 Single molecules bonded covalently to gold have been studied by scanning tunneling spectroscopy and some of them are unimolecular rectifiers, studied as single molecules, as shown by the groups of Luping Yu (University of Chicago) and Ashwell (later at Lancaster University, UK).The driving idea in UE (also called molecular-scale electronics) is that properly designed "electroactive" molecules, of between 1 and 3 nm in length, can supplant silicon-based devices to reduce circuit component sizes, providing concomitant increase in maximum integrated circuit speeds.However, amplification had not been realized , and the chemical interactions between metal electrodes and molecules are complex.