SECONDARY-ELECTRON EMISSION FROM POROUS SOLIDS

Porous structure can strongly change the electric behavior of material submitted to bombardment by energetic electrons: strong electric fields (108 V/m) can grow within the pores, because of the small sizes of these pores. We give a model of porous material that enables us to emphasize and illustrate the enhancement of the yield of secondary-electron emission (and the broadening in frequency of its profile) in a porous medium, compared to that in bulk material. Here we have considered materials of astrophysical interest [graphite, iron, aluminum (Al2O3), and silica]. The enhancement is characterized by two emission peaks for small energies of the primary electrons and by an increase of the yield roughly by a factor of 4 for large energies (>1 keV). © 1995 The American Physical Society.