Electrons flowing across the boundary between two materials are the foundation of many key technologies, from flash memories to batteries and solar cells. Now researchers have directly observed and clocked these tiny cross-border movements for the first time, watching as electrons raced seven-tenths of a nanometer – about the width of seven hydrogen atoms – in 100 millionths of a billionth of a second. Led by scientists at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University, the team made these observations by measuring tiny bursts of electromagnetic waves given off by the traveling electrons – a phenomenon...