Surface modification of a polyamide 6 film by He/CF4 plasma using atmospheric pressure plasma jet

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.     

Influence of processing parameters on atmospheric pressure plasma etching of polyamide 6 films

This study is designed to systematically investigate how various factors, such as treatment duration, output power, oxygen gas flux, jet to substrate distance, and moisture regain, influence atmospheric pressure plasma etching rate of polyamide 6 (PA 6) films. The etching rate increased as the output power, oxygen gas flux, and moisture regain increased. As the treatment time increased, the etching rate increased first and then decreased. When the substrate was too close or too far from the nozzle, the etching rate was almost not measurable. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show an increased surface roughness after the plasma treatment. X-ray photoelectron spectroscopy (XPS) shows a decreased carbon content and an increased oxygen content after the plasma treatment. T-peel strength shows an improved bonding strength between the PA 6 films and an adhesive tape after the plasma treatment.     

Influence of aramid fiber moisture regain during atmospheric plasma treatment on aging of treatment effects on surface wettability and bonding strength to epoxy

One of the main differences between a low-pressure plasma treatment and an atmospheric pressure plasma treatment is that in atmosphere, the substrate material may absorb significant amount of water which may potentially influence the plasma treatment effects. This paper investigates how the moisture absorbed by aramid fibers during the atmospheric pressure plasma treatment influences the aging behavior of the modified surfaces. Kevlar 49 fibers with different moisture regains (MR) (0.5, 3.5 and 5.5%, respectively) are treated with atmospheric pressure plasma jet (APPJ) with helium as the carrier gas and oxygen as the treatment gas. Surface wettability and chemical compositions, and interfacial shear strengths (IFSS) to epoxy for the aramid fibers in all groups are determined using water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and micro-bond pull out tests, respectively. Immediately after the plasma treatment, the treated fibers have substantially lower water contact angles, higher surface oxygen and nitrogen contents, and larger IFSS to epoxy than those of the control group. At the end of 30 day aging period, the fibers treated with 5.5% moisture regain had a lower water contact angle and more polar groups on the fiber surface, leading to 75% improvement of IFSS over the control fibers, while those for the 0.5 and 3.5% moisture regain groups were only 30%.     

Formation of a high hydrophilic/hydrophobic contrast surface on PET substrates by ECR generated sulfur hexafluoride plasma

High hydrophilic/hydrophobic contrast surfaces on polyethylene terephthalate (PET) substrates were formed by shadow mask technique in electron cyclotron resonance generated sulfur hexafluoride plasma atmosphere. The X-ray photoelectron spectroscopy (XPS) analyses indicate that the unmasked PET surfaces contained a high proportion of the CF₂-CF₂ groups, and therefore were hydrophobic with large water contact angle. However, the surface wettability was found to increase drastically on the masked PET surfaces. This could be resulted from a mass of COF (acid fluoride) compounds observed by XPS on the masked film surfaces. The COF compounds could react with atmospheric moisture to form -COOH groups, which in turn increased the surface wettability. In addition, the surface wetting property of the masked areas was found to change significantly with the plasma treatment time, the mask-to-substrate distance and the storage time after the treatment. The best contract in water contact angle obtained from the treated PET samples was larger than 100° after 168 h of storage.     

Modification of surface properties of polyamide 6 films with atmospheric pressure plasma

To investigate the effect of the different plasma gases treatment on the surface modification of atmospheric pressure plasma, polyamide 6 films were treated using pure helium (He), He/O₂ and He/CF₄, respectively. Atomic force microscopy (AFM) showed rougher surface, while X-ray photoelectron spectroscopy (XPS) revealed increased oxygen and fluorine contents after the plasma treatments. The plasma treated samples had lower water contact angles and higher T-peel strength than that of the control. The addition of small amount of O₂ or CF₄ to He plasma increases the effectiveness of the plasma treatment in polymer surface modification in terms of surface roughness, surface hydrophilic groups, etching rate, water contact angle and bonding strength.     

Fluorocarbon plasmas for nanotexturing of polymers: A route to water-repellent antireflective surfaces

In this work the roughening of polystyrene by means of radiofrequency plasmas fed with CF₄ has been studied. The effect of the Ar addition to the feed, the input power and the treatment duration has been investigated in terms of etching and fluorination degree. Wettability and reflectance performances of selected textured surfaces, coated with a fluorocarbon film from a C₄F₈ fed plasma, have been characterized. All the considered surfaces, even those poorly structured, once coated, show slippery superhydrophobicity, while antireflective transparency appears to be limited to precise texturing characteristics.     

Atmospheric pressure plasma with a flat spiral electrode

A new kind of electrically isolated flat spiral electrode for generating homogeneous atmospheric pressure plasmas is proposed. A sinusoidal voltage (5 kV_pk–pk, 48 kHz) has been applied to the electrode. The high voltage is generated with a dc supply voltage of only 4 V, based on the electrical characteristics of a resonant circuit. Plasma was generated in closed spaces in helium with air impurities, with or without using a second grounded electrode. The gas temperature was of around 324 K and the plasma was tested for the paperboard hydrophilicity and transparent film for printer wettability modifications.     

Use of the 447 nm He I line to determine electron concentrations

The helium 447 nm complex line has been excited in a wall-stabilized arc fed at atmospheric pressure by pure He, He-H₂, He-Ne-H₂ or He-Ar-H₂ mixtures. Photoelectric endon observations of the central part of the arc channel were made with high spatial (1/600) and spectral (53,000) resolution.A collection of 88 helium 447 nm line profiles, of which 75 were recorded simultaneously with H_β and Ne I or Ar II line profiles, yielded information about the electron concentration (2 X 10²⁰-2 X 10²² m^-3), temperature and relative ion composition of the plasma. Plots have been made of the forbidden to allowed peak separations (S), forbidden to allowed relative intensities of the peaks (F/A) and dips (i.e. the minimum intensities between lines) to allowed peak intensities (D/A) as functions of electron concentration, temperature and ionic composition in different plasmas.The peak separations depend only on the electron concentration. Other characteristic line-profile parameters (F/A and D/A) show weak ion motion with a strong electron-concentration influence. We propose simple formulae, which may be useful for practical determinations of the electron concentrations in helium-containing plasmas with an accuracy of ±15% and without taking into account either the chemical composition of the plasma or the temperature.     

Review of Laser-Induced Plasma,Its Mechanism,and Application to Quantitative Analysis of Hydrogen and Deuterium

Abstract

A comprehensive review of important progress achieved over the last 30 years regarding knowledge of laser-induced plasmas generated by CO₂ and Nd:YAG lasers in a variety of ambient gases is presented in this article, as well as research results on the extension of laser-induced breakdown spectroscopy (LIBS) for quantitative analysis of light elements, especially hydrogen and deuterium. First, the formation of shock wave–induced expanding secondary plasma in low-pressure ambient gases is discussed along with the dynamic characteristics of the secondary plasma expansion process. The unique advantages of low-pressure gas plasma are explained in relation to the successful detection of the sharp H and D emission lines. The experimental results using helium ambient gas are presented with emphasis on the role of He gas plasma in introducing an additional delayed excitation mechanism involving the helium metastable excited state, which resulted in the complete resolution of H and D emission lines, separated by only 0.18 nm. The development of a laser precleaning treatment and special double-pulse techniques further produced a linear calibration line with zero intercept applicable to quantitative H and D analyses of zircaloy sample, with either low- or high-pressure ambient He gas. More recent use of a transversely excited atmospheric (TEA) CO₂ laser in place of an Nd:YAG laser has demonstrated the much desired larger excited helium plasma and thereby resulted in significant emission enhancement and improved detection sensitivity.     

Surface morphology changes of poly(ethyleneterephthalate) fabrics induced by cold plasma treatments

Some selective cold plasma processing modify specific surface properties of textile polymeric materials such as their dyeability, wettability and hydrorepellence. To correlate the sample surface changes with the acquired surface properties allows one to obtain information on the chemical and physical processing involved in plasma treatment. In this work, atomic force microscopy (AFM) has been applied to investigate the morphological and topographical surface modifications induced by RF cold plasma processing of poly(ethyleneterephthalate) (PET) fabrics. Rms surface roughness and surface area of the samples are measured before and after the treatments. The morphology changes have been analysed as a function of the treatment time and air gas pressure. Measurements have been performed also using plasmas produced by different gases such as He, Ar, SF₆ and CF₄. The PET shows different behaviour with different gas plasmas. In the case of air, He and Ar gases the sample surface modifications seem to be mainly due to etching effects, while the fluorine atoms grafting probably is responsible for surface rearrangement process using SF₆ and CF₄ gases. As a consequence different surface properties are produced in the plasma treated samples. Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.     

Spatial Uniformity of Atmospheric Pressure Discharges: A Simulation Study

Spatial uniformity is important in most applications of dielectric barrier discharges operating at atmospheric pressure. However, such uniformity is not easily achieved. Under many conditions, a filamentary structure usually develops. In this paper, we employ a two‐dimensional self‐consistent fluid model to explore the influence of several factors on the evolution of spatial structure of dielectric barrier discharges. In particular, we contrast the behavior of discharges in pure helium and He‐N₂ gas mixture, which represent the reduction in breakdown voltage of gas during the evolvement of uniform glow discharge plasma. The transformation from filamentary to uniform mode of discharge plasma is analyzed by the phenomenon of coalescence of filaments and we investigate the effect of several external discharge parameters, such as driving frequency and effect of overvoltage, and the dielectric constant of the barrier material for the uniform and filamentary discharge plasmas. This simulation study is useful to describe the spatio‐temporal profiles of electron density in different phases of the filamentary, uniform Townsend and glow discharge regimes under various constraints. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of fluorine-based plasma treatment on morphology and chemical surface composition of biocompatible silicone elastomer

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been used to investigate the effect of reactive ion etching (RIE) on poly(methylhydrogensiloxane-co-dimethylsiloxane) surface in fluorine-based plasmas. Polysiloxane layers supported on the standard silicon wafers were etched using SF₆ + O₂ or CF₄ + O₂ plasmas. SEM studies show that the polysiloxane morphology depends on plasma chemical composition strongly. Presence of a columnar layer likely covered with a fluorine rich compound was found on the elastomer surface after the CF₄ + O₂ plasma exposure. After the SF₆ + O₂ or CF₄ + O₂ plasma treatment the polysiloxane surface enriches with fluorine or with fluorine and aluminum, respectively. Different morphologies and surface chemical compositions of the silicone elastomer etched in both plasmas indicate different etching mechanisms.     

大气环境下氦气等离子体中化学过程数值模拟

建立一个大气化学程序用以模拟大气压下（地面附近）或低压（高空）情况下混合气体（氦气中混入少量空气）中产生等离子体后的化学过程。给出了电子寿命和主要带电粒子的随时间演化图。电子寿命在大气压下要长于大气等离子体，但在低压情况下这个结论不成立。电子数密度在一很长一段时间内不服从指数衰减规律。     

The role of vibrational temperature variations in a pulsed dielectric barrier discharge plasma device

The use of dielectric barrier discharge (DBD) plasmas has become a practical way to carry out surface treatment where precise control of the plasma parameters, such as rotational and vibrational temperatures (T_rot and T_vib), is required. As the T_vib of an atmospheric pressure plasma jet appears to be the most important parameter related to the improvement of surface treatments, in this work, we analysed two methods to increase the values of T_vib in a DBD plasma jet device. One of the methods is to reduce the exit size (ø) of the DBD reactor, which results in an increase in the measured T_vib values, due to an increase in the pressure inside the reactor. The other method is to change the gas flow rate (GFR) used to produce the plasma jets. This leads to a T_vib reduction when the GFR is increased in the case of using helium or nitrogen as the working gas, but the opposite happens (an increase in the T_vib values) when argon is used, with different phenomena causing the variation of T_vib in each situation.     

Nonselective vertical etching of GaAs and AlGaAs/GaAs in high pressure capacitively coupled BCl3/N2 plasmas

We studied nonselective, vertical dry etching of GaAs and AlGaAs/GaAs structure in high pressure capacitively coupled BCl₃/N₂ plasmas. The operating pressure was fixed at 150 m Torr. We found that there was an optimized process condition for nonselective and vertical etching of GaAs and AlGaAs/GaAs at the relatively high pressure. It was noted that there was a range of % N₂ (i.e. 20–40%) where nonselective etching of GaAs over AlGaAs could be achieved in the BCl₃/N₂ mixed plasma. We also found that dry etching of GaAs and AlGaAs/GaAs structure provided quite vertical and smooth surface when % N₂ was in the range of 0–20% in the BCl₃/N₂ plasma. The maximum etch rates for GaAs (0.41 μm/min) and AlGaAs/GaAs structure (0.42 μm/min) were obtained with 20–30% N₂ composition in the plasma.     

Elucidating surface properties of dry-etched ZnO using H2/CH4 and H2/CH4/Ar plasma

This paper reports a study of reactive ion etching (RIE) of n-ZnO in H₂/CH₄ and H₂/CH₄/Ar gas mixtures. Variables in the experiment were gas flow ratios, radio-frequency (rf) plasma power, and total pressure. Structural and electrical parameters of the etched surfaces and films were determined. Both the highest surface roughness and highest etching rate of ZnO films were obtained with a maximum rf power of 300 W, but at different gas flow ratios and working pressures. These results were expected because increasing the rf power increased the bond-breaking efficiency of ZnO. The highest degree of surface roughness was a result of pure physical etching by H₂ gas without mixed CH₄ gas. The highest etching rate was obtained from physical etching of H₂/Ar species associated with chemical reaction of CH₄ species. Additionally, the H₂/CH₄/Ar plasma treatment drastically decreased the specific contact and sheet resistance of the ZnO films. These results indicated that etching the ZnO film had roughened the surface and reduced its resistivity to ohmic contact, supporting the application of a roughened transparent contact layer (TCL) in light-emitting diodes (LEDs).     

Surface modification of polytetrafluoroethylene film using single liquid electrode atmospheric- pressure glow discharge

Polytetrafluoroethylene films are treated by room temperature helium atmospheric pressure plasma plumes, which are generated with a home-made single liquid electrode plasma device. After plasma treatment, the water contact angle of polytetrafluoroethylene film drops from 114°to 46°and the surface free energy increases from 22.0 mJ/m2 to 59.1 mJ/m2. The optical emission spectrum indicates that there are reactive species such as O2+ , O and He in the plasma plume. After plasma treatment, a highly crosslinking structure is formed on the film surface and the oxygen element is incorporated into the film surface in the forms of -C-O-C-, -C=O, and -O-C=O groups. Over a period of 10 days, the contact angle of the treated film is recovered by only about 10 , which indicates that the plasma surface modification is stable with time.     

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO₂- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO₂-COOH was used to enhance the compatibility between SiO₂ and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO₂-COOH composites with low content of EBS and SiO₂-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO₂-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO₂-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO₂-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO₂-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO₂-COOH was 0.2 wt%, the SiO₂-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (T_m), degree of crystallinity (X_c), and crystallization temperatures (T_c) of PA 6/EBS/SiO₂-COOH composites were lower than the pure PA 6.     

Plasma processing

Low pressure, non-equilibrium, weakly to partially ionized gas discharge plasmas are used for a variety of surface materials processing applications. The most extensive applications are in microelectronics manufacturing, where plasma sputtering, etching, stripping, cleaning and film deposition play key roles in this growing industry. Up to 30% of all process steps in integrated circuit manufacture involve low pressure plasmas in one way or another. The rapid pace of process and product technological change in this industry, coupled with the unique capabilities of plasma processing for extremely finely controlled surface modification, offers new opportunities to plasma scientists     

Arc plasma jet cleaning of the silicon surface before CoSi2/Si contact formation

Cleaning of the silicon surface before Co film deposition is a key procedure in the synthesis of silicide (CoSi₂) and, hence, in the production of the metal-semiconductor contact. This study deals with a new method of surface cleaning using arc plasma jet treatment (APJT) at atmospheric pressure. The results show that cleaning of the Si surface using APJT (Ar/CCIF₃) improves the Schottky barrier contact parameters in comparison with conventional wet HF final cleaning and additional cleaning using in situ Ar-ion-beam sputter etching. Moreover, substantially longer time of wafer exposure to air between final cleaning and metal deposition is acceptable. Auger electron spectroscopy shows that APJT removes oxygen from the Si surface.