Structural properties of Ge/Si(001) nano-islands by diffraction anomalous fine structure and multiwavelength anomalous diffraction

8 pags, 6 figs, 2 tabsIn the present paper, we aim to show the interest of combining Multiwavelength Anomalous Diffraction (MAD) and Diffraction Anomalous Fine Structure (DAFS) spectroscopy, in grazing incidence, to obtain structural properties (composition, strain and atomic ordering) of semiconductor heterostructures and nanostructures. As an example we report on preliminary results obtained on a series of Ge/Si(001) nano-island samples: pyramides and domes on nominal and prepatterned surfaces. For free standing domes, it is shown that the Ge content strongly depends on the growth condition with a tendency to increase from the bottom to the top of the nano-islands. There is also some indication of atomic ordering in the upper part of the islands. For small, capped pyramids, we show that the Diffraction Anomalous Fine Structure spectroscopy is the unique non destructive method that allows to recover the actual Ge content, the in-plane and out-of-plane strain and to detect atomic ordering. © EDP Sciences and Springer 2009

Excitation Intensity Driven PL Shifts of SiGe Islands on Patterned and Planar Si(001) Substrates: Evidence for Ge-rich Dots in Islands

For randomly nucleated SiGe/Si(001) islands, a significantly stronger blue-shift of the PL spectra as a function of the excitation intensity is observed when compared to islands grown on patterned substrates side by side within the same run in a solid source molecular beam epitaxy chamber. We ascribe this different PL behavior to the much larger inhomogeneity of the Ge distribution in islands on planar substrates when compared to islands grown on pit-patterned ones, as observed previously. 3D band-structure calculations show that Ge-rich inclusions of approximately 5 nm diameter at the apex of the islands can account for the observed differences in the PL spectra. The existence of such inclusions can be regarded as a quantum dot in an island and is in agreement with recent nano-tomography experiments

Direct determination of strain and composition in InGaAs nano-islands using anomalous grazing incidence x-ray diffraction

International audienc

Unit cell structure of the wurtzite phase of GaP nanowires : X-ray diffraction studies and density functional theory calculations

We present structural characterization of the wurtzite crystal structure of GaP nanowires, which were recently shown to have a direct electronic band gap. The structural parameters of the wurtzite phase do consist of two lattice parameters and one internal degree of freedom, determining the Ga-P bond length along the c direction. Using density functional theory calculations, we study the influence of the internal degree of freedom on the band structure. By synchrotron x-ray diffraction studies near the Ga-K edge we determine the lattice parameters a = 3.8419 ° A and c = 6.3353 °A as well as the internal degree of freedom u = 0.37385 with high accuracy. We find that different Ga-P bond lengths are not equal, in contrast to the case in the zinc blende bulk phase. As a result, a spontaneous polarization is predicted for wurtzite GaP

Unit cell structure of the wurtzite phase of GaP nanowires : X-ray diffraction studies and density functional theory calculations

We present structural characterization of the wurtzite crystal structure of GaP nanowires, which were recently shown to have a direct electronic band gap. The structural parameters of the wurtzite phase do consist of two lattice parameters and one internal degree of freedom, determining the Ga-P bond length along the c direction. Using density functional theory calculations, we study the influence of the internal degree of freedom on the band structure. By synchrotron x-ray diffraction studies near the Ga-K edge we determine the lattice parameters a = 3.8419 ° A and c = 6.3353 °A as well as the internal degree of freedom u = 0.37385 with high accuracy. We find that different Ga-P bond lengths are not equal, in contrast to the case in the zinc blende bulk phase. As a result, a spontaneous polarization is predicted for wurtzite GaP

Microstrain distribution mapping on CuInSe2 thin films by means of electron backscatter diffraction, X ray diffraction, and Raman microspectroscopy

The investigation of the microstructure in functional, polycrystalline thin amp; 64257;lms is an important con tribution to the enhanced understanding of structure property relationships in corresponding devices. Linear and planar defects within individual grains may affect substantially the performance of the device. These defects are closely related to strain distributions. The present work compares electron and X ray diffraction as well as Raman microspectroscopy, which provide access to microstrain distributions within individual grains. CuInSe2 thin amp; 64257;lms for solar cells are used as a model system. High resolution electron backscatter diffraction and X ray microdiffraction as well as Raman microspectroscopy were applied for this comparison. Consistently, microstrain values were determined of the order of 10 4 by these three techniques. However, only electron backscatter diffraction, X ray microdiffraction exhibit sensitivities appropriate for mapping local strain changes at the submicrometer level within individual grains in polycrystalline material

Intergrowth Structure and Aluminium Zoning of a Zeolite ZSM-5 Crystal as Resolved by Synchrotron-Based Micro X-Ray Diffraction Imaging

Zeolites represent an important group of heterogeneous catalysts and are heavily used in the petrochemical and refining industries.[1] Since their discovery, zeolites with MFI topology, namely ZSM-5, have been utilized in a number of large-scale industrial applications. The unique combination of acidic properties and pore architecture[2] enabled their use as solid acid catalysts in the alkylation of arenes,[3] the oligomerization of light olefins,[4] and the methanol-to-hydrocarbon reaction.[5] The internal crystallographic architecture, microand mesoporosity, as well as the 3D distribution of Brønsted acid sites play a crucial role in the catalytic performance of zeolites

Using focused x-ray beams to investigate single nanostructures

International audienc