jp4063059_si_001.pdf (134.01 kB)
Structure of Normal-Alkanes Adsorbed on Hexagonal-Boron Nitride
journal contribution
posted on 2014-02-06, 00:00 authored by Thomas Arnold, Matthew Forster, Achilles Athanasiou Fragkoulis, Julia E. ParkerWe report the structures
of submonolayer films of the homologous
series of normal-alkanes hexane (C6H14) to hexadecane
(C16H34) adsorbed on the surface of hexagonal-boron
nitride (h-BN), as determined by X-ray powder diffraction. These n-alkanes are demonstrated to form solid monolayers and
exhibit structures that are similar to those seen on graphite but
with some important differences. Each n-alkane studied
shows a fully commensurate structure, even at submonolayer coverage.
Hexane and octane adopt structures in which the molecules are arranged
in a “herringbone” pattern (2 × m√3abn for CnHn+2, where abn is the unit cell parameter
of the underlying h-BN surface, n = 6 or 8 and m = (2n – 2)/2). Heptane, nonane,
and undecane–hexadecane adopt structures in which the molecules
within adjacent lamellae are arranged with their principal axis parallel
to each other (√3 × mabn for CnHn+2, where n = 7, 9, 11–16 and m = n + 2). Decane is a transitional case
with evidence of both structure types, depending on coverage and temperature.
This transitional case occurs for shorter molecules on h-BN than on
graphite, indicating a difference in the relative balance of intermolecular
and molecule–surface interactions that has significant implications
for the phase behavior of adsorbates on these two surfaces.