SCANNING-TUNNELING-MICROSCOPY USING CHEMICALLY-MODIFIED TIPS

Monolayers of 1-octadecanol, 1-chlorooctadecane, and 1-octadecanoic ac id were observed with scanning tunneling microscopy(STM). Chemical mod ification of STM tips allowed recognition of functional groups in mono layers of 1-octadecanol and 1-octadecanoic acid. Enhanced contrasts fo r hydroxyl and carboxyl residues were observed with gold tips modified with several aromatic mercaptans that can form hydrogen bonds (4-merc apto-pyridine, 4-aminothiophenol, 4-hydroxythiophenol). On the other h and, no such enhancements were observed in monolayers of 1-chlorooctad ecane. The enhanced contrasts for the OH and COOH groups seem to be du e to electron tunneling through hydrogen bonds formed between the func tional groups on tip and sample. These results suggest that tailored m odification of STM tips may become a general method for the recognitio n of specific chemical species and functional groups in STM images.