Publications

2016

• VUV emission spectroscopy combined with H- density measurements in the ion source Prometheus I
  
  • Aleiferis S.
  • Laulainen J.
  • Svarnas P.
  • Tarvainen O.
  • Bacal M.
  • Béchu Stéphane
  , 2016, 1869, pp.030045. Prometheus I is a volume H- negative ion source, driven by a network of dipolar electron cyclotron resonance (ECR) sources (2.45 GHz)1–3. The vacuum-ultraviolet (VUV) emission spectrum of low-temperature hydrogen plasma is potentially related to molecular and atomic processes involved directly or indirectly in the production of negative ions4. In this work, VUV spectroscopy has been performed in above source Prometheus I. The acquired VUV spectra are correlated with the negative ion densities, as measured by means of laser photodetachment5, and the possible mechanisms of negative ions production are considered. The well-established H- formation process of dissociative attachment to vibrationally excited molecules6 is evaluated, while additional production paths (e.g. neutral resonant ionization7,8) are tested. The obtained results indicate that for the source Prometheus I, the dominant formation process is dissociative attachment. (10.1063/1.4995765)
  DOI : 10.1063/1.4995765
• Effect due to plasma electrode adsorbates upon the negative ion current and electron current extracted from a negative ion source
  
  • Bacal M.
  • Wada M.
  , 2017, 1869, pp.030025. The intensity of negative hydrogen (H−) ion current and that of electron current extracted from a negative ion source show different characteristics against the change in plasma electrode bias depending upon the material covering the plasma electrode surface. The knowledge of these characteristics is of importance for a proper design of an efficient H− ion source. This paper discusses this subject based upon two kind of experiments i) experiments with plasma electrodes covered with tungsten or tantalum evaporated from filaments made of these metals ii) experiments with caesium covered plasma electrode. The tantalum and caesium covered plasma electrodes lead to an enhancement of the extracted H− ion current by a factor of 2 compared to the tungsten coverage on the plasma electrode. The electron current is also affected by the material covering the plasma electrode. The reasons for observing these characteristics are also elucidated. oral presentation (10.1063/1.4995745)
  DOI : 10.1063/1.4995745
• Influence of the concentration of H<SUB>2</SUB> on the structure of a nanosecond discharge in different H<SUB>2</SUB>/air mixtures at atmospheric pressure for plasma assisted applications
  
  • Kobayashi Sumire
  • Bonaventura Z.
  • Tholin Fabien
  • Popov N.A.
  • Bourdon Anne
  , 2016.
• Plasmas interacting with liquids: Energy transfer and chemistry an engineer approach
  
  • Rousseau Antoine
  , 2016.
• Multiresolution on arbitrary domains for time dependent PDEs. Application to streamer simulations
  
  • Lee Pierre-Louis
  • Bonaventura Z.
  • Duarte Max
  • Bourdon Anne
  • Massot Marc
  , 2016.
• Interesting Physics in Boring Plasmas: Validation & Open Issues
  
  • Dif-Pradalier Guilhem
  • Ghendrih Ph.
  • Sarazin Y.
  • Diamond P.H.
  • Garbet X.
  • Grandgirard V.
  • Gürcan Özgür D.
  • Hennequin Pascale
  • Morel Pierre
  • Vermare Laure
  , 2016.
• Numerical and experimental study on the dynamics of a $\mu$s helium plasma gun with various amounts of O$_2$ or N$_2$ admixtures
  
  • Viegas Pedro
  • Damany Xavier
  • Iséni Sylvain
  • Pouvesle Jean-Michel
  • Eric Robert
  • Bourdon Anne
  , 2016. Recently to tailor the generation of reactive species in plasma jets for biomedical applications, several research groups [1-5] have studied the use of admixtures (mostly O2 and N2) to the helium buffer. Furthermore, there exists also a recent interest for the consideration of electric field associated with the plasma plume delivery over tissues in comparison with the previously reported potent effects of the pulsed electric fields [6]. So far, most experiments have been dedicated to the study of the plasma plume. For endoscopic treatments, it is also important to better understand and optimize the propagation of discharges in long dielectric tubes as catheters. In this work, we present an experimental and numerical study on the dynamics of a s helium plasma discharge with N2 or O2 admixture in a long dielectric tube. In a previous work [5] we have compared experiments and simulations for different amounts of nitrogen admixture added to the buffer gas at the inlet of the plasma gun. In this work, in experiments, we first compare with results obtained previously in N2 with results obtained with O2 admixture added in the helium buffer at the inlet of the plasma gun hollowed electrode but also alternatively downstream along the helium plasma propagation inside long dielectric capillaries to change the plasma jet properties. In simulations, a 2D fluid model is used. For comparison purposes, the geometries of the set-ups used for simulations and experiments are as close as possible and the same applied voltage waveforms are used with a 2 μs rise time and two peak voltages of 10 and 16 kV. In order to study the influence of different amounts of N2 and O2 admixture on the helium discharge dynamics, detailed kinetic schemes have been used. In both He/N2 and He/O2 mixtures, the influence of Penning and charge exchange reactions on the discharge structure and dynamics are studied. We present results on the comparison of experimental and numerical results obtained on the velocity of the discharge front for various amounts of N2 and O2 and different applied voltages. Second, we compare time-resolved measurements and simulations of longitudinal and radial electric fields associated with plasma propagation in the dielectric tube and in the plasma plume. Acknowledgments P.V. is supported by xxxxx fellowship, and X.D. by INEL/Region Centre-Val de Loire fellowship. References [1] T. Darny, E. Robert, S. Dozias and J.M. Pouvesle Proc. of the 5th Int. Conf. on Plasma Medicine, Nara, Japan (2014) [2] S. Iseni, S. Zhang, F. van Gessel, S. Hofmann, B. van Ham, S. Reuter, K.-D. Weltmann and P. Bruggeman New J. Phys. 16 123011 (2014) [3] Reuter S, Tresp H, Wende K, Hammer M, Winter J, Masur K, Schmidt-Bleker A and Weltmann K IEEE Trans. Plasma Sci. 40 2986–93 (2012) [4] van Gessel B, Brandenburg R and Bruggeman P Appl. Phys. Lett. 103 064103 (2013) [5]A. Bourdon, T. Darny, F. Pechereau, J.M. Pouvesle, P. Viegas, S. Ideni, E. Robert, Plasma Sources Sci. Technol 25 035002 (2016) [6] Zhang Q, Zhuang J, von Woedtke T, Kolb J F, Zhang J, Fang J and Weltmann K-D Appl. Phys. Lett. 105 104103 (2014)
• Sorbent track: Quantitative monitoring of adsorbed VOCs under in-situ plasma exposure
  
  • Jia Zixian
  • Rousseau Antoine
  Scientific Reports, Nature Publishing Group, 2016, 6, pp.31888. Sorbent-TRACK is a new device developed to monitor adsorption and surface oxidation of pollutants under direct plasma exposure. It is based on direct transmitted Fourier Transformed Infrared (FTIR) spectroscopy. A pyrex reactor under controlled gas pressure and composition is inserted on the infrared beam of a commercially available Nicolet 5700 FTIR spectrometer. A substrate holder is located on the optical path of the infrared beam. A thin pellet of a dedicated catalyst (CeO 2 in the present work) is inserted in a substrate holder and can be exposed to direct plasma treatment using a Dielectric Barrier Discharge. The time resolution of Sorbent-TRACK is limited by the time resolution of the Nicolet 5700 FTIR spectrometer and close to 30 s. The dynamic of the adsorption and plasma oxidation of acetone and isopropanol on CeO 2 are studied and intermediates are monitored. Performances and sensitivity of Sorbent-TRACK are reported Adsorption and oxidation of acetone leads to production of adsorbed isobutene and acetic acid, where oxidation of isopropanol gives mainly to adsorbed acetone, mesityl oxide and acetate. An increase of the plasma power leads to an increase of the isopropanol and acetone oxidation rate and a related increase of the production of adsorbed intermediates. (10.1038/srep31888)
  DOI : 10.1038/srep31888
• New insights into the Non Thermal Continuum radiations: The Cluster Whisper perspective
  
  • Canu Patrick
  • Décréau Pierrette
  • Rochel Grimald S.
  , 2016. The Whisper instruments on board each of the four Cluster spacecraft exploring the Earth magnetosphere, routinely observe the Non Thermal Continuum emissions (NTC). The various and combined points of view provided by 4 spacecraft in the 2-80 kHz frequency range allow the detection of the different forms of these emissions, narrow band and broad band, emitting from source regions in the plasmapause boundary layer, close to the magnetic equator but also at mid latitude. This paper presents selected examples of new knowledge gained on the NTC radiations, locations and mechanisms, coming from the 15 years of observations of Cluster-Whisper.
• Plasmas for Energy and Fusion
  
  • Morel Pierre
  , 2016.
• Air treatment using plasma-sorbent coupling
  
  • Rousseau Antoine
  , 2016.
• Dynamics of inductive plasmas in Cl<SUB>2</SUB>, O<SUB>2</SUB> and Cl<SUB>2</SUB>/O<SUB>2</SUB> mixtures: quantitative diagnostics and numerical modelling
  
  • Marinov Daniil
  • Foucher Mickaël
  • Gibson Andrew
  • Chabert Pascal
  • Booth Jean-Paul
  , 2016.
• Continuous gps network in vietnam and results of study on the total electron content in the south east asian region
  
  • Hu Le Huy
  • Lan Tran Thi
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Bourdillon A.
  • Hu J.
  • Hung Vu Tuan
  • Thang Nguyen Chien
  • Thanh Le Truong
  • Thanh Nguyen Ha
  Vietnam Journal of Earth Sciences, Vietnam Academy of Science and Technology (VAST), 2016, 38 (2), pp.153 - 165. This study presents the continuous GPS network in Vietnam and the results of the study on time variations of the total electron content (TEC) in the South East Asian equatorial ionization anomaly (EIA) for the 2006-2013 period. In each year we observe a semiannual pattern of TEC diurnal variation in all the stations with its maximum amplitude at the equinox. In both hemispheres, the amplitude of the crest is larger in northern spring equinox than in autumn from 2006 to 2008 (descending phase of solar cycle) and smaller in spring than in autumn from 2009 to 2011 (increasing phase of solar cycle), from 2012-2013 (maximum period of solar cycle) the amplitudes of the crests in spring and autumn are equivalent. We also observe an asymmetry between the amplitude and the position of the two crests of ionization. There is a very high level of correlation between the amplitude of the TEC at the two crests and the sunspot number is approximately equal to 0.9. During the deep solar minimum 2008-2009, the amplitude of crests of ionization becomes small during several months in summer and winter (about 20 TECu). The results show that both crests move more significantly equatorward in winter than in other seasons and there is a tendency for both crests to appear earlier in winter and later in summer. In the solar minimum years, the amplitudes of the crests are minimal; the positions of the crests are nearer the magnetic equator and the crests appear earlier than in other years. (10.15625/0866-7187/38/2/8598)
  DOI : 10.15625/0866-7187/38/2/8598
• Magnetic reconnection in turbulence: from Cluster to MMS and beyond
  
  • Retinò Alessandro
  • Sundkvist D.
  • Matthaeus W. H.
  • Vaivads A.
  • Califano F.
  • Khotyaintsev Y. V.
  • Le Contel Olivier
  • Sorriso-Valvo L.
  • Chasapis A.
  • Lavraud Benoit
  • Valentini F.
  • Servidio S.
  • Rossi C.
  • Camporeale E.
  , 2016, 41, pp.D2.4-3-16. Magnetic reconnection is a universal energy dissipation mechanism occurring in space and astrophysical magnetized plasmas. Such plasmas are frequently in a turbulent state, raising the fundamental question of the role reconnection for energy dissipation in turbulence. Understanding reconnection in turbulence is of pivotal importance to explain phenomena such as particle acceleration in stellar atmospheres, the heating of interplanetary and interstellar media as well as particle energization in accretion disks and cosmic rays acceleration. Many numerical simulations support the role of reconnection for efficiently dissipate turbulent energy and heat and accelerated particles. Such simulations indicate that reconnection occurs in small-scale current sheets spontaneously forming within the turbulence. Yet experimental evidence of reconnection in turbulence has been provided only recently thanks to high resolution in situ measurements by modern spacecraft. Here we present ESA/Cluster and more recent NASA/MMS observations in near-Earth space showing evidence of reconnection in turbulence and its importance for energy dissipation and particle energization. We also discuss implications for upcoming spacecraft missions such as Solar Orbiter and Solar Probe Plus, as well as for missions currently under study pahse such as ESA/THOR.
• Gordon Research Conference 2016 for Plasma Processing Science: Plasmas with Complex Interactions: Exploiting the Non-Equilibrium
  
  • Starikovskaia Svetlana
  , 2016.
• Quantitative Diagnostics of Inductively-coupled Radiofrequency Plasmas in Cl<SUB>2</SUB>, O<SUB>2</SUB> and mixtures
  
  • Booth Jean-Paul
  • Foucher Mickaël
  • Gibson Andrew
  • Marinov Daniil
  , 2016. Inductively-coupled plasmas in molecular, electronegative gases are widely used for plasma processing of surfaces, for instance in CMOS manufacture. The complexity of these systems is such that they can only be described by multi-physics models which describe both the plasma physics and the molecular collisional processes. However, there has been little rigorous validation of these models by comparison to quantitative measurements of particle densities over a wide range of parameter space. We have chosen to study the Cl2/O2 system partly because of the industrial process relevance but also because methods exist to measure the density, and energy distributions, of most of the particles present. Electron densities were measured by microwave hairpin resonator. Absolute Cl and O atom densities were determined by Two-photon Absorption Laser-Induced Fluorescence [1, 2]. We have constructed a new ultra-low noise broadband UV-visible absorption bench[3], which allows the measurement of the densities of ground state Cl2 molecules and ClxOy reaction products, as well as vibrationally excited states of O2 [3] and Cl2 [4]. Gas temperatures are determined by Doppler-resolved IR laser absorption spectroscopy of argon metastable atoms (added in small quantity), and showing that high gas temperatures (up to 2000K) can be reached. This comprehensive data set will be presented, along with comparison to different (0D and 2D cylindrical) models References [1] J.P. Booth, Y. Azamoum, N. Sirse, and P. Chabert, Journal of Physics D-Applied Physics, 45, 195201. (2012) 195201 [2] N. Sirse, J.P. Booth, P. Chabert, A. Surzhykov, and P. Indelicato, Journal of Physics D: Applied Physics, 46, (2013) 295203 [3] M. Foucher, D. Marinov, E. Carbone, P. Chabert, and J.-P. Booth, Plasma Sources Science & Technology, 24, (2015) 042001 [4] D. Marinov, M. Foucher, E. Campbell, M. Brouard, P. Chabert, and J.-P. Booth, Plasma Sources Science & Technology, in press, (2016)
• Atmospheric pressure plasma jets: high density, controllable sources of reactive species
  
  • Gibson Andrew
  • O'Niell C.
  • O'Connell D.
  • Gans T.
  , 2016. Non-thermal plasmas produced at atmospheric pressure offer unique environments for the conversion of stable molecular gases into reactive species at room temperature. As such, investigations are undergoing as to how they might be utilized in biomedical, industrial and environmental applications. A key requirement in such applications is the control and optimisation of the reactive species produced by the plasma source. The generation of reactive species at low gas temperature is possible in such plasma sources due to the lack of thermodynamic equilibrium between electrons and heavy particles. This means that electrons can be accelerated to energies on the order of several eV, sufficient to break chemical bonds and create excited species, while heavier particles remain near room temperature. This thermal non-equilibrium is typically attained using radio-frequency (rf) fields which preferentially accelerate electrons. The sensitivity of electrons to rf fields leads to the possibility to tailor the electron properties, and consequently the reactive species densities, by modifying the magnitude and shape of the voltage waveform. In this work a 1D fluid plasma model has been used to investigate the effect of changing the voltage waveform on reactive species densities in a He/O2 atmospheric pressure plasma jet. It is found that by changing the magnitude of the voltage waveform at constant frequency (either 13.56 or 40.68 MHz), the densities of atomic oxygen and ozone produced by the plasma can be controlled independently. Furthermore, changing the shape of the voltage waveform by the superimposition of the two frequencies [1] allows for enhanced production of high energy threshold reactive species, in this case metastable helium in the 23S1 state, while the densities of species with low electron energy production requirements, such as atomic oxygen, remain comparatively constant. The physical mechanisms behind these changes and the potential implications from an application perspective will be discussed. Acknowledgement: Funding is acknowledged through the LABEX Plas@Par project, ANR-11-IDEX-0004-02, UK EPSRC Manufacturing Grant (EP/K018388/1) and the York-Paris Collaborative Research Centre. References [1] C. ONeill, J. Waskoenig and T. Gans, Appl. Phys. Lett., 101, 154107 (2012)
• The role of gas kinetics and surface interaction probabilities in simulations of industrial plasma sources at low pressure
  
  • Gibson Andrew
  • Foucher Mickaël
  • Marinov Daniil
  • Chabert Pascal
  • Gans T.
  • Guerra V.
  • Kushner M.J.
  • Booth Jean-Paul
  , 2016. Non-thermal plasmas produced at low pressure are commonly used in a wide variety of industrial processing applications such as the etching and deposition of nano-scale structures in the semiconductor industry, systems for electric propulsion of spacecraft and negative ion sources for the heating of fusion-relevant plasmas. In many applications the design of processes or plasma sources is informed by self-consistent plasma simulations. These simulations require a wide variety of fundamental data as input such as electron-heavy particle collision cross sections, heavy particle reaction rate coefficients and probabilities for the reaction of plasma produced species with surfaces. The methods required, both theoretically and experimentally, to generate the above data are extremely varied and as such the degree to which these data are known for any given plasma system varies significantly from process to process. As a result a major limitation of state-of-the-art plasma simulations is the knowledge of this fundamental collision data. In this work a self-consistent 2D plasma simulation [1] is used to investigate the role of surface interaction probabilities, specifically the thermal energy accommodation coefficient and the atomic oxygen recombination probability, with regard to their influence on the plasma properties in an oxygen inductively coupled plasma (ICP) of the type commonly used in plasma etching applications. It is found that both parameters have a significant effect on the atomic oxygen flux and ion bombardment energy at the substrate holder, two key control parameters for nano-metric precision etching. Acknowledgement: Funding is acknowledged through the LABEX Plas@Par project, ANR-11-IDEX-0004-02, UK EPSRC Manufacturing Grant (EP/K018388/1) and the York-Paris Collaborative Research Centre. References (1) M. J. Kushner, J. Phys. D: Appl. Phys., 42, 194013 (2009)
• Atmospheric pressure plasmas as sources of reactive oxygen and hydrogen species for biomedical applications
  
  • Schröter Sandra
  • Gibson Andrew
  • Bredin Jérôme
  • West A.
  • Wijiaikum A.
  • Niemi K.
  • Dedrick J.
  • Foucher Mickaël
  • de Oliviera N.
  • Joyeux D.
  • Nahon L.
  • Booth Jean-Paul
  • Wagenaars E.
  • Gans T.
  • O'Connell D.
  , 2016. Cold atmospheric pressure plasmas (APPs) are known sources of reactive oxygen, nitrogen and hydrogen species(1,2), and therefore offer a great potential to be used for biomedical applications, where these species play an important role. The electrons and heavy particles in these plasmas are not in a thermal equilibrium, allowing for high electron temperatures (around a few eV), leading to the very active chemistries necessary for the production for reactive species. The gas temperature stays around room temperature, which is favourable for the treatment of biological samples. However, in order for APPs to achieve widespread usage in therapeutics, controlled production of the species of interest is essential. At atmospheric pressure, diagnostics on these reactive species are challenging, due to short particle lifetimes and significant spatial inhomogeneity, especially in the plasma effluent region, which is usually where the interaction with biological samples takes place. Additionally, impurities in the plasma source coming from ambient air can significantly change the plasma chemistry. In this work we investigate a radio-frequency (RF) atmospheric pressure plasma jet (APPJ) running in Helium (He). By introducing different levels of humidity (H2O), we can significantly change the production of several reactive species such as atomic oxygen (O), atomic hydrogen (H) and hydroxyl radicals (OH). A 0-dimensional chemical kinetics model(3) is used in order to investigate the plasma chemistry, giving insight into the plasma kinetics involving 65 species, including electrons, positive and negative ions, and ground state and excited neutral species. We also carry out experimental investigations using picosecond Two-photon Absorption Laser-Induced Fluorescence(4), vacuum ultra-violet high-resolution Fourier-Transform Absorption Spectroscopy(5), and ultra-violet Broad-Band Absorption Spectroscopy(6) to quantify O, H and OH in the plasma and compare with simulation results. We find that H and OH increase non-linearly when the H2O content of the feed gas is increased. The trend for O is strongly dependent on the concentration of air impurities present in the APPJ. The authors acknowledge support by the UK EPSRC (EP/K018388/1 & EP/H003797/1) and the York-Paris Low Temperature Plasma Collaborative Research Centre. This work was performed within the LABEX Plas@par project and received financial state aid, managed by the Agence National de la Recherche as part of the programme Investissements davenir (ANR11-IDEX-0004-02). References (1) M. G. Kong et al., New J. Phys. 2009, 11, 115012. (2) D. B. Graves, J. Phys. D: Appl. Phys. 2012, 45, 263001. (3) S. D. Stafford et al., J. Appl. Phys. 2004, 96, 2451. (4) J. Bredin et al., Picosecond-TALIF measurements of atomic oxygen in RF driven atmospheric pressure plasma jets, 67th Gaseous Electronics Conference, Raleigh, NC (Nov 2014) (5) K. Niemi et al., Appl. Phys. Lett. 2013, 103, 034102. (6) M. Foucher et al., Plasma Sources Sci. Technol. 2015, 24, 042001.
• Vibrational excitation in O<SUB>2</SUB> and Cl<SUB>2 </SUB> inductively-coupled plasmas and DC discharges
  
  • Booth Jean-Paul
  • Foucher Mickaël
  • Marinov Daniil
  • Gibson Andrew
  • Chabert Pascal
  • Annusova Adriana
  • Guerra V.
  , 2016. Low-energy electrons can interact with molecules to cause vibrational excitation with large cross-sections due to the presence of resonances. This can be important for a number of reasons. Firstly these processes can absorb significant energy from the plasma electrons, affecting the electron energy distribution and potentially (via vibration-translation (VT) energy transfer) cause substantial gas heating. Secondly, the presence of vibrationally excited molecules may significant increase the rates of reactive collisional processes, including electron dissociative attachment and electron impact dissociation into neutral atoms. However, the cross-sections of these processes are often poorly known since they are extremely difficult to measure directly, and reliable theoretical calculations are only now appearing for simple diatomic molecules. We are studying discharges in pure O2 and pure Cl2 at low pressure, using a combined experimental and modelling approach. Notably we have measured the vibrational distributions for the first time, using high-sensitivity ultra-broadband ultraviolet absorption spectroscopy. In parallel we are modelling these systems using a detailed self-consistent 0D global model.
• The role of surface interaction probabilities in reactive plasma modelling
  
  • Gibson Andrew
  • Foucher Mickaël
  • Marinov Daniil
  • Chabert Pascal
  • Gans T.
  • Guerra V.
  • Kushner M.J.
  • Booth Jean-Paul
  , 2016. This work concerns the role played by atomic species surface recombination coefficients and thermal energy accommodation coefficients at surfaces in plasmas produced in oxygen and chlorine. It is shown that these quantities significantly affect the dissociation fraction and neutral gas temperature predicted by self-consistent plasma simulations of an inductively coupled plasma source, and therefore have a major effect on the overall plasma equilibrium. By comparison of the model with experimental measurements the values of both surface interaction probabilities are derived as a function of neutral gas pressure.
• Plasma-surface interaction: Heterogeneous processes of atmospheric gases
  
  • Marinov Daniil
  • Guaitella Olivier
  • Guerra V.
  • Booth Jean-Paul
  • Rousseau Antoine
  , 2016. Surface kinetics plays a central role in many plasma applications ranging from low pressure technological plasmas to plasma-catalyst systems and thermal protection for space re-entry. From the microscopic perspective, heterogeneous reactions in plasmas involve multiple elementary steps (adsorption, desorption, diffusion, recombination) that usually take place on poorly characterized disordered surfaces. Regardless of the great number of works devoted to the study of plasma-surface interactions, the underlying reaction mechanisms are still not fully understood and a lot of uncertainty still remains. In this paper, we summarize our recent experimental studies of the kinetics of adsorption, desorption and recombination of oxygen and nitrogen atoms on dielectric surfaces in contact with low pressure plasmas. Obtained results challenge existing models of atomic recombination on surfaces and stimulate the development of new models. For example, it is found that adsorbed atoms exhibit a distribution of reactivity which has to be taken into account in simulations. We demonstrate that Dynamic Monte Carlo techniques are particularly suited for simulation of heterogeneous processes on realistic disordered surfaces.
• Highly vibrationally excited O<SUB>2</SUB> molecules in low pressure oxygen plasmas: 1. Broad-band absorption spectroscopy
  
  • Marinov Daniil
  • Foucher Mickaël
  • Guaitella Olivier
  • Engeln Richard
  • Chabert Pascal
  • Guerra V.
  • Booth Jean-Paul
  , 2016. The kinetics of vibrationally excited O2 molecules in low pressure oxygen plasmas is studied using broadband absorption spectroscopy. A high-sensitivity setup based on a laser-plasma light source, achromatic optics and an aberration-corrected spectrograph allows the measurement of absorbances as low as 10-5. Two discharge types are investigated: a radiofrequency ICP (p = 10 80 mTorr, Prf = 100500 W) and a dc glow discharge (p = 100 4000 mTorr, I = 10 50 mA). Multiple absorption bands are detected across the spectral range 200-440nm, corresponding to the Schumann-Runge transitions of O2 molecules. Despite very different plasmas parameters, both discharges demonstrate very similar densities of excited O2(v) (v>3) . The measured VDFs in levels v = (4 19 can be approximated by a bi-Maxwellian distribution with the tail temperature as high as 6000 K.
• Modelling of tailored ion energy distributions for plasma processing applications
  
  • Diomede P.
  • Lafleur Trevor
  • Booth Jean-Paul
  • Longo S.
  • Economou D. J.
  , 2016. Several modeling techniques were employed to calculate ion energy distributions on plasma electrodes under different configurations used to obtain a desired (tailored) distribution. In particular, hybrid Particle in Cell with Monte Carlo Collisions (PIC-MCC)/fluid simulations were performed in a combined computationalexperimental study of capacitively coupled plasmas sustained by tailored voltage waveforms, PIC/MCC simulations were employed to study pulsed plasmas with the application of a synchronous bias on a boundary electrode in the afterglow and a semianalytic model was developed to study plasmas sustained by independent sources in contact with a substrate electrode with a tailored bias voltage waveform.
• Experimental and simulation study of capacitively coupled oxygen discharges driven by tailored voltage waveforms
  
  • Derzsi A.
  • Bruneau Bastien
  • Lafleur Trevor
  • Booth Jean-Paul
  • Korolov Ihor
  • Gibson Andrew
  • Gans T.
  • Donko Z.
  , 2016. We report experimental and particle-based kinetic simulation studies of low-pressure capacitively coupled oxygen plasmas driven by tailored voltage waveforms. Experimental results on the dc self-bias voltage, the electrical power deposition, the flux density and flux-energy distribution of positive ions, as well as spatiotemporal distribution of the plasma emission are compared with simulation data for a wide range of operating conditions. A good agreement between simulation and experiment is found, which shows that the collision-reaction model underlying the simulations describes reasonably the complicated chemistry of oxygen plasmas.