Core-Hole Screening, Electronic Structure, and Paramagnetic Character in Thin Films of Organic Radicals Deposited on SiO2/Si(111)

We investigate thin films of a pyrene derivative of the nitronyl nitroxide radical deposited on SiO2/Si(111). By using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy, we study the electronic structure of the system. From photon energy-dependent analysis, we suggest the occurrence of a shake-up transition consisting of a dipole excitation of a core electron into a valence orbital and a monopole ionization of a valence electron. The persistence of the paramagnetic character is explored by electron spin resonance spectroscopy.