  To optimize electron energy toward in-situ imaging large bio-samples up to
10-um thickness with nanoscale resolution, we implemented an analytical model
based on elastic and inelastic characteristic angles [1]. This model can be
used to predict the transverse beam size broadening as a function of electron
energy while the probe beam traverses through the sample. As result, the
optimal choice of the electron beam energy can be realized. While the sample
thickness is less than 10 um, there exists an optimal electron beam energy
below 10 MeV regarding a specific sample thickness. However, for samples
thicker than 10 um, the optimal beam energy is 10 MeV, and the ultimate
resolution could become worse with the increase of the sample thickness.
