Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

The technique of energy selected electron diffraction gives information about amorphous structures which can be used to characterize amorphous materials in terms of their structure. The diffraction data can be used to refine models obtained using molecular dynamics, resulting in physically reasonable models consistent with the diffraction data.

The electron microscope provides an ideal environment for the structural analysis of small volumes of amorphous and polycrystalline materials by collecting scattering information as a function of energy loss and momentum transfer. The scattering intensity at zero energy loss can be readily processed to a reduced density function G(r), providing information on nearest neighbour distances and bond angles[l]. Figure 1(a) shows the G(r) for glassy carbon, a turbostratic form of graphite. The three nearest neighbours in glassy carbon (labelled 1-3 in figure 1) are at 1.42 Å, 2.44 Å and 3.75 Å respectively. These distances correspond to the first three nearest neighbours in a graphite sheet and are expected in glassy carbon which is know to have good in-plane graphitic order. In figure 1(b) the G(r) of cathodic arc deposited tetrahedral amorphous carbon is shown. This material contains a high fraction of diamond-like bonding[2] and has a 1st nearest neighbour peak at 1.52 Å.

The strain in GeSi/Si strained layer heterostructures is studied as a function of ion-irradiation and thermal annealing conditions and correlated with the defect microstructure in the GeSi alloy layer. For room temperature irradiation, compressive strain within the alloy layer increases with increasing ion fluence for both low (projected range of ions within the alloy layer) and high energy (projected range of the ions greater than alloy thickness) irradiation. In contrast, elevated temperature irradiation results in an increase in strain for low-energy irradiation, but a decrease for high-energy irradiation. For example, strain relaxation is observed in layers irradiated with I MeV 28Si+ at 253 °C. During subsequent annealing to 750 °C, the strain is partially recovered but relaxes again at temperatures > 750°C. This behavior is shown to be consistent with the evolution of intrinsic (vacancy-type) defects within the alloy layer.