Adsorption and electronic properties of PTCDA molecules onSi(111)−(7×7): Scanning tunneling microscopy and first-principles calculations

Abstract

Scanning tunneling microscopy ͑STM͒ experiments and density-functional theory ͑DFT͒ calculations are combined to unravel the complex shifts and splittings of molecular orbitals ͑MOs͒ for the prototype system of a single -conjugated molecule bonded to a semiconductor surface. Intramolecular resolution in STM images of 3,4,9,10-perylene tetracarboxylic dianhydride ͑PTCDA͒ on Si͑111͒-͑7 ϫ 7͒ cannot be understood as resulting from a simple rigid shift of the MOs of the free molecule. DFT calculations and simulations of STM images with realistic tips show large splittings of the original MOs that contribute in a complex way to the tunnel current and are understood under symmetry and charge-transfer arguments. The system is characterized by a strong, partially ionic covalent bonding involving the carboxyl groups of the PTCDA and the Si dangling bonds.

Adsorption of PTCDA on Si(001) − 2 × 1 surface

“…One possible reason of the disagreement concerning the dianhydride group might be that we simulated the STM images based on the Tersoff Hamann model, but not by simulating the tunneling current from a realistic STM tip model to the molecule on the surface. 25 Figures 6(e) and 6(f) show top and lateral views of the calculated atomic coordinates for the type A3, respectively, which correspond to that in Fig. 4(c).…”

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.…”

“…In the present paper, two prototypical examples that have been studied by STM are reviewed. The first one deals with PTCDA adsorption on Si(111)‐(7 × 7) surfaces . The second one is related to the adsorption and growth of the first molecular layers on Ge(111)‐c(2 × 8) …”

“…The initial stages of PTCDA adsorption on Si(111)‐(7 × 7) surfaces was investigated by Nicoara et al combining experimental STM measurements and first‐principles DFT calculations. Figure shows representative STM images of single PTCDA molecules adsorbed at RT on a Si(111)‐(7 × 7) surface.…”

“…d) Schematics of the adsorption geometry of PTCDA on Si(111)‐(7 × 7). Reproduced with permission . Copyright 2010, American Physical Society.…”