Argon Gas Plasma Research Articles

Functional nanostructures generated by plasma-enhanced modification of polypropylene fibre surfaces

Polypropylene (PP) fibres have an extensive range of applications, including filtration, composites, biomaterials and electronics. In these applications, the surface properties of the fibres are particularly important. This paper presents examples of the use of gas plasma technology to create functional nanostructures on PP fibre surfaces, which render the surfaces hydrophilic. It is also shown how these treatments can be regulated to produce the desired level of hydrophilicity for a given application. Three principal modifications have been performed, to create functional nanostructures: plasma activation with oxygen gas plasma, grafting of polyacrylic acid following argon gas plasma treatment, and plasma-enhanced deposition of silver. Atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM) were employed to characterise the morphology, surface structure and composition of the fibres treated by gas plasma.

Excitation of Doubly‐Charged Ion Emission Lines from a Grimm‐Style Glow Discharge Plasma—Comparison Between Yttrium and Zirconium

Spectra of yttrium and zirconium emitted from a Grimm‐style glow discharge plasma were investigated to elucidate the excitation mechanism of doubly‐charged ionic lines when using argon–helium mixed gas as well as argon gas alone. The energy sum for exciting doubly‐charged ion species of yttrium is slightly smaller compared to the case of zirconium, which yields an interesting correlation in the excitation energy between their ionic species and excited species of helium or argon. The Y III emission lines which were assigned to the 4p65p–4p65s(4p64d) transitions could be observed in the argon–helium mixed gas plasma, but those were hardly excited with argon gas only. The Zr III emission lines did not appear in the spectra emitted by the argon gas plasma nor by the mixed gas plasma. A possible explanation for these phenomena is that the excitation of these ionic species is caused principally by collisional energy transfer from helium species to the analyte atoms.

Block copolymer micelle nanolithography

Au-nanoclusters between 2 and 8 nm in diameter were deposited onto solid substratesin different pattern geometries. The basis of this approach is the self-assembly ofpolystyrene-b-poly[2-vinylpyridine(HAuCl4)]diblock copolymer micelles into uniform monomicellar films onsolid supports such as Si-wafers or glass cover slips. HAuCl4as metallic precursor or a single solid Au-nanoparticle caused by reduction of theprecursor are embedded in the centre of diblock copolymer micelles. Subsequenthydrogen, oxygen or argon gas plasma treatment of the dry film causes depositionof Au-nanoparticles onto the substrate by entire removal of the polymer. TheAu-dot patterns resemble the micellar patterns before the plasma treatment.Separation distances between the dots is controlled by the molecular weight of thediblock copolymers. The limitation of the separation distance between individualdots or the pattern geometry is overcome by combining self-assembly ofdiblock copolymer micelles with pre-structures formed by photo or e-beamlithography. Capillary forces of a retracting liquid film due to solventevaporation on the pre-structured substrate push micelles in the corners of thesedefined topographies. A more direct process is demonstrated by applyingmonomicellar films as negative e-beam resist. Micelles that are irradiated byelectrons are chemically modified and can hardly be dissolved from thesubstrate while non-exposed micelles can be lifted-off by suitable solvents.This process is also feasible on electrical isolating substrates such as glasscover slips if the monomicellar film is coated in addition with a 5 nm thickconductive layer of carbon before e-beam treatment. The applicationof cylindrical block copolymer micelles also allows for the formation of4 nm wide lines which can be 1–50 µmlong and also be organized in defined aperiodic structures.

A Study of Environmentally Friendly Titanium Pretreatments for Adhesive Bonding to a Thermoplastic Composite

AbstractThe increased use of fibre reinforced polymer composites for aircraft structures have highlighted the need for reliable methods of bonding these materials to metallic components such as titanium. There is also a need for a simple test to evaluate adhesive bonds with dissimilar substrates, while under load and in a variety of environments. In this study the Boeing wedge test has been adapted for use with metal to composite adhesive bonds. A flexural rigidity matching approach was used with the addition of a backing beam to the composite coupon. The titanium adherends were surface pre‐treated using novel environmental benign methods, namely argon gas plasma and silicon sputtering. Sodium hydroxide anodisation, which is currently used industrially and alumina grit blasting were used as benchmarks. The composite, glass fire reinforced polyphenylene sulphide was alumina grit blasted. An environmental cycle was used to mimic a typical aircraft service cycle; joints were subjected to 24‐hour cycles of ambient, 60 °C water immersion, 60 °C dry and –55 °C dry for 12 days. Crack propagation and locus of failure were monitored after each cycle.

Determination of 129I/127I isotope ratios in liquid solutions and environmental soil samples by ICP-MS with hexapole collision cell

The determination of 129I in environmental samples at ultratrace levels is very difficult by ICP-MS due to a high noise caused by Xe impurities in argon plasma gas (interference of 129Xe+), possible 127IH2+ interference and an insufficient abundance ratio sensitivity of the ICP mass spectrometer for 129I/127I isotope ratio measurement. A sensitive, powerful and fast analytical technique for iodine isotope ratio measurements in aqueous solutions and contaminated soil samples directly without sample preparation using ICP-MS with a hexapole collision cell (ICP-CC-QMS) was developed. Oxygen is used as reaction and carrier gas for iodine thermal desorption via the gas phase from solid environmental material in the sample introduction device coupled on-line to ICP-CC-QMS. A mixture of oxygen and helium as reaction gases in the hexapole collision cell was applied for reducing disturbing background intensity of 129Xe+. After optimization of measurement procedures the detection limit for 129I+ in aqueous solution was 8 × 10−13 g ml−1, which is better by about two orders of magnitude in comparison to the detection limit for 129I+ in sector field ICP-MS. The detection limit for direct 129I+ determination in contaminated environmental (soil) samples via gas-phase desorption without any additional sample preparation was 3 × 10−11 g g−1 (30 ppt). Furthermore, the results of the determination of 129I/127I isotope ratios at the 10−5–10−6 level in synthetic laboratory standards and environmental soil samples from contaminated areas are given.

High performance materials

It is now well known that traces of hydrogen or nitrogen in the argon plasma gas in glow discharge optical emission spectrometry (GD-OES) may affect the sputtering rate. More seriously, such traces can also selectively affect the absolute and relative intensities of individual lines, and thereby have a major effect on the accuracy of analytical results. This problem is becoming more severe as the potential of GD-OES as an analytical tool is steadily increasing, and the technique is now used for the analysis of more complex samples.The results presented form part of an extensive study of the effects of hydrogen and nitrogen on the spectra of a number of elements — Fe, Ti, V, Ni, Zn etc. Two systems have been used to record the spectra for the present results — high resolution Fourier transform spectroscopy at Imperial College, London, and the LECO GDS500A, with CCD spectrometer at LECO Instrumente, Plzeň. The two approaches have yielded consistent results.During the analysis of the data for Fe II and Ti II spectra, it has become clear that asymmetric charge transfer involving hydrogen ions (H-ACT) is a very important selective excitation mechanism for spectral lines with a total excitation energy close to 13.6 eV, the ionisation potential of hydrogen. Detailed evidence for this mechanism is presented. The magnitude of the effect varies for different elements and spectral lines but great care must be taken before choosing ionic lines with a total excitation energy of between 12.5–14 eV for analytical use.

Reduction in surface resistivity of polymers by plasma source ion implantation

The surface resistivity of several polymers such as poly(styrene/butadiene copolymer), modified poly(phenyleneoxide), poly(ethylene terephthalate), and polyimide was improved by the argon gas plasma source ion implantation (Ar-PSII) technique equipped with a mesh-type conducting grid. With the grid, the surface resistivities of the modified polymers decreased up to 11 orders of magnitudes at a high ion dose, and remained nearly at the same values after 3 months. The PSII treated polymer sample with the grid provided more uniformly modified surface and lower surface resistivity than that treated without the grid. The extent of the decrease in surface resistivity depended on the polymer structures and physical properties. However, the surface resistivity was independent of the sample thickness, the grid size, and the grid height. Surface analyses using scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy provided the useful information on modified surfaces.

Surface modification of polymethyl methacrylate intraocular lenses with the mixture of acrylic acid and acrylamide via plasma‐induced graft copolymerization

AbstractAn approach is presented for the graft copolymerization of acrylic acid (AAc) and acrylamide (AAm) mixture onto the surfaces of polymethyl methacrylate intraocular lenses (PMMA IOLs) treated with an Argon gas plasma, followed by the exposure to the oxygen atmosphere. In this case, peroxides formed by the plasma treatment are likely to be responsible for initiating the graft copolymerization. The amount of peroxides on the surface of PMMA IOLs was determined using 1,1‐diphenyl‐2‐picrylhydrazyl, and the maximum amount was found with the plasma treatment at 30 W for 20 s under 5 mTorr pressure. The surfaces of the grafted PMMA IOLs were characterized using Fourier transform infrared spectroscopy‐attenuated total reflectance (FTIR‐ATR), electron spectroscopy for chemical analysis, and contact angle meter. The FTIR‐ATR spectrum of PMMA‐g‐AAc‐AAm showed the characteristic band of PAAc at 1580 cm−1 together with those of PAAm at 1670 and 1630 cm−1, confirming that the copolymer of AAc and AAm was successfully grafted onto the surfaces of PMMA IOLs. The experimental data of O1s/C1s and N1s/C1s reasonably concurred with the calculated data, a strong indication that the pH value of the reaction medium at 3.77 could produce a graft with an equal molar ratio. Surface tension of the samples increased to 52 dyn/cm due to the graft of the hydrophilic monomers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2361–2366, 2002

The antibacterial activities of hydrophilic-modified nonwoven PET

The hydrophobic surface of nonwoven PET with surface inertia has limited the practical bioapplications. In this study, nonwoven PET was activated by argon gas plasma and subsequently water-soluble monomers (acrylamide and itaconic acid) were grafted onto the PET by UV-induced surface graft polymerization. After the plasma activation and/or grafting, the hydrophobic surface of nonwoven was modified into a hydrophilic surface. To improve wound healing, the following three biocides have been used in this study: (1) AgNO 3 solution complexes, (2) Vinyl quarternary ammonium salt (VQAS) and (3) chitosan. For Ag + ion impregnation and VQAS grafting, the amount of these biocidal materials on the surface increases when the monomer concentration increases. However, for the chitosan immobilization, the chitosan amounts seemingly decrease with an increase in the chitosan concentration. For biocidal properties, the Ag + ions produce best result. However, the VQAS grafting is most durable against the flushing water.

Characterization of a simple glow discharge coupled to a time of flight mass spectrometer for in-depth profile analysis

The capabilities of a simple glow discharge (GD) ion source coupled to an on-axis time-of-flight (TOF) mass spectrometer (MS) have been investigated in terms of several parameters of interest for in-depth profile quantification, including crater shapes, sample sputtering rates, sensitivity and mass resolving power. The GD ion source used here is a simple prototype constructed in our laboratory and designed to be easy and quickly exchanged with the inductively coupled plasma (ICP) source of a commercial ICP-(TOF)MS. Experiments showed that good crater shapes, with walls “perpendicular to” and base “parallel to” the sample's surface can be obtained for samples with different matrices, provided that a “sampler cone” in the interface between the GD chamber and the TOF is used; otherwise, an inhomogeneous sputtering in the sample is observed, ruining the crater shapes. The GD-(TOF)MS system developed offers a mass resolving power (full width at half maximum) of 2800 for 207Pb in the digital detection mode and 1700 in the analog mode. Furthermore, promising results have been obtained for possible use of polyatomic ions (formed between the argon plasma gas and a major element in the sample) as a quantitative indicator of the corresponding element. This approach could be very useful as an alternative strategy for the simultaneous determination of major, minor and trace elements, without saturation of the detector, by GD-(TOF)MS.

Sterilization of Sutures by Low Temperature Argon Plasma

Nondegradable and biodegradable, mono- and multifilament, natural and synthetic sutures were sterilized by treating in an argon gas plasma glow-discharge system at different glow-discharge powers (10, 20 and 40 watt) and exposure times (5, 15 and 30 min). All of the sutures (except plain and chromic catguts) were successfully sterilized. Plain and chromic catgut could not be sterilized even at very high discharge power and exposure time. A five watt discharge and 5 min of exposure time were considered optimal conditions for argon plasma sterilization without changing the desired suture mechanical properties (extensibility, knot-pull breaking and tensile strengths).

Gas contamination during plasma welding in Al–Li alloy 2195

Keyhole and cover pass variable polarity plasma arc welds were made on aluminium alloy 2195 with measured contamination levels of nitrogen, oxygen, and hydrogen. Contamination levels ranged from less than 10 to 500 ppm in both the argon plasma gas and the helium shield gas. It was found that nitrogen leads to more severe porosity than either hydrogen or oxygen, and that rear shielding is required for keyhole welding of Al–Li 2195 alloy to protect the weld from nitrogen in the atmosphere. Both nitrogen and oxygen contamination produced a dark surface on the weld bead, which comprised metallic aluminium particles, nucleated in the melt, that had aggregated at the surface of the weld pool.

Gas contamination during plasma welding in Al–Li alloy 2195

Keyhole and cover pass variable polarity plasma arc welds were made on aluminium alloy 2195 with measured contamination levels of nitrogen, oxygen, and hydrogen. Contamination levels ranged from less than 10 to 500 ppm in both the argon plasma gas and the helium shield gas. It was found that nitrogen leads to more severe porosity than either hydrogen or oxygen, and that rear shielding is required for keyhole welding of Al–Li 2195 alloy to protect the weld from nitrogen in the atmosphere. Both nitrogen and oxygen contamination produced a dark surface on the weld bead, which comprised metallic aluminium particles, nucleated in the melt, that had aggregated at the surface of the weld pool.

Investigations on the Use of Radiofrequency Glow Discharge Optical Emission Spectrometry for In-depth Profile Analysis of Painted Coatings

The use of a radiofrequency glow discharge (rf GD) for in-depth profile analysis of painted steel materials by optical emission spectrometry (OES) was investigated. The types of sample selected as models were coated steel films currently in use for the manufacture of corrosion-resistant car bodies. The study was focused on three critical aspects: evaluation of the risk of melting of the painted samples, optimization of the craters obtained (both for the paints and for the metallic base) and possibilities of conversion of ‘intensityversus time’ profiles into ‘concentration versus depth’ in such samples. A suitable system for refrigeration of the source was first studied in order to avoid melting of the painted samples. In addition, with the aim of obtaining flat crater profiles, the discharge operation conditions and design of the source were investigated. Results showed that after optimization of the conditions and appropriate design of the source, very flat crater profiles, without accumulation of redeposited material in the area of the crater rims, could be obtained for both metallic films and non-conductive coatings, while problems with melting of painted layers were eliminated. Finally, the search for a method for in-depth quantification was addressed. The in-depth profile measurements were carried out at constant pressure. Significant changes in the excitation efficiency were observed after the discharge reached the interface between the non-conductive and metallic layers. However, the use of an emission line of argon (plasma gas) as internal standard proved to be a promising approach to quantitative depth-profile analysis, an unsolved problem in rf GD-OES.

Effect of sampler orifice diameter on dry plasma inductively coupled plasma mass spectrometry (ICP-MS) backgrounds, sensitivities, and limits of detection using laser ablation sample introduction

High backgrounds from polyatomic ions, formed from the argon plasma gas, impurities in the gas supply and atmospheric air entrainment of especially H, C, N, O, and Ar, are a limitation to Inductively Coupled Plasma-Mass Spectrometric (ICP-MS) analysis, especially for analytes with masses below 80 Dalton. When a “dry” plasma is utilized, instead of the more common “wet” plasma created when solution nebulization sample introduction is used, the relative contribution of air entrainment becomes more important. In this study, the sample introduction system used was an in-house constructed laser ablation microprobe designed for small volume sampling of geological materials. An enhanced sensitivity VG PQII+“S” ICP-MS was applied with different sample cone orifice diameters. Background, signal to background ratio, and detection limits are reported for ablated NIST glass reference material (SRM 612). By a reduction of the sample cone orifice diameter from 0.7 mm to 0.5 mm, the background was lowered by factor of ca. 100 in the low mass range and by a factor of ca. 10 in the higher mass range, while similar sensitivities were maintained. The reduced background improved the limits of detection from ca. 1 mg/μg/g to <0.5 μg/g in 10 μm diameter pits and from ca. 100 ng/g to <10 ng/g in larger, 30 μm pits.

Whisker growth on sputtered AlSn (20 wt.% Sn) films

AlSn films (20 wt.% Sn) with a thickness of 20 μm were prepared by magnetron sputter deposition in an argon gas plasma. It has been found that the oxygen content in the argon gas during deposition strongly influences film properties and surface morphology. From 0.005% up to 0.02% oxygen the films show a uniform and fairly smooth surface characterized by a roughness (RZ) of 3–5 μm. From 0.05 up to 0.15% oxygen numerous whiskers of different shape and dimensions appear on the film surface. The whisker growth leads to an increase of surface roughness with peak values around 25 μm. Above 0.5% oxygen no whiskers can be found on the film surface, but the film morphology changes from a dense structure to a loosely bonded one built up by spherolitic crystals. The microhardness of the films increases from 95 to 155 HV (Vickers hardness) with increasing oxygen content. Increasing either substrate temperature (110–160 °C) or film thickness (2–50 μm) increases the surface roughness from 2 to 25 μm or from 2 to 65 μm, respectively, whereas moderately low roughness (8 μm) can be obtained at argon gas pressures above 1 Pa.

Surface modification of spectra™‐900 polyethylene fibers using RF‐plasma

AbstractRF‐plasma polymerization and bonding of allylamine onto ultrahigh molecular weight polyethylene (UHMWPE) “Spectra™‐900” is described using an inductively coupled plasma reactor. This process was found to enhance the interfacial strength between the fibers (Spectra‐900) and room‐temperature‐cured epoxy matrix up to fivefold. Fibers covalently coated with allylamine plasma showed no loss in tensile strength, while argon gas plasma pretreatment of the same fibers caused up to 10% reduction in tensile strength depending on the energy and duration of the treatment. Optimum treatment was attained through a short argon plasma etching (15 s), followed by allylamine polymerization and coating for 3 min. The coating process was found to protect the fiber surface from etching by plasma ion bombardment. A loss of 19% of the original diameter was found during the 15 s precoating etching with argon plasma, indicating the sensitivity of the fiber structure to plasma etching.

Sensitivity comparison in a microwave-induced plasma gas chromatographic detector: effect of plasma torch design

Optical-emission measurements and reflected-power measurements are used to evaluate the analytical performance of a water-cooled capillary plasma torch and a tangential flow torch in a 2.45-GHz microwave-induced argon plasma gas chromatographic detector. The design of a new-water-cooled capillary plasma torch is presented. The sensitivites and limits of detection are compared using the two torches and the same microwave power supply, resonant cavity, and detection circuitry

Pulsed-glow discharge/matrix isolation method for the production and trapping of organic ions: application to para-dimethoxybenzene

A new technique for the production and trapping of organic ions in rare-gass matrices is introduced. A pulsed-glow discharge produces the ions which are repelled from a hemispherical wire-mesh grid held at a high positive (or negative) potential toward the cold (12 K) sample window of a closed-cycle cryostat where they are deposited. The radical cation of para-dimethoxybenzene (PDMOB) has been formed by this method in sufficient quantities to observe a number of its infrared spectral bands for the first time. The electronic absorption spectrum of the cation matches well with results obtained by γ-irradiation of PDMOB in s-butylchloride matrices at 77 K and by oxidation of adsorbed PDMOB in Cu-exchanged montmorillonite clay. The introduction of CCl 4 into the argon plasma gas stream significantly enhances the number of ions produced and trapped.

Investigations on mixed-gas plasmas produced by adding nitrogen to the plasma gas in ICP-MS

Additions of nitrogen were made to the argon plasma gas of an inductively coupled plasma (ICP) used as an ion source in mass spectrometry (MS). The studies were carried out at constant nebulizer gas flow rate and uptake rate (i.e. constant nebulization efficiency), with the percentage of nitrogen in the plasma gas (from 0 to 10%) and the power (from 1.0 to 1.4 kW) as the only variables. For each set of operating conditions, the analytical characteristics were assessed for 56Fe +, 57Fe +, 76Se + and 78Se +. The best results were obtained at 1.2 kW where, although the sensitivity was reduced by a factor of up to 5 upon addition of nitrogen to the plasma, the stability of the plasma was improved, resulting in similar (Se) or improved (Fe) detection limits, by up to a factor of 4. A study of the effect of a matrix containing up to 0.1 M Na was also carried out (at 1.2 kW) while the percentage of nitrogen in the plasma gas was raised from 0 to 10%. The results show that the non-spectroscopic interference of Na can be reduced. In fact, with 5% nitrogen in the plasma gas, the effect of 0.01 M Na was essentially eliminated. Furthermore, the accuracy and precision of the 57Fe +/ 56Fe + and 76Se +/ 78Se + isotopic ratios were found to improve as the amount of nitrogen was increased. For instance, the precision of the mean 57Fe +/ 56Fe + ratio measured in solutions containing from 0 to 0.1 M Na improved by an order of magnitude with 10% nitrogen in the plasma, and that of 76Se +/ 78Se + improved by a factor of 4, which is still quite significant, given the high 76Ar + background in comparison with the relatively low abundance of 76Se +. Overall, the results suggest that an Ar-N 2 mixed-gas plasma may be a better ion source for MS than an all argon ICP.