Real-time monitoring of phase transitions of vacuum deposited organic films by molecular beam deposition LEED

We describe a special low energy electron diffraction (LEED) system that allows us to record diffraction patterns during the adsorption process of vacuum-deposited organic thin films. With this instrument that combines Knudsen cells within a reverse view LEED instrument we can evaporate three different organic materials independently and simultaneously from each other. In contrast to conventional LEED, this molecular beam deposition LEED (MBD-LEED) allows us to study the kinetics of structural phase transitions from the sub-monolayer regime up to several layers without changing the position of the sample which is located on a temperature-controlled sample holder. The performance of the device is demonstrated by a growth study of perylene-3,4,9,10-tetracarboxylic-dianhydride on Ag(110). A phase transition was in situ observed after the preparation of a single domain oriented homogeneous monolayer ("brick stone") structure to a condensed ("herring bone") structure which is commensurate in one direction. (C) 1998 Elsevier Science B.V. All rights reserved.