H. Jaffrezic

Temperature influence during nitrogen implantation into steel

Abstract Nitrogen ion implantations in a XC06 steel are performed at different temperatures. The nitrogen profiles are measured using the narrow 429 keV resonance of the 15 N(p, αγ) 12 C nuclear reaction. The iron and nitrogen chemical states are determined by conversion electron Mossbauer spectroscopy (CEMS). The chemical composition of the implanted layer is also studied by means of X-ray photoelectron spectroscopy (XPS). A strong variation of the nitrogen profiles is shown at temperatures between 20 and 200°C. This temperature effect differs from that of post annealings. The formation of a superficial peak due to e-carbonitride phases increasing with temperature is observed for implantations performed from 100°C. An evolution of iron nitride and carbonitride phases is observed as a function of implantation temperature.

Boron analysis of thin layers using prompt nuclear techniques

We present the use of boron nuclear analysis in order to determine the boron depth distribution in implanted layers and the stoichiometry of thin NiBx, FeNIBx and TiBx films. For this purpose several nuclear reactions that have already given analytical results could be considered (11B(p, α)2α, 11B(p, γ)12C, 10B(d,p)11B, 10B(d, n)11 etc.). The 11B(α, α) reaction has been chosen and we have studied its excitation function between 3.50 and 7.50 MeV. It displays in particular an interesting plateau between 5.92 and 6.04 MeV. In this 120 keV region the reaction cross section is nearly constant and rather high (σcm = 310 mb/sr). It allows us to take advantage of the nuclear contribution of the elastic scattering and to make a quantitative analysis with a good sensitivity and a depth resolution of about 20 nm. We have compared these reaction performances with those of the resonant nuclear reaction 11B(p, γ) at 163 keV and of the 11B(p, α1) reaction at 660 and 163 keV. Advantages and disadvantages of these reactions for boron profiling are discussed.

Diffusion studies using ion beam analysis

Abstract The combination of ion implantation with nuclear methods such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Spectroscopy (NRS) or Elastic Recoil Detection Analysis (ERDA) has shown to be well adapted to the study of impurity migration in solids induced by either thermal annealing or irradiation. This paper gives some typical examples studied in more detail in our laboratory. Among them, the determination of thermodynamical data (diffusion coefficients, activation energies) from the analysis of the evolution of implanted species is rather classical. As an illustration the diffusion study of lanthanum implanted into apatite using RBS is presented. This work is of interest with regard to nuclear waste storage in geological sites where apatites are possible migration barriers to radioactivity and lanthanum is a representative fission product. The second study taken from the metallurgical field concerns the determination of the nitrogen diffusion coefficient into aluminium using NRS. Finally, a study concerning hydrogen diffusion in an a-SiC:H material (plasma facing materials) induced by deuterium bombardment will be presented. The hydrogen profiling is performed using ERDA.

Iron-implanted sintered alumina studied by RBS, CEMS AND SEM techniques

Abstract Sintered plates of alumina have been implanted at room temperature with 1.2 × 10 17 57 Fe + /cm 2 at 110 keV. Rutherford backscattering spectrometry and conversion electron Mossbauer spectrometry have been used to characterize respectively the depth distribution and charge states of iron. A theoretical approach of the as-implanted iron profile has been carried out by using a modified TRIM code which takes into account the fluence, the sputtering effects and the modification of the surface composition during ion bombardment. The iron profile and charge-state evolutions after isochronal air annealings from 200° C to 1600° C have been investigated. Correlations with the surface topography evolution investigated by SEM are proposed.

Sputtering yield and residual vacuum influence during titanium implantation into iron

Abstract Ti implantation into iron-based alloys is known to improve tribological properties (low friction and wear) by formation of an amorphous Fe-Ti-C surface layer due to the interaction of the carbonaceous molecules in the residual vacuum with the surface during implantation. To state precisely the conditions of this amorphous-layer formation, thin evaporated iron targets were implanted with 110 keV Ti ions at room temperature with fluences ranging from 6 × 1016 to 3 × 1017 Ti/cm2 and at different residual pressures. Samples were analysed using backscattering spectrometry with 5.7 MeV 4He ions to obtain titanium profiles and to follow the evolution of sputtering yield versus fluence and residual vacuum pressure, and also for determining the amount of carbon and oxygen incorporated on the Ti-implanted surface as a function of fluence and pressure. Theoretical calculations of sputtering and high-fluence Ti distributions were performed and compared to experimental data. The importance of the reactions that occur between the implanted surface and the residual gases in the vacuum during implantation (C and O competition) is discussed.

Characterization of polycrystalline α-Al2O3, zirconium implanted and annealed at various temperatures

Abstract Polycrystalline α-Al2O3 samples implanted with 50–190 keV Zr ions from 5 × 1016 to 2.5 × 1017 ions/cm2 have been investigated. A physico-chemical characterization of the as-implanted specimen has been carried out. By using XPS. it is shown that the four chemical states ZrO2, Al2O3, Al and Zr are present in the implanted layer. Moreover, TEM indicates no precipitate formation. Thermal annealings have been performed between 700 and 1600°C for one hour in an oxidizing atmosphere. RBS and SEM techniques, used to follow the evolution of the zirconium versus the annealing temperature, show that under air, from 700°C, zirconium is entirely oxidized. Up to 1000°C small oxide precipitates are formed. The ZrO2 grain size increases with temperature between 1200 and 1600°C. At 1600°C a heterogeneous distribution of ZrO2 nodules (∼ 0.7 ω) is observed in conjunction with Zr release from the surface (~ 60% of Zr loss). Moreover, this study is completed by in situ annealing TEM observations.

Zirconium oxidation under high-energy heavy-ion irradiation

This paper concerns the study of zirconium oxidation under irradiation with high energetic Xe ions. The irradiations were performed on the IRRadiation SUD (IRRSUD) beam line at Grand Accelerateur National d’Ions Lourds of Caen. The oxygen partial pressure was fixed at 10−3Pa and two temperature conditions were used, either 480°C reached by Joule effect heating or 280°C due to Xe energy deposition. Zirconia was fully characterized by Rutherford backscattering spectrometry, scanning electron microscopy, and grazing angle x-ray diffraction. Apparent diffusion coefficients of oxygen in ZrO2 were determined from these experiments by using a model which takes into account a surface exchange between oxygen gas and the ZrO2 surface. These results are compared with thermal oxidation data.

Modelization of nitrogen diffusion induced by the formation of a surface carbonitride layer

Nitrogen implantations were performed into iron at a fluence of 1017 15N cm−2, an energy of 50 keV, a temperature of 150 °C, two vacuum pressures (2×10−3 and 6×10−5 Pa), and five current densities (6, 18, 24, 40, 60 μA cm−2). Experimental profiles display a preferential nitrogen migration towards the surface. In order to interpret the variation of the depth distribution shapes versus the pressure and the current density, a calculation model is elaborated. This model takes into account the presence of the contamination carbon at the sample surface. A comparison between experimental and simulated profiles is presented. An interpretation of the carbon role is proposed. The different hypothesis on the nitrogen migration mechanisms are reviewed.

Aggregation of iron implants in silver

Abstract The local environment of 110 keV 57 Fe ions implanted at room temperature in Ag was studied by conversion electron Mossbauer spectroscopy (CEMS). The dose of implants varied from 10 15 to 5 × 10 16 ions/cm 2 . For the low fluences iron appears in the form of monomers and dimers, for medium fluences iron trimers and bigger aggregates were found in addition. At the highest dose iron precipitates mainly in the form of magnetically ordered metallic particles. From the concentration dependent probability of each fraction the binding energies of Fe dimer (−170 meV) and trimer (−296 meV) were calculated by minimizing the configurational free energy.

Argon irradiation damage at a Cu/Al2O3 interface for different alumina structures

The evolution of damages at a Cu/Al2O3 device interface after Ar+ irradiation, depending on alumina structure, and the effect of surface roughness on sputtering have been studied. A polycrystalline Cu/Al2O3 bilayer and polycrystalline Cu on amorphous alumina were irradiated with 400 keV Ar+ ion beam at doses ranging from 5 × 1016 to 1017 Ar+/cm2 at room temperature. The copper layer thicknesses were between 100 and 200 nm. RBS analysis was used to characterize the interface modification and to deduce the sputtering yield of copper. The SEM technique was used to control the surface topography. A RBS computer simulation program was used to reproduce experimental spectra and to follow the concentration profile evolutions of different elements before and after ion irradiation. A modified TRIM calculation program which takes into account the sputtering yield evolution as well as the concentration variation versus dose gives a satisfactory reproduction of the experimental argon distribution. The surface roughness effect on sputtering and the alumina structure influence at the interface on mixing mechanisms are discussed.