Internal Reflection Configuration Research Articles

Imaging gold nanoparticles in living cell environments using heterodyne digital holographic microscopy

This paper describes an imaging microscopic technique based on heterodyne digital holography where subwavelength-sized gold colloids can be imaged in cell environments. Surface cellular receptors of 3T3 mouse fibroblasts are labeled with 40 nm gold nanoparticles, and the biological specimen is imaged in a total internal reflection configuration with holographic microscopy. Due to a higher scattering efficiency of the gold nanoparticles versus that of cellular structures, accurate localization of a gold marker is obtained within a 3D mapping of the entire sample's scattered field, with a lateral precision of 5 nm and 100 nm in the x,y and in the z directions respectively, demonstrating the ability of holographic microscopy to locate nanoparticles in living cell environments.

Analysis of the coupling of light into a metal-dielectric composite waveguide structure and its application for use as a wavelength-band selection filter

We analyzed and experimentally tested a metal-dielectric composite waveguide structure. After coating the surface of the metal layer in the Kretschmann attenuated total internal reflection configuration with a dielectric layer, we explain the coupling of incident light into the coated layer. After finding the dispersion relationships for the layered media including the metal-dielectric composite waveguide, we can determine a solution for its existence in a complex domain. By inscribing a periodic grating structure in the dielectric layer of the metal-dielectric composite waveguide, we experimentally verify the coupling of incident light on the metal-dielectric composite waveguide structure and propose its application for use as a wavelength-band selection filter.

FTIR investigations of phase transitions in an asymmetric azomethine liquid crystal

The liquid crystalline (LC) behavior of a literature-reported asymmetric azomethine compound (4-[4-(n-butyloxy)-benzylideneimino]-chlorobenzene, Cl.O4) was investigated by using optical polarized light microscopy, differential scanning calorimetry and medium-wide angle X-ray diffraction. FTIR in attenuated total internal reflection configuration was employed to study the microstructural changes occurring during phase transitions of the azomethine. Spectral modifications, associated with molecular conformation rearrangements, allowing the change of the molecular shape from a LC organization to another, have been found. The spectral analysis gave significant evidences for the different phase transitions, thus proving the efficiency of such method for investigating LC materials.

A comparison of infrared spectroscopic methods for the study of heterogeneous reactions occurring on atmospheric aerosol proxies

In this paper, the heterogeneous reaction between oleic acid and ozone has been studied using infrared spectroscopy in two distinctly different experimental configurations. The effect of the experiment on the observed products and rates of reaction is compared in order to derive a better understanding of some of the variations in oleic acid reaction rates reported by a range of researchers. One set of measurements is made using thin films of oleic acid in an attenuated total internal reflection configuration, and it is shown that a treatment in which the ATR evanescent wave is convolved with a moving reaction front is essential for the extraction of reliable kinetic data. The results are compared to similar measurements in a recently developed aerosol flow tube equipped with a cross-beam infrared spectroscopic probe. Rates of reaction in the aerosol phase are observed to be approximately 10 times faster and possible reasons for this discussed.

Ellipsometry study of ultra thin layers of evaporated gold

AbstractOptical properties of ultra thin (from 1 to 40 nm) films of gold evaporated on glass and silicon were studied with the method of spectroscopic ellipsometry in both external and internal reflection configurations as well as with the UV‐visible absorption spectroscopy. The results obtained showed a gradual shift of the plasmon peak from 580 nm for 1 nm thick films to more than 1000 nm for thick (40 nm) gold films. Such phenomenon can be interpreted in terms of quantum confinement of surface plasmons in gold islands. The threshold of the metal‐dielectric transition was found at the film thickness between 4 and 5 nm. Thiolation of the surface of glass has resulted in a slight decrease in the effective thickness of gold layer and respective smaller blue shift of n (λ) and k (λ) dispersion curves, however no dramatic changes were observed in the film morphology. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Heterodyne holographic microscopy of gold particles

We report experimental results on heterodyne holographic microscopy of subwavelength-size gold particles. The apparatus uses continuous green-laser illumination of the metal beads in a total internal reflection configuration for dark-field operation. Detection of the scattered light at the illumination wavelength on a charge-coupled-device array detector enables 3D localization of brownian particles in water.

A comparison between chemical and sputtering methods for preparing thin-film silver electrodes for in situ ATR-SEIRAS studies

Stable silver thin films were prepared either by chemical deposition or by argon sputtering on germanium and silicon substrates, respectively, and used as electrodes for in situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. The spectra obtained for acetate anions adsorbed from neutral solutions showed a noticeable intensity enhancement (SEIRA effect). This enhanced absorption has been related to the surface structure of the films that have been characterized by ex situ STM and in situ electrochemical measurements (lead underpotential deposition, UPD). STM images of the chemically deposited silver films show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, and the absence of flat domains. On the other hand, STM images of the films deposited by argon sputtering show mean grain sizes around 30 nm for a film growth rate of 0.05 nm s −1 and 70 nm for a film growth rate of 0.005 nm s −1. In this latter case, atomically flat domains up to 50 nm wide have been observed. This observation is consistent with a more defined voltammetric profile for lead UPD, that indicates a higher degree of surface order. Moreover, the roughness factor obtained from the charge density involved in lead UPD in the case of the sputtered silver film is lower than that measured for the chemically deposited silver film. All these structural data can be connected with the observations on the effect of deposition conditions of the silver film on the SEIRA effect for adsorbed acetate. Maximum enhancement is observed for chemically deposited films and sputtered films at high deposition rate for which the grain size is around 40–60 nm. The increase of the grain size for the sputtered silver films deposited at decreasing deposition rates can be related to the observed decrease in the SEIRA effect.

Giant Goos-Hänchen displacement enhanced by dielectric film in frustrated total internal reflection configuration

It is predicted that the Goos-Hänchen displacement in the usual frustrated total internal reflection configuration can be resonantly enhanced greatly by coating a dielectric thin film onto the surface of the first prism when the angle of incidence is larger than the critical angle for total reflection at the prism-vacuum interface and is smaller than but close to the critical angle for total reflection at the prism-film interface. Theoretical analysis shows that the displacement of transmitted beam is about half the displacement of reflected beam in the thick limit of the vacuum gap between the two prisms. This is to be compared with the relation in the usual symmetric double-prism configuration that the displacement of transmitted beam is equal to the displacement of reflected beam. Numerical simulations for a Gaussian incident beam of waist width of 100 wavelengths reveal that when the dielectric thin film is of the order of wavelength in thickness, both the reflected and transmitted beams maintain well the shape of the incident beam in the thick limit of the vacuum gap. So largely enhanced displacements would lead to applications in optical devices and integrated optics.

Flip-Flop in Adsorbed Bilayers

There is very rapid exchange between molecules between an adsorbed (supported) bilayer and solution. Complete exchange of a bilayer occurs within seconds; the actual exchange process may be faster but is limited by the resolution of our technique. The exchange process was monitored by infrared spectroscopy, which can independently monitor deuterium-labeled and unlabeled surfactants, and surface selectivity was achieved by using an internal reflection configuration. Total exchange requires exchange of both the inner and outer layer. We demonstrate that the desorption of a monolayer into water is extremely slow, yet exchange of the inner layer into surfactant solution is extremely fast when a bilayer is present. This shows that flip-flop for an adsorbed bilayer is very fast. Rapid flip-flop at interfaces is in sharp contrast to the extremely slow rate of flip-flop in vesicles. We hypothesize that the rapid rate of flip-flop in adsorbed layers is a consequence of surface-induced defects; in free vesicles, the defects are closed by the film pressure.

Costa de fiordes da Patagônia central, Chile, morfologia submarina e fácies acústicas

This study interprets acoustic sub-bottom profiles and submarine 3D models of some of fjords adjacent to Campo de Hielo Patagonico Sur (Southern Patagonian Icefield), Chile. The overdeepened fjord basins show irregular morphology and distinctive landforms associated with a grounding-line, ice tongues and icebergs sedimentary system. Acoustic reflectors display two main facies: chaotic and laminated, according the internal reflection configuration and the external geometry. The sediments probably were deposited during the Holocene deglaciation, as shown by the visible reflectors of sub-bottom profiler. The geometry of the depocenters and the acoustic reflectors characteristic show evidence of pre-existing topography and bathymetry influence. Due to the great water depths of the fjord basins, terminal margins may have a mix of floating and grounded cliff behaviour, albeit the predominant temperate glacial regime.

Coherent optical reflectance from a monolayer of large particles adsorbed on a glass surface

We develop a coherent-scattering model for the reflection of light from a monolayer of large particles and low surface coverage. The model takes into account multiple scattering between particles of the monolayer and with the substrate, and it can be used around the critical angle in an internal reflection configuration. We compare the results of the model with our own reflectivity data taken with latex particles adsorbed on a glass-water interface and with a simpler effective-medium model.

Thickness measurements on transparent substrates based on reflection ellipsometry I Optical effects of high-refractive-index additional layers

Theoretical studies were conducted for thickness measurements using transparent substrates on the external and internal reflection configurations. For three-phase systems consisting of ambient, film, and substrate, the refractive index of the substrate could be optimized to obtain the high sensitivity of an ellipsometric quantity delta to the film thickness and the small susceptibility of delta to errors in the incident angle. It was shown that the combination of an ordinary glass substrate and an additional dielectric layer with an appropriate layer thickness works as a synthetic high-index single substrate (SHIS). The optical effect of the combination was approximately described by use of the effective refractive index of SHIS. A method to select the refractive index of the additional layer was also given.

Coherent reflection of light from a turbid suspension of particles in an internal-reflection configuration: Theory versus experiment

We compare a recently developed coherent-scattering model for the reflectance of light from a turbid colloidal suspension of particles with experimental measurements. The experimental data were obtained in an internal reflection configuration around the critical angle using a glass prism in contact with a monodisperse colloidal suspension of latex particles, and a polydisperse suspension of TiO2 particles. First, we review the coherent scattering model and extend it to the case of polydisperse suspensions in an internal reflection configuration. The experimental data is then compared with results of the coherent scattering model and results obtained assuming that the colloidal system can be treated as a homogeneous medium with an effective index of refraction. We find that the experimental results are not compatible with the effective medium model. On the other hand, good fits to the experimental curves can be obtained with the coherent scattering model.

ATR−SEIRAS Study of the Adsorption of Acetate Anions at Chemically Deposited Silver Thin Film Electrodes

The adsorption of acetate anions at silver thin film electrodes has been studied by in-situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. Stable silver thin films were chemically deposited on germanium substrates. Ex-situ STM images show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, respectively. The thickness of the silver film, measured by AFM, is typically around 10 nm for a deposition time of 10 min and increases up to 50 nm for a deposition time of 20 min. Roughness factors around 2.3 have been obtained for the silver films from the charge involved in lead underpotential deposition (UPD). A noticeable enhancement of the infrared absorption of adsorbed species (SEIRA effect) is observed when the silver films are used as electrodes under internal total reflection conditions. Maximum intensities of the adsorbate bands were observed for a deposition time of 10 min and an angle of incidence around 65 degrees . The potential-dependent infrared spectra of acetate and interfacial water are consistent with previously proposed models involving the existence of weakly hydrogen-bonded water molecules at potentials below the potential of zero charge and the reorientation of water molecules at potentials above the potential of zero charge. Results reported in this work suggest a weak interaction between acetate and water molecules adsorbed at the silver thin film electrodes.

Surface Effects on the Coherent Reflection of Light From a Polydisperse Colloid

We consider the coherent reflection of light from a dilute polydisperse random system of particles. We focus our attention on the effects of the variation of the size distribution function induced near a flat solid interface. We also present a comparison of the theory with experimental results of the coherent reflectance of light in an internal reflection configuration. Introduction The coherent reflection and transmission of light in random systems of particles is potentially a useful tool to characterize highly scattering particles, colloids and composite materials. By coherent we mean the wave corresponding to the average electromagnetic field which is obtained by averaging over all possible configurations of the system (configurational average). The coherent transmission of electromagnetic waves through random systems of particles has been studied by several authors since long ago (1). More recently, the coherent reflection of an electromagnetic wave from a half space of randomly located particles has been studied using a very intuitive approach (3), which turned out to be closely related to the so called effective-field approximation (4) and valid only for a dilute suspension of particles. We will call this approach the coherent-scattering model. For relatively dense systems a more elaborate procedure, called the quasi-crystalline approximation (2), has been also developed. This latter approximation is rather intensive numerically, and since we are exploring here the importance of surface effects on the reflectance, we will restrict ourselves to dilute colloidal systems where the inversion of experimental data can be easily done. We should also add that we have performed already experiments to test and to validate the coherent-scattering model finding that it can reproduce well the experimental data (5). However, when dealing with polydisperse systems of particles in the presence of a flat interface between the matrix material and a homogeneous medium, the mere presence of the interface changes the density and size distribution over a region of the order of the width of the size distribution function. This region of variable density and size distribution may be called the surface region. In this paper we propose an iterative procedure to take into account in the reflectance calculations the presence of the surface region and compare its effects with the ones of a simpler approximation that we call the sharp-surface approximation. Finally, we also present a comparison between reflectance calculations using the coherent-scattering model and experimental data of light reflectance from a polydisperse colloidal suspension of latex particles, in an internal-reflection configuration.

Fluctuation of Thermal Lens Signal in Total Internal Reflection Configuration from Phospholipid Bilayer

When a phospholipids bilayer with a metallochromic indicator was measured by total internal reflection with thermal lens spectrometry, the signal was more fluctuated than that of a dye solution. To clarify the difference of the signal fluctuation for the bilayer and the dye solution, power spectra of the results were obtained by a Fourier transform. In a lower frequency region, the intensity of the power spectrum for the phospholipid bilayer measurement was higher than that for the dye solution measurements. We supposed that the fluctuation was caused by the heterogeneity of the bilayer, or aggregation of the dye molecules in the bilayer, or both. Signals at different temperatures were obtained, and these power spectra were compared with each other. The spectra lower than 0.05 Hz increased as the temperature became higher, and agreed with the expected result.

Sum-frequency generation spectroscopy applied to model biosensors systems

Vibrational information recorded by infrared-visible sum frequency generation spectroscopy was used to study the adsorption of a derivated vitamin (biocytin) on different substrates and its subsequent reaction with a protein (avidin). No reaction is observed on metallic substrates. When the experiments are carried out with a CaF 2 substrate in the total internal reflection configuration, significant changes of the CH and NH vibrations can be related to the specific bonding of avidin to biocytin.

Wet chemical cleaning of InP surfaces investigated by in situ and ex situ infrared spectroscopy

Wet chemical cleaning is central to semiconductor device processing. For InP-based optoelectronic devices, controlling wet processing is challenging because of the high reactivity of InP surfaces in ambient air. In situ techniques are therefore critical to monitor and understand wet chemical etching and oxidation. We have combined in situ and ex situ Fourier transform infrared absorption spectroscopy, in direct transmission and multiple internal reflection configurations, with ex situ x-ray photoelectron spectroscopy to investigate the wet-chemical removal of “epi-ready” oxides on InP(100). Even dilute solutions of HCl, HF, or H2SO4 are found to completely remove the epi-ready oxides. For both HCl and HF, the InP surface is left unpassivated, exhibiting rapid recontamination and reoxidation upon air exposure. In contrast, H2SO4 aggressively etches the surface, and forms a thick and fragile oxide cap that can be washed away during a subsequent water rinse. This systematic in situ vibrational study of InP oxide chemistry provides a basis for a mechanistic understanding of wet chemical etching and oxidation.

Modeling and experimental verification of the performance of TIRF-sensing systems for oligonucleotide microarrays based on bulk and integrated optical planar waveguides

The detection of hybridization events on oligonucleotide microarrays in real time can be performed, using the optical principle of total internal reflection fluorescence (TIRF). We have investigated and compared three TIRF-sensing configurations using two bulk and one integrated optical planar waveguide as transducer platforms for oligonucleotide microarrays, which have been brought in contact with flow cells. Based on the ray optics model, expressions were derived for the calculation of the intensity of the CCD-camera signal generated by solved fluorophores in the flow cell volume. A noise analysis was performed and expressions for the calculation of the detection limit of the surface fluorophore density were derived. With a bulk optical single total internal reflection configuration a detection limit of 3.74 molecules/μm 2, with a bulk optical multiple total internal reflection configuration a detection limit of 1.83 molecules/μm 2 and with the integrated optical waveguide (IOW) configuration a detection limit of 0.013 molecules/μm 2 was numerically estimated based on background data of the bulk volume signal. The derived analytical expressions address the full system, including light source, optical waveguide and the detection unit and can serve as a tool for TIRF-system design.

Sulphate adsorption at chemically deposited silver thin film electrodes: time-dependent behaviour as studied by internal reflection step-scan infrared spectroscopy

Stable silver thin films were chemically deposited on a germanium substrate. Ex-situ STM images showed that these films are formed by grains with a diameter between 20 and 100 nm. The silver films have been used as the working electrode in infrared spectroelectrochemical experiments with an internal reflection (Kretschmann) configuration. The adsorption of sulphate anions in neutral or slightly acidic solutions has been studied. The high intensity of the S–O stretching bands in the absorption spectra allowed the monitoring of the time-dependent behaviour of the adsorption/desorption processes in time-domain step-scan experiments.