Thin films of platinum based metalloporphyrines: synthesis, photoemission and AFM studies
Ionov, Andrey1; Belogorokhov, Alexander1; Bozhko, Sergey1; Chaika, Alexander2; Trophymov, Sergey2; Rumyantseva, Valentina1; Vyalikh, Denis1
1Russian Federation;
2Saint Helena

The electronic structure and topography of tetraphenylporphyrin (TPP) and Pt-based Pt-TPP(p-COOCH3)4; Pt-TPP(m-OCH3)4; Pt-TPP(m-OCH3Cl2)4 thin films were studied by PES and AFM. Samples were prepared by evaporation under UHV in situ and by means of deposition from the CHCl3 solution self-assembling techniques onto Si(100), mica and Cu substrates. The surface of samples were cleaned for PES in situ by heating at 400 K, the pressure was about 1×10-9 mbar. The HRPES studies of VB and core levels were performed in the RGBL BESSY II using photon energies 120-600 eV at normal emission. Total resolution was about 120 meV. All elements of compounds were found in XPS spectra. In TPP spectra two peaks of N1s at 399.8 and 397.8 eV (BE range) were assigned to sp3 and sp2 nitrogen respectively. In metalloporphyrins charge distribution is more uniform for N1s spectra of Pt2+-TPP(m-OCH3)4 and other metalloporphyrins. Different peaks at 285 and 286.2 eV were seen in the C1s spectra that are related to the unequivalent C atoms in the molecules (aromatic and C-N-C groups). The valence band is formed by peaks corresponding to pi (2- 12 BE range) and sigma states (8-16 eV) of porphyrins macrocycles. Peak of C2s states in TPP and metalloporphyrins lied at 18 eV in VB spectra. XPS and UPS studies have also demonstrated higher thermal stability of Pt-TPP(m-OCH3)4 and Pt2+-TPP(p-COOCH3)4 in UHV compared with Pt-TPP(m-OCH3Cl2)4.
AFM studies of thin films structure show that the structure of solid-phase films determined by their chemical nature, supramolecular structure and interaction with substrates. It was shown that substrates affect the deposited layers structure at earlier stages of the layer formation. These films self-assemble onto air into partially ordered large rod-shaped and flat supramolecular nanostructures on flat substrates, with an average size in nanoscale, where the molecules are approximately parallel and cofacial to one another.
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