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Principles involving the electronic structure of group VI metal-metal multiple bonded complexes are examined in order to provide insights into the intramolecular and intermolecular interactions of these systems. Examination of chromium, molybdenum and tungsten tetracarboxylate thin films by ultraviolet photoelectron spectroscopy has provided the first experimental evidence for the location of the σ ionization in dimolybdenum tetracarboxylate quadruple bonded complexes. These compounds have significant intermolecular interactions as thin films which destabilizes ionization of the valence σ state, allowing it to be experimentally observed. This is supported by the observed destabilization of the σ ionization feature of the ditungsten analogue in going to the thin film. The Cr₂(O₂CCH₃)₄ comparison shows a destabilization of the leading predominantly metal ionizations consistent with the broad range of M-M bond lengths observed for Cr₂ complexes. The Group VI M₂(mhp)₄ and M₂(chp)₄ [mhp=6-methyl-2-oxo-pyridine and chp=6-chloro-2-oxo-pyridine] complexes are also examined. The geometric constraints imposed on the compounds by the ligand effectively block intermolecular interaction axial to the metal-metal bond in the solid state. Comparison of the two ligand spectra, Hmhp and Hchp, has provided a unique opportunity to assign ionizations previously attributed to the keto form of the Hmhp tautomers. The spectra of the complexes exhibit minimal relative shifting of ionization features in going to the thin films because of this constraint. A band previously believed to be due to spin orbit coupling is assigned to the σ ionization in the ditungsten complex. The overall ionization band profiles of the two series correlate well, metal by metal, with the expected shifting due to substitution of the more electronegative chlorine atoms for a methyl group. The synthesis and characterization of Mo₂(N-t-butyl-acetamide)₄, the first tetraamidodimetal compound without large rings with delocalized pi structure, is described. The single crystal X-ray structure is presented, revealing the novel (one of three examples) cis configuration of the MoN₂O₂ ligand set. The Mo-Mo bond length of 2.063 Å is one of the shortest seen to date. A preliminary gas phase He I valence spectrum is reported.

Materials in the form of thin films that have been deposited from the vapor phase are significantly different from similar bulk materials, both optically and mechanically, because of their columnar structure and consequent porosity. Their porosity have been verified in different ways. The effects of the pores on optical and mechanical performance and, in particular, the influence of water adsorption, have also been demonstrated. Three techniques used for investigating optical instabilities in thin films are given. They all involve sharp resonances. The resonances are associated either with surface plasmons, metal-dielectric narrowband filters, or all dielectric narrowband filters. These resonances are very sensitive functions of layer properties and hence can be used to detect and measure changes in the layers, particularly those that are induced by adsorption of moisture. Moisture adsorption in thin films is a complex process that occurs unevenly in patches. Using resonance techniques, the adsorption isotherms of change in refractive index, of growth rate in patch size, and of peak wavelength shift, which are all important in characterizing the porosity of films, have been measured. Some effects that locally increase film porosity and create central pores that permit water to penetrate into multilayer structures have been investigated. Based on these results, some suggestions for preventing water adsorption in films are then made. Moisture penetration into thin film structures is the major source of optical coating instability and it is therefore very important that the mechanisms of penetration by understood. Some deductions of the mechanisms are made from the experimental results.

We consider in this work the contribution of anisotropic microstructure to polarization effects in thin films. The microstructure is pictured by a simple model as composed of identical columns with elliptical cross section elongated in a direction perpendicular to that of the vapor incidence. The asymmetry in columnar structure that results from oblique deposition is identified as the common source for the significant dichroism and birefringence observed in metal and dielectric films, respectively. A four-dimensional theory for multilayer systems is presented that starts from first principles, unifies previous treatments for particular cases of film anisotropy, and properly handles the most general case of elliptically polarized mode propagation. In this framework and from a set of polarimetric measurements, a simple method is devised, with explicit consideration of the anisotropic microstructure, for the determination of the physical thickness and principal refractive indices of a single dielectric film. A sequence of transmittance measurements is performed with a zirconium oxide film deposited at 65° and, substrate role and instrumental errors considered, good agreement is obtained between theory and experiment. Spectrophotometer data for a narrowband filter with 21 layers deposited at 30° is shown to confirm theoretical predictions of peak positions with Angstrom resolution. A hypothetical metal film is discussed that reproduces the essential features observed in the optical behavior of an aluminum film deposited at 85°. Potential applications and suggestions for future work are included.

Surface-plasmon polaritons propagating on thin metal films bounded by dielectrics of nearly equal refractive indexes comprise two bound modes. Calculations indicate that, while the modes are degenerate on thick films, both the real and the imaginary components of the propagation constants for the modes split into two branches on successively thinner films. Considering these non-degenerate modes, the mode exhibiting a symmetric (antisymmetric) transverse profile of the longitudinally polarized electric field component, has propagation constant components both of which increase (decrease) with decreasing film thickness. Theoretical propagation constant eigenvalue (PCE) curves have been plotted which delineate this dependence of both propagation constant components on film thickness. By means of a retroreflecting, hemispherical glass coupler in an attenuated total reflection (ATR) configuration, light of wavelength 632.8 nm coupled to the modes of thin silver films deposited on polished glass substrates. Lorentzian lineshape dips in the plots of reflectance vs. angle of incidence indicate the presence of the plasmon modes. The real and imaginary components of the propagation constraints (i.e., the propagation constant and loss coefficient) were calculated from the angular positions and widths of the ATR resonances recorded. Films of several thicknesses were probed. Results which support the theoretically predicted curves were reported.

An organic Schottky barrier cell, consisting of a thin layer of the organic semiconductor, GaPc-Cl, in contact with gold on one side and an electrolyte containing a redox couple on the other, was developed as a solar energy conversion device. Schottky barriers were formed at both interfaces. Film morphology, as determined by the sublimation rate, was the major determinant of the photoelectrochemical behavior. An optimum film consisted of a single layer of crystallites about 1.0 micron in thickness, tightly packed together to give a non-porous film. Thinner films did not develop the full theoretical photopotential, and pores acted as recombination sites, decreasing the efficiency. Both negative and positive photopotentials could be developed, depending on the redox couple used. The photopotential, was found to be proportional to the differences between the Fermi level of the Au and the formal potential of the redox couple. Hydrogen evolution was possible with up to 0.1% solar efficiency on a platinized version of the optimum electrode. Results from photocurrent action spectra and pulsed laser photocoulostatics, showed the potential drop across the film was not linear, but formed a potential well about 0.1 eV deep, which captured charge carriers and decreased the efficiency. From scanning electron microscope studies, phthalocyanines, such as AlPc-Cl, GaPc-Cl, and InPc-Cl, with bulky anions were found to form block-like crystal structures favorable for use in Schottky barrier cells. Phthalocyanines with transition metals in the +2 oxidation state, such as FePc and MgPc, were found to form long needles, which were not favorable for use in Schottky barrier cells.

The incentive for conducting Degenerate Four Wave Mixing (DFWM) within guided wave devices is two-fold: (1) By coupling the optical beams into guided wave devices, the optical power densities can be increased orders of magnitude due to the tight confinement of the beams. Such an increase in power density means a concomitant increase in conversion efficiency of the signal beam. (2) The potential signal processing applications of DFWM (logic gates, switching, correlation/convolution), particularly for ultra-fast serial processing, would be better exploited, and adjoined to existing integrated circuit technology, by such an integrated optic/guided wave approach. In this dissertation we describe experiments and present data confirming the presence of DFWM within a planar glass thin film with carbon disulphide as the nonlinear cover medium. Optical pulses from a Q-switched, frequency doubled Nd:YAG laser are coupled into the glass film. The nonlinear polarization required to produce the desired conjugate signal is generated within the CS₂ by the evanescent tails of the guided input beams as they probe the nonlinear cover medium. The signals measured agree well with theory, but because they were so small in magnitude, signal-to noise ratios were small due to stray background radiation scattering from beamsplitters and other associated optics. Additionally, recent studies (Jain & Lind, 1983) indicate nonlinear responses in semiconductor (CdS/Se) doped glasses, commercially available as color glass filters, that are orders of magnitude higher than corresponding nonlinearities within CS₂, in addition to possessing subnanosecond response times. We have performed experiments upon such glasses in an effort to fabricate nonlinear optical waveguides within them via ion-exchange techniques. We have successfully fabricated single mode planar guides, but they are currently too lossy to allow demonstration of any guided wave nonlinearities. Also, we describe experiments in which we have measured (bulk) DFWM grating lifetimes with greater precision than previously reported. Results indicate a fast (20 to 50 pico-seconds, depending on the particular glass) electronic response, superimposed upon, but clearly distinguishable from, a slower (10's of nanoseconds) thermal response.

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We established measurement and analysis techniques necessary to investigate the optical properties of some transition metal compounds: specifically the carbides and nitrides of Ti, Zr, and Hf. Two distinct techniques determined the optical constants of these films: a Nestell-Christy method to invert measurements of thickness, reflection, and transmission and a Kramers-Kronig analysis of reflection. The compositions of the samples were evaluated by X-ray diffraction, Auger spectroscopy, scanning electron microprobe analysis, and nuclear analysis. We found it possible to correlate these materials' optical and electronic properties and relate these to compositional changes. The ability to engineer a specific optical response of materials is discussed. Additions of carbon and nitrogen change the optical properties in a specific manner; the roles of these elements as electron donors and their effect on the location and population of the d electron bands with respect to the Fermi level are postulated.

No description available.