COMPLEX SYSTEMS AND BIOMEDICAL SCIENCES
Organothiol monolayer formation directly on muscovite mica, W. de Poel (a), S.J. Brugman (a), K.H. van de Ven (a), A. Gasseling (a), J. de Lange (a), E.R. Townsend (a), A.H. Engwerda (a), M. Jankowski (b), M. Blijlevens (a), B.L. Werkhoven (c), J. Drnec (b), F. Carla (b),
R. Felici (b), A. Tuladhar (c), N.M. Adhikari (c), J.J. De Yoreo (c), J.A. Elemans (a), W.J. van Enckevort (a), A.E. Rowan (a) and E. Vlieg (a), Angew. Chem. Int. Ed. 59, 2323-2327 (2020); https://doi.org/10.1002/anie.201913327. (a) Radboud University, Nijmegen (The
Netherlands) (b) ESRF (c) Utrecht University (The Netherlands) (d) Pacific Northwest National Laboratory, Richland (USA)
 D. Tabor, J. Colloid Interface Sci. 75, 240 (1980).  J.W. Rayleigh, Nature 43, 437-439 (1891).  R.G. Nuzzo & D.L. Allara, J. Am. Chem. Soc. 105, 4481-4483 (1983).  J. Aizenberg et al., J. Am. Chem. Soc. 121, 4500-4509 (1999).
PRINCIPAL PUBLICATION AND AUTHORS
interest in self-assembled monolayers, molecular machines and nanotechnology. One type of self-assembled monolayer has been particularly popular: organothiol monolayers on gold . This class of self-assembled monolayers has yielded a body of research that includes thousands of publications and a wide variety of applications, ranging from tuning the chemical resistance of surfaces to creating molecular sensors.
While the gold substrate that is typically used for organothiol layers is usually evaporated onto a flat single-crystal of muscovite mica, in this work,
organothiol layers were grown directly onto the muscovite mica crystal instead, demonstrating that gold is not necessary to support a stable organothiol monolayer (Figure 46). The layers are simple to make: a piece of muscovite mica crystal is cleaved, submerged in a solution containing an organothiol, rinsed to remove excess material and then dried. A wide range of different organothiol molecules were used to grow such layers. Atomic force microscopy, surface X-ray diffraction on beamline ID03, and vibrational sum-frequency generation IR spectroscopy were employed to study the layers. The latter technique showed that organothiol monolayers were present on the surface. Atomic force microscope measurements showed that the layers were (water) stable and flat over areas as large as 1 cm2. Nano-etching and surface X-ray diffraction was employed to show that most of the layers were monolayers or bilayers. The orientation of the molecules with respect to the surface was also studied to investigate whether the layers were ordered. The main difference between monolayers grown directly on muscovite mica and those grown on gold is that the former are not ordered (in-plane). This feature allows for additional applications where molecular order is not desired.
The fact that the surface ions of muscovite mica can be exchanged can be exploited. By changing the surface cations, it is possible to tune the interaction strength of the muscovite mica surface with the organothiol. This affects the mobility of the monolayers and the rate at which a nano-shaved area heals. To demonstrate that these layers can be used for the same applications as layers grown on gold, the layers were used as substrates for calcite crystal growth (Figure 47). Similar to calcite crystals grown on organothiol layers grown on gold , it was possible to select the polymorph and affect the crystal size, but a dependence of crystal orientation based on the used organothiol was not observed. This was to be expected, due to the layers not being ordered in-plane.
Fig. 46: Schematic of an organothiols self-assembled monolayer formed directly on a muscovite mica. The bonding occurs through the sulfur atoms (yellow).
Fig. 47: Scanning electron micrograph of calcite crystals grown
epitaxially (i.e., with orientational order),
on a thiol monolayer. The crystals have a
size of around 20 µm.