Optical Properties of Germanium in the Far Ultraviolet

Abstract

Reflectance measurements for Ge films evaporated in situ are reported for 16 wavelengths between 490 and 1610 Å, corresponding to photon energies of 25.2 and 7.7 eV. Measurements were taken after 3-min exposures to ambient pressures of 5×${10}^{-7\mathrm{}}$ Torr. Reflectance values at a number of angles of incidence were used to compute the optical constants: the refraction index $n$, the extinction coefficient $k$, and the real and imaginary parts of the frequency-dependent dielectric constant $\epsilon \left(\omega \right)={\epsilon }_1+i{\epsilon }_2$. Values are also presented for the characteristic electron energy-loss functions, i.e., the volume loss, $-\mathrm{Im}{\epsilon }^{-1\mathrm{}}$, and the surface loss, $-\mathrm{Im}{(\epsilon +1)}^{-1\mathrm{}}$. The quantity $-\mathrm{Im}{\epsilon }^{-1\mathrm{}}$ peaked at 16.1 eV and had a half-width of 3.9 eV. Electron oscillator strengths, summed between 8 and 25 eV, gave a $\hslash {\omega }_p$ value of 13.7 eV. The present data are in better agreement with the accepted plasma theory than are previous data. Some changes of optical characteristics caused by exposure to ambient pressures and air are presented.