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Transition metal nitrides, as is the case of NbN, exhibit an attractive mixture of physical, chemical and mechanical properties and can be used to overcome a severe constraint of pure niobium, that is the high oxidation rate for temperature above 400 °C. In this work nitrogen ions were implanted into niobium by means of plasma based ion implantation (PBII) and high temperature PBII (HTPBII) in order to produce NbN on the surface of the material. In the case of HTPBII the treatment was performed in the temperature of 1000 °C and 1250 °C. In the process, negative pulses of 10 kV/20 μs/500 Hz were applied to Nb samples for 1 h. The depth of the modified layer reached up to 4.5 μm due to the diffusion of nitrogen atoms implanted into the material. X-ray diffraction spectra showed the presence of ɛ-NbN, β-Nb2N and γ-Nb4N3 phases. Wear rate was reduced from 1.5 × 10−2 mm3/Nm up to 2.6 × 10−6 mm3/Nm for treated samples at high temperature in comparison with pristine samples, while friction coefficient was reduced from 0.8 to 0.25. Hardness was significantly increased. Surface topography was measured by optical profilometry. Surface roughness increases with the sample temperature but it remains lower than the one obtained by conventional PBII, very probably due to the heating method, which was performed by electron bombardment.

The aim of this study was to evaluate the correlation between patients' and dentist's assessment of dentures and to correlate these variables with objective measures of masticatory function. A sample of 28 edentulous individuals was selected, all wearing both complete dentures for at least 6 months and with no signs or symptoms of temporomandibular joint disorders. They rated their level of satisfaction with their dentures from 0 to 100 by means of a visual analogue scale, and dentures were scored by a dentist from 0 to 9 considering functional aspects. Tooth wear was evaluated on the posterior teeth of dentures considering the lack of occlusal anatomy. Masticatory performance and swallowing threshold tests were performed with an artificial test food (Optocal), and the median particle size was determined by the sieving method. The results showed that the mean satisfaction value of volunteers with their dentures was 49·1 and the median score of dentist's evaluation was 6. The Spearman correlation coefficient revealed no significant correlation between patients' and dentist's assessment of dentures (P>0·05). The median particle size for masticatory performance and swallowing thresholds was 5·5 ± 1·0 and 4·9 ± 1·2 mm, respectively. Data of both masticatory tests showed no significant correlation with patients' satisfaction or with dentist's evaluation of dentures. There was no difference of food comminution between subjects with and without excessive posterior tooth wear. It can be concluded that dentist's and patients' assessment of dentures were not correlated, and no correlation was observed between these variables and masticatory function.

When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mossbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer. (c) 2005 Elsevier B.V. All rights reserved.

Nitrogen Plasma Immersion Ion Implantation (PIII) has been used to modify the surface chemical structure of Ultra High Molecular Weight Polyethylene (UHMWPE). Grinding and polishing processes based on abrasive papers and alumina pastes have been evaluated with regard to their results on the improvement of polymer surface roughness, which has shown to be of crucial importance for hardness characterization. Raman spectroscopy, XPS, and Nanoindentation tests were used to characterize the modified surfaces. Experimental results has shown that UHMWPE surface mechanical properties such as hardness and elastic modulus can be improved by induced chain cross-linking between the macromolecules on the polymer surface caused by nitrogen PIII. The new material formed on the surface is Diamond Like Carbon (DLC). As a significant improvement in hardness was obtained by DLC synthesis on the treated surface, it is expected a dramatic improvement of abrasion resistance and overall durability of prostheses made with PIII treated UHMWPE.

Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 degreesC) glow discharge nitriding with low-pressure (8 x 10(-2) Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases Of gamma(N), and gamma were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides ion implantation at moderate energy (10–50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nitriding. Surface modification of aluminum alloy 5052, Ti6Al4V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 kV and then ion nitrided at low pressure with bias of −800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20% using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather well-defined nitrogen enriched regions with different N contents: high (25–30 at.%) in a surface layer and medium (∼10%) in a subsurface layer.

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 μs duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp3/sp2 bonded carbon in the modified layer was obtained by suitable fitting of the XPS C 1s energy peak, using a four-curve fitting procedure, which recognizes a portion of C–O and CO surface bonding. The XPS results for N 1s peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering.

Hybrid surface modification involving plasma immersion ion implantation (PIII) and ion nitriding has been attempted. DC cathode nitrogen glow discharges with 600–1000 V, 50–300 mA were typically obtained using the sample support as the cathode and the vacuum chamber as the anode. In this mode, sample temperatures of 500–600 °C can be reached easily while PIII at 10 kV, 50 μs and 400 Hz alone can provide about 300 °C heating. Combining these two highly conformal treatments and achieving high temperature, high efficiency three dimensional ion implantation is our objective. X-ray diffractions (XRD and high resolution XRD in the glancing mode) showed effects of ion nitriding in the AISI 304 stainless steel samples surface which indicate very thick nitrided layer, especially when operating the glow discharge in the low pressure but with high temperature nitriding mode. Auger electron spectroscopy and microhardness measurements confirmed nitriding in the sample surface. The hybrid treatment (PIII/ion nitriding) is expected to improve further these surfaces.

Historical perspective of the development of PIII devices at the Instituto Nacional de Pesquisas Espaciais (INPE) is given, together with the description of the present system under operation and our overall results on this three-dimensional implantation research. Starting with an ignitron switched pulser (1 pulse per 3 min) and an intermittent microwave plasma, we improved our PIII system developing a pulse forming network (PFN) based pulser (20 Hz), 2 years later. We also improved our plasma source towards a DC, highly stable, medium density glow discharge system. A much faster hard tube pulser was recently incorporated to our PIII system (670 Hz) allowing us to achieve good implantation results in different materials. Presently, we are testing a recently purchased RUP-4 commercial pulser to obtain arc prevented, 1.1 kHz, square pulses for new experiments in this active field of PIII research.

A simple dc glow discharge with controlled plasma floating potential was applied as a novel source for plasma immersion ion implantation with excellent results. The glow discharge source is normally used for the conditioning of fusion device chambers, taking advantage of the available high accelerating potential which is necessary for the ion bombardment of the walls. Combining an electron-emitting hot filament with this source, it was possible to get a stable discharge at pressures as low as 8?10-4 mbar and, operating it with potentials lower then 70?V, it was possible to reduce the Si sample etching down to zero from 2500???seen at potentials of native 350?V, when exposure times of 750?min were used in the sample's surface subjected to plasma ion implantation of nitrogen. As a result, retained ion doses of 1.5?1017?cm-2 were obtained in etching-free Si surfaces.

A DC glow discharge plasma source was used in a plasma immersion ion implantation (PIII) experiment providing nitrogen plasmas with densities of 1–3 ×10 10 cm −3 and temperatures of 5–10 eV. Nitrogen ions were extracted from these plasmas and implanted in a variety of immersed samples (Al 5040, SS 304, Si) using repetitive high voltage pulses from two types of sources: PFN pulser and a hard tube pulser. Due to the high potential present in our plasma (350 V), a significant sputter etching of the samples surface occurred at long irradiation times. An electron shower source was used to lower this potential allowing its control from 0 to 350 V. Operating the plasma source at potentials below 70 V reduced the sputtering to negligible levels and a retained dose of 1.5×10 17 cm −2 was achieved in a silicon surface, after irradiation of 1500 min. For plasma with potential of 350 V (no electron shower), the retained doses in Al 5040 and SS 304 samples were smaller than 5×10 16 cm −2 , for same plasma and pulser conditions (but 2500 min irradiation), confirming the deleterious effects of sputtering measured in Si samples. Upon using the higher repetition rate pulser, the treatment time was reduced by a factor of 700, thus easing considerably the sputtering problem.

A dc glow discharge source with controlled plasma potential was developed for application in plasma immersion ion implantation processing of materials surfaces. This type of ion implantation system allows cost effective surface modification of workpieces with complex shapes. The effects of the nitrogen plasma etching during the plasma immersion ion implantation process was studied using Si wafers as monitors, as we varied the externally controlled plasma potential between 0 and 350 V. When the plasma potential is controlled below 70 V, the ion implantation is dominant, otherwise the etching overtakes. The nitrogen implanted silicon wafers were analyzed by high resolution x-ray diffraction and Auger electron spectroscopy which revealed successful implantation of ions with accumulated nitrogen dose of 1.5×1017 cm−2, for the low potential case.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:05:36Z No. of bitstreams: 1 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) Made available in DSpace on 2013-08-22T19:05:36Z (GMT). No. of bitstreams: 1 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) Previous issue date: 2005-12-01 Made available in DSpace on 2013-09-30T18:11:07Z (GMT). No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Previous issue date: 2005-12-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:27:55Z No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Made available in DSpace on 2014-05-20T13:27:55Z (GMT). No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Previous issue date: 2005-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) SAE 1020 construction steel is widely used as mortar reinforcement and small machine parts, but aside good surface properties as high ductility, hardness and wear resistance, its surface is prone to severe corrosion. As it is known, Chromium in amount over 12%-13% in the Fe alloys renders them resistance to several corrosive attacks. SAE 1020 samples were recovered with Chromium film and then bombarded either by nitrogen Ion Beam (IB) or Plasma Immersion Ion Implantation (PIII) to recoil implant Cr atoms in the Fe matrix. Samples treated by 100 keV N+ IB showed irregular, thin Cr profile, remaining a part of the film on the surface, to about 10 nm. Samples treated by 40 kV N PIII presented Cr layer of about 18% at., ranging to around 90 nm. Cr of the film was implanted in the Fe matrix in an almost flat profile. Results of corrosion test showed good performance of the PIII treated sample. The IB treated sample showed some enhancement over the non-treated reference and the only Cr film deposited sample showed no modification on the corrosion behavior as compared to the non-treated reference sample. Instituto Nacional de Pesquisas Espaciais Laboratório de Combustão e Propulsão Science and Technology Analyst INPE LAP Laboratório Associado de Plasma INPE LAP Laboratório Associado de Sensores e Materiais UNESP FEG Depto. de Física e Química Forschungszentrum Rossendorf UNESP FEG Depto. de Física e Química

The aim of this study was to evaluate the correlation between patients' and dentist's assessment of dentures and to correlate these variables with objective measures of masticatory function. A sample of 28 edentulous individuals was selected, all wearing both complete dentures for at least 6 months and with no signs or symptoms of temporomandibular joint disorders. They rated their level of satisfaction with their dentures from 0 to 100 by means of a visual analogue scale, and dentures were scored by a dentist from 0 to 9 considering functional aspects. Tooth wear was evaluated on the posterior teeth of dentures considering the lack of occlusal anatomy. Masticatory performance and swallowing threshold tests were performed with an artificial test food (Optocal), and the median particle size was determined by the sieving method. The results showed that the mean satisfaction value of volunteers with their dentures was 49·1 and the median score of dentist's evaluation was 6. The Spearman correlation coefficient revealed no significant correlation between patients' and dentist's assessment of dentures (P0·05). The median particle size for masticatory performance and swallowing thresholds was 5·5 ± 1·0 and 4·9 ± 1·2 mm, respectively. Data of both masticatory tests showed no significant correlation with patients' satisfaction or with dentist's evaluation of dentures. There was no difference of food comminution between subjects with and without excessive posterior tooth wear. It can be concluded that dentist's and patients' assessment of dentures were not correlated, and no correlation was observed between these variables and masticatory function.

As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES). The presence of nitrogen, from hitting process, caused little effect on the surface hardness, as SAE 1020 steel is not suitable for nitriding hardening. Corrosion tests of the PIII-treated samples showed significant enhancement in the steel behaviour under chloride medium attack.

To improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments mixing PIII and ion nitriding processes. A combination of high pressure (4 x 10(1)Pa), moderate temperature (up to 450degreesC) glow discharge nitriding with low pressure (8 x 10(-2)Pa) and low DC bias voltage ion nitriding (or DC PIII) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of gamma(N) and epsilon were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 x) of the sample which could also enhance its wear properties. Surface modification of T16Al4V alloy and SS304 steel by a combination of PIII and subsequent ion nitriding was investigated as well. Nitrogen ions were implanted into the specimens at 15 keV and then ion nitrided at ! low pressure (7 x 10(-2)Pa) with a bias of -800 V. Compared to the untreated samples, the hardness of Ti6Al4V alloy and the steels could be improved significantly. AES results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.

SAE 1020 is a widely used plain carbon steel, as mortar reinforcement in buildings and small machine parts. But aside from good mechanical properties, its surface suffer from severe corrosion and high wear rate, due to modest hardness. Chromium (Cr) in excess of 12% in Fe alloys renders them resistant to several corrosive attacks. So we tried to introduce Cr in such amounts into the surface of that steel. Cr films were deposited by electron beam on SAE 1020 steel. Bombarding the Cr film either by nitrogen Plasma Immersion Ion Implantation (PIII) or nitrogen ion beam (IB), Cr atoms were recoil introduced into the Fe matrix. Normally, in the recoil process, heavy atoms are used, but in this set of experiments we used a relatively lighter atom, viz. nitrogen. SRIM simulation was used to show Cr atoms range in the steel matrix after being hit by nitrogen atoms. AES analysis showed ranges far beyond the calculated figures and in percentages above 13at. %, enough to the purposes of these works. Preliminary corrosion results showed remarkable enhancement under corrosive attack.

Implantation of nitrogen ions into stainless steel in combination with oxidation often results in a decrease or even complete removal of the chromium in the nitrogen containing outermost surface layer. While iron nitrides can be formed easily by this method, due to the absence of chromium, the formation of chromium nitrides is impossible and the beneficial influence of chromium in the steel for corrosion resistance cannot be used. To overcome this problem we use the following hybrid technique. A thin chromium layer is deposited on steel and subsequently implanted with nitrogen ions. Chromium can be implanted by recoil into the steel surface and thus the formation of iron/chromium nitrides should be possible. Both beam line ion implantation and plasma immersion ion implantation are used. Due to the variation of the process parameters, different implantation profiles and different compounds are produced. The produced layers are characterized by Auger electron spectroscopy, conversion electron Mossbauer spectroscopy and X-ray diffraction. The obtained results show that due to the variation of the implantation parameters, the formation of iron/chromium nitrides can be achieved and that plasma immersion ion implantation is the most suitable technique for the enrichment of chromium in the outermost surface layer of the steel when compared to the beam line implantation.

High-resolution X-ray diffraction methods have been used to characterize nitrogen-doped silicon obtained by plasma immersion ion implantation (PIII). The Si wafers were implanted with the plasma potential controlled at 70 V, and a plasma density of 1.5×10 10 cm −3 . The high voltage pulser was operated with peak voltage of 10 kV, 6 μs pulse duration and repetition frequency of 20 Hz. Auger electron spectroscopy (AES) measurements were carried out revealing successful implantation of ions with accumulated nitrogen dose of 1.5×10 17 cm −2 . The (0 0 4) Si rocking curve (ω-scan) was measured in a high resolution X-ray diffractometer equipped with a Ge(2 2 0) four crystal monochromator before and after implantation. A small distortion of the Si(0 0 4)-rocking curve was clearly observed for the as-implanted sample. This rocking curve was simulated by dynamical theory of X-ray diffraction, assuming a Gaussian strain distribution through the implanted region and using the data from the nitrogen profile obtained from the Auger measurements. With these assumptions, a good agreement between the measured and simulated rocking curves was obtained.

In the present study we use x-ray diffraction methods to characterize the surface of Si wafers irradiated with nitrogen by Plasma Immersion Ion Implantation. This is a non-line-of-sight ion implantation method, which allows three-dimensional treatment of materials including semiconductors, metals and dielectrics. The atomic concentration profiles in the implanted Si wafers were measured by Auger electron spectroscopy. The (004) Si rocking curve ( omega-scan) was measured in a high resolution x-ray diffractometer equipped with a Ge (220) four-crystal monochromator before and after implantation. A distortion of the Si (004)-rocking curve was clearly observed for the as-implanted sample. This rocking curve was successfully simulated by dynamical theory of x-ray diffraction, assuming a Gaussian strain profile through the implanted region. The analysis made by x-ray difraction and Auger electron spectroscopy revealed successful implantation of ions with ac- cumulated nitrogen dose of 1.5 x 10(17) cm-3 .The Si wafers can be used as high sensitivity monitors in the Plasma Immersion Ion Implantation process, especially at the low dose range.

A combined surface modification treatment consisting of ion nitriding at high pressure and high temperature, followed by a cycle at low pressure, both cycles using a gas mixture of (N-2/H-2):(50/50) in pressure, was applied to stainless-steel AISI 304. In the first cycle, in a glow discharge at 4x10(-1) mbar and temperatures of 400- 450 degreesC, high-pressure nitriding was applied to the samples. In the second cycle, in a glow discharge at 8x10(-4) mbar, low-pressure nitriding was applied to the samples. Applying this sequential hybrid treatment alternately, good nitriding was obtained. X-ray diffraction (XRD) measurements showed the effects of this hybrid ion nitriding in the AISI 304 surface, indicating thick nitrided layers, confirmed by Auger electron spectroscopy (AES). Conversion electron Mossbauer spectroscopy, combined with AES and XRD, showed phases and compounds induced by such treatments. Vickers hardness measurements showed great enhancement in the surface hardness. Applying other combinations of gas mixtures and cycles, produced diverse results in the surface, like the induction of alpha- and epsilon-phases.