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Arcos T.D.L.,Ruhr University Bochum | Layes V.,Ruhr University Bochum | Gonzalvo Y.A.,Hiden Analytical Ltd. | Gathen V.S.-V.D.,Ruhr University Bochum | And 2 more authors.
Journal of Physics D: Applied Physics | Year: 2013

Current-voltage characteristics within the temporal pulse were recorded in high-power pulsed magnetron sputtering discharges for different target materials. These curves allowed identifying at a first glance the existence of separated plasma regimes clearly differentiated by the plasma conductivity and by the spatial arrangement of the plasma emission. We could establish that regimes of high plasma conductivity are univocally associated to the self-organization of the plasma in well-defined ionization zones. As the applied power is gradually increased, the high conductivity regime is abruptly replaced by a regime of high current and low plasma conductivity, associated to homogeneous plasma emission. © 2013 IOP Publishing Ltd. Source


Bruggeman P.,TU Eindhoven | Bruggeman P.,Ghent University | Bruggeman P.,Loughborough University | Iza F.,Loughborough University | And 6 more authors.
Plasma Sources Science and Technology | Year: 2010

In this paper it is shown that electronic quenching of OH(A) by water prevents thermalization of the rotational population distribution of OH(A). This means that the observed ro-vibrational OH(A-X) emission band is (at least partially) an image of the formation process and is determined not only by the gas temperature. The formation of negative ions and clusters for larger water concentrations can contribute to the non-equilibrium. The above is demonstrated in RF excited atmospheric pressure glow discharges in He-water mixtures in a parallel metal plate reactor by optical emission spectroscopy. For this particular case a significant overpopulation of high rotational states appears around 1000 ppm H2O in He. The smallest temperature parameter of a non-Boltzmann (two-temperature) distribution fitted to the experimental spectrum of OH(A-X) gives a good representation of the gas temperature. Only the rotational states with the smallest rotational numbers (J ≤ 7) are thermalized and representative for the gas temperature. © 2010 IOP Publishing Ltd. Source


De Los Arcos T.,Ruhr University Bochum | Schroder R.,Ruhr University Bochum | Gonzalvo Y.A.,Hiden Analytical Ltd. | Schulz-Von Der Gathen V.,Ruhr University Bochum | Winter J.,Ruhr University Bochum
Plasma Sources Science and Technology | Year: 2014

The behaviour of Cu and Cr HiPIMS (high power impulse magnetron sputtering) discharges was investigated by a combination of optical emission spectroscopy, energy-resolved mass spectrometry and optical imaging, for the complete current-voltage characteristic range achievable within our experimental conditions. Inflection points typical of HiPIMS current-voltage characteristics separate plasma regimes perfectly differentiated in terms of flux composition of species towards the substrate, deposition rate, and the nature of plasma self-organization. The reorganization of the HiPIMS plasma into spokes (areas of high ionization over the target) is associated to one regime of high plasma conductivity, where also deposition rate is limited. This spoke-dominated regime can be substituted by a homogeneous regime at higher powers, where there is an increase of deposition rate, which is driven mostly by an increase in the flux of metal neutrals and metal double-charged ions. The relevance of secondary electron emission mechanisms for the support of the spoke-dominated regime in reactive and non-reactive sputtering conditions is discussed. © 2014 IOP Publishing Ltd. Source


Sa J.,Queens University of Belfast | Fernandes D.L.A.,University of Aveiro | Aiouache F.,Queens University of Belfast | Goguet A.,Queens University of Belfast | And 5 more authors.
Analyst | Year: 2010

Monolithic catalysts are widely used as structured catalysts, especially in the abatement of pollutants. Probing what happens inside these monoliths during operation is, therefore, vital for modelling and prediction of the catalyst behavior. SpaciMS is a spatially resolved capillary-inlet mass spectroscopy system allowing for the generation of spatially resolved maps of the reactions within monoliths. In this study SpaciMS results combined with 3D CFD modelling demonstrate that SpaciMS is a highly sensitive and minimally invasive technique that can provide reaction maps as well as catalytic temporal behavior. Herein we illustrate this by examining kinetic oscillations during a CO oxidation reaction over a Pt/Rh on alumina catalyst supported on a cordierite monolith. These oscillations were only observed within the monolith by SpaciMS between 30 and 90% CO conversion. Equivalent experiments performed in a plug-flow reactor using this catalyst in a crushed form over a similar range of reaction conditions did not display any oscillations demonstrating the importance of intra monolith analysis. This work demonstrates that the SpaciMS offers an accurate and comprehensive picture of structured catalysts under operation. © 2010 The Royal Society of Chemistry. Source


Loch D.A.L.,Sheffield Hallam University | Gonzalvo Y.A.,Hiden Analytical Ltd. | Ehiasarian A.P.,Sheffield Hallam University
Surface and Coatings Technology | Year: 2015

Inductively Coupled Impulse Sputtering (ICIS) removes the need for a magnetron, whilst delivering equal or higher ion-to-neutral ratios compared to other ionised PVD technologies such as High Power Impulse Magnetron Sputtering (HIPIMS). This is especially advantageous for the sputtering of magnetic materials, as these would shunt the magnetic field of the magnetron, thus reducing the efficiency of the sputtering and ionisation process. ICIS produces highly ionised metal-dominated plasma inside a high power pulsed RF-coil with a magnet free high voltage pulsed DC powered cathode.ICIS operation with magnetic target materials has not been attempted so far. The paper aims to clarify the effects of power and pressure on the chemistry of the deposition flux and is the first investigation of the microstructure of ICIS deposited coatings.Modelling based on the intensity of the optical emission spectra (OES) is conducted for the first time on the excited species of Ni and Ar in relation to the applied RF-power. Sputtered species show a linear intensity increase for increasing peak RF-power and constant process gas pressure.The influence of increasing process gas pressure on the ionisation was studied at a constant peak RF-power for pressures. For pressures below 8. Pa the intensity rises, but then remains constant for pressures up to 26. Pa.The microstructure of Ni coatings shows columnar dendritic or globular growth depending on the ionisation degree. In relation to the film thickness on the top of the substrate, the bottom coverage of unbiased vias with an aspect ratio of 4:1 was 15% and for lower aspect ratios of 1.5:1 was 47.5%.The current work has shown that the concept of combining a pulsed RF driven coil with a magnet-free pulsed DC powered cathode works well for the sputtering of magnetic material in a stable plasma. © 2014 Elsevier B.V. Source

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