Low-energy molecular exciton in indium/perylene-3,4,9,10-tetracarboxylic dianhydride system observed by electronic energy loss spectroscopy

Electronic and Vibrational Spectroscopies Applied to Organic/Inorganic Interfaces

“…Here it was first suggested that there is a chemical reaction between In atoms and the carboxylic group in PTCDA on the basis of the observation of a new valence state formed close to the Fermi level. Later, the In/PTCDA system was studied using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS), a combination of metastable atom electron spectroscopy (MAES) with ultraviolet photoelectron spectroscopy (UPES), low-energy electron diffraction (LEED), and high-resolution electron energy loss spectroscopy (HREELS) . From these studies, it was concluded that, as a result of a chemical reaction between In and PTCDA, In 4 PTCDA is formed at the interface 153 and that the new HOMO state appearing close to the Fermi level originates from a widely spread π molecular orbital mixed with the In-5p z atomic orbital.…”

“…Regarding the interface formation of indium with the perylene derivatives, there still is a controversy: PES studies indicate a strong reaction between In and PTCDA via the CO bonds, whereas more recent near-edge X-ray absorption fine structure revealed the presence of a fractional charge transfer between the PTCDA or DiMe-PTCDI molecules and indium . Nakamura et al evidenced a strong interaction when In is deposited onto very thin films of PTCDA (i.e., 0.2 nm Å). On the other hand, our recent PES results (not included in this review) show that the strength of interaction depends on the film morphology, i.e., the size of the organic island and/or surface smoothness.…”

Electron Energy Loss of Terrylene Deposited on Au(111): Vibrational and Electronic Spectroscopy

“…Many HREELS studies are focused on the vibrational degrees of freedom of the selected molecules . However, the electronic properties of organic semiconductor films , (molecular exciton band gap) have also been measured with HREELS, using an electron beam with moderately high energy (10 eV or higher) as excitation and looking for energy losses in the range of 1–5 eV (8000–40000 cm –1 ) where these transitions occur. These observations can be compared with optical spectroscopy in solution .…”