Scanning tunneling microscopy and molecular orbital calculation of thymine and adenine molecules adsorbed on the Si(100)2x1 surface

The nucleic acid base molecules adenine and thymine adsorbed on Si(100)2 x 1 surfaces have been imaged by scanning tunneling microscopy (STM). The molecular images exhibit distinct shapes corresponding to the expected shapes for adenine and thymine. Semi-empirical molecular orbital calculations reveal the local surface density of states for the adsorbed molecules on the Si surface. These calculated features and adsorption sites are in good agreement with the molecular images observed in STM.