Plasma Source Ion Implantation Research Articles

Time-resolved evolution of collisional transient sheath in plasma source ion implantation

In this work, an analytical model for the time-resolved dynamics of the collisional transient sheath in the plasma source ion implantation (PSII) process is developed. The presented model can forecast the temporal dependence of the implanted ion flux and sheath width in the collisional transient sheath. During the PSII process, the effects of some physical parameters such as applied voltage and gas pressure on the pattern of sheath growth are discussed. It is found that the ion flux can get higher values by increasing the gas pressure during the matrix sheath while the dynamics of ions in the expanding sheath are restricted to the collisionality condition, and ion flux is reduced impressively. Moreover, these results are demonstrated that the increase of the applied voltage causes the high rate of sheath expansion and electric field and then ion flux. The final value of the ion velocity in the expanded sheath tends to the ion Bohm velocity.

MOSFET Gate Driver Circuit Design for High Repetitive (200 kHz) High Voltage (10 kV) Solid-State Pulsed-Power Modulator

Solid-state pulsed-power modulators can effectively generate high repetition rate pulses, which are required in applications where the process rate depends on the repetition rate, e.g., plasma source ion implantation and deposition, plasma immersion ion milling, and diamond-like carbon coating. In this article, a solid-state pulsed-power modulator for generating high repetitive pulses is developed. Active pull-down circuits and designed metal-oxide-semiconductor field-effect transistor (MOSFET) gate drivers are applied to the modulator without increasing its size. The drivers enable a fast rise, fall time, and minimize pulsewidth, which are effective for high-repetition-rate pulse applications. The developed modulator exhibits a maximum output pulse voltage of ±10 kV, maximum output pulse current of 50 A, pulsewidth between 200 ns and 10 us, maximum pulse repetition rate of 200 kHz, and average output power of 10 kW. The operation principle of the designed MOSFET gate driver is analyzed in detail. Experimental results show that the modulator operates stably at a high repetition rate of 10 kV and 200 kHz and the feasibility of this proposed circuit for high repetition rate operation are verified.

Diamond-Like Carbon Films with Low Internal Stress by a Simple Bilayer Approach

Amorphous carbon films with a high hardness usually suffer from high internal stress. To deposit films with a hard top surface but reduced internal stress, a simple bilayer approach was used. Films were prepared by plasma source ion implantation, using only hydrocarbon precursors. The single layer with the highest hardness (deposited by a low direct current (DC) voltage and radio frequency (RF) generation of the plasma) has the highest internal stress with more than 3.5 GPa. By adding an interlayer with a lower hardness, the resulting stress of the bilayer film can be reduced to below 1.4 GPa while maintaining the high hardness of the top layer. By avoiding metallic interlayers or dopants within the films, the deposition process can be kept simple and cost-effective, and it is also suitable for three-dimensional samples.

The Influence of Preparation Conditions on the Structural Properties and Hardness of Diamond-Like Carbon Films, Prepared by Plasma Source Ion Implantation

Diamond-like carbon (DLC) films were prepared from a hydrocarbon precursor gas by plasma source ion implantation (PSII), in which the plasma generation and the film deposition were coupled; i.e., the plasma was generated by the applied voltage and no additional plasma source was used. Several experimental parameters of the PSII process were varied, including the sample bias (high voltage, DC or pulsed), gas pressure, sample holder type and addition of argon in the plasma gas. The influence of the deposition conditions on the carbon bonding and the hydrogen content of the films was then determined using Raman spectroscopy. Nanoindentation was used to determine the hardness of the samples, and a ball-on-disk test to investigate the friction coefficient. Results suggest that films with a lower sp2 content have both a higher hydrogen content and a higher hardness. This counterintuitive finding demonstrated that the carbon bonding is more important to hardness than the reported hydrogen concentration. The highest hardness obtained was 22.4 GPa. With the exception of a few films prepared using a pulsed voltage, all conditions gave DLC films having similarly low friction coefficients, down to 0.049.

Deposition of diamond-like carbon films on insulating substrates by plasma source ion implantation

Plasma source ion implantation (PSII) is a technique that is suitable for implantation as well as film deposition. Since it involves a high voltage that is applied to the sample holder to attract ions from the plasma to the sample, an influence can be expected in case that either the whole substrate or a part of it is nonconductive. Diamond-like carbon (DLC) films were deposited by PSII, using C2H2 as precursor. The substrates were silicon samples that were placed on a large, horizontally oriented conductive sample holder in three different ways: 1) directly on the holder, 2) with an alumina block of 5 mm height between holder and sample, and 3) with an alumina block of 12 mm height between holder and sample. A high voltage (pulse or DC) was applied directly to the sample holder. The plasma was generated by this voltage or, in some experiments, by an additional RF signal, which was applied to a plate that was oriented parallel to the sample holder in a distance of 100 mm. The investigation of the effect of the presence of the insulating alumina block on the film properties focused on the deposition rate, the hydrogen content and film structure, the surface roughness, the hardness and the friction coefficient of the films.

Preparation of Aniline-Based Nitrogen-Containing Diamond-Like Carbon Films with Low Electrical Resistivity

The intrinsic high electrical resistivity of diamond-like carbon (DLC) films prevents their use in certain applications. The addition of metal or nitrogen during the preparation of the DLC films leads to a lower resistivity of the films, but it is usually accompanied by several disadvantages, such as a potential contamination risk for surfaces in contact with the film, a limited area that can be coated, deteriorated mechanical properties or low deposition rates of the films. To avoid these problems, DLC films have been prepared by plasma source ion implantation using aniline as a precursor gas, either in pure form or mixed with acetylene. The nitrogen from the precursor aniline is incorporated into the DLC films, leading to a reduced electrical resistivity. Film properties such as hardness, surface roughness and friction coefficient are nearly unchanged as compared to an additionally prepared reference sample, which was deposited using only pure acetylene as precursor gas.

Pulsed Power Modulator With Active Pull-Down Using Diode Reverse Recovery Time

This paper presents a pulsed power modulator with a new structure that utilizes the reverse recovery characteristics of diodes to achieve an effective pull-down circuit configuration. The proposed configuration for active pull-down applicable to negative pulsed power applications with a high-voltage direct switching method is implemented by adding a diode to the pulse discharging path of the modulator, instead of using a pull-down resistor. The diode is forward-biased while an output pulse voltage is applied to the load. When the pulse voltage applied to the load is removed, the residual energy in the load is quickly discharged through the reverse recovery path of the diode so that the pull-down function of the pulsed power supply system is efficiently performed. The operating principle of the proposed system is described, and each operating mode is analyzed in detail. In addition, the feasibility of the proposed system configuration is examined through various simulation results. Finally, it is proven that the proposed system can be used effectively in pulsed power application fields through a practical experiment in plasma source ion implantation applications.

Surface Structuring of Diamond-Like Carbon Films by Chemical Etching of Zinc Inclusions

A diamond-like carbon (DLC) film with a nanostructured surface can be produced in a two-step process. At first, a metal-containing DLC film is deposited. Here, the combination of plasma source ion implantation using a hydrocarbon gas and magnetron sputtering of a zinc target was used. Next, the metal particles within the surface are dissolved by an etchant (HNO3:H2O solution in this case). Since Zn particles in the surface of Zn-DLC films have a diameter of 100–200 nm, the resulting surface structures possess the same dimensions, thus covering a range that is accessible neither by mask deposition techniques nor by etching of other metal-containing DLC films, such as Cu-DLC. The surface morphology of the etched Zn-DLC films depends on the initial metal content of the film. With a low zinc concentration of about 10 at.%, separate holes are produced within the surface. Higher zinc concentrations (40 at.% or above) lead to a surface with an intrinsic roughness.

Dielectric constant, AC conductivity and impedance spectroscopy of zinc-containing diamond-like carbon film UV photodetector

We report on the dielectric constant, conductivity, impedance spectroscopy and current-voltage characteristic of zinc contain diamond-like carbon (Zn-DLC) films prepared by a combination of plasma source ion implantation with magnetron sputtering of a zinc target. The frequency variation of the AC conductivity follows Jonscher's power law. The temperature variation of the frequency exponent indicates that the charge carriers follow a correlated barrier hopping conduction mechanism. The frequency dispersion of real and imaginary part of the dielectric constant obeys a modified Cole-Cole equation. The space charge conductivity, free charge conductivity and relaxation time of the Zn-DLC thin films are temperature dependent. The relaxation time decreases with increase in temperature. The Nyquist plot of complex impedance spectroscopy is simulated by a simple electrical equivalent circuit. The imaginary part of the complex impedance shows a relaxation peak, which shifts towards the high frequency side with an increase in temperature. The temperature dependent current-voltage (I-V) characteristic shows a non-linear type behaviour which follows the Poole-Frenkel (PF) emission model. To investigate the photosensitivity of an Ag/Zn-DLC/Si device, we placed it in dark and UV light condition and measured the (I-V) characteristic at room temperature. The dark current density and photocurrent density follow the PF model and a modified PF model respectively.

Properties of iodine containing diamond-like carbon films prepared by plasma source ion implantation

The addition of halogens to diamond-like carbon (DLC) films provides attractive film properties, e.g. a hydrophobic surface combined with an improved corrosion protection. The use of iodine is of interest in this regard because of its additional marked influence on the band gap and therefore on the optical properties of the film. Instead of solid iodine, the gaseous precursor trifluoroiodomethane (CF3I) was used to prepare iodine containing DLC films. In contrast to our earlier experiments, a lower voltage was used in the plasma based preparation process thereby extending the iodine concentration range. The film properties, such as halogen content, bonding, water contact angle and corrosion protection were evaluated. The iodine containing DLC films are suitable to be deposited on polymer materials.

Preparation of anatase films from titanium containing diamond-like carbon films

Carbon can play a decisive role in the preparation of the titanium dioxide modification anatase. Amorphous titanium containing diamond-like carbon films are a suitable basis for this process. Those films can be deposited by a process that combines reactive magnetron sputtering with plasma source ion implantation, using a mixture of argon and ethylene (C2H4) for the plasma. After film deposition, annealing of the samples for 1 h at a fixed temperature between 723 K and 873 K in ambient atmosphere led to oxidation and crystallization. Colorless pure anatase was observed after annealing.

Effect of carbon ion implantation on the tribology of metal-on-metal bearings for artificial joints.

Metal-on-metal (MoM) bearings have become popular due to a major advantage over metal-on-polymer bearings for total hip arthroplasty in that the larger femoral head and hydrodynamic lubrication of the former reduce the rate of wear. However, concerns remain regarding adverse reactions to metal debris including metallosis caused by metal wear generated at the taper-head interface and another modular junction. Our group has hypothesized that carbon ion implantation (CII) may improve metal wear properties. The purpose of this study was to investigate the wear properties and friction coefficients of CII surfaces with an aim to ultimately apply these surfaces to MoM bearings in artificial joints. CII was applied to cobalt-chromium-molybdenum (Co-Cr-Mo) alloy substrates by plasma source ion implantation. The substrates were characterized using scanning electron microscopy and a 3D measuring laser microscope. Sliding contact tests were performed with a simple geometry pin-on-plate wear tester at a load of 2.5 N, a calculated contact pressure of 38.5 MPa (max: 57.8 MPa), a reciprocating velocity of 30 mm/s, a stroke length of 60 mm, and a reciprocating cycle count of 172,800 cycles. The surfaces of the CII substrates were generally featureless with a smooth surface topography at the same level as untreated Co-Cr-Mo alloy. Compared to the untreated Co-Cr-Mo alloy, the CII-treated bearings had lower friction coefficients, higher resistance to catastrophic damage, and prevented the adhesion of wear debris. The results of this study suggest that the CII surface stabilizes the wear status due to the low friction coefficient and low infiltration of partner materials, and these properties also prevent the adhesion of wear debris and inhibit excessive wear. Carbon is considered to be biologically inert; therefore, CII is anticipated to be applicable to the bearing surfaces of MoM prostheses.

Preparation of Metal-Containing Diamond-Like Carbon Films by Magnetron Sputtering and Plasma Source Ion Implantation and Their Properties

Metal-containing diamond-like carbon (Me-DLC) films were prepared by a combination of plasma source ion implantation (PSII) and reactive magnetron sputtering. Two metals were used that differ in their tendency to form carbide and possess a different sputter yield, that is, Cu with a relatively high sputter yield and Ti with a comparatively low one. The DLC film preparation was based on the hydrocarbon gas ethylene (C2H4). The preparation technique is described and the parameters influencing the metal content within the film are discussed. Film properties that are changed by the metal addition, such as structure, electrical resistivity, and friction coefficient, were evaluated and compared with those of pure DLC films as well as with literature values for Me-DLC films prepared with a different hydrocarbon gas or containing other metals.

Properties of Zinc-containing Diamond-like Carbon Films Prepared by Plasma Source Ion Implantation

Properties of Zinc-containing Diamond-like Carbon Films Prepared by Plasma Source Ion Implantation

Long-term thermal stability of Si-containing diamond-like carbon films prepared by plasma source ion implantation

The long-term stability of silicon-containing diamond-like carbon films was investigated. The samples were prepared by plasma source ion implantation with a mixture of tetramethylsilane (TMS) and acetylene (C2H2) using negative high voltage pulses. The film composition was changed by varying the flow rates of the TMS and C2H2 gases, resulting in a Si content from 0 to 44 at.%. After deposition the films were annealed at temperatures from 523 K to 773 K for 168 h in ambient air. The effect of the Si content on the structure, the mechanical and tribological properties of the DLC films was investigated. A silicon oxide layer is produced on the surface of the film which improves the thermal stability. Mechanical and friction characteristics of the Si-DLC were not much affected by the long-term thermal annealing if the temperature was kept below 573 K.

Preparation of Ag-containing diamond-like carbon films on the interior surface of tubes by a combined method of plasma source ion implantation and DC sputtering

Adhesive diamond-like carbon (DLC) films can be prepared by plasma source ion implantation (PSII), which is also suitable for the treatment of the inner surface of a tube. Incorporation of a metal into the DLC film provides a possibility to change the characteristics of the DLC film. One source for the metal is DC sputtering. In this study PSII and DC sputtering were combined to prepare DLC films containing low concentrations of Ag on the interior surfaces of stainless steel tubes. A DLC film was deposited using a C2H4 plasma with the help of an auxiliary electrode inside of the tube. This electrode was then used as a target for the DC sputtering. A mixture of the gases Ar and C2H4 was used to sputter the silver. By changing the gas flow ratios and process time, the resulting Ag content of the films could be varied. Sample characterizations were performed by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, atomic force microscopy and Raman spectroscopy. Additionally, a ball-on-disk test was performed to investigate the tribological properties of the films. The antibacterial activity was determined using Staphylococcus aureus bacteria.

DLC coating of interior surfaces of steel tubes by low energy plasma source ion implantation and deposition

Abstract The plasma source ion implantation (PSII) process can be used for the treatment of the interior surfaces of tubes. Typically, this is done with higher ion energies of 10 keV or more. The resulting film thickness and the properties of the DLC film usually show a dependence on position, i.e. the distance from the edge of the tube. In order to investigate whether this effect is also present with lower energies (and if so, to what extent), deposition was carried out at negative pulse voltages of −5 kV. A diamond-like carbon (DLC) film was deposited by using acetylene as the plasma gas. The substrate consisted of stainless steel tubes with an inner diameter of 20 mm and a length of 100 and 200 mm, respectively. The distribution of the thickness, film composition, structure, surface morphology and friction coefficient as a function of the position inside the tube were investigated. The results of this low energy treatment were compared with investigations which employed higher ion energies.

Effects of Mg-ion and Ca-ion implantations on P. gingivalis and F. nucleatum adhesion

The purpose of this study was to evaluate the effects of ion implantation on Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) bacterial adhesion. Titanium (Ti) discs of 15 mm diameter and 1 mm in thickness (n = 42, 7 per group) were fabricated. Magnesium (Mg) and calcium (Ca) ions were implanted into the Ti surfaces using a plasma-source ion-implantation method. The roughness, chemistry, morphology, and contact angle of the titanium surfaces were analyzed using scanning electron microscopy, Rutherford back-scattering spectroscopy, Auger electron spectroscopy, and contact angle meter. P. gingivalis and F. nucleatum strains were cultured in anaerobic conditions at 37°C for 72 hours, and all titanium specimens were dipped in the bacterial suspension at 37°C for 24 hours. Specimens were examined at 1,000× magnification using a fluorescence microscope. The number and total area of bacteria in each of 10 separate fields were determined by computer imaging analysis method. The resulting data was analyzed to assess the significance of observed differences based on the method of the surface treatment, ion implantation. The number of P. gingivalis and F. nucleatum attached to the Mg-(927 and 227, respectively) and Caionimplanted (1325 and 231, respectively) surfaces were greater than those attached to the non-implanted surfaces (306 and 98, p <.001). Total area occupied by P. gingivalis adhesion was greater than those of F. nucleatum in the Mgand Caion-implanted surfaces (p <.001). The types of ion and bacteria did not affect the amount of bacterial adhesion. Ion implantation enhanced the adhesions of P. gingivalis and F. nucleatum. Non-specific bonding derived from the electrostatic force affected by positively charged ions might be the predominant factor in bacterial adhesion. The possibility of specific bonding could not be ruled out in the Ca-ion- implanted surface.

Enhanced discharge of high power pulsed magnetron sputtering coupling with high voltage

Plasma source ion implantation and deposition, as an effective technology to produce functional coatings with high adhesion and density, possesses the wide application prospect, especially in the deposition of coatings that work in high loading service conditions. The key component of this technology is the metal plasma source, which is now based on pulsed cathodic arc with complex source structure and magnetic filtration because of the macro-droplets in the ion flux. In this paper, we present another metal plasma source, high power pulsed magnetron sputtering (HPPMS), and investigate the discharge characteristics at different coupling high-voltages by optical emission spectroscopy. The results show that significant improvements are found in the discharge target current and main particles in the plasma. The improvement in gas discharge by the coupling high-voltage is greater than in metal discharge which could increase obviously in the self-sputtering stage with higher target voltage discharge. Last but not least, in this paper we discuss the discharge enhancing mechanism of coupling high-voltage. It is found that the self-excited glow discharge of coupling high-voltage, the hollow-cathodic effect induced by face-to-face negative voltages of HPPMS and coupling high-voltage, and the enhanced ambipolar diffusion of the coupling high-voltage can all play a considerable role in HPPMS discharge.

Experimental investigation of plasma recovery during the pulse-off time in plasma source ion implantation

Experimental results pertaining to the plasma recovery process during the pulse-off time in plasma source ion implantation are presented. A series of experiments conducted in low-pressure argon plasma with various pulse voltages and pulse-on times reveals that the plasma recovery time is almost linearly proportional to the sheath thickness at the switch-off time. However, for sheaths larger than several centimeters, the plasma recovery times are observed to be shorter than those predicted by a simple theoretical model, expressed as 5s/uB where uB and s are the Bohm speed and the sheath thickness at the switch-off time, respectively. The reduction of plasma recovery time is found to be the consequence of realistic plasma parameters such as non-uniform density and ion drift velocity distributions in front of a target, which were not considered in the theoretical model.