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Team leader : Lorenzo Rigutti
Team members : L. Rigutti (MCF), W. Lefebvre (PR), R. Lardé (MCF), I. Blum (IR)
The team's quest for the ultimate performance of the atomic probe is hampered by the intrinsic physical limitations of the technique. The control of the laser illumination is dependent on both the material of interest and the shape of the sample. It becomes technically difficult to ensure optimal control without precise knowledge of geometric, structural, and/or chemical information. Image reconstruction is faced with the same dilemma, it is necessary to know the sample to reconstruct it correctly. In order to overcome these limitations, the scientific instrumentation team has launched several innovative projects coupling APT to other techniques and advanced microscopies.
TEM-APT coupling
The coupling of tomographic atom probe analysis and electronic imaging on the same sample can have several objectives: i) to improve tomographic atom probe reconstructions (by determining the geometrical input parameters of the reconstruction algorithm); ii) to produce a more complete characterization of a nano-object (by adding chemical, structural information...); iii) to design a new instrument exceeding the current potentialities of the tomographic atomic probe
microPL - APT coupling
Another way to improve the instrument is developed in the team. Part of the activities of the ERIS team is developed around the combination of optical spectroscopy techniques and APT assisted by laser pulse. The medium term objective of this research activity is to develop a Laser Pulse Assisted Atom Probe including a micro-photoluminescence spectroscopy (µPL) bench. This coupled approach aims at studying the radiation-matter interaction taking place during a APT experiment in an original way, in particular thanks to the information contained in the photoluminescence and extinction spectra of the field emission peaks illuminated by the same laser used to trigger the ion evaporation. The possibility to study the photoluminescence of a nano-object as it is evaporated in APT will allow, for example, to obtain spectral profiles giving access to the signature of a single emitter in systems containing several emitters (e.g. quantum boxes), or how the optical properties of a single emitter vary as it gradually evaporates.
These preparatory studies have already led to striking results, such as the one illustrated, where an InGaN/GaN quantum well system extracted from a semiconductor microfilm was analyzed in succession by µPL, high-resolution scanning transmission electron microscopy (HR-STEM) and APT. This system constitutes the active region of the III-N based light-emitting diodes and has thus a considerable technological importance. The set of measurements allowed to explain the influence of the structure of the quantum wells - in terms of crystal symmetry, distribution of the alloy atoms composing the quantum wells, and presence of extended defects - on the optoelectronic properties of the studied systems. For the wealth of information obtained, this original correlative microscopy approach opens up unprecedented possibilities for the study of the relationship between structure and optics in systems such as quantum wells and quantum boxes, with potential openings to functional materials of low dimensionality.
These preparatory studies have already led to landmark results where an InGaN/GaNext quantum well system from a semiconductor microfilm has been analyzed in succession by µPL, high resolution scanning transmission electron microscopy (HR-STEM) and APT. This system constitutes the active region of the III-N based light emitting diodes and thus has a considerable technological importance. The set of measurements allowed to explain the influence of the structure of the quantum wells - in terms of crystal symmetry, distribution of the alloy atoms composing the quantum wells, and presence of extended defects - on the optoelectronic properties of the studied systems. For the wealth of information obtained, this original correlative microscopy approach opens unprecedented possibilities for the study of the relationship between structure and optics in systems such as quantum wells and quantum boxes, with potential openings to functional materials of low dimensionality.
FIM-APT coupling
A better understanding of the aging mechanisms of materials requires accurate experimental data on the concentration and spatial distribution of crystalline defects (point defects and extended defects) as well as on their interactions with their atomic environments. Although indirect observation techniques of point defects have existed for several years, there is currently no routine tool to quantify and analyze their spatial distributions in 3D with atomic resolution. The development of such a tool would therefore constitute a major advance for the study of defects in materials at the atomic scale. The study and modeling of aging mechanisms in the presence of a high concentration of defects is today an important research axis considering the industrial interest that it represents. Field effect ion microscopy (FIM) appears as a tool of choice to develop a 3D imaging technique of point defects and clusters of defects in metals. It allows to observe the surface of a sample and its defects at the atomic scale. Moreover, the electric field at the surface of the tip evaporates the surface atoms of the sample, one by one. To take full advantage of the potential presented by ion microcopy, GPM is developing the 3D FIM. Preliminary studies conducted at GPM and by other groups have shown that it is possible to visualize in 3D the crystal lattice in direct space as well as clusters of vacancies forming sub-nanometer cavities that are difficult to observe by other techniques
FEM-APT coupling
Advanced experiments are developed to enrich our understanding of the field emitter (the tip). Thus the physical nature (metallic, semi-metallic, 2D electron gas,...) of the surface of a material under field is a question that must be addressed to push the technique to its limits. Answers can be provided by the fine measurement of the energy of electrons emitted from the tip.