18 research outputs found
The tomographic atom probe: A quantitative three-dimensional nanoanalytical instrument on an atomic scale
International audienceThe 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 10Ă10 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 a precision of a few tenths of a nanometer. The mass resolution M/ÎM (FWHM) of the apparatus is close to 200
The tomographic atom probe: A quantitative three-dimensional nanoanalytical instrument on an atomic scale
International audienceThe 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 10Ă10 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 a precision of a few tenths of a nanometer. The mass resolution M/ÎM (FWHM) of the apparatus is close to 200
Performance of the multiple events position sensitive detector used in the tomographic atom probe
International audienceThe tomographic atom probe (TAP) is the first 3D atom probe based around the use of a parallel position encoding system. This contribution will be focused on the implementation and the study of the TAP position sensitive detector. In the first part, it will be shown why this detector necessarily has to be sensitive to simultaneous events and the detector principle will be described. Then performance and limitations of the TAP will be discussed and related to the detector performance itself. Critical points such as spatial resolution, mass resolution or detection efficiency will be quantified. \textcopyright 1995
In-Situ Survey System of Resistive and Thermoelectric Properties of Either Pure or Mixed Materials in Thin Films Evaporated Under Ultra High Vacuum
The study of thermoelectric and resistive in situ
behaviours depending on temperature for thin films of either pure or composite
materials obtained under ultra-high vacuum, is very interesting, since they can
be used as strain gauges or superficial resistances. However, studies become
particularly difficult when the measurements generate very low-level electrical
signals. Indeed, these turn out to be hardly detectable because of the
perturbations brought by the experimental environment. The apparatus described
below allows for the measurement of resistance with a relative uncertainty of
, resistance variation with an absolute uncertainty of
2Â m and thermoelectric e.m.f. of about 2Â V. Films studied in the
laboratory generally exhibit resistances lower than 100Â and resistance
variations due to temperature variations of about a few ohms. So this device
has sufficient technical characteristics for our studies. It can be connected
to a PC, which allows for easy data collection and treatment.L'étude des comportements résistif et thermoélectrique
in situ en fonction de la température de couches minces de matériaux
simples ou composites obtenus en milieu raréfié s'avére intéressante en
vue d'applications comme jauge de contrainte ou résistance superficielle mais
particuliÚrement délicate lorsque les mesures donnent naissance à des
signaux Ă©lectriques de trĂšs faible amplitude. Ces derniers deviennent en
effet difficilement décelables en raison des perturbations apportées par
l'environnement expérimental. Le systÚme qui est décrit ici permet de
mesurer des résistances avec une certitude relative de et
d'apprécier des variations de résistance de 2 m et des f.e.m.
thermoélectriques de l'ordre de 2 V. Les couches étudiées au
laboratoire prĂ©sentent gĂ©nĂ©ralement des rĂ©sistances infĂ©rieures Ă
100 et des variations de résistance dues aux variations de
température de l'ordre de quelques . Le dispositif de mesure
présente donc des caractéristiques techniques suffisantes pour nos
études. Connecté à un PC il permet l'acquisition des données et un
traitement rapide
The Rouen energy-compensated atom probe
International audienceThe 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. \textcopyright 1994
Performance of the multiple events position sensitive detector used in the tomographic atom probe
International audienceThe tomographic atom probe (TAP) is the first 3D atom probe based around the use of a parallel position encoding system. This contribution will be focused on the implementation and the study of the TAP position sensitive detector. In the first part, it will be shown why this detector necessarily has to be sensitive to simultaneous events and the detector principle will be described. Then performance and limitations of the TAP will be discussed and related to the detector performance itself. Critical points such as spatial resolution, mass resolution or detection efficiency will be quantified. \textcopyright 1995
The Rouen energy-compensated atom probe
International audienceThe 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. \textcopyright 1994
An atom probe for three-dimensional tomography
International audienceELECTRIC-field-induced evaporation of ions from a needle-like surface, and their subsequent identification by time-of-flight mass spectrometry, forms the basis of the atom-probe technique1. This has proved to be a powerful analytical tool2,3, permitting the quantitative determination of material composition in a small selected region of the surface (depths of 1â5 nm) with single-layer resolution. Positional information for the atoms within each layer is lost, however. In contrast, the field-ion microscope3 provides atomic-resolution images of surfaces, but without information about the nature of the atoms. Several attempts have been made to combine these two techniques by extending the time-of-flight measurement into two dimensions, but they have been limited by their inability to identify all chemical species4 or to combine spatial and temporal information for multiple events5, especially for ions with very similar mass-to-charge ratios6. Here we make use of a recently developed7 multiple-impact detector to construct a position-sensitive atom probe with sufficiently high temporal resolution (of the order of 10 ns) to avoid these earlier problems; thus, reliable composition and position data can be obtained at the same time. We illustrate the performance of this instrument by imaging the three-dimensional distribution of chemical heterogeneities in a nickel-based alloy on a near-atomic scale
TRANSMISSIBLE ENTERITIS IN YOUNG GUINEA FOWL
International audienc