Ion-induced electron emission - monitoring the structure transitions in graphite

The temperature dependence of ion-induced electron emission yield gamma under 30 keV Ar+ ion impacts at incidence angles theta = 0-80 degrees under dynamically steady-state conditions has been measured for polygranular graphite POCOAXF-5Q. The fluencies were 10(18)-10(19) ion/cm(2), the temperatures varied from the room temperature (RT) to 400 degrees C. The RHEED has shown that same diffraction patterns correspond to a high degree of disorder at RT. At high temperature (HT), some patterns have been found similar to those for the initial graphite surfaces. The dependence (T) has been found to be non-monotonic and for normal and near normal ion incidence manifests a step-like increase typical for a radiation induced phase transition. At oblique and grazing incidence (theta > 30 degrees), a broad peak was found at T-p = 100 degrees C. An analysis based on the theory of kinetic ion-induced electron emission connects the behavior of gamma (theta,T) to the dependence of both secondary electron path length lambda and primary ion ionizing path length R-e on lattice structure that drastically changes due to damage annealing. (c) 2004 Elsevier B.V. All rights reserved.