Relevance of the EEL spectroscopy for in-situ studies of the growth mechanism of copper-phthalocyanine molecules on metal surfaces: Al(100)

TL;DR

This study uses reflection electron energy loss spectroscopy (EELS) to investigate the early growth stages of copper-phthalocyanine molecules on Al(100), revealing charge transfer effects and molecular orientation during film formation.

Contribution

It demonstrates the effectiveness of EELS in analyzing the electronic structure and growth mechanism of CuPc molecules on metal surfaces in situ.

Findings

Charge transfer from Al substrate to CuPc's LUMO affects electronic structure.

Coverage-dependent shifts in Al surface plasmon frequency observed.

Molecular plane orientation is nearly perpendicular to the substrate in thicker films.

Abstract

Reflection electron energy loss spectroscopy (EELS) in specular and off specular geometry has been employed to study the early stage of the copper phthalocyanine (CuPc) growth on Al (100) substrate. EEL spectroscopy has been a useful tool in order to study electronic structure of molecular films also in the submonolayer regime. The electronic structure of the first deposited layer of CuPc is strongly influenced by charge transfer from the Al substrate to the lowest unoccupied molecular orbital (LUMO). The strong molecule-substrate interaction gives rise to a coverage dependent frequency shift of the Al surface plasmon. Successive layers have essentially the electronic structure of the molecular solid. Momentum resolved EELS measurements reveal that, in the case of the thicker film investigated (22 \AA), the plane of the molecule is almost perpendicular to the surface of the substrate.