Thermopower measurements in molecular junctions

Abstract

The measurement of thermopower in molecular junctions offers complementary information to conductance measurements and is becoming essential for the understanding of transport processes at the nanoscale. In this review, we discuss the recent advances in the study of the thermoelectric properties of molecular junctions. After presenting the theoretical background for thermoelectricity at the nanoscale, we review the experimental techniques for measuring the thermopower in these systems and discuss the main results. Finally, we consider the challenges in the application of molecular junctions in viable thermoelectric devices.

Thermal conductance and thermoelectric figure of merit of C60 -based single-molecule junctions: Electrons, phonons, and photons

“…In particular, recent experimental advances have made possible to study key aspects of energy and heat conduction in molecular junctions such as thermoelectricity [3], Joule heating [4], and thermal conductance [5]. In this sense, the investigation of phonon transport in these atomic-scale junctions is presently attracting a lot of attention for two basic reasons.…”

Nanoscale Organic Thermoelectric Materials: Measurement, Theoretical Models, and Optimization Strategies

“…[50] To overcome the limitations of STM and CP-AFM technique in thermoelectric measurement of molecular devices, many techniques have been developed including scanning tunneling microscopic break junction (STMBJ), mechanically controlling break junction (MCBJ), electromigrated break junction (EBJ), and thermoelectric atomic force microscope (ThAFM). [51] For nanomaterials, electrical conductance, and thermopower measurement is easier to perform than heat conductance measurement. The thermopower can be obtained by measuring the thermal voltage after establishing a temperature gradient over a device.…”

“…Although, these methods have been widely used to study molecular device, there is still some drawback in STM and CP‐AFM techniques, that is, the covalent bond between molecular and tip usually cannot be formed which leads the uncertain of contact type of tip and molecular . To overcome the limitations of STM and CP‐AFM technique in thermoelectric measurement of molecular devices, many techniques have been developed including scanning tunneling microscopic break junction (STMBJ), mechanically controlling break junction (MCBJ), electromigrated break junction (EBJ), and thermoelectric atomic force microscope (ThAFM) …”

Roles of vacuum tunnelling and contact mechanics in single-molecule thermopower

“…Recently, there has been growing interest in exploring quantum confinement effects in low-dimensional structures for better thermoelectrics67891011. Alike the nanomaterials investigated to date, such as superlattices12, nanotube/nanowires13, and quantum dots14, a single-molecule interconnected to metallic electrodes is a quantum system having discrete electronic states that promise giant thermopower by chemically-engineering the electronic structures through optimizing the molecular architectures15161718. Much progress has been accomplished in understanding and controlling the single-molecule thermoelectric transport properties, such as length dependence192021, intermolecular interactions22, and gate control23, owing to the advance in experimental techniques to address the electron and heat transport in molecular bridges17.…”

“…Alike the nanomaterials investigated to date, such as superlattices12, nanotube/nanowires13, and quantum dots14, a single-molecule interconnected to metallic electrodes is a quantum system having discrete electronic states that promise giant thermopower by chemically-engineering the electronic structures through optimizing the molecular architectures15161718. Much progress has been accomplished in understanding and controlling the single-molecule thermoelectric transport properties, such as length dependence192021, intermolecular interactions22, and gate control23, owing to the advance in experimental techniques to address the electron and heat transport in molecular bridges17. In sharp contrast, the roles of electrode-molecule contacts on the thermoelectric properties have remained almost unexplored2425 albeit the theoretically predicted impact on the electronic structures2627282930, due mostly to the technical difficulty to evaluate the geometrical dependence of thermoelectricity in molecular junctions that requires a reliable method to form and hold a molecular bridge for long-enough time to measure their thermoelectric properties and meanwhile controllably deform the configurations at an atomistic level.…”