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.

This work concerns the vacuum deposition of novel thin films that exhibit nonlinear optical effects due to their unusual microstructure. We discuss four different materials: 1) Tilted columns of aluminum-oxide 2) Gold particles in aluminum-oxide 3) Cadmium sulpho-selenide particles in aluminum-oxide 4) Silver particles in zinc-sulphide. We begin with a description of the vacuum system and some the techniques used to characterize the optical and structural properties of the films. This leads to our study of second-harmonic generation (SHG) in aluminum-oxide thin films deposited at an angle to the evaporant source. We show that SHG is very sensitive to the non-isotropic microstructure that results from such a deposition. and the behavior of the SHG signal with sample orientation provides insight to the symmetry properties of the microstructure. In a related study we show that AU/Al₂O₃ composite films produce a large SHG signal. We investigate the dependence of the strength of the SHG signal with fill-fraction of gold and show that it increases quadratically. in agreement with theory. The third material we discuss is cadmium sulpho-selenide doped aluminumoxide. We describe attempts at nucleating semiconductor crystallites in a variety of hosts through a process of co-deposition and subsequent annealing. We also deposit alternate layers of CdS-Se and Al₂O₃ with the semiconductor layer thin enough that interspersed crystallites form. This results in suspended. isolated crystallites similar to the doped-glass materials of interest to nonlinear optics. A waveguide of a CdS/Al₂O₃ "sandwich" demonstrates optical nonlinearity through a power-dependent prism coupling experiment, and the degree of nonlinearity is much greater than undoped glass, though less than doped glass. The final section of the dissertation is a theoretical description of nonlinear optical behavior in a novel composite material consisting of metal particles in a nonlinear dielectric host. We assume the enhanced field around the resonating particles drives the host locally nonlinear through either a Kerr-type or thermal nonlinearity. We calculate the change in optical properties of the medium due to this effect and show that for a system of silver in zinc-sulphide the nonlinearity can be significant.

Mo-Si thin films have proven applications in semiconductor devices and x-ray optics. Since their performance in these applications is extremely sensitive to interface roughness, it is important to understand the nucleation and growth mechanisms which affect the microscopic interface structure. Investigations of the initial stages of interface formation in the Mo-Si system were carried out by depositing fractional-monolayer Mo films onto Si(100)-(2x1) and Si(111)-(7x7) surfaces using Molecular Beam Epitaxy (MBE) with feedbackcontrolled electron-beam evaporation, and by characterizing these ultra-thin Mo films using in situ Reflection High-Energy Electron Diffraction (RHEED), LowEnergy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), and xray Photoelectron Spectroscopy (XPS). Continuous growth of multiple Mo coverages on a single Si wafer was accomplished with a technique developed for these experiments, involving a moveable substrate shutter. The coverages were corrected for the deposition profile (due to growth chamber geometry) with ex situ Rutherford Backscattering Spectroscopy (RBS) data and computer modelling. The growth mode was determined using Auger intensity measurements. In order to correct for the time dependence of the Auger intensities due to trace surface contamination and instrumental drift, a technique was developed which used Auger measurements on bulk Si and Mo to further normalize the intensity data for the fractional-monolayer coverages of Mo. The AES results in this dissertation show that for relatively slow Mo deposition (i.e. rates of approximately 0.05 Angstroms per second) onto either (100) or (111) Si substrates maintained at low temperatures (i.e. 100 °C), the first atomic monolayer of Mo is deposited in a non-layer-by-layer fashion, implying interdiffusion and/or agglomeration of the Mo overlayer. The LEED and RHEED results on similar samples show that the Mo layer is non-crystalline, i.e. there is no long-range periodicity. In addition, the deposition of Mo destroys the periodicity of the underlying Si atoms. For these deposition conditions, both the growth mode and the lack of crystallinity are independent of Si surface crystal structure.

The performance of multilayer thin film optical filters depends largely on the microstructure of the component layers. This microstructure varies with the deposition parameters inside the coating chamber. By controlling these parameters, optical filters can be produced to exacting specifications. In 1947, R. M. Rice established the technique of bombarding the substrate with electrons of several kilovolts as the fils were being deposited. This process improved the durability of zinc sulfide films dramatically. This study was performed to quantitatively analyze the effects of bombardment on film microstructure and subsequent effects on optical and mechanical properties. I installed an electron source filament inside the coating chamber and electrically isolated the substrate holder, which was connected to a positive high voltage supply. An accelerating loop placed just above the filament enhanced its efficiency. The source was calibrated by measuring the current through the substrate holder. Single layer films of five different materials were deposited, each at its own set of electron bombardment parameters. The microstructure was analyzed with an X-ray diffractometer and a transmission electron microscope. Optical properties were measured with guided waves, induced absorption, and spectrophotometric analysis. Film durability was analyzed with scotch tape, eraser, and controlled humidity tests. Antimony trioxide films showed a shift in lattice orientation, but this did not affect columnar structure or macroscopic quantities. Potassium hexafluorozirconate films showed elimination of both crystal structure and columnar growth, resulting in slightly reduced durability and some absorption. Silicon monoxide films suffered no change in structure or properties. Zinc sulfide films demonstrated the change in crystal structure, which was quantified and shown to improve moisture resistance. Optical properties were unaffected. Magnesium fluoride films showed a slight increase in crystallinity with only subtle changes in durability and optical properties. Generally, electron bombardment reduced or rearranged crystal structure. The effects on macroscopic properties varied with each material, with no clear trend evident.

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.

No description available.

No description available.