Molecular Orientation and Site Dependent Charge Transfer Dynamics at PTCDA/TiO₂(110) Interface Revealed by Resonant Photoemission Spectroscopy

Abstract

Charge transfer dynamics across the interface of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) organic molecules and the reduced rutile TiO 2 (110) 1 × 1 surface has been investigated using core-hole clock implementation of resonant photoemission spectroscopy (RPES). It is found that ultrafast charge transfer from PTCDA molecules to TiO 2 substrate takes place on the time scale of 8−20 fs due to their strong electronic coupling. Moreover, the charge transfer time scale at the PTCDA/TiO 2 (110) interface shows evident orientational dependence which varies with the molecular site owing to different electronic coupling strengths.

Oxidation of Rubrene Thin Films: An Electronic Structure Study

“…One can easily observe from the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 10 HOMO peak (fig 1) shows that HOMO-LUMO gap increases with exposure. This indicates that the rubrene films become more insulating with ambient exposure 24,25 . The peaks labeled α and γ are assigned to transitions from carbon atoms at the tetracene backbone whereas the peak labeled β is mostly associated to the excitations within the four phenyl side groups of rubrene 26 .…”

TiO2(110) Charge Donation to an Extended π-Conjugated Molecule

“…The local molecular orientation resembles that observed for perylenetetracarboxylic-dianhydride, PTCDA, 24 which was reported to favor a fast (dynamical) charge transfer from the molecule to the substrate. 25 The oxidation state of the molecule in the overlayer can be monitored by comparing the occupied and unoccupied molecular orbitals, MOs, as measured by X-ray photoemission (XPS) and near-edge X-ray absorption spectroscopy (NEX-AFS), respectively. The charge distribution in the surface and near surface layers of TiO 2 can be probed by measuring the characteristic DS in the gap of titania that occurs upon injection of electrons (independently of the mechanism 8,17,26 ).…”

Scanning probe microscopy studies on the adsorption of selected molecular dyes on titania

“…Komolov et al [27] and Cao et al [29–30] investigated very high coverage densities, i.e., multilayer assemblies (up to a few nanometres thick) of molecules on the (110) face of rutile titania using spectroscopic techniques. For a few nanometre thick overlayers, the formation of an interfacial potential barrier due to band bending in the substrate, the molecular polarization in the organic film, and an increase in the work function have been reported [27].…”

“…For a few nanometre thick overlayers, the formation of an interfacial potential barrier due to band bending in the substrate, the molecular polarization in the organic film, and an increase in the work function have been reported [27]. More detailed analyses of the electronic structure, molecular orientations, energy level alignment and charge transfer dynamics have been provided by Cao et al [29–30]. The authors showed that strong coupling between the PTCDA molecules and the TiO 2 substrate results in charge transfer time scales of the order of 8–20 fs [30].…”

“…More detailed analyses of the electronic structure, molecular orientations, energy level alignment and charge transfer dynamics have been provided by Cao et al [29–30]. The authors showed that strong coupling between the PTCDA molecules and the TiO 2 substrate results in charge transfer time scales of the order of 8–20 fs [30]. Additionally, ordering of the molecules in the layers is shown to vary from a slightly tilted geometry, to a disordered one, and to a nearly flat-lying geometry as the coverage density increases from the submonolayer to monolayer, and to multilayer regimes [29].…”