Understanding the complex interplay between molecular functionalities and ferromagnetic surfaces, such as cobalt, is of interest for many diverse technologies ranging from catalysis to organic spintronics.  The formation of thiol-containing molecular monolayers on template-stripped cobalt and oxidized cobalt surfaces was followed with X-ray photoelectron spectroscopic (XPS) measurements and electronic transport measurements. We contrasted the self-assembly of octadecanethiol (ODT) and mercaptohexadecanoic acid (MHA), finding the self-assembly of the bifunctional molecule is profoundly different.  In particular, the cobalt surface exhibits a very different interface following self-assembly of the MHA species. We examine two different models of the interface formation based on the results, and discuss the impact of this Co/molecule interface on electron transport through Co/molecule/Si molecular junctions. Our results provide insight into ex-situ modification and functionalization of ferromagnetic interfaces. Nanometer-scale control of the oxide thickness at the MHA-Co interface is quite challenging and manifests in having profound effects on the electron transport by altering the effective tunneling distance or providing a more resistive current pathway. This work has provided insight into the reactive nature of the cobalt oxide in solution enabling the opportunity to prepare a nearly oxide-free ex-situ molecule-cobalt interface. The electrical measurements together with the interface structure derived from XPS provide comprehensive evidence that a molecular layer could have profound influence on the Co substrate and hint that further understanding could enable researchers to tune the local interfacial structures for desired applications in technologies where surface engineering could impact organic spintronics, medical implants, catalysis, pigments, and surface cobalt coatings.

Impact of self-assembled monolayers on (oxidized) cobalt for Si-based molecular electronic junctions

249th National Meeting (2015)

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