Imaging of layered semiconductor clusters by scanning tunneling microscopy: Bi₂S₃ on graphite and gold substrates

We present scanning tunneling microscope images of Bi₂S ₃ clusters deposited on the surfaces of graphite and gold. We observed similar images on both substrates, discerning the disk-like structures expected for clusters having layered symmetry. The images of highest quality were obtained for 600-atom clusters roughly 100 Å in lateral extent and 25 Å thick. The difficulty in characterizing clusters with smaller lateral dimension suggests that clusters must be bound to the surface with a critical adsorption energy in order to obtain stable images.