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 × 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. π–π 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.

The reaction mechanism and regioselectivity of methyl oxirane (C3H6O) adsorbed on Si(111)-(7 × 7) have been studied using high-resolution electron energy loss spectroscopy (HREELS), in situ scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The experimental results demonstrate that methyl oxirane chemically binds to Si(111)-(7 × 7) through both dative-bonded addition and ring-opening reaction via cleavage of C–C or one C–O bond within the epoxy group. The STM images also reveal that the adsorption is site-selective with a preference for center adatoms on the faulted half of the (7 × 7) unit cell. The DFT calculations further show that breaking the C(CH3)–O bond is most kinetically favorable with a relatively small barrier of ∼3 kcal/mol. The dative-bonded states are observable on the surface only after three adjacent adatom–rest atom pairs within one-half unit cell are fully reacted with the methyl oxirane molecules during the ring-opening reaction.

Adsorption of butadiene monoxide on Si(111)-(7×7) has been scrutinized by high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The experimental results indicate that surface reaction occurs through a [2+2]-like cycloaddition, which is further supported by the DFT studies.