In a thin aluminum film, millions of tiny metal grains are packed together like grains in granite. Where three such grains meet, a triple junction arises — a line along which three boundaries intersect. Previously, it was considered merely a meeting point, but now, peering into the atomic scale, scientists have seen: it is an independent defect with its own personality.

Using electron microscopy and computer modeling, they managed to reconstruct the exact structure of such a junction. It turns out that it has a Burgers vector — a measure of how strongly the crystal lattice is distorted, just like an ordinary dislocation (a linear defect inside a crystal). The energy of the junction follows the same laws as that of a single dislocation.

The most surprising discovery: for the same boundaries, different variants of triple junctions are possible, and nature chose not the most energetically favorable one. It seems that the rearrangement of the junction into a more favorable state proceeds too slowly, as if the metal lacks the time or energy to 'settle down comfortably.' This is important for understanding how metal behaves under heating, deformation, or aging.