  Aging dynamics in thin films of poly(methyl methacrylate) (PMMA) have been
investigated through dielectric measurements for different types of aging
processes. The dielectric constant was found to decrease with increasing aging
time at an aging temperature in many cases. An increase in the dielectric
constant was also observed in the long time region ($\ge$11h) near the glass
transition temperature for thin films with thickness less than 26nm. In the
constant rate mode including a temporary stop at a temperature $T_a$, the
memory of the aging at $T_a$ was found to be kept and then to be recalled
during the subsequent heating process. In the negative temperature cycling
process, a strong rejuvenation effect has been observed after the temperature
shift from the initial temperature $T_1$ to the second temperature
$T_2$($=T_1+\Delta T$) when $\Delta T\approx -20$K. Furthermore, a full memory
effect has also been observed for the temperature shift from $T_2$ to $T_1$.
This suggests that the aging at $T_1$ is totally independent of that at $T_2$
for $\Delta T\approx -20$K. As $|\Delta T|$ decreases, the independence of the
aging between the two temperatures was found to be weaken, $i.e.,$ the
effective time, which is a measure of the contribution of the aging at $T_1$ to
that at $T_2$, is a decreasing function of $|\Delta T|$ in the negative region
of $\Delta T$. As the film thickness decreases from 514nm to 26nm, the $|\Delta
T|$ dependence of the effective time was found to become much stronger. The
contribution of the aging at $T_2$ to that at $T_1$ disappears more rapidly
with increasing $|\Delta T|$ in thin film geometry than in the bulk state.
