Effects arising from the intercalation of excess oxygen in Bi-O layer has been observed at room temperature using atomic force microscopy. The excess oxygen is incorporated by oxygenating the pure sample. The oxygen is trapped between the alternating Bi-O layers along the b direction. This leads to a change in the local interatomic bond length along the b axis, while the periodicity remained invariant along the a axis. In addition, in-plane atomically resolved structure of single crystal has been imaged at room temperature using AFM. The lattice spacings indicate that the observed structure corresponds to the in-plane bismuth and oxygen positions. Furthermore, high-resolution scanning tunneling spectroscopy measurements show that oxygen doping increases the Bi-O layer density of states near the Fermi level giving rise to metallicity, whereas the pure sample reveals a semiconducting energy gap in the tunneling spectrum.© 1995 American Institute of Physics.