Research Area - Microscopic Techniques and Applications
Research Area: Transmission Electron Microscopy Methods
The main fields of activity in transmission electron microscopy methods development include the design and implementation of advanced software and hardware solutions to be used for sub-Ångström microscopic analyses. Furthermore these state-of-the-art techniques have been applied successfully to topical problems in solid state research..
To describe our work in more detail, relevant activities would include the development and refinement of exit-plan wave function retrieval algorithms (TrueImage) and software solutions for the ultra-precise measurement of residual lens aberrations (ATLAS). These numerical approaches are complemented by fundamental electron optics research in the field of chromatical and spherical aberration-corrected transmission electron microscopy, with special emphasis on the evaluation of contrast transfer and resolution limits for sub-Ångström microscopy.
Research Area: Transmission Electron Microscopy Applications
Present research areas in electron microscopy applications cover:
· the analysis of ferroelectric complex niobates with tetragonal tungsten bronze which are of significant interest for a variety of device applications. In many cases, thin layer structures are required, whose properties, due to their particular structure, are sensitively dependent on film structure and orientation.
Employing negative Cs imaging (NCSI), the atomic configuration of both the cation and oxygen columns at the heterointerface may be revealed. Corresponding measurements unfold a pathway to tailor the film orientation of niobates on perovskites for optimising the film properties for device applications.
· the investigation of lattice defects in complex oxides. For these purposes, chemical elements with a low nuclear charge such as oxygen are imaged under NCSI conditions, which is especially useful in cases where the atoms are situated at a very close distance to strongly scattering heavy atoms.
An alternative HRTEM technique going beyond the pure correction of the spherical aberration is the numerical retrieval of the quantum-mechanical electron exit-plane wave function using a focal series of images. This technique is applied for solving a variety of challenging defect structure issues on an atomic scale.
· the measurement of locally inhomogeneous crystal distortions on the atomic scale in the vicinity of lattice imperfections and across heterointerfaces in electoceramics and semiconductors. For these purposes micrographs taken under NCSI conditions or phase images retrieved from a focal series of high-resolution images are measured, in the quest for accuracy in determining atom column positions in the picometre range.
For illustration purposes, the figure at the top of this section displays a phase image evaluated from a through focus series of 15 experimental micrographs of a faulted double stacking fault ribbon in GaAs viewed along the  zone axis. In the phase image, atomic column positions are superimposed and dumbbell distortions are indicated as examples showing their dependence on specific positions along the crystallographic  direction.
The lower graphs display the measured average projected bond length and misorientation angles of the dumbbells along the (111) direction. The lattice planes belonging to the double stacking fault ribbon are indicated in light grey.
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Research area: Scanning tunnelling microscopy
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