Hybrid States and Charge Transfer at a Phthalocyanine Heterojunction: ${\mathrm{MnPc}}^{\delta +}/{{\mathbf{F}}_{16}\mathrm{CoPc}}^{\delta -}$

Using photoelectron spectroscopy we demonstrate charge transfer at an interface between two well-known transition metal phthalocyanines, MnPc and ${\mathrm{F}}_{16}\mathrm{CoPc}$, resulting in charged ${\mathrm{MnPc}}^{\delta +}$ and ${\mathrm{F}}_{16}{\mathrm{CoPc}}^{\delta -}$ species. Moreover, the transferred charge is substantially confined to the two transition metal centers. Density functional theory calculations reveal that a hybrid state is formed between the two types of phthalocyanines, which causes this charge transfer. For the hybrid state the Mn $3d_{xz}$ interacts with the Co $3d_{z^2}$ orbital leading to a two-level system. As only the lower of the two hybrid states is occupied, the charge is directly transferred to the Co $3d_{z^2}$ orbital.

Figure 1

Evolution of the C $1s$ core level photoemission profile upon deposition of ${\mathrm{F}}_{16}\mathrm{CoPc}$ on a 3 nm thick layer of MnPc. We additionally show the results of a modeling of the data using an appropriately weighted sum (dashed line) of an otherwise unchanged photoemission profile of the two individual phthalocyanines (filled areas).

Figure 2

Co $2p_{3/2}$ core level photoemission spectra of a thin and thick ${\mathrm{F}}_{16}\mathrm{CoPc}$ layer on top of MnPc. Also shown is the corresponding result for a ${\mathrm{F}}_{16}\mathrm{CoPc}$ monolayer on Au(100) [19].

Figure 3

(a) Co $2p_{3/2}$ and (b) Mn $2p_{3/2}$ core level photoemission spectra for a $\mathrm{MnPc}/{\mathrm{F}}_{16}\mathrm{CoPc}$ heterojunction when MnPc is deposited on a 3 nm thick ${\mathrm{F}}_{16}\mathrm{CoPc}$ layer.

Figure 4

Interaction of the MnPc and ${\mathrm{F}}_{16}\mathrm{CoPc}$ states in the $\mathrm{MnPc}\mathrm{\text{−}}{\mathrm{F}}_{16}\mathrm{CoPc}$ dimer close to the Fermi level. The Mn $3d_{xz}$ and the Co $3d_{z^2}$ orbitals hybridize to form a two-level system.