A method of imaging ultrathin foils with very low energy electrons

We demonstrate the possibility to examine the free-standing foils of thicknesses in units of nm in the scanning low energy electron microscope, using both reflected and transmitted electrons. Very high contrast has been obtained in dependence on the thickness and structure of the foil. A contribution of secondary electrons to the forward scattered electron signal is discussed and a way of suppressing it is presented. Examples of reflected, total transmitted and dark field transmitted electron signal for two graphene-like samples are shown. Dependence of the transmitted signal on the electron energy is observed.

► Overlapped graphene flakes were imaged with a high contrast at very low energies.
► The energy dependence of the transmissivity of the graphene was measured.
► Maximum transmissivity of the graphene was obtained at 5 eV.