Electron inelastic mean free path in MoO3 thin films

Abstract

Determination of the electron inelastic mean free path (IMFP) in complex and functional materials is a fascinating problem for which scattered results can be found in present literature. Knowledge of the IMFP is crucial in determining the probing depth of several important techniques based on the collection of electrons excited by external probes. In particular no experimental data can be found for several oxides including MoO${}_3$, a promising material used in several forms for applications. To the purpose of measuring the IMFP, we performed accurate constant initial state (CIS) Si2p photoemission experiments on Si wafers covered with layers of amorphous MoO${}_3$ of variable thickness, using synchrotron radiation in a variable photon energy range 135–280 eV at the BEAR beamline at Elettra. In particular the SiO${}_x$ photoemission peak has been analyzed, selecting only those photoelectrons which originate from the native oxide layer of the silicon wafer. The electron Inelastic Mean Free Path has been derived using a first-order treatment for elastic scattering. This latter is justified by the particular experimental conditions, namely the use of a thin overlayer and a small analyzer acceptance angle. Present IMFP results are compared with previous semi-empirical models, improving our present knowledge of the IMFP curve in amorphous MoO${}_3$ and opening new experimental possibilities for accurate measurements of the probing depth in functional materials.