Molecular electronics exploiting sharp structure in the electrode density-of-states. Negative differential resistance and Resonant Tunneling in a poled molecular layer on Al/LiF electrodes

Density-functional calculations are used to clarify the role of an ultrathin LiF layer on Al electrodes used in molecular electronics. The LiF layer creates a sharp density of states (DOS), as in a scanning-tunneling microscope (STM) tip. The sharp DOS, coupled with the DOS of the molecule leads to negative differential resistance (NDR). Electron transfer between oriented molecules occurs via resonant tunneling. The I-V characteristic for a thin-film of tris (8-hydroxyquinoline)- aluminum (AlQ) molecules, oriented using electric-field poling, and sandwiched between two Al/LiF electrodes is in excellent agreement with theory. This molecular device presents a new paradigm for a convenient, robust, inexpensive alternative to STM or mechanical break-junction structures.