Formation of Si/organic interfaces using alkyne-functionalized cyclooctynes—precursor-mediated adsorption of linear alkynes versus direct adsorption of cyclooctyne on Si(0 0 1)

Abstract

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.

Efficient Hierarchical Models for Reactivity of Organic Layers on Semiconductor Surfaces

“…The first adsorbed molecule steers the next one through dispersion attraction towards adjacent sites [36]. Hence, an ordered first layer is formed on Si(001) [14] with a maximum coverage of Θ = 0.5 monolayers (ML) CCO with a complete ML being defined as one adsorbate per surface dimer. Here, we model the experimental system by considering an idealized CCO/Si(001) interface that is uniform and defect free.…”

“…In order to further reduce the termination energy, steric demand is increased by replacing both methyl groups with tert-butyl groups in linker 15. An alternative to steric demand is strain engineering, with successively shorter linkers (11>12>13>18) or more rigid backbones (14). Lastly, the option of chemically tuning the linker through adding electron withdrawing groups (EWG) on the dienophile is explored.…”

“…Finally, this efficient model is used to provide coverage dependent adsorption energies and suggest synthetic principles for the prevention of unwanted growth termination reactions for organic layers on semiconductor surfaces. Commonly, interface formation on solid semiconducting substrates is studied in ultrahigh vacuum (UHV) [14]. However, synthetic routes towards organic layers are often first investigated and optimized in solution [15].…”

Organic Functionalization at the Si(001) Dimer Vacancy Defect – Structure, Bonding and Reactivity

“…The reaction networks are more complex than on the pristine surface where acetylene adsorbs barrierless into the final state (on-top) [23] while for ethylene and cyclooctyne a short lived intermediate exists [11,22,26].…”

“…Cyclooctyne (Figure 1b) has been found to be an excellent platform molecule [9,10]. When the adsorption is done with bifunctional anchor molecules, such as ethynyl-cyclopropyl-cyclooctyne [11] or methyl enolether functionalized cyclooctyne [12], additional organic layers can be grown on the first layer [13]. Up to now, most of the work on organic thin-layer growth on semiconductor surfaces has focused on pristine substrates while some studies considered step edges [14,15].…”