Nanopowders of amorphous SiO2, with typical particle sizes of 30-80 nm, were treated under non-equilibrium plasma conditions created by a capacitively coupled (CC) RF discharge in pure methane or ethane. The gas flow rate was varied between 0.02-0.06 slpm, with reactor pressures maintained between 1000 and 5000 Pa, and applied RF power inputs between 700 and 1500 W. The plasma properties were monitored through measurements of the C2 rotational and the atomic hydrogen excitation temperatures. The compositions of the gases that passed through the plasma were analyzed by mass-spectrometry. In spite of the evidence indicating the presence of CnH2n+2 and CnH2n (n=1-3) species, as well as acetylene, in the discharge, the homogeneous formation of soot was not observed. At the same time, introduced nanoparticles acted as centers for the inception and growth of C:H thin coatings in the form of polymer-like hydrocarbon layers, whose thickness lay between < 5 - 30 nm. The results of TEM, IR spectroscopy, thermo-gravimetric and precision calorimetric analyses performed on the plasma treated powders provided evidence for the formation of an amorphous, high density C:H matrix on particles' surfaces.