Abstract
The wetting behavior of ethylene adsorbed on MgO(100) was investigated from 83-135 K using high resolution
volumetric adsorption isotherms. The results are compared to ethylene adsorption on graphite, a prototype adsorption
system, in an effort to gain further insight into the forces that drive the observed film growth. Layering transitions for
ethylene on MgO(100) are observed below the bulk triple point of ethylene (T=104.0 K). The formation of three
discrete adlayers is observed on the MgO(100) surface; onset of the second and third layers occurs at 79.2 ( 1.3 K and
98.3(0.9 K, respectively. Thermodynamic quantities such as differential enthalpy and entropy, heat of adsorption, and
isosteric heat of adsorption are determined and compared to the previously published values for ethylene on graphite.
The average area occupied by a ethylene molecule on MgO(100) is 22.6 ( 1.1A ° 2 molecule-1. The locations of two phase
transitions are identified (i.e., layer critical temperatures at Tc2
(n=1) at 108.6 ( 1.7 K and Tc2
(n=2) at 116.5 ( 1.2 K) and a
phase diagram is proposed. Preliminary neutron diffraction measurements reveal evidence of a monolayer solid with a
lattice constant of ∼4.2A ° . High resolution INS measurements show that the onset to dynamical motion and monolayer
melting take place at ∼35 K and ∼65 K, respectively. The data reported here exhibit a striking similarity to ethylene on
graphite which suggests that molecule-molecule interactions play an important role in determining the physical
properties and growth of molecularly thin ethylene films.