X-ray photoemission spectroscopy characterization of electrochemical growth of conducting polymer on oxidized Si surface

Abstract

Electrochemical growth of conducting polymer polythiophene (PT) film on an oxidized Si(100) wafer was closely investigated by x-ray photoemission spectroscopy (XPS). The initial stage of polymer growth was investigated by analyzing the core-level energies and spectral profiles of the atomic components. The oxidized Si surface was also closely characterized by XPS using curve fitting of Si 2p and Si 2s core-level spectra to determine precisely covalent states of Si at surface layers. The XPS spectra of Si 2p and Si 2s of the oxidized substrate surface was composed of five peaks which correspond with Si valence values, such as Si, Si+, Si2+, Si3+, and SiO2. The core-level energy positions of those different states were determined by XPS. The Si wafer was prepared through several stages of a wet cleansing process. Scanning tunneling microscopy image of nanoscale ordered native oxide surface was obtained. The native SiO2 layers remained and was probed by Fourier transform infrared spectroscopy reflection absorption spectroscopy and XPS measurements. Electrochemical PT growth at the initial stage was implemented on the oxidized SiO2 surface on Si(100) substrate. The obtained XPS spectra of Si 2p showed that the Si2+ and Si3+ peaks associated with polymer deposition shrank. This experimental result reflects the interface linkage between the organic polymer chain and the Si oxidized layer such as S–O–Si. The bonds between organic and inorganic species such as S–Si are also suggested by analysis of the S 2p3∕2,1∕2 core-level profile.