Highly sensitive optical monitoring of molecular film growth by organic molecular beam deposition

Reflectance anisotropy spectroscopy (RAS) has been employed to study in situ the growth of thin α-sexithiophene films by organic molecular beam deposition onto an organic substrate. A large anisotropy can be detected by following the line shape evolution of the RAS spectrum; in addition, the signal variation at a fixed wavelength is used to monitor the film growth. The signal intensity scales with the deposited thickness, demonstrating a very high sensitivity of RAS to less than 1/50 of a monolayer. Evidence of the advantages of RAS to monitor in real time the growth of molecular films and to probe in situ their properties is therefore obtained.