ACCURATE STRUCTURE FACTOR MEASUREMENTS BY CONVERGENT BEAM ELECTRON DIFFRACTION. M. Saunders, P. A. Midgley, T. D. Walsh and R. Vincent, H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, UK.

Quantitative Convergent Beam Electron Diffraction (CBED) is now emerging as the most accurate generally applicable method of low-order structure factor measurement for inorganic materials [1,2]. Using an energy-filter attached to a conventional Transmission Electron Microscope (TEM) it is possible to acquire diffraction patterns arising from electrons that have undergone predominantly elastic scattering. The theory of electron diffraction has now developed to the stage where accurate simulations of elastic scattering can be performed. The new techniques of quantitative CBED rely on adjusting the simulation until a best fit is obtained between the theory and experiment. The variable parameters include the low-order structure factors we wish to measure, the sample thickness and various scaling constants. Using silicon as a test case we have demonstrated [1] that quantitative CBED is as accurate as the best X-ray Pendellosung measurements [3]. A description of the zone-axis pattern matching technique developed by Bird and Saunders [4] will be given and the results for the silicon test case will be compared to the best X-ray and theoretical values. More recent results showing the application of the technique to other materials such as Ge, diamond, III-V semiconductors and metals such as Ni and Cu will also be discussed.

[1] M. Saunders, et al. (1995) Ultramicroscopy 60, 311.

[2] J.C.H. Spence and J.M. Zuo (1992) Electron Microdiffraction, Plenum, New York.

[3] Z.W. Lu, et al. (1993) Phys. Rev. B47(15), 9385 and references therein.

[4] D.M. Bird and M. Saunders (1992) Ultramicroscopy, 45, 241.