Range Of Optical Constants Research Articles

Optical performance of amorphous hydrogenated carbon layers: range of optical constants achievable

The optical properties of differently deposited amorphous carbon layers have been investigated by spectrophotometric means from the middle infrared up to the visible spectral region. The optical constants of the layers could be calculated by a numerical procedure that combines features of single-wavelength methods and multiwavelength methods. Depending on the deposition technique applied, the optical constants of the layers have been found to vary over a wide range. Thus, refractive index values could be established between 1.6 and 2.9, while IR-absorption coefficients vary between 20/cm and 40,000/cm. The optical performance of the layers is thus nonuniform and may be influenced by the selection of suitable deposition parameters. Due to the potentially wide range of optical constants of amorphous carbon, various possibilities exist for the application as an optical thin film material. Applications such as selective absorber coatings for solar physical purposes are discussed as well as mechanically and chemically resistant antireflection coatings on high-refractive index semiconducting materials (silicon, germanium).

Reflection-absorption of ultrathin films on the surface of semiconductors and dielectrics by the method of IR spectroscopy

For the parameter of the change in the reflection coefficient owing to the presence of a film on the surface and thus the sensitivity of the method we employed the ratio of the difference of the reflection coefficients of a pure substrate and a substrate with a film to the reflection coefficient for the pure substrate AR/R = (R~ ~ usually called in the literature the absorption factor, for which calculations have been performed for a wide range of optical constants and angles of incidence andpolarization direction of IR radiation. The values of the optical constants were given for strongly absorbing materials for the example of the absorption band near ii00 cm-* of an SiO2 film [2] and for weakly absorbing materials for a film of organic material with n~ = 1.3 and k~ = 0.14 The absorbing film was assumed to be homogeneous, isotropic, and with plane-parallel interfaces at the substrate and external medium. The case of reflection of electromagnetic radiation from the film--substrate system under the given assumptions was studied in detail in [6]. The exact expression for the reflection coefficient as a function of the optical constants of the bounding media, the ratio of the film thickness to the wavelength of the radiation, and the angle of incidence can be represented in the following form, convenient for programming: