Abstract
We have investigated the adsorption of hexacontane (C60H122) on hexagonal boron nitride (hBN) using atomic force microscopy (AFM). The molecules can be deposited either by sublimation or from solution and form lamellar rows with dimensions of the order of 0.1–1 μm in three different rotational domains. High-resolution AFM images reveal that, similar to alkanes on graphite, the molecules are adsorbed parallel to the lattice vectors of hBN and we show using molecular mechanics that this corresponds to the lowest energy configuration. Lamellar rows with the same periodicity are observed even when several layers of hexacontane are deposited, although there is some orientational disorder in these multilayers. We also observe heat-induced modification of hexacontane, including recrystallization. We compare our results with recent X-ray studies of alkane adsorption on hBN and discuss the possible role of alkanes on steering molecular self-assembly on hBN.
Highlights
Over the past few decades, there has been a continuing interest in the adsorption of alkanes on surfaces, since they play important roles in catalysis,[1,2] lubrication,[3] and passivation.[4]
We find, using atomic force microscopy (AFM), that the alkanes lay flat on the surface with the molecular axis parallel the zigzag direction of hexagonal boron nitride (hBN), forming lamellar rows, similar to those formed by longchain alkanes deposited on graphite
The lines are very similar to those observed when alkanes adsorb on graphite and form lamellar rows in which the linear molecules are stacked perpendicular to the row axis
Summary
Over the past few decades, there has been a continuing interest in the adsorption of alkanes on surfaces, since they play important roles in catalysis,[1,2] lubrication,[3] and passivation.[4] The adsorption of these readily available, low-cost, and nontoxic materials on various surfaces has been studied in depth, on metals[5−7] and graphite,[8−15] where they provide a route to promote complex organization through twodimensional supramolecular assembly.[16−20] In parallel, the recent surge in activities in two-dimensional materials[21] has led to a renewed interest in hexagonal boron nitride (hBN), a structural isomorph of graphite This layered material can serve as an atomically flat tunneling barrier,[22] is mostly free of charge impurities,[23] and when used as a substrate for graphene, greatly improves electrical performance.[24] It has been shown that hBN, both in the form of monolayers (MLs) grown on metals[25−28] and thicker exfoliated flakes,[29] can support the formation of two-dimensional supramolecular assemblies. All images were obtained in AC (tapping) mode unless stated otherwise
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