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In this paper atom probe tomography is used to explore early stage clustering in aluminum alloys. Two novel concepts for a modification of clustering are discussed. Control of early stage clustering is welcome from an application point of view since clustering deteriorates strength evolution during the industrial heat treatment of the important class of Al-Mg-Si precipitation-hardenable alloys. Nanoscale early stage clusters are very diffcult to observe and atom probe tomography is the best technique to visualize and chemically measure Si or Mg-containing clusters in aluminum alloys. Restrictions remain in achieving the ultimate quantification of such small solute aggregates by atom probe tomography, such as detection efficiency, local magnification effects, surface migration of solute atoms, and unresolved issues with the reconstruction procedure. Here we investigate one of these restricting effects, namely the migration of solute atoms during atom probe tomography measurements. In particular Si is found to be preferentially localized or absent at certain crystallographic poles in aluminum, which derogates the experimental results gained from atom probe tomography studies of clustering in Si-containing aluminum alloys. This artifact is investigated for different specimen temperatures, detection rates and pulse fractions during atom probe tomography measurements. Optimal strategies to analyze small-scale solute clusters in Si-containing aluminum alloys are presented. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) has been used to study InxGa1-xAs quantum dots buried in GaAs. The dots have an average base width of 16.1±1.1 nm and height of 3.5±0.3 nm, but a wide range of sizes. APT composition profiles across the dots are similar to a previous study by cross-sectional scanning transmission electron microscopy, but show significant gallium incorporation (average x=0.22±0.01). The direct three-dimensional nature of the APT data also reveals the complex spatial distribution of indium within the dots. Data such as these are vital for optimizing the performance of quantum dot materials and devices. [ABSTRACT FROM AUTHOR]

Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Standard atom probe tomography spatial reconstruction techniques have been reasonably successful in reproducing single crystal datasets. However, artefacts persist in the reconstructions that can be attributed to the incorrect assumption of a spherical evaporation surface. Using simulated and experimental field evaporation, we examine the expected shape of the evaporating surface and propose the use of a variable point projection position to mitigate to some degree these reconstruction artefacts. We show initial results from an implementation of a variable projection position, illustrating the effect on simulated and experimental data, while still maintaining a spherical projection surface. Specimen shapes during evaporation of model structures with interfaces between regions of low- and high-evaporation-field material are presented. Use of two-and three-dimensional projection-point maps in the reconstruction of more complicated datasets is discussed., (© 2010 The Authors Journal of Microscopy © 2010 Royal Microscopical Society.)

A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the (13)C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this paper we present depth profiles of a high-k layer consisting of HfO(2) with an embedded sub-nm thick ZrO(2) layer obtained with atom probe tomography (APT). In order to determine suitable measurement parameters for reliable, reproducible, and quantitative analysis, we have investigated the influence of the laser energy and the specimen temperature on the resulting elemental composition. In addition we devise a procedure for local background subtraction both for the composition and the depth scale that is crucial for gaining reproducible results. We find that the composition of the high-k material remains unaffected even for extreme laser energies and base temperatures, while higher laser energies lead to an accumulation of silicon at the upper interface of the high-k layer. Furthermore we show that APT is capable of providing sub-nm depth resolution for high-k materials with high reproducibility, good compositional accuracy, and high measurement yield., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A precipitation hardened maraging TRIP steel was analyzed using a pulsed laser atom probe. The laser pulse energy was varied from 0.3 to 1.9 nJ to study its effect on the measured chemical compositions and spatial resolution. Compositional analyses using proximity histograms did not show any significant variations in the average matrix and precipitate compositions. The only remarkable change in the atom probe data was a decrease in the ++/+ charge state ratios of the elements. The values of the evaporation field used for the reconstructions exhibit a linear dependence on the laser pulse energy. The adjustment of the evaporation fields used in the reconstructions for different laser pulse energies was based on the correlation of the obtained cluster shapes to the TEM observations. No influence of laser pulse energy on chemical composition of the precipitates and on the chemical sharpness of their interfaces was detected., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Atom Probe Tomography (APT) consists of analyzing a needle-shaped specimen on an atom-by-atom basis. In recent years, instruments have become commercially available, enabling the sequential analysis of the same specimen in both laser- and voltage-pulsed modes. In this contribution, a comparison of field evaporated end-forms as a function of the voltage and laser power is presented for silicon. Electron microscopy is utilized for visual inspection of the final tip end-forms. The field of evaporation for silicon is calculated based on these radius measurements for voltage and laser pulsing. Electron microscopy and analysis of the atom probe data show that the specimen end-forms for both pulsing modes can be different. We have observed two effects on the shape of a field-ion emitter when irradiated by a focused laser beam. One is a change in the 3-dimensional topology of the emitter due to different crystallographic orientations. Secondly, exposure to focused laser beam from one side may lead to a non-hemispherical tip shape especially when reasonably high laser energy is utilized. For comparison purposes to the laser mode, the voltage pulse evaporated tip end form is also analyzed for different specimen temperatures. Consequently, evaporation fields are calculated for different temperatures and laser conditions for silicon.