Transmission Spectra Of Thin Films Research Articles

Laboratory Infrared Spectra (2.3-23 μm) of SO 2 Phases: Applications to Io Surface Analysis

Mid-infrared spectra (∼2-25 μm) of various SO 2 phases (some known to be present on Jupiter's satellite Io) contain diagnostic band features that can be used with observational data of Io to learn about its surface and atmospheric composition. A key portion of this spectral range (2-5 μm) will be accessible to the Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft now headed for Jupiter. Our lab work provides reflectance spectra of SO 2 phases for: (1) comparison with IR spectra of Io, (2) identification of compositional species on Io, and (3) mapping the spatial distribution of SO 2 phases on Io. Spectra at 4 cm -1 resolution were measured for a variety of phase states of SO 2 including SO 2 gas, SO 2 frost, SO 2 slab ice, SO 2 liquid, and adsorbed SO 2. Detailed lab spectra and band identifications including some new identifications are given for several varieties of each of these phases with particular emphasis on the 2- to 6-μm regions. We also produced a variety of surface textures for condensed SO 2, ranging from frosts with many peculiar (reticulated) textures to solid slab or glaze ice and liquid. The different frost textures result from different growth conditions (such as temperature, pressure, gas-supply rate, and substrate composition). All the optically thick frosts and ices that we produced have reflectance spectra that are essentially identical, regardless of texture. Previously reported IR spectra of solid SO 2 in other investigations were usually produced as transmission spectra of films of ice, not reflectance spectra of frost or ice surfaces. Our work shows that transmission spectra of thin films are not adequate to represent all features that may be present in reflectance spectra of macroscopic frost or ice on planetary bodies like Io; this is because thin-film samples provide optical pathlength insufficient to produce detectable absorption bands at wavelengths where bands are strong in reflectance spectra of optically thick deposits (or in transmission spectra of thick (few millimeters) monocrystals). Reflection spectra, as opposed to transmission spectra, also allow easier simulation of frost thickness effects and better reproduction of hand shapes that will actually be observed in planetary spectral observations. Our results indicate that one can estimate phase state and concentration level for condensed SO 2 on Io using the principal band ( v1 + v3) in the 4-μm region; for example, we found that the v1 + v3 band-minimum position is dependent on: (a) phase state of the SO 2, (b) thickness of frost or ice, and (c) instrument resolution. SO 2 ice or frost thickness (on a millimeter scale or less) can also be assessed by the 4-μm band shape characteristics and by the presence or absence of several other weaker bands; we have done this for In spectra and find that significant fractions of In must be covered by thick (>2 mm) frost. We have successfully used our lab spectra to identify and assign new hands in Io observational data reported previously by other researchers. We developed NIMS-equivalent spectra of various SO 2 phases showing what NIMS should "see" on Io at various spectral sampling strategies (resolutions): our lab data will provide a basis for NIMS to distinguish and map the distribution of various SO 2 phases on Io's surface and also identify such phases on other Galilean satellites if detectable quantities exist there.

Interpretation of reflection and transmission spectra for thin films: transmission

The optical behavior of a thin film, that is, peak positions and intensities, is discussed for transmission under a thin-film approximation. The infrared transmission spectra of thin films, both standing films and those on dielectric substrates, are simulated for s and p polarization at various angles of incidence. For spectral simulation, the matrix method is used in conjunction with noise-free complex refractive indices based on the dispersion theory. The peak positions in the simulated spectra are compared with transverse optic and longitudinal optic frequencies based on the macroscopic theory. The simulated peak intensities for the standing films are compared with the prediction based on the thin-film approximation. Furthermore, it is found from the spectral simulation for thin films on dielectric substrates that the peak intensity for a thin film may depend on the thickness and refractive index of the substrate.

Infrared dispersion of the hydrogen-bonded pentachlorophenol-pyridine complex

Thin film transmission spectra of binary solutions of pentachlorophenol in pyridine were measured in the 4200–500 cm −1 range. From these data the spectra of both components of the complex refractive index and of the complex electric permittivity were obtained in the studied IR region. The molar vibrational polarization of the H-bonded complex was determined and compared with data obtained from previously studied pentachlorophenol complexes.

The infrared dielectric function of liquid CDCl3

Abstract The spectra of both components of the complex refractive index and of the complex electric permittivity of liquid deuterochloroform (CDCl 3 ) were estimated in the infrared region from thin film transmission spectra studied previously. The contribution of principal modes to the molar vibrational polarization of the studied molecule was determined and discussed.

Thin film transmission spectra of liquid CDCl 3 in the infrared

Thin film transmission spectra of neat liquid CDCl 3 were obtained in the 3500–250 cm −1 region. From these data the spectra of both components of the complex refractive index were calculated. The imaginary part was used to calculate integrated intensities and other spectral parameters for the principal bands. The obtained results were compared with literature data and discussed.

Optical Effects in IR Spectroscopy: Thickness-Dependent Positions of Absorbance Lines in Spectra of Thin Films

Optical effects give rise to thickness-dependent positions of absorbance lines ( v0) in the normal-incidence transmission spectra of thin films. Two reasons can be distinguished. Simple Fresnel refraction on the boundaries of the film shifts the line toward higher wavenumbers, with the maximum increment at small film thicknesses ( d). The second effect is due to multiple reflectance. The interference fringes cause the oscillations of the absorbance line around the mean value, which is defined by the effect of the boundaries. Both effects are more pronounced for broad lines. Whereas for the strong bands the first effect dominates, for the weaker ones both can be seen. The effective dielectric constant of the medium increases the first effect and diminishes the second one. Theoretically predicted vo ( d) curves compare well with absorption line positions in silicon nitride and silicon oxide films deposited on silicon wafers.

A simple procedure to remove the interference fringes from optical spectra

In order to eliminate interference fringes from experimental optical spectra, the authors describe a simple numerical procedure. Examples of practical applications to transmission spectra of thin films and layer compounds are given. The practical and theoretical limits of applicability are also examined.

Determination of the morphology and effective optical constants of non-ideal thin films

Optical techniques are widely used as non-destructive methods for determining the thickness and effective optical constants of vacuum deposited thin films. Implicit inmany such analyses is the use of an ideal morphological model of a thin film. The morphology of vacuum deposited thin films, however, may be far from ideal. The influence of morphological features on normal incidence reflectance and transmittance spectra of thin films is discussed. In particular, the interpretation of the non-ideal surface of a thin film as either a region giving rise to scattering of incident light or, by applying effective medium theory, as a region of graded refractive index will be considered. The results of a comparative study of the normal incidence reflectance and transmittance spectra of a number of sputtered thin films using both surface scattering and surface region of graded refractive index models is presented. It is shown that the latter model is preferred for films with surface features with dimensions of up to a considerable fraction of wavelength. The implications of these normal incidence results for ellipsometric measurements are also discussed.

Determination of the morphology and effective optical constants of non-ideal thin films

Optical techniques are widely used as non-destructive methods for determining the thickness and effective optical constants of vacuum deposited thin films. Implicit inmany such analyses is the use of an ideal morphological model of a thin film. The morphology of vacuum deposited thin films, however, may be far from ideal. The influence of morphological features on normal incidence reflectance and transmittance spectra of thin films is discussed. In particular, the interpretation of the non-ideal surface of a thin film as either a region giving rise to scattering of incident light or, by applying effective medium theory, as a region of graded refractive index will be considered. The results of a comparative study of the normal incidence reflectance and transmittance spectra of a number of sputtered thin films using both surface scattering and surface region of graded refractive index models is presented. It is shown that the latter model is preferred for films with surface features with dimensions of up to a considerable fraction of wavelength. The implications of these normal incidence results for ellipsometric measurements are also discussed.

Optical Constants of Cuprous Halide Crystals in the Far-Infrared Region at 2 K

Optical constants of CuCl, CuBr and CuI crystals in the far-infrared region have been determined by the Kramers-Kronig analysis of the reflection spectra at 2 K. The dielectric constants of CuCl are found to be inconsistent with the interpretation of the triplet structure by Vardeny and Brafman. The Kramers-Kronig analysis of the transmission spectra of thin films has also been tried but it has given incorrect values of the optical constants in the reststrahl region. The absorption spectra of the three cuprous halide crystals in the far-infrared region, including the side-band region as well as the reststrahl region, are shown in a summarized way.

Refractive indices of CuInSe 2, CuInSe 2 and CuGaTe 2

Refractive index dispersion in the photon energy range from 0.5 eV to the fundamental gap energy is determined for CuInSe 2, CuInTe 2 and CuGaTe 2 by measuring and analysing optical transmission spectra of thin films. Control measurements on GaAs thin films demonstrate the reliability of the method.

Transmission spectra of thin films which contain alkali metal anions and/or trapped electrons

Transmission spectra of thin films which contain alkali metal anions and/or trapped electrons

Temperature dependence of infrared spectra of TTF(TCNQ) thin films on KBr

We report transmission spectra of thin films of TTF(TCNQ) grown on KBr, in the range 400–4000 cm −1. Infrared spectra exhibit the strong modifications of the molecular vibrations in the complex.

Rapid assessment of weathering stability from exposure of polymer films. I. Real and simulated weathering of commercial ABS terpolymers

AbstractChanges in the infared transmission spectra of thin films were used to follow the natural and artificial weathering of ABS terpolymers. Photo‐oxidation of the polybutadiene moiety, which is the major process involved, occurs only after a well‐defined amount of ultraviolet energy has been absorbed. Therafter, unsaturation decreases in a first‐order manner with respect to UV energy absorbed. Under artificial conditions with constant UV intensity, energy absorbed is synonymous with time, but this is not so in natural exposure because of the variability of solar energy and its UV content. The method permits rapid comparison of commercial grades of ABS with the advantage of using natural conditions. It has been shown that pigmentation (3.6 phr brown and 1.25 phr carbon black) increases weathering stability two‐ and fourfold respectively, as assessed by induction energy and rate of disappearance of unsaturation.

Infrared internal reflectance spectroscopic studies of protein-polysaccharide interactions

Comparison of infrared attenuated total reflectance (IR-ATR) and transmission spectra of thin films of neutral and anionic polysaccharides showed that the ATR reflectivity technique resolved the OH deformation mode of the polysaccharides to a greater extent than the corresponding transmission spectra. In addition, the SO stretch band of fucan was a broad band at 1247 cm −1 in the transmission spectrum whereas the ATR spectrum split the band into a doublet at 1256 cm −1 and 1218 cm −1. Interactions between polysaccharides and between polysaccharides and gelatin were detected by noting decreases in intensities and shifts in the frequencies in the OH deformation bands of the polysaccharides, and, in the presence of gelatin, with concomitant shifts in the frequencies of the Amide I and II bands of the protein. Complex formation in which hydrogen bonding was involved was detected in thin films of the following biopolymeric mixtures: glycogen—gelatin, glycogen phosphate—gelatin, glycogen—fucan, fucan—gelatin, and fucan—gelatin in the presence of glycogen.

Infra-Red Spectra of Rubber and High Polymers

The transmission spectra of thin films of the following materials have been measured between 2.2μ and 14.8μ: crude rubber, soft and hard vulcanized rubber, thermoprene, polyvinylchloride, Neoprene and Pliofilm. The spectrum of rubber resembles that of the long chain paraffins more closely than do those of the polymers, polyvinylchloride, Neoprene and Pliofilm, all of which contain chlorine and have distinctive spectra. Vulcanization of rubber with 2.3 percent sulfur gives rise to no new bands in the region 2.2μ to 12.5μ characteristic of molecular cross bonding. Some of the bands in these materials are identified with valence vibrations.