Entropy, the Silent Killer of Aromaticity of Adsorbed Pyridine on Si(100) and Ge(100)

This paper studies the chemical attachment of pyridine on two semiconductor surfaces, Si(100) and Ge(100), at low coverages. We use thermodynamic arguments to show that the aromaticity of pyridine is preserved in both cases at low temperatures. At high temperatures, a transition toward nonaromatic structures-tetrapod structure for Si(100) and dipod structure for Ge(100)-occurs without cleavage of C-H bonds. We show that this transition can be explained by the tiny entropy increase associated with the disappearance of aromaticity.