ORCID Profile
0000-0003-2391-5943
Current Organisation
Empa, Swiss Federal Laboratories for Materials Science and Technology
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Publications
Analysis of edge threading dislocations b→=12〈110〉 in three dimensional Ge crystals grown on (001)-Si substrates
Publisher: AIP Publishing
Date: 31-08-2015
DOI: 10.1063/1.4929422
Abstract: Threading dislocations (TDs) in germanium (Ge) crystals epitaxially grown on a patterned (001)-silicon (Si) substrate are investigated using transmission electron microscopy (TEM) techniques. Analysis of dislocations performed on the Ge crystals reveals 60° and edge TDs with Burgers vector b→=12〈110〉. High-angle annular dark-field scanning TEM (HAADF-STEM) is used to observe the core of the edge TDs at atomic scale. Pairs of TDs with b→=12〈110〉 are present in the material running parallel at small distances between them (0.5–1.5 nm). The observation of such parallel dislocation pairs in Ge has not been documented before. The interaction between the edge dislocation pairs is obtained experimentally from the high-resolution HAADF-STEM images by applying geometrical phase analysis. The experimental strain maps are compared to analytical calculations based on the anisotropic elastic theory demonstrating a good match between them.
Strongly Confined CsPbBr3 Quantum Dots as Quantum Emitters and Building Blocks for Rhombic Superlattices
Publisher: American Chemical Society (ACS)
Date: 31-01-2023
Direct Imaging of Dopant Clustering in Metal–Oxide Nanoparticles
Publisher: American Chemical Society (ACS)
Date: 10-07-2012
DOI: 10.1021/NN3021212
Abstract: Dopant atoms are used to tailor the properties of materials. However, whether the desired effect is achieved through selective doping depends on the dopant distribution within the host material. The clustering of dopant atoms can have a deleterious effect on the achievable properties because a two-phase material is obtained instead of a homogeneous material. Thus, the examination of dopant fluctuations in nanodevices requires a reliable method to chemically probe in idual atoms within the host material. This is particularly challenging in the case of functionalized nanoparticles where the characteristic length scale of the particles demands the use of a high-spatial-resolution and high-sensitivity technique. Here we demonstrate a chemically sensitive atomic resolution imaging technique which delivers direct site-specific information on the dopant distribution in nanoparticles. We employ electron energy-loss spectroscopy imaging in a scanning transmission electron microscope combined with multivariate statistical analysis to map the distribution of Ba dopant atoms in SrTiO(3) nanoparticles. Our results provide direct evidence for clustering of the Ba dopants in the SrTiO(3) nanoparticles outlining a possible explanation for the presence of polar nanoregions in the Ba:SrTiO(3) system. The results we present constitute the first ex le of site-specific atomic resolution spectroscopy of foreign atoms in doped nanoparticles and suggest a general strategy to ascertain the spatial distribution of impurity atoms in nanocrystals and hence improve the performance of nanoparticle-based devices.
From plastic to elastic stress relaxation in highly mismatched SiGe/Si heterostructures
Publisher: Elsevier BV
Date: 08-2016
Enhancing elastic stress relaxation in SiGe/Si heterostructures by Si pillar necking
Publisher: AIP Publishing
Date: 31-10-2016
DOI: 10.1063/1.4966948
Abstract: We demonstrate that the elastic stress relaxation mechanism in micrometre-sized, highly mismatched heterostructures may be enhanced by employing patterned substrates in the form of necked pillars, resulting in a significant reduction of the dislocation density. Compositionally graded Si1−xGex crystals were grown by low energy plasma enhanced chemical vapour deposition, resulting in tens of micrometres tall, three-dimensional heterostructures. The patterned Si(001) substrates consist of micrometre-sized Si pillars either with the vertical {110} or isotropically under-etched sidewalls resulting in narrow necks. The structural properties of these heterostructures were investigated by defect etching and transmission electron microscopy. We show that the dislocation density, and hence the competition between elastic and plastic stress relaxation, is highly influenced by the shape of the substrate necks and their proximity to the mismatched epitaxial material. The SiGe dislocation density increases monotonically with the crystal width but is significantly reduced by the substrate under-etching. The drop in dislocation density is interpreted as a direct effect of the enhanced compliance of the under-etched Si pillars, as confirmed by the three-dimensional finite element method simulations of the elastic energy distribution.
Using Electrons As a High-Resolution Probe of Optical Modes in Individual Nanowires
Publisher: American Chemical Society (ACS)
Date: 16-10-2009
DOI: 10.1021/NL902266N
Abstract: While nanowires show increasing promise for optoelectronic applications, probing the subwavelength details of their optical modes has been a challenge with light-based techniques. Here we report the excitation of dielectric optical waveguide modes in a single GaN nanowire using transition radiation generated by a 1 nm diameter electron beam. This spatially resolved study opens important gateways to probing the optical modes of more complex nanostructures, fundamental for optimization of optoelectronic device performance.
Highly Mismatched, Dislocation‐Free SiGe/Si Heterostructures
Publisher: Wiley
Date: 03-12-2015
Abstract: Defect-free mismatched heterostructures on Si substrates are produced by an innovative strategy. The strain relaxation is engineered to occur elastically rather than plastically by combining suitable substrate patterning and vertical crystal growth with compositional grading. Its validity is proven both experimentally and theoretically for the pivotal case of SiGe/Si(001).
Integration of GaN Crystals on Micropatterned Si(0 0 1) Substrates by Plasma-Assisted Molecular Beam Epitaxy
Publisher: American Chemical Society (ACS)
Date: 18-09-2015
Method to measure spatial coherence of subangstrom electron beams
Publisher: AIP Publishing
Date: 14-07-2008
DOI: 10.1063/1.2957648
Abstract: A method is described for measuring the intensity distribution of the electron source in a scanning transmission electron microscope (STEM) fitted with an objective lens aberration corrector. The method is applied to a Cs-corrected 300kV field emission gun TEM/STEM, which is found to have an effective source size of 0.56Å full width at half maximum (FWHM) under optical conditions suitable for high resolution STEM imaging. This corresponds to a probe intensity distribution at the specimen plane of 0.72Å FWHM using a probe-forming aperture of 25mrad and including the measured residual lens aberrations.
Strain Engineering in Highly Mismatched SiGe/Si Heterostructures
Publisher: Elsevier BV
Date: 11-2017
Atomic-scale structural characterization of grain boundaries in epitaxial Ge/Si microcrystals by HAADF-STEM
Publisher: Elsevier BV
Date: 04-2019
Optimization of exit-plane waves restored from HRTEM through-focal series
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.ULTRAMIC.2009.10.015
Abstract: Atomic-resolution transmission electron microscopy has largely benefited from the implementation of aberration correctors in the imaging part of the microscope. Though the dominant geometrical axial aberrations can in principle be corrected or suitably adjusted, the impact of higher-order aberrations, which are mainly due to the implementation of non-round electron optical elements, on the imaging process remains unclear. Based on a semi-empirical criterion, we analyze the impact of residual aperture aberrations on the quality of exit-plane waves that are retrieved from through-focal series recorded using an aberration-corrected and monochromated instrument which was operated at 300kV and enabled for an information transfer of approximately 0.05nm. We show that the impact of some of the higher-order aberrations in retrieved exit-plane waves can be balanced by a suitable adjustment of symmetry equivalent lower-order aberrations. We find that proper compensation and correction of 1st and 2nd order aberrations is critical, and that the required accuracy is difficult to achieve. This results in an apparent insensitivity towards residual higher-order aberrations. We also investigate the influence of the detector characteristics on the image contrast. We find that correction for the modulation transfer function results in a contrast gain of up to 40%.
Measurement of effective source distribution and its importance for quantitative interpretation of STEM images
Publisher: Elsevier BV
Date: 07-2010
Machine learning in scanning transmission electron microscopy
Publisher: Springer Science and Business Media LLC
Date: 03-03-2022
Effect of thermal annealing on the interface quality of Ge/Si heterostructures
Publisher: Elsevier BV
Date: 09-2019
Strain relaxation in epitaxial Ge crystals grown on patterned Si(001) substrates
Publisher: Elsevier BV
Date: 2017
Related Organisations
University Of California Davis & Lawrence Berkeley National Lab
Location: United States of America
Lawrence Berkely National Laboratory
Location: United States of America
Empa, Swiss Federal Laboratories For Materials Science And Technology
Location: Switzerland
Related Funding Activities
No related grants have been discovered for Rolf Erni.