N1s and C1s Near-Edge X-ray Absorption Fine Structure Spectra of Model Systems for Pyridine on Si(100): A DFT Simulation

Abstract

This work presents a density functional theory (DFT)-based computational investigation of the near-edge X-ray absorption fine structure (NEXAFS) spectra of pyridine on the Si(100) surface. The accurate modeling of the adsorbate system is tackled by a preliminary optimization of the surface and of the molecules adsorbed on it performed by a periodic slab methodology. From the optimized periodic structures, suitable finite clusters are then cut out and used for the calculation of core excitation energies and oscillator strengths of the adsorbed pyridine. Various adsorption modes are considered, and for each of them, the polarized spectra at the N K edge and the C K edge of the pyridine have been simulated with the transition potential scheme to include the core hole relaxation effect. Careful analysis of the calculated polarized features and the intensity trend with the change of polarization reveals important information on specific details of the adsorption geometries and supports the comparison with expe...