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image gallery of electron micrographs

local deformation of gallium and arsenic dumbbells near stacking faults
Locally inhomogeneous distortions of gallium and arsenic atomic dumbbells in the vicinity of a faulted double stacking fault ribbon in GaAs viewed along the [110] zone axis.

The top image displays a phase image evaluated from a through focus series of 15 experimental micrographs. In the phase image, atomic column positions are superimposed and dumbbell distortions are indicated exemplarily in dependence on specific positions along the crystallographic [111] direction.

The lower graphs display 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 lighter grey colour.

K. Tillmann, L. Houben, and A. Thust


tilt boundaries in beta tantalum crystallites
Beta-phase tantalum nanocrystallite viewed along the [001] zone axis. Singly occupied tantalum columns (black dots) with distances as small as 0.126 nm are superimposed by to the experimental amplitude image of the exit-plane wavefunction evaluated from a through-focus series of 15 experimental HRTEM micrographs.

The nanocrystallite as a whole is found to be composed of four grains highlighted by different colours and rotated against each other by multiples of 30° with mainly <100> and <110> segment directions. The formation of these boundaries may be well explained by considering atomic mispositioning processes taking place during agglomeration.

K. Tillmann and A. Thust


atomic resolution imaging of beta tantalum
High-resolution micrograph of a beta-phase tantalum nanocrystallite viewed along the [001] zone axis and recorded with Cs = - 40 µm under optimum defocus conditions. The 2 x 2 unit-cell insertion to the micrograph shows a calculated image assuming t = 1.5 nm, Z = 11.6 nm, A1 = 4.2 nm (110°), B2 = 70 nm (340°) and A2 = 120 nm (0°) as simulation parameters.

The three images below the micrograph display the corresponding structure model together with the projected potential map and a calculated image assuming A1 = B2 = A2 = 0 at otherwise fixed calculation parameters.

K. Tillmann and A. Thust


displacements associated with extrinsic stacking faults in gaas
Atomic scale imaging obtained by using a spherical aberration corrected high-resolution transmission electron microscope together with a quantiative analysis of elastic lattice distortions in the proximity of lattice defects. The upper image shows a multiple stacking fault in GaAs laterally bound by a partial dislocation with a projected Burgers vector b = a/6 [112].

This phase image was reconstructed from a through-focus series of experimental micrographs. Contour representation of the lattice displacements along the crystallographic [112] direction with reference to the dashed red framed area as gained from the analysis of the phase image by strain mapping algorithms.

K. Tillmann, A. Thust and K. Urban


imaging of lomer type dislocation cores in gaas
High-resolution image of a pure edge dislocation of Lomer type with b = a/2 [110] located at the interface between a GaAs substrate (below) and a lattice mismatched InGaAs epilayer.The image shows the phase of the exit-plane wave function as retrieved from a through-focus series of experimental images taken with the centre's aberration corrected Philips CM-200 electron microscope. Due to an information limit well below 1.3 Ångström atomic column positions right up to the dislocation core are clearly resolved. A single detached atomic column at the images centre directly reveals the existence of dislocation of glide set type.

K. Tillmann, A. Thust and K. Urban


compositional intermixing of algaas/gaas heterostructures
Cross-sectional high-resolution micrograph showing an AlAs layer embedded in a GaAs matrix epitaxially grown by molecular beam epitaxy under low temperature conditions and taken along the [100] projection.

The contour plot shows the local distribution of the intensity of the (200) beam amplitude as gained from a quantitative analysis of the micrograph. This plot may be applied in order to calculate a chemical composition profile across the heterointerfaches yielding the local aluminium content x(Al) on a lattice plane monolayer distance level.

K. Tillmann and M. Lentzen


plastic relaxation of ingaas/gaas island structures
High-resolution micrograph of an InGaAs island grown by molecular beam epitaxy on GaAs. Representing a Stranski-Krastanow system, InGaAs forms three-dimensional islands when deposited on lattice mismatched GaAs. Above a critical volume the islands lower their elastic strain energy by the formation of interfacial misfit dislocations (arrows) in those parts of the layers characterised by the highest local elastic strain density.

K. Tillmann and A. Förster


finite element simulations of the thin foil relaxatikon of tem samples
Coloured representation of the elastic strain distribution inside an elastically relaxed transmission electron microscopy specimen characterized by a limited thickness  along the direction of the electron beam. Quantification yields local crystal tilts in the order of typical Bragg angles for high-energy electron diffraction hence significantly influencing the image contrast of high-resolution micrographs.

K. Tillmann and M. Lentzen


   
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