The {001} surfaces of n-C23H48 paraffin
crystals have been investigated by ex situ alternative contact mode atomic
force microscopy (AC-AFM). Although the crystals were scanned in air, without
any solution present and below the melting temperature of n-C23H48, crystal
growth or etching was revealed in all experiments, independently of the
AC-AFM;I settings. Formation of 2D islands, growing spirals and pinning
of advancing steps have been observed. It is shown that these crystal growth
phenomena, which involve the nucleation and the propagation of monomolecular
steps, are induced by the presence of the AFM tip. From temperature- and
melting point-dependent measurements it is concluded that the observed
crystal growth on n-C23H48 crystals is caused by a combination of local
heating by the AFM laser beam and the action of capillary forces at the
AFM tip, which generate a liquid paraffin bridge between tip and specimen
surface. Control over the occurrence of growth versus etching was limited
and is associated with the amount of paraffin stored in the liquid bridge.This
type of ex situ investigations gives a good opportunity to study melt growth
on a molecular scale, which would have been impossible with AFM in situ
experiments, because of the extremely high requirements for temperature
control needed for that case. Despite the different mechanism from that
in 'real' melt growth experiments, the current system behaves remarkably
similarly. Furthermore, the method may be suitable for surface patterning
applications. (C) 2000 Elsevier Science B.V. All rights reserved.