Electronic structure of thin film TiOPc studied by means of X-ray absorption and photoelectron spectroscopies

Alfredsson, Ylvi; Rensmo, Håkan; Sandell, A.; Siegbahn, Hans

doi:10.1016/j.elspec.2009.05.002

Cited by 10 publications

(22 citation statements)

References 40 publications

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“…Several studies found that TiOPc on graphite (Highly Oriented Pyrolytic Graphite -HOPG) grows with its backbone parallel to the surface plane and with the oxygen atom pointing away from the substrate. [12][13][14] The same has been observed for other non-planar Pc molecules like VOPc 15,16 or AlCl-Pc. 17,18 However, some studies devoted to TiOPc on Ag(111) suggested a tilted orientation, 19,20 that could not be confirmed by more recent investigations.…”

Section: Introductionsupporting

confidence: 75%

Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

Lerch¹,

Fernández

Ilyn

et al. 2017

J. Phys. Chem. C

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We have investigated the electronic structures of axially oxo functionalized titanylphthalocyanine (TiOPc) on Ag(111) by X-ray and ultraviolet photoelectron spectroscopy, two-photon photoemission, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Furthermore, we use complementary data of TiOPc on graphite and planar copper phthalocyanine (CuPc) on Ag(111) for a comparative analysis. Both molecules adsorb on Ag(111) in a parallel orientation to the surface, for TiOPc with an oxygen-up configuration. The interaction of nitrogen and carbon atoms with the substrate is similar for both molecules while the bonding of the titanium atom to Ag(111) in the monolayer is found to be slightly more pronounced than in the CuPc case. Ultraviolet photoemission spectroscopy reveals an occupation of the lowest unoccupied molecular orbital (LUMO) level in monolayer thick TiOPc on Ag(111) related to the interaction of the molecules and the silver substrate. This molecule-metal interaction also causes an upward shift of the Ag(111) Shockley state that is transformed into an unoccupied interface state with energies of 0.23 and 0.33 eV for the TiOPc mono-and bilayer, respectively, at the Brillouin zone center.

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Section: Introductionsupporting

confidence: 75%

Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

Lerch¹,

Fernández

Ilyn

et al. 2017

J. Phys. Chem. C

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“…The spectra from the different molecules are very similar and consistent with published data for TiOPc. 20,21 The position of the low-energy peak, at 398.1 eV, is unchanged in all spectra. The only noticeable difference is the intensity ratio of the double feature centered at 399.9 eV.…”

Section: ■ Results and Discussionmentioning

confidence: 91%

“…The GT1 spectrum exhibits well-resolved peak structure in the 2p 3/2 manifold with features similar to those in previously published data for TiOPc. 20,21 Comparison of the spectra from the four molecules shows that the pair GT1/GT6 exhibits very similar features and peak positions, and likewise for GT2/GT7. These pairs of molecules contain the same axial ligands, indicating that the peripheral groups have less influence at the Ti 2p edge, as one might expect from their large distance from the central Ti atom.…”

Section: ■ Results and Discussionmentioning

confidence: 96%

Influence of Axial and Peripheral Ligands on the Electronic Structure of Titanium Phthalocyanines

et al. 2013

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To discover how molecular changes affect the electronic structure of dye molecules for solar cells, we have investigated four titanium phthalocyanines customized by axial and peripheral ligands (monodentate oxo versus bidentate catechol and tert-butyl versus tert-butylphenoxy, respectively). X-ray absorption spectroscopy and photoelectron spectroscopy were combined with density functional theory (DFT) and crystal-field multiplet calculations to characterize the Ti 3d and N 2p valence electrons that form the frontier orbitals. When a monodentate oxo axial ligand was replaced by a bidentate catechol ligand, the multiplet structure of the Ti 2p-to-3d transitions was found to change systematically. The most noticeable change was an additional transition into the low-lying 3d xy level, which is attributed to a reduction in local symmetry from 4-fold to 2-fold at the Ti center. An increase of the Ti 2p core-level binding energy was observed in the bidentate complex and compared to a calculated core-level stabilization. DFT predicts a change of the LUMO from the inner phthalocyanine ring to the Ti d xy orbital and a reversal of the high-lying d x 2 −y 2 and d z 2 orbitals. The N 1s edge was calculated using time-dependent density functional theory (TDDFT) and compared to experiment.

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“…To address this issue, complementary carbon K-edge X-ray absorption (C 1s NEXAFS) dichroism measurements are performed, as this method allows a determination of the molecular orientation independent of the degree of crystalline order . Remarkably, despite the general interest in TiOPc’s electronic signature, there is little NEXAFS data available to date. , In particular, high-resolution C 1s NEXAFS data are yet not reported, which might be related to the requirement of particularly pristine beamline optics with low carbon contamination. To provide reference data for a structurally well-defined TiOPc layer, at first C 1s NEXAFS spectra are recorded for a 10 nm film prepared at 360 K, which are depicted in Figure a.…”

Section: Resultsmentioning

confidence: 99%

Titanylphthalocyanine Films on Ag(111): An Epitaxial Metal/Organic Heterosystem with an Exceptional Smooth Surface

2019

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The fabrication of smooth organic semiconductor films with homogeneous thickness is of key importance for the improvement of organic electronic devices and realization of well-defined molecular heterostructures. Although many π-conjugated molecular materials form highly ordered monolayers on (single) crystalline metal substrates, further deposition typically obeys a Stranski–Krastanov growth and results in considerable layer roughness. Here, we examine the evolution of titanylphthalocyanine (TiOPc) films on Ag(111) for thicknesses ranging from an initial seed layer to thick multilayers (200 nm) by combining scanning probe microscopy [scanning tunneling microscopy (STM) and atomic force microscopy (AFM)] with X-ray diffraction and synchrotron-based photoelectron spectroscopy [X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption spectroscopy (NEXAFS)]. While the crystallinity of the TiOPc films increases with substrate temperature during growth, even at temperatures close to the onset of desorption, extended and molecularly flat islands are formed, which cover more than 80% of the substrate area resulting in exceptional smooth layers. The crystalline TiOPc films exclusively exhibit the phase I polymorph where molecular planes are oriented nearly parallel to the substrate surface and adopt an alternating (up/down) stacking of their titanyl groups forming stable bilayer units. Similar to the first bilayer, TiOPc multilayers are also epitaxially aligned with respect to the substrate. STM and AFM data further show that the macroscopic film roughness is essentially due to rotational domain boundaries in the seed layer which are not overgrown and result in characteristic macroscopic trenches. The high crystalline ordering and exceptional smoothness make this metal/organic heterosystem particularly suitable as a molecular spacer layer and allows for thickness-dependent studies of optoelectronic excitations and their dynamics.

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Electronic structure of thin film TiOPc studied by means of X-ray absorption and photoelectron spectroscopies

Cited by 10 publications

References 40 publications

Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

Influence of Axial and Peripheral Ligands on the Electronic Structure of Titanium Phthalocyanines

Titanylphthalocyanine Films on Ag(111): An Epitaxial Metal/Organic Heterosystem with an Exceptional Smooth Surface

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