银在不同波长下的折射率与介电常数数据

Optical Constants of Mer poor agreement at 460 ~ but converge and become equal at about 1000 N. The agreement for both n and k is good at 3600 A, where the data of Leveque et al. [35] and Winsemius et al. [33] meet. The data of the latter group show only fair agreement with the data of Dold and Mecke [ 14] where their data overlap. If the data of Dold and Mecke [14] are used to calculate the normal-incidence reflectance R, a spectrum with a broad peak at 5 #m results. The reflectance should increase monotonically with increasing wavelength. Neglect of the anomalous skin effect causes a calculated R to be too high at longer wavelengths, not lower. The cause of the peak probably is erroneously low k values at longer wavelengths. The measured reflectance of silver is higher than that given by the data presented here, and it increases smoothly to longer wavelengths. It should be noted that in the longer-wavelength region, the spectra are expected to be somewhat sample dependent, for the electron relaxation time depends on impurity content and crystallite size to an extent sufficient to appear in the spectra. See the discussion of the data for gold.
350 Xl
David W. Lynch and W. R. Hunter
SILVER (Ag)
From among the many studies of the optical properties of Ag [1-36], four have been chosen as representative. They are (1) the data of Hagemann et al. [28] from approximately 1.5 to 460 A, (2) the data of Leveque et al. [35] from 460 to 3600/I., (3) the data of Winsemius et al. [33] from 3600 A to 2.07 #m, and (4) the data of Dold and Mecke [14] from 1.265 to 10 #m. Table IX lists the values of n and k and the pertinent references. These data are plotted in Fig. 9 as smooth curves. Hagemann et al. [28] prepared their samples by evaporating thin films of silver onto substrates of collodion that were supported on copper screens of the type used for electron microscopy. The evaporation was done from resistance heated boats at a pressure of about 5 x 10 - 7 torr at rates of 1050 A/sec. The plastic substrates were dissolved away, leaving Ag films on copper screens. These processes required exposing the Ag films to air before measurements. Transmission measurements were made from 13 to 150 eV to obtain an absorption spectrum that was extended by using the data of others [10, 15, 22, 24, 26] to provide an absorption spectrum large enough for a Kramers-Kronig analysis. Leveque et al. [35] prepared their samples by the evaporation of silver in a vacuum of about 10- 7 torr. Reflectance measurements were made in the same chamber, and so there was no exposure to air. A variety of substrates was used, but for the data reported, the substrates were Pyrex plates at room temperature. Reflectance measurements were made in the 3.5-30-eV region by using synchrotron radiation. These data were augmented prior to KramersKronig analysis by using absorptance data, A = 1 - R, in the 0.1-2.8-eV region (Weaver [36]), a smooth interpolation to the reflectance at 3.5 eV, a reflectance derived from the absorption coefficient data of Haensel et al. [22] between 30 and 150 eV and the data from Hagemann et al. [28] for higher energies. Winsemius et al. [33] used polycrystalline silver of 99.999+~ purity. Sam: ples were spark-cut from larger pieces and electrolytically and chemically polished [37]. The samples were then transferred in air to a reflectometer, where they were vacuum annealed at 700 K for four or more hours. Values of n and k were obtained by using a polarimetric method described by Beattie [38]. Dold and Mecke [14] evaporated 99.99+~ pure silver onto polished glass plates from a Mo boat. The substrate temperature was not stated but was probably room temperature. Polarimetric measurements were made in air to obtain n and k. Henke et al.'s L39] data showed good agreement with that of Hagemann et al. [28], especially from 80 to 124 A. At 460 A the n spectra of Hagemann et al. [28] and Leveque et al. [35] are in very close agreement, but they diverge to longer wavelengths. The k spectra of these two sets of investigators
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