  This study presents a detailed examination of the lattice distortions
introduced by glancing incidence Focussed Ion Beam (FIB) milling. Using
non-destructive multi-reflection Bragg coherent X-ray diffraction we probe
damage formation in an initially pristine gold micro-crystal following several
stages of FIB milling. These experiments allow access to the full lattice
strain tensor in the micro-crystal with ~25 nm 3D spatial resolution, enabling
a nano-scale analysis of residual lattice strains and defects formed. Our
results show that 30 keV glancing incidence milling produces fewer large
defects than normal incidence milling at the same energy. However the resulting
residual lattice strains have similar magnitude and extend up to ~50 nm into
the sample. At the edges of the milled surface, where the ion-beam tails impact
the sample at near-normal incidence, large dislocation loops with a range of
burgers vectors are formed. Further glancing incidence FIB polishing with 5 keV
ion energy removes these dislocation loops and reduces the lattice strains
caused by higher energy FIB milling. However, even at the lower ion energy,
damage-induced lattice strains are present within a ~20 nm thick surface layer.
These results highlight the need for careful consideration and management of
FIB damage. They also show that low-energy FIB-milling is an effective tool for
removing FIB-milling induced lattice strains. This is important for the
preparation of micro-mechanical test specimens and strain microscopy samples.
