Adsorption of PTCDA on Ge(001)

Abstract

Adsorption of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on the Ge(001) surface was studied using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and the density-functional theory (DFT) calculations. Only single adsorption configuration of the PTCDA molecule was observed at low coverages on the Ge(001) at room temperature, unlike on the Si(001) where several adsorption configurations were reported. This indicates that the PTCDA molecules on the Ge(001) were more mobile than those on the Si(001). Atomic structure of the adsorption configuration on the Ge(001) was determined by comparison between the STM experiments and the DFT calculations. Bias-dependent STM images, STS, and calculated projected density of state curves show nontrivial hybridization of molecular orbitals with surface states of the Ge substrate. Interactions of the PTCDA molecule with the Ge and the Si surfaces were in detail analyzed by the DFT calculation, considering five main competing contributions to the adsorption energy: formation energy of polar covalent Ge–O (Si–O) bonds, energy of molecular deformation, interaction energy of Ge atoms with the perylene core of PTCDA, energy of dimer buckling deformation, and van der Waals interaction energy. The analysis explains different adsorption behaviors between the Ge and the Si substrates.

First-principles calculations of hybrid inorganic–organic interfaces: from state-of-the-art to best practice

“…Moreover, it should be kept in mind that STM measures the local density of states, not the positions of the atoms, and that the appearance of an adsorbate in STM can be deceiving. [124][125][126][127][128][129][130][131] Also, the composition of the substrate surface and its impact on the interface structure is often not a priori clear. Many metal-organic interfaces incorporate adatoms from the substrate, 8,82,132,133,[133][134][135][136][137][138][139] which have a decisive impact on the geometry of the organic layers as well as the interface properties.…”

Graphene nanoribbons initiated from molecularly derived seeds

“…3 . Prior studies have moreover shown that PTCDA molecules, prior to their dehydrogenation, are mobile on Ge(001) at temperatures >180 °C and that non-covalent interactions among PTCDA molecules are favorable under particular arrangements leading to clustering 56 , 57 . While their mobility following dehydrogenation has not yet been studied, the PAH molecules studied, here, likely remain hydrogenated throughout the initiation stage and at the beginning of the nanoribbon growth stage (as the temperature is increased from room temperature to 920 °C) thereby providing the opportunity for PAH diffusion and/or clustering and further establishing the plausibility of the scenario presented in Fig.…”

Growth of PTCDA Films on Various Substrates Studied by Scanning Tunneling Microscopy and Spectroscopy

“…PTCDA growth has been investigated on pristine silicon and germanium surfaces, like Si(111), Si(001), Ge(111), and Ge(001), as well as on III–V semiconductor compound surfaces, like GaAs(001) and InSb(001), among others. In the present paper, two prototypical examples that have been studied by STM are reviewed.…”