Transmission electron microscopes regularly produce data which has a dynamic range that exceeds the capabilities of the recording media used, particularly in diffraction patterns. Hardware solutions such as readable phosphor imaging plates have existed since the 1990s, but in recent years the advent of robust CCD digital cameras capable of capturing high intensities in a transmission electron microscope has made image acquisition fast and straightforward. However, all CCD cameras have a saturation limit, making imaging of low intensities difficult when an image is dominated by strong features. Here we present a simple and effective tool to overcome this limitation through acquisition of multiple images and software processing to produce high dynamic range electron images.

I have found the best way to cleave [001]-oriented silicon wafers is rather different compared to GaAs or InP. The problem is that Si prefers to cleave on (111) planes rather than (110) and so one gets an angled face with the cleave, which is usually rather uneven and often doesn't run straight. This is even worse when cleaving close to an existing edge, which attracts the crack front as it propagates. Good for making low-angle cleaved specimens, but a problem otherwise. It is possible to make Si cleave on (110) by cleaving the wafer without any support.

A systematic distortion in high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, which may be caused by residual electrical interference, has been evaluated. Strain mapping, using the geometric phase methodology, has been applied to images acquired in an aberration-corrected STEM. This allows this distortion to be removed and so quantitative analysis of HAADF-STEM images was enabled. The distortion is quantified by applying this technique to structurally perfect and strain-free material. As an example, the correction is used to analyse an InAs/GaAs dot-in-quantum well heterostructure grown by molecular beam epitaxy. The result is a quantitative measure of internal strain on an atomic scale. The measured internal strain field of the heterostructure can be interpreted as being due to variations of indium concentration in the quantum dot.

Transmission electron microscopy has been used to study the atomic and dislocation structure of deformed and undeformed Σ13 {510} boundary in Si. It is shown that there are several alternative structures for this boundary, which may be separated by imperfect and partial grain boundary dislocations. It is also shown that the dissociation of crystal lattice dislocations which interact with the boundary during deformation results is far more complicated than simple geometrical models applicable in monatomic materials predicts.

The reactions between misfit dislocations arriving by glide at the interface between an In0.12Ga0.88As/GaAs multilayer and a GaAs substrate are analysed and reported. The glide forces for the (a/2)<110> dislocations are calculated as a function of vicinal tilt from (001) to (100). It is observed that the 4% changes in the magnitude of the force for a 2° vicinal angle are not sufficient to significantly alter the relative linear densities of the different types of dislocation.

There is considerable interest at present in the mechanisms of tilting of epitaxial films, such that low index planes in layer and substrate have slightly different orientations. There are two primary causes of this effect: a) coherency strains and b) the action of misfit dislocations. It is important to distinguish between the two effects, particularly in the case of strained layers used for band-gap engineering. Using a recent formulation of the Frank-Bilby equation for the dislocation content of interfaces, it is shown how planes may be rotated in coherent layers due to both the Poisson effect and anisotropic misfit. An advantage of the Frank-Bilby equation is that it allows consideration of semicoherent layers. It is shown that a side effect of misfit dislocation introduction can be to introduce a further rotation of the epitaxial layer. Both these effects have been measured experimentally. The amount and the sense of rotation is compared to theory.

It is well known that it becomes energetically favourable for misfit dislocations to be introduced into strained epitaxial layers above a certain ‘critical’ layer thickness, hc. To date, theoretical calculations of hc have only been made for cases of isotropie misfit - i.e. cases where the misfit is the same for every direction in the interface. Using a new formulation of the Frank-Bilby equation and the concept of coherency dislocations, it is now possible to treat cases of anisotropie misfit, such as silicon on sapphire (SOS). The method used to obtain the critical thickness is described, and values of hc and equilibrium dislocation density are given for various materials systems.