Surface Exciton Polariton in ZnO

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.

The damping properties of surface polaritons, especially long‐range surface plasmon‐polaritons (LRSP) in asymmetric layer structures are analyzed taking into account the presence of a coupling prism. Both, the response treatment to calculate attenuated‐total‐reflection (ATR) spectra and the virtual mode treatment are used. Two different types of virtual modes are analyzed. One of them describes the propagation properties of the surface polariton in the presence of both intrinsic and radiative damping. The other type describes a surface polariton with a driving field and hence this mode allows to find out the optimum conditions for the ATR experiment. These two modes are investigated in detail and the results of the numerical calculation are presented in graphical form. The results for the ATR configuration show that in asymmetric embedded silver layers the propagation length exceeds the value for the symmetric embedded one significantly.

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.

Tilt angles of liquid crystal molecules, 5CB, have been investigated in the liquid crystal cells with the polyimide (PI) LB alignment films on the aluminum electrodes using the attenuated total reflection (ATR) measurement. The ATR properties were evaluated from the surface plasmon polariton (SPP) and the guided wave excitation modes (GWEM) when various DC voltages were applied to the cell. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones using a three layers model. Furthermore, the electric field intensities in the cell were calculated at several incident angles.

A dialkylsubstituted imidazolium iodide ionic liquid (1-methyl-3-[3-(trimethoxy-lambda4-silyl)propyl]imida-zolium iodide, MTMSPIm+I-) was prepared with the intention of using it as a quasi-solid-state electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of Grätzel design, while the analogous electrolyte in a gel state was made by the addition of tetramethoxysilane (TMOS) in the molar ratio MTMSPIm+I-:TMOS = 1:1. The structure of the MTMSPIm+I- in its non-hydrolyzed and hydrolyzed states and in its fully condensed form, obtained after ageing the sols for various times (from a few hours to a few weeks) and heating them at 200 degrees C (fully condensed form), was studied employing time-dependent infrared attenuated total reflection (ATR) and 29Si NMR spectroscopic measurements. The structure of the condensed species was correlated with the viscosity and the specific conductivity measurements of MTMSPIm+I- sols and TMOS/MTMSPIm+I- gels during their ageing. The final product of the condensation of MTMSPIm+I- sols was described as a positively-charged ladder-like polysilsesquioxane with Tn end groups exhibiting a single T3 signal in 29Si NMR spectra and characteristic doublet bands at 1138 and 1049 cm(-1) in IR. This structure was retained to a large extent in TMOS/MTMSPIm+I- gels, confirming their nanocomposite structure. The results of the ATR infrared time-dependent spectroscopic studies showed that in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to shifts in the vibrational band positions in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined and the results applied in this work.

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.

Theoretical studies of surface phonon polariton in wurtzite AlInN ternary alloy

Non-local dielectric functions on the nanoscale: electronic polarization and fluctuations

Evaluation of liquid crystal molecules on polyimide LB films using attenuated total reflection measurement

Aggregation of silver colloidal particles in the hydrosol via chemisorption of octadecanethiol (ODT) molecules was investigated based on in situ UV–visible transmission and infrared attenuated total reflection (ATR) measurements. As‐prepared silver hydrosol exhibits a single absorption peak at 395 nm because of the plasma resonance of the metal particles. Upon addition of ODT‐dissolved ethanol to the hydrosol, the resonance band red‐shifts and broadens, the detailed features of which depend on the ODT concentration and elapsed time. Both the red‐shift and the broadening are attributed to particle aggregation in the solution via ODT chemisorption. Aggregation on a germanium prism surface by the addition of ODT‐dissolved ethanol to the hydrosol was investigated using infrared ATR spectroscopy. At moderate ODT concentrations, intense aggregation via ODT chemisorption occurs strongly on the prism surface, allowing observation of ODT absorption bands. Angle‐dependent infrared ATR measurements for the ethanol and ODT molecules at the prism/solution interface clearly show that aggregation on the prism surface proceeds via the exclusion of ethanol. Copyright © 2004 John Wiley & Sons, Ltd.

A fully automated titration system with infrared detection was developed for investigating interfacial chemistry at high pressures. The apparatus consists of a high-pressure fluid generation and delivery system coupled to a high-pressure cell with infrared optics. A manifold of electronically actuated valves is used to direct pressurized fluids into the cell. Precise reagent additions to the pressurized cell are made with calibrated tubing loops that are filled with reagent and placed in-line with the cell and a syringe pump. The cell's infrared optics facilitate both transmission and attenuated total reflection (ATR) measurements to monitor bulk-fluid composition and solid-surface phenomena such as adsorption, desorption, complexation, dissolution, and precipitation. Switching between the two measurement modes is accomplished with moveable mirrors that direct the light path of a Fourier transform infrared spectrometer into the cell along transmission or ATR light paths. The versatility of the high-pressure IR titration system was demonstrated with three case studies. First, we titrated water into supercritical CO2 (scCO2) to generate an infrared calibration curve and determine the solubility of water in CO2 at 50 °C and 90 bar. Next, we characterized the partitioning of water between a montmorillonite clay and scCO2 at 50 °C and 90 bar. Transmission-mode spectra were used to quantify changes in the clay's sorbed water concentration as a function of scCO2 hydration, and ATR measurements provided insights into competitive residency of water and CO2 on the clay surface and in the interlayer. Finally, we demonstrated how time-dependent studies can be conducted with the system by monitoring the carbonation reaction of forsterite (Mg2SiO4) in water-bearing scCO2 at 50 °C and 90 bar. Immediately after water dissolved in the scCO2, a thin film of adsorbed water formed on the mineral surface, and the film thickness increased with time as the forsterite began to dissolve. However, after approximately 2.5 h, the trend reversed, and a carbonate precipitate began to form on the forsterite surface, exposing dramatic chemical changes in the thin-water film. Collectively, these applications illustrate how the high-pressure IR titration system can provide molecular-level information about the interactions between variably wet scCO2 and minerals relevant to underground storage of CO2 (geologic carbon sequestration). The apparatus could also be utilized to study high-pressure interfacial chemistry in other areas such as catalysis, polymerization, food processing, and oil and gas recovery.

An apparatus for the study of solution phase kinetics using FT-IR spectroscopy has been developed. The observation chamber consists of an integrated tangential mixer-flow cell and a ZnSe element permitting attenuated total reflectance (ATR) measurements. The short optical pathlength afforded by ATR allows mid-IR observation of chemical reactions in aqueous solution, including the spectral region near the water bending vibration (1640 cm−1). High hydraulic backpressures required to force solution rapidly through a thin layer flow cell are not necessary with the ATR flow cell because the optical pathlength and the flow cross-section have been decoupled, allowing for a relativity large flow chamber when compared with instruments incorporating a transmission flow cell. Overall system performance has been evaluated using the hydrolysis of methylchloroacetate as a test reaction. The feasibility of observing reactions with initial half-lives of approximately 250 ms is demonstrated. The system is very robust, with little risk of damaging the optics during routine maintenance.

It is well known that the development and determination of optical properties of ultrathin films is an important issue in many technological areas. In this work organic polyethylene (PE) and cobalt phthalocyanines (CoPc) ultrathin films were deposited over metal films using the r.f. sputtering and thermal evaporation techniques, respectively. Attenuated total reflection (ATR) measurements for the system organic film/metal at the surface plasmon resonance (SPR) were used for determining the thicknesses and optical properties of the PE and CoPc thin films. Thicknesses of the order of some nanometers were found, fitting the theoretical multilayer ATR model, for p polarization monochromatic light, to the experimental reflection data. The dielectric function of CoPc ultrathin films was determined at a wavelength of 632.8 nm. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Contents and author index

The Attenuated Total Reflection Method