Growth mechanism of thin solid film of long chain compounds on the surface of KCl substrate in molecular level

Abstract

The growth mechanism of a long chain compound, calcium stearate, (CH 3(CH 2) 16COO) 2Ca, having the molecular orientation parallel to the surface of the KCl substract is investigated with transmission electron microscopy using the Ge decoration method. After forming thin solid films in vacuo at 25°C, the substrate temperature ( T s) was raised to 30–60°C for a few minutes. The slender growth hillocks preferentially grow in a configuration, in which the molecules lie on the surface and epitaxially arrange along the 〈110〉 axes of the KCl substrate. The growth rate is evaluated determining the increase in length of these growth hillocks as a function of elapsing time treated at different T s. In addition, the density of growth hillocks per unit area is found to be inversely proportional to T s. From the dependence of the growth rate and surface diffusion velocity on the annealing temperature, we have obtained the activation energies, 98 and 50 kJ/mol, whose values correspond to the crystal growth of growth hillocks and surface diffusion of molecules, respectively.