AVS 63rd International Symposium & Exhibition
    Surface Science Wednesday Sessions
       Session SS+AS+EM-WeA

Paper SS+AS+EM-WeA2
Chemoselective Adsorption of Functionalized Cyclooctynes on Silicon

Wednesday, November 9, 2016, 2:40 pm, Room 104D

Session: Semiconductor Surfaces and Interfaces
Presenter: Michael Durr, Justus Liebig University Giessen, Germany
Authors: M. Reutzel, Philipps-Universität Marburg, Germany
N. Munster, Philipps-Universität Marburg, Germany
M.A. Lipponer, Philipps-Universität Marburg, Germany
C. Langer, Justus Liebig University Giessen, Germany
U. Hofer, Philipps-Universität Marburg, Germany
U. Koert, Philipps-Universität Marburg, Germany
M. Durr, Justus Liebig University Giessen, Germany
Correspondent: Click to Email
The adsorption of organic molecules on silicon surfaces has been subject of intense research due to the potential applications of organic functionalization of silicon surfaces in semiconductor technology. The high reactivity of the silicon dangling bonds, however, presents a major hindrance for the first basic reaction step of such a functionalization, i.e., chemoselective attachment of bifunctional organic molecules on the pristine silicon surface. Due to the high reactivity of the dangling bonds, each functional group of a bifunctional molecule adsorbs with an initial sticking coefficient close to unity and thus the final adsorption product will typically consist of a mixture of molecules adsorbed via different functional groups.

We overcome this problem employing cyclooctyne as the major building block of our strategy. Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, cyclooctyne derivatives with different functional side groups are shown to react on Si(001) selectively via the strained cyclooctyne triple bond while leaving the side groups intact. The origin of this chemoselectivity is traced back to the different adsorption dynamics of the functional groups involved. We show that cyclooctyne's strained triple bond is associated with a direct adsorption channel on the Si(001) surface, in contrast to most other organic molecules which adsorb via weakly bound intermediates. In these intermediate states, the molecules have a finite lifetime and are often mobile and free to rotate on the surface. This allows the bifunctional molecule to sample the surface with the strained triple bond during its finite lifetime in the trapped state and in consequence, bifunctional molecules with a strained triple bond as one functional group will end up with this group attached to Si(001) even if the initial interaction proceeds via the second functional group.

Chemoselectivity can thus be achieved even on the highly reactive Si(001) surface when exploiting the adsorption dynamics of the respective reaction channels.