Furthermore, the potential at which the strongest hydrophobic force was measured corresponds to the potential where the flotation recovery of covellite reaches a maximum, indicating a close relationship between the two. Direct force measurements were also conducted to study the mechanism of copper-activation of sphalerite. The force measurements conducted with unactivated sphalerite in 10⁻³ M KEX solutions did not show the presence of hydrophobic force while the results obtained with copper-activated sphalerite at pH 9.2 and 4.6 showed strong hydrophobic forces. However, at pH 6.8, no hydrophobic forces were observed, which explains why the flotation of sphalerite is depressed in the neutral pH regime. Direct force measurements were also conducted using hornblende in xanthate solutions to study the mechanism of inadvertent activation and flotation of rock minerals. The results show the presence of long-range hydrophobic forces when hornblende was activated by heavy metal cations such as Cu²⁺ and Ni²⁺ ions. The strong hydrophobic forces were observed at pHs above the precipitation pH of the activating cation. These results were confirmed by the XPS analysis of the activated hornblende samples. Force measurements were conducted between silanated silica surfaces to explore the relationship between hydrophobicity, advancing contact angle (CA), and the magnitude (K) of hydrophobic force. In general, K increases as Contact Angle increases and does so abruptly at Contact Angle=90°. At the same time, the acid-base component of the surface free energy decreases with increasing CA and K. At CA>90°, GammaS^AB approaches zero. Based on the results obtained in the present work a mathematical model for the origin of the hydrophobic force has been developed. It is based on the premise that hydrophobic force originates from the attraction between large dipoles on two opposing surfaces. The model has been used successfully to fit the measured hydrophobic forces using dipole moment as the only adjustable parameter. However, the hydrophobic forces measured at CA>90° cannot be fitted to the model, indicating that there may be an additional mechanism, possibly cavitation, contributing to the appearance of the long-range hydrophobic force. / Ph. D.

This thesis presents work done investigating methods for constructing patterns on the nanometer scale. Various methods of nanolithography using atomic force microscopes (AFMs) are investigated. The use of AFMs beyond their imaging capabilities is demonstrated in various experiments involving nanografting and surface electrochemical modification. The use of an AFM to manipulate a monolayer of thiols deposited on a gold substrate via nanografting is shown in our work to enable chemical modification of the surface of the substrate by varying the composition of the monolayer deposited on it. This leads to the selective deposition of various polymers on the patterned areas. Conditions for enhancing the selective deposition of the self-assembled polymers are studied. Such conditions include the types of polymers used and the pH of the polyelectrolyte solutions used for polymer deposition. Another method of nanolithography is investigated which involves the electrochemical modification of a monolayer of silanes deposited on a silicon substrate. By applying a potential difference and maintaining the humidity of the ambient environment at a certain level we manage to change the chemical properties of select areas of the silane monolayer and thus manage to establish selective deposition of polymers and gold nanoparticles on the patterned areas. Parameters involved in the patterning process using surface electrochemical modification, such as humidity levels, are investigated. The techniques established are then used to construct circuit elements such as wires. / Ph. D.

A compact model representing the dynamics between piezoelectric voltage inputs and cantilever probe positioning, including nonlinear surface interaction forces, for atomic force microscopes (AFM) is considered. By considering a relatively large cantilever stiffness, singular perturbation methods reduce complexity in the model and allows for faster responses to Van der Waals interaction forces experienced by the cantilever's tip and measurement sample. In this study, we outline a nonlinear near-optimal feedback control approach for non-contact mode imaging designed to move the cantilever tip laterally about a desired trajectory and maintain the tip vertically about the equilibrium point of the attraction and repulsion forces. We also consider the universal instance when the tip-sample interaction force is unknown, and we construct cascaded high-gain observers to estimate these forces and multiple AFM dynamics for the purpose of output feedback control. Our proposed output feedback controller is used to accomplish the outlined control objective with only the piezotube position available for state feedback. / Master of Science / In this thesis, the idea of an atomic force microscope (AFM), specifically the applications of the non-contact mode, will be discussed. An atomic force microscope (AFM) is a tool that measures the surface height of nanometer sized samples. To improve the speed and precision of the machine under a non-contact mode objective, a controller is designed based on optimality and is applied to the system. The system contains a series of equations designed to steer the system towards a desired trajectory and minimal vibrations. Given the complexity of the system, resulting from nonlinearities, we will apply singular perturbation principles on the system's stiffness property to separate the larger problem into two smaller ones. These two problems are inserted into a near-optimal controller and a series of simulations are conducted to demonstrate performance. Alongside this, we will outline an observer to estimate the unknown dynamics of the system. These estimates are then applied to our controller to demonstrate that only the AFM's piezotube position is to be known in order to estimate and control the remaining dynamics of the system.

Diesel particulate matter (DPM) is the solid portion of diesel exhaust, which occurs primarily in the submicron range. It is complex in nature, occuring in clusters and agglomerated chains, and with variable composition depending on engine operating conditions, fuel type, equipment maintenance, etc. DPM is an occupational health hazard that has been associated with lung cancer risks and other respiratory issues. Underground miners have some of the highest exposures to DPM, due to work in confined spaces with diesel powered equipment. Large-opening mines present particular concerns because sufficient ventilation is very challenging. In such environments, reliable DPM sampling and monitoring is critical to protecting miner health. Though complex, DPM is made up primarily of elemental (EC) and organic carbon (OC), which can be summed to obtain total carbon (TC). The Mine Safety and Health Administration (MSHA) currently limits personal DPM exposures in metal/non-metal mines to 160 µg/m3 TC on an 8-hour time weighted average. To demonstrate compliance, exposures are monitored by collecting filter samples, which are sent to an outside lab and analyzed using the NIOSH 5040 Standard Method. To support real-time results, and thus more timely decision making, the Airtec handheld DPM monitor was developed. It measures EC, which is generally well correlated with TC, using a laser absorption technique as DPM accumulates on a filter sample. Though intended as a personal monitor, the Airtec has application as an engineering tool. A field study is reported here which demonstrated the usefulness of the Airtec in tracking temporal and spatial trends in DPM. An approach to sensitizing the monitor to allow "spot checking" was also demonstrated. Since DPM in mine environments generally occurs with other airborne particulates, namely dust generated during the mining process, DPM sampling must be done with consideration for analytical interferences. A common approach to dealing with mineral dust interferences is to use size selectors in the sampling train to separate DPM from dust; these devices are generally effective because DPM and dust largely occur in different size ranges. An impactor-type device (DPMI) is currently the industry standard for DPM sampling, but it is designed as a consumable device. Particularly for continuous monitoring applications, the sharp cut cyclone (SCC) has been suggested as a favorable alternative. In another field study reported here, the effect of aging (i.e., loading as an artifact of sampling) on the DPMI and SCC was investigated. Results suggest the effective cut size of the DPMI will be reduced much more rapidly than that of the SCC with aging — though even in a relatively high dust, high DPM environment, the DPMI performs adequately. In a third field study, the possibility of attachment between DPM and respirable dust particles was investigated. Such a phenomenon may have implications for both reliable sampling and health outcomes. Data collected by transmission electron microscope (TEM) on samples collected in the study mine showed that DPM-dust attachment does indeed occur. Moreover, the study results suggest that respirable particulate sampling — as opposed to submicron sampling, which is currently used — may be favorable for ensuring that oversized DPM is not excluded from samples. This strategy may require additional sample preparation to minimize dust interferences, but methods have been previously developed and were demonstrated here. / Master of Science / Diesel particulate matter (DPM) is the solid portion of diesel exhaust, which occurs primarily in the submicron range (i.e., less than one micron). It generally forms as agglomerated chains or clusters. The size and shape is dependent on the engine operating conditions, fuel type, equipment maintenance, etc. DPM is an occupational health hazard that has been associated with lung cancer risks and other respiratory issues. Underground miners have some of the highest exposures to DPM, due to work in confined spaces with diesel powered equipment. In such environments, reliable DPM sampling and monitoring is critical to protecting miner health. Though complex, DPM is made up primarily of elemental (EC) and organic carbon (OC), which can be summed to obtain total carbon (TC). Exposure to DPM, as regulated by the Mine Safety and Health Administration (MSHA) is monitored by collecting filter samples, which are analyzed using the NIOSH 5040 Standard Method. To support real-time results, and thus more timely decision making, the Airtec handheld DPM monitor was developed. Though intended as a personal monitor, the Airtec has application as an engineering tool. A field study is reported here which demonstrated the usefulness of the Airtec in tracking changes of DPM in specific locations as well as over time. An approach to sensitizing the monitor to allow “spot checking” or making very quick assesments in a location was also demonstrated. DPM in mine environments generally occurs with other airborne particulates, namely dust generated during the mining process. Sampling must be completed to avoid these interferences by sampling DPM only. Since DPM and dust typically occur in different size ranges, size selectors in the sampling train are used to separate DPM from dust. An impactor-type device (DPMI) is currently the industry standard for DPM sampling, but it is designed as a one time use item. Particularly for continuous monitoring applications, the sharp cut cyclone (SCC) has been suggested as a favorable alternative. In another field study reported here, the effect of aging (i.e., multiple monitorings using the same size selector) on the DPMI and SCC was investigated. Results suggest the effective cut size of the DPMI will be reduced much more rapidly than that of the SCC with aging – though even in a relatively high dust, high DPM environment, the DPMI performs adequately. In a third field study, the possibility of attachment between DPM and respirable dust particles was investigated. Such a phenomenon may have implications for both reliable sampling and health outcomes. Using microscopy, samples collected in the study mine showed that DPM-dust attachment does indeed occur. Moreover, the study results suggest that respirable particulate sampling – as opposed to submicron sampling, which is currently used – may be favorable for ensuring that oversized DPM is not excluded from samples. This strategy may require additional sample preparation to minmize dust interferences, but methods have been previously developed and were demonstrated here.

In this study, we have developed a high performance multi-photon microscopic system to perform second- harmonic (SH) imaging on a tooth and a KTP crystal . The high sensitivity of the system allows acquisition rate of 300 seconds/frame with resolution at 512¡Ñ512 pixels. The surface SH signal generated from the tooth and the KTP crystal is also carefully verified through micro-spectroscopy, polarization rotation and wavelength tuning. In this way, we can ensure the authenticity of the signal. KTP crystal and the enamel that encapsulates the dentine is known to possess highly ordered structures. The anisotropy of the structure is revealed in the microscopic SH images of the tooth and the KTP crystal samples.