Conventional electronic devices are traditionally made from bulk materials. Bulk methods have inherent limits, and are growing increasingly demanding and costly. Thus, the idea was born that the components could instead be built up atom by atom in a chemistry lab (bottom up) as opposed to carving them out of bulk material (top down). In single molecule electronics, the bulk material is replaced by single molecules. That is, instead of creating structures by removing or applying material after a pattern scaffold, the atoms are put together in a chemistry lab. The molecules used have properties that resemble traditional electronic components such as a wire, transistor, or rectifier. This concept of using a molecule as a traditional electronic component was first presented by Aviram and Ratner in 1974, when they proposed a theoretical molecular rectifier composed of donor and acceptor sites which are insulated from one another.