Aromatic hydrocarbon (perylene, coronene) and tetracontane films are
shown to produce useful convergent-beam electron diffraction (CBED)
patterns under low-dose and low-temperature conditions. These were
obtained using a Zeiss LEO-921 electron microscope with an omega energy
filter at liquid helium and nitrogen temperatures. The usefulness of
patterns showing CBED disks of constant intensity (“blank
disks,” indicating kinematic scattering) for structure analysis
is investigated, with the aim of avoiding film-bending artifacts. Using
CBED patterns from thicker areas, sample thickness was experimentally
determined using either two-beam or three-beam patterns. Koehler mode
illumination (a new form of SAD pattern offering smaller areas) was
also used, and the possibility of obtaining structure factor moduli
using the kinematic and two-beam approximations was investigated by
comparing measured diffraction intensities with experimental ones for
these known structures. The commonly used approximation
|F| ∼ Ig (intended
to account for bending) was found to be a worse approximation than the
two-beam approximation with well-defined excitation error for these
microdiffraction experiments. A new multiwavelength method of
retrieving structure factor moduli and thickness from microdiffraction
patterns using two-beam theory is demonstrated for tetracontane.