J.M. Sarrau

The tomographic atom probe: A quantitative three‐dimensional nanoanalytical instrument on an atomic scale

The physical architecture and the performance of a quantitative three‐dimensional atom probe recently constructed are described. The development of such an instrument relies on the design of a multi‐impact position sensitive detector. The multidetection system that we have developed is based on the use of a 10×10 anode array placed behind a two microchannel plate assembly in a chevron arrangement. The spread of charge between the microchannel plate and the multianode is used to derive the position of ion striking the detector. Spatial coordinates can be calculated for multiple and simultaneous time‐of‐flight events. The procedure used for the derivation of ion positions from charge measurements is given. Specific experiments were carried out in order to determine the intrinsic spatial resolution of the multidetector. Three‐dimensional reconstruction of two‐phase materials are provided and illustrate the performance of this new apparatus. The reconstructed images demonstrate that atoms are positioned with ...

Atom-probe microanalysis of a nickel-base superalloy

A FIM atom-probe has been used to investigate the phase compositions in a Nb-Mo bearing nickel based superalloy. The composition of γ′ precipitates in fully heat-treated conditions was found to vary with their mean sizes. The matrix analyses revealed the presence of fine secondary precipitates (30 to 100 Å) which occupy 10 pct of the overall volume of the material. The high spatial resolution of the atom-probe allowed the γ-γ′ interface characterization. Composition profiles show that the transition between the phases occurs within one interplanar spacing. Finally, a long range order study of the ordered γ′ phase has been performed. The analysis of the L12 type (Ni, X)3 (Al, Y) precipitates, made on an atomic plane-by-plane basis, shows how alloying elements substitute for Ni and Al in the γ′ sublattice. The observed results, expressed in terms of occupancy probabilities for both types of sites, indicate that Ti, Nb, and Mo preferentially occupy Al sites while Cr and Co substitute for Ni.

On the development of a 3D tomographic atom-probe

Abstract The development of a three-dimensional atom-probe relies on the design of a position sensitive detector. The multidetection system that we have developed is based on the use of a 10 × 10 anodes array placed behind two microchannel-plates assembly in a chevron arrangement. The spread of charge between MCP and the multianode is used to derive the position of ions striking the detector. Spatial coordinates can be calculated for multiple and simultaneous time-of-flight events. The procedure that we have used for the derivation of ions positions from charge measurement is given and preliminary results are described.

Performance of an energy compensated time-of-flight mass spectrometer

Abstract This paper describes the performance of an energy compensated time-of-flight atom probe. The compensating system is of the Poschenrieder type with a large acceptance angle. The mass resolution is measured as a function of the acceptance angle. The role of the fringe field correction electrodes is studied. The observed mass resolution is compared to that predicted by the second order Poschenrieder theory.

The Rouen energy-compensated atom probe

Abstract The energy-compensated atom probe developed in Rouen is based on the original instrument built in 1978. Since, several improvements were added. Some extensions, among which a Poschenrieder-type energy compensator and a spatial resolution controlling diaphragm, have been adapted to it. The main characteristics of this instrument are presented.