  The highly energetic electrons in a transmission electron microscope (TEM)
can alter or even completely destroy the structure of samples before sufficient
information can be obtained. This is especially problematic in the case of
zeolites, organic and biological materials. As this effect depends on both the
electron beam and the sample and can involve multiple damage pathways, its
study remained difficult and is plagued with irreproducibity issues,
circumstantial evidence, rumours, and a general lack of solid data. Here we
take on the experimental challenge to investigate the role of the STEM scan
pattern on the damage behaviour of a commercially available zeolite sample with
the clear aim to make our observations as reproducible as possible. We make use
of a freely programmable scan engine that gives full control over the
tempospatial distribution of the electron probe on the sample and we use its
flexibility to obtain mutliple repeated experiments under identical conditions
comparing the difference in beam damage between a conventional raster scan
pattern and a newly proposed interleaved scan pattern that provides exactly the
same dose and dose rate and visits exactly the same scan points. We observe a
significant difference in beam damage for both patterns with up to 11 %
reduction in damage (measured from mass loss). These observations demonstrate
without doubt that electron dose, dose rate and acceleration voltage are not
the only parameters affecting beam damage in (S)TEM experiments and invite the
community to rethink beam damage as an unavoidable consequence of applied
electron dose.
