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COVER ARTICLE

Radiative heat transfer in nanophotonics: From thermal radiation enhancement theory to radiative cooling applications
Liu Yang, Pan Deng, Chen Wen, Wang Wen-Qiang, Shen Hao, Xu Hong-Xing
2020, 69 (3): 036501. doi: 10.7498/aps.69.20191906
Abstract +
Thermal radiation, as a ubiquitous physical phenomenon, plays an important role in various research fields of science and engineering. Traditional understanding of thermal radiation mainly relies on Planck’s law, which describes the energy exchanging efficiency of entire thermal radiation process. However, recent studies indicated that comparing with the macroscopic object obeying Planck’s law, the thermal radiation in nanophotonic structures is obviously abnormal. This is due to the fact that the nanostructures’ featured size or neighboring space are much smaller than the thermal wavelength. It is important to notice that by well designing the material, size, and structure pattern, the thermal radiation is tunable and controllable. Furthermore, the nanophotonic structures enabling the radiative cooling effects promise to possess the tremendous applications including energy, ecology, etc. In this review paper, firstly, we briefly describe the fundamental theory of thermal radiation, as well as the history and latest progress, such as, enhanced radiative heat transfer, the near-field radiation in two-dimensional materials, and the overall far-field enhancement. Secondly, we focus on the newly available daytime radiative cooling system, which is based on metamaterials or desired nanophotonic structures, pursuing the best cooling performances. Finally, we detail the checklists of remarkable applications, ranging from building cooling and dew collection to solar cell cooling. In addition, we also point out the broad future of radiation cooling technology of nanometer optical materials in promoting the management and transformation of desert ecological environment.

COVER ARTICLE

Controllable growth of GeSi nanowires on trench patterned Si(001) substrate
Gao Fei, Feng Qi, Wang Ting, Zhang Jian-Jun
2020, 69 (2): 028102. doi: 10.7498/aps.69.20191407
Abstract +
Controllable growth of nanowires is a prerequisite for addressability and scalability of nanowire quantum devices. By combining top-down nanofabrication and bottom-up self-assembly, site-controlled GeSi nanowires with two (105) facets can be grown on Si (001) substrate with pre-patterned trenches. Trenches along the [100] or [010] crystallographic direction with 60 nm in width and 6 nm in height are fabricated on Si substrate by electron beam lithography and reactive ion etching. Subsequently, a 60-nm-thick Si buffer layer is grown at 330–400 ℃ on the patterned substrate to improve the surface quality. The facets at the tip of the trenches transform into (11n) after depositing the Si buffer layer. Self-organized GeSi nanowires form inside the trenches by depositing the 6-nm-thick Si67Ge33 film at 450 ℃ followed by 1 h annealing at 510 ℃. The GeSi nanowires are (105)-faceted with an average height of approximately 7 nm. Furthermore, we systematically study the influence of annealing temperature, Ge concentration and pattern period on the formation of site-controllable GeSi nanowire on a patterned Si (001) substrate. The GeSi nanowires can be formed only inside the trenches within a specific annealing temperature ranging from 500 ℃ to 520 ℃. It is also discovered that GeSi nanowires are very sensitive to Ge concentration, as they cannot form at lower Ge concentration due to a large nucleation energy barrier. In contrast, high Ge concentration will lead to the discontinuity of nanowires caused by higher atomic diffusion barrier. The generated GeSi nanowires in the trenches exhibit similar dimensions at different pattern periods, which indicates that the growth process is thermodynamically determined. Overall, we realize the controllable growth of the GeSi nanowires, while the length of nanowires can reach the millimeter even centimeter scales, replying on the patterned trench length. The above results offer a controllable growth method of the Ge nanowires, which could potentially lead to the scalability of the Ge quantum devices on Si substrates.

COVER ARTICLE

Strong coupling between metasurface based Tamm plasmon microcavity and exciton
Wu Han, Wu Jing-Yu, Chen Zhuo
2020, 69 (1): 010201. doi: 10.7498/aps.69.20191225
Abstract +
In this paper, the Tamm plasmon and its interaction with excitons in a plasmon microcavity consisting of metasurface, dielectric spacer, distributed Bragg reflector (DBR) are studied. The reflection phase of light on the surface can be controlled by changing the structure parameters in the metasurface. When the thickness of the dielectric spacer layer of the microcavity structure keeps unchanged, the resonance position of the Tamm plasmon mode supported by the microcavity structure can be adjusted by varying the structure parameters of the metasurface, and thus providing more degrees of freedom for regulating the Tamm plasmon mode. In addition, by comparing the traditional metal thin film-dielectric spacer-DBR structure, we find that the introduction of metasurface and its regulation of reflection phase can make the metasurface-dielectric spacer-DBR structure support the Tamm plasmon mode resonance at the same wavelength under a smaller thickness of spacer. And combining the local characteristics of the super-surface field, the model volume of Tamm plasmon can be reduced effectively. On this basis, we compare the interaction of traditional and metasurface-based Tamm plasmon with single-layer tungsten disulfide (WS2), and find that metasurface-based Tamm plasmon can produce stronger photon-exciton coupling and obtain larger Rabi splitting.

COVER ARTICLE

Experimental study on fission reaction rate induced by D-T neutron in depleted uranium shell
Han Zi-Jie, Zhu Tong-Hua, Lu Xin-Xin, Qin Jian-Guo, Wang Mei, Jiang Li, Yang Bo
2019, 68 (15): 152501. doi: 10.7498/aps.68.20181717
Abstract +
Fission reaction rate is an important index for validating and checking the neutron transportation and fission power in nuclear engineering. The experimental data can be used in benchmark validation of cross sections, and in studying the correlation of fission power with the thickness of uranium sphere shell. There are five assemblies of depleted uranium shells used in this work, the inner radii of which are all fixed at 13.1 cm, while their outer radii are 18.1, 19.4, 23.35, 25.4 and 28.5 cm, respectively. The D-T neutron source is generated in the center of the assemblies, the yield of which is about 3 × 1010−4 × 1010 s–1. In horizontal plane across the center of the assemblies, the fission rates at positions along the radial direction are measured in the direction with 45° inclining with respect to the incident D+ beam. Due to the disturbance to assemblies and neutron field, the activation foil of uranium is a suitable choice rather than fission chamber or capture detector. The material of activation foil is the same as that in the experimental assemblies. Considering the accurate fission yield of 143Ce, the objective nuclides are selected. The total fission yield of 143Ce is contributed by 238U and a little 235U. For calculating the total fission yiled of 143Ce, the neutron energy range of 0−15 MeV is divided into eight subranges. By measuring the 293 keV gamma rays from the fission product 143Ce in activation foils with a TRANS-SPEC-DX100 HPGe detector, with a relative efficiency 40%, the fission rates and the trends at positions along the radial direction in the five assemblies are obtained based on the 143Ce fission product yield. The fission rate ranges from 5.28 × 10–29 to 7.58 × 10–28 sn-1·nuclide–1, with the relative uncertainty in a range from 6% to 11%. The Monte Carlo transport code MCNP5 and continuous energy cross section library ENDF/BV.8 are used for analyzing the fission rate distribution in the assemblies, and the experiemtal configuration, including the wall of the experimental hall is described in detail in the model. The calculated results are compared with the experimental ones and their agreement is found to be in an uncertainty range.

COVER ARTICLE

Domain decomposition based integral equation modeling of 3-dimensional topography in frequency domain for well electromagnetic field
Li Jing-He, He Zhan-Xiang, Meng Shu-Jun, Yang Jun, Li Wen-Jie, Liao Xiao-Qian
2019, 68 (14): 140202. doi: 10.7498/aps.68.20190330
Abstract +
As an efficient geophysical exploration technology, well electromagnetic method is particularly applicable to oil and gas exploration in China's complex terrain areas (deserts, mountains, etc.). A serious influence of topographic relief area on the electromagnetic response of well is inevitable but challenging. To the best of our knowledge, there is no literature on modeling the electromagnetic response of three-dimensional (3D) topography with well electromagnetic method. Based on the domain decomposition, an integral equation method is presented to simulate the electromagnetic response of 3D topography in frequency domain via the well electromagnetic method. Compared with the finite difference and finite element method based on partial differential equation, this method is very efficient in simulating topographic response without huge computation or truncation boundary error accumulation or special boundary condition requirements. Firstly, an induction coefficient is defined according to the topographic relief situation. Then the computational domain consisting of the target body, background medium and 3D topography is divided into reference model, background medium and the distribution of target body medium area. According to the characteristics of each sub-region, Anderson algorithm is an analytic solution based on Gaussian filtering, which is used to provide the primary field from the excited sources in surface. And then, the stable double conjugate gradient-fast Fourier transform is incorporated into integral equation algorithm to obtain the fast 3D terrain shaft frequency domain electromagnetic responses. By comparing the calculation results using the new algorithm presented in this paper with the analytical solutions of Anderson algorithm for half-space model with surface electromagnetic method, the precision and the efficiency of this new algorithm are demonstrated. And the ability to model the electromagnetic responses of 3D topography is shown by comparing with the published results of 3D boundary integral equation. Thus, the high accuracy and high efficiency of the new algorithm presented in this paper are validated. Finally, the influence of 3D valley topography on electromagnetic field response of surface to borehole electromagnetic (SBEM) observation system is presented and analyzed. It is observed that the response of SBEM is seriously disturbed by the field of 3D valley topography which is necessarily removed. The research results presented in this paper are of significance for guiding the identification and correction of electromagnetic topographic effect from 3D SBEM.

Rapid Communication

  

COVER ARTICLE

Coherent rainbows come from liquids
Sun Tian-Jiao, Shang Ya-Xuan, Qian Xuan, Ji Yang
2018, 67 (3): 034205. doi: 10.7498/aps.67.20172663
Abstract +
When the highly-intensive and highly-directional white light from pulsed fiber laser is focused into water, many directional and colorful rings, coherent rainbows, are observed. The laser generates bubbles with similar sizes in the water, which serve as scatters. The intensive light leads to spatial self-phase modulation and thus generates the coherent rainbows. Such a phenomenon has been observed in many kinds of liquids.