Dissertations / Theses on the topic 'Inductively coupled radio frequency plasma'

The electrodeless plasma discharge is typically driven by radio frequency (RF) power supply within the range (0.2 ¡
40 MHz). The applied power is coupled into the plasma inductively called inductively coupled plasma (ICP). RF ICP technique has achieved significance importance in a diversity of research and industrial applications for over the last threes decades. It is still required to undertake both theoretical and experimental research. In this work, RF ICP technique is applied on the torch modeling in 2D. Based on extended electromagnetic vector potential representation, an axisymmetric model in 2D is proposed for the calculations of the electromagnetic fields in an RF ICP torch. The influence of axial vector potential is included to the vector potential formulations. This is achieved by imposing a helical current carrying wire configuration. The corresponding governing equations are solved numerically by applying finite element method (FEM) using commercial partial differential equation solver (Flex PDE3). Based on this model, the plasma behavior and properties are examined in terms of plasma parameters. Besides, a comparative iii analysis is made between proposed model called helical configuration and the one currently available in the literature called circular configuration. This study shows relatively little difference between temperature fields predicted by two models. However, significant difference is observed between corresponding flows and electromagnetic fields. Especially, tangential flow which is observed in helical configuration vanishes in circular configuration. The proposed model offers an effective means of accounting for the variations of the helical coil geometry on the flow and temperature fields and achieving a better representation of the electromagnetic fields in the discharge. Finally, it is concluded that minimum number of turns (n = 2) yields significant difference between two models whereas, maximum allowable number of turns yield no distinctions on the results of two models in terms of azimuthally applied current. However, axial effect of current still exists but very small with respect to the result obtained with minimum number of turns.

Direct solid sampling is an area of analytical research that has generated a large amount of interest in recent years. Two analysis systems offering fast and nondestructive methods of determining the elemental composition of substances, without requiring complicated sample preparation procedures, are laser ablation inductively coupled plasma mass spectroscopy (LA-ICPMS) and radio frequency glow discharge mass spectroscopy (rf-GDMS). A Cetac LSX-200 laser system coupled to a LECO Renaissance ICPMS was utilized to analyze coal and ash samples prepared by incorporation into a lithium borate matrix to form a disk. In addition, a VG 9000 Glow Discharge Mass Spectrometer (GDMS) with Nier-Johnson reverse ion optic geometry, equipped with a radio frequency source (rf-source), was used for the determination of nonconductors or insulators in addition to the normal metals and semiconductors previously determined by dc-source analysis. Further addition of a pulse generator to the rf-source resulted in a variable duty cycle, allowing greater ionization efficiency without the risk of catastrophic damage to the sample. The results of this research indicate that the LA-ICPMS system can be used to directly determine the composition of ash samples, with further method development, and that the Prf-GDMS system can be used successfully to analyze nonconductive solid samples including bone tissue.

Tato diplomová práce se zabývá problematikou plazmového nanášení bioaktivních keramických povlaků hydroxylapatitu s využitím technologie radio-frekvenčně buzeného indukčně vázaného plazmatu. Cílem bylo optimalizovat proces a nanést kompaktní hydroxylapatitové povlaky na substráty z titanové slitiny Ti6Al4V. Nanesené vzorky byly následně podrobeny analýzám povrchové drsnosti, mikrostruktury a fázového složení. Ze získaných výsledků byly vyvozeny závěry, které byly srovnány s dalšími odbornými pracemi zabývajícími se příbuznou problematikou.

Thesis (M.S.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains v, 36 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 21).

The International Thermonuclear Experimental reactor (ITER), the world’s largest experimental facility in the realm of nuclear fusion for energy production, requires two Neutral Beam Injectors (NBI) rated for the total power of 33 MW for plasma heating and current drive. The ITER NBI includes an ion source which can produce 40 A of D¯ ions beams for 3600 s, accelerated at the energy of 1 MeV. The requirements for the ITER NBI are quite demanding and have never been achieved before all together in a single device. This specifically called for a development of the ITER Neutral Beam Test Facility (NBTF) called PRIMA (Padova Research on ITER Megavolt Accelerator) to carry out an international R&D program for the achievement of the ITER NBI requirements and the optimization of the operation in advance of the future use in ITER. The facility will host two experiments, SPIDER (Source for the Production of Ions of Deuterium Extracted from RF plasma), the full-size prototype of ITER RF ion source, and MITICA (Megavolt ITER Injector and Concept Advancement), the full-scale prototype of the ITER heating NBI. The NBTF in Padova, Italy, is ready, MITICA is currently under construction and SPIDER has been in operation since beginning of June 2018. The NBI ion source was initially based on filament type arc source, while for ITER the inductively coupled (IC) radio frequency (RF) ion source have been finally chosen in 2007. This is because RF sources present several advantages with respect to arc solutions; they have fewer parts and require less maintenance. In these ion sources, radio frequency plasma is generated at the frequency of 1 MHz and is characterized by high RF power density and low operational pressure (around 0.3 Pa). In the last decades, IC ion sources have been developed, studied and experimented at the Max-Planck-Institut für Plasmaphysik (IPP) in Garching, Germany. The most recent one is ELISE (Extraction from a Large Ion Source Experiment), which is able to operate with both Hydrogen and Deuterium gas species and has half the size of ITER NBI source. Other accompanying activities have been recently launched at Consorzio RFX, Padova, Italy within the ITER NBI work program; one of them is a relatively small ion source called NIO1 (Negative Ion Optimization 1) working at 2 MHz, developed in order to gain experience on ion source operation and to study specific physics and engineering topics on a more flexible and accessible device than the SPIDER and MITICA. In addition, a small experimental test facility called HVRFTF (High Voltage Radio Frequency Test Facility) based on a high voltage resonance circuit that feeds a couple of electrodes in vacuum has been started at Consorzio RFX in 2014 to address and study the voltage holding capability of the RF components in the ion source at 1 MHz. The research endeavor during the three years of my PhD was carried out in the frame of the RF R&D task of the NBTF work-program at Consorzio RFX and during the mobility periods at the IPP. I have had the opportunity to work on two main lines: the first was dedicated towards the study of the RF power transfer efficiency of IC RF ion sources and the development of suitable models that will permit to explore possible improvements (in the future). In fact, the higher the efficiency, the lower can be the feeding power to the ion source and this may lead to a lower requirement both for cooling and for electrical insulation of the RF circuit components installed on the source. I have studied and analyzed several plasma heating mechanisms (like ohmic and stochastic heating in particular) and I have developed an electrical model which is responsible for describing the power transfer to the plasma. The first approach was based on a transformer model, and then a multi current filament model has been developed. This model is capable to account for the currents in the passive metallic structure within the driver region of the ion source and with this; it is able to overcome the main limitation of the transformer model. Furthermore, I have integrated all the models to develop a novel methodology to evaluate the efficiency of the RF power transfer to the hydrogen plasma in a cylindrical source. Then, I have implemented the methodology in a MATLAB® code and applied it to the driver of ELISE and NIO1 ion sources showing the results in terms of plasma equivalent resistance and power transfer efficiency obtained as a function of applied frequency and plasma parameters (electron density and gas pressure). The second part of my work was directed towards the design, construction and set-up of the HVRFTF. I gave an important contribution in terms of the electrical characterization of the RF resonance circuit components (mainly the two solenoid coupled inductor), thermal analysis of the electrodes placed inside the vacuum vessel, analyses and design of an efficient shielding from the electro-magnetic radiations foreseen during the operation of the test facility. All this contributed towards the success in the set-up of the test facility which is now in operation. The thesis is structured as follows: Chapter 1 and 2 are introductory chapters on the present energy scenario in the world, the role of the thermo-nuclear fusion and the main fusion experimental device called ITER. The requirement of additional heating systems in ITER along with the description of Neutral beam injection (NBI) system and relevant ion sources (SPIDER, ELISE and NIO1) are presented in these chapters. Then, the thesis is divided into two main parts: Part 1 – From Chapter 3 to Chapter 6 - describes my work on the power transfer efficiency to the plasma of the inductively coupled radio frequency ion sources. Part 2 – From Chapter 7 to chapter 10 - summarizes first the aim of the HVRFTF then reports my contribution to its design and set-up. Lastly, the overall conclusion highlighting the most significant results obtained from the research described in both the parts of the thesis is discussed and a further possible research activity is highlighted for the future work. Throughout the journey of the PhD, I have had the opportunity to grow and acquire different research competences ranging from conceptual studies, modeling activities, practice on several numerical codes and also experimental work, in an international context.
Il reattore sperimentale ITER, il più grande esperimento nel settore della produzione di energia da fusione nucleare, richiede di essere equipaggiato con due sistemi d’iniezione di fasci di particelle neutre (chiamato ITER NBI nel seguito), caratterizzati da una potenza complessiva di 33 MW, per contribuire al riscaldamento del plasma e controllo della relativa corrente. ITER NBI comprende una sorgente di ioni negativi che può produrre un fascio di ioni di deuterio accelerati all’energia di 1 MeV, per una durata di 3600 s. L’insieme dei requisiti richiesti ad ITER NBI non sono mai stati raggiunti contemporaneamente nello stesso esperimento. Ciò ha motivato lo sviluppo di un’infrastruttura sperimentale: “the ITER Neutral Beam Test Facility (NBTF)”, chiamata anche PRIMA (Padova Research on ITER Megavolt Accelerator), che ha lo scopo di portare avanti un progetto di ricerca internazionale finalizzato alla dimostrazione della possibilità di raggiungere i requisiti specificati per ITER NBI e alla crescita di conoscenza e competenza nella sperimentazione, prima dell’uso futuro in ITER NBTF ospiterà due esperimenti: SPIDER (Source for the Production of Ions of Deuterium Extracted from an RF plasma), il prototipo a piena scala della sorgente a ioni negativi di ITER NBI, e MITICA (Megavolt ITER Injector and Concept Advancement), il prototipo a piena scala dell’intero ITER NBI. NBTF è stata completata ed ha sede a Padova, in Italia; MITICA è attualmente in costruzione e SPIDER è in operazione dall’inizio di giugno 2018. La sorgente di ioni scelta inizialmente per ITER NBI era del tipo ad arco, ma dal 2007 il progetto dell’NBI è stato sviluppato considerando sorgenti di ioni prodotti in un plasma generato secondo il principio dell’accoppiamento induttivo a radiofrequenza (RF). Queste sorgenti presentano diversi vantaggi rispetto alle sorgenti ad arco: hanno un numero minore di componenti e richiedono minor manutenzione. Le sorgenti RF di ITER NBI operano alla frequenza di 1 MHz, sono caratterizzate da una densità di potenza piuttosto elevata e basso valore di pressione del gas all’interno della camera (0,3 Pa circa). Queste tipologie di sorgenti ioniche sono state studiate e sviluppate negli ultimi decenni presso il Max-Planck-Institut für Plasmaphysik (IPP), dove sono stati realizzati e testati diversi dispositivi sperimentali. Il più recente di essi, chiamato ELISE (Extraction from a Large Ion Source Experiment), è caratterizzato da dimensioni pari a metà di quelle previste per la sorgente ionica di ITER NBI. Altre attività sperimentali di supporto alla ricerca e sviluppo in questo settore sono state avviate presso il Consorzio RFX; una di queste consiste nella realizzazione di una sorgente a ioni negativi relativamente piccola, chiamata NIO1 (Negative Ion Optimization 1), che lavora alla frequenza di 2 MHz, sviluppata per fare esperienza sul funzionamento di sorgenti di ioni negativi e studiare problematiche specifiche di interesse per ITER NBI in un apparato sperimentale molto più flessibile ed accessibile rispetto a SPIDER e MITICA. Inoltre, la realizzazione di un ulteriore dispositivo sperimentale, chiamato HVRFTF (High Voltage Radio Frequency Test Facility), basato su un circuito risonante in alta tensione che polarizza una coppia di elettrodi in vuoto, è stata avviata presso il Consorzio RFX nel 2014 per studiare specifiche problematiche relative alla tenuta della tensione in vuoto di componenti del circuito a radiofrequenza della sorgente di ioni a 1MHz. Il lavoro di ricerca durante i tre anni del mio PhD è stato portato avanti nell’ambito del programma di ricerca e sviluppo sulle sorgenti ioniche a radiofrequenza presso il Consorzio RFX, e durante i periodi di “mobility” presso il laboratorio IPP. Ho avuto l’opportunità di approfondire due tematiche principali: la prima era indirizzata allo studio dell’efficienza del trasferimento di potenza al plasma delle sorgenti di ioni tipo IC RF e allo sviluppo di modelli allo scopo di esplorare in futuro possibili miglioramenti. Infatti, maggiore è l’efficienza, minore è la potenza richiesta al generatore e ciò comporta requisiti meno severi per il sistema di raffreddamento e sollecitazioni inferiori in termini di tensione elettrica applicata. Ho studiato i diversi meccanismi di riscaldamento del plasma (come il riscaldamento ohmico ed in particolare il riscaldamento stocastico) ed ho studiato come descrivere il trasferimento di potenza ad un plasma di idrogeno. Il primo modello sviluppato si basa sullo schema del trasformatore; successivamente ho contribuito significativamente a sviluppare un modello “a multi filamenti” di corrente. Questo modello riproduce le correnti indotte nelle strutture passive presenti nella regione del driver della sorgente di ioni ed è in grado di superare le limitazioni del modello del trasformatore. Ho integrato tutti i modelli per sviluppare una nuova metodologia per la stima dell’efficienza del trasferimento di potenza nei plasmi di idrogeno generati in sorgenti cilindriche. Ho poi implementato la metodologia in MATLAB®, applicandola ai casi delle sorgenti ioniche di ELISE e NIO1, presentando i risultati ottenuti in termini di stima della resistenza equivalente di plasma e di efficienza del trasferimento di potenza come funzione della frequenza applicata e dei parametri di plasma (densità elettronica e pressione del gas). La seconda parte del mio lavoro si è svolta nell’ambito dello sviluppo della HVRFTF. Ho dato importanti contributi che sono consistiti nella caratterizzazione dei componenti del circuito risonante a radiofrequenza (in particolare dell’induttore composto da due solenoidi accoppiati magneticamente), nelle analisi termiche degli elettrodi posti nella camera da vuoto, nelle analisi e progetto di un sistema di schermatura efficace delle radiazioni elettromagnetiche generate dall’operazione dell’esperimento. Tutto ciò ha contribuito al positivo completamento dell’apparato sperimentale, attualmente in funzione. La tesi è strutturata come segue: I capitoli 1 e 2 sono di tipo introduttivo sull’attuale scenario energetico, sul ruolo della fusione termonucleare controllata e del principale esperimento internazionale ITER. In questi capitoli inoltre sono presentati i requisiti del sistema di riscaldamento del plasma di ITER, la descrizione del sistema di iniezione di neutri (NBI) e delle sorgenti ioniche di interesse (SPIDER, ELISE e NIO1). Poi, la tesi è suddivisa in due parti: Parte 1- dal capitolo 3 al capitolo 6- che tratta del lavoro che ho svolto sul problema dell’efficienza del trasferimento induttivo di potenza al plasma nelle sorgenti ioniche. Parte 2 - dal capitolo 7 al capitolo 10- che riassume lo scopo della “HVRFTF” e descrive il mio contributo al suo progetto e realizzazione. Infine, nelle conclusioni ho discusso i più significativi risultati ottenuti dal lavoro di ricerca presentato nelle Parti 1 e 2 di questa tesi evidenziando i possibili sviluppi futuri. Durante il percorso del dottorato di ricerca, ho avuto l'opportunità di crescere e acquisire diverse competenze di ricerca che vanno dagli studi concettuali, alle attività di modellizzazione, alla pratica su diversi codici numerici e anche al lavoro sperimentale, in un contesto internazionale.

The single and dual frequency ICPs are studied in this thesis, mostly in oxygen; a simple electronegative gas. The diagnostics used here include; PROES, laser photodetachment and, Hairpin and Langmuir probes. Many issues of the fundamental understanding were investigated which include; the influence of the electronegativity on the electron density, E-H mode transition, collisionless heating, RF biased ICPs and the pulsed ICPs. The changes in the electronegativity are found here to be related to the heating mechanisms in the plasma. ICPs are well known to operate in E or H mode, depending on the applied power. The PROES measurements showed that both capacitive and inductive power couplings are simultaneously present in stable E and H modes, close to the transition. The individual contribution of capacitive and inductive power is also estimated here, using some new techniques. In pulsed ICPs, E and H like modes with simultaneous contribution of the capacitive and inductive couplings are also observed. The PROES measurements in the H-mode of ICPs, operated in the collisionless pressure regime, shows axially two maxima structure in the discharge, possibly because of the negative power absorption in the middle of the ICPs. The spatio-temporal excitation measurements in a RF biased ICPs (or dual frequency ICPs) showed that the coupling of the bias with tile capacitive coupling of the coil play a . significant role in the electron heating. The power and pressure regime where RF bias significantly influences the electron density and heating, is identified. The measurements also indicate the limitations of the independent control of the ion flux and energy. The phase between the ICP and bias could be used to decrease or enhance the influence of bias on electron heating. The electron density measurements showed that the RF bias can improve the radial uniformity and edge to centre electron density ratio.

An atmospheric pressure radio frequency capacitively coupled plasma (CCP) has been developed and characterized for applications in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and gas chromatography (GC). The CCP torch was initially designed as an atom reservoir for carrying out elemental analysis using atomic absorption. Functionally, the device consists of two parts, the CCP discharge tube and the tantalum strip electrothermal vaporization sample introduction system. The torch design provides for very effective energy transfer from the power supply to the plasma by capacitive coupling. Therefore, the plasma can be generated at atmospheric pressure with a flexible geometry. The plasma can be operated at very low rf input powers (30-600 W) enabling optimal conditions for atom resonance line absorption measurements. Absorption by the analyte takes place within the plasma discharge which is characterized by a long path length (20 cm) and low support gas flow rate (0.2 L/Min). Both of these characteristics ensure a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of 3.5-40 pg. A preliminary measurement gave a Fe I excitation temperature of approximately 4000 K for the discharge. At this temperature, potential chemical interferences are likely to be minimal. Chemical interferences for Fe, Al, As, Ca, Co, Cd, Li, Mo and Sr were negligible in the determination of silver. Chloride interference, which is prevalent in GF-AAS, was not found. The amount of Ag found in a SMR#1643b (NIST) water sample was 9.5 ± 0.5 ng/g which fell in the certified range of 9.8 ± 0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added to the SRM and recoveries were found to be in a range from 105 % to 96.2 %. The RSD obtained for 7 replicates of 270 pg silver was 4.6 %. The results for the CCP AES are even more promising. The interferences of thirteen elements are negligible in the determination of silver. The chloride interference was not found. The detection limits for Ag, Cd, Li, Sb and B are 0.7, 0.7, 2, 80 and 400 pg respectively. The amount of silver found in a SRM#1643b (NIST) water sample was 9.3 ± 0.5 ng/g which also fell in the certified range of 9.8 ±0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added into the SRM#1643b (NIST) samples; the recoveries were found to range from 97 % to 104 %. The RSD obtained for 7 analyses of 270 pg silver were 1.5 % for CCP-AES. It was also found that the signal to noise ratios (S/N) are higher in the AES mode than those in the AAS mode in the same CCP atomizer. In order to exploit advantages inherent in both GF-AAS and I CP-AES, an atmospheric pressure capacitively coupled plasma sustained inside a graphite furnace was developed. This source combines the high efficiency of atomization in furnaces and the high efficiency of the excitation in atmospheric pressure plasmas. In general, plasma sources are able to effectively excite high-lying excited states for most metals and non-metals and can also ionize vaporized elements. Therefore the possibility exists of using non-resonance lines to avoid the effects of self-absorption at high analyte concentrations. Ion lines may also be used in cases where they provide better sensitivity or freedom from spectral interferences. This source also offers the ability to independently optimize vaporization and excitation. However, the most important aspect of this new source is that it can be used for simultaneous, multielement determinations of small sized samples in a graphite furnace atomizer, a design which has been proven to be effective over many years of use. Preliminary quantitative characteristics of this new atmospheric pressure plasma emission source have been studied. The detection limit for Ag of 0.3 pg is lower than the value of 0.4 pg reported for GF-AAS. Variants of the CCP, including a gas chromatography (GC) detector, combinations of laser ablation - CCP, rf sputtering - CCP direct solid analysis, and its application as an intense spectral lamp have been developed and are reported in this dissertation.
Science, Faculty of
Chemistry, Department of
Graduate

Recently proposed space missions such as Darwin, LISA and NGGM have encouraged the development of electric propulsion thrusters capable of operating in the micro-Newton (N) thrust range. To meet these requirements, radio frequency (RF) gridded ion thrusters need to be scaled down to a few centimetres in size. Due to the small size of these thrusters, it is important to accurately determine the thermal and performance parameters. To achieve this, an RF ion thruster model has been developed, composed of plasma discharge, 2D axisymmetric ion extraction, 3D electromagnetic, 3D thermal and RF circuit models. The plasma discharge model itself is represented using 0D global, 2D axisymmetric and 3D molecular neutral gas, and Boltzmann electron transport sub-models. This is the rst time such a holistic/comprehensive model has been created. The model was successfully validated against experimental data from the RIT 3.5 thruster, developed for the NGGM mission. Afterwards, the computational model was used to design an RF gridded ion thruster for an Ion Beam Shepherd (IBS) type space debris removal mission. Normally, the IBS method requires two thrusters: one for impulse transfer (IT) and one for impulse compensation (IC). This thesis proposes a novel thruster concept for the IBS type missions where a single Double-Sided Thruster (DST) simultaneously producing ion beams for the IT and IC purposes is used. The advantage of DST design is that it requires approximately half the RF power compared with two single-ended thrusters and it has a much simpler sub-system architecture, lower cost, and lower total mass. Such a DST thruster was designed, built and tested, with the requirements and constraints taken from the LEOSWEEP space debris removal mission. During the experimental campaign, a successful extraction of two ion beams was achieved. The thesis has shown that it is possible to control the thrust magnitudes from the IT and IC sides by varying the number of apertures in each ion optics system, proving that the DST concept is a viable alternative for the LOESWEEP mission.

This thesis presents the results of numerical models used to investigate the influence of the operating conditions of a micro atmospheric pressure plasma jet, on the electron dynamics, ionisation/sustainment mechanisms and resultant plasma chemistry. The aim is to determine the, optimum operating conditions of this discharge for enhancing and controlling the underlying plasma processes and production/composition of useful reactive species. Both nonlinear frequency coupling and pulsed excitation have been shown to influence the underlying processes governing the electron dynamics in radio-frequency driven atmospheric pressure plasmas, here the effects of operating a micro atmospheric pressure 'plasma jet (μ-APPJ) using dual frequency (2F) and pulsed excitation are explored. Several multi-scale numerical models based on hydrodynamic equations with a semi-kinetic treatment of the electrons are used to investigate the influence of the operating mode on the plasma dynamics and chemistry. The models consider a helium background gas with a small molecular admixture of either Nitrogen or Oxygen, and range in complexity, with the most complex model accounting for 184 reactions amongst 20 species. Each model is found to agree well with experimental benchmarks. Using 2F excitation, it is found that variations of power density, voltage ratio and phase relationship provide separate control over the electron density, mean electron energy and electro-negativity. Using Pulsed excitation, variations of the pulse width and repetition rate are also found to directly influence the electron density, mean electron energy and electro-negativity. In both cases this is exploited to directly influence the phase dependent and time averaged effective EEPF, which enables tailoring of the EEPF for enhanced control over the plasma chemical kinetics. This is shown to allow control over the production and composition of useful reactive species, namely reactive oxygen species.

Plasma processing on industrial scale is becoming increasingly complex, demanding new strategies for process control and monitoring. Of particular interest is the energy transport in the interface region between the non-equilibrium low-pressure plasma and the surface. The individual plasma components have varying properties and exhibit different dynamics, which enable numerous chemical and physical modifications of surfaces simultaneously. Measurements of the in-situ surface condition and important chemically active radical species are extremely challenging. The most promising approach to overcome these challenges to achieve advanced process control is the active coupling of numerical simulations and experiments. In this regard, numerical simulations are a well-established technique to study fundamental plasma parameters and plasma dynamics for a variety of discharge sources. The utilised numerical simulation is an experimentally benchmarked 1D fluid model, with semi-kinetic treatment of electrons and an improved energy dependent ion mobility treatment. This model is applied for a geometrically symmetric and asymmetric capacitively coupled oxygen RF discharge. Within the investigated pressure range of 10 Pa - 100 Pa the simulations predict that changing surface conditions have a significant effect on dynamics of the plasma-surface interface. In particular, the surface loss probability and lifetime of metastable singlet delta oxygen as well as the secondary electron emission coefficient are identified to substantially influence the electronegativity and the plasma sheath dynamics on a nanosecond timescale. Phase resolved optical emission spectroscopy measurements, utilising different surface materials, confirm these predictions by comparing measured and simulated excitation features for three different optical emission lines. Through the synergistic coupling of numerical simulations and experiments, the surface work functions as well as other key surface parameters are assessed. Furthermore, the use of an advanced actinometry technique, demonstrated by coupling simple electron kinetic simulations and optical measurements, enables measurements of the spatial distribution of radical atomic oxygen densities and local electron energies over the total discharge volume.

The performance of commercial Radio Frequency Identification (RFID) tags is primarily limited by present techniques used for tag antenna design. Currently, industry techniques rely on identifying the RFID tag application (books, clothing, etc.) and then building antenna prototypes of different configurations in order to satisfy minimum read range requirements. However, these techniques inherently lack an electromagnetic basis and are unable to provide a low cost solution to the tag antenna design process. RFID tag performance characteristics (read-range, chip-antenna impedance matching, surrounding environment) can be very complex, and a thorough understanding of the RFID tag antenna design may be gained through an electromagnetic approach in order to reduce the tag antenna size and the overall cost of the RFID system. The research presented in this thesis addresses RFID tag antenna design process for passive RFID tags. With the growing number of applications (inventory, supply-chain, pharmaceuticals, etc), the proposed RFID antenna design process demonstrates procedures to design tag antennas for such applications. Electrical/geometrical properties of the antennas designed were investigated with the help of computer electromagnetic simulations in order to achieve optimal tag performance criteria such as read range, chip-impedance matching, antenna efficiency, etc. Experimental results were performed on the proposed antenna designs to compliment computer simulations and analytical modelling.

碩士
國立中興大學
材料科學與工程學系所
98
This study investigates the effects of different radio-frequency (rf) powers on the properties of carbon coatings on optical fibers that are prepared by thermal chemical vapor deposition enhanced with inductively coupled plasma. Methane (16 sccm) and nitrogen (4 sccm) were used as the precursor gases, and rf powers were set between 0 and 400 W. The deposition temperature, working pressure, and deposition time were set to 975 ℃, 4 kPa, and 2 hours, respectively. The coating thickness, microstructure, surface roughness, surface property, electrical property, and low-temperature morphology of carbon coatings were investigated by field emission scanning electron microscopy, X-ray diffraction spectrometer, Raman scattering spectrometer, X-ray photoelectron spectrometer, atomic force microscopy, contact angle meter, four-points probe, and optical microscopy. The results indicate that the deposition rate increases as the rf power increases from 0 to 200 W, but the deposition rate decreases as the rf power exceeds 200 W. The mean crystallite size (Lc) increases with increasing the coating thickness, but the degree of ordering and in-plane crystallite size (La) decrease. Moreover, when the rf power increases, the carbon coatings have more sp2 carbon atoms and become graphite-like. The results also show that the surface roughness is inversely related to the water contact angle. As the rf power increases from 0 to 400 W, the electrical resistivity of carbon coatings decreases from 56.96 to 14.01 Ω‧μm. Finally, based on the low-temperature morphologies of carbon coatings, as the coating thickness exceeds 76 nm, the carbon coating has the ability to withstand thermal stress, and is good for use as a hermetical optical fiber coating.

碩士
國立中興大學
材料科學與工程學系所
103
This study investigates the effects of different radio-frequency (rf) powers on the properties of carbon thin films prepared by thermal chemical vapor deposition (thermal CVD) enhanced with inductively coupled plasma. The residual gases in the thermal CVD process, thickness, microstructure, and electrical properties of carbon thin films are investigated by residual gases analyzer, field emission scanning electron microscopy, X-ray diffractometer, Raman scattering spectrometer, X-ray photoelectron spectrometer, and four-points probe. Residual gases analysis results reveal that the main species in the gas phase contain H2, CH3, CH4, C2H, C2H2, HCN, and N2 (or C2H4), in which H2 decreases with increasing the rf power, but HCN increases with increasing the rf power. Experimental results indicate that the deposition rate of carbon thin films decreases with increasing the rf power; this is because the increase of HCN suppresses the deposition of carbon films. The crystallinity and the ordering degree of carbon thin films increase with increasing the rf power. This is because the decrease of the deposition rate enhances the rearrangement of carbon atoms, which results in the increase of average grain size of carbon films. The number of sp2 carbon sites decreases with increasing the rf power; this is because the increase of the hydrogen content suppresses the formation of the sp2C=C bonds. Finally, the electrical resistivity of carbon thin films increases with increasing the rf power, this is resulted from the decrease of the number of the sp2 C=C bonding.

碩士
國立中興大學
材料科學與工程學系所
98
This study investigates the effects of different radio frequency (rf) powers on the properties of carbon films prepared by thermal chemical vapor deposition enhanced with inductively coupled plasma. The film thickness, microstructure, surface morphology, and electrical property of carbon films were investigated by field emission scanning electron microscopy, X-ray diffraction spectrometer, Raman scattering spectrometer, atomic force microscopy, contact angle meter, and four-points probe. The results indicate that the deposition rate increases as the rf power increases. Because the peak intensity of the substrate is much stronger than that of the graphite, the mean crystallite size（LC）has no trend with respect to the rf power. The in-plane crystallite size（La）decreases as the rf power increases. The ID/IG value increases as the rf-power increases, so the structure of carbon films becomes more disorder. The surface roughness of carbon films first decreases with increasing the rf power, but then increases as the rf power is over 250 W. The contact angle of carbon films increases with increasing the rf power in the beginning, but then decreases as the rf power is over 300 W. The electrical resistivity of the carbon films first decreases with increasing the rf power, but then increases as the rf power is over 300 W.

碩士
國立中興大學
材料科學與工程學系所
103
This study investigates the effects of different radio-frequency (rf) powers on the properties of carbon thin films that are prepared by thermal chemical vapor deposition enhanced with inductively coupled plasma (ICP). Ethylene (16 sccm) and Ammonia (4 sccm) were used as the precursor gases, and rf powers were set as 0W、100W、200W、300W and 400 W. The deposition temperature, working pressure, and deposition time were set to 1248 K, 4 kPa, and 2 hours. Alternatively, the residual gases, coating thickness, microstructure, surface roughness, surface property, and electrical property of carbon coatings were investigated by Residual gases analyzer, Field emission scanning electron microscopy, X-ray diffraction spectrometer, Raman scattering spectrometer, X-ray photoelectron spectrometer, Atomic force microscopy, Contact angle meter, and Four-points probe, respectively. The results indicate that if the rf power increases from 0 to 400 W, the deposition rate decreases. This is because the H2 molecules or the carbon deposited in the ICP zone increases with the rf powers. The mean crystallite size (Lc) and in-plane crystallite size (La) increase with decreasing the coating thickness, and thus, the degree of ordering increases. Moreover, when the rf-power increases, sp2 carbon atoms easily become sp3 carbon atoms, so the content of sp2 atoms in the carbon coatings decreases. Besides, the results also show that when the rf- power increases, the water contact angle (water-proofing) decreases that is resulted from the decrease of sp2 carbon atoms; the surface roughness decreases from 0 to 200 W and then increasing. As the rf power increases from 0 to 400 W, the electrical resistivity of carbon thin films increases from 12.32 to 16.23 Ω‧μm. This is because the sp2 carbon atoms decrease with increasing the rf power.

碩士
國立中山大學
物理學系
86
In this work, we set up an inductively-coupled-plasma-enhance-chemical-vapor-deposition system and grow SiC thin film on Si(1OO) and Si(l13) at low temperature and high frequency. The source gases were SiH4, CH4, and the gas mixed with Ar95% and H25%. The influence of the growth of thin films from different source gases flow ratio, different plasma RF power, different plasma RF frequency and different substrate temperature have been studied. By FTIR spectroscopy investigation, the carbon content on the thin films increases for more CH4 flow, higher frequency of Rf plasma and higher power of RF plasma during the deposition. For higher substrate temperature, the hydrogen content on the thin film decreases but the oxygen content on the thin film increases. The C/Si atom ratio on the thin films has been analyzed by EPMA. All samples were etched by the solution mixed with HF48%:HN0365%=10:3 As C/Si atom ratio of the thin films is above 0.267, Despite of that Si substrate is etched, the SiC film is acid resistive and can remain a smooth and reflective surface. XRD analyses show these thin films containing both of the SiC and Si amorphous structures. TEM analyses reveal that on the thin film the crystalline structures exist, when the C/Si atom ratio was above 0.515.

碩士
國立清華大學
工程與系統科學系
107
Capacitively coupled plasma (CCP) has been widely employed for etching and deposition processes. The purpose of this study is to investigate the effect of Tailored Voltage Waveforms (TVWs) on the plasma characteristics of SiH4/H2 plasma, a fluid model based numerical simulation analysis is employed to investigate the fundamental discharge characteristics of the basic physical and chemical mechanisms occurring in the plasma reactor. The TVWs in this study divided into two categories: consist of two frequencies and four frequencies. The first type of TVWs are consist of two equal-voltage sine waves, which are the fundamental frequency 13.56 MHz and the second harmonic frequency 27.12 MHz. Different waveforms can be generated by tuning the relative phase between two frequencies. When the absolute values of positive and negative extremes in TVWs are different, the voltages across the two sheaths are different. At the phase θ = 45° and θ =135°, the difference between the absolutes of positive and negative extreme is maximum. Define these waveforms are V45 and V135, when phase angle are 45 and 135 degree. Simulation results show that when the waveform is V45, the sheath voltage in front of ground electrode is 63 and 49% lower than V135 and single frequency 13.56 MHz, respectively. It is because of the voltage in front of powered is bigger, resulting in higher electron temperature and power density at the side of power electrode. Due to the sheath voltage in front of ground electrode is smaller, thus decrease the potential gradient and ion bombardment effect. In addition to the analysis of the plasma characteristics. This study also analyzes the flux ratio of SiH2/SiH3 and H/SiH3 reaching the substrate. Simulation results showed that the SiH2/SiH3 ratio decreased approximately 50% when the waveform is V45 compared to V135. This is because the electron temperature at the ground electrode is lower when the waveform is V45, which in turn reduces the rate of formation of SiH2. However, the H/SiH3 ratio reaching the substrate is within 10% of the V135 and the single frequency 13.56 MHz. Since the defect density and crystallinity of the film directly proportional to flux ratio of SiH2/SiH3 and H/SiH3, respectively, the simulation results show that TVWs V45 can reduce the defect density in the film without affecting the crystallinity. The second type of TVWs consists of 13.56MHz and its second, third and fourth harmonic frequencies. When θ is 0 and π, the waveform define as “peak” and “valley”. Comparing with V45 and V135, these waveforms having a larger difference ratio between the absolute values of the positive voltage and the negative voltage. Simulation results show that the ion energy is the smallest in waveform “peak”, and the SiH2/SiH3 flux ratio reaching the substrate is 10% and 40% lower than V45 and single frequency 13.56 MHz, respectively. Therefore, the simulation results show that TVWs "peak" can reduce the defect density in the film but does not affect the crystallinity compared to V45 and single frequency 13.56 MHz. Finally, TVWs "peak" simulation results show that the decrease of flux ratio SiH2/SiH3 can explain the microstructure ratio decrease in the literature [3], so the film quality improve under the TVWs “peak”.