An ultra-stable setup for measuring electrical and thermoelectrical properties of nanojunctions

Abstract

We present a setup that is excellently suited to measure the electrical and thermoelectrical transport across single-molecule junctions at both room temperature and low temperatures. It employs a sandwich configuration of two silicon carbide chips each equipped with metallic electrodes. Upon compression with an external piezo/spring mechanism, fine-tuned displacement control is achieved such that ultrastable atomically thin nanojunctions can be established. As a consequence of its stability, the setup gives access to point-by-point comparisons of electrical and thermoelectrical transport across single-molecule contacts. As a first demonstration of the capabilities of our setup, we present experiments with gold-molecule-gold contacts. Investigating a large ensemble of nanojunctions, each fully characterized by current-voltage characteristics and thermovoltage, correlations between these quantities are uncovered which can be rationalized within the Landauer transport picture. When including characteristics with resonant features, the Seebeck coefficient adds the decisive parameter to fully describe datasets within a resonant tunneling model. The setup provides further potential of controlling additional parameters as it is optically fully transparent. It also allows for nearly arbitrary material combinations for electrode-nanoobject object-electrode nanojunctions.

Thermoelectricity of near-resonant tunnel junctions and their relation to Carnot efficiency

“…However, when connecting the implications of the model with realistic experiments, further contributions should be considered that reduce this efficiency: (i) an electronic contribution with flat 15 that provides an offset conduction in tunneling experiments, enclosing unspecified spectrally broad tunneling channels (electronic background transparency) and (ii) a vibrational heat conductance in addition to the electronic heat conduction. Both do not contribute to thermovoltage.…”

“…Direct evidence is given by peaks in continously shifting their position from negative to positive bias voltages upon closing the junction (see Fig. 2 (b), S5 – S7 for near-resonant peaks and 15 ). Additionally, closing curves of both G and S are shown.…”

“…Two SiC chips with electrodes are placed in a sandwich configuration. The ultra-stable distance between the electrodes is adjusted via a piezo-spring mechanism 15 . Chip temperatures and are monitored via on-chip resistance thermometry.…”

“…The recent development of squeezable nanojunctions (SNJ) 15 gives access to such phenomena. We started our investigation with metallic junctions at various distances.…”

“…The SNJ technique allows due to its extreme stability an immediate comparison of S and G , along with the additional information provided by the full I ( V ) of every single configuration, i.e. for the very same atomistic structure 15 . We identify so far obscured correlations between these quantities.…”