Adsorption of ethynyl-cyclopropyl-cyclooctyne (ECCO), an alkyne-functionalized cyclooctyne, on Si(0 0 1) was studied by means of x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Together, XPS and STM results clearly indicate chemoselective adsorption of ECCO on Si(0 0 1) via a [2+2] cycloaddition of the strained triple bond of cyclooctyne without reaction of the ethynyl group. The results are compared to the adsorption of acetylene on Si(0 0 1): C 2 H 2 adsorbs on Si(0 0 1) via a precursor-mediated reaction channel as it was shown by means of temperature dependent measurements of the sticking probability as well as by means of STM experiments at variable temperature. On the other hand, cyclooctyne adsorbs on Si(0 0 1) via a direct reaction channel. This qualitative difference in the reaction pathways of the two functionalities leads to the observed chemoselective adsorption of ECCO via the strained triple bond of cyclooctyne. As the ethynyl group stays intact, monolayers of ECCO on Si(0 0 1) form a well defined interface between the silicon substrate and further organic molecular layers which can be attached to the ethynyl functionality.

Adsorption of methanol on Si(001) was studied by means of X-ray photoelectron spectroscopy (XPS), molecular beam techniques, and scanning tunneling microscopy (STM) at surface temperatures between 50 and 800 K. Even at lowest temperatures, only the final reaction products, i.e., a silicon bound methoxy group and a Si−H entity, were observed in the XPS and STM experiments. However, the initial sticking probability drops with increasing surface temperature, indicating that the reaction proceeds via an intermediate state. Two final configurations with the dissociation products adsorbed either on one or two silicon dimers were observed; their branching ratio does not change with temperature, indicating very similar, low conversion barriers for the two pathways.

Tip-induced hopping of the ethyl fragment (−C2H5) of diethyl ether molecules reacted on Si(001) was shown to be a field-driven process. Although the hopping rate increases continuously with increasing bias voltage, it remains constant when varying the tunneling current. No hopping events are observed at 50 K. The process is thus concluded to be thermally activated with the respective energy barrier being reduced by the applied electric field. At a positive sample bias, the field in the tunneling gap is strong enough to effectively depolarize and thus weaken the covalent Si–C bond. The effect of this depolarization on the hopping barrier is quantified and compared to the strength of the electric field.

The reaction dynamics of allyl methyl ether (AME) on Si(001) was studied by means of molecular beam techniques. The reaction of this bifunctional molecule comprising an ether and an alkene group was found to proceed via an intermediate state as deduced from the temperature dependence of the initial sticking probability s0. At constant surface temperature Ts, s0 decreases continuously with increasing kinetic energy Ekin, indicating a non-activated adsorption channel. Qualitatively and quantitatively, the energy dependence is almost identical to the adsorption dynamics of diethyl ether on Si(001). We attribute this to a similar nature of the intermediate state, which largely determines the adsorption dynamics. In consequence, this indicates a predominant role of the ether group and a minor influence of the C=C double bond on the adsorption dynamics of AME on Si(001).

Atomic-scale chemical modification of surface-adsorbed ethyl groups on Si(001) was induced and studied by means of scanning tunneling microscopy. Tunneling at sample bias >+1.5 V leads to tip-induced C–H cleavage of a β-hydrogen of the covalently bound ethyl configuration. The reaction is characterized by the formation of an additional Si–H and a Si–C bond. The reaction probability shows a linear dependence on the tunneling current at 300 K; the reaction is largely suppressed at 50 K. The observed tip-induced surface reaction at room temperature is thus attributed to a one-electron excitation in combination with thermal activation.