Abstract

The conformation of molecules on surfaces is decisive for their functionality. In the case of the endofullerene paramagnet Sc₂TbN@C₈₀ the conformation is linked to an electric and a magnetic dipole moment. Therefore a workfunction change of a substrate with such molecules on the surface suggests the system to be magnetoelectric. Here one monolayer of Sc₂TbN@C₈₀ has been studied on h-BN/Ni(111). The molecules assume a hexagonally close packed lattice aligned with the substrate high symmetry directions. The structure is incommensurate and arranges at a periodicity of ≈4.3×4.3 substrate unit cells. At low temperatures a C₈₀ (2×2) superstructure is observed. Valence band photoemission spectroscopy shows a temperature induced 0.3 eV shift on the C₈₀ molecular orbitals to lower binding energies that is parallel to a workfunction increase. From comparison of the molecular orbital angular photoemission intensity distributions it is conjectured that the molecules undergo a change in conformation between 30 and 300 K. This phase transition is centred at 125 K as observed with high resolution x-ray photoelectron spectroscopy that shows the core levels of the atomic species on the molecules to shift parallel to the workfunction. The temperature dependence can be described with a two level model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. The experimental findings are backed by density functional theory for the diamagnetic sibling of Sc₂TbN@C80: Sc₂YN@C80. The calculations rationalize the incommensurate structure, indicate a permanent electric dipole moment of Sc₂YN@C₈₀ and predict the room temperature N 1s x-ray photoelectron spectrum.

Abstract

The conformation of molecules on surfaces is decisive for their functionality. In the case of the endofullerene paramagnet Sc₂TbN@C₈₀ the conformation is linked to an electric and a magnetic dipole moment. Therefore a workfunction change of a substrate with such molecules on the surface suggests the system to be magnetoelectric. Here one monolayer of Sc₂TbN@C₈₀ has been studied on h-BN/Ni(111). The molecules assume a hexagonally close packed lattice aligned with the substrate high symmetry directions. The structure is incommensurate and arranges at a periodicity of ≈4.3×4.3 substrate unit cells. At low temperatures a C₈₀ (2×2) superstructure is observed. Valence band photoemission spectroscopy shows a temperature induced 0.3 eV shift on the C₈₀ molecular orbitals to lower binding energies that is parallel to a workfunction increase. From comparison of the molecular orbital angular photoemission intensity distributions it is conjectured that the molecules undergo a change in conformation between 30 and 300 K. This phase transition is centred at 125 K as observed with high resolution x-ray photoelectron spectroscopy that shows the core levels of the atomic species on the molecules to shift parallel to the workfunction. The temperature dependence can be described with a two level model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. The experimental findings are backed by density functional theory for the diamagnetic sibling of Sc₂TbN@C80: Sc₂YN@C80. The calculations rationalize the incommensurate structure, indicate a permanent electric dipole moment of Sc₂YN@C₈₀ and predict the room temperature N 1s x-ray photoelectron spectrum.

Abstract

The conformation of molecules on surfaces is decisive for their functionality. In the case of the endofullerene paramagnet Sc₂TbN@C₈₀ the conformation is linked to an electric and a magnetic dipole moment. Therefore a workfunction change of a substrate with such molecules on the surface suggests the system to be magnetoelectric. Here one monolayer of Sc₂TbN@C₈₀ has been studied on h-BN/Ni(111). The molecules assume a hexagonally close packed lattice aligned with the substrate high symmetry directions. The structure is incommensurate and arranges at a periodicity of ≈4.3×4.3 substrate unit cells. At low temperatures a C₈₀ (2×2) superstructure is observed. Valence band photoemission spectroscopy shows a temperature induced 0.3 eV shift on the C₈₀ molecular orbitals to lower binding energies that is parallel to a workfunction increase. From comparison of the molecular orbital angular photoemission intensity distributions it is conjectured that the molecules undergo a change in conformation between 30 and 300 K. This phase transition is centred at 125 K as observed with high resolution x-ray photoelectron spectroscopy that shows the core levels of the atomic species on the molecules to shift parallel to the workfunction. The temperature dependence can be described with a two level model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. The experimental findings are backed by density functional theory for the diamagnetic sibling of Sc₂TbN@C80: Sc₂YN@C80. The calculations rationalize the incommensurate structure, indicate a permanent electric dipole moment of Sc₂YN@C₈₀ and predict the room temperature N 1s x-ray photoelectron spectrum.

Abstract

The conformation of molecules on surfaces is decisive for their functionality. In the case of the endofullerene paramagnet Sc₂TbN@C₈₀ the conformation is linked to an electric and a magnetic dipole moment. Therefore a workfunction change of a substrate with such molecules on the surface suggests the system to be magnetoelectric. Here one monolayer of Sc₂TbN@C₈₀ has been studied on h-BN/Ni(111). The molecules assume a hexagonally close packed lattice aligned with the substrate high symmetry directions. The structure is incommensurate and arranges at a periodicity of ≈4.3×4.3 substrate unit cells. At low temperatures a C₈₀ (2×2) superstructure is observed. Valence band photoemission spectroscopy shows a temperature induced 0.3 eV shift on the C₈₀ molecular orbitals to lower binding energies that is parallel to a workfunction increase. From comparison of the molecular orbital angular photoemission intensity distributions it is conjectured that the molecules undergo a change in conformation between 30 and 300 K. This phase transition is centred at 125 K as observed with high resolution x-ray photoelectron spectroscopy that shows the core levels of the atomic species on the molecules to shift parallel to the workfunction. The temperature dependence can be described with a two level model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. The experimental findings are backed by density functional theory for the diamagnetic sibling of Sc₂TbN@C80: Sc₂YN@C80. The calculations rationalize the incommensurate structure, indicate a permanent electric dipole moment of Sc₂YN@C₈₀ and predict the room temperature N 1s x-ray photoelectron spectrum.