Starting from a Fixed Geometry: Real-Time XPS Investigation of a Surface Reaction with Controlled Molecular Configurations

Abstract

Ether cleavage on the silicon (001) surface was investigated for a well-defined configuration of the ether group with respect to the underlying Si substrate. In order to maintain the reactants in a fixed orientation with respect to each other, cyclooctyne ether was chemoselectively attached on Si(001) via the strained triple bond of cyclooctyne. In this configuration, the ether group of this bifunctional molecule remains intact and its geometry with respect to the substrate is given by the cyclooctyne ring as a linker. The kinetics of the further reaction of the ether group at elevated temperatures was then investigated by means of real-time X-ray photoelectron spectroscopy using synchrotron radiation. A low activation barrier was deduced, which is interpreted in terms of the controlled configurations realized in the experiment in correlation with the underlying reaction mechanism.

Combined XPS and DFT investigation of the adsorption modes of methyl enol ether functionalized cyclooctyne on Si(001)

“…At high coverage and reduced temperature, the reaction of the enol ether group with the surface is suppressed. In particular, ether cleavage is suppressed at lower temperatures, in accordance with previous work on the reaction of ether‐functionalized cyclooctynes on Si(001) [15,41] . With the latter preparation scheme (multilayer adsorption at 150 K, tempering to 300 K), the highest contribution of intact MEECO molecules to the total coverage was obtained (approx.…”

Click Chemistry in Ultra‐high Vacuum – Tetrazine Coupling with Methyl Enol Ether Covalently Linked to Si(001)

“…This is mainly based on the fact that conventional click reactions are typically developed in solution and can require a catalyst; they are thus not compatible with a UHV‐based approach. On the other hand, highly reactive semiconductor surfaces are typically prepared under UHV conditions and vacuum‐based click chemistry could lead to predictable tailored layer‐by‐layer synthesis on such surfaces without the experimental challenge of transferring the samples from UHV to solution (and reverse) [5] …”

“…It has to be taken into account that the adsorbed MEECO on the Si(001) surface already accounts for three peaks in the O 1s spectra (Figure 3(d)), as discussed in detail in a previous work [12] . In brief, these components can be assigned to the intact ether group (534.1 eV), [16] oxygen from the ether group reacted on silicon (532 eV), [17] and a C=O group as a product of CH 2 abstraction (532.7 eV) [18] . In Figure 3(c), the spectrum of the tetrazine/enol‐ether coupling product is shown.…”

Alkyne-Functionalized Cyclooctyne on Si(001): Reactivity Studies and Surface Bonding from an Energy Decomposition Analysis Perspective

“…Here, it is crucial that the second functional group reacts considerably slower with the surface than the cyclooctyne group to ensure selective adsorption (Figure 1). Following this recipe, several cyclooctyne derivates were experimentally and computationally designed and studied previously [18,22,23,41,[56][57][58][59].…”