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Study of Silylated Glass Surface

The soda-lime glass samples were etched with hydrochloric acid and heat treated 550 K in air. Then samples were silylated was with hexamethyl-disiloxane vapour in a sealed glass ampoule.

The acid treatment performed under moderate conditions leads to the complete depletion of Na, K, Ca and a partial depletion of Al to a depth far beyond the detection limit of XPS. The heat treatment did not stimulate reappearance of K and Ca in the surface layers to levels above the detection limit.

Two types of carbon atoms were found: the hydrocarbon type from the methyl groups and a H-C-O type contamination. Two types of oxygen and silicon could be distinguished. The smallest peaks can be identified as those originating from the supposed (CH3)3-Si-O type surface species, while the larger ones originate from the oxygen and silicon atoms of the glass surface network.

Sylilated glass surface

Peak Binding energy
(atomic %)
C1s 286.1   2.4 contamination
  284.1 11.5   ( 3 ) -CH3
O1s 533.2 46.7   ( 2 ) Si-O-Si, Si-OH
  531.5   3.6   ( 1 ) (CH3)3Si-O-
Si2p 103.8 27.2   ( 1 ) Si-O-Si, Si-OH
  102.2   3.9   ( 1 ) (CH3)3Si-

As it can be seen, the atomic % values for the (CH3)3SiO-group show an excellent consistency with the expected 3:1:1 ratio. The binding energy values are in good accordance with the literature. The ratio of the corresponding bulk Si and O atoms is also close to 2, which means that OH groups can hardly be found on the silylated surface.

I. Bertóti, M. Mohai, M. Révész, G. Alexander: Surface Composition of Glasses: Modifications Induced by Chemical and Heat Treatments.
Vacuum 37(1-2), 129 (1987).