Scanning tunneling microscopy of organic molecules and monolayers on silicon and germanium (001) surfaces

High-resolution scanning tunneling microscopy has been used to investigate the adsorption of a variety of unsaturated organic molecules on the (001) s urface of silicon and germanium. Results are presented for a number of prot otypical alkenes, conjugated and non-conjugated dienes, and aromatic compou nds. These include cyclopentene, 1,5-cyclooctadiene: norbarnadiene, 2,3-dim ethyl- 1,3-butadiene, and benzene on the Si(001) surface, and for cyclopent ene on the Ge(001) surface. Factors controlling the selectivity of various reaction pathways and the consequences for preparation of ordered organic o verlayers are discussed.