Materials that convert heat directly into electricity have been useful for some niche applications, like powering deep-space probes. But they've been too expensive and inefficient for their potential killer app: harvesting immense amounts of energy from the waste heat generated by power plants and cars. Now researchers at the University of California, Berkeley, have shown that a cheap organic material can make electricity from heat, potentially opening the way to affordable "thermo­electrics."

The researchers trapped a few organic molecules between a sheet of gold and the ultrasharp gold tip of a scanning tunneling microscope. They heated the gold surface and used the microscope tip to measure the voltage created by the junction of molecule and metal. A large-scale heat-­conversion system will require a process for arranging multiple layers of such junctions between two sheets of metal, one for applying heat and the other for harvesting electricity.