  The kinetics of the sorption and the subsequent desorption of 4He by the
starting graphite oxide (GtO) and the thermally reduced graphene oxide samples
(TRGO, Treduction = 200, 300, 500, 700 and 900 C) have been investigated in the
temperature interval 1.5 - 20 K. The effect of the annealing temperature on the
structural characteristics of the samples was examined by the X-ray diffraction
(XRD) technique. On lowering the temperature from 20 K to 11-12 K, the time of
4He sorption increased for all the samples, which is typically observed under
the condition of thermally activated diffusion. Below 5 K the characteristic
times of 4He sorption by the GtO and TRGO-200 samples were only weakly
dependent on temperature, suggesting the dominance of the tunnel mechanism. In
the same region (T<5 K) the characteristic times of the TRGOs reduced at higher
temperatures (300, 500, 700 and 900 C) were growing with lowering temperature,
presumably due to the defects generated in the carbon planes on removing the
oxygen functional groups (oFGs). The estimates of the activation energy (Ea) of
4He diffusion show that in the TRGO-200 sample the Ea value is 2.9 times lower
as compared to the parent GtO, which is accounted for by GtO exfoliation due to
evaporation of the water intercalated in the interlayer space of carbon. The
nonmonotonic dependences Ea vs T for the GtO samples treated above 200 C are
determined by a competition between two processes - the recovery of the
graphite carbon structure, which increases the activation energy, and the
generation of defects, which decreases the activation energy by opening
additional surface areas and ways for sorption. The dependence of the
activation energy on treatment temperature correlates well with the contents of
the crystalline phase in GtO varying with a rise of the annealing temperature.
