For years, researchers have developed thin films of bismuth telluride (Bi2Te3) — which converts heat into electricity or electricity to cooling — on top of gallium arsenide (GaAs) to create cooling devices for electronics. But while they knew it could be done, it was not clear how — because the atomic structures of those unlikely pair of materials do not appear to be compatible. Now researchers have solved the mystery, opening the door to new research in the field.