  Physical vapor deposition can be used to prepare highly stable organic glass
systems where the molecules show orientational and translational ordering at
the nanoscale. We have used low-dose four-dimensional scanning transmission
electron microscopy (4D STEM), enabled by a fast direct electron detector, to
map columnar order in glassy samples of a discotic mesogen using a 2 nm probe.
Both vapor deposited and liquid cooled glassy films show domains of similar
orientation, but their size varies from tens to hundreds of nanometers,
depending on processing. Domain sizes are consistent with surface diffusion
mediated ordering during film deposition. These results demonstrate the ability
of low-dose 4D STEM to characterize mesoscale structure in a molecular glass
system which may be relevant to organic electronics.
