Simulation of Decoherence in Fluctuation Electron Microscopy

Fluctuation Electron Microscopy (FEM) examines the scattering statistics from small volumes of thin amorphous materials to detect the presence of medium-range order (MRO) [1]. By now it has been thoroughly demonstrated, by both modeling and simulations, that FEM is extraordinarily sensitive to MRO, much more than high-resolution diffraction and high-resolution imaging. Experiments have confirmed this sensitivity [2-4]. There are two key contributing factors to this sensitivity. First, FEM examines the variance of the scattering statistics, which is the second moment of the intensity distribution. Essentially, FEM examines the speckliness of the diffraction data. This means that it examines four-body correlations, whereas diffraction alone examines the first moment of intensity, and examines pair-correlations. The four-body terms are much more sensitive to medium-range correlations. The second key factor, which in this era of aberration-corrected microscopy may come as a surprise, is that it is a low-resolution technique. The sensitivity of FEM to MRO is maximized when the resolution is comparable to the length scale of the MRO.