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-crystal substrates in order to study the electronic structure and interaction between the DNA bases. The adenine and thy-mine molecular images are different, with distinct shapes and lateral dimensions that reflect the contours of the calculated molecular orbitals. Thus, adenine has triangular protrusions with lateral dimensions of similar to 0.8 nm and thymine has round features of diameter similar to 0.45 nm. Adenine tends to form dimers whereas thymine forms islands even at low eoverages.