Evolution of the properties of helium nanobubbles during in situ annealing probed by spectrum imaging in the transmission electron microscope

Abstract

Helium bubbles can form in a wide variety of materials and are of significance in a great variety of circumstances, ranging from electronics through nuclear physics or geology to outer-space exploration. However, their properties remain elusive, especially at the nanometer scale. Here, the authors study by means of transmission electron microscopy the structural modification and, simultaneously, the helium emission from individual nanosized bubbles in silicon during $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0.333em}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ annealing. It is shown that, surprisingly, helium emission takes place at temperatures where bubble migration has barely begun. Analytical modeling of helium emission suggests that helium is in its solid state in the most highly pressurized bubbles.