281 research outputs found
An improved reconstruction procedure for the correction of local magnification effects in three-dimensional atom-probe
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
Nanostructure and properties of a Cu-Cr composite processed by severe plastic deformation
A Cu-Cr composite was processed by severe plastic deformation to investigate
the role of interphase boundaries on the grain size reduction mechanisms. The
as-deformed material exhibits a grain size of only 20nm. This gives rise to a
dramatic increase of the hardness. Some deformation induced Cu super saturated
solid solutions were clearly exhibited and it is shown that they decrease the
hardness. The formation of such supersaturated solid solution and their
influence on the mechanical properties are discussed
Atom probe tomography spatial reconstruction: Status and directions
In this review we present an overview of the current atom probe tomography spatial data reconstruction paradigm, and explore some potential routes to improve the current methodology in order to yield a more accurate representation of nanoscale microstructure. Many of these potential improvement methods are directly tied to extensive application of advanced numerical methods, which are also very briefly reviewed. We have described effects resulting from the application of the standard model and then introduced several potential improvements, first in the far field, and, second, in the near field. The issues encountered in both cases are quite different but ultimately they combine to determine the spatial resolution of the technique
Reflections on the spatial performance of atom probe tomography in the analysis of atomic neighbourhoods
Atom probe tomography is often introduced as providing "atomic-scale" mapping
of the composition of materials and as such is often exploited to analyse
atomic neighbourhoods within a material. Yet quantifying the actual spatial
performance of the technique in a general case remains challenging, as they
depend on the material system being investigated as well as on the specimen's
geometry. Here, by using comparisons with field-ion microscopy experiments and
field-ion imaging and field evaporation simulations, we provide the basis for a
critical reflection on the spatial performance of atom probe tomography in the
analysis of pure metals, low alloyed systems and concentrated solid solutions
(i.e. akin to high-entropy alloys). The spatial resolution imposes strong
limitations on the possible interpretation of measured atomic neighbourhoods,
and directional neighbourhood analyses restricted to the depth are expected to
be more robust. We hope this work gets the community to reflect on its
practices, in the same way, it got us to reflect on our work.Comment: Submitted to Microscopy & Microanalysis to be part of the special
issue assocaited to the APT&M 2020 conferenc
Revealing atomic-scale vacancy-solute interaction in nickel
Imaging individual vacancies in solids and revealing their interactions with
solute atoms remains one of the frontiers in microscopy and microanalysis. Here
we study a creep-deformed binary Ni-2 at.% Ta alloy. Atom probe tomography
reveals a random distribution of Ta. Field ion microscopy, with contrast
interpretation supported by density-functional theory and time-of-flight mass
spectrometry, evidences a positive correlation of tantalum with vacancies. Our
results support solute-vacancy binding, which explains improvement in creep
resistance of Ta-containing Ni-based superalloys and helps guide future
material design strategies.Comment: Submitted to Physics Review Lette
Behavior of molecules and molecular ions near a field emitter
The cold emission of particles from surfaces under intense electric fields is a process which underpins a variety of applications including atom probe tomography (APT), an analytical microscopy technique with near-atomic spatial resolution. Increasingly relying on fast laser pulsing to trigger the emission, APT experiments often incorporate the detection of molecular ions emitted from the specimen, in particular from covalently or ionically bonded materials. Notably, it has been proposed that neutral molecules can also be emitted during this process. However, this remains a contentious issue. To investigate the validity of this hypothesis, a careful review of the literature is combined with the development of new methods to treat experimental APT data, the modeling of ion trajectories, and the application of density-functional theory simulations to derive molecular ion energetics. It is shown that the direct thermal emission of neutral molecules is extremely unlikely. However, neutrals can still be formed in the course of an APT experiment by dissociation of metastable molecular ions
A Photonic Atom Probe coupling 3D Atomic Scale Analysis with in situ Photoluminescence Spectroscopy
Laser enhanced field evaporation of surface atoms in Laser-assisted Atom
Probe Tomography (La-APT) can simultaneously excite phtotoluminescence in
semiconductor or insulating specimens. An atom probe equipped with appropriate
focalization and collection optics has been coupled with an in-situ
micro-Photoluminescence ({\mu}PL) bench that can be operated during APT
analysis. The Photonic Atom Probe instrument we have developped operates at
frequencies up to 500 kHz and is controlled by 150 fs laser pulses tunable in
energy in a large spectral range (spanning from deep UV to near IR). Micro-PL
spectroscopy is performed using a 320 mm focal length spectrometer equipped
with a CCD camera for time-integrated and with a streak camera for
time-resolved acquisitions. An exemple of application of this instrument on a
multi-quantum well oxide heterostructure sample illustrates the potential of
this new generation of tomographic atom probe.Comment: 22 pages, 4 figures. The following article has been accepted by the
Review of Scientific Instruments. After it is published, it will be found at
https://publishing.aip.org/resources/librarians/products/journals
Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires
GaAs/Al-GaAs core-shell nanowires fabricated by molecular beam epitaxy contain quantum confining structures susceptible of producing narrow photoluminescence (PL) and single photons. The nanoscale chemical mapping of these structures is analyzed in 3D by atom probe tomography (APT). The study allows us to confirm that Al atoms tend to segregate within the AlGaAs shells towards the vertices of the hexagons defining the nanowire cross section. We also find strong alloy fluctuations remaining AlGaAs shell, leading occasionally to the formation of quantum dots (QDs). The PL emission energies predicted in the framework of a 3D effective mass model for a QD analyzed by APT and the PL spectra measured on other nanowires from the same growth batch are consistent within the experimental uncertainties. (C) 2014 AIP Publishing LLC
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