SENSITIVITY AND ACCURACY OF CBED PATTERN-MATCHING

When establishing the feasibility of matching experimental and theoretical convergent-beam electron diffraction (CBED) patterns to recover structure-factor information it is important to investigate the accuracy of the results obtained and the effects of random and systematic errors. The effects of counting noise in a digital data-collection system are studied, together with various sources of systematic error. The sensitivity of parts of the pattern to specific structure-factor parameters is analysed via the calculation of analytic gradients of the intensity with respect to those parameters. All calculations are based on diffraction at the [110] axis of GaP, using simulated CBED patterns as idealised "experimental" data. The results indicate that, provided care is taken to minimise the effects of systematic errors, low-order structure factors may be extracted from experimental data with an accuracy approaching 0.1%.