  The structure of the adsorbed layer of alkali ions on the surface of
colloidal silica solutions with a particle size of ~27 nm has been studied by
reflectometry and diffuse scattering of synchrotron radiation with a photon
energy of about 71 keV. Electron density profiles in the direction
perpendicular to the surface have been reconstructed from experimental data and
spectra of the correlation function of heights in the surface plane have been
obtained. The revealed deviation of the integral and frequency characteristics
of the roughness spectra of the silica sol surface from predictions of the
capillary-wave theory is of a fundamental character. This deviation is due to
the contribution from roughnesses with low spatial frequencies and to the
interference of diffuse scattering from different layer interfaces of the
surface structure.
