Self-Assembled Molecular Wires and Highly Ordered Monolayer: Thiazole on Ge(100)

Adsorption of organic molecules on Ge(100) is important because of its potential applications in organic-semiconductor devices and semiconductor fabrication. On Ge(100), buckled Ge dimers composed of up-Ge and down-Ge atoms align to dimer rows separated by troughs. Adsorption of thiazole on Ge(100) surfaces was investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Two distinct features were observed when coverages were less than 0.25 monolayer (ML), including feature I on top of down-Ge atoms and feature II in dimer troughs. At 0.25 ML, feature II dominates and forms a highly ordered c(4 x 2) pattern. For coverage >0.25 ML, feature I self-assembles to one-dimensional molecular wires. DFT calculations reveal that feature I can be attributed to thiazole binding vertically to the down-Ge through N-Ge dative bonds, while feature II can be related to cross-dimer [4 + 2] cycloadducts through two C-Ge bonds. pi-pi interaction between T-shaped and parallel-displaced pairs of feature I facilitate the formation of the molecular wires. Our results indicate that thiazole may have application in both molecular electronics as well as Ge surface processing.