  The topological insulators represent a unique state of matter where the bulk
is insulating with an energy gap while the surface is metallic with a Dirac
cone protected by the time reversal symmetry. These characteristics provide a
venue to explore novel quantum phenomena in fundamental physics and show
potential applications in spintronics and quantum computing. One critical issue
directly related with the applications as well as the fundamental studies is
how the topological surface state will behave under ambient conditions (1
atmosphere air and room temperature). In this paper, we report high resolution
angle-resolved photoemission measurements on the surface state of the
prototypical topological insulators, Bi2Se3, Bi2Te3 and Bi2(Se0.4Te2.6), upon
exposing to ambient conditions. We find that the topological order persists
even when the surface is exposed to air at room temperature. However, the
surface state is strongly modified after such an exposure. Particularly, we
have observed the formation of two-dimensional quantum well states near the
surface of the topological insulators after the exposure which depends
sensitively on the original composition, x, in Bi2(Se3-xTex). These rich
information are crucial in utilizing the surface state and in probing its
physical properties under ambient conditions.
