Project IX – Electronic and phononic contributions to friction

Contributors: R. Nieminen, A. Foster, U. Valbusa, C. Boragno, N. Agrait

The electronic contributions to friction remain a poorly understood aspect of nanotribology. Direct simulation of nano-scale friction processes including all electronic effects is at present beyond the capabilities of computer resources. However, much insight can be gained by studying the properties of several generic "quantum" contacts. Ab initio studies (A. Foster, R. Nieminen) of the properties of nanowires on various metallic, semi-conducting and insulating surfaces provides important information on the electronic states at interfaces and this can be directly applied to understanding the important electronic processes in nanoscale friction.

Experiments are performed with nanocontacts (quantum contacts) measuring the electrical and mechanical properties simultaneously (N. Agrait). Typically these experiments are performed at liquid helium temperature, which gives a better control over the enviroment. In the latest experiments, atomic wires or chains of up to 7 atoms freely suspended between two electrodes were investigated. The forces to form and deform these nanostructures are measured. The inelastic scattering of the electrons with the phonons of the chain is measured, which makes possible to study the phonon spectra of atomic chains as they are submitted to strain.

Electronic contribution to friction are also studied at the National Institute of Physics of Matter (INFM; U. Valbusa, C. Boragno) to investigate the possible reduction of friction by the superconductive transition (Pb) and ferromagnetic transition (Ni). The experiment will be done in collaboration with other groups (Mistura Padova, Tosatti Trieste and Bortolani Modena).