Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

High-precision but low-accuracy structure factor measurements – A new approach to measuring the thermal vibration of atoms (#57)

Philip N.H. Nakashima 1 , Boer Tan 1
  1. Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia

We present a new approach of simultaneously matching many 2-beam convergent beam electron diffraction (CBED) patterns collected from different thicknesses for the same diffraction geometry.  The result is structure factor measurement with a precision exceeding that of quantitative CBED (QCBED), applying full many-beam calculations of near zone-axis CBED patterns [1, 2], by an order of magnitude or more.  The accuracy of the measurements by this 2-beam approach, which is computationally less intensive by many orders of magnitude, is greatly lacking due to the effects of the ever-present other beams that perturb the measurements.

As long as the perturbations due to the other beams are kept constant, i.e. the scattering geometry is kept the same, then experiments that do not depend on the absolute value of the structure factors, but their relative magnitudes, stand to benefit greatly from this new-found level of precision (which is often of the order of ±0.01%).

Here we apply this approach to the measurement of the Debye-Waller factor of aluminium in the range 95°K to 365°K.  Measurements were made at intervals of 10°K in this range and we compare our results with those from other methods available in the literature [3].

  1. [1] P.N.H. Nakashima, Phys. Rev. Lett. 99 (2007), 125506
  2. [2] P.N.H. Nakashima and B.C. Muddle, Phys. Rev. B 81 (2010), 115135.
  3. [3] L.-M. Peng, S.L. Dudarev and M.J. Whelan, High-Energy Electron Diffraction and Microscopy (Oxford University Press, 2004).