Densely Packed ZnTPPs Monolayer on the Rutile TiO₂(110)-(1 × 1) Surface: Adsorption Behavior and Energy Level Alignment

Abstract

The adsorption of a densely packed Zinc(II) tetraphenylporphyrin monolayer on a rutile TiO(110)-(1×1) surface has been studied using a combination of experimental and theoretical methods, aimed at analyzing the relation between adsorption behavior and barrier height formation. The adsorption configuration of ZnTPP was determined from scanning tunnel microscopy (STM) imaging, density functional theory (DFT) calculations and STM image simulation. The corresponding energy alignment was experimentally determined from X-ray and UV-photoemission spectroscopies and inverse photoemission spectroscopy. These results were found in good agreement with an appropriately corrected DFT model, pointing to the importance of local bonding and intermolecular interactions in the establishment of barrier heights.

Unveiling universal trends for the energy level alignment in organic/oxide interfaces

“…14,15,47 In UPS and XPS, the kinetic energy of electrons ejected from the sample by excitation from monoenergetic photons reflects the density of occupied states in the system. In IPS the photon energy distribution associated with the decay of a monoenergetic beam of electrons directed to the sample reflects the density of unoccupied states.…”

“…Core levels were probed using X-ray photoemission spectroscopy excited by Al Kα radiation, and the valence band electrons were examined using He II (40.8 eV) excited ultraviolet photoemission spectroscopy. 14,15 In both cases, electron energy distribution was measured using a cylindrical mirror analyser. IPS was performed using a grating spectrometer with a primary electron energy of 20.3 eV.…”

“…These interfaces have been studied using a combination of experimental and theoretical techniques in previous publications. [14][15]18 Herein, we review the main results and discuss the similarities and differences found in these different paradigmatic cases, putting these results in a more general perspective. Also, in order to get new insights (and better understand the connection between these different cases), we present a new proof-of-concept analysis in which we apply a "theoretical" bias potential between the organic and the oxide, Δ, and analyse the energy level alignment at these interfaces as a function of Δ.…”

“…12 However, effects such as electron charge transfer upon molecular adsorption with possible space charge layer formation in the oxide, as well as the nature of the chemical interaction of the organic on the oxide surface, are important considerations in any attempt to fully understand such interfaces. [13][14][15][16][17][18] In this perspective we analyse the physicochemical mechanisms that control energy level alignment at the interface between a prototypical metal oxide surface, TiO 2 (110), and different organic monolayers with dissimilar properties, PTCDA, 18 Zn-TPP 15 and TCNQ.…”

Thermally induced anchoring of a zinc-carboxyphenylporphyrin on rutile TiO2 (110)

“…Consequently, many different porphyrin-titania systems have been investigated under ultra-high vacuum (UHV) conditions by scanning probe techniques and photoelectron spectroscopy (PES). [21][22][23][24][25][26][27][28][29][30][31] Carboxylic acid substituents have often been used for immobilization of porphyrins on TiO 2 . 14,19 However, for relatively large porphyrins, which have been evaporated to the surface, it is often not clear if the anchoring group really undergoes reaction with the surface.…”