Plasma Immersion Ion Processing Research Articles

The effect of acetylene flow rate on the uniform deposition of thick DLC coatings on the inner surface of pipes with different draw ratios

Thick multilayered DLC coatings were deposited on the inner surface of pipes with different draw ratios by hollow cathode plasma immersion ion processing (PIIP). By tuning the acetylene (C2H2) flow rate, the change of plasma density caused by different draw ratios can be compensated to fulfill the uniform deposition of thick DLC coatings along the pipes. The influence of C2H2 flow rate on the mechanical and tribological properties of the DLC coatings were investigated. With the increase of draw ratio, the deposition temperature and gas pressure declined, and the plasma density became more asymmetrical in the axial direction. Increasing the flow rate can timely replenish the plasma inside the pipe and resolve the mass depletion problem, resulting in better thickness and structure uniformity of the DLC coatings. The greatest deposition rate of 28.6 μm/h was obtained at the 250 sccm C2H2 flow with a draw ratio of 5:1. The results of Raman spectrum and XPS indicated that the content of sp2-carbon bonds decreased with the increasing draw ratio for lower impact energies of ions. The higher sp3 carbon bonds content contributed to the formation of carbonaceous transfer layers, which resulted in the lower friction coefficient and wear rate.

Development of diamond-like carbon-coated electrodes for corrosion sensor applications at high temperatures

Coupled multielectrode array sensors have been used as online and real-time monitors for localized corrosion in both laboratory and field systems. Multiple miniature electrodes made of materials identical to the engineering component of interest are used as sensing electrodes. However, these devices have an upper operating temperature limit of approximately 70 °C because crevice formation between the electrode and the mounting material impairs their performance. In this paper, a crevice-free electrochemical sensor for corrosion monitoring at temperatures above 100 °C is presented. A diamond-like carbon thin film was deposited on the sensing electrodes using plasma immersion ion processing and its properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and laser Raman spectroscopy. The effectiveness of the diamond-like carbon film in protecting the Alloy 22 (Ni-22Cr-13Mo-3Fe-3W) electrodes in a corrosive NaCl–NaNO 3–KNO 3 salt mixture at 150 °C was demonstrated. The effective corrosion monitoring capability of the new electrochemical sensor at high temperatures was attributed to the pinhole-free microstructure, high electrical impedance, and high corrosion-resistance properties of the diamond-like carbon film.

Surface modification of stainless steel drills using plasma-immersion nitrogen ion implantation

Better protective and functional coatings on dental drills are increasingly demanded for their desired mechanical, tribological or chemical properties. We have studied the surface modification of steel dental drills, with an aim to increasing both their cutting life and corrosion resistance in dentistry using low-energy plasma-immersion nitrogen implantation over different temperature ranges. The temperature of the drills was controlled by varying the implantation voltage. Following implantation, tests showed that the microhardness of the nitrided drill surfaces was approximately one order higher than that of untreated drills and the corrosion tolerance was found to increase with growing temperature of the plasma-immersion process.

Structure and optical properties of plasma immersion ion processed boron-alloyed diamondlike carbon films

Boron (B)-alloyed diamondlike carbon (B-DLC) films were prepared on polymethyl methacrylate (PMMA), glass, and silicon (100) using an inductive radio frequency Ar + C2H2 + B2H6 plasma immersion ion processing (PIIP) technique. The composition of the B-DLC films was measured by ion beam analysis techniques, and the bonding structure was characterized by infrared and Raman spectroscopy. The incorporation of B2H6 gas into the PIIP deposition introduced B-C bonds into the DLC structure, resulting in increased sp3-carbon bonding and improved optical performance. The energetic activation of the deposition atoms, induced by the ion bombardment during the PIIP film growth, enhanced the properties of the B-DLC films deposited on dielectric and transparent optical materials. With B-alloying and an optimized deposition energy of 40–135 eV, B-DLC films were synthesized with B-alloying up to 10.4 at.%, high hardness, high refractive index, and optical transmittance that is higher than that of unalloyed DLC films. The experimental results indicate that C-B hybridization and ion-energy transfer are critical to the synthesis of these hard and transparent B-DLC films.

Morphology of Fibroblastic Cells Cultured on Diamond-Like Carbon Coatings Produced by Plasma Immersion Using AFM and SEM

For the potential use of diamond-like carbon (DLC) coating for biomedical applications, it would be important to evaluate the biological effects of these coatings. In this study, DLC coatings were deposited on glass coverslips using the plasma immersion process, which produces films with adhesion properties superior to those prepared with conventional techniques. Scanning electron microscopic and atomic force microscopic observations were used to study the morphology of fibroblasts growth on DLC coatings.

Titanium Oxide (TiO<sub>2</sub>) Coatings Produced on Titanium by Oxygen-Plasma Immersion and Cell Behaviour on TiO<sub>2</sub>

Plasma immersion process was investigated as a method for producing bioceramics coatings on metallic implants due to its advantages, which include the production of coatings on three-dimensional workpieces, with high density and superior adhesion. In this process, the oxygen plasma was utilized to form titanium oxide on titanium substrate. The structure, composition and surface morphology were studied using scanning electron microscopy (SEM) and X-ray diffraction. In addition a preliminary study has also been carried out, on TiO2-coated and uncoated titanium substrates, to analyse the in vitro biocompatibility (cytotoxicity evaluation and cell morphology).

Tissue Response in the Femur of Rats After Implantation of Diamond-Like Carbon Coatings on Ti-13Nb-13Zr Produced by Plasma Immersion

Diamond-like carbon (DLC) coatings were deposited on titanium alloy (Ti-13Nb-13Zr) by plasma immersion process. DLC-coated Ti alloy and uncoated Ti were investigated in an animal model using the femoral condyles of rats for intervals of 4 and 12 weeks postoperatively. The interface between the implants and bones of the femoral condyles were analysed using scanning electron microscopy (SEM) by backscattering. The results showed that the DLC coatings were well tolerated in both periods.

Mechanical properties and anti-corrosion behavior of the diamond-like carbon films

Diamond-like carbon (DLC) films with different pulse widths were prepared on Si and NiTi alloys by plasma immersion ion processing (PIIP). The mechanical properties and corrosion behavior of the DLC films are investigated. The results show that the qualitative sp 3 / sp 2 ratio obtained from Raman spectra and the nano-hardness is decreased with the increase of the pulse width, and the DLC films obviously increase the surface hardness of NiTi alloy and decrease its friction coefficient and markedly improve its corrosion resistance.

Atomic Force Microscopic Observations of Diamond-like Carbon (DLC) Films Produced by Plasma Immersion and Fibroblasts Cultured on DLC

Diamond-like carbon (DLC) films have been intensively studied with a view to improving orthopaedic implants. Studies have indicated smoothness of the surface, low friction, high wear resistance, corrosion resistance and biocompatibility [1-4]. DLC coatings can be deposited using various techniques, such as plasma assisted chemical vapour deposition (PACVD), magnetron sputtering, laser ablation, and others [5]. However it has proved difficult to obtain films which exhibit good adhesion. The plasma immersion process, unlike the conventional techniques, allows the deposition of DLC on three-dimensional workpieces, even without moving the sample, without an intermediate layer, and with high adhesion [6], an important aspect for orthopaedic articulations. In our previous work, DLC coatings were deposited on silicon and Ti-13Nb-13Zr alloy substrates using the plasma immersion process for the characterization of microstructure, mechanical properties and corrosion behaviour [7-9]. Hardness, measured by a nanoindenter, ranged from 16.4-17.6 GPa, the pull test results indicate the good adhesion of DLC coatings to Ti-13Nb-13Zr, and electrochemical assays (polarization test and electrochemical impedance spectroscopy) indicate that DLC coatings produced by plasma immersion can improve the corrosion resistance [9].

Chemical bonding investigation of amorphous hydrogenated Si–N alloys deposited by plasma immersion ion processing

Amorphous hydrogenated Si–N (a-SiN x :H) alloys were deposited by plasma immersion ion processing using a working pressure of 1.3 Pa of mixtures of SiH 4 and N 2. Films with N/Si ratios from 0.6 to 1.2 were obtained, as determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERD). A fixed total H content of 9 at.% was observed in all films. Chemical bonding was investigated by infrared, Raman and X-ray photoelectron (XPS) spectroscopies. These techniques revealed a complex Si chemical environment that evolves towards that of Si 3N 4 for higher N/Si ratios. This evolution was correlated with the increase of film hardness.

Hardness, hydrophobic and optical properties of fluorine and boron co-alloyed diamond-like carbon films

Fluorine (F) and boron (B) co-alloyed diamond-like carbon (FB-DLC) films were prepared on polymethyl methacrylate (PMMA), polycarbonate, glass, and silicon 〈100〉 wafer using a B 2H 6+C 2H 2+C 2F 6 plasma immersion ion processing (PIIP) technique. The chemical composition and atomic bonding of FB-DLC films were analyzed to investigate their influence on the hardness, optical band gap and contact angles of water. Compared to B-alloyed or F-alloyed DLC films, BF-alloyed DLC films exhibited enhanced hardness, high optical gap energy, and improved hydrophobic properties.

Structure and properties of fluorine and boron co-alloyed diamond-like carbonfilms

Fluorine (F) and boron (B) co-alloyed diamond-like carbon (FB-DLC) films were preparedon polymethyl methacrylate (PMMA), polycarbonate, glass, silicon and Mo sheets by the plasma immersion ion processing (PIIP) technique. A pulse glow dischargeplasma was used for the PIIP deposition and was produced at a pressure of 1.33 Pa from acetylene(C2H2), diborane(B2H6), andhexafluoroethane (C2F6) gas. The composition of FB-DLC films was measured by using the ion beam analysistechniques, and the bonding structure was characterized by IR and Raman spectroscopies.The co-alloying of F and B into DLC films resulted in the formation of F–C and B–Chybridized bonding structures. The levels of the F and B concentrations affected thecomposition, chemical bonding and properties as was evident from the changes observed inhydrogen concentration, optical gap energy, hardness, friction coefficient, and contact angleof water on films. Compared to B-alloyed or F-alloyed DLC films, the F and Bco-alloyed DLC films exhibited a reduced hydrogen concentration, high hardnessand optical gap energy, and improved hydrophobic and tribological properties.

Application of hydrocarbon plasmas for modifying near-surface characteristics of bearing steel

The near-surface hardness and wear resistance of AISI 52100, a widely used bearing steel, have been enhanced by energetic ion bombardment using a plasma immersion process. Test flat samples of the steel were immersed in a plasma of methane or acetylene and pulse biased to a negative voltage so as to result in either ion implantation of carbon into the steel surface or deposition of diamond-like carbon film onto its surface. The nanometer size scale surface roughness of the initial sample flats was generally retained after the plasma surface treatments. The surface treatments were carried out with the samples at near-room temperature, which is an important consideration for this type of steel because of its relatively low softening temperature. However, by intentionally using the energy of the bombarding ions to marginally heat the surface of the samples, the depth of the carbon ion implanted layer could be increased by over a factor of two while maintaining the bulk hardness of the steel at acceptable levels.

Fundamentals of pulsed plasmas for materials processing

Pulsed plasmas use much higher power during each pulse compared to continuously operated plasmas. This feature and the appearance of additional new variables such as pulse duty cycle can lead to new, flexible, sometimes enabling processes for surface modification and thin film deposition, as discussed for plasma immersion ion processing, high power pulsed sputtering, thin film deposition with pulsed cathodic arcs and metal plasma immersion ion implantation and deposition. In all of these processes, transient sheaths are of great importance. The fundamentals of plasma sheaths are briefly reviewed. It is argued that the often-considered ion matrix sheath is only an educational case, whereas most realistic transient sheaths obey a time-dependent Child law. The recovery of pulsed sheaths is usually less considered than the formation of sheaths. If the pulse fall time normalized by the inverse ion plasma frequency is much greater than unity, sheath collapse can be simply described by a retreating Child law sheath. In the opposite case, electrons refill the ion space charge and complete recovery of the boundary layer is determined by ambipolar diffusion from the bulk plasma. The case of high power pulsed sputtering is discussed in greater detail, especially the appearance of a kink in the current–voltage characteristic, which changes its slope for current densities exceeding approximately 600 mA/cm 2. It is suggested that high pulse power opens the possibility that self-sputtering can occur during each pulse, especially for target materials of high sputter yield. The necessary condition for self-sputtering is αβγ>1, where α, β and γ are the ionization probability, ion return probability and sputter yield, respectively.

Influence of carbon content and average energy of deposited ions on mechanical and optical properties of Si–C–N films grown by plasma ion immersion processing

Amorphous silicon nitride and silicon carbonitride films were deposited by the plasma immersion ion processing technique. The SiCxNy films were obtained in the range of compositions 0⩽x/(x+y)⩽0.53. Gas pressure during the deposition was kept around 0.13 Pa (1 mTorr) and SiH4, N2, Ar, and C2H2 gas mixtures were used. The composition of the film grown without addition of C2H2 was close to that of Si3N4. With the addition of C2H2 the areal density of Si and N atoms remains almost constant, whereas the concentration of C increases. The addition of carbon to the films causes a decrease in hardness from 13.5 to 0.85 GPa, a reduction in the band gaps from about 5 to about 2 eV, and a decrease in the refractive index from about 1.63 to 1.5. The density of the films with the addition of carbon decreases from 2.37 to 0.46 g/cm3. The evolving physical properties in these films are shown to result from both the increasing fraction of C2H2 in the gas mixture and a reduction in the average energy imparted to the growing film during deposition.

Dependence of optical properties and hardness on carbon content in silicon carbonitride films deposited by plasma ion immersion processing technique

Materials with Si–C–N composition are of great interest due to their remarkable properties such as high hardness and oxidation resistance. In this study amorphous silicon nitride and silicon carbonitride films were deposited on glass, fused silica, and carbon substrates by the plasma immersion ion processing technique. Gas pressure during the deposition was kept around 0.13 Pa (1 mTorr) and SiH 4, N 2, Ar and C 2H 2 gas mixtures were used. Film hardness, composition and UV–visible optical absorption were characterized using nanoindentation, ion beam analysis techniques, and UV–visible spectroscopy, respectively. The films exhibit high transparency in the visible and near UV regions. Addition of the carbon to the films causes decrease in the density of the films, as well as decrease in hardness and transparency. These results suggest that in the low energy regime of PIIP the deposition of hard carbon composites with nitrogen and silicon does not take place.

Fluorine and boron co-doped diamond-like carbon films deposited by pulsed glow discharge plasma immersion ion processing

Fluorine (F) and boron (B) co-doped diamond-like carbon (FB-DLC) films were prepared on different substrates by the plasma immersion ion processing (PIIP) technique. A pulse glow discharge plasma was used for the PIIP deposition and was produced at a pressure of 1.33 Pa from acetylene (C2H2), diborane (B2H6), and hexafluoroethane (C2F6) gas. Films of FB-DLC were deposited with different chemical compositions by varying the flow ratios of the C2H2, B2H6, and C2F6 source gases. The incorporation of B2H6 and C2F6 into PIIP deposited DLC resulted in the formation of F–C and B–C hybridized bonding structures. The levels of the F and B concentrations effected the chemical bonding and the physical properties as was evident from the changes observed in density, hardness, stress, friction coefficient, and contact angle of water on films. Compared to B-doped or F-doped DLC films, the F and B co-doping of DLC during PIIP deposition resulted in the formation of films that possessed a reduced hydrogen concentration an...

Influence of ion and neutral flux on the properties of diamond-like carbon from pulsed glow discharges of acetylene

The deposition rates, composition and mechanical properties of diamond-like carbon (DLC) coatings deposited using pulsed glow discharges of acetylene (C 2H 2) have been studied as a function of deposition bias and gas pressure. The data show that a −4-kV bias is one order of magnitude more efficient than a bias of −8 kV for depositing DLC via plasma immersion ion processing (PIIP). Sputtering is the suspected cause for the reduced deposition efficiency at −8 kV. A methodology for comparing the magnitude of the ion and neutral flux is used to show that neutrals dominate the deposition process under all conditions tested. The necessary data are shown to prove that the coating hardness is independent of gas pressure when the ion flux, J i, is less than 10% of the total flux, J d. If J i/ J d is greater than 10%, then increasing the gas pressure reduces the coating hardness to levels below 15 GPa. The implications of these results regarding sheath thickness, deposition rates and throughputs for large-area processing (many m 2) are discussed.

Effect of carrier gas on the deposition of titanium carbo-nitride coatings by a novel organo-metallic plasma immersion ion processing technique

Using a novel organo-metallic chemical vapor deposition plasma immersion ion processing technique, titanium carbo-nitride (Ti–C–N) coatings were deposited from an organo-metallic CVD precursor, tetrakis-dimethylamino titanium. Different carrier gases (acetylene, ammonia, argon and nitrogen) were made to flow through the precursor reservoir at 20 sccm so that the coating composition could be modified. Deposited coatings had thickness in the range of 300–1000 nm as determined by surface profilometry. Titanium concentrations in the coatings ranged from 10.8 to 15.1 at%. Hardness values of these coatings ranged from ≈8–14 GPa while residual stresses were in the range from −440 to −100 MPa, as determined by nanoindentation and wafer curvature techniques, respectively. Coefficient of friction values ranged from 0.2 to 0.45, and were lowest for coatings with low titanium content. Hardness, coefficient of friction and residual stress increased with increasing titanium content. Wear resistance was determined by a pin-on-disk technique and wear coefficients ranged from 0.005×10 −6 to 2×10 −6 mm 3/N m, increasing with increasing hardness indicating an abrasive wear mechanism.

Thermal Stability and Wetting Properties of Cr–O–C Coatingssynthesized by Plasma Immersion Ion Processing

Microcrystalline Cr-O-C films, synthesized by the plasma immersion ion processing technique, were annealed in vacuum and air at 700 °C for different times so their thermal stability could be evaluated. The study showed that annealing does not greatly change the chemical composition of the Cr–O–C films but induces a transformation ofthe film structure from the mixed phases of Cr2O3, CrO2, and CrC1.13O0.12 to the dualphases of Cr3C2, and Cr2O3. In addition, the annealed Cr–O–C films exhibit excellentnonwetting qualities to liquid aluminum despite the presence of pin holes. The contactangle of resolidified molten aluminum against the Cr–O–C films was found to be ashigh as 120–150°. The aluminum contact angle was found not to vary with thermal aging of the Cr–O–C films. The Cr–O–C films showed high hardness (16–24 GPa) and good wear resistance as compared to the steel substrates (H13 and 304 stainless steels)used in this study.