| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF+SS-ThA |
| Session: | Metal Halide Perovskites, Other Organic/Inorganic Hybrid Thin Films |
| Presenter: | Julian Heep, Justus-Liebig-University, Giessen, Germany |
| Authors: | C. Laenger, Justus-Liebig-University, Giessen, Germany J. Heep, Justus-Liebig-University, Giessen, Germany P. Nikodemiak, Philipps-University, Marburg, Germany T. Bohamud, Philipps-University, Marburg, Germany P. Kirsten, Justus-Liebig-University, Giessen, Germany U. Hoefer, Philipps-University, Marburg, Germany U. Koert, Philipps-University, Marburg, Germany M. Duerr, Justus-Liebig-University, Giessen, Germany |
| Correspondent: | Click to Email |
Controlled organic functionalization of the Si(001) surface may play an important role in the efforts towards further miniaturization of silicon based electronic devices. The first step of such an organic functionalization in terms of organic molecular layer deposition on Si(001) would be the chemoselective adsorption of bifunctional molecules on silicon: whereas one functionality binds to the surface, the other stays intact for the attachment of further layers. This task, however, is complicated by the high reactivity of the dangling bonds with respect to almost all organic functional groups. As a consequence, bifunctional organic molecules typically react via both functional groups on the silicon surface. We solved this problem using cyclooctyne as the main building block of our strategy. The strained triple bond of cyclooctyne reacts via a direct reaction channel, in contrast to most other organic functional groups, which react on Si(001) via a metastable intermediate. This makes the latter ones effectively unreactive in competition with the direct pathway of cyclooctyne’s strained triple bond [1].
In this work, we focus on the preparation of a functionalized organic layer on Si(001) using an alkyne-functionalized cyclooctyne, i.e., ethynyl-cyclopropyl-cyclooctyne (ECCO). If the ECCO molecule binds chemoselectively to the silicon substrate via cyclooctyne’s strained triple bond, the terminal, linear triple bond of the ECCO molecule can be employed for the attachment of the second layer of molecules, e.g., via alkyne-azide coupling. We first show that the linear triple bond follows an indirect reaction pathway via a weakly bound intermediate. XPS and STM results then clearly indicate that ECCO adsorbs selectively on Si(001) via a [2+2] cycloaddition of cyclooctyne’s strained triple bond. No indication for a reaction via the ethynyl group was detected. This chemoselectivity was observed for all coverages, starting from the isolated molecules up to saturation coverage of one monolayer [2]. The ECCO molecules can thus form an organic functionalization of the Si(001) surface which can be used for controlled attachment of further molecular layers.
[1] Reutzel, et al., J. Phys. Chem. C 120 26284 (2016).
[2] C. Länger, et al., J. Phys.: Condens. Matter 31 034001 (2019).