  Grain boundary character distributions (GBCD) are routinely measured from
bulk microcrystalline samples by electron backscatter diffraction (EBSD) and
serial sectioning can be used to reconstruct relative grain boundary energy
distributions (GBED) based on the 3D geometry of triple lines, assuming that
the Herring condition of force balance is satisfied. These GBEDs correlate to
those predicted from molecular dynamics (MD); furthermore, the GBCD and GBED
are found to be inversely correlated. For nanocrystalline thin films,
orientation mapping via precession enhanced electron diffraction (PED) has
proven effective in measuring the GBCD, but the GBED has not been extracted.
Here, the established relative energy extraction technique is adapted to PED
data from four sputter deposited samples: a 40 nm-thick tungsten film and a 100
nm aluminum film as-deposited, after 30 and after 150 minutes annealing at
400{\deg}C. These films have columnar grain structures, so serial sectioning is
not required to determine boundary inclination. Excepting the most
energetically anisotropic and highest population boundaries, i.e. aluminum
{\Sigma}3 boundaries, the relative GBED extracted from these data do not
correlate with energies calculated using MD nor do they inversely correlate
with the experimentally determined GBCD for either the tungsten or aluminum
films. Failure to reproduce predicted energetic trends implies that the
conventional Herring equation cannot be applied to determine relative GBEDs and
thus geometries at triple junctions in these films are not well described by
this condition; additional geometric factors must contribute to determining
triple junction geometry and boundary network structure in spatially
constrained, polycrystalline materials.
