title: Electronic Structure and Band Gap of Fullerenes on Tungsten Surfaces: Transition from a Semiconductor to a Metal Triggered by Annealing.
abstract: The understanding and control of molecule-metal interfaces is critical to the performance of molecular electronics and photovoltaics devices. We present a study of the interface between C60and W, which is a carbide-forming transition metal. The complex solid-state reaction at the interface can be exploited to adjust the electronic properties of the molecule layer. Scanning tunneling microscopy/spectroscopy measurements demonstrate the progression of this reaction from wide band gap (>2.5 eV) to metallic molecular surface during annealing from 300 to 800 K. Differential conduction maps with 104scanning tunneling spectra are used to quantify the transition in the density of states and the reduction of the band gap during annealing with nanometer spatial resolution. The electronic transition is spatially homogeneous, and the surface band gap can therefore be adjusted by a targeted annealing step. The modified molecules, which we call nanospheres, are quite resistant to ripening and coalescence, unlike any other metallic nanoparticle of the same size. Densely packed C60and isolated C60molecules show the same transition in electronic structure, which confirms that the transformation is controlled by the reaction at the C60-W interface. Density functional theory calculations are used to develop possible reaction pathways in agreement with experimentally observed electronic structure modulation. Control of the band gap by the choice of annealing temperature is a unique route to tailoring molecular-layer electronic properties.
authors.affiliation: Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Monazami
authors.affiliation: Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States.|Department of Materials Science and Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: John B
authors.initials: JB
authors.lastname: McClimon
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: James
authors.identifier: http://orcid.org/0000-0003-0508-2175
authors.initials: J
authors.lastname: Rondinelli
authors.affiliation: Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States.
authors.forename: Petra
authors.identifier: http://orcid.org/0000-0002-4544-5906
authors.initials: P
authors.lastname: Reinke
keywords: density functional theory; electronic structure; fullerene; molecule−metal interfaces; scanning tunneling microscopy/spectroscopy