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Programme and Book of Abstracts

Ricoh Arena, Coventry

10th and 11th October 2018

16th Technological Plasma Workshop Ricoh Arena, Coventry

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Notes

There are more notes pages at the back of this booklet

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Contents

Conference Dinner Arrangements 5

Conference Schedule 6

Abstracts for Invited presentations 10

Abstracts for Contributed Presentations 14

Abstracts for Poster Presentations 23


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TPW Background

The Technological Plasma Workshop (TPW) is principally a UK‐based international forum on the

science and technology of plasmas and gas discharges. Delegates from all countries are very

welcome to participate in this workshop.

Since the EPSRC Technological Plasma Initiative in 1997, technological plasmas have found

applications in diverse fields ranging from nano‐science energy, through biomedicine and

environment, to space exploration. They offer major collaboration opportunities for academic

and industrial communities and exciting career prospects for younger scientists and engineers.

To support a full realisation of these opportunities, TPW aims to foster academic‐industry

collaboration and to engage young plasma scientists with a scientific programme anchored by

leading plasma scientists. The workshop will comprise invited talks, contributed presentations

and a poster session.

In 2011, TPW became a conference of the Institute of Physics (IOP) Plasma Physics Group and

since 2014 TPW has been held in conjunction with the Vacuum Expo and the Vacuum

Symposium. The conference is currently co‐sponsored by the IOP Plasma Physics Group and the

IOP Dielectrics & Electrostatics Group.

Scientific Committee

Professor Adrian Cross

University of Strathclyde

Chairman

Dr Felipe Iza

Loughborough University

Co‐chair

Professor Timo Gans

University of York

Dr Mark Bowden

University of Liverpool

Mr John Simmons

RF Services, UK

Organising Committee

Dr Felipe Iza


Mr Alec Wright


Professor Adrian Cross


Dr Nadarajah Manivannan

Brunel University


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Conference Dinner

The conference dinner will be held at Playwrights Bar & Bistro. A three course meal is included in

your conference fee but any drinks must be bought by you.

The table is booked for 19:00, so please arrive at the restaurant by 18:55.

Please make your own way from the conference venue to the restaurant located next to the

cathedral, 4‐6 Hay Lane Cathedral Quarter Coventry CV1 5RF.

If you have any problems getting to the restaurant, then you can call the organising committee on

07825 167453.

A number of transport options are available:

If you are driving then there are several car parks located close to the restaurant

o West Orchards Car Park, Smithford Way, Coventry, CV1 1GF

o Belgrade Plaza Car Park, Ringway Hill Cross, Coventry, CV1 4AJ

o Bishop Street Car Park, Tower Street, Coventry, CV1 1JN

Taxi‐ the address for the restaurant is 36‐42 Corporation Street, Coventry, CV1 1GF

o www.allenstaxis.com or 02476 55 55 55

Bus‐ there is several buses that can get you to the restaurant. A google maps search is the

most efficient way of finding the next bus, however the 20 or 20A bus routes go from near

the arena to near the restaurant.


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Conference Schedule Wednesday 10th October 2018

10:00 – 12:00 Vacuum Expo opens

12:00 – 13:00 Registration and hang posters (Vacuum Expo Exhibition Hall)

Session 1 Chair: Dr Felipe Iza, Loughborough University, UK

13:00 – 13:05 Welcome, introduction and announcements

Adrian Cross

13:05 – 13:50 Challenges & Opportunities for Thermal Plasma Abatement of PFC gases (invited)

Simone Magni, Edwards

13:50 – 14:10 Plasma‐Enhanced Pulsed Laser Deposition of metal‐oxide thin films

Erik Wagenaars, University of York

14:10 – 14:30 Crystallization of Diamond and Silicon NCs in an atmospheric pressure microplasmas

Bruno Alessi, University of Ulster

14:30 – 14:50 Coffee break

Session 2 Chair: Professor Paul May, University of Bristol

14:50 – 15:35 Plasma cathode electron generators for 3D printing and welding applications (invited)

Colin Ribton, TWI

15:35 – 15:55 Texture evolution of Molybdenum for photovoltaic applications deposited by HIPIMS

Daniel Loch, Sheffield Hallam University

15:55 – 16:15 Cryogenic Pellet Ablation Modelling in Hot Magnetised Plasmas

Kyle Martin, University of Glasgow

Session 3: Poster session

16:15 – 17:30 Poster session (Vacuum Expo Exhibition Hall). The day one poster prize presentation will be at 16:30.

19:00 Conference dinner


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Playwright, 4‐6 Hay Lane, Cathedral Quarter, Coventry, CV1 5RF

Thursday 11th October 2018

09:00 – 10:00 Vacuum Expo (Vacuum Expo Exhibition Hall)

Session 4 Chair: Professor Adrian Cross, University of Strathclyde, UK

10:00 – 10:20 Antimicrobial efficacy of in situ plasma‐generated ozone is effective in inactivation of P. aeruginosa biofilms in drains and water‐submerged surfaces Meg Zajac, University of Glasgow

10:20 – 10:40 Plasma driven epoxidation

Sui Wang, Loughborough University

10:40 – 11:00 Mixing in Liquid Treated by an Atmospheric Pressure Plasma Jet: The Importance of Surface Tension Gradient

Faraz Montazersadgh, Loughborough University

11:00 – 11:20 Discussion about future TPW meetings

11:20 – 11:50 Coffee Break

Session 5 Chair: Dr Declan Diver, University of Glasgow, UK

11:50 – 12:10 Control of electron, ion and neutral dynamics in radio‐frequency electrothermal microthrusters

Scott J. Doyle, University of York

12:10 – 12:30 The Observation and Effects of the Spikes in Power Caused by a Modulated DBD Plasma

Junchen Ren, Loughborough University

12:30 – 12:50 Pittsburgh Green as a Potential Chemical Probe for Atomic Oxygen

Alexander Wright, Loughborough University

12:50 – 13:00 Closing remarks

TPW Organising Committee

13:00 – 13:30 Lunch

13:00 – 15:00 Poster Prize Award Ceremony and visit to Vacuum Expo

15:00 Departure


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List of poster contributions

Advanced engineering of nanomaterials using atmospheric pressure plasma jet (APPJ)

Avishek Dey, Paheli Ghosh, Gauthaman Chandrabose, Satheesh Krishnamurthy, Nicholas Braithwaite

The Open University

Surface production of negative ions from nitrogen doped diamond using hydrogen and deuterium plasmas

Gregory J. Smith, Roba Moussaoui, Alix Gicquel, Jocelyn Achard, James Ellis, Timo Gans, James P. Dedrick, and Gilles Cartry

University of York

Investigation on the RONS and bactericidal effects induced by He+O2 cold plasma jets: in openair and in an airtight chamber

Han Xu, Dingxin Liu, Weitao Wang, Michael G Kong

Xi’an Jiaotong University

Investigation of pseudospark plasma‐sourced sheet electron beam for application in high power millimetre wave radiation generation

H. Yin, L. Zhang, W. He, and A. D. R. Phelps and A.W. Cross


The interaction of gas‐plasma jets with liquids: modelling and experiments

Chinasa J. Ojiako, Dmitri Tseluiko, Roger Smith, Hemaka Bandulasena


Investigation of the physico‐chemical properties of an atmospheric‐pressure DBD operating in two distinct homogenous modes

K McKay, D Donaghy, F He, J Bradley

University of Liverpool

Surface treatment for adhesion improvement of glass and PMMA adherends for optical applications in hostile environments

V. Bagiatis, G.W. Critchlow, D. Price



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Carboxylation in Flow Chemistry using a DC Plasma System

M. Shaban, A. Randi, B.R. Buckley and F. Iza


Space Averaged Mathematical Model of Pulse Powered Atmospheric Pressure Air Plasma

Faraz H. Montazersadgh, Alexander Wright, Alexander Shaw, Felipe Iza


Plasma effects on microbubble formation in gas‐liquid interface across a microfluidic plasma reactor.

O. Ogunyinka, A. Wright, G. Bolognesi, F. Iza, H. Bandulasena


Pre‐treatment of a faecal simulant for bio‐ethanol production with a novel microbubble enhanced DBD plasma reactor

A. Wright, A. Marsh, A. Shaw, G. Shama, F. Iza, H. Bandulasena


Atmospheric – pressure plasma device for CO2 conversion and utilization

A.Randi, A. Shaw, U. Wijayantha, F. Iza, B.R. Buckley


Quantemol Database: Complex Chemistry Reduction and Chemistry Set Generation

Adetokunbo Ayilaran, Jonathan Tennyson, Sebastian Mohr, Martin Hanicinec, Dan Brown, Anna Dzarasova


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Technological Plasma Workshop 2018

Abstracts for Invited Presentations


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Challenges and Opportunities for Thermal Plasma Abatement of PFC gases Mike Czerniak1, Simone Magni1, Toshihiko Nishiyama2, Kazuro Sugiura2

1 Edwards Limited, Kenn Business Park, Kenn Road, Clevedon, BS21 6TH, UK 2 Edwards Japan Limited, 1078-1, Yoshihashi, Yachiyo-shi, Chiba, 276-8523, Japan

[email protected]

Edwards, part of Atlas Copco Vacuum Technique business area, is world leader in vacuum and abatement solutions. We operate in many industrial and R&D sectors and in particular our products are integral to the semiconductors manufacturing process.

For semiconductors fabs the challenges to maintain a high chip throughput has to keep up with the environmental challenges. As a matter of fact, a large number of toxic, flammable or green-house gases (GHG) are employed or generated during the production process. These gas effluents have to be securely "destroyed" to comply with the safety and environmental regulations as well as to reduce the CO2 footprint of these industries. These requirements have driven the installation of many point of use (POU) abatement systems in the sub-fab.

Over the years, abatement combustors have become established as the “best known method” to convert the gas effluent into substances which are no longer noxious or easier to handle and remove. However, more recently, strong market drivers push for non-fuel POU abatement as a complementary choice to the widely-used combustors, which employ natural gas or LPG to sustain the thermal abatement reactions. Thermal plasmas can answer to this quest for a non-fuel abatement solution, particularly for regions where fuel gas is not available or prohibitively expensive. In specific, DC-arc torches can be integrated into affordable POU abatement systems. These systems can achieve significant GHG abatement and have an advantage of easier scalability.

In comparison to other applications of DC-arc torches, the challenge of POU abatement is to guarantee a high electrode lifetime – which in turn results into a high uptime for the abatement systems – in a generally more corrosive environment. Also the thermal efficiency of the assembly comprising the torch and the reaction zone has to be addressed to achieve the lowest cost of operation possible. Hydrogen radicals are widely present as a by-product of combustion in burners and are pivotal for GHG abatement. The inherent lack of these radicals constrains DC-arc torch in a different abatement strategy. Co-generated CF4 from other PFC gases and generally minimizing abatement by-products are challenges worthy to discuss as peculiar to DC-arc torch systems.


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Plasma cathode electron generators for 3D printing & welding applications

C Ribton1, S de Pozo1, A Sandeman1,2 1TWI Ltd, Granta Park, Abington, Cambridge CB21 6AL

2 Loughborough University, Leicestershire LE11 3TU [email protected]

Electron beam guns are widely used for materials processing – vacuum melting, welding and more recently 3D printing using either powder beds or wire. Almost all electron guns in use employ a thermionic emitter as the source of electrons. These emitters are usually a directly heated tungsten filament through which a high current passes to bring the cathode up to a temperature of some 2700K. The emission density at this temperature is some 7Acm-2.

The process reliability depends upon the reproducibility of beam characteristics. Unfortunately, the filaments can distort, wear or evaporate. This has become a significant problem in many applications. Electron beam machines are often used for high value, high integrity components such as aero engine rotors or medical implants. Small changes in the cathode mount position or geometry can lead to significant changes in manufacturing quality. This requires lengthy acceptance testing following cathode changes. Productivity could be improved by extending cathode life. As 3D printing is used for ever larger components, the build time can be several days and the cathode cannot be changed without causing a defect in the part.

Some measures have been taken to extend cathode lifetimes by the use of indirectly heated buttons, which are back-bombarded with an electron or laser beam. Within this work, we have examined the use of a plasma as an alternative source of electrons in a gun, rather than a thermionic cathode.

Fig. 1 shows a comparison of thermionic and plasma cathodes. Plasmas offer a number of advantages over thermionic cathodes. They do not wear and the gas is constantly replenished. They also have a fast response time as they have very low thermal inertia. Thus, they can be used to rapidly pulse the electron beam, which is a requirement for many applications.

Figure 1. (a) Thermionic cathode; (b) Plasma cathode.

A plasma as a source of electrons must have a number of characteristics. The emissivity requires that there is a sufficient population density in the proximity of an aperture – through which electrons will be accelerated into the main field of the electron gun. It is also necessary for this density to be maintained by the creation of more free electrons – ultimately there will be an


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electron current from the walls of the plasma chamber through the gun to the work piece. To gain a greater understanding of the plasma with the aim of optimising the cathode design, experimental and software simulation tools are being used.

The optical emission spectrum has been examined for different configurations whilst extracting a beam from the plasma [1]. By using plasma gas that is well documented (argon) it has been possible to examine the relative intensity of spectral lines associated with ionisation events. Much of the spectrum seen is from excitation without ionisation. The higher energy lines from ions capturing free electrons are an indication of the electron density and the potential merit of the plasma configuration as an electron source. In maximising the electron density we have moved from plane electrodes to hollow cathode geometries and from RF excitation to DC plasmas.

We are also examining the use of particle-in-cell (PIC) software to simulate the plasmas, see Fig. 2 for a DC plasma excitation. Parallel plate models have been constructed, but modelling of hollow cathode geometries presents its own challenges related to the higher electron density. The plan is to construct a hollow cathode model that is closer to the real gun, instead of the parallel plate model that we have simulated up to now. This should allow us to understand better the hollow cathode effect and to reach a point of using simulation as a guide towards an optimised plasma gun design.

Figure 2. (a) PIC particles reaching stability; (b) Electron density across a cylindrical gap.

At the moment, the simulation model is of the plasma chamber only. The next step will be to simulate the area at the aperture with the same PIC model. As we have a dynamic flow of gas through the cathode, pressure gradients exist, but not all simulation software packages can model this. Thus, a software review has been carried out which looks at this and other key features needed to simulate our particular plasma chamber experiment. Two packages have been identified as the potential candidates (VSim and XOOPIC) [2,3] and at this time we are using both for the plasma chamber simulations.

S. del Pozo, C. Ribton and D. R. Smith, "Investigation of RF and DC plasma electron sources for material processing applications," 2017 Eighteenth International Vacuum Electronics Conference (IVEC), London, 2017, pp. 1-2. doi: 10.1109/IVEC.2017.8289676

Nieter, C., & Cary, J. R. (2004). VORPAL: A versatile plasma simulation code. Journal of Computational Physics, 196(2), 448–473. https://doi.org/10.1016/j.jcp.2003.11.004

Verboncoeur, J. P., Langdon, A. B., & Gladd, N. T. (1995). An object-oriented electromagnetic PIC code. Computer Physics Communications, 87(1–2), 199–211. https://doi.org/10.1016/0010-4655(94)00173-Y


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Abstracts for Contributed Presentations


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Plasma-Enhanced Pulsed Laser Deposition of metal-oxide thin films

David Meehan1, Sudha Rajendiran1, Andrew Rossall2, Erik Wagenaars1 1 York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, UK

2 School of Computing & Engineering, University of Huddersfield, Huddersfield, HD1 3DH, UK [email protected]

Plasma-Enhanced Pulsed Laser Deposition (PE-PLD) is a novel technique for depositing metal-oxide thin films. It combines traditional PLD of metals with a low-temperature oxygen background plasma to create metal-oxide thin films. Potential advantages of the PE-PLD technique are: the use of metal targets which are cheaper and easier to fabricate than metal-oxide targets, a wider tuning ratio of the stoichiometry and the lack of substrate heating needed to achieve high-quality films, allowing the direct deposition on plastic substrates. So far, the PE-PLD technique has only been investigated numerically [1]. Here we present the first experimental proof-of-concept results for copper oxide and zinc oxide thin films. These are wide-bandgap semiconductors with many (potential) applications, e.g. solar cell fabrication, supercapacitors, touch screens and bio sensors. In our proof-of-concept study we show that using PE-PLD, we can deposit stoichiometric, high-quality, poly-crystalline films of ZnO, Cu2O and CuO. Figure 1(a) shows the Energy-Dispersive X-ray spectroscopy (EDX) analysis of the composition of the film. Further analysis of the samples using Medium Energy Ion Scattering (MEIS) confirm these stoichiometries throughout the film [2]. The crystalline phases of the films were investigated with X-Ray Diffraction (XRD) and the results for copper oxide are shown in figure 1(b). These deposited films proof to be polycrystalline with a mixture of phases of Cu2O and CuO.

Figure 2. (a) EDX analysis and (b) XRD analysis of PE-PLD deposited films

Deposition rates are 1-3 nm/min, comparable to traditional PLD. Importantly, PE-PLD does not need substrate heating or post-annealing to achieve high-quality films, allowing us to deposit films directly on sensitive substrates such as flexible polypropylene (PP) films.

S. Rajendiran, A.L. Rossall, A.R. Gibson, E. Wagenaars, Surf. Coat. Technol., 260 (2014) 417-423 A.K. Rossall, J. van den Berg, D. Meehan, S. Rajendiran, E. Wagenaars, NIMB, (2018), in press.


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Crystallization of Diamond and Silicon NCs in an atmospheric pressure

microplasma

Alessi Bruno, Manuel Macias-Montero, Paul Maguire, Davide Mariotti University of Ulster, Northern Ireland

alessi‐[email protected]

Atmospheric pressure micro-plasmas made recently their appearance as valuable tools for nanomaterial synthesis [1]. They offer at the same time a cheap alternative to low pressure plasmas and some unique peculiarities. For example, the non-thermal character makes them suitable for treating temperature sensitive materials as polymers or biomaterials, and the high ratio of energetic electrons allows to activate chemical reactions which are otherwise hard to achieve, as well as a low selectivity from the point of view of employable precursors. Flowing molecular gases through the plasma region usually brings the formation of nanoparticles, and for some elements the crystalline state is reached under gas temperatures which are lower than the expected for crystallization. The high degree of collisionality due to the ion-neutral interactions is responsible for the selective heating of particles surface inside the plasma, allowing to achieve higher effective temperatures on them [2]. In this work we synthesize Silicon nanoparticles from a Silane/H2/Argon plasma and obtain different phases, from purely crystalline 2-3 nm particles to slightly bigger purely amorphous ones and mixed phases in intermediate conditions. Also, ultra-small nanodiamonds have been produced using a metalorganic precursor, ferrocene, usually known for its ability to catalyse the formation of carbon nanotubes in chemical vapour deposition processes. The nanodiamonds produced here are 3-5 nm and the process is faster in respect to previous studies. Then, using mainly optical diagnostics, we obtain the plasma parameters relative to the synthesis processes and test a steady-state model which explains the rise in temperature at nanoparticles surface above the crystallization threshold in the case of Si nanoparticles, and can explain their phase and size distribution. [1] Mariotti, Davide, and R. Mohan Sankaran. "Microplasmas for nanomaterials synthesis." Journal of Physics D: Applied Physics 43.32 (2010): 323001 [2] Askari, S., Levchenko, I., Ostrikov, K., Maguire, P. & Mariotti, D. Crystalline Si nanoparticles below crystallization threshold: Effects of collisional heating in non-thermal atmospheric-pressure microplasmas. Appl. Phys. Lett. 104, (2014)


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Texture evolution of Molybdenum for photovoltaic applications deposited by HIPIMS

Daniel A. L. Loch, Arutiun P. Ehiasarian HIPIMS Technology Centre, Sheffield Hallam University, Sheffield, UK,

[email protected]

The back contact of photovoltaic devices has a major influence on the efficiency of the cells. Back contacts need to have low resistivity to reduce energy losses and need to be as reflective as possible to allow for more photons to be absorbed. Molybdenum has been identified as a good candidate that fulfils both these requirements. The influence of HIPIMS on the coating properties of Molybdenum on soda lime glass is not known. In this study the effect of HIPIMS deposition parameters on the microstructure, texture, resistivity and reflectivity are examined and plasma parameters will be correlated with the coating properties. A voltage-pulse time matrix was devised varying the voltage from 800 - 1500 V and the pulse time was increased from 60 - 1000 μs in 5 steps. Processes were operated at 0.22 Pa (LP) and 0.44 Pa (HP). The Mo II / Mo I ratio shows that the intensity is constant over all pulse time settings between 1150 V and 1350 V at LP, while for HP the ratio is constant over all voltages and decreases rapidly between 60-125 μs. Mass spectroscopy measurements taken in the middle of the pulse;

show a broad Mo2+ peak between 1 - 10 eV, which with increasing pulse time has a tail with an energy of up to 25 eV (Fig.1). Single layer deposition at LP resulted in poor adhesion and low resistivity. At HP the adhesion was good with high resistivity. Multilayer coatings with a HP base layer and LP top layer were found to have good adhesion with lower resistivity than single HP layers. SEM micrographs revealed that for increasing voltage the size of the rice like grain structure reduces with increasing voltage (Fig.2). These results show that HIPIMS can be used effectively to deposit tailored Mo back contacts with good adhesion and low resistivity.

Figure 3 Energy resolved MS of Mo2+ at 0.44 Pa and 1500 V.

Figure 4 SEM image of Mo with a pulse time of 1000us at a pressure of 0.44 Pa deposited with varying voltages a) 800V b) 1500V.


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Cryogenic Pellet Ablation Modelling in Hot Magnetised Plasmas

Martin F K1, Wilson A D1, Diver D1 1Astronomy and Astrophysics, School of Physics and Astronomy, Kelvin Building, University of

Glasgow, Glasgow, G12 8QQ [email protected]

The development of efficient refuelling schemes for tokamaks is essential for the success of fusion as an energy source. There are several techniques for replenishing the fuel, and one of the most promising is pellet injection, in which a cryogenic pellet of fuel is fired at speeds of a few 100 m/s into the tokamak plasma. This solid structure is ablated by the ambient plasma, dispersing fuel through the chamber. The ablation of this pellet creates a dense cloud of neutral particles which interacts with the background plasma, creating strong transient ionization and density gradients and making the evolution of the pellet-plasma system a complex gas-plasma problem. We attempt to model this process holistically by extending evaporative surface models (e.g. the “D2” law [1]) and collisional plasma processes (informed by cloud profile diagnostics) in order to infer the ablation rate, density structure, cloud terminal radius and pellet size as a function of time, balancing mass-transfer and ionization rates, diffusion and sheath evolution. Fluid instabilities may play a role in the strongly sheared flows between contrasting density media. This project brings a combination of theoretical and computational modelling to bear on a fusion technology problem.

Figure 5. (a) The prescribed ablation rates which inform the size of the pellet and cloud at all times; (b) The density profiles of the ablatant cloud with the solved terminal cloud size for several times.

Cazabat A M and Guena G, Evaporation of macroscopic sessile droplets, 2010, Soft Matter, 6, 2591 - 2612


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Antimicrobial efficacy of in situ plasma-generated ozone is effective in inactivation of Pseudomonas aeruginosa biofilms in drains and water-

submerged surfaces

Pajak-Zajac MZ1, Buckley A1, Potts HE2, Barton D2, Smith A3, Diver DA1

1 School of Physics and Astronomy, University of Glasgow; 2 Anacail Ltd., Glasgow; 3 University of Glasgow Dental School, Glasgow Dental Hospital and School

[email protected]

A reduction in biofilm bioburden is demonstrated using in situ cold-plasma-generated ozone, showing that this practical technique has potential for decontaminating inaccessible periodically wetted surfaces. The method ionizes the ambient air to produce the ozone (and other radicals) without presenting a general environmental hazard [1]. A key advantage of using a gaseous biocide over a liquid one is the former’s ability to penetrate small-scale surface features without being restricted by surface tension limitations. Drains that harbour biofilms on interior surfaces can be decontaminated effectively by the plasma system: the drain inlet is covered and sealed by the device itself, and the water trap completes the seal on the outlet [2]. The levels of ozone generated are sufficient to reduce significantly the bioburden in biofilms, even when such biofilms are partially or wholly submerged in water. Additionally, we show that such ozone treated surfaces do not promote biofilm re-growth. Biofilms in drains, known to be resistant to conventional liquid chemical surface cleaning, can pose a serious health challenge in critical environments [3, 4]. The demonstrated efficacy of the technique presented here in such contexts commends the method for effective cleaning of not only drains, but other biofilm-prone surfaces, including sanitary ware and medical devices.

Diver, D.A. and H. Potts, Plasma Generation Apparatus and Use of the Plasma Generation Apparatus, E.P. Office, Editor. 2010.

Potts, H. and D. Diver, Drain decontamination system, in ESPACENET, I.P. Office, Editor. 2015: UK. Walker, J. and G. Moore, Pseudomonas aeruginosa in hospital water systems: biofilms, guidelines, and

practicalities. Journal of Hospital Infection, 2015. 89(4): p. 324-327. Wingender, J., Hygienically Relevant Microorganisms in Biofilms of Man-Made Water Systems, in Biofilm

Highlights, H.C. Flemming, J. Wingender, and U. Szewzyk, Editors. 2011. p. 189-238.


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Plasma driven epoxidation

Wang Sui1,2, Alexander Wright3, Benjamin R. Buckley4, Liu Dingxin2, Wang Xiaohua2, Felipe Iza1

1Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU

2State Key Laboratory of Electrical Insulation and Power Equipment, Centre for Plasma Biomedicine, Xi’an Jiaotong University, Xi'an City 710049, P. R. China

3 Department of Chemical Engineering, Loughborough University, Leicestershire, LE11 3TU, UK

4Department of Chemistry, School of Science, Loughborough University, Leicestershire, LE11 3TU, UK

Epoxides are key building blocks in organic synthesis and are important intermediates in the preparation of many natural products [1]. Epoxides are typically prepared by reacting alkenes with sacrificial mono-oxygen donors, such as peracides. The ultimate scheme for synthesizing epoxides would be the direct reaction of alkenes with pure oxygen as this would eliminate the waste stream altogether. In this work we explore the feasibility of synthesizing epoxides using oxygen as the source of oxygen and cold atmospheric-pressure plasma as the means to drive the epoxidation.Cold atmospheric pressure He+O2 plasma provides an economic and efficient way for producing atomic oxygen [2].

Treated liquid samples were analyzed using gas chromatography mass spectrometry (GCMS) to identify and quantify products. Benzaldehyde and trans-stilbene epoxide are the main two products and their concentration increase with the duration of the treatment as well as with the fraction of O2 in the feed gas. Formation of benzaldehyde is attributed to the well documented ozonolysis reaction of trans-stilbene with ozone produced in the plasma. Increasing the oxygen concentration in the feed gas favours the formation of ozone over atomic oxygen [2] and therefore the epoxide to benzaldehyde ratio decreases with increaeing oxygen fraction in the feed gas. These results demonstrate the feasibilty of tunable plasma-driven ozonolysis and epoxidation of alkenes.

Figure 1: (a) Schematic diagram of the experimental setup. (b) Concentration ratio of trans-stilbene epoxide to benzaldehyde as a function of the gas admixture and treatment time. (c) Reduction of benzaldehyde formation when the

solution is bubbled with N2 before the treatment. [1] P. C. B. Page, C. A. Pearce, Y. Chan, P. Parker, B. R. Buckley, G. A. Rassias, and M. R. J.

Elsegood, J. Org. Chem., 2015. [2] D. X. Liu, M. Z. Rong, X. H. Wang, F. Iza, M. G. Kong and P. Burggeman, Plasma Process.

Polym., 2010.


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Mixing in Liquid Treated by an Atmospheric Pressure Plasma Jet: The Importance of Surface Tension Gradient

Faraz Montazersadgh1, Abdulkadir Hussein Sheik2, Alexander Wright2, Alex Shaw1, H. C.

Hemaka Bandulasena2, Felipe Iza1

1 Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom

2 Chemical Engineering Department, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom.

Recent advancements in plasma-liquid interaction ranges from chemical disinfection, medicine and agriculture to nano-material fabrication and analytical chemistry [1][2]. While there is a rapid growth in plasma-liquid applications, guidelines for system design and reactor optimization are limited. To study the main mechanisms affecting the mass transfer between an atmospheric pressure plasma jet (APPJ) and a liquid medium, a batch reactor was designed and investigated. Computational and experimental results show that while the external gas flow and the natural convection imposed by temperature gradients play a more significant role in the liquid mixing patterns than electrically driven forces, the surface tension gradient can completely reverse the flow patterns and local velocity magnitude if the surface tension increases locally as a result of the chemical reactions triggered by the plasma (figure 1). This can significantly affect the mixing efficiency and treatment time in various applications. For small-scale batch reactors, long and deep vessels enhance mass transfer in cases where the liquid shows surfactant characteristics and the local surface tension is increased by the plasma while wide and shallow containers are more suitable in cases where the gas flow is the main factor governing the liquid flow pattern.

Figure 1. Simulated local velocity field during plasma treatment for de-ionized water-salt (a-I) and for de-ionized water-salt and 1% mass PVA (b-I). The local velocity direction is reversed, and the magnitude is increased as confirmed by PIV

analysis plotted in (a-II) and (b-II). [1] S. K. Kang, H. Y. Kim, G. S. Yun, and J. K. Lee, “Portable microwave air plasma device for wound

healing,” Plasma Sources Sci. Technol., vol. 24, no. 3, p. 035020, 2015.

[2] U. R. Kortshagen, R. M. Sankaran, R. N. Pereira, S. L. Girshick, J. J. Wu, and E. S. Aydil, “Nonthermal plasma synthesis of nanocrystals: Fundamental principles, materials, and applications,” Chem. Rev., vol. 116, no. 18, pp. 11061–11127, 2016.


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Control of electron, ion and neutral dynamics in radio-frequency electrothermal microthrusters

Scott J. Doyle1, Andrew R. Gibson1, Teck. S. Ho2, Rod W. Boswell2, Christine Charles2, Mark J.

Kushner3 and James P. Dedrick1

1York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DD, UK

2Space Plasma, Power and Propulsion Laboratory, Research School of Physics and Engineering, The Australian National University, ACT 0200, Australia

3University of Michigan, Department of Electrical and Computer Engineering, 1301 Beal Ave., Ann Arbor, MI 48109-2122, USA

[email protected]

The development of low-power and compact propulsion sources is of significant interest for meeting the increasingly demanding challenges of space missions [1]. Radio-frequency (rf) hollow cathode plasma thrusters operate by heating the neutral propellant gas and therefore do not require a space-charge neutralizer. To maximise thrust-power efficiency, it is important to control the spatial and temporal deposition of electrical power into the plasma. In this study, we investigate the mechanisms for electron, ion and neutral heating in the recently developed Pocket Rocket electrothermal microthruster [2, 3]. Fluid-kinetic simulations undertaken with the Hybrid Plasma Equipment Model [4] corroborate measurements of the electron-impact excitation rate via phase-resolved optical emission spectroscopy. This enables the mechanisms for power deposition to the propellant to be investigated with respect to an α-γ mode transition and pressure gradient on-axis [5]. Prospects for achieving enhanced control of charged and neutral-particle dynamics, and thereby the thrust-power efficiency, via dual-frequency ‘tailored’ voltage waveforms are also discussed. We wish to thank J. Flatt, R. Armitage, K. Niemi and P. Hill for their technical assistance and acknowledge financial support from the Engineering and Physical Sciences Research Council (EP/M508196/1). The participation of M. J. Kushner was supported by the US National Science Foundation and the US Department of Energy Office of Fusion Energy Science. [1] I. Levchenko et al. Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers. Applied Physics Reviews 5, 011104 (2018) [2] C. Charles and R. W. Boswell. Measurement and modelling of a radiofrequency micro-thruster. Plasma Sources Science and Technology 21, 022002 (2012) [3] T. S. Ho, C. Charles, and R. W. Boswell. Performance modelling of plasma microthruster nozzles in vacuum. Journal of Applied Physics 123, 173301 (2018) [4] M. J. Kushner. Hybrid modelling of low temperature plasmas for fundamental investigations and equipment design. Journal of Physics D: Applied Physics 42, 194013 (2009) [5] S. J Doyle, A. R. Gibson, J. Flatt, T. S. Ho, R. W. Boswell, C. Charles, P. Tian, M. J. Kushner and J. Dedrick. Spatio-temporal plasma heating mechanisms in a radio frequency electrothermal microthruster. Plasma Sources Science and Technology 27, 085011 (2018)


23

The Observation and Effects of the Spikes in Power Caused by a Modulated DBD Plasma

Junchen Ren1, Faraz Montazersadgh1, Alexander Wright1,2, Alexander Shaw1, Hemaka

Bandulasena2, Felipe Iza1

1 Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, United Kingdom

2 Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, United Kingdom

[email protected]

Ozone is often a key reactive species produced from a plasma discharge with systems developed to maximise the production of the gas. To keep the gas temperature low and thus maximise the efficiency the discharge can be modulated with the ratio of the on to off-time (duty cycle) examined [1]. This study investigates the effect when the duty cycle is fixed at 30 % and the on-time varied between 1 ms, 10 ms and 100 ms. Results were collected from both experimental analysis and from a 0D numerical model. It was found that when modulating the plasma, there is a sharp peak in power at the beginning of each pulse which produced high energy electrons promoting an increased production of ozone. Shorter on-times were also found to aid in the production of ozone as the reduced off-time meant a high level of atomic oxygen could be maintained producing ozone without any applied power.

Figure 6. The overlap for the instantons plasma power at 1 ms on-time with the captured OES spectrum and the fit used for the computational power

Šimek M, Pekárek S and Prukner V 2010 Influence of power modulation on ozone production using an AC surface dielectric barrier discharge in oxygen Plasma Chem. Plasma Process. 30 607–17


24

Pittsburgh Green as a Potential Chemical Probe for Atomic Oxygen

Alexander Wright1,2, Helena Jablonowski2, Hemaka Bandulasena1, Thomas von Woedtke2, Benjamin R. Buckley3, Kristian Wende2, and Felipe Iza4

1 Department of Chemical Engineering, Loughborough University, Leics. LE11 3TU, UK 2 ZIK plasmatis at Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-

Hausdorff-Str. 2, 17489 Greifswald, Germany 3Department of Chemistry, School of Science, Loughborough University, Leics. LE11 3TU, UK

4Wolfson School Of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, Leics. LE11 3TU, UK

[email protected]

In many research communities, the lack of accurate aqueous measurement techniques for reactive oxygen species (ROS) is a major challenge. This has led to an increasing interest in the development of ROS chemical probes for species such as H2O2 [1], •OH [2], and O2

–• [3]. However, often highlighted as a downfall of these probes is there lack of selectivity giving false positive results [4].

Pittsburgh Green (PG) has previously been shown to be a O3 specific probe and we wished to evaluate PG for application in complex multi-species systems. This was achieved through comparison with spin probe enhanced EPR spectroscopy using TEMPD-HCl. However, we observed that PG could in fact be a useful probe for atomic oxygen (•O), thus providing, for the first time, a detection method for liquid phase •O.

The development of a detection method for liquid phase •O could be of significant interest to communities interested in ROS characterisation. We have also elucidated here the limitation of ROS species detection in the presence of DMSO. Furthermore, this study highlights the caution that is required when performing probe measurements in multi-species systems.

Figure: (a) shows the experimental set up and how the kINPen was used as a source of ROS with different treatment distances. (b) and (c) shows the measured probe concentrations of PG and TEMP-HCL when using a nitrogen and synthetic air curtain respectively. [1] Z. Machala, B. Tarabova, K. Hensel, E. Spetlikova, L. Sikurova, and P. Lukes, Plasma Process. Polym.,

2013. [2] T. J. Mason, J. P. Lorimer, D. M. Bates, and Y. Zhao, Ultrason. - Sonochemistry, 1994. [3] B. Kalyanaraman, M. Hardy, R. Podsiadly, G. Cheng, and J. Zielonka, Arch. Biochem. Biophys., 2017. [4] P. WARDMAN, Free Radic. Biol. Med., 2007.

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26

Advanced engineering of nanomaterials using atmospheric pressure plasma jet (APPJ)

Avishek Dey1, Paheli Ghosh1, Gauthaman Chandrabose1, Satheesh Krishnamurthy1, Nicholas Braithwaite2

1School of Engineering and Innovation, The Open University , UK 2School of Physical Sciences, The Open University , UK

[email protected]

Plasma processing of materials has grown to be a key technology for various industrial applications. Low pressure plasmas have found wide applications; they require expensive vacuum systems and need orderly maintenance. Atmospheric pressure plasma jets (APPJs) on the other hand are less technically demanding. APPJs can generate a high flux of active species and offer promising alternatives to low pressure plasmas for surface treatment. For an APPJ the plasma is not confined within the dimensions of the electrodes and can be directed towards the desired region.[1] Our research is aimed at three novel applications of atmospheric pressure plasmas: synthesis, printing and functionalization of nanomaterials. In terms of printing we have been able to successfully demonstrate the patterned deposition of various organic and inorganic nanomaterials e.g. graphene oxide (GO), Spiro-OMeTAD and metal oxide inks. By carefully controlling the plasma parameters such as gas composition, flow rate and applied voltage, we are able to tune the chemical, electronic and crystal structure of these materials. A low power (5 W) plasma jet operated with He+O2 has been used to transform the crystal structure of CuO/TiO2 composite, enhancing its photo-electrochemical properties.[2] Also, by designing a high power plasma jet we are able to print GO on flexible substrates in addition to tuning its chemical and electrical properties. [3] Spiro-OMeTAD is conventionally used as an organic hole-transport material in perovskite solar cell. We have also succeeded in depositing thin films of Spiro-OMeTAD using APPJ along with controllably changing its electronic band structure. This is expected to lead to enhanced solar cell efficiency.

Figure 7. (a) XRD pattern of CuO/TiO2 composite showing strurla evolution with APPJ functionalisation ; (b) C K-edge NEXAFS spectra of APPJ printed GO revealing the ability to tune the chemical properties in-situ with APPJ deposition ; (c) controlling the electronic and structure of APPJ deposited Spiro-OMeTAD thin films, proven from the UPS spectra.

Dey, A., Chroneos, A., Braithwaite, N. S. J., Gandhiraman, R. P., & Krishnamurthy, S. (2016). Plasma engineering of graphene. Applied Physics Reviews, 3(2), 021301.

Golda, J., Held, J., Redeker, B., Konkowski, M., Beijer, P., Sobota, A., Schulz-Von Der Gathen, V. (2016). Concepts and characteristics of the “COST Reference Microplasma Jet.” Journal of Physics D: Applied Physics, 49(8).

Dey, A., Krishnamurthy, S., Bowen, J., Nordlund, D., Meyyappan, M., & Gandhiraman, R. P. (2018). Plasma Jet Printing and in situ Reduction of Highly Acidic Graphene Oxide. ACS Nano, 12(6), 5473–5481.

(a) (b) (c)


27

Surface production of negative ions from nitrogen doped diamond using hydrogen and deuterium plasmas

Gregory J. Smith1

* , Roba Moussaoui2, Alix Gicquel3 , Jocelyn Achard3, James Ellis1

, Timo Gans1

, James P. Dedrick1 , and Gilles Cartry2

1 York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DD, UK

2 Physique des Interactions Ioniques et Molėculaires, service 241, Centre de St Jérôme, 13397 Marseille Cedex 20, Aix Marseille University / CNRS

3 LSPM, CNRS-UPR 3407 Universit Paris 13, Avenue J. B. Clément, F-93430 Villetaneuse Labex

[email protected]

Sources of negative ions are of significant interest for numerous applications, including the production of neutral beams necessary for the heating of magnetic confinement fusion plasmas. Current methods to create negative ions in these applications utilise caesium deposited onto the inside of the ion source, but this introduces complex engineering challenges. Diamond, or dielectric materials similar to diamond, are a prospective alternative to caesium and so understanding the production of negative ions from dielectric surfaces is an important research objective. This study builds on investigations into the influence of n and p -type doped diamond and the mechanisms for surface production of negative ions with dielectrics. Microcrystalline diamond coated surfaces were negatively biased and exposed to a 2 Pa, 26 W deuterium plasma in order to bombard them with deuterium ions. This process creates negative ions at the diamond surface that are measured using mass spectrometry. By comparing the number of negative ions coming from the surfaces of various samples of nitrogen and boron doped diamond, it is shown that doping diamond positively influences the number of negative ions produced at the surface of the sample whilst under low energy (10 eV/nucleon) positive ion bombardment. Using diamond or diamond-like surfaces as alternatives to caesium holds promise for increased reliability of neutral beam injection devices for magnetic confinement fusion. The results of this study demonstrate that doping diamond has an important effect on this mechanism. Acknowledgements The authors would like to acknowledge the experimental support of Jean Bernard Faure, the PIIM surface group, and the administrative support of the York plasma institute. The financial support of the EPSRC Centre for Doctoral Training in fusion energy is gratefully acknowledged under financial code EP/L01663X/1. Also acknowledged is the financial support of the French Research Agency (ANR) project: H INDEX TRIPLED under grant ITER-NIS (ANR BLAN08-2 310122) ‘ITER-Negative Ion Sources’.


28

Investigation on the RONS and bactericidal effects induced by He+O2 cold plasma jets: in open air and in an airtight chamber

Han Xu, Dingxin Liu, Weitao Wang, Michael G Kong

State Key Laboratory of Electrical Insulation and Power Equipment, Center for Plasma Biomedicine, Xi’an Jiaotong University, Xi’an 710049, P. R. China

[email protected]

As a main way for discharge, atmospheric pressure plasma jet (APPJ) has the indubitable advantage that they are able to transport the plasma with various reactive species to a separate region for treatment applications. In most studies, there would inevitably be air mixing into plasma as the plasma jet in open air. However, certain study reports that the afterglow gas of He + O2 plasma (without the air mixing) also can lead to high bactericidal activity, and this afterglow gas can be used for sterilization. In addition, many research groups have studied that the biological effect of the plasma jet can be significantly improved when the additive O2 is added into the working gas, for the concentrations of several ROS which considered to play an important role are increased a lot. So, which reactive species plays an important role in the bactericidal effects of the He + O2 plasma jets? How much the concentrations of aqueous reactive species can be affected by air mixing in the interaction of He + O2 plasma and aqueous solution. In this paper, the He+O2 plasma jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the plasma jet in open air has higher densities of gaseous reactive species, higher concentration of aqueous H2O2, but lower concentrations of aqueous OH and O2-. In addition, increasing of O2 ratio in He in both plasma jets causes linear decreasing of the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase of additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of additive O2 presence or absence in He plasma jet. The concentrations trends of O2- for both the plasma jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- (SOD) is used, indicating that O2- should be a main antibacterial agent.


29

Investigation of pseudospark plasma-sourced sheet electron beam for application in high power millimetre wave radiation generation

H. Yin, L. Zhang, W. He, and A. D. R. Phelps and A.W. Cross,

Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, UK

[email protected]

High quality high current electron beams are required for high power millimetre wave radiation generation to answer the demands in high data rate mobile communications, high resolution radar and spectroscopy, etc. Nevertheless, as the radiation frequency goes up into millimetre wave range, a sheet-shaped electron beam displays much better performance compared with a pencil-shaped beam. This is because a sheet beam is of larger cross section than a pencil beam so that a higher sheet beam current can be achieved. However the formation and focusing and propagation of a sheet electron beam is challenging especially when the beam has to be transported down through a structure of small transverse cross-section in the sub-millimetre range. For this reason, pseudospark discharge has been recently investigated for high current sheet electron beam generations on the basis that it has shown to be an excellent pencil electron beam sources in various experiments [1-5]. The outstanding feature of using a pseudospark discharge for electron beam production is the formation of an ion channel following the pseudospark anode, which enables the beam to propagate and eliminates the need for a guiding magnetic field. When a high voltage is applied to the hollow cathode, the electric field across the anode-cathode gap penetrates a short distance into the hollow cathode region due to the small cathode aperture. A PS discharge will occur if the pressure in the system is suitably low (typically 50-500 mTorr) so that the discharge is at the left-hand side (with respect to the minimum) of the Paschen curve. A PS discharge basically evolves through three stages, 1) Townsend discharge; 2) hollow cathode discharge; 3) final conductive stage. Electron beams with moderate beam current and high energy can be obtained in the second hollow cathode stage for direct applications. The beam current reaches its maximum in the final conductive discharge stage, while the beam energy rapidly decreases due to the breakdown between the gaps. Post-acceleration of the pseudospark beam generated in the third stage could result in desirable beam of combined high beam current and energy. An experimental investigation of the pseudospark sheet beam generation was carried using a system consisted of a pseudospark discharge section and a post-acceleration unit. A high quality sheet beam of size of 2.0 mm×0.25 mm was generated and used in the generation of millimetre wave radiation successfully. This opens exciting future applications ahead. [1] W. He.,L. Zhang, et al, “Generation of broadband terahertz radiation using a backward wave oscillator and pseudospark-sourced electron beam”, Appl. Phys. Lett. 107, 133501 (2015). [2] J. Zhao, H. Yin, L. Zhang, G. Shu, W. He, et al, “Influence of the electrode gap separation on the pseudospark-sourced electron beam generation”, Phys. Plasmas 23(7) 073116 (2016) [3] Y. Yin, W. He, L. Zhang, H. Yin, C. W. Robertson and A. W. Cross, “Simulation and Experiments of a W-band Extended Interaction Oscillator based on a pseudospark-sourced electron beam,” IEEE Trans. Electron Devices, vol. 63, no. 1, pp. 512 - 516, Jan. 2016. [4] G. Shu, W. He, L. Zhang, Y. Yin, J. Zhao, A. W. Cross, A. D. R. Phelps, “Study of a 0.2THz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam,”IEEE Trans. Electron Devices，vol. 63, no. 12, pp. 4955-4960, Dec. 2016.


30

The interaction of gas-plasma jets with liquids: modelling and experiments

Chinasa J. Ojiakoa, Dmitri Tseluikoa, Roger Smitha, Hemaka Bandulasenab

aDepartment of Mathematical Science, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK,

bDepartment of Chemical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK

[email protected]

Gas-plasma interactions with liquids find applications in industries and medicine. We aim to model the interaction of a plasma jet with a liquid accounting for hydrodynamics, electro-hydrodynamics and chemical kinetics. This involves the calculation of flows generated in the gas and liquid, the rate at which the generated long-lived and short-lived plasma species are transferred to the liquid as well as the associated chemical reactions. Plasma is artificially generated by subjecting a neutral gas (for example, helium, argon) to a strong electromagnetic field to a point where an ionised gaseous substance becomes increasingly electrically conductive.

We start by modelling gas (air, helium and argon) jets striking a liquid (water) surface, both with and without the presence of an electric field. This forms a cavity in the liquid and generates eddies which are responsible for mixing and mass transfer of species to the liquid.

The hydrodynamic problem is solved using both the CFD package in COMSOL and also using a thin film approximation. Both models are compared to each other and also to experiment. Good agreement with interface shapes was obtained.

When a plasma strikes a liquid, there is also an associated electric field and the plasma itself can also be quite hot. These two effects are decoupled and analysed separately. Modelling shows that there is a substantial difference with the flow patterns compared to the purely hydrodynamic problem with the interface distortion being much less due to the conflict between the electric field and the momentum transfer from the jet, in agreement with the experimental results.


31

Investigation of the physico-chemical properties of an atmospheric-pressure DBD operating in two distinct homogenous modes

K McKay1, D Donaghy1, F He2, J Bradley1 1Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool, L69 3GJ, United Kingdom, 2School of Physics, Beijing Institute of Technology,

PO Box 327, Beijing 100081, People’s Republic of China [email protected]

Using ambient molecular beam mass spectrometry we have examined the ionic content of two distinct homogenous modes produced in a helium-based atmospheric-pressure parallel plate dielectric barrier discharge. By applying 10 kHz microsecond voltage pulses with nanosecond rise times and 10 kHz sinusoidal voltage waveforms two distinctly different glow and Townsend modes were produced, respectively. Results showed significant differences in the dominant ion species produced in the two modes. In the Townsend mode, molecular oxygen ions, atomic oxygen anions and nitric oxide anions were the most abundant species, however, in the glow mode water clusters ions and hydrated nitric oxygen anions dominated. Several hypotheses are put forward to explain these differences, including low electron densities and energies in the Townsend mode, more efficient ionization of water molecules through penning ionization and charge exchange with other species in glow mode, and large temperature gradients due to the pulsed nature of the glow mode, leading to more favourable conditions for cluster formation. At high powers in the glow mode a reversal in hydrated ion trends was also observed, this was particularly evident for the negative ion species, this was thought to be due to higher gas temperatures being achieved, leading to suppression of cluster formation.

Figure 8. (a) DBD-MS set up (b) positive ion chemistry for (a) Townsend and (b) glow modes

Kirsty McKay et al 2018 Plasma Sources Sci. Technol. 27 015002

(a) (b)


32

Surface treatment for adhesion improvement of glass and PMMA adherends for optical applications in hostile environments

V. Bagiatis1, G.W. Critchlow1, D. Price 1Department of Materials, Loughborough University, Loughborough, Leicestershire LE11 3TU

[email protected]

Joining of optical elements with adhesives presents challenges when dissimilar materials are used and when they are used in hostile environments; for example, these might include temperature changes, shock and vibration. A further complication is incurred when optical transparency is required and stability under exposure to UV radiation. Flexible adhesives like RTV silicones have the capability to absorb stresses and thermal expansion [1] especially when two adherends with significantly different coefficients of thermal expansion like glass (9x10-

6 m/(m K)) and PMMA (75x10-6 m/(m K)) , are being used. However, such adhesives do not form strong joints with untreated glass or polymer surfaces. An appropriate surface preparation can improve significantly the adhesion strength [2]. In the current project various surface treatments have been assessed with a focus on atmospheric pressure plasma treatment (APPT) with oxygen and argon or helium admixture.

Figure 9. AFM images of PMMA surface before (A) and after 30 seconds of atmospheric pressure argon plasma treatment (B)

Figure 2. Water contact angle of untreated glass surface (left) and after plasma treatment (right)

Figures 1 and 2 show the influence of the plasma process on the surface topography and wettability on surfaces of PMMA and glass. These data were correlated with adhesive joint strength data which showed the efficacy of the optimised plasma process. To evaluate the effect of the surface treatment (APPT and silane-based primers) of the glass and PMMA substrates on the strength of the adhesive bond, lap shear tests according to ASTM C961 – 15 were performed using a displacement loading rate of 10 mm/min in ambient temperature.

1. E. A. S. Marques, Lucas F. M. da Silva, M. D. Banea & R. J. C. Carbas (2015) Adhesive Joints for Low- and High-Temperature Use: An Overview, The Journal of Adhesion, 91:7,556-585

2. Norouzi, A.R., Nikfarjam, A. & Hajghassem, (2018) PDMS–PMMA bonding improvement using SiO2 intermediate layer and its application in fabricating gas micro valves, H. Microsystem Technologies, 24: 2727.


33

Carboxylation in Flow Chemistry using a DC Plasma System

M. Shaban1, A. Randi2, B.R. Buckley2 and F. Iza1

1Wolfson School of Mechanical, Electrical and Manufacturing Engineering 2Department of Chemistry

Loughborough University, Loughborough LE11 3TU, United Kingdom [email protected]

At a rate of over 30 billion tons per year, carbon dioxide (CO2) gas represents one of the largest sources of human waste. Scientists have approached the challenge of CO2 reformation with a variety of tools and techniques but existing approaches are not mutually exclusive and usually overlap with one another, yielding hybrid methods such as electro catalytic and photo electro catalytic reduction processes [1-2]. An alternative approach is to inject free electrons from the gas-phase into the liquid from a plasma or gas discharge. Plasma electrochemistry, also called glow discharge electrolysis, is an electrochemistry technique where one (or both) of the electrodes in an electrolytic cell is replaced by a plasma. In this research, we developed a DC plasma reactor to investigate more about plasma electrochemistry using CO2 as a raw material.

In this work, we used atmospheric-pressure plasma in Helium as a cathode to electrochemically reduce carbon dioxide in aqueous solution. Using chemistry analytical techniques (Gas Spectrometry Mass Chromatography), we show that electrons reduce CO2 to form the carboxyl radical anion CO2, which then reacts with trans-Stilbene (Substrate) to form carboxylic Acid (2,3 Diphenylpropanoic Acid). The overall efficiency (Percentage yield) of the reaction is close to 10 % and current efficiency reaches up to 80 % in certain conditions for a CO2 saturated DMF in contact with plasma for 20 minutes in continuous flow. However, given the known reaction scheme and efficiency of electrons, this efficiency should increase depending on several factors. Figure 1 show cross sectional view of continuous flow plasma driven reaction cell.

Figure 10 Continuous flow DC plasma device.

J. T. Gudmundsson and A. Hecimovic, “Foundations of DC plasma sources,” Plasma Sources Sci. Technol, vol. 26, 2017.

H. M. Jhong, S. Ma, and P. J. A. Kenis, “Electrochemical conversion of CO 2 to useful chemicals : current status , remaining challenges , and future opportunities,” Curr. Opin. Chem. Eng., vol. 2, no. 2, pp. 191–199.


34

Space Averaged Mathematical Model of Pulse Powered Atmospheric Pressure Air Plasma

F.H. Montazersadgh1, A. Wright1,2 and A. Shaw1, F. Iza1

1Wolfson School of Mechanical, Electrical and Manufacturing Engineering 2Chemical Engineering

Loughborough University, Loughborough, Leics. LE11 3TU, United Kingdom

[email protected]

Althoughnumericalstudieshavebeenperformedonatmosphericpressureplasmaspreviously[1‐3]acomprehensiveresearchoutliningtheexacteffectsofpulsedpowerinputisyettobedone.It has been observed experimentally that the same peak power input delivered with different duty cycles results in a significant difference in effluent gas composition that do not scale linearly with the duty cycle.

To gain further insight into the underlying physicochemical mechanisms that underpin this behaviour, aspaceaveragedmathematicalmodeldescribingapulsepoweredatmosphericpressureairplasmawas developed. Two input power profileswith 5% and 45%duty cycleswere comparedwith asimilarDBDexperimentalsetup.Theatmosphericpressuredryairplasmamodelconsistedofmorethan380reactionsand36speciesdevelopedaccordingto[1].Thesystemofequationswasthensolved by a zero‐dimensional globalmodelwith a stiff differential equation solver and variabletime steps in Matlab TM. To verify the model results, long‐lived species densities and the gastemperature was measured in a simple DBD plasma. Gas temperature was measured using athermocouple located as close as possible to the plasma medium and effluent gasses weremeasuredusingFTIR.

The results show that while the gas temperature plays an important role in the gas densityevolution, it isnottheonlyeffective factor.Initially, higher density of long-lived species is obtained with the higher duty cycle because the plasma is on during longer periods of time and therefore more plasma products accumulate throughout the same simulation period. Short-lived species also accumulate to a degree as they do not have enough time to perish in between pulses, whereas in the lower duty cycle case short-lived species are mostly consumed before reaching the next power pulse. This trend changes for ozone at t=10 seconds when non-ozone producing chemical pathways are favoured because of higher gas temperature in the higher duty cycle and the ‘poisoning’ of the background gas as NOx species accumulate and quench the ozone produced.


35

Plasma effects on microbubble formation in gas-liquid interface across a microfluidic plasma reactor.

O. Ogunyinka, A. Wright, G. Bolognesi, F. Iza, H. Bandulasena

1Wolfson School of Mechanical, Electrical and Manufacturing Engineering 2Department of Chemistry

Loughborough University, Loughborough LE11 3TU, United Kingdom [email protected]

Atmospheric-pressure plasmas has increasingly been studied for their potential in many applications, such as water treatment, generation of reactive species, biological applications, and material synthesis [1]. This study involves the use of atmospheric-plasma in microscale to transfer plasma reactive species to organic liquid via microbubbles gas-liquid interface. Hence, plasma interaction with microbubbles is a topic to investigate.

An innovative microfluidic reactor has been designed to enhance the mass transfer rate and harness of plasma reactive species in plasma-liquid interface. This device is capable of transferring the reactive species into various aqueous solution for treatment. The microfluidic device is a cross-junction co-flowing regime that generates microbubbles. This insures the maximum transfer of the species due to the large interfacial area to volume ratio of microbubbles. This device is likewise a dielectric barrier discharge (DBD) plasma, that is facilitated by using two aluminium tapes, acting as electrodes, placed in the bulk of the device across the gas flow microchannel to generate an electric discharge.

So far, the device has been used to investigate the effect of plasma discharge on a conventional gas-liquid microbubble formation in microfluidics. This was conducted by observing the formation and size of the microbubbles with plasma (electric field applied on the gas flow) and without plasma. It was observed that the plasma discharge resulted in an increase on the microbubble size and an alteration in the formation mechanism. It was concluded that the primary factor for these effects was a variation in the volumetric flow of the gas when the gas is discharged. The change in temperature between the gas and the plasma was analysed.

P. Lukes et al., “Atmospheric plasma generates oxygen atoms as oxidizing species in aqueous solutions,” J. Phys. D Appl. Phys, vol. 49


36

Pre-treatment of a faecal simulant for bio-ethanol production with a novel microbubble enhanced DBD plasma reactor

A. Wright, A. Marsh, A. Shaw, G. Shama, F. Iza, H. Bandulasena Chemical Engineering, Loughborough University, LE11 3TU, United Kingdom

[email protected]

It is now widely known both within and outside of the scientific community there is a shortage of renewable energy options to replace the diminishing supply of fossil fuels. In recent years biomass has been seen as a sustainable alternative to provide a transport fuel for the growing number of vehicles on the roads. Here a cellulose rich product is fermented to form ethanol via an intermediary of glucose. However the existing methods for the breakdown of cellulose are either energy intensive or have a high consumption of chemicals. Atmospheric pressure plasma has been identified as one way of reducing the cost of biomass pre-treatment.1

Several biomass feed stocks have been investigated but feasibility is limited due to cost of production and processing. One feed stock that is not limited by these factors is faecal slurry which is high in cellulose and is seen as a waste to many. In this study cellulose, one of the major components of faecal slurry2 was treated in a microbubble enhanced DBD plasma reactor. The degree of solubility in sodium hydroxide and the percentage of realised sugars when hydrolysed were used a measure of effectiveness.

Figure 1 (a) shows that as the cellulose is treated the solubility rapidly increases over the first 30 minutes before plateauing and reaching a maximum after 90 minutes. This indicates that the highly crystalline structure of the cellulose is being broken by the reactive species produced from the plasma. This is further evident in figure 1 (b) which shows how the glucose concentration is higher for a cellulose samples that has been treated for a longer period of time.

Figure 11: (a) shows the effect of pre-treatment time on the solubility of cellulose and (b) the measured glucose concentration.

References: 1. Esrey, S.A. (2000). Towards a recycling society. Ecological sanitation – closing the loop to food security.

In proceedings of the international symposium, 30–31 October, 2000. Bonn, Germany. GTZ, GmbH. 2001

2. A. Wright et al. (2017). Dielectric Barrier Discharge Plasma Microbubble Reactor for Pretreatment of Lignocellulosic Biomass. AIChE.

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37

Atmospheric-pressure plasma device for CO2 Conversion and Utilization

A.Randi1, B.R. Buckley1, F. Iza2, U. Wijayantha1, A. Shaw2

1Department of Chemistry, Loughborough University, United Kingdom 2Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough

University, United Kingdom

[email protected]

The increasing levels of CO2 in the atmosphere and its consequential impact on global warming is driving many research groups to develop ways to use CO2 as raw material. For example, to produce feedstocks, or fuels.

A wide variety of approaches to carbon dioxide utilisation have been reported employing homogeneous catalysis, heterogeneous catalysis, photocatalysis, photoreduction and electrochemical reduction. Formic Acid was produced with very high Faradaic efficiency on metals. Copper catalysis was found to be successful in reducing CO2 to hydrocarbons.

Besides the reduction of greenhouse gases, by producing feedstocks using CO2 will greatly reduce our dependence of fossil fuels for chemical synthesis. Our previously reported electrochemical processes have proven to be successful in terms of electron transfer between substances at room temperature and atmospheric pressure (See Scheme), in this we have explored the use of substituted acetylenes (See Scheme) to give selectively mono-carboxylated products.

Atmospheric-pressure plasmas interacting with organic liquids offer a new possibility for chemical synthesis that remains largely unexplored. Here we report on the results obtained with a Jet device in which chemical reactions are triggered in an organic liquid by an atmospheric-pressure plasma.

As a proof-of-concept, we considered the incorporation of CO2 into an alkyne to form a carboxylic acid. Here we explore plasma reduction. A CO2 saturated solution of diphenylacetylene in Tetra-n-butylammonium iodide (Bu4NI), Dimethylformamide (DMF) and Argon DC plasma is used as a gaseous cathode to provide electrons for the reduction of CO2. Gas chromatography Mass Spectroscopy (GCMS) and Nuclear Magnetic Resonance (NMR) analysis indicate the formation of 2,3 diphenylpropanoic acid with good selectivity although further optimization is needed to increase yield and increase the current efficiency of the device.

[1] Jhong HM, Ma S, Kenis PJ Electrochemical Conversion of CO2 to useful chemicals: current status, remaining challenges, and future opportunities, Chemical Engineering 2013 2: 191-199.

[2] C. Richmonds, M. Witzke, B. Bartling, S. W. Lee, J. Wainright, C. Liu, and R. M. S. Electron-Transfer Reactions at the Plasma -Liquid Interface. Journal of the American Chemical Society, 2011 133, 17582–17585.


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The fate of plasma-generated oxygen atoms in aqueous solution

A Shaw1, J Benedikt2, M Mokhtar Hefny3, BR Buckley1, S Schäkermannf3, JE Bandow3, F Iza1

1 Loughborough University, United Kingdom 2 Christian-Albrecht-Universität zu Kiel, 24098 Kiel, Germany

3 Future University in Egypt, Cairo, Egypt 4 Ruhr-Universität Bochum, 44780 Bochum, Germany

[email protected]

Non-equilibrium radio-frequency (RF) atmospheric-pressure He/0.6%O2 plasma has been used to study the fate of plasma-generated oxygen atoms in aqueous solutions. An RF COST jet[1] was used to generate plasma using standard and 18O-labeled O2 gas and the effluent was directed to an aqueous solution containing phenol as a chemical probe. Comparison of the mass spectrometry and gas chromatography-mass spectrometry data of the plasma treated solutions provides clear evidence that O(aq) originating from the gas phase enters the liquid readily and reacts directly with phenol, without any intermediate reactions with water molecules. This study demonstrates the great potential of atmospheric-pressure plasma source as a source of O(aq) atoms and the possibility of these atoms to directly interact with organic compounds in aqueous solutions.

Figure 1. The reaction pathways of O atoms in the gas phase and the phenol solution. The solid arrows summarize the main reaction pathways, and the broad arrows in the background indicate the gas and liquid

movement[2].

[1] Golda J et al. 2016 J. Phys. D. Appl. Phys. 49

[2] Benedikt J et al. 2018 Phys. Chem. Chem. Phys. 20 12037–42


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Quantemol Database: Complex Chemistry Reduction and Chemistry Set Generation

Adetokunbo Ayilaran1, Jonathan Tennyson12, Sebastian Mohr1, Martin Hanicinec12, Dan Brown1, Anna Dzarasova1

1Quantemol Ltd, 2University College London [email protected]

Quantemol DB1 is a web-based supported database of electron and heavy particles collisional data. Apart from data and cross sections for collisional and reactive processes, QDB also offers pre-assembled and validated self-consistent chemistry sets for plasma modelling applications. However, many of these chemistry sets may not reflect the exact plasma operating conditions that benefit the user – meaning there is a necessity to reduce chemistry sets based upon user application. Even so, there are more stringent conditions on using these chemistry sets in 2D and 3D modellers and it has been identified particularly with 3D modellers such as COMSOL that solution convergence is particularly difficult when the chemistry set is above 50 pathways.

The next stage of QDB aims to unveil a new chemistry generator which serves to not only build tailored chemistry sets for the user based upon a large library of reaction data, but to also aid in its reduction using a combination of 0D modelling and sensitivity analysis. These numerical methods aim to identify the major reactions and species for a given parameter range in order to produce the smallest possible chemistry sets without a loss of significant information.

The automatic generation of chemistry sets is under development and features rigorous algorithms based upon numerical methods2 to sense test chemistries for dynamic outputs based upon pressure and power. This generator would become the standard for chemistry set design and would fit the added functionality of QDB; being able to output these chemistry sets as input files for various modelling software’s.

Figure 12. (a) Electron Density; (b) Electron Temperature; (c) F Density

Figure 1. illustrates the effect of chemistry set reduction on a complex CF4/O2/N2/H2 discharge between 1 mTorr and 30 mTorr. The full chemistry set was 400 reaction pathways with 52 species whilst the reduced set was 84 reaction pathways with 26 species. Essential source and loss pathways were identified with this method and this resulted in a chemistry set reduction.

J. Tennyson et al., "QDB: A new database of plasma chemistries and reactions", Plasma Sources Science and Technology 26, 055014 (2017).

M. M. Turner, "Uncertainty and Sensitivity Analysis in Complex Plasma Chemistry Models", Plasma Sources Science and Technology 25, 015003


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programme and book of abstracts - tpw-uk.orgtpw-uk.org/docs/book_of_abstracts_2018.pdf · abstracts...

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