Thermal desorption of Langmuir-Blodgett monolayers

Abstract

A quartz crystal microbalance was used to study thermal desorption of LB layers of stearic acid (SA) and dipalmitoyl phosphatidic acid (DPPA) from Si(111) and Si(100) surfaces. Desorption follows first-order kinetics. A single monolayer of SA desorbs with an activation energy E a of 129±8 kJ mol −1, and a DPPA monolayer has E a = 42±7 kJ mol −1. In both cases E a is independent of coverage. For both SA and DPPA, the second and third monolayers of a three-monolayer LB film desorb at room temperature leaving a more strongly bound first layer for which E a now depends on coverage. Changes in the properties of the first layer are attributed to structural alteration induced by the application of higher layers.