Control radiative heat transfer and Casimir force by regulating chemical potential of photons [electronic resource]
Keywords: Applied Physics.

The control of radiative heat transfer and Casimir force is very important for theoretical studies as well as practical applications. For radiative heat transfer, especially when the system operates in the near-field regime, the ability to control the heat transfer rate can lead to many applications, for example thermal transistor, thermal rectification and solid-state refrigeration. For Casimir force, the ability to change the direction of the force from attraction to repulsion is very crucial for nano-scale and micron-scale devices. This thesis explores one of the most promising approaches for the control of radiative heat transfer and the Casimir force, by regulating the chemical potential of photons. To realize this approach, the system typically has semiconductor components. The advantage of using a non-zero chemical potential of photons is that only a small positive or negative bias on a semiconductor can result in a significant change in either the heat transfer rate or the Casimir force. Compared to the traditional approaches, this approach should be more reliable in experimental realizations. In Chapter 1, I will give a brief introduction to chemical potential of photons and discuss its implications. Then I will discuss the radiative heat transfer in the near-field regime, and how it can be controlled in the presence of an external bias that is used to regulate the chemical potential of photons. I will also discuss the possibility of controlling the Casimir force with such external bias in the case of thermal non-equilibrium. Chapter 1 serves as the background for all the following chapters. In Chapter 2, I will discuss a solid-state device that can achieve electroluminescent refrigeration by forward biasing the semiconductor to achieve a non-zero chemical potential of photons. In this chapter, a very detailed theoretical framework based on fluctuational electromagnetism is presented, and a very simple analytical model that can be used to evaluate the performance of the device is also developed. Then the performance of the device in the idea case, and also the impacts of all possible non-idealities in the device are also discussed in detail. In Chapter 3, I will present a device with significantly improved performance by using a wide-band-gap light emitting diode as the cold side and a non-polar photovoltaic cell as the hot side. In addition, the proposed device also incorporates the idea of thermophotonics, where the generated electric power by the photovoltaic cell can be used to electrically pump the light emitting diode. The performance of the device is analyzed in detail in the contexts of both ideal case and the case with non-idealities. In Chapter 4, I will introduce another type electroluminescent device, where instead of a forward bias on the cold side, here a reverse bias is applied to the hot side. Similar to Chapter 2, a detailed theoretical framework as well as a simple analytical model is presented. The choice of the materials and the performance of such device are also discussed through exact numerical simulations. In Chapter 5, I will discuss the control of non-equilibrium Casimir force in the presence of a non-zero chemical potential of photons. By performing exact numerical simulations of the force in a sphere-plate geometry, the behaviors of the Casimir force in the case where the plate is forward biased, and the case where the sphere is forward biased, are discussed. In addition, we show that repulsive Casimir force can be achieve for a large range of gap separations between the plate and the sphere with an external bias on the plate. In Chapter 6, I will discuss a potential problem in the design of a thermophotovoltaic system for waste heat recovery, and propose ways that can mitigate the affects of such problem. Several different designs of thermophotovoltaic systems are evaluates using fluctuational electromagnetic formalism and detailed balance analysis. In Chapter 7, I will summarize the studies in this thesis, and provide a few suggestions for the future work.