VIS-XUV Optical Constants and Electronic Band Parameters of a Tin-Oxo Cage Photoresist (Sn₁₂O₂₄C₅₂H₁₂₀)

Abstract

Energy band parameters and VIS-XUV optical constants were measured on a Tin-Oxo cage photoresist by employing reflection electron energy loss spectra (REELS) and secondary electron–electron energy loss spectroscopy (SE2ELCS). Different kinematic conditions were chosen for the two reflection loss spectra in order to disentangle contributions of volume and surface losses. The normalized differential inverse inelastic mean free path (nDIIMFP) was extracted and fitted to a model dielectric function, described as a sum of Drude-type oscillators. The oscillator parameters were used to calculate the energy loss function (ELF) and the electron inelastic mean free path (IMFP). An energy gap of E<inf>g</inf>= 6.6 ± 0.5 eV was determined from the onset of the energy loss function. The energetic distance between the valence band maximum (E<inf>VBM</inf>, or highest occupied molecular orbital, HOMO) and the vacuum level (E<inf>vac</inf>) was established by electron-pair spectroscopy by measuring the smallest energy loss leading to emission of a secondary electron. This was found to be 9.9 ± 0.5 eV, giving the electron affinity as χ = E<inf>VBM</inf>– E<inf>vac</inf>– E<inf>g</inf>= 3.3 ± 0.8 eV. The valence bandwidth was estimated from the coincidence data to be E<inf>v</inf>= 8.5 eV.