Filled and empty states of Zn-TPP films deposited on Fe(001)-p(1×1)O

Abstract

Zn-tetraphenylporphyrin (Zn-TPP) was deposited on a single layer of metal oxide, namely an Fe(001)-p(1×1)O surface. The filled and empty electronic states were measured by means of UV photoemission and inverse photoemission spectroscopy on a single monolayer and a 20 monolayer thick film. The ionization energy and the electron affinity of the organic film were deduced and the interface dipole was determined and compared with data available in the literature.

Self-assembly of C60 on a ZnTPP/Fe(001)–p(1 × 1)O substrate: observation of a quasi-freestanding C60 monolayer

“…In Figure 5b , the evolution of the work function for the different samples is presented. Starting from the bare substrate, the work function is reduced by about 0.3 eV after the deposition of 1 ML of ZnTPP, in agreement with previous measurements [ 42 ]. Such a decrease has been ascribed to charge transfer from ZnTPP to the Fe(001)– p (1 × 1)O substrate.…”

An In-Depth Assessment of the Electronic and Magnetic Properties of a Highly Ordered Hybrid Interface: The Case of Nickel Tetra-Phenyl-Porphyrins on Fe(001)–p(1 × 1)O

“…To strengthen this conclusion, we evaluated the HOMO-LUMO gap of the samples. The HOMO and the LUMO energies are determined by evaluating the rising edges of the respective features, as shown in Figure 3 b,c [ 23 , 44 ]. To help the correct evaluation of the LUMO, a linear background was subtracted.…”

Room temperature magnetism of ordered porphyrin layers on Fe

“…For the latter, taken as representative of low-interacting MTPP having no free coordination sites, we detected the formation of a wetting layer with a (5 Â 5) periodicity, characterized by an electronic structure similar to that of free-standing molecules. 17,35,36 These results depict a regime of "partial decoupling" with the substrate, characterized by the absence of strong hybridization, which might nevertheless support non-negligible interactions such as those of an exchange type, leading to a ferromagnetic ordering of MTPP magnetic moments. Conversely, the strong interaction between ZnTPP and bare Fe(001) is reflected in (i) a loss of the surface order [due to a reduced mobility of the molecules in contact with the substrate and linked to the absence of a low energy electron diffraction (LEED) pattern] and (ii) a quenching of those photoemission features related to the tetrapyrrole ring (see below for more details).…”

“…Conversely, the strong interaction between ZnTPP and bare Fe(001) is reflected in (i) a loss of the surface order [due to a reduced mobility of the molecules in contact with the substrate and linked to the absence of a low energy electron diffraction (LEED) pattern] and (ii) a quenching of those photoemission features related to the tetrapyrrole ring (see below for more details). 17,36 Molecular deposition was performed in a ultrahigh vacuum system (base pressure as low as 10 À8 Pa) equipped with dedicated chambers for the substrate preparation and the deposition of the organic layers. 37 The Fe(001)-p(1 Â 1)O substrate was prepared by first depositing a thick (about 500 nm) Fe layer on top of MgO(001) and subsequently dosing 30 L [1 langmuir (L) ¼ 10 À6 TorrÁs] of molecular oxygen with the surface kept at 450 C. Excess oxygen was finally removed by flash-heating up to 700 C. MTPP molecules were evaporated from a BN crucible held at about 300 C and their flux [kept at about 0.3 molecular layers (ML) per minute] was monitored by means of a quartz microbalance.…”

“…The shift of the molecular features away from E F observed with PES (IPES) at 4.0 ML coverage (panel a) is due to a less efficient screening of the photoemission hole (extra electron) by the substrate with respect to the ML configuration. 17,36 The HOMO and LUMO features are related to electronic states localized on the main tetrapyrrole ring of the CoTPP molecule, while the other features can be either related to photoemission from the ring (label "R") or from the four peripheral phenyl groups (labeled "Ph"). 17,43 According to this analysis, the spectra from the bare Fe(001)-p(1 Â 1)O surface provide only an approximate description of the substrate contribution at ML coverage, a result that we attribute to the combined effect of electronic modifications occurring at the interface and the distortion of the substrate photoemission signal by scattering from the molecular layer, particularly effective when working, as in the present case, with a finite-acceptance spectrometer.…”