Mean escape depth of signal photoelectrons ejected from solids by polarized x rays

Quick development of synchrotron radiation facilities and prospective applications of photon beams of a variable energy in spectroscopy of solids and interfaces prompts further studies of photoemission induced by polarized soft x rays. One of the most important characteristics in surface sensitive spectroscopies is the mean escape depth of signal electrons leaving a sample without being scattered inelastically. In this article a simple analytical expression for the average escape depth of photoelectrons ejected by polarized x rays is found by means of the depth distribution function obtained by solving the transport equation. The dependence of the escape depth on the type and the degree of photon polarization is predicted. This effect is due to the anisotropy of the initial angular distribution of photoelectrons and elastic scattering they suffer on their way out of the target. The variation of the mean escape depth with the type and the degree of polarization as well as with the emission direction from the target is quite well pronounced and may reach up to 100% with respect to the value determined by the inelastic mean free path in the usual x-ray photoelectron spectroscopy formalism. The dependence of the escape depth on the azimuthal and polar emission angles is studied in detail. In the special case of unpolarized x rays the expression for the average escape depth reduces to the result found earlier.