INITIAL GROWTH OF INSULATING OVERLAYERS OF NACL ON GE(100) OBSERVED BY SCANNING-TUNNELING-MICROSCOPY WITH ATOMIC-RESOLUTION

The epitaxial growth start of an insulating NaCl film on a Ge(100) sur face was directly imaged by scanning tunneling microscopy. Atomic reso lution was achieved for islands of the first NaCl double layer with up right-standing NaCl dipoles. The tunneling current is preferentially d etermined by occupied Ge states extending into the NaCl layer. The res ults corroborate and extend the earlier proposed ''carpetlike'' growth mode of the NaCl layer over monoatomic Ge steps, even for small NaCl islands submonolayer coverage.