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Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains ix, 99 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 144 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xvi, 162 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Bibliography : leaves 211-216 / 216 leaves : ill ; 20 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1994?

The work in this thesis was aimed at the preparation of low energy surfaces via the surface attachment of fluorinated surfactant molecules. Such surface functionalisation routes are highly dependent on the chemical nature of the substrate surface. For this reason the choice of substrate materials is both all important and extremely limited. To make the process of more general appeal a method for pre-treating the substrate, using cold plasma polymerisation reactions, followed by surfactant coupling to the plasma polymer has been devised. Using this approach, the surfactant coupling process is now dependent on the surface chemistry of deposited plasma polymers and independent of substrate characteristics. In order to form highly functionalised surfaces, likely to undergo further reactions, the plasma polymerisation of acrylic acid, ally! amine and allyl alcohol was investigated. Highly functionalised acid, amine and alcohol surfaces, as shown by X-ray Photoelectron Spectroscopy (XPS) and Infrared Spectroscopy (IR), were produced by optimisation of pulsed plasma conditions. Measurement of deposition rates during plasma polymerisation reactions indicated that polymerisation can occur during the off-time of the pulsed plasma period, most likely via free radical polymerisation pathways. Highly functionalised plasma polymer surfaces thus formed were shown to couple to fluorinated surfactant molecules. The mechanism of surfactant attachment has been suggested to be ionic attraction between opposite charges on the surfactant molecule and the plasma polymer in aqueous solution. The surfaces formed give rise to oleophobic/hydrophilic behaviour. This is in marked contrast to the usual liquid repellent attributes of conventional polyelectrolyte- fluorosurfactant complexes formed by solution phase synthesis.

Radio frequency (rf) atmospheric pressure glow discharges (APGDs) have received growing attention for their exciting scope of new science and their immense potential for widespread applications. While geometrically similar to conventional low-pressure discharges used in the semiconductor industry for decades, rf APGDs present new physics that require investigation. This thesis presents an experimental and computational study of helium rfAPGDs aimed at making a contribution to the current understanding of these discharges and enabling their optimization for different applications. The timely interest and significance of this work is highlighted by the publication of different parts of this thesis in 10 peer-reviewed international journals. Starting with the electron trapping in rf APGDs, the thesis looks into the electron heating mechanism responsible for sustaining the discharges, the influence of the rf excitation frequency on the discharge characteristics, the role of impurities in the discharge chemistry as well as the evolution of the discharge as the size is reduced down to microplasma dimensions. The findings of this research are based on the synergistic use of electrical measurements, optical diagnostics and self-developed computational models. With the knowledge gained from this thesis, rf-APGDs can be readily used for a wide-range of applications including biological decontaminations, nanostructure fabrication and portable gas analyzers.

In the aerospace industry, gas discharges have gained importance with the exploration of their performance and capabilities for flow control and combustion. Tunable properties of plasma make gas discharges efficient tools for various purposes. Since the scales of plasma and the available technology limit the knowledge gained from experimental studies, computational studies are essential to understand the results of experimental studies. The temporal and spatial scales of plasma also restrict the numerical studies. It is a necessity to use an idealized model, in which enough physics is captured, while the computational costs are acceptable.<br><br>In this work, numerical simulations of different low-pressure gas discharges are presented with a detailed analysis of the numerical approach. A one moment model is employed for DC glow discharges and nanosecond-pulse discharges. The cheap-est method regarding the modeling and simulation costs is chosen by checking the requirements of the fundamental processes of gas discharges. The verification of one-moment 1-D glow discharges with constant electron temperature variation is achieved by comparing other computational results.<br><br>The one moment model for pulse discharge simulation aims to capture the information from the experimental data for low-pressure argon discharges. Since the constant temperature assumption is crude, the local field approximation is investigated to obtain the data for electron temperature. It was observed that experimental data and computational data do not match because of the stagnant decay of electron number densities and temperatures. At the suggestion of the experimental group, water vapor was added as an impurity to the plasma chemistry. Although there was an improvement with the addition of water vapor, the results were still not in good agreement with experiment.<br><br>The applicability of the local field approximation was investigated, and non-local effects were included in the context of an averaged energy equation. A 0-D electron temperature equation was employed with the collision frequencies obtained from the local field approximation. It was observed that the shape of the decay profiles matched with the experimental data. The number densities; however, are less almost an order of magnitude.<br><br>As a final step, the two-moment model, one-moment model plus thermal electron energy equation, was solved to involve non-local effects. The two-moment model allows capturing of non-local effects and improves agreement with the experimental data. Overall, it was observed that non-local regions dominate low-pressure pulsed discharges. The local field approximation is not adequate to solve these types of discharges.

Τις τελευταίες δεκαετίες, οι διεργασίες πλάσματος με τάση διέγερσης ραδιοσυχνότητας χρησιμοποιούνται ολοένα και περισσότερο και απαντώνται σε διάφορες εφαρμογές όπως στην εναπόθεση υλικών, στην επεξεργασία επιφανειών κα. Αυτό έχει ως αποτέλεσμα οι εκκενώσεις αίγλης ραδιοσυχνότητας να προσελκύσουν έντονο επιστημονικό ενδιαφέρον. Μπορεί τα τελευταία χρόνια να έχει σημειωθεί σημαντική πρόοδος στον τομέα αυτό ωστόσο υπάρχει ακόμα και σήμερα ενδιαφέρον που αφορά το σχεδιασμό των συστημάτων αυτών καθώς και την ανάπτυξη μεθόδων που αφορούν την επαναληψιμότητα των διεργασιών καθώς και τον έλεγχο των ιδιοτήτων του πλάσματος. Ένας από αυτούς τους τομείς είναι ο ηλεκτρικός χαρακτηρισμός ηλεκτροδίων ραδιοσυχνότητας πηγών πλάσματος και η εύρεση της κατανεμημένης εμπέδησής τους και ακολούθως ο υπολογισμός της καταναλισκόμενης ισχύος σε εκκενώσεις αίγλης. Αυτές οι τεχνικές μπορούν να μας προσφέρουν σημαντικές πληροφορίες για τους μηχανισμούς και τα φαινόμενα που λαμβάνουν χώρα σε εκκενώσεις ραδιοσυχνότητας, οι οποίες αν στη συνεχεία αξιοποιηθούν να μας οδηγήσουν στον ακριβή προσδιορισμό και έλεγχο των συνθηκών. Στην εργασία αυτή αναλύονται μέθοδοι από τις οποίες προκύπτουν αποτελέσματα που αφορούν παραμέτρους του πλάσματος μέσω μετρήσεων τάσης, ρεύματος και διαφοράς φάσης σε κάποιο σημείο εξωτερικά του αντιδραστήρα. Παρουσιάζονται τα αποτελέσματα ηλεκτρικών μετρήσεων σε εκκενώσεις αργού που πραγματοποιήθηκαν σε μια χωρητικά συζευγμένη πηγή πλάσματος. Αρχικά παρουσιάζεται ο ηλεκτρικός χαρακτηρισμός της πηγής και αναλύονται τρεις μέθοδοι για τη μέτρηση και τον υπολογισμό της καταναλισκόμενης ισχύος της εκκένωσης. Στην πρώτη μέθοδο οι ηλεκτρικές μετρήσεις χρησιμοποιούνται για το προσδιορισμό ενός ισοδύναμου ηλεκτρικού κυκλώματος με κατανεμημένα στοιχεία (πυκνωτές, πηνία αντιστάσεις) το οποίο μπορεί να περιγράψει την εμπέδηση ανάμεσα στο σημείο μέτρησης εξωτερικά του αντιδραστήρα και την επιφάνεια του ηλεκτροδίου ραδιοσυχνότητας. Το ισοδύναμο αυτό κύκλωμα επιλύεται με βάση τους κανόνες του Kirchhoff και προκύπτουν οι τιμές της μιγαδικής τάσης και ρεύματος της εκκένωσης. Στη δεύτερη μέθοδο, η τάση καθώς και το ρεύμα της εκκένωσης υπολογίζονται μέσω ενός πίνακα ABCD, τα στοιχεία του οποίου έχουν υπολογιστεί από μετρήσεις σε ανοικτό και βραχυκυκλωμένο κύκλωμα. Η τρίτη μέθοδος, μοιάζει αρκετά με τη δεύτερη μόνο που έχει το πλεονέκτημα να είναι πιο απλή λόγω του ότι δεν απαιτεί τη μέτρηση της φάσης της εμπέδησης (της φάσης της τάσης σε σχέση με την τάση του ρεύματος). / Over the last decades, plasma processing has been widely used in various applications such as the deposition of thin films, surface modification, dry etching etc. As a result, radio-frequency discharges have attracted particular scientific interest. Despite the steps forward, there are still open issues especially concerning the design of plasma systems and the effective control of plasma parameters. A part of these issues is related to the electrical characterization of the stray impedance of the plasma electrode and the subsequent measurement and calculation of the real power consumption during the process. These techniques can lead to better understanding of the plasma processes and can also lead to more stable, reliable and almost ideal performing plasma systems. The aim of this study is to point out externally measured non-intrusive plasma parameters that could ease design, control and transferability of plasma conditions. In this work we demonstrate results of electrical characteristics of argon discharges carried out in a high vacuum capacitively coupled parallel plate reactor. Initially, the electrical characterization of the plasma reactor is presented and three methods for measuring and calculating the real power consumed in the discharge are analyzed.. At the first method, the electrical measurements are used to determine a simple equivalent circuit that can describe the parasitic impedances that interfere between the point of measurement and the RF electrode’s surface. The equivalent circuit model is then solved through Kirchhoff’s laws and values of the complex electrode’s voltage and current are obtained from the measured voltage and current at some point located outside the reactor. At the second method, the reactor is treated as a two-port network. The electrode’s voltage and current are calculated through the ABCD matrix of the reactor whose values a, b, c, d are extracted from open and short circuit measurements. The third method is a simplification of the second method as it does not require the phase of the impedance (the phase of the voltage relative to the current) for the calculations.