Epitaxial growth and electronic properties of well ordered phthalocyanine heterojunctions MnPc/F16CoPc

Abstract

We have prepared phthalocyanine heterojunctions out of MnPc and F16CoPc, which were studied by means of X-ray absorption spectroscopy. This heterojunction is characterized by a charge transfer at the interface, resulting in charged MnPc(δ +) and F16CoPc(δ -) species. Our data reveal that the molecules are well ordered and oriented parallel to the substrate surface. Furthermore, we demonstrate the filling of the Co 3d(z(2)) orbital due to the charge transfer, which supports the explanation of the density functional theory, that the charge transfer is local and affects the metal centers only.

Surface chemistry of porphyrins and phthalocyanines

“…For C 60 F 48 / ZnTPP/Au(1 1 1), but not for C 60 /ZnTPP/Au (1 1 1), strong integer charge transfer over the organic/organic interface was observed, causing structural disorder and molecular distorsion [632]. (Note that similar studies have been performed for interfaces between multilayers, for example for MnPc/CoPcF 16 , where an interfacial charge transfer from MnPc to CoPcF 16 was observed [633]. )…”

Charge transfer from and to manganese phthalocyanine: bulk materials and interfaces

“…A further example in which a charge transfer across an interface results in new physical properties at this interface is provided by bringing together MnPc and F 16 CoPc. Highly ordered interfaces of this kind were realized by depositing one of the two phthalocyanines on a gold(100) single crystal, which resulted in well-oriented thin films [ 125 – 127 ]. Subsequently, the partner phthalocyanine was deposited on top, which finally gave rise to well-ordered heterojunctions as revealed by polarization dependent X-ray absorption spectroscopy (XAS) studies [ 127 ].…”

“… N 1s excitation spectra as obtained using X-ray absorption spectroscopy (adapted from [ 127 ]). Corresponding data for (c) a 2.0 nm thick MnPc film on Au(100), (b) an additional 0.6 nm thick F 16 CoPc overlayer on MnPc, and (a) a relatively thick F 16 CoPc overlayer (3 nm) are depicted.…”

“…The observed intensity variations show that the respective phthalocyanine molecules are arranged parallel to the substrate surface with a very high degree of orientation. The mean deviation from exactly parallel lying molecules is only about 5% [ 127 ]. This very high degree of order is also kept across the MnPc/F 16 CoPc interface, as can be seen from Fig.…”

Energy-level alignment at interfaces between manganese phthalocyanine and C60

“…Also, the orientation of phthalocyanine molecules has been used to influence the C 60 energy levels at respective junctions [55]. It is further known that MnPc and other transition-metal-phthalocyanine molecules grow in a flat lying manner on Au(100) [49,56], while on top of C 60 they exhibit an edge-on orientation (i.e., they stand up) [57–58]. This then can cause a different energy-level alignment as the ionization depends on the molecular orientation in the layers [53].…”