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Two thin aluminum nitride films have been prepared on sapphire substrates by molecular beam epitaxy technique. Then alkaline and acidic washing were used to remove the back-metal-coating of the sapphire substrate for one of the samples. (It caused also partial film dissolution). The surface polariton (SP) spectra have been measured by attenuated total reflection (ATR) technique. The measured SP dispersion is compared with one calculated using the literature film parameters. Due to the resonance interaction of sapphire substrate SP with the film transverse optical (TO) phonon the splitting of the dispersion curve of sapphire SP was found. The resonance takes place only for the frequency of the film TO phonon polarized along the surface of the anisotropic AlN film (perpendicular to the optical axis). The analysis of ATR and external reflectivity spectra shows the presence of some transition layer between the substrate and the film.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text V. M. Zolotarev, "Development of methods and techniques for attenuated total reflection (ATR) spectroscopy," J. Opt. Technol. 67, 309- (2000) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The infrared spectra of thin solid films of carotenoids on supports were investigated using multiple attenuated total reflection (ATR) spectroscopy technique. The specimens were obtained by the evaporation of 1 or 2 drops of appropriate solution of carotenoid on the both sides of quickly rotating ATR element. The carotenoids investigated were β-carotene, canthaxanthin, and lycopene. Retinal and retinyl acetate as related compounds were also studied. Multiple ATR infrared spectra of amorphous and crystalline films were recorded and compared with the corresponding spectra of the compounds in solutions and in bulk crystalline state (in KBr disks). The spectra of amorphous films were shown to be almost identical to the spectra of investigated compounds in solutions whereas in the spectra of crystalline (or partly crystalline) films the same band splittings as in the spectra of crystalline specimens appear. The values of the effective film thickness were calculated for all the compounds investigated and it was shown that the films studied were thin surface ones. The ATR technique was applied to the investigation of reactivity of the polyenes, patrticularly with the atmospheric oxygen in the dark and under illumination by visible and ultraviolet light. The oxidation is accompained by the graduate disappearence of the δ=C-H absorption band at 966 cm−1. The consumption of polyenic double bonds is accompained by the formation of carbonyl and hydroxyl absorption bands. Mechanisms of the initial stages of the process are proposed for different polyenes.

The subsurface structure of many technically applied materials is characterized by alterations of the composition (swelling or surface reactions on polymers, leaching of glasses etc.). Attenuated total reflection (ATR) spectroscopy is a powerful tool for analyzing such surface regions. Because of problems with optical contact the ATR method is difficult to handle in practice. Based on variable angle ATR‐FTIR spectroscopy a straightforward method has been established which can detect compositional inhomogeneities in subsurface regions or across layers. The method works as follows: (i) making ATR measurements at two different angles of incidence without changing the sample, (ii) normalizing the ATR absorbance spectra by using an appropriate band of the substrate as an internal standard, (iii) calculating difference spectra of the normalized spectra. In the case of a homogeneous material the difference spectrum virtually vanishes whereas in the case of an inhomogeneous surface region the difference spectrum reflects the compositional gradient. The method has been tested at polyamide-12 foils: (a) chemically cleaned, (b) treated with initiator, and (c) treated with pluronic. The experimental findings have been supported by spectra modelling. Based on an optical multilayer model the ATR spectra of a homogeneous polymer and of the same material with a slightly altered surface layer have been calculated for different angles of incidence. By applying steps (ii) to (iii) the experimental results are confirmed.

A merge of the experimental methods of attenuated total reflection (ATR) and grating-coupling (GC) yields a very versatile single tool for the study of elementary crystal surface excitations. In this study, a theoretical account of the combined method of ATR and GC (ATRGC) for probing surface polaritons in a thin film composite is given. The basic ATR experimental set-up is considered but with the additional feature that a classical grating of shallow grooves is deposited on only one of the interfaces of the thin film specimen. The main results of the investigations undertaken here are the first-order reflectivities, which in fact arise due to the presence of a grating. The thin film specimen consists of spherical metallic grains systematically embedded in a host medium, both constituents being surface-active. The dispersion curves of these modes are found to be elevated to higher frequencies as the fractional volume content of the grain constituents, the so-called filling factor, is increased. Surface polariton structures occurring in a reflectivity spectrum are therefore expected to shift to higher frequencies as a direct consequence of increasing the filling factor.

Remote detection of natural corrosion of aluminum alloy has been demonstrated using optical fiber Fourier transform infrared evanescent wave absorption spectroscopy. This technique is a particular example of Attenuated Total Reflectance (ATR) spectroscopy. Significant absorption features in the spectral range from 3300 to 3700 wavenumbers have been recorded. For comparison, spectra of the same corrosion samples of aluminum have also been collected using a zinc selenide crystal as the ATR element. Both optical fiber and crystal ATR evanescent wave absorption spectra of pure aluminum hydroxide were recorded for reference. Formation of aluminum hydroxide is a major product of corrosion in aluminum and aluminum alloys. A four wavenumber resolution Michelson interferometer spectrometer was combined with a seven bounce zinc selenide crystal to make the ATR spectral reference measurements. The same interferometer spectrometer was used with 200 micrometer core diameter multimode chalcogenide optical fibers to make the evanescent wave absorption measurements simulating the remote detection process. The data was collected with one or two meter lengths of 500 micrometer diameter fibers which were decoated for 20 cm of their length. The optical fiber absorption measurements are very sensitive and can detect a very small amount of material which is in contact with the decoated fiber core. The qualitative results reported here demonstrate that the technique of optical fiber evanescent wave absorption spectroscopy may be used to monitor industrial corrosion of aluminum alloys and that quantitative analyses of this type of spectral data are possible.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Since the introduction of attenuated total reflection (ATR) spectroscopy for the characterization of materials, attempts have been made to relate the measured reflectivity (R) to the absorption coefficient (α) of the absorbing material of interest. The common approach is limited to the low absorption case under the assumption R∼exp(-αde), where de is an effective thickness, which is evaluated for the lossless case. In this Letter, a more detailed derivation leads to R=exp(-βdp/2), enabling the definition of an ATR-effective absorption coefficient β and the penetration depth dp of the electric field in the absorbing material. It is found that β∼4πε2/λ, where ε2 is the imaginary part of the complex dielectric function of the absorbing material, and λ is the wavelength. An alternative formulation is R=exp(-αdef), where def is a generalized effective thickness for arbitrary strength of absorption which reduces to de in the low absorption limit. The experimental data for water, the biopolymer chitosan, and soda-lime glass prove the reliability of the ATR-effective absorption coefficient in the infrared range.

We have investigated the spatial distribution of electric and magnetic fields and propagation characteristics of surface polaritons in ultrathin films with the thickness of less than 10 nm. The long-range surface polariton configuration, such as the dielectric/ultrathin film/dielectric geometry, was employed. For Ag thin film, the propagation lengths have been calculated by using effective dielectric constants evaluated from experiments or by a semi-empirical method. The propagation length monotonically increases with decreasing the thickness of Ag film. We have found that there is a sharp resonance in attenuated total reflection (ATR) spectra even for a s-polarized light.

Two simple techniques using single-crystal specimens in polarized infrared attenuated total reflection (ATR) spectroscopy were developed for structural studies of molecular crystals, in particular of long-chain compounds. The first technique relates to a rotatory change of sample setting around the normal of the sampling plane of an internal reflection element (IRE) in the p-polarized ATR measurement. This is a simple method to distinguish whether a transition moment is parallel to a certain crystal face. The inclination manner of hydrocarbon chains constructing an orthorhombic polyethylene subcell can be easily determined. Another technique relates to the employment of intermediate polarizations between p and s settings of incident infrared radiation, which allows three-dimensional structural analysis. The evanescent electric field is estimated for a simple model system. Linearly polarized incident radiation generates an elliptical electric field in a specimen. By combining a rotatory change of sample setting, the long axis of the elliptical electric field can be directed in any direction in a fixed coordinate system located on a specimen. Transition moments nearly parallel to the long axis are emphasized in spectra. The phase difference between the p and s components of evanescent waves has a large influence on the elliptically polarized electric field. For a multiple reflection IRE, the polarization of ATR spectra depends on the sampling position, which can be ascribed to a phase jump of the guided infrared radiation at every reflection.

Theoretical studies of surface phonon polariton in wurtzite AlInN ternary alloy

The theoretical principles of internal reflection spectroscopy (IRS), also known as attenuated total reflectance (ATR) spectroscopy, are discussed. The origin of the absorption spectra in the IRS configuration with a lower refractive index sample material in contact with the higher refractive index internal reflection element (IRE) is described. The significance and differences in the depth of penetration and the effective thickness parameters are discussed in detail. An experimental strategy is described for the determination of the actual depth of sampling into the rarer sample material, and the quantitative comparison of the so‐determined “sampling depth” is compared to the theoretical depth of penetration. A comparison of the thick (bulk) film and thin film cases is given. A discussion of the practical considerations necessary to perform experimental IRS measurements is given, including necessary considerations for quantitative calibration. Several results of quantitative determinations on polymers are presented to exemplify the calibration procedures.

The surface exciton polaritons associated with the A, B and C excitons in ZnO are investigated by the attenuated total reflection (ATR) measurements. The concept of the surface admittance is introduced to understand the characteristic nature of the surface polaritons in anisotropic ZnO crystal. The experimental ATR spectra and the dispersion curves for the respective excitons are analyzed taking account of the anisotropic and non-local exciton dielectric functions and of the surface layer effect. The real and virtual surface polariton modes are identified on the B exciton from the experimental dispersion curves for particular geometries. Besides, a pseudo-surface mode is observed as additional ATR dips and is interpreted as the guided-wave mode propagating along an optical wave-guide-like structure, ZnO-surface layer-MgF 2 gap, under specific conditions.

In Malaysia, peat make up for around 7.5 % of the entire land area. The positive effect of the vast wet organic compounds accumulates over a long time has stored high content of soil’s carbon which are highly useful as fuel and biomass energy generation. Thus, this study gives an outline of peat pellet as potential biofuel energy. The peat pellets were soaked into several kinds of flammable additives such as petrol, kerosene and diesel. The percentages of 69.41 % of carbon, 28.73% of oxygen and 0.97% of silicon were obtained using Energy Dispersive X-ray (EDX). The Fourier-Transformed Infrared (FTIR)- Attenuated Total Reflectance (ATR) Spectroscopy was used to identify the sample. From the spectra, it reveals that most of the additives contribute mainly functional groups with hydroxyl, alcohol and phenol groups were found leading to higher boiling and melting points. The heat combustion properties of peat pellets were evaluated using a calorimeter technique by boiling off 50 ml and 100 ml of water. The pellet with diesel has the highest Q-values and combustion rate due to larger number of carbons in rigid molecular structure. The high amount of unique chemical compound found naturally in diesel known as cetane, ignites effortlessly when heated gives diesel additional advantages in shorter ignition delays as well as longer duration of combustion.

Structural integrity of antigens upon adsorption and release is not only important for investigating vaccine immunogenicity, but also for the epitope specificity of the resulting immune response and hence therapeutic efficacy. Moreover, the structural information is also important for understanding the mechanism of how adjuvants can enhance the immune response. However, little is known about an antigen′s structure when it is adsorbed on and subsequently released from aluminium adjuvants. In this study, the structures of two protein antigens, bovine serum albumin and β‐lactoglobulin, were investigated using Fourier transform infrared–attenuated total reflection (FTIR–ATR) spectroscopy. The secondary structures of both model antigens change when adsorbed to aluminium hydroxide. The structural perturbation depends on the amount of adsorbed protein. Maximal adsorption gives a more native‐like structure. This may indicate that protein is adsorbed in different manners depending on the concentration. The adsorbed antigens are released using phosphate buffer pH 7.4 (PB). The recovery is approximate 80% after 40 min in the presence of PB. The recovery curves of both proteins also indicate two different adsorption modes. FTIR–ATR and circular dichroism (CD) spectroscopy yield similar results suggesting that the adsorbed antigens refold to their native‐like state after release.

Experimental observation of exciton surface polaritons on a polymerized diacetylene crystal