Thickness determination of a nanofilm by means of a temperature factor

A new method to analyze the thickness of a very thin film without any substrates, which is called here “nanofilm”, has been developed. When it is composed of the stacking of more than 10 atomic layers, the thickness can be easily determined by counting the number of lattice fringes observed in high-resolution transmission electron microscopy images of its cross section, which arise at puckered sites. For thinner films however, this is not the case, since it is so flexible that the diffraction condition quickly varies depending on sites and HRTEM images do not necessarily reflect the exact number of stacking layers. The flexibility closely relates to the thickness. This means that the thickness can be determined by the quantitative analysis of electron diffraction intensity, which takes an apparent temperature factor into account. We have applied this method to a carbon nanofilm (CNF) and succeeded in clarifying the number of stacking layers unambiguously. It has been proved that a single sheet of graphene, which is a carbon hexagonal plane, exists in a CNF as one of its components.