Although significant progress in the understanding of nanocontacts has been achieved in the last few years, there are still many fundamental open questions concerning the influence of the enhanced chemical reactivity or changes of mechanical and transport properties during atomic-scale contact formation/breaking. We aim to study both experimentally and theoretically the electron transport at atomic scale. Main goal is to understand the relation between mechanical and electrical properties of atomic contacts.

We perform simultaneous STM/AFM measurements where the tunneling current and forces acting between SPM probe and sample are recorded together. The experimental measurements are completed by the state-of-art theoretical analysis based on the combination of the total energy DFT calculations and Green’s function methods [1,2]. In particular, we investigated the electron transport during the formation of the chemical bond between an apex atom and Si adatom on the Si(111)-(7x7) surface [1]. We found a striking decrease of the tunneling current in a near-to-contact regime. This effect is driven by the substantial local modification of the atomic and electronic structure of the surface. The chemical reactivity of the adatom dangling bond states that dominate the electronic density of states close to the Fermi level and their spatial localization result in a strong modification of the electronic current. 

We have also simulated the formation of gold monoatomic chains [3]. Our calculations showed that, even for a noble metal like Au where the barrier for dissociation in the surface is more than 1 eV, the enhanced chemical reactivity of these stressed Au monoatomic wires (due to the reduced dimensionality and the applied strain) makes the dissociation possible (with a barrier around 0.1 eV) and explains the fractional conductance peaks, that are associated to the resulting atomic hydrogen adsorbed on the Au wire [3]. These observations provide insight into possible new ways to control the catalytic process in the nanoscale. 

1. P. Jelinek, M. Svec, P.Pou, R. Perez and V. Chab, “Tip-Induced Reduction of the Resonant Tunneling Current on Semiconductor Surfaces” Phys. Rev. Lett. 101, 176101 (2008).
2. J.M. Blanco, C. Gonzalez, P. Jelinek, J. Ortega, F. Flores, and R. Perez, "First-principles simulations of STM images: From tunneling to the contact regime" Phys. Rev. B 70, 085405 (2004).
3. P. Jelinek, R. Perez, J. Ortega, and F. Flores "H₂ Dissociation over Au Nanowires and the Fractional Conductance Quantum" Phys. Rev. Lett. 96, 046803 (2006).