Designing molecular rectifiers and spin valves using metallocene-functionalized undecanethiolates: one transition metal atom matters

Abstract

By using the first-principles method, here we have theoretically investigated the effects of the head group on the rectifying and spin filtering properties of metallocenyl-functionalized undecanethiolate molecular junctions. It is found that the rectifying performance as well as the rectification direction of the molecular junctions can be largely modulated by choosing different metallocenyl head groups, i.e., chromocene (CrCp2), manganocene (MnCp2), ferrocene (FeCp2), cobaltocene (CoCp2), and nickelocene (NiCp2). More interestingly, large or even perfect spin filtering efficiency can be obtained for molecular junctions embedded with a magnetic metallocenyl head group (CrCp2, MnCp2, CoCp2, or NiCp2). Further analysis reveals that all of the frontier molecular orbitals around the Fermi energy are localized on the metallocenyl head group, which results in their monotonic evolutions under positive and negative bias voltage due to the electrostatic effect of external bias voltage. This contributes to the rectification observed for the molecular junctions. Meanwhile, alignments of the frontier molecular orbitals with respect to the Fermi energy and their spin properties can be dramatically changed by the metallocenyl head group, which essentially leads to the inversion of rectification direction and the remarkable spin filtering effect. Our result provides a feasible way to optimize the rectifying performance of alkanethiolate based molecular diodes, and it also suggests a good platform to obtain a high or even perfect spin filtering efficiency that has a wide use in the field of molecular spintronics.