Heat dissipation in atomic-scale junctions

Abstract

Atomic and single-molecule junctions represent the ultimate limit to the miniaturization of electrical circuits 1 . They are also ideal platforms to test quantum transport theories that are required to describe charge and energy transfer in novel functional nanodevices.Recent work has successfully probed electric and thermoelectric phenomena 2-8 in atomicscale junctions. However, heat dissipation and transport in atomic-scale devices remain poorly characterized due to experimental challenges. Here, using custom-fabricated scanning probes with integrated nanoscale thermocouples, we show that heat dissipation in the electrodes of molecular junctions, whose transmission characteristics are strongly dependent on energy, is asymmetric, i.e. unequal and dependent on both the bias polarity and the identity of majority charge carriers (electrons vs. holes). In contrast, atomic junctions whose transmission characteristics show weak energy dependence do not exhibit appreciable asymmetry. Our results unambiguously relate the electronic transmission characteristics of atomic-scale junctions to their heat dissipation properties establishing a framework for understanding heat dissipation in a range of mesoscopic systems where transport is elastic. We anticipate that the techniques established here will enable the study of Peltier effects at the atomic scale, a field that has been barely explored experimentally despite interesting theoretical predictions 9-11 . Furthermore, the experimental advances described here are also expected to enable the study of heat transport in atomic and molecular junctions-an important and challenging scientific and technological goal that has remained elusive 12,13 .Charge transport is always accompanied by heat dissipation (Joule heating). This process is well understood at the macroscale where the power dissipation (heat dissipated per unit time) is volumetric and is given by j 2 ρ, where j is the magnitude of the current density and ρ is the In this work, we overcome this challenging experimental hurdle by leveraging custom- Seebeck coefficient of the thermocouple. We note that R P and S TC were experimentally determined to be 72800 ± 500 K/W and 16.3 ± 0.2 µV/K, respectively (see SI).We began our experimental studies, at room temperature, by trapping single molecules of 1,4-benezenediisonitrile (BDNC, see Fig. 1c) between the Au electrodes of the NTISTP and the substrate using a break junction technique 5,20 . We first obtained electrical conductance versus displacement traces by monitoring the electrical current under an applied bias while the NTISTPsubstrate separation was systematically varied. In order to probe heat dissipation we created stable Au-BDNC-Au junctions with a conductance that is within 10% of the most probable low-bias conductance 20 . We studied heat dissipation in 100 distinct Au-BDNC-Au junctions, at each bias, to obtain the average temperature rise (ΔT TC, Avg ) and the time-averaged power dissipation in the NTISTP (Q P, Avg ) for both positive and negative biases. Here,...

Heat transport through atomic contacts

“…Furthermore, the temperature of the MEMS platform is strongly affected by the Joule effect and can even lead to a net increase of temperature in the platform instead of a net cooling through the atomic contact. The results (see SI) confirm our interpretation, and the underlying assumption that heat dissipation in atomic scale gold contacts occurs symmetrically in the electrodes, as shown recently 9 . The temperature difference across the contact varied within certain limits due to the aforementioned Joule dissipation effects and parasitic conductance effects.…”

“…This result is valid both in the tunneling regime and in the contact regime because transport occurs elastically. Specifically, because gold has a very low energy dependent transmission function T(E) half of the STM power is dissipated in the membrane and half in the tip when working with low bias voltages 9 .…”

“…Using these techniques, charge transport in atomic junctions has been studied intensively 2,3,4,5 , and, more recently, Joule dissipation 9,10 and thermoelectric effects 11,12 have been successfully probed. Recently, heat dissipation was measured in current-carrying single gold-gold contacts by means of STM with an integrated micro thermocouple in the tip 9 . It was shown that heat dissipates symmetrically into the two contacts, confirming that the electron transmission function T(E) of the junction element around the Fermi energy of the metallic contacts governs this phenomenon.…”

“…In calculating the total heat provided to the membrane ̇T OT , the power dissipated in the STM circuit PSTM has to be accounted: ̇T OT = H + STM . For this, we consider symmetric power dissipation at the junction level, owing to the weakly energydependent transmission function of gold 9 .…”

Dynamic Transport in a Quantum Wire Driven by Spin–Orbit Interaction

“…The dissipated heat could be measured by the scanning thermal microscopy [27], but a detailed consideration of the heat release involving the kinetics of the phonon subsystem is beyond the scope of the present letter.…”