Charge transport in vertically aligned, self-assembled peptide nanotube junctions.

The self-assembly propensity of peptides has been extensively utilized in recent years for the formation of supramolecular nanostructures. In particular, the self-assembly of peptides into fibrils and nanotubes makes them promising building blocks for electronic and electro-optic applications. However, the mechanisms of charge transfer in these wire-like structures, especially in ambient conditions, are not yet fully understood. We describe here a layer-by-layer deposition methodology of short self-assembled cyclic peptide nanotubes, which results in vertically oriented nanotubes on gold substrates. Using this novel deposition methodology, we have fabricated molecular junctions with a conductive atomic force microscopy tip as a second electrode. Studies of the junctions' current-voltage characteristics as a function of the nanotube length revealed an efficient charge transfer in these supramolecular structures, with a low current attenuation constant of 0.1 Å(-1), which indicate that electron transfer is dominated by hopping. Moreover, the threshold voltage to field-emission dominated transport was found to increase with peptide length in a manner that depends on the nature of the contact with the electrodes. The flexibility in the design of the peptide monomers and the ability to control their sequential order over the nanotube by means of the layer-by-layer assembly process, which is demonstrated in this work, can be used to engineer the electronic properties of self-assembled peptide nanotubes toward device applications.

Controlling the anisotropic magnetic dipolar interactions of PbSe self-assembled nanoparticles on GaAs.

We report on the observation of an anisotropic magnetic dipolar interaction that results from binding PbSe nanoparticles (NPs) to GaAs surfaces by an organic linker. The observed dependence of the blocking temperature on the alignment of the linking molecule relative to the surface normal indicates that the anisotropy is caused by the attachment of the organic linker to the NPs. The presented results may serve as a strategy for fine-tuning the magnetic interactions and anisotropy on surfaces.