IMAGING OF NUCLEIC-ACID BASE MOLECULES ON PD(110) SURFACES BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy (STM) images have been obtained for the nucleic acid bases, adenine and thymine, deposited on Pd(110) single-c rystal substrates in order to study the electronic structure and inter action between the DNA bases. The adenine and thy-mine molecular image s are different, with distinct shapes and lateral dimensions that refl ect the contours of the calculated molecular orbitals. Thus, adenine h as triangular protrusions with lateral dimensions of similar to 0.8 nm and thymine has round features of diameter similar to 0.45 nm. Adenin e tends to form dimers whereas thymine forms islands even at low eover ages.