N. Moncoffre

Analysis of boron by charged particle bombardment

Abstract The determination of boron concentration in thin films, semiconductors or other materials requires techniques providing good depth resolution and high sensitivities. For this purpose nuclear analysis techniques can be powerful tools and this paper presents a review of the nuclear reactions essentially with charged particles (p, α, d) that have been used (including charge particle activation analysis). Irradiation with neutrons is also considered, in particular with the very sensitive 10 B(n, α) 7 Li reaction due to the strong absorption of neutrons is boron. With the aim to search for reactions producing better depth resolutions, elastic recoil detection based technique (ERDA, ERCS) on boron are discussed. The performances of these nuclear reactions are compared with other methods, in particular with SIMS, AES, XPS and, using recent developments, the electronic microprobe.

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.

Nitrogen profiling in nitride films and nitrogen-implanted samples using the 14N(α, α) and14N(α, p) reactions at 6 MeV incident energy

We investigate the nitrogen profiling potentially using incident alpha particles from 5 to 7 MeV. In this energy range the alpha scattering cross sections on light elements are substantially larger than the Rutherford cross sections and therefore lead to competitive sensitivity. Moreover, another advantage is the high mass resolution which allows to profile simultaneously carbon, nitrogen and oxygen. n nThe analysis of TiN, NbTiN films and nitrogen implanted steel are presented. The inclusion, in the simulation program, of the 14N(α, α) and14N(α, p) cross sections allows to get a complete reproduction of the spectra and authorizes to determine accurately the nitrogen profile. Such a dual nitrogen analysis improves profile determination in case of thick analyzed layers. The sensitivity limits connected to the alpha scattered yield on steel substrate are 1016 and 5 × 1016 N atoms/cm2 for the 14N(α, α) and14N(α, p) reactions, respectively.Abstract We investigate the nitrogen profiling potentially using incident alpha particles from 5 to 7 MeV. In this energy range the alpha scattering cross sections on light elements are substantially larger than the Rutherford cross sections and therefore lead to competitive sensitivity. Moreover, another advantage is the high mass resolution which allows to profile simultaneously carbon, nitrogen and oxygen. The analysis of TiN, NbTiN films and nitrogen implanted steel are presented. The inclusion, in the simulation program, of the 14 N (α, α) and 14 N (α, p ) cross sections allows to get a complete reproduction of the spectra and authorizes to determine accurately the nitrogen profile. Such a dual nitrogen analysis improves profile determination in case of thick analyzed layers. The sensitivity limits connected to the alpha scattered yield on steel substrate are 1016 and 5 × 1016 N atoms/cm2 for the 14 N (α, α) and 14 N (α, p ) reactions, respectively.

A comparison between ion implantation into sapphire and polycrystalline alumina

Abstract The effect of ion implantation and of post-annealing treatments on the surface modifications of sapphire has been widely investigated. In particular, relationships between the microscopic state and the macroscopic properties of implanted sapphire have been established. High-dose ion implantation has been carried out in polycrystalline alumina to a smaller extent. Surface mechanical properties are modified due to surface segregation and precipitation of new phases induced by post-implantation heat treatments. These results are reviewed and a comparison between implantation and annealing effects on single-crystalline and polycrystalline materials is conducted. There have been a lot of reports on surface amorphization of sapphire which depends on the particular species implanted and on the implantation temperature. Observed results for polycrystalline alumina do not differ in this respect for the cases studied. The main differences that will be discussed in this article are attributed to grain boundaries. Charged particle bombardment notably disturbs charge equilibria between grain boundaries and grain bulk. Moreover, it has been shown that during post-implantation heat treatments the orientation relationships of newly created phases are strongly dependent on the initial sapphire orientation. These phase orientations are difficult to put in evidence for polycrystals for which each grain represents a single crystal itself. A comparison of the mechanical property changes obtained for both types of alumina structures is also discussed.

Copper, iron and zirconium implantation into polycrystalline α-Al2O3

Abstract Polycrystalline α-Al2O3 samples have been implanted by 1017 Zr, Fe or Cu ions/cm 2 at 110 keV in order to form oxide precipitates in the near-surface region after annealing in air. A chemical and microstructural characterization has been performed on the as-implanted surface and on the samples annealed in the temperature range from 600 to 1600°C. The nature of the chemical phases and the precipitate evolution have been characterized by combining RBS, XPS, GXRD, CEMS, TEM and SEM techniques. XPX, CEMS and TEM experiments on as-implanted specimens detect copper, iron and zirconium as Cu° (small metallic precipitates), Fe° (small α-iron precipitates), FeII (associated with FeAl2O4), and FeIV (metastable state), Zr° and ZrIV (ZrO2) in the as-implanted region. Analyses carried out after heat treatments between 600 and 1000 °C indicate a complete surface oxidation in this temperature range. Additionally, some precipitates appear along grain boundaries. Annealing at temperatures ranging from 1000 to 1600°C leads to drastic surface composition changes. The stability and size of the different observed precipitates (ZrO2, AlFeO3, Fe2O3, Fe3O4, CuO, CuAl2O4) strongly depend on the annealing temperature.

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.

Physicochemical and tribological characterization of titanium or titanium plus carbon implanted AISI M2 steel

Abstract AISI M2 steel samples were implanted with 110 keV titanium ions at fluences ranging from 5 × 1016 to 4 × 1017 Ti cm-2. Titanium plus carbon dual implantation was also studied. Titanium distribution profiles were determined using the 48Ti(p,γ)49V resonant nuclear reaction. The incorporation of carbon and oxygen from residual gases was studied as a function of titanium fluence and residual pressure using nuclear backscattering spectrometry at 5.7 and 7.5 MeV He+ ion energies respectively. A competition phenomenon between carbon and oxygen incorporation is pointed out. Analysis of the phases formed was performed using conversion electron Mossbauer spectroscopy. Fe(Ti) solid solution, a-FexTi100−x and superficial a-Fe-Ti-C amorphous phases were identified. Tribological tests involving a ball (Al2O3 or 52100) and disc contact were performed to characterize the friction behaviour of the implanted surface. It is shown that titanium or titanium plus carbon implantation leads to a reduction in the friction coefficient. The wear tracks and debris were examined using scanning electron microscopy and electron microprobe cartography. For the two types of balls a reduction in the wear track width was observed together with oxidation of the wear debris. The tribological improvement observed depends not only on the presence of the superficial a-Fe-Ti-C amorphous layer but also on the surface chemical reaction during the wear process.

Effects of annealing environment on surface chemical phases of iron-implanted sintered alumina

Abstract Annealing in various environments was performed on high-dose (10 17 ions/cm 2 , 110 keV) iron-implanted polycrystalline alumina samples in order to study the nature of the chemical phases formed during the recovery of the implanted layer. The influence of oxygen partial pressure was studied by comparing samples annealed in air and in argon environments. Anneals in a reducing environment (pure H 2 ) were also performed. Conversion electron Mossbauer spectroscopy and Rutherford backscattering spectrometry clearly reveal the importance of the annealing atmosphere on the nature of the surface phases in the temperature range 600–1600 °C.