SYNCHROTRON-RADIATION PHOTOEMISSION AND SCANNING AUGER MICROPROBE STUDY OF HYDRATED SILICA

Synchrotron radiation photoemission and scanning Auger microprobe analysis are used to study the surface chemical composition of hydrated silica. Si-OH species produce a high-binding energy peak in photoemission spectra when Si2p electrons possess the same attenuation length of SiLVV electrons. Conversely, no spectral change is observed in SiLVV, OKVV, and SiKLL regions relative to the case of anhydrous silica. The presence of silanol species is evidenced by the I(OKVV)/I(SiLVV) intensity ratio which is meaningfully higher in hydrated silica than in anhydrous silica, and this ratio varies laterally up to nearly 50% as a function of position on the surface. On the contrary, the I(OKVV)/I(SiKLL) is virtually equal to the value of anhydrous silica, and shows no appreciable lateral dishomogeneity. The diagnostical capabilities of photoemission and Auger techniques in detecting chemical changes in silica are discussed on the grounds of: (i) the chemical shift, (ii) the experimental band width and, (iii) the electron attenuation length associated with a particular spectral transition,