Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 226.06K | Year: 2013
Electron attachment plays an important role in radiation chemistry, for example in DNA damage and ozone depletion. Detailed understanding and quantification of electron attachment processes in isolated molecules and condensed environments is therefore essential to model radiation effects on the nanoscale. My EPSRC CAF probes electron attachment dynamics and reactive pathways in selected biomolecular clusters, building on recent advances such as the observation of electron driven proton transfer in Watson Crick pairs [Bowen et al. ChemPhysChem 11 (2010) 880]. However, relatively little is known about how clustering modifies the absolute probabilities for electron attachment induced processes. While theoretical calculations by my collaborators Fabrikant and Gorfinkiel [J. Chem. Phys. 136 (2012) 184301] have provided evidence for strong enhancements in specific cluster configurations, absolute experimental data for electron attachment to clusters are extremely rare. This project is centered on developing an original technique to produce neutral mass-selected beams with known target density for electron attachment experiments. The method involves neutralization of mass-selected cluster anions by electron photo-detachment from specific weakly-bound anionic states, with minimal change in stability and hence dissociation. The project will provide a breakthrough in quantifying the effects of the local chemical environment on electron attachment induced processes.
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.
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.
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.
Sa J.,Queen's University of Belfast |
Fernandes D.L.A.,University of Aveiro |
Aiouache F.,Queen's University of Belfast |
Goguet A.,Queen's 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.
Ehiasarian A.P.,Sheffield Hallam University |
Vetushka A.,Sheffield Hallam University |
Gonzalvo Y.A.,Hiden Analytical Ltd. |
Sfrn G.,Research Institute for Technical Physics and Materials Science |
And 2 more authors.
Journal of Applied Physics | Year: 2011
HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N2 atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (Id) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti1, Ti2 and atomic nitrogen N1. Ti1 ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3 1016 m-3. Plasma density, and ion flux ratios of N1: N2 1 and Ti1: Ti0 increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high Id, N1+: N 2 1+ ≥ 1 and Ti1+: Ti0+ ≥ 1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As Id reduced and N1+: N 2 1+ and Ti1+: Ti0 dropped below 1, the film texture switched to strong 111 with a dense structure. At very low Id, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed. © 2011 American Institute of Physics.
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.
Chater R.J.,Imperial College London |
Shollock B.A.,Imperial College London |
McPhail D.S.,Imperial College London |
Smith A.J.,Hiden Analytical Ltd. |
Cooke G.,Hiden Analytical Ltd.
Surface and Interface Analysis | Year: 2014
Two microscopes with focused ion beam (FIB) columns in the Department of Materials, Imperial College, have been fitted with SIMS probes (Hiden EQS 1000). Both probes have differential pumping to maintain the vacuum in the probe below 5 × 10-6mbar irrespective of the main operating and imaging conditions of the microscopes. In both microscopes, standard operations include the injection of oxygen-containing species close to the sputter site. This process is also a technique for SIMS analysis instrumentation to enhance positive ion yields during sputtering where an oxygen primary ion beam for dynamic SIMS analysis is not available. The aim of this paper is to describe the compatibility of the differentially pumped SIMS probe with the normal specifications of microscopes. In particular, the modern field emission gun-SEM instrument's (Zeiss Auriga) ability to provide ultra-high spatial resolution SIMS in combination with electron microscopy imaging, energy dispersive spectroscopy and electron backscatter diffraction. In the second instrument, an ion microscope (FEI FIB200), the installed system is additional to the existing FEI SIMS probe. Simultaneous detection of positive and negative secondary ions from the same sputtered crater is obtained on this instrument with the two SIMS probes. Copyright © 2014 John Wiley & Sons, Ltd.
Chater R.J.,Imperial College London |
Smith A.J.,Hiden Analytical Ltd |
Cooke G.,Hiden Analytical Ltd
Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics | Year: 2016
A secondary ion mass spectrometer (SIMS) instrument is described that is configured with two SIMS detectors that are both low-field extraction, quadrupole-based filters. Secondary ions are generated by sputtering with a liquid-metal ion gallium source and column of the type that is common on two-beam electron microscopes. The gallium ion beam, or focused ion beam achieves sub-100 nm focus with a continuous current of up to 300 pA. Positive secondary ions are detected by one SIMS detector, and simultaneously, negative secondary ions are detected by the second SIMS detector. The SIMS detectors are independently controlled for recording mass spectra, concentration depth profiles, and secondary ion images. Examples of simultaneous positive and negative SIMS are included that demonstrate the advantage of this facility for surface analysis and depth profiling. The SIMS secondary ion collection has been modeled using the ray tracing program simion ("simion", Scientific Instrument Services, Inc., Ringoes, NJ, 08551-1054, see http://www.simion.com) in order to understand the interaction of the secondary ions of opposite polarities in the extraction volume for the purpose of optimizing secondary ion collection. © 2016 American Vacuum Society.
Oh J.-S.,University of Liverpool |
Aranda-Gonzalvo Y.,Hiden Analytical Ltd. |
Bradley J.W.,University of Liverpool
Journal of Physics D: Applied Physics | Year: 2011
Using molecular beam mass spectroscopy, time-resolved measurements of the ionic species inthe plasma plume of an atmospheric-pressure helium microplasma jet are made for a range ofexcitation frequencies (5, 10 and 25 kHz) and source-instrument orifice distances (1, 7 and11 mm). Ionic species can only be observed in the visible plasma plume, with the mainpositive species being N + 2 (65.26%) and O+ 2 (21.11%), and a few percentages of N+, O+,NO+and He +. For the negative ions, the majority species are O- 3 (22.68%), O- 2 (H2O) (10.49%)and a large range of minority species observed, namely O- n, OH- n , (H2O)- n , CO- n and clusters,O-m(H2O)n, (OH) n m(H2O)n, O- n (CO 3) and CO- 3 (H2O)n. The flux of ions created from airspecies, such as NO+ and O-3 , is seen to be maximized at a distance of several millimeters fromthe nozzle, whereas the He+ concentration continually decreases with distance from the exitorifice. The time-resolved measurements (time resolution down to 2μs) show that positiveions appear twice in one full period of the voltage waveform, correlated directly with positiveand negative current peaks. The rise and fall times of the positive ions are typically tens of μs.In contrast, the appearance of negative ions is correlated only with the negative part ofdischarge current, with one main peak in the detected ionic flux seen per cycle. The rise timeof the negative ions is about 10μs, independent of mass; however, we observed longer decaytimes, from 100 to 150μs, increasing with mass. With increased driving frequency, the timemodulation in the ionic fluxes is reduced, particularly for the negative species that show almostconstant fluxes at 25 kHz throughout the cycle. The observations can be understood through asimple picture of the interaction of the He jet and the moist ambient air. The results indicatethat the discrete plasma 'bullets' and their afterglow tail, that forms the jet, carry an associatedpositive or negative current depending on the time of their creation in the voltage cycle. © 2011 IOP Publishing Ltd.