Measurement of electron transmission through tilted thick specimens with an ultrahigh voltage electron microscope

Electron transmission through tilted epoxy-resin film specimens with thicknesses of 1 and 5 microm has been measured under different accelerating voltages and diameters of the objective aperture in a 3 MV ultrahigh voltage electron microscope. Measurements show that the linearity between the logarithmic electron transmission and effective thickness of the tilted specimens holds valid only for some smaller effective thicknesses. However, the higher accelerating voltage leads to a wider linear attenuation range. The linear range can reach 7 microm for the 3 MeV incident electrons. Moreover, the measurements were analyzed with the electron-scattering theory. Actually, the high-energy electrons are capable of penetrating much thicker specimens, but many electrons elastically scattered at large angles cannot be collected as useful signals because of being blocked by the objective aperture in the mode of amplitude contrast. The need for further investigations was suggested to determine theoretically the electron transmission through a thick low-Z specimen and its exponential attenuation range.