SCANNING-TUNNELING-MICROSCOPY OF N2H4 ON SILICON SURFACES

The chemistry of N2H4 on Si(100)2 x 1 and Si(111)7 x 7 has been studie d using scanning tunneling microscopy. At low coverages on Si(100)2 x 1 at room temperature the adsorption sites are distributed randomly on the surface and are imaged as dark spots in the dimer row by the STM. Upon annealing the substrate at 600 K, both isolated reaction product s, as well as clusters of reaction products are formed on the surface. The STM images show that the majority of the isolated reaction produc ts are adsorbed symmetrically across the dimers. Based on previous HRE ELS data, these are most likely NHx groups. However, the clusters are not well resolved. Because of this we speculate that they are not simp ly symmetrically adsorbed NHx groups, but likely have a more complicat ed internal structure. At higher coverages, the STM images show that t he predominant pathway for adsorption is with the N-N bond parallel to the surface, in agreement with HREELS studies of this system. On Si(1 11)7 x 7, the molecule behaves in a manner which is similar to NH3. Th at is, at low coverages the molecule adsorbs preferentially at center adatoms due to the greater reactivity of these sites, while at higher coverages it also reacts with the corner adatoms. (C) 1997 Elsevier Sc ience B.V.