Reflectance anisotropy spectroscopy: A probe to explore organic epitaxial growth

Reflectance anisotropy spectroscopy (RAS) is demonstrated to be particularly suitable for studying the deposition of organic epitaxial layers in ultrahigh vacuum by organic molecular beam epitaxy, thanks to its high sensitivity and applicability in situ. In the case of α -quaterthiophene, both homoepitaxy and heteroepitaxy have been monitored, demonstrating the crystallinity of the films up to tens of monolayers and the epitaxial relation to the substrate. In both cases, optical RAS data are compared to the results of ex situ characterization of the same samples by atomic force microscopy.