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The ternary semiconductor alloy Al0.25Ga0.75N has been analyzed by means of correlated photoluminescence spectroscopy and atom probe tomography (APT). We find that the composition measured by APT is strongly dependent on the surface electric field, leading to erroneous measurements of the alloy composition at high field, due to the different evaporation behaviors of Al and Ga atoms. After showing how a biased measurement of the alloy content leads to inaccurate predictions on the optical properties of the material, we develop a correction procedure which yields consistent transition and localization energies for the alloy photoluminescence. [ABSTRACT FROM AUTHOR]

Sputtered (TbCo2.5 25 nm/Fe 20 nm) multilayers have been analyzed by laser-assisted tomographic atom probe. It allowed us to perform three-dimensional reconstructions of the layers and to determine their composition at the atomic scale. From the concentration profiles inside the multilayer, we show that the diffused interfaces are not symmetric and that a stronger Fe-Co mixing is present at the top of the crystalline iron layers as compared to the top of amorphous TbCo layers. [ABSTRACT FROM AUTHOR]

Low temperature (675 °C) epitaxial in situ doped Si layers (As, 1.5 at. %) were analyzed by atom probe tomography (APT) to study clustering in a highly arsenic-doped silicon layer. The spatial distribution of As atoms in this layer was obtained by APT, and the distance distribution between first nearest neighbors between As atoms was studied. The result shows that the distribution of As atoms is nonhomogeneous, indicating clustering. Those clusters, homogeneously distributed in the volume, are found to be very small (a few atoms) with a high number density and contain more than 60% of the total number of As atoms. [ABSTRACT FROM AUTHOR]

Abstract: A model devoted to the modelling of the field evaporation of a tip is presented in this paper. The influence of length scales from the atomic scale to the macroscopic scale is taken into account in this approach. The evolution of the tip shape is modelled at the atomic scale in a three dimensional geometry with cylindrical symmetry. The projection law of ions is determined using a realistic representation of the tip geometry including the presence of electrodes in the surrounding area of the specimen. This realistic modelling gives a direct access to the voltage required to field evaporate, to the evolving magnification in the microscope and to the understanding of reconstruction artefacts when the presence of phases with different evaporation fields and/or different dielectric permittivity constants are modelled. This model has been applied to understand the field evaporation behaviour in bulk dielectric materials. In particular the role of the residual conductivity of dielectric materials is addressed. [Copyright &y& Elsevier]

We investigate the mechanisms of a laser-assisted atom probe tomography technique. In this method, a sub-wavelength tip is subjected both to a very strong static electric field and to a femtosecond laser pulse. As a result, ions are ejected from the tip one by one. By using femtosecond lasers, one can analyze not only metals but also semiconductors and dielectric materials. To better understand the ejection process, a numerical model is developed based on the drift-diffusion approach. The model accounts for such effects as field penetration, hole and electron movement, and laser absorption. For the given value of the dc field, a substantial band bending and an increase in hole density at the surface of the silicon tip are observed. This bending effect changes silicon absorption coefficient at the surface and significantly increases recombination time of laser-induced carriers. [ABSTRACT FROM AUTHOR]

Abstract: Data collected in atom probe tomography have to be carefully analysed in order to give reliable composition data accurately and precisely positioned in the probed volume. Indeed, the large analysed surfaces of recent instruments require reconstruction methods taking into account not only the tip geometry but also accurate knowledge of geometrical projection parameters. This is particularly crucial in the analysis of multilayers materials or planar interfaces. The current work presents a simulation model that enables extraction of the two main projection features as a function of the tip and atom probe instrumentation geometries. Conversely to standard assumptions, the image compression factor and the field factor vary significantly during the analysis. An improved reconstruction method taking into account the intrinsic shape of a sample containing planar features is proposed to overcome this shortcoming. [Copyright &y& Elsevier]

A tomographic atom probe (TAP) in which the atoms are field evaporated by means of femtosecond laser pulses has been designed. It is shown that the field evaporation is assisted by the laser field enhanced by the subwavelength dimensions of the specimen without any significant heating of the specimen. In addition, as compared with the conventional TAP, due to the very short duration of laser pulses, no spread in the energy of emitted ions is observed, leading to a very high mass resolution in a straight TAP in a wide angle configuration. At last, laser pulses can be used to bring the intense electric field required for the field evaporation on poor conductive materials such as intrinsic Si at low temperature. In this article, the performance of the laser TAP is described and illustrated through the investigation of metals, oxides, and silicon materials. [ABSTRACT FROM AUTHOR]

Investigation of wüstite (FeO), iron (Fe), and silicon (Si) specimens by infrared laser assisted three dimensional atom probe tomography shows evidence of confined surface absorption of the laser energy as the mechanism of laser assisted field evaporation for high band gap materials. The absorption region is shown to be located on the laser illumination side, close to the specimen apex. A simple model based on thermal diffusivity and spatial extent of the absorption region is derived and applied to the experimental results. The values of thermal diffusivity thus obtained are in good agreement with the published data. [ABSTRACT FROM AUTHOR]

Using laser assisted atom probe tomography, we investigate the surface recombination processes of a subwavelength Si tip illuminated by an ultrashort laser pulse under high electric field. In practice, by changing the laser wavelength, we demonstrate the presence of a very long electron-phonon relaxation time at the surface. It is experimentally shown that this behavior is common to indirect band gap semiconductors. Furthermore, a simple model is developed in this paper to explain laser wavelength dependence of our experimental results and estimate the surface recombination time. [ABSTRACT FROM AUTHOR]

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011. [ABSTRACT FROM PUBLISHER]

Abstract: This work presents an original method for cluster selection in Atom Probe Tomography designed to be applied to large datasets. It is based on the calculation of the Delaunay tessellation generated by the distribution of atoms of a selected element. It requires a single input parameter from the user. Furthermore, no prior knowledge of the material is needed. The sensitivity of the proposed Delaunay cluster selection is demonstrated by its application on simulated APT datasets. A strong advantage of the proposed methodology is that it is reinforced by the availability of an analytical model for the distribution of Delaunay cells circumspheres, which is used to control the accuracy of the cluster selection procedure. Another advantage of the Delaunay cluster selection is the direct calculation of a sharp envelope for each identified cluster or precipitate, which leads to the more appropriate morphology of the objects as they are reconstructed in the APT dataset. [Copyright &y& Elsevier]

The implantation profile of boron in silicon annealed at 600°C for 1h as given by laser-assisted wide-angle atom probe was found to be in good agreement with secondary ion mass spectrometry data. Numerous boron clusters in the form of tiny platelets (3–6nm diameter, 2nm thick) were identified and interpreted as boron interstitial clusters (BICs). These BICs contained on average 7at.% B with a core level that reaches 10at.%. [Copyright &y& Elsevier]

Abstract: In the interaction between ultrafast laser pulses and a field emitter both optical and thermal processes are involved. In this paper, these physical process, and their timescales, are experimentally explored. Simple models are proposed to explain the observed experimental behaviour, and the influence of various parameters are investigated. In the case of optical processes, it is shown that the optical field is greatly enhanced at the tip apex, and that field evaporation could be induced by an optical non-linear effect called optical rectification. In the case of thermal processes, it is shown that the temperature rise because of light absorption can be determined and that the cooling process of the tip surface can be studied by pump probe measurements. [Copyright &y& Elsevier]

Abstract: The structural and chemical properties of advanced nano-devices with a three-dimensional (3D) architecture have been studied at the nanometre scale. An original method has been used to characterize gate-all-around and tri-gate silicon nanowire transistor by combining electron tomography and atom probe tomography (APT). Results show that electron tomography is a well suited method to determine the morphological structure and the dimension variations of devices provided that the atomic number contrast is sufficient but without an absolute chemical identification. APT can map the 3D chemical distribution of the atoms in devices but suffers from strong distortions in the dimensions of the reconstructed volume. These may be corrected using a simple method based on atomic density correction and electron tomography data. Moreover, this combination is particularly useful in helping to understand the evaporation mechanisms and improve APT reconstructions. This paper demonstrated that a full 3D characterization of nano-devices requires the combination of both tomography techniques. [Copyright &y& Elsevier]

Highlights: [•] Overview/opinion on the topic of spatial reconstruction for atom probe tomography is provided. [•] The standard reconstruction methodology is discussed, including limitations and their causes. [•] Computational methods to simulate field evaporation processes are reviewed. [•] Reconstruction issues in the far and near field are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Abstract: FePt nanoclusters dispersed in a Cr matrix have been investigated by laser-assisted atom probe tomography. The results were analysed according to simulated evaporation experiments. Three–dimensional (3D) reconstructions reveal the presence of nanoclusters roughly spherical in shape, with a size in good agreement with previous transmission electron microscopy observations. Some clusters appear to be broken up after the evaporation process due to the fact that the Cr matrix has a lower evaporation field than Fe and Pt. It is thus shown that the observed FePt nanoclusters are chemically homogeneous. They contain Fe and Pt in equiatomic proportions, with no core–shell structure observed. [Copyright &y& Elsevier]