ICMCTF2011 Session G3: Atmospheric and Hybrid Plasma Technologies

Wednesday, May 4, 2011 8:00 AM in Room Royal Palm 4-6

Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic G Sessions | Time Periods | Topics | ICMCTF2011 Schedule

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8:00 AM G3-1 Atmospheric Pressure Plasma Treatment of Polymers for Ink-Jet Deposition of Flexible Solar Cell Platforms
Daphne Pappas, Victor Rodriguez-Santiago, M.S. Fleischman, Andres Bujanda (U.S. Army Research Laboratory); Viral Chhasatia, Brandon Lee, Ying Sun (Drexel University)

The use of low-cost, high-volume inkjet printing technologies for the delivery of solution processed photovoltaic materials onto flexible substrates has shown great potential over bulky, rigid silicon technologies and is likely to be at the forefront of revolutionary solar cell manufacturing processes. The main advantages of inkjet printing over other commonly used deposition techniques lie in its high repeatability, pattern flexibility, and roll-to-roll compatibility. The ease of fabrication via low temperature evaporation and/or solution processing opens up a potentially wide market for these energy harvesting and storage devices to be integrated onto or into other applications such as textiles, composite and packaging materials.

However, the use of polymer-based flexible platforms raises some technical challenges related to poor adhesion between the substrates and the deposited materials, as well as the development of conformal, pinhole-free coatings. To overcome these issues, we employed atmospheric plasma technology to functionalize the surface of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) substrates prior to the subsequent coating with ZnO nanorods and CdSe nanoparticles, which act as photosensitive materials. The goal of this work is to investigate the contribution of the He-O2 and He-H2O plasma pretreatment step to the surface properties of PEN and PET. Towards this direction, we used contact angle goniometry, x-ray photoelectron spectroscopy and scanning electron microscopy to study the physicochemical changes of the plasma treated polymers. Results show improved hydrophilicity due to the grafting of oxygen-containing groups which are expected to participate in the formation of covalent bonds with the photoactive coatings. Also, we studied the effect of ink-jetting parameters, including drop volume, velocity, frequency, temperature, substrate translational speed, orifice/substrate offset distance, and others, on the microstructure of the deposited photoactive materials on the flexible substrates.

8:20 AM G3-2 Investigation on the Discharge Formation Mechanisms and Surface Analysis of SiO2-Like Layers on Polymers Synthesized Using High Current Dielectric Barrier Discharge at Atmospheric Pressure
Mauritius van de Sanden, Antony Premkumar Peter (Eindhoven University of Technology, Netherlands); Sergey Starostin, Hindrik de Vries (FUJIFILM, Netherlands); Mariadriana Creatore (Eindhoven University of Technology, Netherlands)
The dielectric barrier discharge is recognized as a promising tool for PECVD of thin films at atmospheric pressure. Emerging applications including encapsulation of flexible solar cells and flexible displays requires low costs production of transparent uniform and dense layers with low level of coating defects. Among the two discharges Townsend like discharge (TD) and glow like discharge (GD) the latter offers more flexibility for the high growth rates in plasma enhanced deposition. In this investigation we demonstrate the utilization of glow like discharge in, He free, industrially relevant gas mixture comprising Ar/N2/O2/HMDSO for the deposition of high quality silica like films on large area polymeric substrates (PET or PEN) in a roll-to-roll configuration. While the discharge physics exhibiting the glow like behaviour is investigated via fast ICCD camera, voltage-current waveforms and optical emission spectroscopy, the deposited silica like films is comprehensively analyzed using AFM, SEM, XPS, SE and FTIR. The time evolution of the diffuse atmospheric discharge showed several phases starting from the initial ignition of the low current Townsend-like mode followed by the transition to glow like discharge which then undergoes lateral expansion providing uniform treatment of the whole substrate width. As a generic characteristic of the developed technology, it is observed that, irrespective of precursors (TEOS or HMDSO) and process gases (Ar, N2 or air) employed, the films are smooth, both locally and globally, and of near stoichiometric silica with very low carbon content (< 2%). Detailed AFM morphology description and surface statistical analysis on SiO2 dynamics showed that no film roughening in growth front and lateral directions observed and the synthesized layers (~ 350 nm) grow in a self-similar fashion following the topology of the substrate. The films are uniform with no defects or particle being incorporated during the deposition process and exhibit excellent barrier performances towards O2 and H2O permeation.
8:40 AM G3-3 Surface Modification of Inks, Coatings and Adhesives - The Interfacial Effects
Rory Wolf (Enercon Industries Corporation)
It is well-documented that polymer film surface modification techniques can greatly improve the acceptance of a wide variety of coatings, adhesives and inks for improved flexible packaging structures. By increasing the hydrophilic characteristics and surface-free energy of polymers, bond strengths can be improved dramatically. It is theorized that interlayer adhesion between ink and coating formulations can also be improved by applying atmospheric plasma surface modification techniques. This study examines experimental data which relate correlations between surface modification and interlayer adhesions of inks, coatings and adhesives.
9:20 AM G3-6 Effects of Coating Morphology on In-Situ Impedance Spectra of Plasma Electrolytic Oxidation Process
Chen-Jui Liang, Aleksey Yerokhin (University of Sheffield, UK); Evgeny Parfenov (Ufa State Aviation Technical University, Russia); Allan Matthews (University of Sheffield, UK)
Plasma electrolytic oxidation (PEO) is an atmospheric pressure surface treatment that provides excellent wear- and corrosion-resistant coatings on light-weight metals, in particular on aluminum. Formation of PEO coatings is affected by different factors, which requires in-depth understanding. New insights into coating formation mechanisms and means of process control can be attained using in-situ impedance spectroscopy which is an emerging characterization and diagnostic tool to study time-variable and non-linear processes, such as PEO. In-situ impedance spectra of the PEO process often feature evidence of distributed and far-out linear elements present in the system; however the nature of such behavior is not always clear. In most cases, the distributed properties are modeled by constant phase elements (CPE) that can be associated with different factors, including variable coating thickness, topology or composition. In this work, the effects of coating morphology on in-situ impedance spectra of the PEO process on Al are studied using fractal approach. The fractal analysis is a useful method to investigate the properties of heterogeneous (e.g. rough, porous or multiphase) materials, which can provide a direct link to the CPE characteristics. The fractal analysis was applied to surface plane and cross-sectional SEM images of PEO coatings with a range of nominal thicknesses produced during different treatment times. Additionally, coating elemental and phase distributions were studied using EDX and nanoindentation mapping respectively. Fractal dimensions of morphological characteristics of PEO coatings were derived and compared to the values of CPE elements obtained from model fitting of the impedance spectra. Further comparisons were made with the results of conventional electrochemical impedance spectroscopy analysis performed on the PEO coatings in working silicate-alkaline electrolytes.
9:40 AM G3-7 The Effect of Current Mode and Discharge Type on the Corrosion Resistance of Plasma Electrolytic Oxidation (PEO) Coated Magnesium Alloy AJ62.
Riyad Hussein, P. Zhang, Xueyuan Nie, Derek Northwood (University of Windsor, Canada)
Magnesium alloys are increasingly being used as lightweight materials in the automotive, defense, electronics, biomaterial and aerospace industries. However, their inherently poor corrosion and wear resistance have, so far, limited their application. In this work, plasma electrolytic oxidation (PEO) process in an environmentally friendly aluminates electrolyte was used to produce oxide coatings with thicknesses of ~80 µm on an AJ62 magnesium alloy. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm – 800 nm) was employed to characterize the PEO plasma. It was found that the plasma discharge behavior significantly influenced the corrosion resistance, microstructure and the morphology of the oxide coatings. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the coating morphology and microstructure, and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution were used to determine the corrosion behaviour. It was found that the corrosion resistance of the coated alloy could be significantly increased by changing the current mode from unipolar to bipolar, where the strong discharges have been reduced or eliminated.
10:00 AM G3-8 An Integrated Microwave Atmospheric Plasma Source
Roland Gesche (Ferdinand-Braun-Institut, Berlin, Germany)
The development of a novel integrated atmospheric microplasma source is presented. A mi-crowave resonator for impedance transformation contains the plasma electrodes. An oscillator circuit containing a GaN HEMT power transistor is directly attached to the resonator. This leads to a compact device, powered by a simple 24 V DC power supply. The integrated con-cept allows a compact and cost efficient realization of a low-power plasma source for small area applications in the medical and industrial field.

The source operates at a frequency of around 2.45 GHz with a maximum oscillator power of 30 W. The complete source module including electrode, resonator and microwave oscillator has a length of approx. 150 mm and a diameter of approx. 30 mm. The visible afterglow plasma flame has a diameter of approx. 1 mm and a length up to 5 mm. The plasma source works with ambient Air as well as with Oxygen, Argon, Helium, and Nitrogen.

Several procedures of microwave characterization including specialized calibration and de-embedding procedures are presented. Ignition voltages are measured as well as transient microwave plasma impedances during ignition which are important for the design of a stable and efficient oscillator.

Data are presented for several applications, e. g. for the surface activation of polymers. The possibilities of integration in manufacturing processes are discussed.

10:40 AM G3-10 Nanocoating System with Focused ICP Atmospheric Plasma Torch for Anti-Reflective Coating
Yuri Glukhoy, Alex Usenko (American Advanced Ion Beam Inc.)

A focused ICP atmospheric plasma torch has been used for yttrium oxide (Y2O3) nanocoating to prolong lifetime of the immersed in a plasma etching chamber parts with the non-flat surfaces like showerheads holes, steps of focusing rings, etc. Although Y2O3 has a high melting point our torch can provide for injected nanoparticles enough residential time in a high temperature area to be completely melted , evaporated in and delivered inside of deep holes , trenches and the porous structures. Another application such a torch is developing the nano-structured arrays used for anti-reflective, anti-glare and light capturing surfaces. It is possible using simultaneously with yttrium oxide as precursor nanopowder of silicon oxide or other material with a low resistance to etching plasma to develop the large scale moth’s eye like repetitive arrays nanostructures with cones approximately 200 nm high and 200 nm apart. But it requests a fine focusing of the torch in combination with a precise motion of substrate and one by one injection of two precursors synchronized with motion.

The torch is sustained by two saddle-like ICP antennas with the different frequencies, i.e. 27.12 and 13.56 MHz. Each antenna comprises two or more spiral coils in a mirror position and in series or parallel connection. These coils are distributed with an angular uniformity and envelop a quartz tube of a plasma reactor. Such a design allows generation of a transversal RF field directed normally to axis of this reactor that broaden and lengthen the high temperature area. . A plasma fluid is fixed on the axis due to buoyancy in the centrifugal force field created by a swirling injection of a discharge gas and two sheath gases in clockwise and a counterclockwise directions . .Such a triple vortex stabilization provides intensive flow rotation and the pressure minimum on the axis and prevents approaching of plasma to the quartz tube. Nevertheless, such a torch is highly charged especially in area of a tip causing diffusing of the spot. We have developed a method of compensation of these charges that minimize such a spot. Behavior of an inductively coupled plasma torch with non-axial generation, mechanisms of balancing of saddle-like antenna coupling, dynamic of the vortex stabilization of the plasma fluid and gas focusing will be discussed.

1. Y.Glukhoy, I. Ivanov RF Atmospheric Plasma Systems for Nanopowder Production and Deposition of Nanocrystallines. AVS 53rd International Symposium, San Francisco, California, November , 2006 CA, USA.

2. Y.Glukhoy. Saddle-like ICP Antenna for RF Atmospheric Plasma Processes. AVS 56th International Symposium, San Jose, California, November , 2009 CA, USA.

11:00 AM G3-12 Plasma Characteristics of Hollow Cathode Discharge in Plasma Ion Implantation of Slender Bore
Chunzhi Gong, Xiubo Tian, Haifu Jiang, Shiqin Yang (Harbin Institute of Technology, China); Ricky Fu, Paul Chu (City University of Hong Kong, China)
Plasma ion implantation has been receiving much interest in interior surface modification of cylindrical bore. However, the uniformity of incident dose relies on plasma characteristics inside the tube, especially for slender tube. Hence, it is very beneficial to produce steady plasma with high density, and to be slightly subject to the restrictions of diameter of tube. Aiming at this object, a novel hollow cathode plasma source is utilized to treat the interior surface of tube in this paper. Stable plasma can be sustained in the tube with dimension such as 30mm in diameter and 200mm in length. The plasma characteristics of the hollow cathode plasma source has been investigated using Langmuir probe with different instrumental parameters including rf power, gas pressure, and length of tube, etc. As for the confined hollow cathode discharge configuration(e.g. in tube), the plasma density decreases from hollow cathode outlet along the axial direction of tube, and plasma density increases with rf power increasing, but it exhibits nonlinear relationship with increasing gas flow and gas pressure. The inner diameter of hollow cathode has a great effect on plasma density.
Time Period WeM Sessions | Abstract Timeline | Topic G Sessions | Time Periods | Topics | ICMCTF2011 Schedule