  Fatigue and aging of materials are, in large part, determined by the
evolution of the atomic-scale structure in response to strains and
perturbations. This coupling between microscopic structure and long time scales
remains one of the main challenges in materials study. Focusing on a model
system, ion-damaged crystalline silicon, we combine nanocalorimetric
experiments with an off-lattice kinetic Monte Carlo simulation to identify the
atomistic mechanisms responsible for the structural relaxation over long time
scales. We relate the logarithmic relaxation, observed in a number of systems,
with heat-release measurements. The microscopic mechanism associated with
logarithmic relaxation can be described as a two-step replenish and relax
process. As the system relaxes, it reaches deeper energy states with
logarithmically growing barriers that need to be unlocked to replenish the
heat-releasing events leading to lower energy configurations.
