ATR Method Research Articles

Nondestructive Analysis of Biological Materials by ATR/FT-IR Spectroscopy. Part II: Potential of the ATR Method in Clinical Studies of the Internal Organs

In our previous paper, we demonstrated the usefulness of ATR/FT-IR spectroscopy in the nondestructive analysis of biological tissues by choosing the eye lens capsule as an example. The ATR technique is an extremely effective means of obtaining in vivo IR spectra of the surface of biological tissues. This nondestructive method provides information about the structure and relative concentration of biological molecules near the surface of biological tissues; in the ATR study of the lens capsule, direct evidence for the existence of collagen helix structure was obtained.

Nondestructive Analysis of Biological Materials by FT-IR-ATR. Method I: Direct Evidence for the Existence of Collagen Helix Structure in Lens Capsule

FT-IR spectra were measured in situ for an albino rabbit lens capsule by use of the ATR method, and the spectrum of water was subtracted. The obtained difference spectra resemble the spectrum of purified Type IV collagen in aqueous solution and show intense bands at 1637 and 1553 cm−1 assignable to the amide I and II modes, respectively. These frequencies are very close to those of the amide I and II bands of a 31 helix. This is direct evidence for the existence of the so-called collagen helix (a slightly modified 31 helix) in the lens capsule. FT-IR spectra were also measured by the diffuse reflectance method for the dried capsule stripped from a dried lens. IR frequencies of the amide I and II bands of the capsule collagen shift from 1637 and 1553 cm−1 to 1654 and 1540 cm−1, respectively, upon going from the intact capsule to the dried one, showing that the collagen helix is converted to a random coil structure upon drying.

Raman Scattering at the CaF2 Crystal Surface Excited by an Evanescent Optical Wave Field

AbstractNew results are given of Raman scattering measurements on the dispersion characteristics of surface‐phonon polaritons at the air—CaF2 interface using the Otto configuration. A phenomenological description of the dispersion relation is also given theoretically as well. The experimental results are in good agreement with the theory. For comparison, the dispersion curve of the surface‐phonon polariton under the same configuration is also measured by the ATR method in the in fared region and the agreement of the results from both the methods is also satisfactory.

Freeze-Drying Fourier Transform Infrared Attenuated Total Reflection Spectroscopy of Surface Adsorbed Layers. Hydration of Adenosine-5'-Phosphoric Acid

A new methodology, suitable for spectral measurements on polar, biologically important molecules, has been developed. The capability of the thallium bromide iodide ATR crystal to adsorb water has been examined and the hydrated crystal surface was used as a substrate for the adsorbed molecules. Diagnostic bands for adsorbed water are reported. A freeze-drying procedure was used to adsorb adenosine-5'-phosphate molecules on the hydrated ATR crystal, and FT-IR spectra of the system were recorded. Different hydrated species of adenosine-5'-monophosphate adsorbed on a water-screened ATR crystal have been observed. The broad bands at 935, 950, and 970 cm−1 are assigned to phosphate groups adsorbed on the thallium bromide-iodide crystal screened by low, medium, and high water coverage, respectively. The high sensitivity of the method is emphasized. The proposed ATR method may be useful for the study of membrane-associated phenomena and models of real-life biological systems with a low solute concentration.

An ATR method for measurement of IR circular dichroic spectra

The present study is an attempt to obtain circular dichroic IR spectra using a conventional ATR attachment provided with a hemicylinder of a high enough refractive index. The measurement is carried out by means of FTIR spectrometers taking a difference spectrum from two ATR experiments. The first one is performed with linearly polarized light of a suitable azimuth while the same azimuth but of opposite sign is used for the second experiment. A theoretical treatment is presented.

Distribution of the degree of conversion over the thickness of the polymer layer on photopolymerization of composites

The kinetic character of the charge in the degree of conversion in different portions of the layer of the polymer formed during photopolymerization of photopolymerized liquid composites has been elucidated. The ATR method has experimentally demonstrated the constancy of the degree of conversion (40–45%) during photopolymerization in a moving (deep in the liquid photopolymerized composite frontal to UV radiation) polymer layer at the polymer-liquid photopolymerized composite interface.

A method of measuring the dielectric functions of thin films by the excitation of SPW in multi-layer system

The attenuated-total-reflection method (ATR) is used to measure the dielectric constant of a thin layer in a prism-metal-dielectric-air system. The addition of the dielectric layer on the metal produces a shift in the dispersion curve and a change in the intensity of the ATR signals compared with the results for the three-layer prism-metal-air system. Both the shift of the dispersion curve and the intensity ratio are found to be linear functions of the thickness of the added layer. The ATR method, therefore, is considered to be a simple and accurate measuring technique of the dielectric functions.

Structure study of very thin Au deposits on Ag by the ATR method

Depot sous vide de couches d'or sur des couches epaisses d'argent. Structure continue ou sous forme d'amas des couches en fonction de leur epaisseur

Quantitative Surface Analysis by Fourier Transform Attenuated Total Reflection Infrared Spectroscopy

The Fourier transform infrared spectroscopic ATR (FT-IR-ATR) method has been applied to quantitative determination of chemical composition of thin surface layers. The powerful capability of the FT-IR-ATR spectral subtraction method was proved to determine poly(dimethylsiloxane) content in the surface layer of Cardiothane 51, which consists of poly(urethane) and poly(dimethylsiloxane) as a minor component, showing the detection limit of 0.2% of the content. An absorbance ratio of a selected band of poly(dimethylsiloxane) relative to a selected band of poly(urethane) was determined by FT-IR-ATR measurements on the pure samples of each of the constituting components that have the same area contacted onto the internal reflection element of Ge. Consideration was also given to the thickness of the surface layer that can be analyzed by the present method, and one half of the penetration depth dp was considered to better represent the thickness of the surface layer measured than dp.

Studies of surface polaritons on magnetic material

The authors have performed numerical calculations for the attenuated total reflection spectra of surface magnon polaritons (SMP) on YIG slabs in the Voigt configuration. It seems that the ATR method can serve as a tool for probing the SMP. A calculation scheme for the SMP on a semi-infinite YIG in the Faraday geometry is presented. The possibility that SMP may occur in a ferromagnetic metal such as nickel is also discussed. The results differ from those obtained by Hartstein and co-workers (1973) who proposed that no surface polaritons exist on ferromagnetic metals.

Applications of surface polaritons for detection and vibrational spectral analysis of thin films on metals and dielectrics

Phonon-polaritons interactions with molecular vibrations of thin films were used for the detection of film oscillator spectral positions. The gap in the polariton branch was proportional to √ ℓ,ℓ being the thickness of the film on dielectric support. The ATR method in the Otto configuration was used for measurements as well as thermal stimulated emission. The vibrational spectra (infrared absorption) of monomolecular films were detected by surface electromagnetic waves (SEW) - surface plasmon-polaritons propagating along the metallic substrate. A comparison of the reflection-absorption method with the SEW broadband (650-2500cm −1) FT-IR method of thin films detection is made. The better sensitivity of the last one is shown. The prism, grating and edge methods of SEW excitations in IR are discussed.

Der einfluss dünner metallischer deckschichten auf die dispersion von oberflächenplasmaschwingungen in gold-silber-schichtsystemen

Abstract Surface plasma oscillations are excited by the ATR method on thin films of gold (silver) with thickness 20 d=550 A ). The influence of these metallic coatings has been studied by the change of the reflected intensity Rp(θ) (position and height of the minimum of reflection and its width). The experimental results are compared with the calculated reflection curves assuming homogeneous smooth coating films. A general good agreement is obtained, except for small coatings of Au (20

Der einfluss dünner metallischer deckschichten auf die dispersion von oberflächenplasmaschwingungen in gold-silber-schichtsystemen

Surface plasma oscillations are excited by the ATR method on thin films of gold (silver) with thickness 20 < d < 130 Å which are evaporated onto substrates of silver (gold) ( d=550 A ̊ ). The influence of these metallic coatings has been studied by the change of the reflected intensity R p(θ) (position and height of the minimum of reflection and its width). The experimental results are compared with the calculated reflection curves assuming homogeneous smooth coating films. A general good agreement is obtained, except for small coatings of Au (20 < d < 50 Å) on Ag.

Application of Infrared ATR Spectroscopy to Liquid Crystals. III

Abstract Infrared absorption measurements of nematic N-(p-ethoxybenzylidene)-p'-cyanoaniline (EBCA) under a DC electric field were performed by means of our previously reported ATR method. DC voltages up to 15V were applied to the nematic liquid crystal 15 μm thick between a silicon ATR prism (probing electrode) and an In2O3-coated glass electrode (opposite electrode). By using this method the orientational behavior of molecules in boundary layers about 1 μm thick at the Si electrode was investigated. The threshold voltage for the dielectric orientation varied from 2 to 6 V depending upon the boundary conditions at the opposite electrode, and the maximum degree of order of homeotropic orientation was found to be 0.6–0.7. A storage effect, in which a homeotropic texture induced by the electric field remains unaltered even if the field is removed or reversed, was observed.

Resonant Interaction of Surface Plasmons with a Dye Monolayer

The interaction of surface plasmons with a dye monolayer having a rather small absorption band is discussed in this paper. Applying the ATR method surface plasmons were excited on a silver surface covered with a monolayer of arachidate (26.8 Å) and a monolayer of the dye. The position, half-width and the depth of the reflection minimum are strongly dependent on the applied wavelength in the region of the absorption line. The essential features of the measured dependencies can be explained by a simple oscillator model.

Arachidate Layers on Ag and Au Substrates Detected by the A T R Method

Monolayers of cadmium arachidate (thickness 26.8 A) are deposited on Ag and Au substrates. They can be detected by the resonance excitation of surface plasmons (ATR method). The number of monolayers is correlated with the displacement of the reflection minimum. The observed values of the position of the minima as well as the shape of the reflection curve are in agreement with the calculated ones, using a refractive index of cadmium arachidate of 1.52 in agreement with other measurements

Investigation of hydrogen capture in ion-bombarded silicon dioxide films by the atr method

Investigation of hydrogen capture in ion-bombarded silicon dioxide films by the atr method

Application of Infrared ATR Spectroscopy to Liquid Crystals. I. Surface-Induced Orientation in Thin Films of Nematic MBBA

Abstract Infrared dichroism of nematic liquid N-(p-methoxybenzylidene)-p-butylaniline (MBBA) was measured using a conventional transmission method and an ATR method. In the former, KBr windows were used as substrates. The degree of orientation order of the homogeneous structure, which was achieved by a rubbing procedure, was obtained to be S=0.40. Using the measured dichroic ratios, the angles between the transition moments and the long axis of the molecule were calculated. The calculated values are in satisfactory agreement with the molecular conformation already suggested. In the ATR method, In2O3-coated glass plates were used as substrates. Rubbing of the In2O3 surface gave a uniform homogeneous orientation with an S value of 0.57. An In2O3 surface treated with dimethyldichlorosilane gave a homeotropic texture with an S value of 0.53. The directions of the transition moments relative to the long axis of the molecule closely agreed with those obtained from transmission spectra.

The effect of thin organic films on the surface plasma resonance on gold

Optical constants of organic monolayers on gold are calculated from shifts in the surface plasmon resonance. Two to several organized layers of cadmium arachidate (each known independently to be 2.68 nm thick) were deposited onto gold films. The angle of minimum attenuated total reflectance changed by about 0.5 degree, corresponding to a Δ k sp of approximately 900 cm -1 for each additional monolayer. Because of the large angular shifts and the simplicity of the ATR method, this technique appears to be an easy and accurate way to determine optical constants and monitor changes in thin (order of nm) interfacial layers on metals.

Spectroscopy of Very thin metal layers on metallic surfaces using optical excitation of surface plasmons

We show how the optical constants of very thin layers deposited on metallic surfaces can be deduced from the modifications of theR p resonances due to excitation of surface plasma waves by the ATR method. The optical constants of discontinuous Au thin layers (thickness <20Å) on Ag surfaces, prepared and studied under ultrahigh vacuum, are determined over the (4000÷6000) Å spectral range.