Interface formation between thin Cu-phthalocyanine films and crystalline and oxidized silicon surfaces

Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on n-Si(1 0 0) and SiO2/n-Si substrates. Evolution of the surface potential and density of unoccupied electronic states located 0–25 eV above vacuum level were measured during the film deposition using an incident beam of low energy electrons using total current electron spectroscopy (TCS), and a new approach based on TCS analysis was developed and applied to studies of charge transfer at the interfaces. The analysis showed that a negative electric charge was transferred from the film to the substrate. A positively charged layer was registered in the CuPc films, which extends over a range from the substrate level and up to 10 nm. At a higher film thickness, bulk CuPc films were formed that have a workfunction of 4.5±0.1 eV. CuPc molecules decompose on the n-Si(1 0 0) substrate due to interaction with the crystalline surface while the film thickness is less than 3 nm. The features of the interfaces observed during formation of the interfaces are analyzed and a model for the extended charge-transfer layer (extended interface dipole) is applied.