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.     

Modification of surface properties of polypropylene (PP) film using DC glow discharge air plasma

The industrial use of polypropylene (PP) films is limited because of undesirable properties such as poor adhesion and printability. In the present study, a DC glow discharge plasma has been used to improve the surface properties of PP films and make it useful for technical applications. The change in hydrophilicity of modified PP film surface was investigated by contact angle (CA) and surface energy measurements as a function of exposure time. In addition, plasma-treated PP films have been subjected to an ageing process to determine the durability of the plasma treatment. Changes in morphological and chemical composition of PP films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap shear strength. The results show that the surface hydrophilicity has been improved due to the increase in the roughness and the introduction of oxygen-containing polar groups. The AFM observation on PP film shows that the roughness of the surface increased due to plasma treatment. Analysis of chemical binding states and surface chemical composition by XPS showed an increase in the formation of polar functional groups and the concentration of oxygen content on the plasma-processed PP film surfaces. T-peel and lap shear test for adhesion strength measurement showed that the adhesion strength of the plasma-modified PP films increased compared with untreated films surface.     

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%.     

Effects of microwave plasma treatment on the field emission properties of printed carbon nanotubes/Ag nano-particles films

The effects of Ar microwave plasma treatment on field emission properties of the printed carbon nanotubes (CNTs) cathode films using Ag nano-particles as binder were investigated. The field emission J-E characteristics were measured at varied plasma treatment time. Significant improvement in emission current density, emission stability and uniformity were achieved for the Ar treated CNTs films, even though the plasma treatment increased the turn on electric field slightly. High-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy revealed the microstructural changes of CNTs after the plasma treatment. The improved field emission properties of CNTs film can be attributed to the generation of a high density of structural defects after treatment, which increased greatly the possible emission active sites. Besides, the formation of the sharpened and open-ended CNTs tips is all helpful for improving the field emission properties of the treated CNTs.     

The effect of oxygen exposure on pentacene electronic structure

We use ultraviolet photoelectron spectroscopy to investigate the effect of oxygen and air exposure on the electronic structure of pentacene single crystals and thin films. It is found that O₂ and water do not react noticeably with pentacene, whereas singlet oxygen/ozone readily oxidize the organic compound. Also, we obtain no evidence for considerable p-type doping of pentacene by O₂ at low pressure. However, oxygen exposure lowers the hole injection barrier at the interface between Au and pentacene by 0.25 eV, presumably due to a modification of the Au surface properties.     

Short-time plasma surface modification of HDPE powder in a Plasma Downer Reactor - process, wettability improvement and ageing effects

The effectiveness of improving the wettability of HDPE powders within less than 0.1 s by plasma surface modification in a Plasma Downer Reactor is investigated. A correlation is revealed between the XPS results (O/C-ratio) and the wettability (contact angle, polar surface tension by capillary rise method). The O₂-content in the plasma feed gas has been adjusted for best wettability properties. XPS results indicate the formation of CO and COOH functional groups on the powder surface. The O/C-ratio increased from 0.0 (no oxygen on the non-treated powder) up to 0.15 for the plasma treated HDPE powder surface. With pure O₂-plasma treatment, a water contact angle reduction from >90° (no water penetration into the untreated PE powder) down to 65° was achieved. The total surface free energy increased from 31.2 to 45 mN/m. Ageing of treated powders occurs and proceeds mostly within the first 7 days of storage. Contact angle measurements and O1s/O2s intensity ratio data support that ageing is mainly a diffusion-controlled process. Nevertheless, XPS results show the presence of oxygen functional groups even after 40 days, which explains why the powder is still dispersible in water without any addition of surfactants.     

RF-CF4 plasma surface modification of paper: Chemical evaluation of two sidedness with XPS/ATR-FTIR

The study was performed to examine the correlation between the initial roughness and surface fluorination of paper under RF-CF₄ plasma environment.Based on the experimental observations, a correlation was observed between surface fluorination and plasma parameters, e.g. RF-power, treatment time and gas pressure. The level of fluorination with RF-CF₄ plasma treatment was found to be extensive in both side of paper. Even very short treatment time, as low as 1 min at 300 W power, provides effective implantation of fluorine (38.7%) on surfaces. It was observed that, CF₄ plasma treatment had a significant effect on the molecular fragmentation on both side of paper. However, the felt side have a much stronger effect on plasma-induced dissociation and fluorination than in the wire side of paper.     

Plasma and surface modeling of the deposition of hydrogenated carbon films from low-pressure methane plasmas

The elementary mechanisms are described which determine the plasma and surface processes during the plasma-enhanced chemical vapour deposition of hydrogenated carbon films from methane. Corresponding model calculations are reviewed and critically discussed in comparison to experimental results. A realistic modeling requires the simultaneous and self-consistent treatment of plasma and surface effects. Several experimental data sets on plasma parameters and the growth and the composition of the films have been reproduced successfully. However, a broader experimental data base is needed for more critical tests of the models. The reliability of the modeling, in particular of the surface effects, is still limited due to the poor availability of elementary data.     

The effect of collisions on wave-breaking in a cold plasma

The effect of electron collisions on reducing the wave-breaking amplitude of resonantly-driven electrostatic fields in a cold plasma is investigated. By means of a simple theory collisions are shown to compete with wave-breaking in dissipating wave energy.     

The effect of low-pressure air plasma treatment on the wettability and surface energy of polyvinyl chloride films

Low-pressure plasma in a RF discharge of air is employed to introduce a polar function to a polyvinyl chloride surface to enhance the wettability and activation. A clear increase in the surface energy of the surface of a polymer due to air plasma treatment was observed. The surfaces become highly hydrophilic after treatment. The effect of plasma treatment on the morphology and wettability of the surfaces were characterized by using a static contact angle measurement and attenuated total reflection-FTIR spectroscopy.     

Bulk periodic structures formation on monocrystalline silicon surface under the action of compression plasma flows

The results of numerical simulation of monocrystalline silicon melting and crystallization under the action of compression plasma flow generated by quasistationary plasma accelerators with regard to phase transformations based on Kolmogorov equation are presented. Temporal and spatial characteristics of melting and crystallization processes for pulses of various forms are discussed. Based on data received and estimates made, the conclusion on substantial role of thermoelectric instability in bulk periodic structures formation was made.     

Study on bacteria adherence properties of Mo surface-modified layer in Ti6Al4V alloy prepared by plasma surface alloying technique

Mo surface-modified layer in Ti₆Al₄V alloy was prepared using plasma surface alloying technique. Microstructure of the modified layer was analyzed using X-ray photoelectron spectroscopy (XPS), rough-meter and GDA750 glow discharge optical emission spectrometer. Phase composition of the Mo surface-modified layer was characterized by D/max 2500 X-ray diffraction. Results show that the Mo surface-modified layers consist of pure Mo surface layer with 〈1 1 0〉 and 〈2 1 1〉 orientations and diffusion layer. Mo 3d, O 1s, C 1s and Ti 2p, O 1s, C 1s XPS spectra are recorded at topsurface in the Mo-modified layer and titanium substrate respectively. Because of the different roughness and microstructure, the Mo surface-modified layer can to some extent inhibit bacteria adherence.     

ADBD plasma surface treatment of PES fabric sheets

Plasma treatment of textile fabrics is investigated as an alternative to the environmentally hazardous wet chemical fabric treatment and pretreatment processes. Plasma treatment usually results in modification of the uppermost atomic layers of a material surface and leaves the bulk characteristics unaffected. It may result in desirable surface modifications, e.g. surface etching, surface activation, cross-linking, chain scission and oxidation. Presented paper contains results of the applicability study of the atmospheric pressure dielectric discharge (ADBD), i.e. dielectric barrier discharge sustaining in air at atmospheric pressure and ambient temperature for synchronous treatment of several sheets of fabric. For tests sheets of polyester fabric were used. Effectivity of the modification process was determined with hydrophilicity measurements evaluated by means of the drop test. Hydrophilicity of individual sheets of fabric has distinctly increased after plasma treatment. Plasma induced surface changes of textiles were also proven by identification of new functional groups at the modified polyester fabric surface. Existence of new functional groups was detected by ESCA scans. For verification of surface changes we also applied high-resolution microphotography. It has shown distinct variation of the textile surface after plasma treatment. Important aspect for practical application of the plasma treatment is the modification effect time-stability, i.e. time stability of acquired surface changes of the fabric. The recovery of hydrophobicity was fastest in first days after treatment, later gradually diminished until reached almost original untreated state.     

Nonlinear surface photoeffect in multi-color laser field: effect of the finite width of the surface potential barrier

Received: 20 September 1998     

Stabilization of discotic liquid organic thin films by ITO surface treatment

Discotic liquid crystals (LCs) are promising materials in the field of electronic components and, in particular, to make efficient photovoltaic cells due to their good charge transport properties. These materials generally exhibit a mesophase in which the disk-shaped molecules can self-assemble into columns, which favorize charge displacement, and may align themselves uniformly on surfaces to form well-oriented thin films. In order to orientate such a columnar thin film on an indium tin oxide (ITO) substrate, the film is heated up to the temperature range of the isotropic liquid phase and subsequently cooled down again. This treatment may lead not only to the desired alignment, but also to dewetting, which leads to an appreciable inhomogeneity in film thickness and to short circuits during the realization of photovoltaic cells. In this article, we describe how this dewetting and the film morphology can be influenced by ITO surface treatments. The chemical modifications of the surface by these treatments were studied by X-ray photoelectron spectroscopy (XPS). Such ITO treatments are shown to be efficient to prevent thin film dewetting when combined with rapid cooling through the isotropic-to-LC phase transition.     

The influence of electrode gap width on plasma properties of diffuse coplanar surface barrier discharge in nitrogen

In this work we have studied the influence of electrode gap width (inter-electrode distance) on plasma properties of the diffuse coplanar surface barrier discharge. The outer conditions and discharge configuration can substantially influence properties of the discharge. Better understanding of these effects can lead to optimization of the discharge parameters for industrial applications. In this work the discharge was operated in nitrogen at atmospheric pressure. The electrode gap width was varied in the range from 0.6 to 2.2 mm. The input voltage, electrode temperature and gas flow was kept constant for all cases. Plasma parameters were studied by the means of time and space resolved optical emission spectroscopy and oscilloscopic measurements. These measurements gave us time and space distribution of discharge luminosity (e.g. intensities of second positive and first negative systems of nitrogen) and 1D-spatial profiles of rotational and vibrational temperature of nitrogen.     

Increased surface roughness by oxygen plasma treatment of graphite/polymer composite

The technology of selective plasma etching was applied to increase the surface roughness of graphite/polymer composite. Etching was performed with a low pressure weakly ionised oxygen plasma created with a RF generator of the output power of 200 W and frequency of 27.12 MHz. The density of charged particles, density of neutral oxygen atoms and the electron temperature was about 1×10¹⁶ m⁻³, 4×10²¹ m⁻³, and 5 eV, respectively. The effects of plasma treatment were observed by scanning electron microscope (SEM), electron microprobe (EMPA) and Talysurf. It was found that the surface roughness was increased by approximately 15 times, from a virgin sample at the roughness of R_a=0.27 μm to a very rough surface with R_a=4 μm. The roughness increased with increasing plasma exposure time. The EMPA results showed that the amount of sulphur in the surface layer decreased with increasing etching time indicating that PPS polymer was the material etched preferentially.     

Observations of extreme ultraviolet emission from plasma produced by capillary discharges

This study reports the results of a pilot experiment concerning observations of extreme ultraviolet emission from plasma produced by the capillary discharges. A few kA current was applied across the gas-filled alumina capillary (1 mm diameter and 8 mm long) to generate radiation in the EUV region (12–63 nm). Spectroscopic studies were carried out by means of a XEUV spectrometer which was upgraded for special lithography purposes. The results obtained from the EUV spectroscopic measurements provided information about the radiation processes from xenon and argon plasma and testifies that given capillary is an effective source of EUV emission. Additionally we showed a simulation which describes plasma dynamics parameters and dynamics of various ionization stages in capillary discharge. Our computer simulation confirmed the presence of ions, which spectra was registered in the experiment.     

Effects of an ultrashort prepulse on soft X-ray generation from an aluminium plasma produced by femtosecond Ti:Sapphire laser pulses

The influence of a prepulse on soft X-ray emission in the range of 50–200 from an aluminium plasma produced by 130 fs Ti: Sapphire laser pulses with an intensity of 10¹⁴ W/cm² at normal incidence is studied. An ultrashort prepulse with an intensity of 10¹³ W/cm² significantly enhances soft X-ray emission when there is a long time separation ( > 100 ps) between the prepulse and an intense main pulse. It is also observed for the first time that a prepulse with a short pulse time separation can slightly reduce soft X-ray emission, contrary to the previous work done using 248 nm laser pulses. This can be explained qualitatively in terms of the dependence of absorption on the length scale.     

The effect of oxygen–oxygen repulsion in the production of water from hydrogen–oxygen reaction on the surface: A computer simulation study

The formation of water from hydrogen–oxygen reaction on a metal surface is of immense importance due to the technological reasons. This reaction has been studied via a thermal mechanism on a Pt single crystal surface where the two molecules, H₂ and O₂, have been adsorbed dissociatively in atomic form. The reaction takes place between the adsorbed atoms through an intermediate OH radical. We have studied this reaction via a thermal (Langmuir–Hinshelwood mechanism) as well as a non-thermal mechanism (precursor mechanism) by the Monte Carlo computer simulations. In this study, we have applied a novel approach based upon the experimental observations that the dissociated oxygen atoms do not sit next to one another on a catalytic surface. Some interesting results like the shifting of the phase transition points, the broadening of the reaction window width and the elimination of the second-order phase transition in the non-thermal reaction mechanism are obtained by considering various possibilities of the reaction scheme. The phase diagrams as well as the snapshots of the surface covered with the reacting species are presented.