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We found that thin antimony films contacted by a single layer of a variety of atoms can form topological surface and interface states in the gap of bulk energy bands that preserve time-reversal symmetry. Using density functional calculation, we have included bismuth, graphene, boron-nitride and boron-doped graphene layers in our investigation. In most cases, Dirac cones are found in the band structures and spin textures indicate no back scattering of conduction electrons. In the case of a BC _3 layer deposited on an Sb film as thin as three bilayers, a Dirac cone consisting mostly of interface states is formed close to the Fermi level. If the composite is gated by an adjustable voltage, electron transport can switch between two modes of opposite spins, and between one or two modes of 100% spin polarization. The results should be very useful in the applications of topological conduction and spintronics.