FRG: Oligomolecular Nanodevices

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

Fast unimolecular rectifiers of electrical current, at the ultimate molecular, i.e. nanometer-scale limit, should occur in molecules that satisfy, in our opinion, three conditions: (1) They should belong to the types D-pi-A or D-sigma-A (D = one-electron donor, pi = covalent "pi-electron" bridge or sigma = covalent " sigma-electron" bridge, A = one-electron acceptor), (20 They should undergo large changes of their dipole moment between their intramolecular intervalence transfer transition. We have demonstrated that a zwitterionic D=pi-A molecule, hexadecylquinolinium tricyanoquinodimethanide (where there is internal electron transfer from D to A in the ground state), is indeed a unimolecular rectifier, between 370 degrees Kelvin and 105 degrees Kelvin, by both nanoscopic methods (scanning tunneling microscopy in air) and macroscopic methods (electrical measurements on "aluminum | monolayer | aluminum" sandwiches, and also "gold | monolayer | gold: sandwiches). %%% For that work, we relied on Langmuir-Blodgett film assembly technology (using a long-chain alkane termination), whose advantage is that it forms compact, well-packed layers, which however may be metastable in orientation, especially under intense electric fields. To make the rectifiers more sturdy and less likely to reorient, we propose to (1) use covalent self-assembly (add silane terminations in the molecule for attachment to OH-covered Si substrates); (2) incorporate polymerizable groups in the molecules. We also propose (3) a molecular transistor, by interspersing between two D-sigma-A or two D-pi-A molecules an electrically addressable gate film, or a gate electrode with a suitable geometry, and thus provide the world's first three-terminal unimolecular device with electronic gain.