F. Abel

Aluminum diffusion in diopside using the27Al(p,γ)28Si nuclear reaction: preliminary results

Abstract We have made a first determination of the diffusion coefficient D of Al in diopside, via a nuclear microanalysis technique: proton energy scanning using the 992 keV resonance of 27 Al(p, γ ) 28 Si. We find D = (0.32 ± 0.07) × 10 −16 cm 2 /s at T = 1180 °C, which is the mean value of two experiments.

Oxygen and silicon self-diffusion in natural olivine at T = 1300°C

Abstract Oxygen and silicon self-diffusion in natural olivine single crystals (Mg 0.89 Fe 0.11 ) 2 SiO 4 from San Carlos, Arizona, have been measured for the first time at T = 1300°C in controlled oxygen partial pressure pO 2 ranging from 10 −4 to 10 Pa. Polished and chemically-etched specimens were heated for several hours in a gas mixture H 2 /CO 2 or H 2 /H 2 18 O. The latter gas mixture provides both the controlled pO 2 and the isotopic reservoir for the 18 O diffusion across the gas-solid interface. For 30 Si diffusion, a thin layer of isotopic forsterite Mg 2 30 SiO 4 (few hundreds of angstroms) was deposited onto the olivine surface. Diffusion profiles for oxygen and silicon were determined using the nuclear reaction 18 O(p, α ) 15 N and Rutherford back-scattering of 2 MeV α particles, respectively. The diffusion coefficients are D ox = 10 −18 ± 0.6 m 2 s −1 for oxygen and D Si = 10 −20 m 2 s −1 for silicon. We conclude from these measurements on San Carlos olivine at T = 1300°C that: (1) Si is the slowest diffusing species in natural olivine, as it is in forsterite, and (2) 30 Si and 18 O diffuse 30 to 200 times faster in olivine than in forsterite.

Nuclear microanalysis : a powerful tool for measuring low atomic diffusivity with mineralogical applications

A knowledge of the diffusion coefficients of the major atomic species in minerals is crucial to the understanding of the deformation mechanisms of rocks, and the calculation of their chemical kinetic behavior. Examples of diffusion-controlled properties include high-temperature creep (silicon diffusion is rate controlling in olivine, Jaoul et al, 1981), the kinetics of subsolidus reactions between minerals (the rate of growth of olivine between an “Si-poor-Fe, Mg-rich” phase like a spinel and an “Si-rich” enstatite is controlled by oxygen diffusion across the growing phase, Borchardt et al., 1979), and the re-equilibration of ion-exchange geothermometers during cooling (e.g., Lasaga, 1983; Ganguly and Saxena, 1987). Diffusion coefficients of interest in rock-forming minerals are sufficiently rapid in many cases to be measurable by conventional experimental techniques for the P-T range of geological interest, some of which have been discussed elsewhere within this volume. However, several diffusion processes of geological interest are too slow to be measured experimentally by the conventional techniques, and thus require high-resolution microanalysis of the diffusion profiles.

Thin-film growth of Sn on Cu(100)

Abstract The deposition of Sn on a Cu(100) surface has been investigated as a function of layer thickness, deposition temperature and subsequent anneal treatment, using a combination of RBS/channeling, LEED and Auger spectroscopy measurements. No evidence of pseudomorphic Sn growth could be detected. At Sn coverages up to about one monolayer, RBS/channeling data indicate that Sn atoms displace a comparable number of Cu atoms from their regular lattice sites, even at the lowest (170 K) deposition temperature studied. LEED studies show evidence of two-dimensional commensurable phase formation whose structure depends strongly on anneal temperature and Sn coverage. Copper-rich phases such as the ϵ-phase (Cu 3 Sn) are not observed at submonolayer Sn coverage, even after a 525 K anneal treatment. Thicker Sn layers exhibit two major anneal stages: formation of the η′-phase (Cu 6 Sn 5 ) around 265 K and its subsequent conversion into the ϵ-phase (Cu 3 Sn) around 420 K. An isochronal anneal measurement yielded activation energies of 0.65 ± 0.05 and 1.07 ± 0.08 eV for interdiffusion of Sn and Cu in the η′- and ϵ-phases, respectively. RBS/channeling data indicate that the resulting η′-phase is partially (10%–20%) aligned with the Cu(100) substrate. No preferential orientation was observed for the ϵ-phase.

Nuclear microanalysis using MeV carbon ion backscattering usefulness and applications.

The amplitude-energy relationships for surface barrier detectors were measured for4He and12C particles, as well as the corresponding energy resolutions. It is shown that the use of12C beams presents no marked advantage for increasing mass or depth resolution. On the other hand pile-up phenomena are drastically reduced by using12C backscattering. Applications are shown to the determination of trace amounts of Sb or Yb near the surface of iron. Gold contaminations of silicon surfaces were precisely measured within minutes down to 5·1011 gold atom/cm2, the limiting sensitivity being of the order of 1010 atom/cm2 for traces of heavy elements, such as Au, Hg, Pb, etc. Sensitivities for lighter elements are discussed.

Oscillating trajectories in planar channeling studied by backscattering from iron crystals

Abstract Backscattering experiments with 1.9 MeV helium ions were performed to study the oscillating trajectories of particles in planar channels of iron crystals. Strong maxima in the planar aligned spectra were observed. A stochastic model yields a good fit to the experimental results.

Complementary use of microanalysis by the direct observation of nuclear reactions and of backscattering induced by charged particles

Techniques are described which combine the use of nuclear reactions and of backscattering to obtain analytical results which would be difficult or impossible to reach using one of these methods only. The principles of stoichiometry determination by plateau height analysis are developed both for backscattering and for narrow resonances of nuclear reactions. Examples of applications are given to the determination of the composition of various thin films of aluminium and silicon oxides, silicon nitrides and calcium fluorides. The analysis of samples smaller than the beam, using backscattered particle monitoring, is presented.

Search for internal oxidation in rare earth-implanted iron☆

Abstract The possibility of “internal oxidation” in Yb-implanted iron is studied via 18 O tracing experiments. For a 400 keV Yb-implantation in iron single crystals, no oxygen diffusion occurs at the Yb depth under implantation or annealing up to 520°C.

Temper embrittlement and intergranular segregation of antimony: A quantitative analysis performed with the backscattering of energetic ions

The intergranular segregation of antimony associated with temper embrittlement in a low carbon manganese steel was quantitatively studied through the backscattering of MeV12C12+ and1214N12+ ions. The principles of the technique and its application to interface segregation problems are briefly explained and its main advantages discussed. The influence of various heat treatments was investigated and shown to strongly influence the segregation taking place in the α field. Segregation could not be detected in the γ field. The kinetics of the phenomenon in the critical range (400° to 600°C) is described. The role of the micro-structure was studied and it is shown that segregation does not occur only at the previous austenitic grain boundaries but at all the disordered high angle boundaries of the structure. The grain boundary Sb content after a reversion and a resegregation treatment was also studied. The results are interpreted in terms of a reversible type of segregation taking place entirely in the α phase.