Analysis of X-Ray Photoelectron Spectra of Silicon-Based Polymers by deMon Density-Functional Calculations Using Model Molecules

The X-ray photoelectron spectra (XPS) of seven silicon-based polymers[ (-Si(CH3)2-)n (PDMS), (-Si(C6H5)(CH3)-)n (PMPS), (-Si(n-C6H13)2-)n (PDHS), (-Si(CH3)2-O-)n (PDMSO), (-Si(C6H5)(CH3)-O-)n (PMPSO), (-Si(CH3)(C6H5)-CH2-)n (PMPSM), and (-Si(C6H5)2-CH2-)n (PDPSM)] in XPS were analyzed by deMon density-functional calculations using model molecules. Calculated Al-Kα valence photoelectron spectra were obtained using Gaussian lineshape functions of an approximate linewidth (0.10Ik): Ik=Ik′−WD, as in previous works. The vertical ionization potential Ik′ was calculated by restricted diffuse ionization (rDI) model. The theoretical spectra showed good agreement with the observed spectra of the polymers between 0–40 eV. The core-electron binding energies (CEBEs) of C1s, O1s and Si2p of the model molecules were calculated by unrestricted generalized-state (uGTS) models. The difference between calculated and the observed CEBEs for C1s reflected WDs of the polymers.