Effect of sample thickness, energy filtering, and probe coherence on fluctuation electron microscopy experiments.

We have explored experimentally the effects of the TEM sample thickness, zero-loss energy filtering, and probe coherence on fluctuation electron microscopy (FEM) experiments implemented using nanodiffraction. FEM measures the variance V of spatial fluctuations in nanodiffraction. We find that V is inversely proportional to the sample thickness, as predicted by earlier models. Energy filtering increases V at all thicknesses we measured. V increases as the coherence of the probe increases. All of these factors must be carefully controlled to obtain quantitatively reliable FEM data.