  Topological insulators(1-8) are a novel form of matter which features
metallic surface states with quasirelativistic dispersion similar to
graphene(9). Unlike graphene, the locking of spin and momentum and the
protection by time-reversal symmetry(1-8) open up tremendous additional
possibilities for external control of transport properties(10-18). Here we show
by angle-resolved photoelectron spectroscopy that the topological sur-face
states of Bi2Te3 and Bi2Se3 are stable against the deposition of Fe without
opening a band gap. This stability extends to low submonolayer coverages
meaning that the band gap reported recently(19) for Fe on Bi2Se3 is incorrect
as well as to complete monolayers meaning that topological surface states can
very well exist at interfaces with ferromagnets in future devices.
