The authors thank Volker Rohwer (Institute of Experimental and Applied Physics, Kiel University) for help with the equipment. The work was supported by the DFG within CRC 1316 Transient Atmospheric Plasmas, in the project Cold atmospheric plasmas for the study of fundamental interaction mechanisms with biological substrates (project-ID BE 4349/5-1), and in the project Plasma-generated nitric oxide in wound healing (project-ID SCHU 2353/9-1).

1. Feed gas supply and controlled atmosphere
<ol>
	<li>Set up the gas supply consisting of all-metal gas lines, avoiding any TPFE or similar plastics tubing24. Keep gas supply lines as short as possible to avoid any impurities and facilitate pumping of the gas supply system.</li>
	<li>Choose the mass flow controllers used to provide the feed gas according to the typical gas flow rates of the COST-Jet. Use working gas with a purity of at least 99.999%. 
	NOTE: The COST-Jet&#8217;s primary working gas is helium. Operation can be realized at flow rates between 100 sccm and about 5000 sccm, with 1000 sccm being the most common value.</li>
	<li>Realize the admixture of reactive gases by a system consisting of multiple mass flow controllers. For smaller admixtures, use a counter-mixing unit to reduce the time needed for the mixing to complete25. 
	NOTE: Common admixtures are oxygen and nitrogen with a flow rate in the order of 5 sccm (0.5% of the working gas).</li>
	<li>Add a valve between the gas supply lines and the jet to prevent moist air entering the gas supply when the device is not in use as water is the most common and most problematic impurity in atmospheric pressure plasmas, critically influencing the plasma chemistry.</li>
	<li>Clean the gas supply lines before the surface treatment, to reduce impurities in the tubing. To do so, either simply set a moderate gas flow of about 1000 sccm helium and flush the supply lines or, preferably, repeatedly pump and refill the supply lines (about three times). 
	NOTE: When simply flushing the gas supply lines, multiple hours might be needed to clean the system, depending on the state of contamination.</li>
	<li>Add a molecular sieve trap or cold trap (e.g., using liquid nitrogen) to the gas supply lines to further reduce the humidity in the feed gas.</li>
	<li>If, instead, a controlled amount of water is desired as a reagent, add a bubbler to the system26,27.</li>
	<li>Consider setting up a controlled atmosphere for your experiment as changes in the composition of the ambient atmosphere might influence chemical reactions in the plasma effluent. 
	NOTE: This effect is likely not very pronounced for the COST-Jet28, since the electric field configuration confines the plasma to the inside of the discharge channel but might play an important role for other CAP devices where the active plasma is partly outside the device.</li>
</ol>
2. Assembly and setup of the device
<ol>
	<li>Connect the COST-Jet device to a gas supply. Directly connect the device to &#188; inch stainless steel Swagelok tubing. Use adapters for different tubing standards.</li>
	<li>Connect the COST-Jet to the power supply using a shielded BNC cable equipped with an SMC connector.</li>
	<li>Connect the integrated electrical probes to an oscilloscope to monitor voltage and current using a 50 Ohm resistor as termination.</li>
	<li>Open the COST-Jet housing and connect a properly compensated commercial voltage probe to the powered copper line as well as a grounded part of the jet (e.g., the Swagelok gas tube) and the oscilloscope.</li>
	<li>Perform a probe calibration routine: Apply a small voltage to the COST-Jet and tune the variable capacitor of the LC-circuit using a screwdriver to reach the optimum coupling (maximize measured voltage). Perform a voltage calibration by comparing the actual voltage (commercial probe) to the measured voltage (implemented probe) using linear regression and calculate a calibration constant. Remove the commercial voltage probe and close the COST-Jet housing.</li>
	<li>Again, apply a small voltage to the COST-Jet and tune the variable capacitor of the LC-circuit using a screwdriver to reach the optimum coupling.</li>
	<li>Ignite a plasma in the COST-Jet device: Firstly, set up a gas flow rate of approximately 1 slpm of helium using mass flow controllers (MFCs). Open the valve between the gas supply system and the COST-Jet last. Then, apply a low voltage to the electrodes and increase the amplitude until the plasma ignites.</li>
	<li>If, upon the first ignition, the electrodes are unclean and impeding the ignition, apply a high initial voltage and quickly reduce it after ignition. Alternatively, use a spark gun to facilitate an easier first ignition.</li>
	<li>Set the operation control parameters (gas flow, applied voltage) to the desired values.</li>
	<li>Give the setup a little warm-up time to allow for thermal stabilization (approx. 20 minutes) to ensure stable and reproducible operation conditions.</li>
	<li>To change the gas composition during the experiments, allow for an approximate 2 minute equilibration time depending on the gas supply setup. 
	NOTE: The COST-Jet is now ready for application.</li>
</ol>
3. Power measurement
<ol>
	<li>Connect the oscilloscope monitoring the voltage and current applied to the COST-Jet to a computer.</li>
	<li>Install the &#8216;COST power monitor&#8217; software to the computer29 which allows real-time power monitoring11,19.</li>
	<li>Adjust the communication between the software and oscilloscope by implementing the required commands for controlling the specific oscilloscope.</li>
	<li>Start the COST power monitor software and switch to the Settings panel. Fill in the correct channels connected to the oscilloscope and the calibration constant determined in step 2.4. 
	NOTE: The Find button can be used to automatically calculate the calibration factor if the commercial voltage probe is attached to the COST-Jet.</li>
	<li>Change to the Sweep panel. Take a reference phase while the plasma is still off by pressing the Find button. Switch off the gas flow before this measurement and apply a voltage that is in the typical range of voltages used for the actual operation of the discharge as the plasma will not ignite in air due to much higher ignition voltage compared to noble gas dominated gas mixtures. Use this measurement to automatically correct for the relative phase shift between voltage and current probes, assuming a 90&#176; phase of the perfect capacitor here.</li>
	<li>Press the Start and Pause button to start or pause the electrical measurements.</li>
	<li>Operate the COST-Jet as desired. Use the actual electrical power calculated from voltage and current amplitudes as well as their phase shift, which are continuously displayed in the software for monitoring and as a control parameter.</li>
</ol>
4. (Solid) surface treatment
<ol>
	<li>Set up a controlled atmosphere for your experiment. 
	NOTE: In the case of the COST-Jet, the controlled atmosphere is less important than for sources with active plasma chemistry outside of the confined discharge channel.</li>
	<li>Clean the gas supply lines as described in step 1.5.</li>
	<li>Set the desired operating parameters and wait for approximately 20 minutes until the COST-jet reaches&#160;a stable temperature.</li>
	<li>Choose the distance between the COST-Jet and the treated surface as the distance determines the amount of reactive species impinging on the treated surface30. Use an xyz-stage to mount the substrate for easy manipulation. 
	NOTE: For the COST-Jet, the safety gap adds one extra millimeter to the distance between the plasma discharge and the treated surface.</li>
	<li>Start the treatment time: Either simply switch on the plasma or use a mechanical shutter. Be aware of a possible voltage overshoot during the switching event leading to a constricted discharge. For better control in the ms range, use a rotatable shutter.</li>
	<li>Treat the sample for the desired amount of time and end the treatment time by switching off the plasma or by use of a shutter.</li>
	<li>If necessary, check the gas flow pattern in front of the target using Schlieren imaging when treating a substrate as effects of surface charging, ion drag forces, or ambient air mixing due to buoyancy can influence the amount of reactive species reaching a surface.</li>
</ol>
5. Liquid treatment
<ol>
	<li>Set up a controlled atmosphere for the experiment.</li>
	<li>Clean the gas supply lines as described in step 1.5.</li>
	<li>Set the desired operating parameters and wait approximately 20 minutes for the COST-jet to reach a stable temperature.</li>
	<li>Choose the distance between the COST-Jet and the treated liquid.</li>
	<li>Pour the liquid to be treated into an adequate container. Use inert material to avoid reactions of potentially generated reactive species in the liquid with the container. Choose the size of the container according to the volume of liquid that is treated.</li>
	<li>Consider the influence of the gas flow on the liquid surface: Depending on the gas flow rate, be aware of a concave meniscus that may form, thus changing the distance between plasma and liquid surface.</li>
	<li>Start the treatment. Avoid pressure surges on the surface of the liquid caused by a sudden change in gas flow as this could cause liquid splashes into the discharge geometry, possibly causing a short circuit and certainly contaminating the plasma. Instead, use a mechanical shutter or slowly increase the gas flow.</li>
	<li>Take into account mixing/stirring of the liquid due to friction between neutral gas flow and liquid surface as this influences transport processes and concentration profiles in the liquid. Additionally, depending on the treatment time, correct for the evaporation of liquid during the treatment (e.g., when calculating reaction constants). Depending on the plasma source, be aware of this evaporation possibly causing back coupling to the discharge, thus changing the plasma chemistry.</li>
	<li>Please also consider that the reactivity with possible reagents in liquids is also affected by the surface activity of this agent. Thus, in some cases, surfactants might play an important role in the interaction between short-lived species and liquids.</li>
</ol>

The authors have nothing to disclose.

Here, we demonstrate the use of an atmospheric pressure plasma jet for surface treatments of different materials. The experimental setup for an atmospheric pressure plasma jet can have a tremendous effect on the plasma parameters, chemistry, and performance and consequently influences the outcome of plasma treatments and is a critical step in the protocol.
As an example, the gas supply lines play an important role regarding the most common impurity in the feed gas of the plasma which is humidity. In particular, the production of reactive nitrogen species in the plasma is reduced while the reactive oxygen species production is favored, due to the low ionization energy of oxygen compared to water molecules and nitrogen35. Winter24 found out that feed gas humidity originating from water molecules on the surface of the inner tube is an order of magnitude higher using polymeric tubes compared to metal tubes due to the higher porosity and storage capacity. It can be reduced by flushing the lines with feed gas. However, drying the line by flushing takes a couple of hours. Therefore, polymeric tubing should be avoided or at least kept as short as possible. These findings are underlined by studies from Gro&#223;e-Kreul25. They compared the effect of polyamide and stainless steel tubing on the plasma chemistry using mass spectrometry. Their measurements confirm water cluster ion formation in the plasma due to water outgassing from polymeric tubes and faster drying times with metal tubes. Additionally, they investigated the effect of gas purification methods such as a molecular sieve trap and a liquid nitrogen cold trap on the plasma chemistry which helped to reduce the amount of impurities by about two orders of magnitude.
Instead of trying to purify the feed gas, there is also the approach of adding a controlled amount of humidity. As this intentional impurity then dominates over the natural impurities and thus controls the plasma chemistry, reproducible conditions are ensured as long as the amount of added humidity is precisely known.
For the ignition of the discharge, the applied voltage to the electrodes can usually simply be increased until the point of breakdown. However, depending on the surface conditions of the electrodes, sometimes a high voltage is necessary. To facilitate ignition, a high voltage spark gun can be used. This can also be useful when trying to ignite an argon discharge in the COST-Jet.
Before applying the COST-Jet to any surfaces, sufficient time should be allocated for the device to equilibrate. When set to the desired control parameters, the COST-Jet needs approximately 20 minutes to reach stable conditions11. During this time, the temperature of the device, the gas temperature as well as the plasma chemistry are reaching a steady state.
For comparison of scientific results, comparable plasma control parameters are necessary. For measuring the electrical input power, the COST power monitor can be used29. The software is open-source and compatible with a range of different types of oscilloscopes. The software operates according to the principle described by Golda19.
In addition to the effect of feed gas humidity on the plasma chemistry, the transport of reactive species from the plasma to the substrate plays an important role in the effluent composition and is another critical step in the protocol. The surrounding atmosphere can influence the species created in the plasma on their way to the substrate. To minimize this influence, two different concepts are used: (i) Firstly, a controlled atmosphere can be set up that consists of the feed gas. Thus, the composition of the surrounding atmosphere can be kept constant. Depending on the purity level required for the treatment, the controlled atmosphere can be realized via protective housings equipped with a one-way valve to prevent overpressure. For higher purity levels, a vacuum chamber with a pump can be used. (ii) Secondly, a controlled atmosphere can be created by using a shielding gas curtain around the plasma effluent36,37. Usually, it consists of an inert gas, but it can also be varied according to the needs of the application.
Fortunately, for the COST-Jet, the influence of the surrounding atmosphere is comparably low. Using isotopic labeling, Gorbanev have shown that for a parallel-field configuration plasma jet, the reactive oxygen and nitrogen species reaching a liquid surface were formed in the plasma gas phase as well as in the region between the plasma nozzle and the sample38,39. In contrast, using the same technique for the COST-Jet, they found out that RONS almost exclusively originated from the plasma phase instead of the surrounding environment28. This is probably due to the electric field being confined to the plasma channel of the COST-Jet discharge. This makes the plasma discharge largely independent of its environment and gives it a certain remote character.
For a longitudinal electric field plasma jet, Darny et al.40 have shown that the polarity of the electric field modifies the gas flow pattern and thus also on the reactive species that reach a target due to ionic wind. The dependence of the reactive species density on the environment was confirmed by measurements by Stancampiano et al.7. They reported on the difference of the number of reactive species created in treated water depending on the electrical characteristics. To compensate for these differences, they had to create a compensating electrical circuit. This behavior is different for the COST-Jet: Figure 5 compares Schlieren images of the COST-Jet without an applied voltage and during operation for two different gas flow rates. The images were taken using a single mirror inline alignment as described by Kelly41. They show how the horizontally aligned COST-Jet effluent hits a flat glass substrate. Both images show the exact same gas flow pattern. This results from the lack of ionic wind due to the absence of charged species in the plasma effluent.
Additionally, the COST-Jet exhibits a very laminar flow pattern. Kelly41 showed Schlieren images similar to the ones presented in Figure 5, for various gas flow rates. Even at comparably high gas flow rates of 2 slpm, the plasma effluent shows no signs of turbulence. At very low gas flow rates of 0.25 slpm and below, the buoyancy of the helium effluent begins to play a role. However, up to 4 &#8211; 5 mm distance from the nozzle, the ambient atmosphere does not influence the gas composition reaching the surface as demonstrated by Ellerweg using mass spectrometry17.
All of the above-mentioned characteristics add to the remote character of the COST-Jet. This makes it an ideal candidate for the controlled, comparable treatment of surfaces.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61801/61801fig05.jpg" /> 
Figure 5: Schlieren images of the COST-Jet with and without applied voltage for two different gas flow rates.&#160;During plasma operation, the gas flow pattern exactly resembles the pattern with only the gas flow. <a href="https://www.jove.com/files/ftp_upload/61801/61801fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Depending on the desired effect on the treated sample, the control parameters gas flow mixture, applied electrical power, and distance between plasma source and surface can be adjusted accordingly. For the COST-Jet, a broad literature database of studies investigating reactive species in the effluent exists. As an example, Willems30 measured the atomic oxygen density using mass spectrometry whereas Schneider42 measured atomic nitrogen densities in the effluent.
The treatment of liquids with atmospheric pressure plasma can cause a variety of possible reaction mechanisms driven by reactive species, ions, photons, or electric fields. Due to the previously described characteristics of the COST-Jet, the effect of the electric field, ions, and photons are negligible compared to plasma sources where the plasma is in direct contact with liquids. Therefore, for studying the effect of short-lived reactive species like atomic oxygen on a phenol solution the COST-jet was used by Hefny43 and Benedikt44. Furthermore, the COST-Jet provides a convenient possibility to compare experiments and numerical simulations of liquid treatment28. As the interaction between plasma and liquid is dominated by the gas flow of reactive species from plasma to the liquid surface, the model complexity can be reduced.
The gas flow induced stirring of the liquid increases the reaction rate between plasma generated reactive species and the liquid. In contrast to surface treatments of solids, the convection of the liquid constantly changes the local concentration of reactants. Additionally, the reaction rates between plasma generated species with reactants in liquid are also affected by the surface activity of these reactants. With increasing surface activity, the concentration of the reactant at the liquid surface increases. These surfactants might play an important role in the reactivity of short-lived species generated by the plasma.
Next to stirring the gas flow impinging on the liquid surface also induces evaporation which must be considered. Using the COST-Jet with short treatment times the evaporation might play a minor role, although still has to be considered for calculating correct reaction rates. The discharge of the COST-Jet is not affected by the evaporation and therefore the plasma chemistry is also not affected. For different plasma sources, where e.g. the plasma is in direct contact with liquid, the plasma chemistry is changing significantly with evaporation as shown by Tian and Kushner45 for a dielectric barrier discharge. Also, for the kINPen, an effect of evaporations was determined46.
Besides these mentioned differences in plasma chemistry that need to be considered for different plasma sources, also the topology of the meniscus induced by gas stream on liquid surface changes. The depth of this meniscus is usually depending on the gas velocity. For plasma sources where the electrode configuration induces a significant electrical field reaching the liquid or even with a plasma in contact with the liquid, this meniscus can be elevated47,48. As shown, several effects need to be considered according to the used plasma source.
In the future, this protocol can be used to conduct and describe surface and liquid treatments using the COST-Jet. It is a stable, reproducible plasma source exhibiting a unique remote character amongst the plethora of different plasma jet designs. The same methods are not limited to the COST-Jet source only and can be modified and adapted to use with any cold atmospheric pressure plasma source.

Cold atmospheric pressure plasmas (CAPs) have attracted increased interest in recent years due to their potential for surface treatment applications. CAPs are characterized by their non-equilibrium properties, enabling complex plasma chemistry with a high density of reactive species while maintaining a low thermal impact on treated samples. Therefore, CAPs are considered in particular for the treatment of biological tissue1,2,3,4. Numerous concepts and designs of CAPs are successfully used for wound disinfection and healing, blood coagulation, and cancer treatment, among other biomedical applications. A large proportion of biological tissue contains liquids. Therefore, research is also increasingly focused on investigating the effects of CAPs on liquid surfaces such as cell medium or water5,6,7.
However, the scientific results often suffer from reliability and reproducibility problems8,9,10. On one hand, the treated biological substrates are subject to natural variations. On the other hand, biological mechanisms were seldom directly attributed to plasma processes (such as electric fields, UV radiation, and long- and short-lived species, etc.). Furthermore, these plasma processes in turn depend strongly on the individual plasma source and the exact type of its application.
Additionally, detailed protocols of treatment procedures are rarely available. This makes it difficult to isolate the influence of a particular plasma parameter on the outcome of the treatment, which renders the obtained results non-transferable.
Therefore recently, various attempts have been made to standardize the treatment of surfaces, tissues, and liquids using cold atmospheric pressure plasmas. Here we present only some selected examples.
<ol>
	<li>To simplify the direct comparison of different plasma sources, a reference source was developed. Inspired by the low-pressure plasma community, a reproducible and stable discharge design (COST-Jet) was developed in the framework of the COST action MP 1101 that can serve as a reference source for future biomedical research11.</li>
	<li>To enable comparability, reference protocols for individual applications were developed. To standardize the comparison of the antimicrobial properties of cold atmospheric pressure plasmas, for example, Mann et al. defined a reference protocol for microorganism treatment by normalizing the treatment time per area unit12.</li>
	<li>For a more flexible approach, Kogelheide et al. developed a method to investigate plasma-induced chemical modifications on macromolecules13. Using tracer compounds such as cysteine and or cysteine-containing glutathione (GSH) in combination with FTIR and mass spectrometry, they tried to extrapolate the chemical modifications on biological substrates. Using this method, several plasma sources such as the COST-Jet, the kinPen, and the Cinogy DBD have already been compared14,15,16.</li>
	<li>To directly compare individual plasma sources, comparable control parameters must be established. Basic plasma parameters such as electron temperature, electron density, and the flux densities of reactive species are hard to measure in atmospheric pressure plasmas since such plasmas are often transient and their dimensions are small. Instead, external control parameters such as generator power, applied voltage or ignition, and arcing points are often used as a reference, especially when comparing results to simulations17,18. More recently, the measured electrical energy consumption has been used as a more reliable control parameter19,20,21.</li>
</ol>
Despite these efforts, comparing the results of different studies may still be impossible, simply due to the challenge of correctly applying a plasma source onto a surface. There are a vast number of prevalent pitfalls that have to be tackled when working with atmospheric pressure plasma applications such as the influence of external electric fields (compensation circuits), feedback loops between plasma and surrounding environment (shielded atmosphere), species transport (ionic wind) and control parameters (voltage, current, power).
The main objective of this work is to provide a thorough, detailed protocol on the application of the COST-Jet for surface treatments. The COST-Jet is a reliable plasma source that was developed for scientific reference purposes rather than for industrial or medical use. It provides reproducible discharge conditions and a broad database of available studies22,23. The COST-Jet is based on a homogeneous, capacitively coupled RF-plasma. Because the electric field is confined perpendicular to the gas flow, charged species are mostly kept in the discharge region and do not interact with the target or the surrounding atmosphere. Additionally, the laminar gas flow ensures reproducible plasma chemical conditions in the plasma effluent.
In this paper, we will address the most common challenges and introduce possible solutions that have been used in the literature. These include proper gas supply, discharge control, ambient atmosphere influence, and surface preparation. Compliance with the protocol presented here should ensure the reproducibility and comparability of the measurements.
The protocol might also serve as an example for other atmospheric pressure sources. It must be refined for other jet plasma sources according to the individual gas flow and electric field configuration. Where applicable, we will try to point out possible adjustments to the protocol. The described steps should be considered and reported on when publishing studies applying atmospheric pressure plasmas to treated samples.

<table>
	<tbody>
		<tr>
			<td>COST power monitor software</td>
			<td>home-built</td>
			<td></td>
			<td>according to www.cost-jet.eu and J Golda et al 2016 J. Phys. D: Appl. Phys. 49 084003</td>
		</tr>
		<tr>
			<td>COST-Jet (including matching circuit)</td>
			<td>home-built</td>
			<td></td>
			<td>according to www.cost-jet.eu and J Golda et al 2016 J. Phys. D: Appl. Phys. 49 084003</td>
		</tr>
		<tr>
			<td>current probe</td>
			<td>home-built</td>
			<td></td>
			<td>integrated into the COST-Jet</td>
		</tr>
		<tr>
			<td>gas supply system</td>
			<td>Swagelok</td>
			<td></td>
			<td>stainless steel</td>
		</tr>
		<tr>
			<td>helium</td>
			<td>Air Liquide</td>
			<td></td>
			<td>99.999 % purity</td>
		</tr>
		<tr>
			<td>mass flow controller (MFC)</td>
			<td>Analyt-MTC</td>
			<td>series 358</td>
			<td>5000 sccm</td>
		</tr>
		<tr>
			<td>MFC</td>
			<td>Analyt-MTC</td>
			<td></td>
			<td>50 sccm</td>
		</tr>
		<tr>
			<td>oscilloscope</td>
			<td>Agilent Technologies</td>
			<td>DSO7104B</td>
			<td>bandwidth 1 GHz, resolution 4 Gsa/s</td>
		</tr>
		<tr>
			<td>oxygen</td>
			<td>Air Liquide</td>
			<td></td>
			<td>99.9999 % purity</td>
		</tr>
		<tr>
			<td>power supply</td>
			<td>home-built</td>
			<td></td>
			<td>according to www.cost-jet.eu and J Golda et al 2016 J. Phys. D: Appl. Phys. 49 084003</td>
		</tr>
		<tr>
			<td>voltage probe</td>
			<td>Tektronix</td>
			<td>P5100A</td>
			<td></td>
		</tr>
		<tr>
			<td>xyz-stage</td>
			<td>Zaber</td>
			<td>ZAB-X-XAZ-LSM0100A-K0059-SQ3</td>
			<td></td>
		</tr>
	</tbody>
</table>

treating surfaces with a cold atmospheric pressure plasma using the cost-jet

In recent years, non-thermal atmospheric pressure plasmas have been used extensively for surface treatments, in particular, due to their potential in biological applications. However, the scientific results often suffer from reproducibility problems due to unreliable plasma conditions as well as complex treatment procedures. To address this issue and provide a stable and reproducible plasma source, the COST-Jet reference source was developed.
In this work, we propose a detailed protocol to perform reliable and reproducible surface treatments using the COST reference microplasma jet (COST-Jet). Common issues and pitfalls are discussed, as well as the peculiarities of the COST-Jet compared to other devices and its advantageous remote character. A detailed description of both solid and liquid surface treatment is provided. The described methods are versatile and can be adapted for other types of atmospheric pressure plasma devices.

Using the methods and equipment described above, we exemplary applied the COST-Jet to different surfaces and liquids. Figure 1 shows the experimental setup used for the treatment including the power supply, gas supply system, voltage and current probes as well as a controlled atmosphere and a mechanical shutter.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61801/61801fig01.jpg" /> 
Figure 1: Experimental setup used for the plasma treatment of surfaces and liquids using the COST-Jet.&#160;A cold trap is used to purify the feed gas. The controlled atmosphere is realized by a pumped vacuum chamber at atmospheric pressure. The mechanical shutter facilitates the time management of solid and liquid surface treatment. The flexible stage allows controlling the distance between the plasma jet and the surface. <a href="https://www.jove.com/files/ftp_upload/61801/61801fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Using the voltage and current probe implemented in the COST-Jet, the dissipated electrical power can be calculated. Figure 2 shows the measured electrical power in a helium plasma generated in five different COST-Jet devices using a gas flow of 1 slpm. All devices show similar behavior. The deviation between the different devices originates from the uncertainty of the power measurement as well as microscopic differences in the setups such as the electrode distance. More detailed measurements of reactive species (e.g., atomic oxygen and ozone), temperature and power as well as bactericidal activity measurements have been performed by Riedel22.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61801/61801fig02.jpg" /> 
Figure 2: Dissipated power as a function of applied voltage in a helium plasma.&#160;The data represents five identical COST-Jet devices34. The small deviations at high voltages are due to uncertainties of the measurement as well as small deviations in the gas discharge channel geometry22. <a href="https://www.jove.com/files/ftp_upload/61801/61801fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 3 shows the etch profile of an a:C-H film for a 3 min treatment with the COST-Jet using a gas flow of 1.4 slpm helium with an admixture of 0.5% oxygen measured using an imaging spectroscopic reflectometer31. The etch pattern shows a circular structure representing the cylindrical symmetry of the plasma effluent. Based on etch profiles in combination with numerical simulations, the surface loss probability of atomic oxygen could be estimated.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61801/61801fig03.jpg" /> 
Figure 3: Etch profile of a plasma-treated a:C-H film.&#160;The dip in the film was etched using a gas mixture of 1.4 slm helium with an admixture of 0.6% oxygen at a voltage of 230 Vrms and a treatment time of 3 min.31 <a href="https://www.jove.com/files/ftp_upload/61801/61801fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 4 shows the occurring vortices in liquid caused by the gas stream impinging on the liquid surface. A laser sheet illuminating tracer particles in the liquid makes it possible to observe the trajectory and velocity of these particles via particle image velocimetry and therefore study the fluid flow32. It is important to consider similar densities of the seeding particles and the fluid so that the trajectories of the particles represent the movement of fluid. With this visualization of the fluid flow measurements and numerical simulations can be compared33. The vortices are due to the surface friction between effluent gas flow and liquid surface. Figure 4 also shows the occurring depression of the liquid surface underneath the gas channel of the plasma jet, the so-called meniscus. It is visualized by a blue line.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61801/61801fig04.jpg" /> 
Figure 4: Photograph of illuminated cornstarch particles in 3 ml of water stirred by the gas flow.&#160;The vortices are due to the surface friction between effluent gas flow and liquid surface. <a href="https://www.jove.com/files/ftp_upload/61801/61801fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Treating Surfaces with a Cold Atmospheric Pressure Plasma using the COST-Jet at JoVE.com

Treating Surfaces with a Cold Atmospheric Pressure Plasma using the COST-Jet

This protocol is presented to characterize the setup, handling, and application of the COST-Jet for the treatment of diverse surfaces such as solids and liquids.

In recent years, non-thermal atmospheric pressure plasmas have been used extensively for surface treatments, in particular, due to their potential in ...

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3.9K Views.  Kiel University. This protocol is presented to characterize the setup, handling, and application of the COST-Jet for the treatment of diverse surfaces such as solids and liquids.

Video: Treating Surfaces with a Cold Atmospheric Pressure Plasma using the COST-Jet

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

Blast Quantification Using Hopkinson Pressure Bars

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures up to many hundreds of megapascals. In this respect the simplicity of the Hopkinson pressure bar has a major advantage in that while the measurement end of the Hopkinson bar can endure and be exposed to harsh conditions, the strain gauge mounted to the bar can be affixed some distance away. This allows protective housings to be utilized which protect the strain gauge but do not interfere with the measurement acquisition. The use of an array of pressure bars allows the pressure-time histories at discrete known points to be measured. This article also describes the interpolation routine used to derive pressure-time histories at un-instrumented locations on the plane of interest. Currently the technique has been used to measure loading from high explosives in free air and buried shallowly in various soils.

This protocol details the use of Hopkinson pressure bars to measure reflected blast loading from near-field explosive events. It is capable of interpolating a pressure-time history at any point on a reflective boundary and as such can be used to fully characterize the spatial and temporal variations in loading produced.

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures ...

The Measurement of Unsteady Surface Pressure Using a Remote Microphone Probe

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various characteristic length scales can result in pressure fluctuations over a wide frequency range. This property of turbulence requires sensing devices to have sufficient sensitivity over a wide range of frequencies. Furthermore, the small characteristic length scales of turbulent structures require small sensing areas and the ability to place the sensors in very close proximity to each other. The complex geometries of the solid bodies, often including large surface curvatures or discontinuities, require the probe to have the ability to be set up in very limited spaces. The development of a remote microphone probe, which is inexpensive, consistent, and repeatable, is described in the present communication. It allows for the measurement of pressure fluctuations with high spatial resolution and dynamic response over a wide range of frequencies. The probe is small enough to be placed within the interior of typical wind tunnel models. The remote microphone probe includes a small, rigid, and hollow tube that penetrates the model surface to form the sensing area. This tube is connected to a standard microphone, at some distance away from the surface, using a "T" junction. An experimental method is introduced to determine the dynamic response of the remote microphone probe. In addition, an analytical method for determining the dynamic response is described. The analytical method can be applied in the design stage to determine the dimensions and properties of the RMP components.

Here, we present a protocol to measure, with high spatial resolution, the unsteady surface pressure in turbulent flows. This method demonstrates the construction of a remote microphone probe (RMP) and the determination of its frequency-dependent, complex transfer function. An analytical determination of the dynamic response is presented and validated.

Microphones are widely applied to measure pressure fluctuations at the walls of solid bodies immersed in turbulent flows. Turbulent motions with various ...

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O2, N2, air, H2O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of &#39;high&#39; voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

An experimental setup was created for the helium-operated kHz frequency plasma jet. The setup includes a cage for the plasma power supply and jet and an in-house built reactor to monitor plasma-induced reactive species without the interference of the ambient atmosphere.

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

New Application of an Atmospheric Pressure Plasma Jet as a Neuro-protective Agent Against Glucose Deprivation-induced Injury of SH-SY5Y Cells

The atmospheric pressure plasma jet (APPJ) has attracted the attention of many researchers from multiple disciplines in recent years because its emissions include multiple types of reactive nitrogen species (RNS) and reactive oxygen species (ROS). Our previous study has shown the cytoprotective effect of the APPJ against oxidative stress-induced injuries. The aim of the present study is to provide a detailed in vitro treatment protocol regarding the neuroprotective applications of helium APPJs on glucose deprivation-induced injury in SH-SY5Y cells. The SH-SY5Y human neuroblastoma-derived cell line was maintained in RPMI 1640 medium supplemented with 15% fetal calf serum. The culture medium was then changed to RPMI 1640 without glucose before APPJ treatment. After a 1 h incubation in a cell incubator, cell viability was determined using Cell Counting Kit 8. The results showed that, compared to the glucose deprivation group, cells treated with APPJ exhibited significantly increased cell viability in a dose-dependent manner, with 8 s/well observed as an optimal dose. Meanwhile, helium flow had no effect on the glucose deprivation-induced cell impairment. Our results indicated that APPJ could be potentially used as a treatment method for the diseases in the central nervous system related to glucose deprivation. This protocol could also be used as a cytoprotective application for other cells with different impairments, but the cell culture and APPJ treatment conditions should be readjusted, and the treatment dose must be relatively low.

A protocol for the neuroprotective application of low-dose atmospheric pressure plasma treatment on glucose deprivation-induced SH-SY5Y injuries.

The atmospheric pressure plasma jet (APPJ) has attracted the attention of many researchers from multiple disciplines in recent years because its emissions ...