Ordered organic monolayers on silicon

ABSTRACT

The ever-growing number of semiconductor-based applications leads to an increasing demand for a modification or functionalization of surfaces with organic molecules. However, while the formation of self-assembled monolayers of organic molecules is well established on metal surfaces, the high density of dangling bonds present on most clean semiconductor surfaces typically reduces the mobility of molecules preventing an ordered growth. A route to overcome this constraint is a modification of the surface, allowing to precisely adjust the substrate-molecule interaction enabling a controlled growth.
In this talk, some recent examples from our group how ordered organic layers can be achieved on modified silicon surfaces are presented. For their investigation, we routinely employ scanning tunneling microscopy and photoelectron spectroscopy, often accompanied by theory calculations from external cooperations partners. The results point out the importance of a suitable modification of the silicon substrate to achieve ordered organic overlayers and the possibility of a tailor-made surface functionalization by carefully selecting the molecule-substrate combination.
One example are monolayers of N-heterocyclic carbenes (NHC), a class of molecules known to be excellent ligands for surface modification. We find the formation of highly ordered NHC monolayers using a silicon surface modified with boron [1,2]. The NHC molecules adsorb in an upright geometry forming a covalent bond with the Si substrate adatoms. Their monolayers are characterized by a high thermal stability and large work function reductions. Surface defects as well as the sidegroups are found to have strong impact on the growth process.
In addition, we have been the first to demonstrate a surface adsorption of N-heterocyclic olefins (NHO), which are close relatives of NHC [3]. We find that NHO bind covalently with ylidic character to the silicon adatoms of the substrate and exhibit good thermal stability. The adsorption geometry is found to depend drastically on the N-substituents: while a flat-lying geometry is favored for small sidegroups, larger sidegroups lead to an upright adsorption. Furthermore, the geometry is found to have strong impact on the quality and properties of the obtained monolayers, e.g. their work function.
Another interesting class of molecules investigated in our group are transition metal phthalocyanines [4]. Here, we were able to achieve highly ordered mono- and multilayers by using different surface modifications with boron [5], indium [6], and rare-earth metals [7].
[1] M. Franz et al., Nat. Chem. 13, 828 (2021).
[2] R. Zielinski et al., J. Mater. Chem. C 11, 7377 (2023).
[3] M. Das et al., Angew. Chem. Int. Ed. 62, e202314663 (2023).
[4] M. Franz, Inorg. Chim. Acta 559, 121771 (2024).
[5] S. Lindner et al., Phys. Rev. B 100, 245301 (2019).
[6] M. Kubicki et al., Appl. Phys. Lett. 119, 133105 (2021).
[7] M. Kubicki et al., J. Phys. Chem. C 128, 13347 (2024).

BIO

Short CV

2009 Diploma in Physics, Technische Universität Berlin
2015 PhD (summa cum laude), Technische Universität Berlin, Institut für Festkörperphysik, Prof. Dr. M. Dähne
Since 2016 Postdoc and habilitation, Technische Universität Berlin, Institut für Festkörperphysik, Prof. Dr. M. Dähne

Scholarships

2009-2011 Scholarship of the state of Berlin (Elsa-Neumann-Stipendium)

Selected publications

A rare earth modified silicon surface as a template for ordered organic growth
M. Kubicki, M. Franz, and M. Dähne
The Journal of Physical Chemistry C 128, 13347 (2024).

Phthalocyanine thin films on Si(111)
M. Franz
Inorganica Chimica Acta 559, 121771 (2024).

N-Heterocyclic olefins on a silicon surface
M. Das, C. Hogan, R. Zielinski, M. Kubicki, M. Koy, C. Kosbab, S. Brozzesi, A. Das, M. T. Nehring, V. Balfanz, J. Brühne, M. Dähne, M. Franz, N. Esser, F. Glorius
Angewandte Chemie International Edition 62, e202314663 (2023).

Controlled growth of ordered monolayers of N-heterocyclic carbenes on silicon
M. Franz, S. Chandola, M. Koy, R. Zielinski, H. Aldahhak, M. Das, M. Freitag, U. Gerstmann, D. Liebig, A. K. Hoffmann, M. Rosin, W. G. Schmidt, C. Hogan, F. Glorius, N. Esser, and M. Dähne
Nature Chemistry 13, 828 (2021).

Growth of ordered two-dimensional cobalt phthalocyanine films on a one-dimensional substrate
M. Kubicki, S. Lindner-Franz, M. Dähne, and M. Franz
Appl. Phys. Lett. 119, 133105 (2021)

Electronic structure of the Si(111)√3×√3R30°-B surface from theory and photoemission spectroscopy
H. Aldahhak, C. Hogan, S. Lindner, S. Appelfeller, H. Eisele, W. G. Schmidt, M. Dähne, U. Gerstmann, and M. Franz
Physical Review B 103, 035303 (2021).