Compositional analysis with atomic column spatial resolution by 5th-order aberration-corrected scanning transmission electron microscopy.
ABSTRACT We show in this article that it is possible to obtain elemental compositional maps and profiles with atomic-column resolution across an InxGa1-xAs multilayer structure from 5th-order aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The compositional profiles obtained from the analysis of HAADF-STEM images describe accurately the distribution of In in the studied multilayer in good agreement with Muraki's segregation model [Muraki, K., Fukatsu, S., Shiraki, Y. & Ito, R. (1992). Surface segregation of In atoms during molecular beam epitaxy and its influence on the energy levels in InGaAs/GaAs quantums wells. Appl Phys Lett 61, 557-559].
SourceAvailable from: Faebian Bastiman[Show abstract] [Hide abstract]
ABSTRACT: The distribution of bismuth in InAs1-xBix/GaAs quantum dots is analyzed by atomic-column resolution electron microscopy and imaging simulation techniques. A random Bi distribution is measured in the case of <0.03 ML/s Bi flux during the InAs growth with no significant variations in the shape or size of quantum dots, resulting in a low redshift and the degradation of the photoluminescence. However, for a 0.06 ML/s Bi flux the lateral indium segregation into the quantum dots is enhanced and Bi is incorporated inside them. As a result, a strong redshift and an increase of the peak intensity are found in this sample.Applied Physics Express 04/2013; 6(4):042103. DOI:10.7567/APEX.6.042103 · 2.73 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: The introduction of semiconductor and metallic nanostructures in photovoltaic materials is an active and promising area of development. This is due to the existence of several characteristics of nanostructures that improve the functionality of photovoltaic materials, for example by an enhancement of efficiency in solar cells, an increase of collected sun light and by the use of up- and down-converters to change the energy of incident photons. Nanostructures for solar cells offer, in comparison with single junction solar cells, new photovoltaic mechanisms for transforming sun light energy into electrical energy. A critical issue to understand the behavior of nanostructures based solar cells is to know their structural characteristics (size, shape, strain, distribution and composition) at nanoscale. In addition to this, the knowledge of the processes of nucleation, segregation and intermixing in nanostructures at nanoscale, and in some cases to atomic scale, is another important point to improve their design. This communication reviews our contribution toward the understanding of these issues and present some prospective studies and experiments in this context, by the use and development of methods based in aberration-corrected scanning transmission electron microscopy, high resolution electron microscopy and other complementary techniques. These methods are applied to several semiconductor nanostructures for intermediate band solar cells and some prospective results are presented in relation to their potential use for nanostructured thin film solar cells. We also present a method to prepare special samples to correlate, in individual or some few nanostructures, high resolution structural properties with other functional properties for the better design of photovoltaic materials. The nanostructures studied by aberration-corrected scanning transmission electron microscopy that are reviewed in this paper consist of III-V quantum dots and wires, silicon wires and strain- compensated stacked nanostructures grown by epitaxial techniques.Photovoltaic Specialists Conference (PVSC), 2011 37th IEEE; 01/2011
[Show abstract] [Hide abstract]
ABSTRACT: In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200kV. Structural damage of the MoS2 sheets has been controlled at 80kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron-matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers.Ultramicroscopy 06/2014; 146C:33-38. DOI:10.1016/j.ultramic.2014.05.004 · 2.75 Impact Factor