Spin State in Perfluorinated FePc Films on Cu(111) and Ag(111) in Dependence on Film Thickness

Abstract

The electronic structure of the central iron ion of perfluorinated iron phthalocyanine (FePcF 16 ) in thin films has been studied on Cu(111) and Ag(111) using polarization dependent X-ray absorption spectroscopy (XAS). The data are compared to FePc on Ag(111). Ligand field parameters have been computed, and multiplet calculations (CTM4XAS) were carried out to simulate XAS spectra. The planar molecules are preferentially oriented lying flat on the substrate surface during the growth of the 1−4 nm thick films. A clear polarization dependence of the Fe L edge absorption spectra is observed, arising from transitions into orbitals with in-plane and out-of-plane character. The shape of the spectra for three to four monolayers of FePcF 16 on Cu(111) is comparable to that of the thin films of FePc on Ag(111). However, a drastic change of the XAS peak shape is observed for thicker FePcF 16 films on both Ag(111) and Cu(111), although the molecular orientation is very similar to coverages consisting of a few monolayers. Since in both cases the film thickness is distinctly beyond the monolayer regime, interface interactions can be ruled out as a possible origin of this behavior. Rather, the different XAS peak shapes seem to indicate that the multiplicity may depend on the detailed arrangement of the FePcF 16 molecules. The large flexibility of the ground state of Fe could be of high interest for spintronic applications.

Influence of the Fluorination of Iron Phthalocyanine on the Electronic Structure of the Central Metal Atom

“…Especially for iron phthalocyanines the electronic structure of the Fe ion may further depend on subtle differences of its surroundings, i.e., the detailed arrangement of neighboring molecules. 57,67 The orientation of planar molecules can be probed by XAS (or near-edge X-ray absorption fine structure, NEXAFS) using linearly polarized synchrotron light. 68−70 Both C 1s-π* and N 1s-π* excitations can be used for determining the orientation of phthalocyanines.…”

FePc and FePcF16 on Rutile TiO2(110) and (100): Influence of the Substrate Preparation on the Interaction Strength

“…The corresponding Fe 2p spectra are shown in Figure S8. The broad multiplet structures of the Fe 2p spectra, which may depend also on the (thickness-dependent) arrangement of the FePcF 16 molecules in thin films [55,56], hamper, however, a more detailed analysis of these spectra. Compared to FePcF 16 on rutile TiO 2 (100) prepared in the presence of oxygen (Figure 11), the N 1s spectra in Figure 13 show distinctly more intense interface components (green peaks in Figure 13b) for low coverages at a binding energy of 401.0 eV, indicating that more molecules undergo a strong interaction at this interface.…”

Interaction Channels Between Perfluorinated Iron Phthalocyanine and Cu(111)

“…A possible reason is a change of spin state as discussed in ref. . However, the dominant feature at 0.5 nm coverage results from an interaction between the central iron ion and the copper substrate, as has been discussed for related systems, such as FePc on Ag(111) .…”

“…At 3.0 nm, new dominant features A3 (Figure a) and B3 appear at higher photon energies, resulting in a drastic change of the shape of the spectra compared to the 1.2 nm film and to FePc in bulk‐like films . This can be explained by a change of the spin multiplicity of the central iron atom, possibly due to a change of the detailed arrangement of molecules as a function of the film thickness . The discussion of the Fe L edge spectra of the thickest film (5.5 nm) is somewhat hindered by the change of the molecular orientation, but also in this case the broad features hint to a higher spin multiplicity compared to Fe in FePc.…”