Argon Plasma Immersion Ion Implantation Research Articles

Improvement of thermoplastic elastomer degradation resistance by low-energy plasma immersion ion bombardment

Thermoplastic elastomers (TPE) have been used instead of traditional elastomers, since they combine the low cost of raw material with easy processing and recyclability. When used in sealing components, the polyester-based TPE, or COPEs, are most common. Although COPEs have mechanical properties similar to those of elastomers, they have limited resistance to corrosion in chlorinated water. Argon Plasma Immersion Ion Implantation (IIIP) treatments were applied to alter the morphology and chemical composition of the COPE surface, with the goal of increasing its chemical inertia in chlorinated water while preserving the desired bulk properties. The effect of ion bombardment energy on the elemental composition, chemical structure, morphology, topography and mechanical properties of COPEs was evaluated, along with whether changes in such properties affected the degradation resistance of the material in chlorinated water. Treatments were performed for 60 min in radiofrequency argon plasmas (13.56 MHz, 5.0 Pa), with the power of the excitation signal varying from 10 to 150 W. Since variations in signal power changed the self-bias potential of the driven electrode, and samples were positioned at this electrode, the ion bombardment intensity was varied in the different treatments. Immediately after treatments, surfaces became more hydrophilic than the as-received ones, but after being aged in air, some samples became hydrophobic. Dehydrogenation was the main alteration attained in chemical composition, inducing changes in the overall chemical structure. Species removal from less resistant regions promoted creation of nanometric structures randomly distributed on the surface but without promoting changes in the volumetric mechanical properties of COPE. The most pronounced surface changes were observed for the sample treated in plasmas at 150 W, which also presented the highest resistance to chlorinated solution. This improvement suggests an increase in COPE performance in practice.

Recent experiments on plasma immersion ion implantation (and deposition) using discharges inside metal tubes

Plasma immersion ion implantation (PIII) of nitrogen inside metallic tubes of different diameters and configurations were attempted recently. PIII tests in practical size metallic tubes of SS304, ranging from 1.1 to 16 cm∅ and length of 20 cm, were carried out as a continued effort in our lab, to explore PIII inside tubes. Tubes in laying down positions and configurations including metallic lid in one side or both sides open were used, as well as, plane sample support placed 10 cm far from the tube mouth and without bias, taking advantage of plasma flowing out the tube. In particular, nitrogen and argon PIIIs were tested for tube inner wall sputtering and deposition studies, running the PIII system in the last configuration of sample support detached from the tube. During the nitrogen ion implantation runs in other cases, it was found that the final temperature of the tubes and the plasma turn-on voltages were both inversely proportional to the dimensions of the tubes, except for the smallest tube tested. High voltage glow and hollow cathode discharges were produced inside the tubes, either alternately, during the pulse or independently, depending on the tube geometry and pulser used (LIITS, a current controlled source or RUP-4, a voltage controlled one). In the case of smallest diameter of 1.1 cm∅, a suspended tube of SS304 was tested using lower power pulser (RUP-4), at its near maximum capability of 1.2 kW. In this case also, very bright plasmas were formed, mainly inside the tube and resulted in high temperature there (~700 °C). Nitrogen uptake was superior for higher temperature PIII treatments (>700 °C), combining ion implantation and thermal diffusion, which allowed the formation of TiN and Ti2N on the Ti alloy samples inside tubes with diameters ≤4 cm. In this paper, detailed discussion of results of above cited PIII tests with diversified tubes and configurations are presented, together with the analysis of the corresponding treated surfaces of the samples inside, outside and on the support detached from the tube.

Acetylene plasma-polymer films treated by argon plasma immersion ion implantation

Structural and surface properties of acetylene plasma polymer films were studied as a function of treatment time via Plasma Immersion Ion Implantation (PIII). The polymer films were obtained from acetylene and argon mixture using radiofrequency glow discharge and then treated by argon PIII. XPS (X-ray photoelectron spectroscopy) was used to analyze the composition of the films before and after PIII treatment. With rising exposure time, XPS revealed an increase of oxygen-to-carbon (O/C) atomic ratio from 0.23 to 2.43. It can be explained by recombination processes between dangling bonds or radicals created in the polymer structure and atmospheric water and/or oxygen. It was observed that the film structure was predominantly formed C-H and C-C bonds, but there was an increment of the C=O proportion bonds upon argon PIII treatment. The wettability of the polymer films was investigated using contact angle measurements for water and diodimethane droplets on the film surface. After the argon ion implantation, the contact angle was reduced from 55 to 24 degrees, attributed to incorporation of polar groups in the polymer structure. Upon aging in atmosphere, all samples lost the high wettability, but the hydrophilic character of the films was maintained. It was used atomic force microscopy (AFM) to investigate the roughness of the samples. After argon PIII treatment, the roughness of the polymer films decreased from 8.1 to 5.5 nm, mainly due to ablation processes like sputtering one. The hardness and elastic modulus of the polymer films were investigated by nanoindentation technique. The hardness was enhanced from 0.68 to 5.35 GPa and the elastic modulus increased from 28 to 97 GPa. In general, the results show that argon PIII turned acetylene plasma polymer films smoother and mechanically more resistant, but its effect depends on treatment time.

Effect of argon ion bombardment on amorphous silicon carbonitride films

Amorphous silicon carbonitride (a-SiCN:H) films were synthesized by radiofrequency (RF) Plasma Enhanced Vapor Chemical Deposition (PECVD) using hexamethyldisilazane (HMDSN) as precursor compound. Then, the films were post-treated by Plasma Immersion Ion Implantation (PIII) in argon atmosphere from 15 to 60 min. The hardness of the film enhanced after ion implantation, and the sample treated at 45 min process showed hardness greater than sixfold that of the untreated sample. This result is explained by the crosslinking and densification of the structure. Films were exposed to oxygen plasma for determining of the etching rate. It decreased monotonically from 33 Å/min to 19 Å/min for the range of process time, confirming structural alterations. Hydrophobic character of the a-SiCN:H films were modified immediately after ion bombardment, due to incorporation of polar groups. However, the high wettability of the films acquired by the ion implantation was diminished after aging in air. Therefore, argon PIII made a-SiCN:H films mechanically more resistant and altered their hydrophobic character.

Etching and structure changes in PMMA coating under argon plasma immersion ion implantation

A thin (120 nm) polymethylmethacrylate coating was treated by plasma immersion ion implantation with Ar using pulsed bias at 20 kV. Ellipsometry and FTIR spectroscopy and gel-fraction formation were used to detect the structure transformations as a function of ion fluence. The kinetics of etching, variations in refractive index and extinction coefficient in 400–1000 nm of wavelength, concentration changes in carbonyl, ether, methyl and methylene groups all as a function of ion fluence were analyzed. A critical ion fluence of 10 15 ions/cm 2 was observed to be a border between competing depolymerization and carbonization processes. Chemical reactions responsible for reorganization of the PMMA chemical structure under ion beam treatment are proposed.

Dependence of ion sheath collapse on secondary electron emission in plasma immersion ion implantation

The collapse of the ion sheath in front of a dielectric substrate during argon plasma immersion ion implantation is investigated using a Langmuir probe. The probe signals during the buildup and collapse of the ion sheath are recorded from a lime glass substrate with a magnesium metal plate placed on top. The collapsing speed of the ion sheath is shown to strongly depend on the secondary electron emission coefficient of the substrate. The authors’ results show that it is possible to derive secondary electron emission coefficients from insulating materials based on the probe signals.

Enhancement of polymer hydrophobicity by SF6 plasma treatment and argon plasma immersion ion implantation

AbstractIn this study sulphur hexafluoride (SF6) plasmas and argon plasma immersion ion implantation (ArPIII) techniques have been applied to improve the hydrophobicity of poly(tetrafluoroethylene) (PTFE), polyurethane and silicone surfaces. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of the polymers. However, exposure of the treated samples to air induced a strong variation in their hydrophobicity as a consequence of post‐plasma reactions between atmospheric species and remnant surface free radicals. X‐ray photoelectron spectroscopy results strongly suggest that for polyurethane and silicone the surface fluorination by SF6 plasmas and the creation of new carbon bonds and radicals are the main agents for hydrophobicity enhancement. The PTFE exposed to ArPIII revealed increases in the contact angles after exposure to air. A significant incorporation of oxygen and the formation of new carbon bonds were revealed by XPS measurements. Copyright © 2003 John Wiley & Sons, Ltd.

Hydrophilization of PVC surfaces by argon plasma immersion ion implantation

Commercial polyvinylchloride (PVC) sheets were treated by plasma immersion ion implantation, PIII. Samples were immersed in argon glow discharges and biased with 25 kV negative pulses. Exposure time to the bombardment plasma changed from 900 to 10,800 s. Through contact angle measurements, the effect of the exposure time on the PVC wettability was investigated. Independent of t, all samples presented contact angles, θ, equal to zero after the treatment. However, in some cases, surface hydrophilization was not stable, as revealed by the temporal evolution of θ. Samples bombarded for shorter periods recovered partially or totally the hydrophobic character while the one exposed for the longest time stayed highly hydrophilic. These modifications are ascribed to the Cl loss and O incorporation as shown by XPS measurements. Furthermore, the mobility of surface polar groups and the variation in the cross-linking degree can also affect the PVC wettability.

Effects of nitrogen and argon plasma-immersion ion implantation on silicon and its oxidation

Nitrogen and argon ions were implanted in silicon at energy of 10 and 20 keV by the plasma immersion ion implantation (PIII) technique. The implantation dose was varied from 10 13 to 10 17 ions/cm 2. Ellipsometric measurements were carried out on the samples implanted at various doses. Silicon wafers implanted with high doses of nitrogen (10 17 ions/cm 2) showed the formation of a SiN x layer. Samples implanted with a high dose of argon (10 16 ions/cm 2) also resulted in an optically transparent, damaged layer of refractive index in the range 2.01–2.32. All the samples were then subjected to various oxidation atmospheres. Retardation of the oxidation rate for nitrogen-implanted samples and enhancement for argon-implanted samples was noted with increasing implantation dose. Metal-oxide semiconductor (MOS) capacitor structures were then fabricated using the oxidised samples. Capacitance–voltage ( C– V) characterisation was carried out to study the electrical properties of the oxidised films. This paper reports the results of electrical and optical measurements carried out on these samples.

Studies on treatment homogeneity of plasma immersion ion implantation by an optical method

The lateral homogeneity of plasma immersion ion implantation (PIII) of three-dimensional objects has been investigated by a simple optical method. It is based on interference colours of thin oxide films of transition metals, such as titanium or tantalum. When these oxides are treated by PIII, their thickness changes as a result of sputter etching. As a result, their colour changes. It is, therefore, possible to judge the lateral treatment homogeneity at a glance with the naked eye. With the example of a model system it is demonstrated how this method works. Cylinders, either compact or with a slot, were partially covered with a strip of tantalum with tantalum oxide on top, and then treated by argon PIII. Following the changes in the colours, gradients in treatment were found on the tops and on the outer sides. In contrast, the inner walls of the cylinders with slots were hardly changed, however, the bottoms of the slots were severely affected. In some cases, the oxide was entirely lost. These findings are explained by the shape of the plasma sheath from which the ions are accelerated and by the resulting ion trajectories.

Thin film oxides as probe for homogeneity measurements of 3-dimensional objects treated by plasma immersion ion implantation

Results on an optical method are presented for investigation of the lateral homogeneity of treatment of 3-dimensional objects by plasma immersion ion implantation (PIII). It is based on interference colours of thin oxide films of transition metals such as titanium, niobium or tantalum. The thickness of the oxides and hence their colour changes when they are sputter etched by the plasma immersion ion bombardment. With the example of cube-shaped samples which are treated by argon PIII, it is demonstrated how this method works. Cube-shaped samples with slots with both inner and outer surfaces are a particularly interesting and illustrative example both for homogeneity effects of PIII and its measurement. It turns out that large differences in ion irradiation intensity between the outer parts and the inner parts of such samples develop. For the outer sides, a gradient in irradiation intensity is found. In contrast, the inner walls are hardly changed. However, by far most the inner bottom side of the samples is affected; it is considerably sputter etched. These unexpected results are explained by the shape of the cathode sheath from which the ions are accelerated and by the resulting ion trajectories.