Abstract
The concept of thermal rectification was put forward decades ago. It is a phenomenon in which the heat flux along one direction varies as the sign of temperature gradient changes. In bulk materials, thermal rectification has been realized at contact interfaces by manufacturing asymmetric effective contact areas, electron transport, temperature dependence of thermal conductivity and so on. The mechanism of thermal rectification has been studied intensively by using both experimental and theoretical methods. In recent years, with the rapid development of nanoscience and technology, the active control and management of heat transport at the nanoscale has become an important task and has attracted much attention. As the most fundamental component, the development and utilization of a nanothermal rectifier is the key technology. Although many research papers have been published in this field, due to the significant challenge in manufacturing asymmetric nanostructures, most of the publications are focused on molecular dynamics simulation and theoretical analysis. Great effort is urgently required in the experimental realization of thermal rectification at the nanoscale, laying a solid foundation for computation and theoretical modeling. The aim of this brief review is to introduce the most recent experimental advances in thermal rectification at the nanoscale and discuss the physical mechanisms. The new nanotechnology and method can be used to improve our ability to further design and produce efficient thermal devices with a high rectification ratio.
Highlights
The same as the electrical current diode concept, thermal rectification is a phenomenon in which heat travels in one preferred direction with high thermal conductivity and in the opposite direction with low conductivity [1]
The second one is the dependence of thermal conductivity on temperature and space, which is one of the mechanisms to explain the thermal rectification in bulk materials
Molecular dynamics simulations show that high heat flux significantly affects the thermal rectification coefficient, but high simulations show that high heat flux significantly affects the thermal rectification coefficient, but high heat flux could not be used in the experiment in order to avoid damage to the test samples
Summary
The same as the electrical current diode concept, thermal rectification is a phenomenon in which heat travels in one preferred direction with high thermal conductivity and in the opposite direction with low conductivity [1]. The involved physical mechanisms for thermal rectification include asymmetric roughness at the contact surface, a thermal potential barrier between material contacts, different temperature dependence of thermal conductivity and so on [5]. The second one is the dependence of thermal conductivity on temperature and space, which is one of the mechanisms to explain the thermal rectification in bulk materials. Thermal conductivity is no longer a single-valued function of temperature It depends on many factors, such as width, defect, surface roughness, etc. For the nanomaterial with asymmetric geometric size or defects, the thermal conductivity is a space-dependent function. In this case, thermal rectification occurs in a single nanomaterial by switching the direction of the temperature gradient. The new nanotechnology and experimental skills discussed in this paper provide clear guidance for the future development of efficient thermal rectifiers at the nanoscale
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