ROLE OF CHAIN-LENGTH ON THE SURFACE-CHEMISTRY OF DIENES STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The scanning tunneling microscope has been used to observe sites selec tion of diene molecules on Si(111) 7X7 as a function of their chain le ngth. The molecules 1,6-heptadiene and 1,7-octadiene can chemisorb on either of three geometries on the surface. The different relative affi nity of the molecules to these sites is explained by matching between the molecules length and the surface sites. For 1,13-tetradecadiene, e ach end of the molecule reacts with a different half of the unit cell.