Current technology has made possible the fabrication of multilayered optical elements for soft x-ray radiation. These structures find a variety of important applications. Difficulties in the design and fabrication of multilayers for soft x-rays are related to the lack of information about the properties of materials in the very thin layers (~5-100 Å) required. Imperfections cause the measured optical properties of the multilayers to deviate strongly from ideal behavior. Realistic calculations of reflectance must take these imperfections into account. We review the pertinent theory, with attention to the problem of including non-ideal properties. We also review characterization techniques suitable for the measurement of relevant structural and stoichiometric parameters of the multilayer. A detailed characterization procedure is presented. This procedure is capable of accurately determining the layer thicknesses, material densities, interfacial rms roughness or diffusion values, crystalline structure, concentration of contaminants, and extent of surface oxidation. The techniques used included low-angle x-ray θ-2θ diffraction with parallel-beam and Bragg-Brentano geometries, wide-film Debye-Scherrer ("Read") camera and Seemann-Bohlin diffractometer, Rutherford backscattering spectroscopy, and transmission electron microscopy. Si/W multilayer mirrors were designed for normal-incidence 210 Å radiation. Samples were fabricated using a magnetically-confined-plasma dc-triode sputtering technique. Our characterization procedure was applied to these samples. To our knowledge, this is the first time such a comprehensive set of characterization techniques has been applied to a multilayer x-ray optical element. The same samples were tested with synchrotron radiation over a wide spectral range, and for several incidence angles. The measured reflectance is in excellent agreement with curves calculated using the information obtained from the characterization results, with no adjustable parameters. The Si/W combination is shown to have good layering characteristics. The near-normal reflectance of the multilayers was 20 to 30 times better than the reflectivity of the best single-surface mirrors at the same wavelengths.

Optical filters and thin film optical devices play an important role in Science and Industry. Several significant applications have emerged in optics, microelectronics and computer technology. In this work, we study some aspects of their design and applications. One class of optical fibers, known as Christiansen filters, are based on scattering phenomena in suspensions of solid particles in a liquid medium. Some new scattering filters in the visible and the near UV regions and their performance characteristics are reported here. Feasibility to fabricate such optical filters in solid matrix form is established. Some applications of these scattering filters are discussed. After an introduction to the optics of homogeneous and isotropic thin films, I discuss the general design of anisotropic thin film media and a scheme implemented to calculate their performance. Optical anisotropy, produced by the growth-induced columnar microstructure in thin films and its effects on the performance of optical filters are studied. Large shifts in the peak wavelength of a typical narrow band filter are predicted. Magneto-optical (MO) thin film media of great importance to erasable optical data storage technology are studied. An approximate technique based on a 2 x 2 matrix formalism is developed to calculate the normal incidence performance of these media. To investigate anisotropic effects, to incorporate more than one magnetic film with arbitrary orientations of magnetization, and to study oblique incidence performance, a completely general 4 x 4 matrix technique is implemented in a computer program. Effects of substrate/superstrate birefringence in the read-out signal of MO media are investigated. Several optimizing design criteria, particularly, the effectiveness in employing appropriate metal or dielectric reflector layers are studied. The influence of the plasma edge of metals in enhancing the polar Kerr rotation of MO media is discussed with illustrations. A contour plot of the Kerr rotation and reflectance is developed to help in the design of these media. An explanation is given for the observation of Kerr rotation enhancement near the plasma reflection edge of the reflector layer adjacent to the active MO layer and in general, where the reflectance spectrum shows a steep gradient.

Optical, electrical, and microstructural effects of Ar ion bombardment and Ar incorporation on thermally evaporated Ag and Al thin films were investigated. The results show that as the momentum supplied to the growing films by the bombarding Ar ions per arriving metal atom increases, refractive index at 632.8 nm increases and extinction coefficient decreases, lattice spacing expands, grain size decreases, electrical resistivity increases, and trapped Ar increases slightly. In Ag films, stress reverses from tensile to compressive; in AI films compressive stress increases. In both films, the change in optical constants can be explained by variation in void volume. The reversal of stress from tensile to compressive in Ag films requires a threshold level of momentum. The increase in electrical resistivity is related to the increase in the void fraction, decrease in the grain size, and increase in trapped Ar in both types of films. Many of these properties correlate well with the momentum transferred, suggesting that the momentum is an important physical parameter in describing the influence of ion beams on growing thin films and determining the characteristics of thin metal films prepared by ion-assisted deposition (IAD). With a low energy ion beam, the Ar concentration in IAD Ag films was negligible. When the bombarded film thickness was less than 5 nm, the electrical resistivity of IAD Ag films tended to decrease slightly from that of the non-IAD film. Using the Bruggeman effective medium theory, a formula for the void fraction at any given wavelength was derived. We investigated optical properties, stoichiometry, chemical bonding states, and structure of aluminum oxynitride thin films prepared by reactive ion-assisted deposition. Variations of optical constants and chemical bonding states are related to the stoichiometry. We found that our amorphous aluminum oxynitride film is not simply a mixture of aluminum oxide and nitride but a compound. A rugate filter using a step-index profile of aluminum oxynitride films was fabricated by nitrogen ion beam bombardment of a growing Al film with backfilled oxygen pressure as the sole variable. The effects of ultrasound-assisted deposition (UAD) on the optical properties of ZrO₂, Ta₂O₅, and MgF₂ films were investigated. UAD is likely to induce oxygen and fluoride deficiencies in oxide and fluoride films and increase the packing density of films.

Theoretical considerations for the use of chalcopyrite ternary I-III-VI₂ compounds in heterojunction photovoltaic conversion devices are presented, followed by an in-depth study of the structural, optical, and electrical characteristics of multi-source evaporated CuGaSe₂ thin films as determined by processing. Film composition was identified as the primary variable for affecting the microstructure and optical-electrical behavior of the films. Film composition was in turn dependent upon elemental flux rates and substrate related effects. Films deposited on glass and bare alumina substrates were richer in selenium than films deposited on molybdenum coated substrates. Cu-poor, near stoichiometeric, and Cu-rich compositions were obtained by varying the Cu/Ga flux ratio. Cu-poor films deposited on bare ceramic substrates were characterized by secondary impurity phase content and a tendency for cubic CuGaSe₂ formation. The cubic nature of optically thin films deposited on glass was substantiated by a lack of crystal field splitting of the valence band as observed by optical absorption measurements. Cubic-tetragonal phase behavior was monitored on optically opaque samples by observation of intensity-independent (112)/(111) x-ray diffraction peak shifts. Cu-poor films on glass were also characterized by surfaces pitting at substrate temperatures in excess of 450°C which may be related to the high surface energy of gallium. Cu-poor films deposited on molybdenum coated alumina substrates exhibited less impurity phase formation and were largely single-phase tetragonal CuGaSe₂. Cu-rich films on all substrates contained CuₓSe impurities and tetragonal CuGaSe₂.

Voltammetric and spectroelectrochemical results are presented for the one-electron reduction of n-heptyl viologen on clean and silane-modified tin oxide, and on ion-beam modified, indium-tin oxide metallized plastic optically transparent electrodes (ITO MPOTE) surfaces. The use of viologens (dialkyl and diaryl 4,4' bipyridium compounds) in redox chromic displays is well known with a number of papers and patents discussing their use. The ability to vary the coloration rates of the electrochromic reaction of these compounds can be strongly influenced by the state of the electrode surface. Potential-step experiments, where the electrode potential is controlled at low overpotentials, has shown that the viologen reduction occurs through a nucleation process. The work here indicates that an "instantaneous nucleation" model appears to be the favored pathway for the n-heptyl viologen reaction. Chronoabsorptometric analysis of the nucleation process is made possible by monitoring the strongly absorbing viologen cation radical. Chronoabsorptometric data can be used to calculate the nucleation site density on an electrode surface. On silane-modified and ion-beam modified electrode surfaces, a more preferred nucleation site is found for the deposition of the first monolayers of viologen. Through the attachment of a silane or the ion-beam modification of an ITO metallized plastic film (ITO MPOTE), a nonpolar layer is created adjacent to the electrode surface. Prior to electrochemical reduction the n-heptyl viologen dication is partioned and concentrated into this nonpolar layer. The effect is a preconcentration of the viologen next to the electrode surface resulting in a fixed number of nucleation sites and an enhancement of the nucleation rate.

This research focuses on the development of spectroelectrochemical sensor formats based on thin film molecular architectures and electrochemical detection of sol-gel encapsulated macromolecular recognition elements. To achieve this goal, there were two major objectives: 1) to demonstrate and characterize conductive polymer grown electrochemically in porous sol-gel thin films with specific regard to the ability of the polymer to mediate charge transfer between sol-gel encapsulated molecules and the electrode surface, and 2) to develop a means to probe the spectroscopic properties of highly absorbent thin films as a function of applied potential. Toward the first objective, diffusion of a derivatized thiophene monomer into a sol-gel thin film and subsequent electropolymerization at an underlying indium-tin oxide (ITO) surface was found to produce a conductive network of polymer capable of mediating electron transfer from encapsulated redox centers in the bulk of the sol-gel film to the electrode surface. At high levels of polymer loading, emergent, sol-gel templated, polymeric structures are formed which extend from the sol-gel surface into the electrolyte solution and exhibit electrochemical properties of ultramicroelectrode arrays. To achieve the second objective, a polychromatic, electroactive attenuated total internal reflectance (EA-ATR) instrument was developed consisting of an indium-tin oxide (ITO) coated glass internal reflection element (IRE). In addition to a high degree of surface sensitivity relative to transmission geometries, this geometry affords acquisition of absorption anisotropy information, via polarization of the incident beam, to determine the orientation distribution in molecular adlayers. To demonstrate these abilities, the orientational distribution of monolayer and bilayer films of perylene and copper phthalocyanine derivatives, respectively, was determined. Furthermore, it was demonstrated that the EA-ATR could be used in a potential-modulated mode (PM-ATR) to study the kinetics of electro-optical switching in conductive copolymer thin films.

No description available.

Various metal phthalocyanines have been used as dyes, catalysts, indicators, electrophotographic receptors and more recently as active elements in chemical sensors and photoconductive materials for solar energy conversion applications. Of the MPc's, VOPc, GaPc-Cl and TiOPc have shown promise for solar energy conversion devices. GaPc-Cl has also shown promise as a chemical sensor. Up to this point in time, the focus of Pc research in this group has been in the direction of characterizing the photoelectrochemical properties of these materials. Recently, solid state studies of TiOPc have been done to determine the electronic properties of a tetravalent metal Pc, such as conductivity and photoconductivity. Such solid state measurements are facilitated by the use of interdigitated microelectrode arrays which are coated with thin films of various Pc's.

The purpose of this investigation was to explore the processing parameters involved in the production of thin film superconductors by spray pyrolysis processing (SPP). The present study is an attempt to optimize the many parameters in SPP. The specific parameters studied were substrate temperature, carrier gas flow rate, substrate materials, solution stoichiometry, spray rate, concentration, starting materials, and substrate to nozzle distance. The effect of these parameters on film stoichiometry and the anticipated superconducting behavior were investigated at some length. Films were routinely produced in a spray chamber designed as a part of this research. Films were analyzed by Rutherford Backscattering Spectroscopy, X-Ray Diffraction, Scanning Electron Microscopy, and Meissner effect measurements.

No description available.