REFERENCES & CITATIONS

My products are used by many companies, research institutes and academic laboratories. Here are some of my customers.

 

My products have been used to perform electrical measurements in many experimental research studies dealing with low pressure CCP and ICP, or atmospheric pressure plasma jets. Here is a list of 32 articles citing my products and published  by my customers in peer-reviewed journals.

 

2024

 

[32] Ozone production by an He+O₂ radio-frequency atmospheric pressure plasma jet driven by tailored voltage waveforms

Benjamin Harris, James Peter Dedrick, Kari Niemi and Erik Wagenaars

Department of Physics, University of York, Heslington, York, YO10 5DD, United Kingdom of Great Britain and Northern Ireland

 

Abstract

Atmospheric pressure plasma jets are efficient sources of reactive oxygen and nitrogen species with potential applications in medicine, materials processing, green industry and agriculture. However, selective control over the production of reactive species presents an ongoing challenge and a barrier to the widespread uptake of these devices in applications. This study therefore investigates the production of ozone by a radio-frequency plasma jet driven with tailored voltage waveforms composed of up to five consecutive harmonics, with a fundamental frequency of 13.56MHz. The plasma is supplied with helium with small admixtures (0.1% - 1.0%) of oxygen gas. The ozone density in the far effluent is measured with Fourier transform infrared spectroscopy and the gas temperature in the plasma channel is determined with optical emission spectroscopy. Voltage waveform tailoring is found to enhance the ozone density in the far effluent of the plasma jet in comparison to operation with single-frequency voltage waveforms. Increasing the number of applied harmonics in the driving voltage waveform for a fixed peak-to-peak voltage enhances the ozone density but significantly increases the gas temperature within the plasma channel. Meanwhile, increasing the number of applied harmonics while maintaining a constant RF power deposition allows the density of ozone in the effluent to be increased by up to a factor of 4 relative to single-frequency operation, up to a maximum density of 5.7×10¹⁴ cm^-3, without any significant change to the gas temperature. This work highlights that tailored voltage waveforms can be used to control the density of ozone delivered through the plasma effluent, marking an important step towards realising the potential of these plasmas for applications.

 

Source: Harris et al., Plasma Sources Sci. Technol. (Accepted for publication) https://www.doi.org/10.1088/1361-6595/ad6587

 

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[31] Self-consistent calculation of the optical emission spectrum of an argon capacitively coupled plasma based on the coupling of particle simulation with a collisional-radiative model

Zoltan Donkó¹, Tsanko Vaskov Tsankov², Peter Hartmann³, Fatima Jenina Tolentino Arellano⁴, Uwe Czarnetzki⁵ and Satoshi Hamaguchi⁶

¹ Wigner Research Centre for Physics, Konkoly-Thege Miklos str. 29-33., Budapest, Budapest, 1121, Hungary
² Institute for Plasma and Atomic Physics, Ruhr University Bochum, Universitätsstraße 150, NCDF 04/297, Bochum, NRW, 44780, Germany
³ Complex Fluids, Wigner Research Centre for Physics, Wigner FK, Konkoly-Thege M. 29-33, Budapest, 1121, Hungary
⁴ Division of Precision Science and Technology and Applied Physics, Osaka University Graduate School of Engineering Division of Precision Science and Technology and Applied Physics, A12 Bldg. 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
⁵ Institut fur Experimentalphysik V, Ruhr-Universitaet-Bochum, Plasma- und Atomphysik , NB 05/692, D-44780 Bochum, Bochum, 44801, Germany
⁶ Center for Atomic and Molecular Technologies, Osaka University, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-city, Osaka 565-0871Japan, Suita, 565-0871, Japan

 

Abstract

We report the development of a computational framework for the calculation of the optical emission spectrum of a low-pressure argon capacitively coupled plasma, which is based on the coupling of a particle-in-cell / Monte Carlo collision simulation code with a diffusion-reaction-radiation code for Ar I excited levels. In this framework, the particle simulation provides the rates of the direct and stepwise electron-impact excitation and electron-impact de-excitation for 30 excited levels, as well as the rates of electron-impact direct and stepwise ionization. These rates are used in the solutions of the diffusion equations of the excited species in the second code, along with the radiative rates between a high number of Ar I transitions. The calculations also consider pooling ionization, quenching reactions, and radial diffusion losses. The electron energy distribution function is computed self-consistently, and the calculations reproduce reasonably well the experimentally measured optical emission spectrum of a symmetric capacitively coupled plasma source operated at 13.56MHz with 300V peak-to-peak voltage, in the 2-100Pa pressure range. The accuracy of the approach appears to be limited by the one-dimensional nature of the model, the treatment of the radiation trapping through the use of escape factors, and the effects of radiative cascades from higher excited levels not taken into account in the model.

 

Source: Donkó et al., J. Phys. D: Appl. Phys. (Accepted for publication) https://doi.org/10.1088/1361-6463/ad4e42

2023

 

[30] A novel and efficient dual-antenna micro plasma thruster

Jin-Heng Zhang^1,2, Xin Yang¹, Lei Chang³, Yong Wang¹, Ying Xia^1,2, Dong Jing^1,2, Hai-Shan Zhou^1,2, Guang-Nan Luo^1,2

¹ Institute of Plasma Physics, HFIPS, Chinese Academy of Sciences, Hefei, 230031, China

² University of Science and Technology of China, Hefei, 230026, China

³ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing, 400044, China

 

Abstract

A novel dual-antenna micro plasma thruster (DMPT) driven by radio-frequency (rf) power supply is proposed and characterized experimentally. The Langmuir probe (LP) and the retarding potential analyzer (RPA) are applied to measure the plasma parameters. The results show that compared to the single-antenna, the dual-antenna yields higher electron density, electron temperature, and ion energy. The measurements from the rf I–V probe indicate that the power coupling efficiency for the dual-antenna is about 2.6 times higher than that for the single-antenna. The plasma potential drop in the plume of the DMPT is the reason for the formation of ion beam. The neutral gas temperature is measured by rovibrational ban matching of the first negative band system of ionic nitrogen (N₂⁺) for operating powers of 20 W up to 100 W. The total thrust of the DMPT has been calculated by the sum of the ion thrust and the neutral gas thrust. The total thrust at 100 sccm argon flow rate and 100 W rf power is ∼2.23 mN, which indicates an up to 168% thrust gain compared to the cold gas thrust, and a significant 11% total thrust is attributed to the ions’ electrostatic acceleration. The specific impulse and thruster efficiency at the above experimental conditions are ∼76 s and ∼0.8%, respectively. These initial results show that the dual-antenna scheme has better performance and is more promising than the traditional single-antenna design for electrodeless micro-electric propulsion. This novel and efficient micro plasma thruster is particularly useful for cubic satellites and scientific experiments in space (such as gravitational wave detection) which require gesture and orbit control of great precision.

 

Source: Zhang et al. Acta Astronautica, Volume 208, Pages 15-26 (2023) https://doi.org/10.1016/j.actaastro.2023.03.033

 

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[29] Fast O atom exchange diagnosed by isotopic tracing as a probe of excited states in nonequilibrium CO₂–CO–O₂ plasmas

Ana Sofia Morillo-Candas¹, Bart L. M. Klarenaar², Vasco Guerra³, and Olivier Guaitella¹

¹ LPP, CNRS, École Polytechnique, Sorbonne Université, Université Paris-Saclay, IP-Paris, 91128,Palaiseau, France

² Department of Applied Physics, EPG, Eindhoven University of Technology, Eindhoven, The Netherlands

³ Instituto de Plasmas e Fus ̃ao Nuclear, Instituto Superior Técnico—Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal

 

Abstract

Oxygen exchange kinetics in CO₂–O₂ and CO–O₂ low-temperature RF plasmas are investigated by isotope tracing. Starting from C¹⁶O₂–¹⁸O₂and C¹⁶O–¹⁸O₂ gas mixtures, we observe a fast incorporation of ¹⁸O into CO and CO₂ that cannot be explained solely by chemical reactions. By comparing our experimental results with those of a kinetic model, we demonstrate that these fast exchange processes can be partly explained by collisions of electronically excited atomic oxygen, O(¹D), with CO₂ and CO molecules. Isotope labeling emerges therefore as a potential tool to trace O(¹D) states, a distinctive species of the dissociation path in CO₂ plasmas, critical to assessing the efficiency of the CO₂ dissociation process. Oxygen atom exchange in collisions between ground-state atomic oxygen and vibrationally excited CO is revealed as another important path of isotope incorporation in nonequilibrium CO₂–CO–O₂ gas mixtures. This mechanism brings information about the vibrational kinetics in the discharge and could potentially contribute to the anomalous isotope enrichment in other out-of-equilibrium conditions, such as in the Earth or Mars atmospheres.

 

Source: Morillo-Candas et al. The Journal of Physical Chemistry C Article ASAP (2023) https://doi.org/10.1021/acs.jpcc.2c08493

 

2022

 

[28] Radio-Frequency linear plasma process for heating of metallic surfaces

Sara Alhomsi¹, Gérard Bauville¹, Stéphane Pasquiers¹, and Tiberiu Minea¹

¹ Laboratoire de Physique des Gaz et des Plasmas, Université Paris-Saclay, CNRS, F-91405 Orsay Cedex, France

 

Abstract

Innovative plasma processing provides localized heating of grounded metallic surfaces under low pressure. Here we exploit a specifically designed Cylindrical Capacitive Coupled Discharge (CCCD), Radio-Frequency (RF) powering the inner cylinder and keeping the outer one grounded. Both cylinders have a longitudinal slit. These slits are aligned to each other and faced to a grounded metallic plate (target) placed underneath. When RF power is applied, the plasma glows inside the inner tube cavity, but it leaks out through the slits and spreads onto the surface of the target as a linear slab of plasma. The parametric study of the process focuses on the nature of gas (Argon and Nitrogen), the pressure range (0.8–50 mbar), the RF power (100–1800 W), and the cylinders/plate gap distance (1 or 8 mm). The optimized operation of the plasma system provides the highest ion production in front of the plate. The fastest heating condition increases the target temperature to 614 °C within 1s exposure to plasma. Furthermore, simulations using the Plasimo™ software package gives several other essential parameters such as the ion flux and their energy carried to the plate. Experimental and numerical results are in good agreement. This device has demonstrated the proof-of-principle for plasma heating of metallic surfaces.

 

Source: Alhomsi et al. Vacuum, 111571 (2022) https://doi.org/10.1016/j.vacuum.2022.111571

 

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[27] Evolution of the bulk electric field in capacitively coupled argon plasmas at intermediate pressures

Mate Vass¹, Sebastian Wilczek¹, Aranka Derzsi², Benedek Horváth², Peter Hartmann² and Zoltan Donkó²

¹ Ruhr-Universität Bochum, Universitätsstraße 150, Bochum, 44801, Germany
² Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly-Thege Miklós str. 29-33, Hungary

 

Abstract

The physical characteristics of an argon discharge excited by a single-frequency harmonic waveform in the low-intermediate pressure regime (5-250 Pa) are investigated using Particle-in-Cell/Monte Carlo Collisions simulations. It is found that, when the pressure is increased, a non-negligible bulk electric field develops due to the presence of a ``passive bulk'', where a plateau of constant electron density forms. As the pressure is increased, the ionization in the bulk region decreases (due to the shrinking of the energy relaxation length of electrons accelerated within the sheaths and at the sheath edges), while the excitation rate increases (due to the increase of the bulk electric field). Using the Fourier spectrum of the discharge current, the phase shift between the current and the driving voltage waveform is calculated, which shows that the plasma gets more resistive in this regime. The phase shift and the (wavelength-integrated) intensity of the optical emission from the plasma are also obtained experimentally. The good qualitative agreement of these data with the computed characteristics verifies the simulation model. Using the Boltzmann term analysis method, we find that the bulk electric field is an Ohmic field and that the peculiar shape of the plasma density profile is partially a consequence of the spatio-temporal distribution of the ambipolar electric field.

 

Source: Vass et al. Plasma Sources Sci. Technol. 31 045017 (2022) https://doi.org/10.1088/1361-6595/ac6361

 

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[26] Impedance Characteristic Analysis and Preliminary Experimental Results of a High-Power RF Plasma Source

Puqiong Yang¹, Bo Liu², Caichao Jiang², Xin Yang², Jianglong Wei², Yahong Xie², Yongjian Xu², Lizhen Liang², Yuanzhe Zhao², Yuanlai Xie², Jinxin Wang² and Chundong Hu²

¹ Southwest Institute of Physics, Chengdu, China / School of Electrical Engineering, University of South China, Hengyang, China

² Institute of Plasma Physics, HFIPS, Chinese Academy of Sciences, Hefei, China

 

Abstract

To study the characteristics of radio frequency (RF) power coupling, RF plasma diagnostics, actively cooled tube, and negative ion production, a plasma source was designed as a small-scale test facility. The matching network was carefully designed and successfully applied to the 2-MHz RF plasma source. In this article, the design method of the matching unit will be presented; with the assistance of this matching unit, the RF plasma source was successfully lit and the reflected power was reduced to a very low level. A V-I probe was installed in front of or in the rear of the matching network, respectively, to in situ measure the RF voltage, current, and phase angle. The equivalent resistance of the RF plasma source was analyzed in detail. The RF power coupling efficiency was derived in two different methods, and the relationship between the coupling efficiency and the equivalent resistance of the plasma source is verified. At the same time, the equivalent resistance of the plasma source was also collected to optimize the matching unit.

 

Source: Yang et al. IEEE Transactions on Plasma Science (Volume: 50, Issue: 4, April 2022) https://doi.org/10.1109/TPS.2022.3154397

2021

 

[25] Experimental and numerical study of the plasma in coaxial capacitive coupled radio frequency discharge

Sara Alhomsi¹, Gérard Bauville¹, Stéphane Pasquiers¹, and Tiberiu Minea¹

¹ Laboratoire de Physique des Gaz et des Plasmas, Université Paris-Saclay, CNRS, F-91405 Orsay Cedex, France

 

Abstract

A coaxial configuration of discharge is proposed for plasma surface treatment and possibly other applications. The reactor is based on a cylindrical structure, with the inner cylinder radio frequency powered (RF, 13.56 MHz) and the outer cylinder grounded, playing the role of a guard ring. The charged species can escape from the inner cavity through two longitudinal slits made in both cylinders, aligned to each other, and producing a linear slab of plasma. Hence, it is possible to project the plasma directly onto a surface placed under the slits, called external plate. The operation of this device is uniform and stable in argon for a large pressure range (0.8–50 mbar). Furthermore, simulations using the Plasimo™ software package were performed to evaluate the plasma parameters and to explain the experimental results. The ion flux on the surface exposed to this plasma increases when RF power increases, and the pressure or gap distance to the plate decreases. This cylindrical capacitive coupled plasma configuration can be very effective for surface treatment of different materials (conductors or insulators) on large area (when the plate or the system is moving perpendicular to the slits) due to energetic ions and active species released from the plasma.

 

Source: Alhomsi et al. Journal of Applied Physics 130, 123302 (2021) https://doi.org/10.1063/5.0060781

2020

 

[24] Decoupling ion energy and flux in intermediate pressure capacitively coupled plasmas via tailored voltage waveforms

Scott James Doyle¹, Andrew Robert Gibson², Rod W Boswell³, Christine Charles⁴ and James Peter Dedrick⁵

¹ Dept. of Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, Sevilla, Andalucía, Spain
² Electrical Engineering and Plasma Technology, Ruhr Univerversitat Bochum, Bochum, Germany
³ Space Plasma, Power and Propulsion Laboratory, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory, Australia
⁴ Space Plasma, Space Plasma, Power and Propulsion Laboratory, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory, Australia
⁵ York Plasma Institute, University of York, York, North Yorkshire, United Kingdom

 

Abstract

The discrete control of ion energy and flux is of increasing importance to industrially relevant plasma sources. The ion energy distribution functions (IEDFs) and net ion flux incident upon material surfaces in intermediate pressure (~ 133 Pa, 1 Torr) radio-frequency capacitively coupled plasmas (rf CCPs) are coupled to the spatio-temporal sheath dynamics and resulting phase-averaged sheath potential. For single frequency driven discharges this co-dependence of ion energy and flux on the sheath potential limits the range of accessible operating regimes. In this work, experimentally benchmarked 2D fluid/Monte-Carlo simulations are employed to demonstrate quasi-independent control of the ion flux and IEDF incident upon plasma facing surfaces in a collisional (~200 Pa, 1.5 Torr argon) rf hollow cathode discharge through the application of multi-harmonic (n > 2) tailored voltage waveforms. The application of variable phase offset n = 5 tailored voltage waveforms affords a significant degree of control over the ion flux Γ_Ar+ and mean ion energy ε_Ar+, modulating each by factors of 2.9 and 1.6, respectively as compared to 1.8 and 1.6, achieved via n=2 dual-frequency voltage waveforms. The disparate modulations achieved employing n=5 tailored voltage waveforms demonstrate a significant degree of independent control over the mean ion energy and ion flux for collisional conditions, enabling access to a wider range of operational regimes. Maximising the extent to which ion energy and flux may be independently controlled enables improvements to plasma sources for technological applications such as plasma assisted material manufacture and spacecraft propulsion.

 

Source: Doyle et al. Plasma Sources Sci. Technol. 29 124002 (2020) https://doi.org/10.1088/1361-6595/abc82f

 

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[23] On the electron density of atmospheric pressure radio frequency dielectric barrier discharge and discharge with bare electrode

Lei Wang¹, Nikola Cvetanovic², Bratislav M. Obradović³, Eusebiu-Rosini Ionita⁴, Gheorghe Dinescu⁵, Christophe Leys¹ and Anton Yu Nikiforov¹

¹ Department of Applied Physics, Ghent University, Ghent, Belgium
² Faculty of Transport and Traffic Engineering, University of Belgrade, Serbia
³ Faculty of Physics, University of Belgrade, Serbia
⁴ National Institute for Laser Plasma and Radiation Physics, Magurele, Romania
⁵ Low Temperature Plasma Physics, National Institute for Laser Plasma and Radiation Physics, Bucharest, Romania

 

Abstract

Atmospheric pressure radio frequency helium plasma with two different designs: dielectric barrier discharge (DBD) and discharge with bare electrode (DBE) were investigated by means of optical emission spectroscopy. Both DBD and DBE can work at relatively low temperature and produce abundant electrons facilitating production of reactive species through electron-impact reactions. Stark broadening method of Hydrogen Balmer beta (H_β) line was employed to analyze the electron density. When electron density is below 10²⁰ m^-3, fine-structure fitting was used to improve the accuracy of electron density estimation. At power ranged 4-20 W, DBD and DBE showed electron density 4.1-6.1 × 10¹⁹ m^-3, and 3.6-8.6 × 10¹⁹ m^-3, respectively. The DBD is more suitable than DBE for biomedical applications due to the wider working power range and lower gas temperature in the range of 316-344 K, depending on the power.

 

Source: Wang et al. Jpn. J. Appl. Phys. 59 SHHB01 (2020) https://doi.org/10.7567/1347-4065/ab5d74

 

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[22] N₂–H₂ capacitively coupled radio-frequency discharges at low pressure. Part I. Experimental results: effect of the H₂ amount on electrons, positive ions and ammonia formation

Audrey Chatain^1,2, Miguel Jiménez-Redondo³, Ludovic Vettier¹, Olivier Guaitella², Nathalie Carrasco¹, Luis Lemos Alves⁴, Luis Marques³ and Guy Cernogora¹

¹ Université Paris-Saclay, UVSQ, CNRS, LATMOS, Guyancourt, France
² LPP, Ecole polytechnique, Sorbonne Université, Institut Polytechnique de Paris, CNRS, Palaiseau, France
³ Centro de Física das Universidades do Minho e do Porto, Universidade do Minho, 4710-057, Braga, Portugal
⁴ Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Univ. Técnica de Lisboa, Lisboa, Portugal

 

Abstract

The mixing of N₂ with H₂ leads to very different plasmas from pure N₂ and H₂ plasma discharges. Numerous issues are therefore raised involving the processes leading to ammonia (NH₃) formation. The aim of this work is to better characterize capacitively-coupled radiofrequency plasma discharges in N₂ with few percents of H₂ (up to 5%), at low pressure (0.3–1 mbar) and low coupled power (3–13 W). Both experimental measurements and numerical simulations are performed. For clarity, we separated the results in two complementary parts. The actual one (first part), presents the details on the experimental measurements, while the second focuses on the simulation, a hybrid model combining a 2D fluid module and a 0D kinetic module. Electron density is measured by a resonant cavity method. It varies from 0.4 to 5 × 10⁹ cm^-3, corresponding to ionization degrees from 2 × 10^-8 to 4 × 10^-7. Ammonia density is quantified by combining IR absorption and mass spectrometry. It increases linearly with the amount of H₂ (up to 3 × 10¹³ cm^-3 at 5% H₂). On the contrary, it is constant with pressure, which suggests the dominance of surface processes on the formation of ammonia. Positive ions are measured by mass spectrometry. Nitrogen-bearing ions are hydrogenated by the injection of H₂, N₂H⁺ being the major ion as soon as the amount of H₂ is >1%. The increase of pressure leads to an increase of secondary ions formed by ion/radical–neutral collisions (ex: N₂H⁺, NH₄⁺, H₃⁺), while an increase of the coupled power favours ions formed by direct ionization (ex: N₂⁺, NH₃⁺, H₂⁺).

 

Source: Chatain et al. Plasma Sources Sci. Technol. 29 085019 (2020),  https://doi.org/10.1088/1361-6595/ab9b1a

 

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[21] Time Evolution of the Dissociation Fraction in rf CO₂ Plasmas: Impact and Nature of Back-Reaction Mechanisms

Ana Sofia Morillo-Candas¹, Vasco Guerra² and Olivier Guaitella¹

¹ LPP, CNRS, École Polytechnique, Univ. Paris-sud, Sorbonne Universités, 91128 Palaiseau, France

² Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal

 

Abstract

The time evolution of the dissociation fraction in a pulsed radio frequency (rf) CO₂ discharge is studied by infrared absorption. A large parametric study performed in a closed reactor brings valuable information about both dissociation and recombination processes. The CO₂ conversion shows a time evolution initially controlled by electron impact dissociation. For longer plasma-on times, the dissociation fraction reaches a steady-state that corresponds to a balance between dissociation processes and back-reaction mechanisms. The characteristic times of vibrational and rotational excitation of CO and CO₂ are measured during a single plasma pulse. The dependence of the CO₂ conversion as a function of pulse duration and frequency is then analyzed, showing the influence of the plasma excitation conditions on the back-reaction mechanisms. The study of CO₂–O₂ and CO–O₂ gas mixtures gives further insight into the impact of the oxygen content in these mechanisms. The global back-reaction rate observed in these experiments is compared with calculated values from rate coefficients available in the literature. The experimental results and preliminary calculations reveal a key role of molecular oxygen and of the metastable electronically excited state CO(a³Π_r) in the back-reaction. Competing processes involving vibrational excited CO are not dominant in our discharge conditions but may become relevant at slightly higher vibrational temperatures.

 

Source: Morillo-Candas et al. J. Phys. Chem. C 2020, 124, 32, 17459–17475 (2020), https://doi.org/10.1021/acs.jpcc.0c03354

2019

 

[20] Investigation of atmospheric pressure RF discharge with coexisting α and γ -modes

Lei Wang¹, Nikola Cvetanovic², Bratislav M. Obradović³, Gheorghe Dinescu⁴, Christophe Leys¹ and Anton Yu Nikiforov¹

¹ Department of Applied Physics, Ghent University, Ghent, Belgium
² Faculty of Transport and Traffic Engineering, University of Belgrade, Serbia
³ Faculty of Physics, University of Belgrade, Serbia
⁴ Low Temperature Plasma Physics, National Institute for Laser Plasma and Radiation Physics, Bucharest, Romania

 

Abstract

An atmospheric pressure radio frequency discharge working at coexistence of α and γ-modes was investigated using electrical and optical measurements. The voltage and current characteristics showed a phase shift which is typical for α mode discharge. Time resolved discharge patterns were captured at a condition favorable for the coexistence of α and γ-modes to assist in analyzing the working mode. Spectral line profile of HeI line at 492.19 nm and its forbidden counterpart was recorded and analyzed to estimate the electric field distribution near the instantaneous cathode. The combined spectroscopic and imaging measurement showed the simultaneous presence of both modes in the plasma volume at certain conditions. The strong He I line Stark broadening and consecutive analysis indicated a presence of a short plasma sheath with a strong electric field, characteristic for γ-mode, whereas a long extending low-field region was attributed to a presence of simultaneous α mode. The electric field analysis method presented here can be used in a case where a very thin plasma sheath exists which is often detected in electrical discharges sustained at atmospheric pressure.

 

Source: Lei Wang et al. Plasma Sources Sci. Technol. 28 055010 (2019),  https://doi.org/10.1088/1361-6595/ab199e

 

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[19] Experimental demonstration of multifrequency impedance matching for tailored voltage waveform plasmas

Junkang Wang¹, Sebastien Dine², Jean-Paul Booth³, and Erik V. Johnson¹

¹ LPICM, CNRS, École Polytechnique, 91128 Palaiseau, France
² SOLAYL SAS, 91400 Orsay, France
³ LPP, CNRS, École Polytechnique, UPMC Univ. Paris-sud, Sorbonne Universités, 91128 Palaiseau, France

 

Abstract

Driving radiofrequency capacitively coupled plasmas by multiharmonic tailored voltage waveforms (TVWs) has been shown to allow considerable control over various plasma properties for surface processing applications. However, industrial adoption of this technology would benefit from more efficient solutions to the challenge of impedance matching the radiofrequency power source to the load simultaneously at multiple harmonic frequencies. The authors report on the design and demonstration of a simple, practical multifrequency matchbox (MFMB) based on a network of LC resonant circuits. The performance of the matchbox was quantified in terms of a range of matchable impedances (when matching a single frequency at a time), as well as for the independence of each match to changes at adjacent harmonics. The effectiveness of the MFMB was demonstrated experimentally on an Ar plasma excited by a three-frequency TVW with a fundamental frequency of 13.56 MHz. Under the plasma conditions studied, the power coupling efficiency (at the generator output) was increased from less than 40% (without impedance matching) to between 80% and 99% for the different exciting frequencies.

 

Source: Wang et al. Journal of Vacuum Science & Technology A 37, 021303 (2019), https://doi.org/10.1116/1.5056205

2018

 

[18] New radio-frequency setup for studying large 2D complex plasma crystals

V. Nosenko, J. Meyer, S. K. Zhdanov, and H. M. Thomas

Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), D-82234 Weßling, Germany

 

Abstract

Complex plasma crystals are popular model systems where various plasma-specific or generic phenomena can be studied at the level of individual particles. Addressing the growing need for larger two-dimensional (2D) plasma crystals, a new plasma setup was built at the DLR Institute of Materials Physics in Space. The setup allows obtaining larger than before, highly ordered 2D plasma crystals and exploring new parameter ranges. It is based on a relatively large (90 cm in diameter) vacuum chamber where a capacitively coupled radio-frequency discharge is used to levitate polymer microparticles. The discharge is created between the lower rf electrode and the grounded chamber walls, the particles levitate in the plasma (pre)sheath above the electrode and are observed by video microscopy through the large top glass window and through the side windows. The first observations of plasma crystals in the new setup are reported.

 

Source: AIP Advances 8, 125303 (2018)  https://doi.org/10.1063/1.5064457

 

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[17] Spatio-temporal plasma heating mechanisms in a radio-frequency electrothermal microthruster

Scott James Doyle¹ , Andrew Robert Gibson¹ , Jason Flatt¹ , Teck Seng Ho² , Rod W Boswell² , Christine Charles² , Peng Tian³ , Mark J Kushner³ and James Peter Dedrick¹

¹ York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DD, UK
² Plasma Research Laboratory, School of Physical Sciences and Engineering, The Australian National University, Canberra, Australia
³ University of Michigan, Dept. of Electrical and Computer Engineering, Ann Arbor, MI 48109-2122, Michigan, USA

 

Abstract

Low power micro-propulsion sources are currently being developed for a variety of space missions. Electrothermal plasma thrusters are of specific interest as they enable spatial control of the power deposition to the propellant gas. Understanding the mechanisms whereby electrical power is coupled to the propellant will allow for optimisation of the heating and fuel efficiencies of electrothermal sources. Previous studies of radio-frequency (rf) plasmas have shown a dependence of the gas and electron heating mechanisms on the local collisionality. This is of particular importance to thrusters due to the large pressure gradients that exist between the inlet and outlet when expanding into vacuum. In this work, phase-resolved optical emission spectroscopy and numerical simulations were employed to study plasma heating in an asymmetric rf (13.56 MHz) electrothermal microthruster operating in argon between 186 - 226 Pa (1.4 - 1.7 Torr) plenum pressure, and between 130 - 450 V (0.2 - 5 W). Three distinct peaks in the phase-resolved Ar(2p 1 ) electron impact excitation rate were observed, arising from: sheath collapse heating, sheath expansion heating and heating via secondary electron collisions. These experimental findings were corroborated with the results of 2D fluid/Monte-Carlo simulations performed using the Hybrid Plasma Equipment Model (HPEM). The influence of each mechanism with respect to position within the plasma source during an α-γ mode transition, where plasma heating is driven via bulk and sheath heating, respectively, was investigated. Sheath dynamics were found to dictate the electron heating at the inlet and outlet, as distinct from the centre of the thruster where interactions of secondary electrons were found to be the dominant electron heating mechanism. Optimisation of the heating mechanisms that contribute to the effective exhaust temperature will directly benefit electrothermal thrusters used on miniaturized satellite platforms.

 

Source: Doyle et al. Plasma Sources Sci. Technol. 27 085011 (2017)  https://doi.org/10.1088/1361-6595/aad79a

 

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[16] Excitation of Ar, O₂, and SF₆/O₂ plasma discharges using tailored voltage waveforms: Control of surface ion bombardment energy and determination of dominant electron excitation mode

Guillaume Fischer¹, Karim Ouaras², Etienne Drahi³, Bastien Bruneau² and Erik V Johnson²

¹ Institut Photovoltaïque d'Ile-de-France (IPVF), 30 RD128, 91120 Palaiseau, France
² LPICM, CNRS, Ecole polytechnique, Université Paris-Saclay, 91128 Palaiseau, France
³ Total SA Renewables, 92069 Paris La Défense Cedex, France

 

Abstract

Using Tailored Voltage Waveforms (TVWs) to excite a low pressure, low-temperature plasma discharge, we compare the behavior of three gas mixtures, namely Ar, O₂, and SF₆O₂ mixtures, the last of which is currently used for the plasma-texturing of silicon wafers for photovoltaics. The primary goal of using TVWs is to control the ion bombardment energy at the surface of the wafer, and this control is demonstrated through retarding field energy analyzer (RFEA) measurements. However, the complicated electrical response of the plasma to such waveforms makes the ab-initio prediction of the ion energy difficult, although by using said RFEA measurements, we show that it can be done approximately by using measured electrical data. In addition, we utilize the response of the plasma to mirror-image "sawtooth" waveforms as a predictor of the dominant electron heating mode (α or drift-ambipolar, DA). At equivalent pressures and coupled powers, the Ar and O₂ mixtures always display behavior associated with electropositive plasmas (a solely α heating mode). However, with the addition of SF₆ to an O₂ gas flow, a transition can be observed towards a behavior associated with a more electronegative plasma (i.e. a dominant DA heating mode). This crossover in the dominant heating mode is observed through the relative self-bias voltage for each type of sawtooth waveform, and is therefore a useful predictor of the dominant electron heating mode in low pressure, cold plasma discharges.

 

Source: G. Fischer et al. Plasma Sources Sci. Technol. 27 074003 (2018)  https://doi.org/10.1088/1361-6595/aaca05

 

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[15] Influence of the RF electrode cleanliness on plasma characteristics and dust-particle generation in methane dusty plasmas

I. Géraud-Grenier¹, W. Desdions¹, F. Faubert², M. Mikikian³, and V. Massereau-Guilbaud¹

¹ Groupe de Recherches sur l’Energétique des Milieux Ionisés (GREMI), UMR 7344 CNRS/Université d’Orléans, Site de Bourges, 63 avenue de Lattre de Tassigny, 18020 Bourges Cedex, France
² Institut Universitaire de Technologie (IUT), 63 avenue de Lattre de Tassigny, 18020 Bourges Cedex, France
³ Groupe de Recherches sur l’Energétique des Milieux Ionisés (GREMI), UMR 7344 CNRS/Université d’Orléans, 14 route d’Issoudun, BP 6744, 45067 Orléans Cedex 2, France

 

Abstract

The methane decomposition in a planar RF discharge (13.56 MHz) leads both to a dust-particle generation in the plasma bulk and to a coating growth on the electrodes. Growing dust-particles fall onto the grounded electrode when they are too heavy. Thus, at the end of the experiment, the grounded electrode is covered by a coating and by fallen dust-particles. During the dust-particle growth, the negative DC self-bias voltage (V_DC) increases because fewer electrons reach the RF electrode, leading to a more resistive plasma and to changes in the plasma chemical composition. In this paper, the cleanliness influence of the RF electrode on the dust-particle growth, on the plasma characteristics and composition is investigated. A cleanliness electrode is an electrode without coating and dust-particles on its surface at the beginning of the experiment.

 

Source: Géraud-Grenier et al. AIP Conference Proceedings 1925, 020024 (2018)  https://doi.org/10.1063/1.5020412

 

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[14] Powder free PECVD epitaxial silicon by plasma pulsing or increasing the growth temperature

Wanghua Chen, Jean-Luc Maurice, Jean-Charles Vanel and Pere Roca i Cabarrocas

LPICM, CNRS, Ecole Polytechnique, 91128 Palaiseau, France

 

Abstract

Crystalline silicon thin films are promising candidates for low cost and flexible photovoltaics. Among various synthesis techniques, epitaxial growth via low temperature plasma-enhanced chemical vapor deposition is an interesting choice because of two low temperature related benefits: low thermal budget and better doping profile control. However, increasing the growth rate is a tricky issue because the agglomeration of clusters required for epitaxy leads to powder formation in the plasma. In this work, we have measured precisely the time evolution of the self-bias voltage in silane/hydrogen plasmas at millisecond time scale, for different values of the direct-current bias voltage applied to the RF electrode and growth temperatures. We demonstrate that the decisive factor to increase the epitaxial growth rate, i.e. the inhibition of the agglomeration of plasma-born clusters, can be obtained by decreasing the plasma OFF time and increasing the growth temperature. The influence of these two parameters on the growth rate and epitaxial film quality is also presented.

 

Source: Chen et al. Journal of Physics D: Applied Physics (2018) https://doi.org/10.1088/1361-6463/aac1ea

2017

 

[13] Experimental benchmark of kinetic simulations of capacitively coupled plasmas in molecular gases

Z Donkó¹, A Derzsi^1,2, I Korolov¹, P Hartmann¹, S Brandt², J Schulze^2,3, B Berger^2,3,4, M Koepke², B Bruneau⁵, E Johnson⁶, T Lafleur⁶, J-P Booth⁶, A R Gibson^6,7, D O'Connell⁷ and T Gans^7
1 Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly-Thege Miklós str. 29-33, Hungary
² Department of Physics, West Virginia University, Morgantown, WV, United States of America
³ Institute for Electrical Engineering, Ruhr-University, Bochum, Germany
⁴ Electrodynamics and Physical Electronics Group, BTU Cottbus, Germany
⁵ LPICM-CNRS, Ecole Polytechnique, Palaiseau, France
⁶ Laboratoire de Physique des Plasmas, CNRS, École Polytechnique, UPMC Univ. Paris 06, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, F-91128 Palaiseau, France
⁷ York Plasma Institute, Department of Physics, University of York, Heslington, York, United Kingdom

 

Abstract

We discuss the origin of uncertainties in the results of numerical simulations of low-temperature plasma sources, focusing on capacitively coupled plasmas. These sources can be operated in various gases/gas mixtures, over a wide domain of excitation frequency, voltage, and gas pressure. At low pressures, the non-equilibrium character of the charged particle transport prevails and particle-based simulations become the primary tools for their numerical description. The particle-in-cell method, complemented with Monte Carlo type description of collision processes, is a well-established approach for this purpose. Codes based on this technique have been developed by several authors/groups, and have been benchmarked with each other in some cases. Such benchmarking demonstrates the correctness of the codes, but the underlying physical model remains unvalidated. This is a key point, as this model should ideally account for all important plasma chemical reactions as well as for the plasma-surface interaction via including specific surface reaction coefficients (electron yields, sticking coefficients, etc). In order to test the models rigorously, comparison with experimental 'benchmark data' is necessary. Examples will be given regarding the studies of electron power absorption modes in O2, and CF4–Ar discharges, as well as on the effect of modifications of the parameters of certain elementary processes on the computed discharge characteristics in O2 capacitively coupled plasmas.

 

Source: Z Donkó et al. Plasma Phys. Control. Fusion 60 014010 (2017) https://doi.org/10.1088/1361-6587/aa8378

 

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[12] Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations

A Wijaikhum¹, D Schröder², S Schröter¹, A R Gibson^1,3, K Niemi¹, J Friderich^4,5, A Greb¹, V Schulz-von der Gathen², D O'Connell¹ and T Gans¹

1 York Plasma Institute, Department of Physics, University of York, York YO10 5DD, United Kingdom
2 Experimental Physics II: Application-Oriented Plasma Physics, Ruhr-Universität Bochum, D-44801 Bochum, Germany
3 LPP, CNRS, Ecole Polytechnique, UPMC Univ. Paris 06, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, F-91128 Palaiseau, France
4 Centre for Plasma Physics, Queen's University Belfast, University Road, Belfast BT7 1NN, United Kingdom
5 Current address: KROHNE Innovation GmbH, Ludwig-Krone-Str.5, D-47058 Duisburg, Germany.

 

Abstract

The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centred at λ = 255 nm. A two-beam setup with a reference beam in Mach–Zehnder configuration is employed for improved signal-to-noise ratio allowing high-sensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N₂ optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zero-dimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O₂ influence the absolute O₃ densities when the rf power is varied.

 

Source: A Wijaikhum et al. Plasma Sources Sci. Technol. 26 115004 (2017) https://doi.org/10.1088/1361-6595/aa8ebb

2016

 

[11] Spatial Dependence of DNA Damage in Bacteria due to Low-Temperature Plasma Application as Assessed at the Single Cell Level

Angela Privat-Maldonado^1,2, Deborah O’Connell², Emma Welch¹, Roddy Vann², Marjan W. van der Woude¹

¹ Centre for Immunology and Infection, Department of Biology and Hull York Medical School, University of York, York, U.K

² York Plasma Institute, Department of Physics, University of York, York, U.K

 

Abstract

Low temperature plasmas (LTPs) generate a cocktail of reactive nitrogen and oxygen species (RNOS) with bactericidal activity. The RNOS however are spatially unevenly distributed in the plasma. Here we test the hypothesis that this distribution will affect the mechanisms underpinning plasma bactericidal activity focussing on the level of DNA damage in situ. For the first time, a quantitative, single cell approach was applied to assess the level of DNA damage in bacteria as a function of the radial distance from the centre of the plasma jet. Salmonella enterica on a solid, dry surface was treated with two types of LTP: an atmospheric-pressure dielectric barrier discharge plasma jet (charged and neutral species) and a radio-frequency atmospheric-pressure plasma jet (neutral species). In both cases, there was an inverse correlation between the degree of DNA damage and the radial distance from the centre of the plasma, with the highest DNA damage occurring directly under the plasma. This trend was also observed with Staphylococcus aureus. LTP-generated UV radiation was eliminated as a contributing factor. Thus valuable mechanistic information can be obtained from assays on biological material, which can inform the development of LTP as a complementary or alternative therapy for (topical) bacterial infections.

 

Source: Privat-Maldonado et al.  Scientific Reports Vol. 6, Article number: 35646 (2016) http://dx.doi.org/10.1038/srep35646

 

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[10] Experimental and simulation study of a capacitively coupled oxygen discharge driven by tailored voltage waveforms

Aranka Derzsi¹, Trevor Lafleur², Jean-Paul Booth², Ihor Korolov¹ and Zoltán Donkó¹

¹ Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly Thege Miklós str. 29-33, Hungary

² Laboratoire de Physique des Plasmas, Ecole Polytechnique-CNRS-Univ Paris-Sud-UPMC, 91128 Palaiseau, France

 

Abstract

We report experimental and particle-based kinetic simulation studies of low-pressure capacitively coupled oxygen plasmas driven by tailored voltage waveforms that consist of up to four harmonics of base frequency 13.56 MHz. Experimentally determined values of DC self-bias and electrical power deposition, as well as flux density and flux-energy distribution of the positive ions at the grounded electrode are compared with simulation data for a wide range of operating conditions. Very good agreement is found for self-bias and flux-energy distribution of the positive ions at the electrodes, while a fair agreement is reached for discharge power and ion flux data. The simulated spatial and temporal behaviour of the electric field, electron density, electron power absorption, ionization rate and mean electron energy shows a transition between sheath expansion heating and drift-ambipolar discharge modes, induced by changing either the number of harmonics comprising the excitation waveform or the gas pressure. The simulations indicate that under our experimental conditions the plasma operates at high electronegativity, and also reveal the crucial role of O₂(a¹Δ_g) singlet metastable molecules in establishing discharge behavior via the fast destruction of negative ions within the bulk plasma.

 

Source: Derzsi et al. Plasma Sources Sci. Technol. 25 015004 (2016) http://dx.doi.org/10.1088/0963-0252/25/1/015004

2015

 

[9] Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

Xiaolong Deng¹, Anton Yu Nikiforov¹, Eusebiu-Rosini Ionita², Gheorghe Dinescu² and Christophe Leys¹

¹ Department of Applied Physics, Ghent University, Sint-Pietersnieuwstraat 41 B4, 9000 Gent, Belgium
² National Institute of Laser, Plasma and Radiation, Magurele-Bucharest, MG-36, Ilfov RO 077125, Romania

 

Abstract

The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 10¹⁸ m⁻³ and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 μm in the plasma sheath region at 10 ns after the current peak, whereas OH(A) emission is uniform along of the interelectrode gap.

 

Source: Deng et al. Appl. Phys. Lett. 107, 053702 (2015) http://dx.doi.org/10.1063/1.4928470

 

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[8] Characteristics of a long and stable filamentary argon plasma jet generated in ambient atmosphere

M Teodorescu¹, M Bazavan², E R Ionita¹ and G Dinescu^1,2

¹ National Institute for Laser, Plasma and Radiation Physics, Magurele, PO Box Mg36, Bucharest, 077125, Romania
² Physics Department, University of Bucharest, Magurele, 077125 Bucharest, Romania

 

Abstract

We present a study of a long (up to 60 mm) and thin (600 μm) plasma jet generated at 13.56 MHz in argon expanding in an open atmosphere from inside of a thin glass tube. The discharge is operated with one annular external electrode on the tube, in the absence of any grounded electrode in the discharge proximity. The study comprises image, spectral and electrical measurements, aiming to define and understand the operating domains of this plasma jet source. Two plasma zones were identified, which coexist: a long filament accompanied by a diffuse discharge. The coexistence of these plasma zones was studied in the power-mass flow rate parameter space. An electric model is proposed, considering the jet as a radiating antenna, which allows the determination of the main electrical parameters like capacitance, resistance and active RF power dissipated in the discharge. The specific zones on the I–V characteristics were assigned to the operating domains observed visually. The spectral emission of plasma has been used to characterize the jet in respect to the gas temperature, excitation temperature and plasma density.

 

Source: M Teodorescu et al. Plasma Sources Sci. Technol. 24 025033 (2015) doi:10.1088/0963-0252/24/2/025033

2014

 

[7] Radio-frequency capacitively coupled plasmas in hydrogen excited by tailored voltage waveforms: comparison of simulations with experiments

P Diomede¹, D J Economou¹, T Lafleur^2,3, J-P Booth² and S Longo⁴

¹ Plasma Processing Laboratory, Department of Chemical & Biomolecular Engineering, University of Houston, Houston, TX 77204-4004, USA
² Laboratoire de Physique des Plasmas, CNRS, Sorbonne Universités, UPMC Univ Paris 06, Univ Paris-Sud, Ecole Polytechnique, 91128 Palaiseau, France
³ ONERA-The French Aerospace Lab, 91120 Palaiseau, France
⁴ Dipartimento di Chimica, Universita' degli Studi di Bari, via Orabona 4, 70126 Bari, Italy

 

Abstract

A combined computational–experimental study was performed of a geometrically symmetric capacitively coupled plasma in hydrogen sustained by tailored voltage waveforms consisting of the sum of up to three harmonics. Predictions of a particle-in-cell with Monte Carlo collisions/fluid hybrid model were in reasonably good agreement compared to data from an array of experimental plasma diagnostics. The plasma was electrically asymmetric, with a dc self-bias developed, for all but a sinusoidal voltage waveform. Hydrogen ions bombarding the electrodes exhibited different ion flux-distribution functions due to their different masses and collisionality in the sheath. Plasma density, ion flux and absolute value of the dc self-bias all increased with increasing the number of harmonics. The energy of ions bombarding the substrate electrode may be controlled by switching the applied voltage waveform from (positive) 'peaks' to (negative) 'valleys'.

 

Source: P Diomede et al. Plasma Sources Sci. Technol. 23 065049 (2014) doi:10.1088/0963-0252/23/6/065049

2013

 

[6] Radio frequency current-voltage probe for impedance and power measurements in multi-frequency unmatched loads

T. Lafleur¹, P. A. Delattre¹, J. P. Booth¹, E. V. Johnson² and S. Dine³

¹ LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

² LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

³ SOLAYL SAS, 91400 Orsay, France

 

Abstract

A broad-band, inline current-voltage probe, with a characteristic impedance of 50 Ω, is presented for the measurement of voltage and current waveforms, impedance, and power in rf systems. The probe, which uses capacitive and inductive sensors to determine the voltage and current, respectively, can be used for the measurement of single or multi-frequency signals into both matched and unmatched loads, over a frequency range of about 1–100 MHz. The probe calibration and impedance/power measurement technique are described in detail, and the calibrated probe results are compared with those obtained from a vector network analyzer and other commercial power meters. Use of the probe is demonstrated with the measurement of power into an unmatched capacitively coupled plasma excited by multi-frequency tailored voltage waveforms.

 

Source: T. Lafleur et al. Rev. Sci. Instrum. 84, 015001 (2013); http://dx.doi.org/10.1063/1.4773540

 

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[5] Radio-frequency capacitively coupled plasmas excited by tailored voltage waveforms: comparison of experiment and particle-in-cell simulations

Pierre-Alexandre Delattre^1,2, Trevor Lafleur¹, Erik Johnson² and Jean-Paul Booth¹

¹ Laboratory of Plasma Physics (LPP), Ecole Polytechnique, CNRS, Palaiseau 91 128, France
² Laboratory of Physics of Interfaces and Thin Films (LPICM), Ecole Polytechnique, CNRS, Palaiseau 91 128, France

 

Abstract

Using a range of different diagnostics we have performed a detailed experimental characterization of a capacitively coupled rf plasma discharge excited by tailored voltage waveforms in argon (3–13 Pa). The applied pulse-type tailored waveforms consist of between 1 and 5 harmonics (with a fundamental of 15 MHz), and are used to generate an electrically asymmetric plasma response, manifested by the formation of a strong dc bias in the geometrically symmetric reactor used. Experimental measurements of the dc bias, electron density, ion current density, ion-flux energy distributions at the electrodes and discharge current waveforms, are compared with a one-dimensional particle-in-cell simulation for the same operating conditions. The experimental and simulation results are found to be in good agreement over the range of parameters investigated, and demonstrate a number of unique features present with pulse-type tailored waveforms, including: increased plasma density and ion flux with the number of harmonics, and a broader control range of the ion bombarding energy.

 

Source: Pierre-Alexandre Delattre et al.  J. Phys. D: Appl. Phys. 46 235201 (2013) doi:10.1088/0022-3727/46/23/235201

 

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[4] Capacitively coupled radio-frequency plasmas excited by tailored voltage waveforms

T Lafleur¹, P A Delattre¹, E V Johnson² and J P Booth¹

¹ LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
² LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

 

Abstract

By applying certain types of 'tailored' voltage waveforms (TVWs) to capacitively coupled plasmas, a dc self-bias and an asymmetric plasma response can be produced, even in geometrically symmetric reactors. Furthermore, these arbitrary applied waveforms can produce a number of interesting phenomena that are not present in typical single-frequency sinusoidal discharges. This electrical asymmetry effect presents emerging possibilities for the improved control of the ion energy and ion flux in these systems; parameters of vital importance to both etching and deposition applications for materials processing. With a combined research approach utilizing both experimental measurements, and particle-in-cell simulations, we review and extend recent investigations that study a particular class of TVW. The waveforms used have a pulse-type shape and are composed of a varying number of harmonic frequencies. This allows a strong self-bias to be produced, and causes most of the applied voltage to be dropped across a single sheath. Additionally, decreasing the pulse width (by increasing the number of harmonics), allows the plasma density and ion flux to be increased. Simulation and experimental results both demonstrate that this type of waveform can be used to separately control the ion flux and ion energy, while still producing a uniform plasma over large area (50 cm diameter) rf electrodes.

 

Source: T Lafleur et al. Plasma Phys. Control. Fusion 55 124002 (2013) doi:10.1088/0741-3335/55/12/124002

2012

 

[3] Hydrogenated microcrystalline silicon thin films deposited by RF-PECVD under low ion bombardment energy using voltage waveform tailoring

E.V. Johnson^a, S. Pouliquen^b, P.A. Delattre^{a, b}, J.P. Booth^b

^a LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

^b LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

 

Abstract

We present experimental results for hydrogenated amorphous and microcrystalline silicon (a-Si:H and μc-Si:H) thin films deposited by PECVD while using a voltage waveform tailoring (VWT) technique to create an electrical asymmetry in the reactor. VWT dramatically modifies the mean ion bombardment energy (IBE) during growth, and we show that for a constant peak-to-peak excitation voltage (V_PP), waveforms resembling “peaks” or “valleys” result in very different material properties. Using Raman scattering spectroscopy, we show that the crystallinity of the material depends strongly on the IBE, as controlled by VWT. A detailed examination of the Raman scattering spectra reveals that the narrow peak at 520 cm^− 1 is disproportionately enhanced by lowering the IBE through the VWT technique. We examine this effect for a range of process parameters, varying the pressure, hydrogen–silane dilution ratio, and total flow of H₂. In addition, the SiH_X bonding in silicon thin films deposited using VWT is characterised for the first time, showing that the hydrogen bonding character is changed by the IBE. These results demonstrate the potential for VWT in controlling the IBE during thin film growth, thus ensuring that application-appropriate film densities and crystallinities are achieved, independent of the injected RF power.

 

Source: E.V. Johnson et al. Journal of Non-Crystalline Solids, Volume 358, Issue 17, 1 Sept. 2012, Pages 1974–1977 doi:10.1016/j.jnoncrysol.2012.01.014

 

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[2] Separate control of the ion flux and ion energy in capacitively coupled radio-frequency discharges using voltage waveform tailoring

T. Lafleur^1,a), P. A. Delattre¹, E. V. Johnson¹ and J. P. Booth¹

^{1 LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France}