  We study the statistics of the number of executed hops of adatoms at the
surface of films grown with the Clarke-Vvedensky (CV) model in simple cubic
lattices. The distributions of this number, $N$, are determined in films with
average thicknesses close to $50$ and $100$ monolayers for a broad range of
values of the diffusion-to-deposition ratio $R$ and of the probability
$\epsilon$ that lowers the diffusion coefficient for each lateral neighbor. The
mobility of subsurface atoms and the energy barriers for crossing step edges
are neglected. Simulations show that the adatoms execute uncorrelated diffusion
during the time in which they move on the film surface. In a low temperature
regime, typically with $R\epsilon\lesssim 1$, the attachment to lateral
neighbors is almost irreversible, the average number of hops scales as $\langle
N\rangle \sim R^{0.38\pm 0.01}$, and the distribution of that number decays
approximately as $\exp\left[-\left({N/\langle N\rangle}\right)^{0.80\pm
0.07}\right]$. Similar decay is observed in simulations of random walks in a
plane with randomly distributed absorbing traps and the estimated relation
between $\langle N\rangle$ and the density of terrace steps is similar to that
observed in the trapping problem, which provides a conceptual explanation of
that regime. As the temperature increases, $\langle N\rangle$ crosses over to
another regime when $R\epsilon^{3.0\pm 0.3}\sim 1$, which indicates high
mobility of all adatoms at terrace borders. The distributions $P\left(
N\right)$ change to simple exponential decays, due to the constant probability
for an adatom to become immobile after being covered by a new deposited layer.
At higher temperatures, the surfaces become very smooth and $\langle N\rangle
\sim R\epsilon^{1.85\pm 0.15}$, which is explained by an analogy with
submonolayer growth.
