ABSTRACT Effects of E x B fields as mechanism to carbon nitrogen plasma immersion ion implantation (PIII) have been investigated. This magnetic configuration when used in PIII allows obtaining high nitrogen plasma density close to the ion... more
ABSTRACT Effects of E x B fields as mechanism to carbon nitrogen plasma immersion ion implantation (PIII) have been investigated. This magnetic configuration when used in PIII allows obtaining high nitrogen plasma density close to the ion implantation region. Consequently, high ions dose on the target is possible to be achieved compared with standard Pill. In this scenario, nitrogen and carbon ions were implanted simultaneously on stainless steel, as measured by GDOES and detected by X-ray diffraction. Carbon-tape disposed on the sample-holder was sputtered by intense bombardment of nitrogen ions, being the source of carbon atoms in this experiment. The implantation of both N and C caused changes on sample morphology and improvement of the tribological properties of the stainless steel.
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ABSTRACT The nitrogen depth profile in polycrystalline AISI 316L austenitic stainless steel after plasma nitriding at temperatures around 400 °C is analyzed by the “trapping–detrapping” model. This model considers the diffusion of... more
ABSTRACT The nitrogen depth profile in polycrystalline AISI 316L austenitic stainless steel after plasma nitriding at temperatures around 400 °C is analyzed by the “trapping–detrapping” model. This model considers the diffusion of nitrogen under the influence of trap sites formed by local chromium atoms. Nitrogen depth profiles in polycrystalline AISI 316L steel simulated on the basis of this model are in good agreement with experimental nitrogen profiles. The enhanced nitrogen diffusivity as well as a plateau-type shape of nitrogen depth profile can be explained. The nitrogen diffusion coefficient at 400 °C is found to be D = 4.81 × 10−12 cm2/s and the diffusion pre-exponential factor D0 (0.837 × 10−3 cm2/s) and detrapping activation energy EB (0.28 eV) were deduced from fitting experimental data. It is known that the nitrogen penetration depth (and nitrogen diffusivity) depends on the crystalline orientation and a tentative to take into account this anisotropy effect and describe nitrogen depth profiles in polycrystalline AISI 316L steel is proposed by using different diffusion coefficients characteristic for each crystallite orientation.Research Highlights►Nitrogen mass transport mechanism in nitrided polycrystalline AISI 316L is analyzed. ►Effects of nitrogen diffusivity anisotropy in plasma nitrided AISI 316L are analyzed. ►The nitrogen diffusion model based on trapping–detrapping mass transport mechanisms.
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Nanocavities and interstitial-type defects formed by neon plasma based ion implantation (PBII) in Si followed by annealing at 900°C have been studied in comparison with conventional ion implantation. Implantations were performed at 250°C... more
Nanocavities and interstitial-type defects formed by neon plasma based ion implantation (PBII) in Si followed by annealing at 900°C have been studied in comparison with conventional ion implantation. Implantations were performed at 250°C and high fluence of ≈5×1016cm−2. Using PBII, a rather uniform layer of cavities is observed from the surface. However, the mean diameter of cavities is smaller due
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To evaluate the mechanical behaviour of CNx thin films deposited on a Ti6Al4V titanium alloy by RF magnetron sputtering, in situ tensile tests in a scanning electron microscope were performed.Sputtered films were deposited on one side of... more
To evaluate the mechanical behaviour of CNx thin films deposited on a Ti6Al4V titanium alloy by RF magnetron sputtering, in situ tensile tests in a scanning electron microscope were performed.Sputtered films were deposited on one side of Ti6Al4V samples using a conventional magnetron sputtering system with a graphite target and Ar/N2 plasma. The amount of nitrogen in film was about
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ABSTRACT Ni-based superalloys are composed of a matrix with an austenitic face-centered cubic (FCC) crystal structure (γ phase) which is generally strengthened by the presence of a high fraction of ordered FCC precipitates γ′ (Ni3(Ti,Al)... more
ABSTRACT Ni-based superalloys are composed of a matrix with an austenitic face-centered cubic (FCC) crystal structure (γ phase) which is generally strengthened by the presence of a high fraction of ordered FCC precipitates γ′ (Ni3(Ti,Al) type) and/or γ″ (Ni3Nb type). Plasma assisted nitriding of various Ni-based superalloys, either polycrystals (Haynes®230, Inconel®718, Udimet®720Li, N18) or single crystals (MC2 and MC-NG), presenting from 100 vol.% to 30 vol.% of γ phase, has been performed at moderate temperature (400 °C) to shed light on the specific responses of the different (δ, γ′, γ″) precipitates under nitriding. Characterizations by glowdischarge optical emission spectroscopy and scanning electron microscopy have evidenced the formation of nitrided layers with thicknesses varying from ~1 μm to ~8 μm depending on alloys and treatment duration. In all alloys, X-ray diffraction on nitrided samples confirms that the γ phase is nitrided, as in austenitic stainless steels, to form the expanded austenitic FCC phase γN, a nitrogen insertion solid solution, with a mean concentration of ~25 at.% N. CrN nitrides were also identified. The incorporation of nitrogen within the precipitates appeared to depend on the alloy microstructure: for polycrystals, regardless of their proportion, the δ, γ′ or γ″ precipitates seem nitrided in similar proportion than the matrix γ although the exact nature (nitrides or expanded δ, γ′, γ″ phases) of the obtained nitrided phaseswas not confirmed. On the contrary, in the single crystalMC2, the γ′ precipitates accommodate amuch lower nitrogen amount, in the range 3–5 at.%.Whatever thematerials, the surface swelling induced by the nitrogen uptake is only relative to the total incorporated nitrogen quantity and is roughly independent on the nature of the nitrided phases.
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ABSTRACT A stable heating source, providing steady temperatures in the range of 200 to more than 1000°C, was used to perform high temperature plasma based ion implantation (PBII) on Ti6Al4V. The precise control of the heating of the... more
ABSTRACT A stable heating source, providing steady temperatures in the range of 200 to more than 1000°C, was used to perform high temperature plasma based ion implantation (PBII) on Ti6Al4V. The precise control of the heating of the samples in vacuum while performing PBII is accomplished by means of an efficient electron source, working independent of the conditions of the discharge.The electrons produced by a low work function (2.1eV) barium, strontium and calcium oxide cathode help with the start-up of the discharge, with the increase of nitrogen ionization and heating of the samples. The large growth of the treated layer thickness was a result of the thermal diffusion of nitrogen, reaching up to 20μm, in the total process time lasting only 100min. Experiments were run by setting a constant substrate temperature during PBII to 800°C but varying the pulse intensity and the duration of the process. Our results showed improvements of the mechanical and tribological properties, and also higher resistance to corrosion of the samples treated by high temperature PBII.
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We have investigated the protective effect of SixCy and SixNy coatings deposited by dynamic ion mixing (DIM) on the oxidation resistance of a Ti6242 alloy (Ti–6Al–2Sn–4Zr–2Mo). The amorphous SixCy (x/y∼1,1) and SixNy (x/y∼2) coatings... more
We have investigated the protective effect of SixCy and SixNy coatings deposited by dynamic ion mixing (DIM) on the oxidation resistance of a Ti6242 alloy (Ti–6Al–2Sn–4Zr–2Mo). The amorphous SixCy (x/y∼1,1) and SixNy (x/y∼2) coatings 0.25–0.21 μm thick respectively were produced by sputtering SiC and Si3N4 targets with a 1.2 keV Ar+ ion beam and the growing films were bombarded with 120 keV Ar+
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Low frequency noise is checked in n-channel single crystalline silicon MOS transistors and polysilicon TFTs. The study is performed on devices operating from below to above threshold regions. Apparent noise parameter (alphaapp) is... more
Low frequency noise is checked in n-channel single crystalline silicon MOS transistors and polysilicon TFTs. The study is performed on devices operating from below to above threshold regions. Apparent noise parameter (alphaapp) is extracted from noise measurements according to the empirical Hooge formula. alphaapp increases in the subthreshold region and decreases above threshold versus the effective gate voltage. For polysilicon TFTs 10-2<alphaapp<1 while for MOSFETs 10-5< alphaapp<10-2. alphaapp is higher in TFTs due to a higher interface defect density. Distribution of defects in the oxide band gap is also determined for TFTs. Results agree with Mc Whorter model.
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ABSTRACT Zirconium nitride (ZrN) is a refractory material with good mechanical and thermal properties. It is therefore a good candidate for hard surface treatment at high temperature. In this work, we report the growth and... more
ABSTRACT Zirconium nitride (ZrN) is a refractory material with good mechanical and thermal properties. It is therefore a good candidate for hard surface treatment at high temperature. In this work, we report the growth and characterization of ZrN by plasma assisted thermal nitridation of zirconium films in a NH3 atmosphere. The process was monitored by in situ monochromatic ellipsometry and the nitrides grown were profiled and analyzed by Auger electron spectroscopy. By using temperatures in the 700-800 °C range, the material obtained is quite close to ZrN, but, depending on experimental conditions, residual oxygen (impurities) can be easily incorporated by reaction with zirconium. The analysis of the ellipsometric data has shown that the nitridation did not occur by simple growth of nitride on zirconium. Auger profiles confirmed the presence of an oxidized zirconium layer localized between the nitrided surface and the remaining metal. This oxidation was observed to occur preferentially during temperature ramping, that is, in the low temperature regime. At high temperature, nitridation is dominant and the incorporated oxygen is exchanged with nitrogen. Oxygen is then partly rejected by diffusion out of the film through the ZrN surface layer and partly by diffusion in the deep zirconium sublayer. By using these observations, a new model of growth with a layered ZrN/ZrOx/Zr film was used to describe in situ ellipsometric data. By comparing the pure thermal and the plasma treatments, the advantages of the plasma assisted treatment become clearly: complete nitridation of the zirconium layer was achieved and the oxygen amounts in the film were substantially reduced.
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To develop items to measure indoor tanning and sunless tanning that can be used to monitor trends in population surveys or to assess changes in behavior in intervention studies. A group of experts on indoor tanning convened in December... more
To develop items to measure indoor tanning and sunless tanning that can be used to monitor trends in population surveys or to assess changes in behavior in intervention studies. A group of experts on indoor tanning convened in December 2005, as part of a national workshop to review the state of the evidence, define measurement issues, and develop items for ever tanned indoors, lifetime frequency, and past-year frequency for both indoor tanning and sunless tanning. Each item was subsequently assessed via in-person interviews for clarity, specificity, recall, and appropriateness of wording. Universities in Tennessee and Virginia, a medical center in Massachusetts, and a high school in New Hampshire. The study population comprised 24 adults and 7 adolescents. Participants understood indoor tanning to represent tanning from beds, booths, and lamps that emit artificial UV radiation, rather than sunless tanning, even though both can be obtained from a booth. Two items were required to distinguish manually applied from booth-applied sunless tanning products. Frequency of use was easier for participants to recall in the past year than for a lifetime. While indoor tanning items may be recommended with confidence for clarity, sunless tanning items require additional testing. Memory aids may be necessary to facilitate recall of lifetime use of nonsolar tanning. In addition, studies that assess reliability and validity of these measures are needed. Since study participants were primarily young and female, testing in other populations should also be considered.