193 research outputs found
Oxford Instruments Plasma Technology gets VG Semicon
No full textAbstractAfter recent speculation, Oxford Instruments Plasma Technology, a wholly owned subsidiary of Oxford Instruments plc, comfirms it has acquired the assets of MBE equipment manufacturer Thermo VG Semicon.Visit www.three-fives.com for the latest advanced semiconductor industry new
Oxford Instruments Plasma Technology gets VG Semicon
No full textAbstractAfter recent speculation, Oxford Instruments Plasma Technology, a wholly owned subsidiary of Oxford Instruments plc, comfirms it has acquired the assets of MBE equipment manufacturer Thermo VG Semicon.Visit www.three-fives.com for the latest advanced semiconductor industry new
Studies of black silicon and black diamond as materials for antibacterial surfaces
No full text‘Black silicon’ (bSi) samples with surfaces covered in nanoneedles of varying length, areal density and sharpness, have been fabricated using a plasma etching process. These nanostructures were then coated with a conformal uniform layer of diamond using hot filament chemical vapour deposition to produce ‘black diamond’ (bD) surfaces. The effectiveness of these bSi and bD surfaces in killing Gram-negative (E. coli) and Gram-positive (S. gordonii) bacteria was investigated by culturing the bacteria on the surfaces for a set time and then measuring the live-to-dead ratio. All the nanostructured surfaces killed E. coli at a significantly higher rate than the respective flat Si or diamond control samples. The length of the needles was found to be less important than their separation, i.e. areal density. This is consistent with a model for mechanical bacteria death based on the stretching and disruption of the cell membrane, enhanced by the cells motility on the surfaces. In contrast, S. gordonii were unaffected by the nanostructured surfaces, possibly due to their smaller size, thicker cell membrane and/or their lack of motility
Deposition of TiN and HfO2 in a commercial 200 mm remote plasma atomic layer deposition reactor
No full textThe authors describe a remote plasma at. layer deposition reactor (Oxford Instruments FlexAL) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200 mm in diam. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2-N2 plasma and the combination of the metallorg. precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, resp. The influence of the plasma exposure time and substrate temp. has been studied and compositional, structural, and elec. properties are reported. TiN films with a low Cl impurity content were obtained at 350 DegC at a growth rate of 0.35 A/cycle with an elec. resistivity as low as 150 micro W cm. Carbon-free (detection limi
Magnetotail dipolarization and associated current systems observed by Cluster and Double Star
No full textA dipolarization and its associated current systems are studied using Cluster, Double Star TC1, and ground-based observations. The Cluster spacecraft are located approximately 16 RE downtail near 0030 LT. The Double Star TC1 spacecraft is located more earthward at approximately 7 RE just before local midnight. Auroral observations by the Wideband Imaging Camera on the Imager for Magnetopause-to-Aurora Global Exploration spacecraft are used to determine the onset times of substorms. It is shown that the magnetic phenomena at the earthward site of a magnetic reconfiguration region are governed by field-aligned currents, which in their turn generate auroral brightenings near the foot points of the spacecraft. It is also shown that the inward and outward motion of the dipolarization front near Cluster has a direct influence on the parallel plasma flow at TC1, indicating a piston mechanism. Just like a piston, the inward moving dipolarization at Cluster pushes in plasma along with the flux transport, which turns to parallel plasma flow at TC1. When the flow reverses at Cluster, i.e., outgoing flux transport, the plasma gets “sucked out” again, which is directly reflected in the plasma data from TC1
Heat transfer properties of laser assisted plasma processing
No full textLaser assisted plasma processing (LAPP) is a novel extension to already established Reactive Atom Plasma (RAP) processing for atmospheric pressure dry chemical etching of silicon based materials; this is mainly applied for optical uses. The development of the new technology involves the implementation of an additional laser energy beam to tune the thermal footprint of the hybrid tool. This will influence the temperature-dependent etching reaction.
The aim of the project was to develop a model to predict the temperature footprint of components of the LAPP tool and assess the suitability of this model in simulating the thermal effects during an actual process. This was undertaken via two routes: model development and experimental temperature investigation. The two materials investigated were Corning Ultra Low Expansion glass (ULE) and also Silicon Carbide (SiC).
The model was developed using Matlab from an established analytical method and evolved for LAPP use. An analytical method based on a Green’s function solution to the heat equation for a moving Gaussian heat source on a surface was chosen as it would be an adaptable and rapid alternative to costly experimental measurements for LAPP.
Experimental temperature measurements were investigated using pyrometers, resistance temperature detectors and thermocouples. Typical LAPP process parameters were investigated for both a laser source and a RAP torch, and the temperature was measured. Additionally, surface reflectivity was measured for appropriate wavelengths for LAPP applications using a Fourier transform infrared spectrometer to determine the absorbed portion of laser energy.
The experimental work conducted using RTDs found strong correlation with the modelling, with 63% of results matching within experimental error. The pyrometer measurements were less successfully replicated, the reason for which is expected to be the cooling of the substrate from its upper surface not being accounted for in the model. Overall trends of temperature rise decreasing with increasing feed speed or decreasing power were observed. Thermocouple characterisation of the RAP torch was approximated using the radiative model
Experimental and Analytical Studies of Merging Plasma Loops on the Caltech Solar Loop Experiment
No full textOf crucial importance for magnetized plasmas is magnetic helicity, a topological quantity that measures the knottedness or twistedness of the magnetic field. A universal relaxation theory, applicable to astrophysical and laboratory plasmas, dictates the evolution of plasmas towards an equilibrium state based solely on helicity content. The Caltech Solar Loop Experiment creates plasma with injected helicity to study this evolution, which can involve the merging of two plasma loops into a single structure. This thesis studies the merging using two techniques. The first is the construction of an array of vacuum photodiodes to measure extreme ultraviolet radiation from the experiment; the data provides information concerning non-equilibrium radiation losses and magnetic reconnection. The second is a Hamiltonian study of particle orbits to explain how particles can transition from being localized from one plasma loop to being shared among two neighboring loops. This shows how the merging process may initiate and also leads to a general theorem where the action variable serves as a Hamiltonian for the orbit-averaged system
Estudo númerico e experimental do processo de deposição e difusão de níquel via plasma em amostras de ferro na configuração ânodo-cátodo confinado
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia MecânicaA aplicação industrial de técnicas de processamento de materiais por plasma vem apresentando um notável crescimento nos últimos anos. Este crescimento deve-se a algumas características particulares destes processos, dentre elas pode-se citar: fácil automação do processo, economia de gases (por trabalhar-se em geral à baixas pressões), vantagens ecológicas (uma vez que tratamentos por plasma são, em geral, não poluentes ou muito pouco poluentes) e qualidade dos tratamentos. Dentre os tratamentos por plasma destacam-se os do tipo físicos (deposição de filmes e sinterização) e os termoquímicos (nitretação, boretação, cementação). O foco do presente trabalho é o estudo experimental e teórico do processo físico de deposição de níquel proveniente da pulverização catódica sobre amostras de ferro. O processo de deposição foi realizado em condições equivalentes às utilizadas na sinterização por plasma na configuração ânodo-cátodo confinado. A amostra (ânodo) foi posicionada concentricamente no interior do cátodo cilíndrico, com espaçamento de 6,25 mm. O cátodo é constituído de Níquel 200 (níquel comercialmente puro) e as amostras de aço IF (interstitial free) e de ferro puro sinterizado. Para os tratamentos foram fixados os seguintes parâmetros: fluxo de gases em 240 sccm (standard cubic centimeter per minute), mistura gasosa em 80% Ar / 20% H2 e temperatura em 1150 °C. Foram estudadas as variações do processo de deposição em função da tensão da fonte (500, 600 e 700 V) e do tempo de processamento (0, 0,5, 1, 1,3 e 2 h). As amostras foram caracterizadas por medidas de ganho de massa, microscopia ótica, microscopia eletrônica de varredura e por micro análise por energia dispersiva de raios X. No estudo teórico, foi utilizado o método dos volumes finitos para a simulação da difusão de massa na amostra e na fase gasosa. Os experimentos mostraram que o processo de deposição ocorre com taxa de deposição constante em relação ao tempo de processamento e que a taxa de deposição varia de maneira linear com a tensão aplicada na fonte, para as condições estudadas. Os resultados do modelo de difusão aplicado para a amostra apresentaram boa concordância com os dados experimentais. Já no modelo para a fase gasosa encontrou-se dificuldade para estimar alguns parâmetros necessários, entretanto este ajudou a esclarecer alguns aspectos importantes na fenomenologia do processo. Estudos mais aprofundados, sobretudo sobre a descarga elétrica, são necessários para completa compreensão deste processo
Estudo de adesão e proliferação celular sobre superfícies de filmes poliméricos modificados por processo de plasma frio com descarga de barreira dielétrica
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Química.Este trabalho descreve a síntese de filmes poliméricos, sua modificação e a avaliação quanto à adesão de espécies celulares. Filmes de poliestireno (PS) e poli (metacrilato de metila) (PMMA) e mistura com 1:1 de composição preparados por casting foram avaliados quanto ao crescimento e proliferação de fibroblastos L-929. Estudos envolvendo modificação da superfície destes polímeros foram desenvolvidos, com resultados promissores decorrentes da utilização de plasma frio através de descarga de barreira dielétrica (DBD) para induzir a modificação da superfície, após planejamento fatorial das condições experimentais. Alterações nas propriedades da superfície com relação às amostras não tratadas foram acompanhadas por medidas de ângulo de contato, energia de superfície, histerese, microscopia eletrônica de varredura (SEM) e SEM com espectrometria de energia dispersiva, microscopia de força atômica (AFM) e espectrometria fotoeletrônica de raios-X. Após o tratamento, excelente aderência e proliferação de células foram observadas em todos os filmes com maior proliferação celular no filme PS/PMMA 1:1. Filmes finos de zeína obtidos por spin coating foram também tratados por plasma frio com DBD. Após o tratamento, uma pequena variação de molhabilidade foi detectada, além de aumento de rugosidade. A adsorção de albumina de soro bovino na superfície dos filmes foi também avaliada. Todos os filmes apresentaram excelente adesão das células L-929 após os dois tratamentos. Resultados preliminares para filmes finos nanoestruturados formados a partir de dois copolímeros em bloco de poliestireno e poli(ácido acrílico) são também descritos. Ambos os filmes, após análise por AFM, apresentaram superfícies mais rugosas e uma significativa melhora na adesão e proliferação das células L-929, o que os torna potenciais biomateriais para aplicação biomédica.This work describes the synthesis of polymeric films, their surface modification and an evaluation of their ability to promote adhesion of cell species. Films formed with the casting technique from poly(styrene) (PS), poly (methyl methacrylate) (PMMA) and a 1:1 mixture of both were evaluated towards the growth and proliferation of L-929 fibroblasts. Studies involving the surface modification of the polymeric films were carried out, with promising results obtained from the use of cold plasma generated by a dielectric barrier discharge (DBD), following a factorial design for optimization of the operating parameters. Changes in the surface properties of the plasma-treated films were evaluated by means of contact angle, surface energy and hysteresis measurements, scanning electron microscopy (SEM) and energy-dispersive SEM, atomic force microscopy (AFM) and X-ray photoelectronic spectrometry. Substantial proliferation of cells was observed on the surface of all plasma-treated films, with a superior performance of the PS/PMMA 1:1 film. Thin films produced from zein using the spin coating technique were also submitted to DBD-cold plasma treatment. A minor variation in the wetability of the plasma-treated films was observed, in addition to increased rugosity. The effect of adsorption of bovine serum albumin on the polymeric film surface was also evaluated. Both surface-based treatments resulted in enhanced adhesion of L-929 cells on the polymeric films. Preliminary results for nanostructured thin films formed from two block copolymers of poly(styrene) and poly(acrylic acid) are also presented. AFM analysis of the surface of both plasma-treated films evidenced increased rugosity, which was accompanied by a substantial improvement in the adhesion and proliferation of L-929 cells, turning these polymeric films into promising biomaterials
Instrument development and plasma measurements on a 200-watt Hall thruster plume
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 117-118).Plume diagnostic instruments were developed and the BHT-200 Hall thruster plume was characterized in order to support ongoing computational plume models. The instruments included a Faraday probe to measure current density, a hot emissive probe to measure plasma potential, and a cold Langmuir probe to measure electron temperature and electron density. Plasma measurements consisted of studying facility and thruster effects on the plume. Facility effects included background pressure and sweep radius, while thruster effects included discharge voltage and flow rate. Experimental results showed that current density is more sensitive to background pressure than to thruster effects, plasma potential is a more direct indicator of plasma density than current flux, and electron temperature and electron density vary substantially across the plume following a polytropic relationship. These experimental results were compared to solutions of a self-similar plume model. Data analyses were also performed using a consistency analysis of the experimental data by deducing plasma potential from Faraday and cold emissive probe data and comparing it to the measured plasma potential from the hot emissive probe. Good agreement was achieved between all experimental data and analysis except in charge exchange dominated regions, since the analyses do not take into account collision effects. Thus, the experimental data obtained can be used to validate computational results.by Yassir Azziz.S.M
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