Experimental determination of electron effective attenuation lengths in silicon dioxide thin films using synchrotron radiation - II. Effects of elastic scattering

The effective attenuation lengths (EALs) of photoelectrons in thin silicon dioxide films on an Si(100) substrate were measured as a function of electr on energy using synchrotron radiation as an energy-tunable excitation sourc e. The ratios of EALs to inelastic mean free paths (IMFPs) calculated from optical data were independent of electron energy from 140 to 1000 eV when t he analyzer axis was normal to the sample surface and the angle between the incident x-rays and the surface normal was 55 degrees. This result indicat es that the effects of elastic electron scattering (in causing the EAL to b e less than the corresponding IMFP) were independent of electron energy for this configuration, The EALs measured with normally incident x-rays and el ectron emission at 55 degrees with respect to the surface normal were large r than EALs for the other configuration, In particular, the difference for the EALs at the two configurations was similar to 25% for electron energies below 200 eV, The angular range suitable for satisfactory angle-resolved a nalyses with x-ray photoelectron spectroscopy should therefore be limited t o <55 degrees when the electron energies are less than similar to 500 eV, C opyright (C) 2000 John Whey & Sons, Ltd.