Kinetic Barrier Against Standing Up of Pentacene Molecules Upon a Pentacene Monolayer

The growth of pentacene thin films on Cu(110)-(2x1)O surface was investigated in situ and in real time using reflectance difference spectroscopy (RDS). Deposition at a substrate temperature of 230K results in a lying-down orientation for all pentacene molecules. Subsequent annealing to a temperature of 350K induces reorientation for molecules above the first monolayer into a standing-up configuration. By a quantitative analysis on the corresponding evolution of the RD signals, the kinetic barrier of 970 +/- 150meV has been deduced for the reorientation of pentacene molecule.