Time Resolved Transport in Molecular Junctions: Measurements and Simulations

Considering the time scale of molecular processes, molecular junctions can be envisioned to be fast electronic components, operating in the sub pico­second range. Yet, while impressive advancements have been achieved in understanding the steady state transport properties of these junctions, their time dependent transport characteristics remain unexplored. Here we propose a joint experimental theoretical scheme to investigate the dynamics of charge transport through molecular junctions. The experimental method is based on the detection of a dc-current I_dc through the junction which is the result of long sequence of picosecond voltage pulse pairs - the pump and the probe pulse - with a controlled delay time, t_del, between both pulses in each pair. The voltage pulses are formed by laser excitation of photo switches. The dynamics of charge transport through the junction is extracted from its corresponding I_dc - t_del ­plots. Variations in these plots can be studied as a function of molecular structure, coupling to the leads, and length as well as amplitude of the voltage pulses. The measured data shall be analyzed by extensive simulations based on a density matrix approach for the molecular junction including molecular vibrations and vibrational relaxation processes. The proposed research is an essential step toward fast nano­scale electronic components in future circuits.