Ultrathin Bi(110) films on Si(111)√3 x √3-B substrates

We studied the structure of ultrathin Bi(110) films on Si(111)root 3 x root 3-B substrates using scanning tunneling microscopy. Atomically flat Bi islands were nucleated on the substrates at room temperature. The edges of these islands were parallel to the short side of the Bi(110) rectangular unit cell. The islands extended along six specific orientations because the rectangular Bi(110) and rhombus root 3 x root 3 unit cells were commensurate at the interface. Bi(110) domains along different orientations coexisted and formed various domain boundary structures on the wide terraces of the islands. In particular, the domains along +/- 87 degrees from the {1 (1) over bar 0} direction were connected perfectly on an atomic scale by changing the direction of the p-like bond of the in-plane zigzag chains locally at the straight domain boundary. No exclusive preference for the black phosphorus structure was observed for the Bi(110) ultrathin films, in contrast to the islands grown on the Si(111)7 x 7 substrate.