SuperSTEM STFC Daresbury Laboratories

Warrington, United Kingdom

SuperSTEM STFC Daresbury Laboratories

Warrington, United Kingdom
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Mancini L.,INSA Rouen | Moyon F.,INSA Rouen | Hernandez-Maldonado D.,INSA Rouen | Hernandez-Maldonado D.,SuperSTEM STFC Daresbury Laboratories | And 9 more authors.
Nano Letters | Year: 2017

The localization of carrier states in GaN/AlN self-assembled quantum dots (QDs) is studied by correlative multimicroscopy relying on microphotoluminescence, electron tomography, and atom probe tomography (APT). Optically active field emission tip specimens were prepared by focused ion beam from an epitaxial film containing a stack of quantum dot layers and analyzed with different techniques applied subsequently on the same tip. The transition energies of single QDs were calculated in the framework of a 6-bands k.p model on the basis of APT and scanning transmission electron microscopy characterization showing that a good agreement between experimental and calculated energies can be obtained, overcoming the limitations of both techniques. The results indicate that holes effectively localize at interface fluctuations at the bottom of the QD, decreasing the extent of the wave function and the band-to-band transition energy. They also represent an important step toward the correlation of the three-dimensional atomic scale structural information with the optical properties of single light emitters based on quantum confinement. © 2017 American Chemical Society.


Mancini L.,CNRS Material Physics Group | Hernandez-Maldonado D.,CNRS Material Physics Group | Hernandez-Maldonado D.,SuperSTEM STFC Daresbury Laboratories | Lefebvre W.,CNRS Material Physics Group | And 7 more authors.
Applied Physics Letters | Year: 2016

The optical properties of m-plane InGaN/GaN quantum wells grown on microwire sidewalls were investigated carrying out a correlative scanning transmission electron microscopy (STEM), atom probe tomography (APT), and micro-photoluminescence study applied on single nanoscale field-emission tips obtained by a focused ion beam annular milling. Instead of assuming simple rectangular composition profiles, yielding misleading predictions for the optical transition energies, we can thus take into account actual compositional distributions and the presence of stacking faults (SFs). SFs were shown to be responsible for a lowering of the recombination energies of the order of 0.1 eV with respect to those expected for defect-free quantum wells (QWs). Such energy reduction allows establishing a good correspondence between the transition energies observed by optical spectroscopy and those calculated on the basis of the QWs In measured composition and distribution assessed by STEM structural analysis and APT chemical mapping. © 2016 AIP Publishing LLC.


Rigutti L.,CNRS Material Physics Group | Mancini L.,CNRS Material Physics Group | Lefebvre W.,CNRS Material Physics Group | Houard J.,CNRS Material Physics Group | And 9 more authors.
Semiconductor Science and Technology | Year: 2016

Compositional disorder has important consequences on the optical properties of III-nitride ternary alloys. In AlGaN epilayers and AlGaN-based quantum heterostructures, the potential fluctuations induced by such disorder lead to the localisation of carriers at low temperature, which affects their transition energies. Using the correlations between micro-photoluminescence, scanning transmission electron microscopy and atom probe tomography we have analysed the optical behaviour of Al0.25Ga0.75N epilayers and that of GaN/AlGaN quantum wells, and reconstructed in three dimensions the distribution of chemical species with sub-nanometre spatial resolution. These composition maps served as the basis for the effective mass calculation of electrons and holes involved in radiative transitions. Good statistical predictions were subsequently obtained for the above-mentioned transition and localisation energies by establishing a link with their microstructural properties. © 2016 IOP Publishing Ltd.


Rigutti L.,CNRS Material Physics Group | Mancini L.,CNRS Material Physics Group | Hernandez-Maldonado D.,CNRS Material Physics Group | Hernandez-Maldonado D.,SuperSTEM STFC Daresbury Laboratories | And 7 more authors.
Journal of Applied Physics | Year: 2016

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. © 2016 AIP Publishing LLC.


PubMed | Acadia University, SuperSTEM STFC Daresbury Laboratories and CNRS Material Physics Group
Type: | Journal: Journal of microscopy | Year: 2016

In this paper, we propose an algorithm to obtain a three-dimensional reconstruction of a single nanoparticle based on the method of atom counting. The location of atoms in three dimensions has been successfully performed using simulations of high-angle-annular-dark-field images from only three zone-axis projections, [110], [310] and [211], for a face-centred cubic particle. These three orientations are typically accessible by low-tilt holders often used in high-performance scanning transmission electron microscopes.

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