Evidencing Intermolecular Effects with Core-Level Photoelectron Spectroscopy via the Accurate Density Functional Calculation of Core−Electron Binding Energies on Model Systems: γ-APS as a Test

Abstract

γ-Aminopropyltrihydroxysilane (γ-APS) is a molecule which is used as an adhesion promoter in microelectronics, for the coating of oxidized silicon wafers with polyimide films. The Si/γ-APS interface has been studied recently using X-ray photoelectron spectroscopy, and evidenced a need for reference spectra of both γ-APS and its thermal byproducts: as γ-APS oligomerizes readily upon warming, no gas phase, reference, or XPS spectrum of this compound can be obtained experimentally. Thus, spectral features emerging from Si/γ-APS interactions are difficult to separate from structural fingerprints of γ-APS alone. This phenomenon further hinders the follow up by XPS of structural modifications the molecule undergoes upon thermal treatments. A recent procedure of computing very accurate core−electron binding energies (CEBEs) via density functional theory (DFT) is used as a guide to propose a pseudo reference spectrum. The computed CEBEs of the various core levels of the isolated molecule are found in excellent ag...