Surface nucleation in the crystallization kinetics of phenanthrene multilayers on Al 2O 3( [formula omitted

Abstract

The glass-to-crystal transition in phenanthrene multilayers on Al 2O 3( 11 20 ) was studied using electronic absorption spectroscopy. Phenanthrene formed a glassy adlayer when adsorbed onto Al 2O 3( 11 20 ) at 90 K. The phenanthrene adlayer crystallized when annealed to 200 K and the electronic absorption spectrum changed dramatically upon crystallization. The pronounced alteration in the absorption spectrum for the S 0 → S 2 transition was used to study the kinetics of the crystallization process. The adlayer crystallization was dependent on phenanthrene coverage and the crystallization kinetics were consistent with surface nucleation followed by crystal growth into the phenanthrene multilayer. An Avrami analysis indicated that the surface nucleation sites were predetermined with a nucleation site density of 7 × 10 11 cm −2 at the Al 2O 3( 11 20 ) surface. The velocity of crystallization in the phenanthrene multilayer was found to be temperature-dependent and measured velocities were 3.0 A ̊ s at 200 K and 9.2 A ̊ s at 202 K.