Giuseppe Foti

Chemical control of electrical contact to sp 2 carbon atoms

Carbon-based nanostructures are attracting tremendous interest as components in ultrafast electronics and optoelectronics. The electrical interfaces to these structures play a crucial role for the electron transport, but the lack of control at the atomic scale can hamper device functionality and integration into operating circuitry. Here we study a prototype carbon-based molecular junction consisting of a single C60 molecule and probe how the electric current through the junction depends on the chemical nature of the foremost electrode atom in contact with the molecule. We find that the efficiency of charge injection to a C60 molecule varies substantially for the considered metallic species, and demonstrate that the relative strength of the metal-C bond can be extracted from our transport measurements. Our study further suggests that a single-C60 junction is a basic model to explore the properties of electrical contacts to meso- and macroscopic sp2 carbon structures.

Efficient calculation of inelastic vibration signals in electron transport: Beyond the wide-band approximation

We acknowledge computer resources from the DCSC, and support from Center for Nanostructured Graphene (Project DNRF58). J.T.L. acknowledges support from the National Natural Science Foundation of China (Grants No. 11304107 and No. 61371015), and the Fundamental Research Funds for the Central Universities (HUST:2013TS032). G.F. and T.F. acknowledge support from the Basque Departamento de Educacion and the UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Economia y Competitividad (Grant No. FIS2010-19609-CO2-00), and the European Union Integrated Project PAMS.

Submolecular Resolution by Variation of the Inelastic Electron Tunneling Spectroscopy Amplitude and its Relation to the AFM/STM Signal

Bruno de la Torre,1, 2, ∗ Martin Švec,1, 2 Giuseppe Foti,1 Ondřej Krejč́ı,1, 3 Prokop Hapala,1 Aran Garcia-Lekue,4, 5 Thomas Frederiksen,4, 5 Radek Zbořil,2 Andres Arnau,4 Héctor Vázquez,1 and Pavel Jeĺınek1, 2, 4, † 1Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Cukrovarnická 10, 162 00 Prague, Czech Republic 2Regional Centre of Advanced Technologies and Materials, Palacký University, Olomouc, Czech Republic. 3Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 180 00, Prague, Czech Republic 4Donostia International Physics Center (DIPC), Paseo Manuel Lardizabal 4, E-20018 San Sebastian, Spain 5Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain

Tip-induced gating of molecular levels in carbene-based junctions

We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Greens functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure.

Adsorbate-driven cooling of carbene-based molecular junctions

We study the role of an NH2 adsorbate on the current-induced heating and cooling of a neighboring carbene-based molecular circuit. We use first-principles methods of inelastic tunneling transport based on density functional theory and non-equilibrium Green’s functions to calculate the rates of emission and absorbtion of vibrations by tunneling electrons, the population of vibrational modes and the energy stored in them. We find that the charge rearrangement resulting from the adsorbate gates the carbene electronic structure and reduces the density of carbene states near the Fermi level as a function of bias. These effects result in the cooling of carbene modes at all voltages compared to the “clean” carbene-based junction. We also find that the direct influence of adsorbate states is significantly smaller and tends to heat adsorbate vibrations. Our results highlight the important role of molecular adsorbates not only on the electronic and elastic transport properties but also on the current-induced energy exchange and stability under bias of single-molecule circuits.