F. De Geuser

Publications (11)17.04 Total impact

• Article: Atom probe tomography and transmission electron microscopy characterisation of precipitation in an Al-Cu-Li-Mg-Ag alloy.

  B Gault, F de Geuser, L Bourgeois, B M Gabble, S P Ringer, B C Muddle
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  ABSTRACT: State-of-the art atom probe tomography (APT) combined with transmission electron microscopy (TEM) were used to investigate the microstructure at different stages of the ageing process of an alloy of composition (at%) Al-1.68%Cu-4.62%Li-0.33%Mg-0.1%Ag. These alloys were shown to exhibit a complex microstructure of T(1) plates and several metastable phases, including θ' and S. We will highlight the early stages of clustering, precipitate interactions and possible solute segregation at the matrix/precipitate interfaces and detail the chemical composition of the different phases.
  Ultramicroscopy 12/2010; 111(6):683-9. · 2.47 Impact Factor
• Article: Advances in the reconstruction of atom probe tomography data.

  B Gault, D Haley, F de Geuser, M P Moody, E A Marquis, D J Larson, B P Geiser
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  ABSTRACT: Key to the integrity of atom probe microanalysis, the tomographic reconstruction is built atom by atom following a simplistic protocol established for previous generations of instruments. In this paper, after a short review of the main reconstruction protocols, we describe recent improvements originating from the use of exact formulae enabling significant reduction of spatial distortions, especially near the edges of the reconstruction. We also show how predictive values for the reconstruction parameters can be derived from electrostatic simulations, and finally introduce parameters varying throughout the analysis.
  Ultramicroscopy 11/2010; 111(6):448-57. · 2.47 Impact Factor
• Article: Determination of matrix composition based on solute-solute nearest-neighbor distances in atom probe tomography.

  F De Geuser, W Lefebvre
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  ABSTRACT: In this study, we propose a fast automatic method providing the matrix concentration in an atom probe tomography (APT) data set containing two phases or more. The principle of this method relies on the calculation of the relative amount of isolated solute atoms (i.e., not surrounded by a similar solute atom) as a function of a distance d in the APT reconstruction. Simulated data sets have been generated to test the robustness of this new tool and demonstrate that rapid and reproducible results can be obtained without the need of any user input parameter. The method has then been successfully applied to a ternary Al-Zn-Mg alloy containing a fine dispersion of hardening precipitates. The relevance of this method for direct estimation of matrix concentration is discussed and compared with the existing methodologies. Microsc. Res. Tech., 2010. (c) 2010 Wiley-Liss, Inc.
  Microscopy Research and Technique 07/2010; · 1.79 Impact Factor
• Source

  Available from: Didier Blavette

  Article: An improved reconstruction procedure for the correction of local magnification effects in three-dimensional atom-probe

  F. De Geuser, W. Lefebvre, F Danoix, F Vurpillot, B. Forbord, D Blavette
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  ABSTRACT: A new 3DAP reconstruction procedure is proposed that accounts for the evaporation field of a secondary phase. It applies the existing cluster selection software to identify the atoms of the second phase and, subsequently, an iterative algorithm to homogenise the volume laterally. This Procedure, easily implementable on existing reconstruction software, has been applied successfully on simulated and real 3DAP analyses.
  07/2009;
• Source

  Available from: Oana Cojocaru-Mirédin

  Article: Clustering and nearest neighbour distances in atom-probe tomography.

  T Philippe, F De Geuser, S Duguay, W Lefebvre, O Cojocaru-Mirédin, G Da Costa, D Blavette
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  ABSTRACT: The measurement of chemical composition of tiny clusters is a tricky problem in both atom-probe tomography experiments and atomic simulations. A new approach relying on the distribution of the first nearest neighbour (1NN) distances between solute atoms in the 3D space composed of A and B atoms was developed. This new approach, the 1NN method, is shown to be an elegant way to get the composition of tiny B-enriched clusters embedded in a random AB solid solution. The theoretical statistical distributions of first neighbour distances P(r) for both random solid solution and solute-enriched clusters finely dispersed in a depleted matrix are established. It is shown that the most probable distance of P(r) gives directly the phase composition. Applications of this model to both one-phase SiGe alloy and boron-doped silicon containing small clusters indicate that this new approach is quite reliable.
  Ultramicroscopy 07/2009; 109(10):1304-9. · 2.47 Impact Factor
• Article: 3DAP measurements of Al content in different types of precipitates in aluminium alloys

  W. Lefebvre, F. Danoix, G. Da Costa, F. De Geuser, H. Hallem, A. Deschamps, M. Dumont
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  ABSTRACT: Three-dimensional atom probe and field ion microscopy have been used to determine the composition of precipitates formed in several types of aluminium-based alloys. Special attention has been paid to local magnification artefacts, which are often suspected to strongly disrupt the precipitates' apparent composition. The charge state of Al ions has been used to identify the nature of precipitates (lower or higher evaporation field than the matrix) and also to determine the origin of Al ions observed in 3D reconstructions. The use of a cluster identification method, which allows erosion concentration profiles to be drawn, has revealed the importance of trajectory overlaps in the measurement of the precipitates' composition. By applying this method to low-evaporation-field precipitates in a 7XXX alloy, good agreement was found between atom probe measurements and observations in transmission electron microscopy and small angles X-ray scattering. Copyright © 2007 John Wiley & Sons, Ltd.
  Surface and Interface Analysis 01/2007; 39(2‐3):206 - 212. · 1.18 Impact Factor
• Article: Atom Probe Tomography II. The Precipitation in Al Base Alloys

  F. De Geuser, W. Lefebvre, P. Auger, F. Danoix, A. Bigot, D. Blavette
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  ABSTRACT: This paper presents two illustrations of the study of phase separation in Al-based alloys by means of tomographic atom probe. In an AlMgSi alloy, calculations of pair correlation functions have revealed that the nature of solute short range order differs from a pre-aged specimen to a non-pre-aged specimen. This results in different responses to aged hardening treatments. Concerning Al3(Zr,Sc)-type dispersoids observed in another Al-based alloy, they are found to display a core-shell structure wherein Zr is mainly present in the dispersoids periphery. This duplex structure is likely to explain the relative stability of Al3(Zr,Sc) dispersoids.
  Advanced Engineering Materials 12/2006; 8(12):1206 - 1209. · 1.18 Impact Factor
• Article: Investigation of an oxide layer by femtosecond-laser-assisted atom probe tomography

  B. Gault, A. Menand, F. de Geuser, B. Deconihout, R. Danoix
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  ABSTRACT: In this letter, we report results obtained from the atom-probe tomography (APT) analysis of an oxide layer developed on a pure iron specimen under low pressure of oxygen. These specimens are generally fragile, and hard to analyze in APT. Here we show that by the use of femtosecond laser pulses, the oxide layer could be field evaporated atom by atom allowing its chemical identification at the atomic scale. The evidence of iron atomic planes through the whole oxide layer suggests that oxygen atoms diffuse though the oxide layer during the first stages of the oxidation process.
  Applied Physics Letters 04/2006; · 3.84 Impact Factor
• Article: Application of Fourier transform and autocorrelation to cluster identification in the three-dimensional atom probe.

  F Vurpillot, F De Geuser, G Da Costa, D Blavette
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  ABSTRACT: Because of the increasing number of collected atoms (up to millions) in the three-dimensional atom probe, derivation of chemical or structural information from the direct observation of three-dimensional images is becoming more and more difficult. New data analysis tools are thus required. Application of a discrete Fourier transform algorithm to three-dimensional atom probe datasets provides information that is not easily accessible in real space. Derivation of mean particle size from Fourier intensities or from three-dimensional autocorrelation is an example. These powerful methods can be used to detect and image nano-segregations. Using three-dimensional 'bright-field' imaging, single nano-segregations were isolated from the surrounding matrix of an iron-copper alloy. Measurement of the inner concentration within clusters is, therefore, straightforward. Theoretical aspects related to filtering in reciprocal space are developed.
  Journal of Microscopy 01/2005; 216(Pt 3):234-40. · 1.63 Impact Factor
• Source

  Available from: Didier Blavette

  Article: 3D atom probe study of solute atoms clustering during natural ageing and pre-ageing of an Al-Mg-Si alloy

  F. De Geuser, W. Lefebvre, D Blavette
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  ABSTRACT: The pair-correlation function applied to 3D Atom Probe reconstructed volumes has been used to study the influence of a pre-ageing treatment (363 K) on the early stages of precipitation at 458K in an Al-Mg-Si 6016 alloy. Mg-Si short-range positive pair correlation (clustering) is shown to form after a pre-ageing treatment. The hetero-atomic clusters are thought to act as preferential nucleation sites and lead to a finer dispersion of precipitates after ageing.
• Source

  Available from: archives-ouvertes.fr

  Article: Correlated field evaporation as seen by atom probe tomography

  F. De Geuser, B Gault, A. Bostel, F Vurpillot
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  ABSTRACT: We have studied the correlation between field evaporated atoms during an atom probe tomography experiment. The evaporated atoms have been shown to be highly correlated both in time and in space. This correlation can be explained by the dynamic distribution of the electric field at the surface of the sample. The evaporation sequence follows the distribution of zones where the electric field intensity is higher. The distance of correlation between successively evaporated atoms corresponds to the mean size of these zones and the time of correlation corresponds to the mean time necessary to evaporate the entire zone.