  Impact collision ion scattering spectroscopy (ICISS), which is a variation of
low energy ion scattering (LEIS) that employs large scattering angles, is
performed on Bi2Se3 surfaces prepared by ion bombardment and annealing (IBA).
ICISS angular scans are collected experimentally and simulated numerically
along the [120] and [-1 -2 0] azimuths, and the match of the positions of the
flux peaks shows that the top three atomic layers are bulk-terminated. A newly
observed feature is identified as a minimum in the multiple scattering
background when the ion beam incidence is along a low index direction.
Calculated scans as a function of scattering angle are employed to identify the
behavior of flux peaks to show whether they originate from shadowing, blocking
or both. This new method for analysis of large-angle LEIS data is shown to be
useful for accurately investigating complex surface structures.
