With the rapid development of micro/nanoscaled technologies, we are confronted with more and more challenges related to small-scale thermal radiation. Thorough understanding and handling of micro/nanoscaled radiative heat transfer is vital for many fields of modern science and technology. For example, proper utilization of near-field thermal radiation phenomenon greatly improves light-electric conversion efficiency. This review introduces theoretical and experimental investigation on near-field thermal radiation, especially progress in application and control of micro/nanoscaled radiative heat transfer, which addresses problems in developing renewable and sustainable energy techniques.

An overview of micro/nanoscaled thermal radiation and its applications

Magnetic plasmons polaritons (MPP) mode has attracted a lot of attentions for the explanation of the interesting spectral features of a series of well-known systems of the metal/insulator/metal (MIM) structure with periodic patterns. In this paper, the resonance frequencies in the range from 75 to 750 THz predicted by the dispersion relation of MIM system are compared with those predicted by the equivalent LC circuit model to explore the physical mechanism of the excited resonance inside MIM structures at some frequencies. The spectral properties are simulated by the rigorous coupled-wave analysis (RCWA) method to verify the results predicted by means of the dispersion relation. The effects of the geometric parameters on the resonance phenomenon are investigated. It is found that the changes of resonance frequencies with geometric parameters predicted by the dispersion relation exhibit similar tendencies as those predicted by the equivalent LC circuit model. The spectral properties of unsymmetrical structures with different feature dimensions are utilized to further explain the physical mechanism of resonant phenomena inside MIM structures. The investigation indicates that MPP is in nature induced by the coupling of internal SPPs at the metal/insulator interfaces.

Investigation on the physical mechanism of magnetic plasmons polaritons

Thermal radiation from silicon microcavity coated with thermochromic film

In the last chapter of this book we will provide a brief introduction to radiative heat transfer in geometries where the pertinent dimensions are measured in nanometers (nm). Research in the field of nanoscale energy transfer has exploded during the past few years, leading to fascinating new problems and devices in microelectronics and microfabrication technology, such as quantum structures, optoelectronics, molecular- and atomic-level imaging techniques, etc. Most radiation is incoherent (multispectral, as well as random in polarization and direction) in the “far field” (a distance of a wavelength or so away from the source), and the radiative transfer equation (RTE) and its solution methods described over the previous chapters are only valid for such incoherent radiation. We noticed in Chapters 2 and 3 (optically smooth surfaces) and Chapter 12 (small particles) that, when distances of the order of the wavelength A are relevant, radiative transfer must be calculated from the full Maxwell's equations presented in Chapter 2. However, Maxwell's equations do not include any radiative emission sources, which must be modeled via what is known as fluctuational electrodynamics, pioneered by Rytov [1, 2].

Nanoscale Radiative Transfer

In this chapter radiative transfer, occurring in systems of “small” size, is discussed. “Small” implies systems in which the size is smaller than or comparable to the wavelength of radiation. Typically, this occurs at the nanoscale. Such radiation is also known as near-field radiation. After a brief discussion of coherence effects, evanescent waves, and surface polaritrons, radiative transfer between two parallel plates (either metal or dielectric) in close proximity, with a vacuum gap in between, is formulated using electromagnetic wave theory together with fluctuational electrodynamics. It is shown that the heat flux between two plates can sometimes exceed the value predicted using Planck's law (or blackbody radiation theory) if the plates are sufficiently close. State-of-the-art models and first principles methods for the prediction of near-field radiation transport are briefly outlined. The final section discusses a few modern-day applications of near-field radiation, such as thermophotovoltaic energy conversion. 

A microscale-structured surface consisting of heavily doped silicon rectangle grating and slotted silver layer is studied for omnidirectional narrowband emitter. Numerical simulation is implemented to obtain spectral emittance in mid-infrared region (6–16 μm) for the transverse magnetic incidence by using the rigorous coupled-wave analysis (RCWA) method. The effects of structural parameters and incident angle on its spectral emittance are investigated. In virtue of the microcavity effect, an omnidirectional narrowband emitter is proposed. By selecting a group of structural parameters, its peak emittance reaches as high as 0.998, and the peak width Δλ/λ of the emittance peak is as narrow as 0.03 at the specified wavelength. The results reveal that our proposed structured surface has the nice spectral features of angular uniformity and wavelength-selective characteristic, which can be applied to design novel narrowband thermal emitters and detectors in the infrared region.

Yutao Zhang

Papers

Spectral Features of an Omnidirectional Narrowband Emitter