Quantitative analysis of CTEM images of small dislocation loops in Al and stacking fault tetrahedra in Cu generated by molecular dynamics simulation
The visibility of conventional transmission electron microscopy (CTEM) images of small crystalline defects generated by molecular dynamics (MD) simulation is investigated. Faulted interstitial dislocation loops in Al smaller than 2 nm in diameter and stacking fault tetrahedra (SFT) in Cu smaller than 4 nm in side are assessed. A recent approach allowing to simulate the CTEM images of computer generated samples described by their atomic positions is applied to obtain bright field and weak beam images. For the dislocation loop-like cluster it appears that the simulated image is comparable to experimental images. The contrast of the g(3.1g) near weak beam image decreases with decreasing size of the cluster but is still 20% of the background intensity for a 2 interstitial cluster. This indicates a visibility at the limit of the experimental background noise. In addition, the cluster image size, which is here always larger than the real size, saturates at about 1 nm when the cluster real size decreases below 1 nm, which corresponds to a cluster of 8 interstitials. For the SFT in Cu the g(6.1g) weak beam image is comparable to experimental images. It appears that the image size is larger than the real size by 20%. A large loss of the contrast features that allows to identify an SFT is observed on the image of the smallest SFT (21 vacancies). (C) 2000 Elsevier Science B.V. All rights reserved.