News

Research activities

First (V)UV-double-monochromator calibration measurements at AG Benedikt in Kiel

To achieve a relative intensity calibration of a (V)UV-monochromator, the use of the double monochromator method is common. Two monochromators work in tandem and the difference in the spectrum from a stable light source of the first monochromator through the second monochromator is utilized to obtain a relative intensity calibration. From July 8th until July 12th, Beatrix Biskup from project B2 of the SFB-TR 87, stayed at the university in Kiel to achieved the monochromator calibration.

The monochromator from Bochum was transported beforehand to the AG Benedikt at CAU (Christian-Albrechts-University) in Kiel. The technical staff made all the preparations necessary for the monochromators from Bochum and Kiel to work together in tandem. Together with Dr. Judith Golda and Prof. Dr. Jan Benedikt in Kiel, Beatrix Biskup did the first test measurements, which could be successfully accomplished. A further cooperation with the research group will be executed in future.

Public relations

Plasma barbeque 2019

On Wednesday July 3rd, the annual Plasma barbeque took place at Ruhr-Universität Bochum. Students from the physics faculty as well as from the electrical engineering could meet PhD students from both faculties and inform themselves about plasma studies in a pleasant atmosphere.

Conferences

Successfull contributions at the 10th HIPIMS conference in Braunschweig

Three members of the SFB-TR87 (EPII) attended the joined Conference on Sputter Technology and on High Power Impulse Magentron Sputtering (HiPIMS) in Braunschweig, June 19-20. This edition of the annual conference was the 10th edition of the international conference on HiPIMS, for the first time combined with the International Conference on Sputter Technology. 
The two day conference featured an international audience from both industry and science. 
Two posters were presented on recent work of the SFB-TR87 concerning the ion beam experiment of the project C7 and the research of project A5 on ion transport in HiPIMS. Julian Held (A5) recieved the young scientist award for the best poster in the category HiPIMS for his contribution "Experimental and computational study of titanium ion movement in the target region of HiPIMS".

Next years HiPIMS conference will be held in Sheffield, UK.

PLASMA RESEARCH

Lightning bolt underwater 

© RUB, Kramer

A plasma tears through the water within a few nanoseconds. It may possibly regenerate catalytic surfaces at the push of a button.

Electrochemical cells help recycle CO2. However, the catalytic surfaces get worn down in the process. Researchers at the Collaborative Research Centre 1316 “Transient atmospheric plasmas: from plasmas to liquids to solids” at Ruhr-Universität Bochum (RUB) are exploring how they might be regenerated at the push of a button using extreme plasmas in water. In a first, they deployed optical spectroscopy and modelling to analyse such underwater plasmas in detail, which exist only for a few nanoseconds, and to theoretically describe the conditions during plasma ignition. They published their report in the journal Plasma Sources Science and Technology on 4 June 2019.

A plasma tears through the water within a few nanoseconds. Following plasma ignition, there is a high negative pressure difference at the tip of the electrode, which results in ruptures forming in the liquid. Plasma then spreads across those ruptures.

Video: Experimentalphysik II

Plasmas are ionised gases: they are formed when a gas is energised that then contains free electrons. In nature, plasmas occur inside stars or take the shape of polar lights on Earth. In engineering, plasmas are utilised for example to generate light in fluorescent lamps, or to manufacture new materials in the field of microelectronics. “Typically, plasmas are generated in the gas phase, for example in the air or in noble gases,” explains Katharina Grosse from the Institute for Experimental Physics II at RUB.

Ruptures in the water

In the current study, the researchers have generated plasmas directly in a liquid. To this end, they applied a high voltage to a submerged hairline electrode for the range of several billionth seconds. Following plasma ignition, there is a high negative pressure difference at the tip of the electrode, which results in ruptures forming in the liquid. Plasma then spreads across those ruptures. “Plasma can be compared with a lightning bolt – only in this case it happens underwater,” says Katharina Grosse.

Hotter than the sun

Using fast optical spectroscopy in combination with a fluid dynamics model, the research team identified the variations of power, pressure, and temperature in these plasmas. “In the process, we observed that the consumption inside these plasmas briefly amounts to up to 100 kilowatt. This corresponds with the connected load of several single-family homes,” points out Professor Achim von Keudell from the Institute for Experimental Physics II. In addition, pressures exceeding several thousand bars are generated – corresponding with or even exceeding the pressure at the deepest part of the Pacific Ocean. Finally, there are short bursts of temperatures of several thousand degrees, which roughly equal and even surpass the surface temperature of the sun.

Water is broken down into its components

Such extreme conditions last only for a very short time. “Studies to date had primarily focused on underwater plasmas in the microsecond range,” explains Katharina Grosse. “In that space of time, water molecules have the chance to compensate for the pressure of the plasma.” The extreme plasmas that have been the subject of the current study feature much faster processes. The water can’t compensate for the pressure and the molecules are broken down into their components. “The oxygen that is thus released plays a vital role for catalytic surfaces in electrochemical cells,” explains Katharina Grosse.  “By re-oxidating such surfaces, it helps them regenerate and take up their full catalytic activity again. Moreover, reagents dissolved in water can also be activated, thus facilitating catalysis processes.”

By Meike Drießen, Translated by Donata Zuber
Recent research achievement

How bacteria protect themselves from plasma treatment 

© Daniel Sadrowski

Plasmas are applied in the treatment of wounds to combat pathogens that are resistant against antibiotics. But bacteria know how to defend themselves.

Considering the ever-growing percentage of bacteria that are resistant to antibiotics, interest in medical use of plasma is increasing. In collaboration with colleagues from Kiel, researchers at Ruhr-Universität Bochum (RUB) investigated if bacteria may become impervious to plasmas, too. They identified 87 genes of the bacterium Escherichia coli, which potentially protect against effective components of plasma. “These genes provide insights into the antibacterial mechanisms of plasmas,” says Marco Krewing. He is the lead author of two articles that were published in the Journal of the Royal Society Interface this year.

A cocktail of harmful components stresses pathogens

Plasmas are created from gas that is pumped with energy. Today, plasmas are already used against multi-resistant pathogens in clinical applications, for example to treat chronic wounds. “Plasmas provide a complex cocktail of components, many of which act as disinfectants in their own right,” explains Professor Julia Bandow, Head of the RUB research group Applied Microbiology. UV radiation, electric fields, atomic oxygen, superoxide, nitric oxides, ozone, and excited oxygen or nitrogen affect the pathogens simultaneously, generating considerable stress. Typically, the pathogens survive merely several seconds or minutes.

In order to find out if bacteria, may develop resistance against the effects of plasmas, like they do against antibiotics, the researchers analysed the entire genome of the model bacterium Escherichia coli, short E. coli, to identify existing protective mechanisms. “Resistance means that a genetic change causes organisms to be better adapted to certain environmental conditions. Such a trait can be passed on from one generation to the next,” explains Julia Bandow.

Mutants missing single genes

For their study, the researchers made use of so-called knockout strains of E. coli. These are bacteria that are missing one specific gene in their genome, which contains approximately 4,000 genes. The researchers exposed each mutant to the plasma and monitored if the cells kept proliferating following the exposure.

“We demonstrated that 87 of the knockout strains were more sensitive to plasma treatment than the wild type that has a complete genome,” says Marco Krewing. Subsequently, the researchers analysed the genes missing in these 87 strains and determined that most of those genes protected bacteria against the effects of hydrogen peroxide, superoxide, and/or nitric oxide. “This means that these plasma components are particularly effective against bacteria,” elaborates Julia Bandow. However, it also means that genetic changes that result in an increase in the number or activity of the respective gene products are more capable of protecting bacteria from the effects of plasma treatment.

Heat shock protein boosts plasma resistance

The research team, in collaboration with a group headed by Professor Ursula Jakob from the University of Michigan in Ann Arbor (USA), demonstrated that this is indeed the case: the heat shock protein Hsp33, encoded by the hslO gene, protects E. coli proteins from aggregation when exposed to oxidative stress. “During plasma treatment, this protein is activated and protects the other E. coliproteins – and consequently the bacterial cell,” Bandow points out. An increased volume of this protein alone results in a slightly increased plasma resistance. Considerably stronger plasma resistance can be expected when the levels of several protective proteins are increased simultaneously.

By Meike Drießen, Translated by Donata Zuber
Conferences

ISPC 24 in Naples

Between June 11th and 14th, the 24th International Symposium on Plasma Chemistry took place in Naples, Italy. A group of seven peole from the CRC 1316 as well as from the SFB-TR 87 joined the meeting. An honour was given to Achim von Keudell, who had a plenary talk on High power impulse magnetron sputtering – extreme plasmas for extreme materials. Also, Julia Bandow from project B8 of the CRC1316 had an invited talk on Plasma meets biotechnology – coupling plasma and enzymatic reactions. Further, Marc Böke had a talk on Separated effects of plasma species and post- treatment on the properties of barrier layers on polymers and Patrick Preissing presented his work on NO production in the COST Reference Microplasma Jet and a dielectric barrier discharge measured by means of Laser Induced Fluorescence (LIF).

Conferences

10th International Workshop on Microplasmas in Kyoto

This year, the 10th edition of the International Workshop on Microplasmas took place in Kyoto. The scope of the workshop are the generation/sources of microplasmas, modelling, and applications (material processing, biomedical material treatments, environmental devices etc.). Around 70 participants from all over the world joined the meeting. A group of nine people from Bochum, especially from the CRC 1316 joined the conference. Finally, two oral presentations and six poster presentations were given by them.

An oral presentation was held by Sebastian Dzikowski from project A6 from the CRC 1316 with the title "Initial ignition behavior of a micro cavity plasma array (MCPA)". Moreover, an invited talk was given by Dr. Volker Schulz-von der Gathen from the CRC with the title "Micro cavity plasma array devices: From first ignition to continuous operation".

Education

International School on Low Temperature Plasma Physics: Basics and Applications

The traditional summer school on low temperature plasma physics will go on in Octobre this year. The summer school takes place in Physikzentrum in Bad Honnef and is from Octobre 5th, 2019 until Octobre 10th, 2019. After the school, the master class will be from Octobre 10th, 2019 until Octobre 12th, 2019.

Participants are welcomed to sign in for registration until June 15th, 2019. Due to limitation in the number of rooms at the Physikzentrum, the attendance is limited.

 

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