Growth and vibrational properties of PTCDA thin films on InSb(1 1 1)A

Abstract

X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) have been used to study the growth of ordered thin films of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on InSb(1 1 1)A. XPS and HREELS spectra of the PTCDA covered surface both show significant differences in the sub-monolayer regime when compared to multilayer PTCDA films. At sub-monolayer coverages the XPS measurements indicate a significant shift in the binding energies of the main C 1s and O 1s peaks when compared to multilayer PTCDA films. HREELS results show that several vibrational modes of the molecule undergo significant changes in intensity and frequency as the PTCDA coverage is increased. Furthermore, the sub-monolayer spectra indicate the presence of softened carboxylic stretching modes. The results are consistent with some charge transfer at the PTCDA/InSb interface during the initial stages of film growth, however there is no spectroscopic evidence for any molecular fragmentation.