Thermo-voltage measurements of atomic contacts at low temperature

Unusually High Thermopower in Molecular Junctions from Molecularly Induced Quantized States in Their Semimetal Leads

The efficiency of a thermoelectric (TE) device depends on the extent to which its electron/hole transport symmetry at the Fermi level is broken. This requirement makes molecular junctions promising for TE applications as their transmission characteristics are highly nonlinear. Yet, in the absence of an efficient method to tune the position of the Fermi level within their transmission landscape, the typical Seebeck values of metal-molecules-metal junctions are |S| ≤ 100 μV/K, while considering their electrical and thermal conductance, it should be |S| ≥ 1 mV/K to be relevant for applications. Here, we report metal-molecules-semimetal junctions with |S| in the required mV/K range. This is achieved by molecularly induced quantized two-dimensional (2D) interfacial states within the semimetal that result in nonlinear features in their transmission properties. The importance of the presented approach goes beyond TE applications as it demonstrates a novel strategy to form and tune 2D interfacial layers within bulk materials by molecular monolayers.

Optical rectification and thermal currents in optical tunneling gap antennas

Electrically-contacted optical gap antennas are nanoscale interface devices enabling the transduction between photons and electrons. This new generation of device, usually constituted of metal elements (e.g. gold), captures visible to near infrared electromagnetic radiation and rectifies the incident energy in a direct-current (DC) electrical signal. However, light absorption by the metal may lead to additional thermal effects which need to be taken into account to understand the complete photo-response of the devices. The purpose of this communication is to discriminate the contribution of laser-induced thermo-electric effects in the photo-assisted electronic transport. We show case our analysis with the help of electromigrated devices.

Alloying-induced spin Seebeck effect and spin figure of merit in Pt-based bimetallic atomic wires of noble metals

The chemical potential of electrodes can be tuned to generate pure thermal spin voltages in certain bimetallic wires of noble metals.

Measuring Single-Molecule Conductance at An Ultra-Low Molecular Concentration in Vacuum

We report on systematic investigation of single-molecule detection mechanisms in break junction experiments in vacuum. We found molecular feature in the conductance traces at an extremely low concentration of molecules of 10 nM. This was attributed to condensation of the molecular solution on the junction surface upon evaporation of the solvent during evacuation. Furthermore, statistical analyses of the temporal dependence of molecular junction formation probabilities suggested accumulation effects of the contact mechanics to concentrate molecules absorbed on a remote area to the tunneling current sensing zone, which also contributed to the capability of molecular detections at the low concentration condition. The present findings can be used as a useful guide to implement break junction measurements for studying electron and heat transport through single molecules in vacuum.

Substantial local variation of the Seebeck coefficient in gold nanowires

Nanoscale structuring holds promise to improve the thermoelectric properties of materials for energy conversion and photodetection. We report a study of the spatial distribution of the photothermoelectric voltage in thin-film nanowire devices fabricated from a single metal. A focused laser beam is used to locally heat the metal nanostructure via a combination of direct absorption and excitation of a plasmon resonance in Au devices. As seen previously, in nanowires shorter than the spot size of the laser, we observe a thermoelectric voltage distribution that is consistent with the local Seebeck coefficient being spatially dependent on the width of the nanostructure. In longer structures, we observe extreme variability of the net thermoelectric voltage as the laser spot is scanned along the length of the nanowire. The sign and magnitude of the thermoelectric voltage is sensitive to the structural defects, metal grain structure, and surface passivation of the nanowire. This finding opens the possibility of improved local control of the thermoelectric properties at the nanoscale.