In order to better understand the electronic structure of silicon, the researchers employed the X-ray laser at LCLS's Matter in Extreme Conditions instrument to subject a sample to pressures over five million times more extreme than Earth's atmospheric pressure. They observed how pressure causes changes on an atomic scale and measured how such changes influence silicon's optical and electronic properties.
Silicon, one of the most well-known semiconductors and the "backbone" of today's technology, becomes a useful electrical conductor under specific conditions; scientists had not previously seen silicon's optical properties at the highest pressure achieved in this investigation.
Although still a metal—meaning it behaves both optically and electrically as most traditional metals—the electronic structures in its crystalline framework resemble the highly directional bonds typically displayed by semiconductors. Their observations also highlighted silicon's exceptional mechanical strength: even at the enormous pressures reached, its structure had only been minimally modified from the original "ideal" lattice formed by single, pure silicon crystals. As researchers push the understanding of materials even further, the researchers highlighted that further insight will help scientists predict even better how semiconductor electronic, optical and material properties can be tuned via engineering and precise synthesis, as we'll gain an ever more detailed knowledge of how their fundamental physical structures are impacted by changing their atomic geometry via applied forces (e.g. pressure)."
