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 Cape films were formed that have a workfunction of 4.5 +/- 0.1 cV. 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. (C) 2002 Elsevier Science B.V. All rights reserved.