Special Issue "Latest Developments in Pulsed Low-Temperature Plasmas"

A special issue of Plasma (ISSN 2571-6182).

Deadline for manuscript submissions: closed (20 December 2018)

Special Issue Editors

Guest Editor
Prof. Dr. James Bradley

Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool, L69 3GJ, UK
Website | E-Mail
Interests: low temperature plasma; plasma-surface interactions; plasma diagnostics
Guest Editor
Dr. Mohammad Hasan

Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool L69 3GJ, UK
Website | E-Mail
Interests: low temperature plasmas; plasma modelling
Guest Editor
Dr. Paul Bryant

Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool L69 3GJ, UK
Website | E-Mail
Interests: low temperature plasmas; complex (dusty) plasmas; magnetised plasmas; plasma diagnostics

Special Issue Information

Dear Colleagues,

Many low temperature plasmas can be considered to be in non-equilibrium, that is to say, the temperature of the plasma electrons is significantly greater than that of the ions and neutral gas species. Such plasmas, whether created at reduced or atmospheric pressure, are a rich source of active species (e.g., positive and negative ions, radicals, neutrals, electrons and photons) that can in many cases be used in a prescribed way to either create or modify (whether physically or chemically) a material surface in contact with it. Importantly, this can be done while maintaining the temperature of the work piece close to room temperature. The unique properties of low temperature plasmas have allowed them to be tailored for a multitude of industrial and manufacturing applications, ranging from functional thin film deposition to plasma decontamination.  

In recent years, the pulsed modulation of low temperature plasmas (low-pressure and atmospheric pressure) has led to enhancements in the plasma characteristics and the processing outcomes. This Special Issue of the journal will concentrate on the reporting of the latest developments in pulsed-plasma technology, with consideration given to a wide range of pulse time-scales from milliseconds to nanoseconds, across a wide range of discharge types and sizes (macro to micro-plasmas) and at both reduced and at atmospheric pressures. Topical areas can include, but should not be limited to, thin-film deposition, plasma polymerization, surface modification and decontamination, etching, plasma chemistry, lighting, plasma ignition and combustion and space thrusters etc. Contributions highlighting the current state-of-the art in either or both diagnostic development and modelling/simulation aspects of pulsed-low temperature plasmas are welcome.

Prof. Dr. James Bradley
Dr. Mohammad Hasan
Dr. Paul Bryant
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Plasma is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) is waived for well-prepared manuscripts submitted to this issue. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Low temperature plasmas
  • Pulsed
  • Diagnostics
  • Modelling
  • Surface modification
  • Deposition
  • Processing applications

Published Papers (5 papers)

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Research

Open AccessFeature PaperArticle
The Effect of Magnetic Field Strength and Geometry on the Deposition Rate and Ionized Flux Fraction in the HiPIMS Discharge
Plasma 2019, 2(2), 201-221; https://doi.org/10.3390/plasma2020015
Received: 2 April 2019 / Revised: 25 April 2019 / Accepted: 6 May 2019 / Published: 13 May 2019
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Abstract
We explored the effect of magnetic field strength |B| and geometry (degree of balancing) on the deposition rate and ionized flux fraction Fflux in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium. The HiPIMS [...] Read more.
We explored the effect of magnetic field strength | B | and geometry (degree of balancing) on the deposition rate and ionized flux fraction F flux in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium. The HiPIMS discharge was run in two different operating modes. The first one we refer to as “fixed voltage mode” where the cathode voltage was kept fixed at 625 V while the pulse repetition frequency was varied to achieve the desired time average power (300 W). The second mode we refer to as “fixed peak current mode” and was carried out by adjusting the cathode voltage to maintain a fixed peak discharge current and by varying the frequency to achieve the same average power. Our results show that the dcMS deposition rate was weakly sensitive to variations in the magnetic field while the deposition rate during HiPIMS operated in fixed voltage mode changed from 30% to 90% of the dcMS deposition rate as | B | decreased. In contrast, when operating the HiPIMS discharge in fixed peak current mode, the deposition rate increased only slightly with decreasing | B | . In fixed voltage mode, for weaker | B | , the higher was the deposition rate, the lower was the F flux . In the fixed peak current mode, both deposition rate and F flux increased with decreasing | B | . Deposition rate uniformity measurements illustrated that the dcMS deposition uniformity was rather insensitive to changes in | B | while both HiPIMS operating modes were highly sensitive. The HiPIMS deposition rate uniformity could be 10% lower or up to 10% higher than the dcMS deposition rate uniformity depending on | B | and in particular the magnetic field topology. We related the measured quantities, the deposition rate and ionized flux fraction, to the ionization probability α t and the back attraction probability of the sputtered species β t . We showed that the fraction of the ions of the sputtered material that escape back attraction increased by 30% when | B | was reduced during operation in fixed peak current mode while the ionization probability of the sputtered species increased with increasing | B | , due to increased discharge current, when operating in fixed voltage mode. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessArticle
Tailoring the Chemistry of Plasma-Activated Water Using a DC-Pulse-Driven Non-Thermal Atmospheric-Pressure Helium Plasma Jet
Plasma 2019, 2(2), 127-137; https://doi.org/10.3390/plasma2020010
Received: 29 January 2019 / Revised: 17 April 2019 / Accepted: 17 April 2019 / Published: 23 April 2019
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Abstract
We investigate the use of a DC-pulse-driven non-thermal atmospheric-pressure He plasma jet in the regulation of hydrogen peroxide (H2O2), nitrite (NO2), nitrate (NO3), and oxygen (O2) in deionized (DI) water. The [...] Read more.
We investigate the use of a DC-pulse-driven non-thermal atmospheric-pressure He plasma jet in the regulation of hydrogen peroxide (H2O2), nitrite (NO2), nitrate (NO3), and oxygen (O2) in deionized (DI) water. The production of these molecules is measured by in situ UV absorption spectroscopy of the plasma-activated water (PAW). Variations in the pulse polarity and pulse width have a significant influence on the resultant PAW chemistry. However, the trends in the concentrations of H2O2, NO2, NO3, and O2 are variable, pointing to the possibility that changes in the pulse polarity and pulse width might influence other plasma variables that also impact on the PAW chemistry. Overall, the results presented in this study highlight the possibility of using DC-pulse-driven plasma jets to tailor the chemistry of PAW, which opens new opportunities for the future development of optimal PAW formulations across diverse applications ranging from agriculture to medicine. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessArticle
A Computationally Assisted Ar I Emission Line Ratio Technique to Infer Electron Energy Distribution and Determine Other Plasma Parameters in Pulsed Low-Temperature Plasma
Plasma 2019, 2(1), 65-76; https://doi.org/10.3390/plasma2010007
Received: 11 February 2019 / Revised: 7 March 2019 / Accepted: 14 March 2019 / Published: 21 March 2019
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Abstract
In the post-transient stage of a 1-Torr pulsed argon discharge, a computationally assisted diagnostic technique is demonstrated for either inferring the electron energy distribution function (EEDF) if the metastable-atom density is known (i.e., measured) or quantitatively determining the metastable-atom density if the EEDF [...] Read more.
In the post-transient stage of a 1-Torr pulsed argon discharge, a computationally assisted diagnostic technique is demonstrated for either inferring the electron energy distribution function (EEDF) if the metastable-atom density is known (i.e., measured) or quantitatively determining the metastable-atom density if the EEDF is known. This technique, which can be extended to be applicable to the initial and transient stages of the discharge, is based on the sensitivity of both emission line ratio values to metastable-atom density, on the EEDF, and on correlating the measurements of metastable-atom density, electron density, reduced electric field, and the ratio of emission line pairs (420.1–419.8 nm or 420.1–425.9 nm) for a given expression of the EEDF, as evidenced by the quantitative agreement between the observed emission line ratio and the predicted emission line ratio. Temporal measurement of electron density, metastable-atom density, and reduced electric field are then used to infer the transient behavior of the excitation rates describing electron-atom collision-induced excitation in the pulsed positive column. The changing nature of the EEDF, as it starts off being Druyvesteyn and becomes more Maxwellian later with the increasing electron density, is key to interpreting the correlation and explaining the temporal behavior of the emission line ratio in all stages of the discharge. Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessArticle
Influence of the On-time on the Ozone Production in Pulsed Dielectric Barrier Discharges
Plasma 2019, 2(1), 39-50; https://doi.org/10.3390/plasma2010005
Received: 12 January 2019 / Revised: 22 February 2019 / Accepted: 25 February 2019 / Published: 4 March 2019
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Abstract
Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. [...] Read more.
Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. In many of these applications, input power modulation is exploited as a means to maintain a low gas temperature. Although the chemical pathways leading to ozone production/destruction and their strong temperature dependence are relatively well understood, the effect of the on-time duration on the performance of these modulated DBDs remains largely unexplored. In this study, we use electrical and optical diagnostics, as well as computational methods, to assess the performance of a modulated DBD device. The well-established Lissajous method for measuring the power delivered to the discharge is not suitable for modulated DBDs because the transients generated at the beginning of each pulse become increasingly important in short on-time modulated plasmas. It is shown that for the same input power and modulation duty-cycle, shorter on-time pulses result in significantly enhanced ozone production, despite their operation at slightly higher temperatures. The key underpinning mechanism that causes this counter-intuitive observation is the more efficient net generation rate of ozone during the plasma on-time due to the lower accumulation of NO2 in the discharge volume. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessArticle
An Inverted Magnetron Operating in HiPIMS Mode
Plasma 2018, 1(2), 277-284; https://doi.org/10.3390/plasma1020024
Received: 1 November 2018 / Revised: 17 November 2018 / Accepted: 26 November 2018 / Published: 27 November 2018
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Abstract
An ionized physical vapor deposition technique for thin ferromagnetic films is proposed. The technique is based on high power impulse magnetron sputtering (HiPIMS) with positive discharge polarity. A gapped-target was employed as the cathode of the magnetron. By applying positive HiPIMS pulses to [...] Read more.
An ionized physical vapor deposition technique for thin ferromagnetic films is proposed. The technique is based on high power impulse magnetron sputtering (HiPIMS) with positive discharge polarity. A gapped-target was employed as the cathode of the magnetron. By applying positive HiPIMS pulses to the anode, sputtered particles inside the magnetron source were ionized and extracted through the gap. Using a discharge current with a peak of about 13 A, an ion flux in the order of 1021 m−2s−1 was obtained at a distance of 45 mm from the magnetron. In addition, deposition rates of up to 1.1 Å/s for nickel films were achieved using a 30 Hz repetition rate and 300 µs pulse width. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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