6 + 0.06|S 21|). The lateral dimensions of the PyC film were 7.2 × 3.4 mm2, i.e., the film was deposited on the silica substrate that fits precisely the waveguide cross-section; S-parameters were measured by subsequent insertion of the specimen into the waveguide. Results and discussion The CVD process parameters and properties of the obtained PyC film are summarized in Table 1. Table 1 Parameters
#BI-D1870 order randurls[1|1|,|CHEM1|]# of the CVD process and physical properties of the obtained PyC film CH4/H2ratio Press. (mBar) Thickness (nm) Roughness R a(nm) Optical transmittance at a wavelength of 550 nm Sheet resistance averaged over ten different samples 75:20 31 25.2 ± 0.8 1.07 37% [8] 200 Ω/sq [8] Ratios of transmitted/input see more (S 21) and reflected/input (S 11) signals measured within 26- to 37-GHz frequency range (K a band) are shown in Figure 2a. Reflectivity R = |S 11|2, transmittivity T = |S 21|2, and absorptivity A = 1 − R − T are presented in Figure 2b. Since the reflectivity and absorptivity of a bare silica substrate are 20% to 25% and 0, respectively,
the substrate contribution dominates the reflected signal (approximately 28% of incident power) in Figure 2, while absorption losses are due to the presence of the PyC film. EM absorption of PyC film is found to be as high as 38% to 20% and slightly decrease with the frequency. Figure 2 EM properties of the 25-nm-thick PyC in K a band. (a) EMI SE and |S 11 | (b) R = |S 11 | 2, T = |S 21 | 2, and A = 1 − R − T. Ratios of transmitted/input (S 21, EMI SE) and reflected/input (S 11) signals measured within 26- to 37-GHz frequency range is presented in (a). Reflectivity (R), transmitivity (T) and absorptivity (A) are connected with the measured S-parameters as the following: R = | S 11 | 2, T = | S 21 | 2, A = 1 − R − T. Both measured and calculated values of R, T, and A Resveratrol are presented in (b). It has been shown [7] that absorbance and reflectivity of the free-standing metal film with thickness much less than the skin depth are frequency independent at normal incidence. In our experiment, the frequency
dependence of reflectance/absorbance is due to (1) waveguide dispersion and (2) interference in the 0.5-mm-thick silica substrate. The detailed theoretical and numerical analysis of these effects requires taking into account the waveguide modes structure and is beyond the scope of this paper. Since the film thickness (25 nm) is much smaller than the EM skin depth for conventional metals (a few microns), which is much smaller than the wavelength (1 cm), the PyC film was expected to be transparent to microwaves. However, we found that in the K a band, the 25-nm-thick PyC film demonstrates reasonably high absorption losses, which results in the EMI SE as high as 4.75 dB at 26 GHz (see Figure 2a). Thus, the 25-nm-thick PyC film has EMI SE comparable with that of 2.5-μm-thick indium thin oxide film [16].