Nitrogen 1s NEXAFS and XPS spectroscopy of NH3 -saturated Si(001)- 2×1: Theoretical predictions and experimental observations at 300 K

In the light of hybrid functional density-functional theory calculations of the core-excited and core-ionized states, this paper discusses original N 1s x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine-structure (NEXAFS) experimental data on the single-domain (vicinal) Si(001)- 2×1 surface saturated by NH3 at 300 K. The theoretical approach enables to discuss the vibrational shape of the N 1s XPS spectrum and quantifies the binding-energy splitting due to intrarow and inter-row hydrogen bondings between amine pairs. The observed N 1s NEXAFS peaks are interpreted through the analysis of the contour maps of the antibonding Kohn-Sham orbitals of the NH2 adsorbate and through the Δ Kohn-Sham calculation of the transition energies, laying a theoretical basis for a discussion of the adsorbate spatial orientation. Finally, suggestions are given for future directions of research to get a further knowledge of a system that has potential applications as a template for molecular layer deposition and supramolecular assembly.