In this work, we applied a dielectric barrier discharge deposition process under atmospheric pressure conditions for the growth of thin coatings with antimicrobial properties on polymer films and textiles. The precursor used was 1,1,3,3-tetramethyguanidine (TMG), and we studied the effect of concentration, deposition time and discharge power on the composition of the deposited coating. X-ray photoelectron spectroscopy, scanning electron and atomic force microscopy were employed to study the impact of plasma parameters on the chemical structure and surface morphology of the deposited coatings. It was observed that for prolonged plasma deposition times, etching and oxidation occurred in the coatings. Both effects adversely affect the desired polymerization process and were reduced through the choice of proper experimental conditions. Also, the wettability of the coating and its stability were investigated. Once the optimal TMG coating was developed, antimicrobial tests were performed on nylon/cotton fabrics coated with the TMG film. Preliminary testing showed that the coated fabrics have high antimicrobial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria, using the AATCC 100 test method. These promising results are an indication that atmospheric plasma processing can provide coatings that can lead to the development of lightweight, breathable textiles with both self-cleaning and antimicrobial properties.

The Fused Hollow Cathode (FHC) atmospheric plasma source has been adapted for generation of a cold plasma submerged in a liquid. The reactor with a special arrangement has been built and used for testing the plasma without and with an auxiliary gas, argon, neon, nitrogen and air, forming bubbles and transporting the plasma into a wide area. The FHC source has been powered either by a pulsed dc generator or rf generator. The pulsed plasmas can be excited at the average power as low as 2 W. Results of first experiments in water, changes in the plasma geometry and measurements of the optical emission spectra from the plasma at different power and gas flow conditions are introduced. Potential applications of the submerged plasmas are briefly discussed.

1. Introduction

DLC film consists of sp3 carbon bonds coexisting with sp2 bonds of carbon atoms, and shows high hardness and self-lubricant properties. Therefore, DLC film is expected to be an excellent material for wear-resistant coatings. DLC films are usually deposited by physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes under low pressure, typically below 10 Pa (1x10-4 atm.). Preparation of DLC films at atmospheric pressure will promote a variety of new applications of the films, because in-process and in-use coating of DLC films will be realized. However, it has been generally believed that it is difficult to deposit DLC films at atmospheric pressure because carbon and hydrocarbon ions are needed to fabricate hard films. Here we report the development of the nanopulse plasma CVD method using a nanopulse generator and the application of the synthesis method for the deposition of DLC films, and show that DLC film can be prepared at atmospheric pressure.

2. Experimental

We performed the deposition of DLC films at subatmospheric pressure (26.7kPa) using the nanopulse plasma CVD method. A stainless-steel an-ode of 10 mm in diameter is set 20 mm above the Si(100) substrate. Positive pulse voltage is applied to the stain-less-steel anode. The streamer discharges are generated between the anode and Si substrate. The diameter of the discharge on the substrate is approximately 20 mm. CH4 and He gases are injected from the gas inlet nozzle. The flow rates of CH4 and He are 3 L/min and 50 L/min, respectively. The flow rate is set approximately tenfold higher than in the conventional CVD method, in order to prevent the polymerization of the hydrocarbon species in the plasma. The applied pulse voltage is 5.0 kV and the maximum current is 19 A. A uniform film of approximately 20 mm in diameter was fabricated on the Si substrate. The deposition area is in good agreement with the area of the streamer discharges generated.

The thickness of the film is approximately 1.6um with a smooth surface. The surface roughness of the film is as low as 0.07 nmRa, as determined by atomic force microscope (AFM) analysis. The Raman spectrum of the deposited film shows that the peak consists of the G-band and D-band, indicating a DLC film. The hardness of the DLC film as measured with a nanoindentor is 21.5 GPa and the elastic modulus is 187 GPa. These results suggest that the DLC film has excellent mechanical performance. Consequently, we fabricated DLC films in open air using pipe-electrode.

The ion energy distribution function (IEDF) plays a major role in plasma based surface modification. The control of IEDFs is therefore strongly desirable, particularly in the context of sputter deposition. Due to their unique properties capacitive multi-frequency discharges are promising candidates not only for sputtering dielectric (non-conductive) materials but also for allowing for tailoring IEDFs.

The paper discusses a technique which enables the tailoring of IEDFs. The technique exploits the electrical asymmetry effect (EAE) in geometrically symmetric and asymmetric capacitive discharges which leads to the generation of a DC self-bias voltage. The DC self-bias voltage as the key parameter for IEDFs can be controlled using the phase shift between the two consecutive harmonics of the driving radio-frequency. By means of self-consistent kinetic plasma simulations performed on Graphics Processing Units (GPUs) it is shown that the energy of ions impinging on both the target and the substrate can be controlled almost independently from the ion flux.

Our linear reactor consists of the12 mm quartz tube with array of tungsten needles, welded alongside and connected to the 13.56 MHz RF generator. Length is enough to provides the passage of nanoparticles with residence time for separation. The DBD discharge is generated at the 100W RF power and the gas flow of 40 clm. Therefore, tandem of the DBD and the ICP atmospheric plasma systems can replace a DC plasma spray low adhesion coating can be a solution for the development of the size unlimited chamber-less coating for transition to 450 mm wafers. The first results show the reduction of cluster contamination verified by SEM and ATF.