Small-angle scattering from porous amorphous substances

Recently, a modulated void structure, i.e. a short-range order in the local arrangement of voids, has been found by small-angle X-ray scattering (SAXS) in heavy-ion-irradiated amorphous silicon a-Si:H. The SAXS intensity S(k) was observed to develop a maximum which increases with irradiation fluence and shifts towards smaller k similar to the case of phase separation. Here, the SAXS spectra from irradiated a-Si:H are compared with S(k) from commercial porous vycor glass - a structure produced by a decomposition process. Furthermore, results are presented of the investigation of the porous structure of glassy carbon as well as the effect of heavy-ion irradiation on this structure. Glassy carbon appears to have number and size of pores comparable to irradiated a-Si:H; the structure function S(k) is, however, quite different and does not exhibit any maximum. Moreover, irradiation with 360 MeV xenon ions leaves the structure function S(k) from porous glassy carbon almost unchanged. The possible origin of these apparently very different small-angle-scattering curves S(k) in amorphous materials with comparable amount of pore volume is discussed.