Effect of target bias on magnetic field enhanced plasma immersion ion implantation

Recent studies have demonstrated that sheath dynamics in plasma immersion ion implantation (PIII) is significantly affected by an external magnetic field, especially in the case when the magnetic field is parallel to the workpiece surface or intersects it at small angles. In this work we report the results from two-dimensional, particle-in-cell (PIC) computer simulations of magnetic field enhanced plasma immersion implantation system at different bias voltages. The simulations begin with initial low-density nitrogen plasma, which extends with uniform density through a grounded cylindrical chamber. Negative bias voltage is applied to a cylindrical target located on the axis of the vacuum chamber. An axial magnetic field is created by a solenoid installed inside the target holder. A set of simulations at a fixed magnetic field of 0.0025 T at the target surface is performed. Secondary electron emission from the target subjected to ion bombardment is also included. It is found that the plasma density around the cylindrical target increases because of intense background gas ionization by the electrons drifting in the crossed E x B fields. Suppression of the sheath expansion and increase of the implantation current density in front of the high-density plasma region are observed. The effect of target bias on the sheath dynamics and implantation current of the magnetic field enhanced PIII is discussed. (C) 2007 Elsevier B.V. All rights reserved.

Amorphous carbon nitrogenated films prepared by plasma immersion ion implantation and deposition

In this work, an investigation was conducted on amorphous hydrogenated-nitrogenated carbon films prepared by plasma immersion ion implantation and deposition. Glow discharge was excited by radiofrequency power (13.56 MHz, 40 W) whereas the substrate-holder was biased with 25 kV negative pulses. The films were deposited from benzene, nitrogen and argon mixtures. The proportion of nitrogen in the chamber feed (R-N) was varied against that of argon, while keeping the total pressure constant (1.3 Pa). From infrared reflectance-absorbance spectroscopy it was observed that the molecular structure of the benzene is not preserved in the film. Nitrogen was incorporated from the plasma while oxygen arose as a contaminant. X-ray photoelectron spectroscopy revealed that N/C and O/C atomic ratios change slightly with R-N. Water wettability decreased as the proportion of N in the gas phase increased while surface toughness underwent just small changes. Nanoindentation measurements showed that film deposition by means of ion bombardment was beneficial to the mechanical properties of the film-substrate interface. The intensity of the modifications correlates well with the degree of ion bombardment. (c) 2006 Elsevier B.V. All rights reserved.

Thin polymer films prepared by plasma immersion ion implantation and deposition

This work describes an investigation of the properties of polymer films prepared by plasma immersion ion implantation and deposition. Films were synthesized from low pressure benzene glow discharges, biasing the samples with 25 W negative pulses. The total energy deposited in the growing layer was varied tailoring simultaneously pulse frequency and duty cycle. The effect of the pulse characteristics on the chemical composition and mechanical properties of the films was studied by X-ray photoelectron spectroscopy (XPS) and nanoindentation, respectively. Analysis of the deconvoluted C 1s XPS peaks demonstrated that oxygen was incorporated in all the samples. The chemical modifications induced structural reorganization, characterized by chain cross-linking and unsaturation, affecting material properties. Hardness and plastic resistance parameter increased under certain bombardment conditions. An interpretation is proposed in terms of the total energy delivered to the growing layer. (C) 2004 Elsevier B.V. All rights reserved.

Numerical simulation of magnetic field enhanced plasma immersion ion implantation

The behavior of plasma and sheath characteristics under the action of an applied magnetic field is important in many applications including plasma probes and material processing. Plasma immersion ion implantation (PIII) has been developed as a fast and efficient surface modification technique of complex shaped three-dimensional objects. The PIII process relies on the acceleration of ions across a high-voltage plasma sheath that develops around the target. Recent studies have shown that the sheath dynamics is significantly affected by an external magnetic field. In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage is applied to a cylindrical target located on the axis of a grounded cylindrical vacuum chamber filled with uniform nitrogen plasma. An axial magnetic field is created by a solenoid installed inside the cylindrical target. The computer code employs the Monte Carlo method for collision of electrons and neutrals in the plasma and a particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field. Secondary electron emission from the target subjected to ion bombardment is also included. It is found that a high-density plasma region is formed around the cylindrical target due to the intense background gas ionization by the magnetized electrons drifting in the crossed ExB fields. An increase of implantation current density in front of high density plasma region is observed. (C) 2007 Elsevier B.V. All rights reserved.

Corrosion behavior of Ti-6Al-4V alloy treated by plasma immersion ion implantation process

Ti-6Al-4V alloy is one of the most frequently used Ti alloys with diverse applications in aerospace and biomedical areas due to its favorable mechanical properties, corrosion resistance and biocompatibility. Meanwhile, its surface can stiffer intense corrosion caused by wear processes due to its poor tribological properties. Thus in the present study, PIII processing of Ti-6Al-4V alloy was carried out to evaluate its corrosion resistance in 3.5% NaCl solution. Two different sets of Ti-6Al-4V samples were PIII treated, varying the plasma gases and the treatment time. The corrosion behavior is correlated with the surface morphology, and the nitrogen content. SEM micrographs of the untreated sample reveal a typical two-phase structure. PIII processing promotes surface sputtering and the surface morphology is completely different for samples treated with N-2/H-2 mixture and N-2 only. The highest penetration of nitrogen (similar to 88 nm), corresponding to 33% of N-2 was obtained for the sample treated with N-2/H-2 mixture for 1:30 h. The corrosion behavior of the samples was investigated by a potentiodynamic polarization method. A large passive region of the polarization curves (similar to 1.5 V), associated with the formation of a protective film, was observed for all samples. The passive current density (similar to 3 x 10(-6) A cm(-2)) of the PIII-treated Ti-6Al-4V samples is about 10 times higher than for the untreated sample. This current value is still rather low and maintains good corrosion resistance. The anodic branches of the polarization curves for all treated Ti-6Al-4V samples demonstrate also that the oxide films break down at approximately 1.6 V, forming an active region. Although the sample treated by N-2/H-2 mixture for 1.30 It has thicker nitrogen enriched layer, better corrosion resistance is obtained for the PIII process performed with N, gas only. (c) 2007 Elsevier B.V. All rights reserved.

Enhanced corrosion resistance of AISI H13 steel treated by nitrogen plasma immersion ion implantation

Electrochemical corrosion measurements of AISI H13 steel treated by Pill process in 3.5% (wt) NaCl solution were investigated. So far the corrosion behavior of AISI H 13 steel by Pill has not been studied. The electrochemical results are correlated with the surface morphology, nitrogen content and hardness of the nitride layer. Ion implantation of nitrogen into H 13 steel was carried out by Pill technique. SEM examination revealed a generalized corrosion and porosity over all analyzed sample surfaces. Penetration of nitrogen reaching more than 20 gm was achieved at 450 degrees C and hardness as high as 1340 HV (factor of 2.7 enhancement over standard tempered and annealed H 13) was reached by a high power, 9 h Pill treatment. The corrosion behavior of the samples was studied by potentiodynamic polarization method. The noblest corrosion behavior was observed for the samples treated by PIII at 450 degrees C, during 9 h. Anodic branches of polarization curves of PIII processed samples show a passive region associated with the formation of a protective film. The passive region current density of PIII treated H13 samples (3.5 x 10(-6) A/cm(2)) is about 270 times lower than the one of untreated specimens, which demonstrates the higher corrosion resistance for the Pill treated H 13 samples. (c) 2007 Elsevier B.V. All rights reserved.

Thin films generated by plasma immersion ion implantation and deposition of hexamethyldisilazane mixed with nitrogen in different proportions

In this work, it was used a plasma system composed of a cylindrical stainless steel reactor, a radio-frequency (13.56MHz) power source fixed at either 25 W or 70 W, a power source with a negative bias of 10kV and a 100Hz pulse. The system worked at an operational pressure of 80mTorr which consisted of varying concentrations of the monomer HMDSN and gaseous nitrogen in ratios: HMDSN (mTorr)/nitrogen (mTorr) from 70/10 to 20/60 in terms of operational pressure. The structural characterization of the films was done by FTIR spectroscopy. Absorptions were observed between 3500 cm(-1) to 3200 cm(-1), 3000 cm(-1) to 2900 cm(-1), 2500 cm(-1) to 2000 cm(-1), 1500 cm(-1) to 700 cm(-1), corresponding, respectively, to OH radicals, C-H stretching bonds in CH2 and CH3 molecules, C-N bonds, and finally, strain C-H bonds, Si-CH3 and Si-N groups, for both the 70 W and the 25 W. The contact angle for water was approximately 100 degrees and the surface energy is near 25mJ/m(2) which represents a hydrophobic surface, measured by goniometric method. The aging of the film was also analyzed by measuring the contact angle over a period of time. The stabilization was observed after 4 weeks. The refractive index of these materials presents values from 1.73 to 1.65 measured by ultraviolet-visible technique.

Plasma-polymerized hexamethyldisilazane treated by nitrogen plasma immersion ion implantation technique

This paper describes the effect of nitrogen Plasma Immersion Ion Implantation (PIII) on chemical structure, refraction index and surface hardness of plasma-polymerized hexamethyldisilazane (PPHMDSN) thin films. Firstly, polymeric films were deposited at 13.56 MHz radiofrequency (RF) Plasma Enhanced Chemical Vapour Deposition (PECVD) and then, were treated by nitrogen PIII from 15 to 60 min. Fourier Transformed Infrared (FTIR) spectroscopy was employed to analyse the molecular structure of the samples, and it revealed that vibrations modes at 3350 cm(-1), 2960 cm(-1), 1650 cm(-1), 1250 cm(-1) and 1050 cm(-1) were altered by nitrogen PIII. Visible-ultraviolet (vis-UV) spectroscopy was used to evaluate film refractive index and the results showed a slight increase from 1.6 to 1.8 following the implantation time. Nanoindentation revealed a surface hardness rise from 0.5 to 2.3 GPa as PIII treatment time increased. These results indicate nitrogen PIII is very promising in improving optical and mechanical properties of PPHMDSN films.

Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed ExB field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.

Effects of the high temperature plasma immersion ion implantation (PIII) of nitrogen in AISI H13 steel

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigation of Plasma Immersion Ion Implantation Process in Magnetic Mirror Geometry

Plasma immersion ion implantation (PIII) with low external magnetic field has been investigated both numerically and experimentally. The static magnetic field considered is essentially nonuniform and is generated by two magnetic coils installed outside the vacuum chamber. Experiments have been conducted to investigate the effect of two of the most important PIII parameters: target voltage and gas pressure. In that context, it was found that the current density increased when the external parameters were varied. Later, the PIII process was analyzed numerically using the 2.5-D computer code KARAT. The numerical results show that the system of crossed E x B fields enhances the PIII process. The simulation showed an increase of the plasma density around the target under the operating and design conditions considered. Consequently, an increase of the ion current density on the target was observed. All these results are explained through the mechanism of gas ionization by collisions with electrons drifting in crossed E x B fields.

A Study of the Effect of Nitrogen and Air Plasma Immersion Ion Implantation Treatments on the Properties of Carbon Fiber

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microbiological Evaluation of Chicken Carcasses in an Immersion Chilling System with Water Renewal at 8 and 16 Hours

Since 2004, Brazil has been the leading exporter of chicken. Because of the importance of this sector in the Brazilian economy, food safety must be ensured by control and monitoring of the production stages susceptible to contamination, such as the chilling process. The goal of this study was to evaluate changes in microbial levels on chicken carcasses and in chilling water after immersion in a chilling system for 8 and 16 h during commercial processing. An objective of the study was to encourage discussion regarding the Brazilian Ministry of Agriculture Livestock and Food Supply regulation that requires chicken processors to completely empty, clean, and disinfect each tank of the chilling system after every 8-h shift. Before and after immersion carcasses were collected and analyzed for mesophilic bacteria, Enterobacteriaceae, conforms, and Escherichia coli. Samples of water from the chilling system were also analyzed for residual free chlorine. The results do not support required emptying of the chiller tank after 8 h; these tanks could be emptied after 16 h. The results for all carcasses tested at the 8- and 16-h time points indicated no significant differences in the microbiological indicators evaluated. These data provide both technical and scientific support for discussing changes in federal law regarding the management of immersion chilling water systems used as part of the poultry processing line.

COLOR STABILITY of SEALED COMPOSITE RESIN RESTORATIVE MATERIALS AFTER ULTRAVIOLET ARTIFICIAL AGING and IMMERSION IN STAINING SOLUTIONS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Surface roughness and hardness of a composite resin: influence of finishing and polishing and immersion methods

This study evaluated the finishing and polishing effect on the surface roughness and hardness of the Filtek Supreme XT, in fluoride solutions. Specimens were prepared (n = 140) with half of the samples finished and polished with Super-Snap (R) disks. The experimental groups were divided according to the presence or absence of finishing and polishing and immersion solutions (artificial saliva, sodium fluoride solution at 0.05%-manipulated, Fluordent Reach, Oral B, Fluorgard). The specimens remained immersed in artificial saliva for 24 hours and were then subjected to initial analysis (baseline) of surface roughness and Vickers microhardness. Next, they were immersed in different fluoride solutions for 1 min/day, for 60 days. Afterwards, a new surface roughness and microhardness reading was conducted. The data were submitted to a two-way ANOVA and Tukey's test (5% significance level). For the comparison of mean roughness and hardness at baseline and after 60 days, the paired Student t test was used. The results showed that the surface roughness and microhardness of the Filtek Supreme XT were influenced by the finishing and polishing procedure, independently of the immersion methods.