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Description
CNT forest of high emissivity, nearly ideal “black-body absorber[1]”, is attracting researchers as a candidate material for the future application of high-sensitive sensor, thermal energy storage device[2], and so on. Recently, metamaterials, electro-magnetic circuit to the incident EM-wave, opened a method to design desired optical properties. We recently reported CNT forest metamaterial in infrared and visible region in order to increase optical and thermal absorbance utilizing FIB nanofabrication [3, 4].
In this paper, metamaterials composed by 1D anisotropic refractive index material of CNT Forests, and the effect of nano-sized patterning on the optical and thermal properties are discussed. Figure 1 shows calculated UV-Vis-IR spectra of vertical- and parallel-aligned metal-nanorod CNT forests to the Electric field (Ez) of incident EM wave, showing good correspondence to the experimental results[5] shown in Fig. 1(d-g). Components of perpendicularly aligned CNTs, which were parallel to the Ez of EM wave, increased reflectance in longer wave length region. Alignment of CNTs had an important role to improve absorption on the metamaterial patterns. Patterning shape effect of CNT forest metamaterials[3-5] will be also discussed in detail.
This work was supported by JSPS KAKENHI Grant Number JP 17K06205, and JP 24560050.
[1] K. Mizuno et al., PNAS 106(15), 6044-6047 (2008)
[2] H. Furuta, JSPS KAKENHI Grant Number JP 17K06205.
[3] A. Pander, et al., Nano-Micro Lett. 9:44 (2017).
[4] H. Miyaji, et al., Dia. Rel. Mat. 83, 196-203 (2018)
[5] A. Pander, K. Ishimoto, H. Furuta, A. Hatta, Proc. of NT15 conference (29.06.2015, Tokyo), p288, (submitted to Vacuum).
Fig.1 (a-c) Calculated Transmittance, reflectance and absorbance spectra by meep FDTD program for the metal-nanorod CNT forests. Ez of EM wave was perpendicular to (a) x-axis and (b) y-axis of CNT alignment, and (c) parallel to z-axis of CNT alignment. (d, e) Highly vertically aligned CNT forests exhibiting low reflectance in 10-degree specular reflectance [5]. (f, g) Low-degree aligned (wavy) CNT forests showing higher reflectance in longer wavelength [5].
