Deborah P. Partlow

Switchable vanadium oxide films by a sol‐gel process

Thin polycrystalline films of VO2 and V2O3 were deposited on a variety of substrates using a sol‐gel process. The orientation, microstructure, optical constants, and optical and electrical switching behavior are presented. These films exhibited sharp optical switching behavior even on an amorphous substrate such as fused silica. The method yields reproducible results and is amenable to the coating of large substrates and curved surfaces such as mirrors and lenses.

Wide spectrum antireflective coating for fused silica and other glasses

A method of forming a laser damage resistant wide-spectrum antireflective coating on fused silica and other glasses has been developed. The single-layer graded-index coating is deposited from a specific polymer solution which is converted to a porous SiO2 film. The size of the pores in the film is first reduced by heat treatment to prevent eventual UV scattering. Refractive-index gradation is achieved by grading this non-scattering porosity using a mild etching agent to a depth which is sufficient to smooth the density transition from air to the substrate glass. The resultant coating provides antireflectivity over the entire transmission range of silica extending to wavelengths as short as 250 nm. Laser damage thresholds as high as 9 J/cm2 at 350 nm have been demonstrated for this coating on fused silica substrates, which makes it particularly suitable for the optics of high-power lasers.

Formation of mullite and other alumina-based ceramics via hydrolytic polycondensation of alkoxides and resultant ultra- and microstructural effects

This manuscript discusses the formation of alumina-based ceramic materials from alkoxide starting materials. Particular attention is given to Al2O3-SiO2 systems, especially mullite. When the oxide network of these materials is formed via chemical polymerization of alkoxides, the ultrastructure of the resultant condensates is fundamentally affected by the nature and kinetics of the condensation reactions. Crystallization of mullite from an amorphous Al6Si2O13 at ∼ 980°C appears to be related to the intimacy and homogeneity of the aluminium-silicon bonding in the precursor networks. Network inhomogeneities due to the different hydrolysis rates of mixed alkoxides diminish by reduction of the chemical encounter rates with water during the hydrolytic polycondensation. Mullite produced from homogeneous and stoichiometric condensate shows a large spontaneous densification at ∼ 980° C. The microstructure of this material shows no indication of a liquid phase at the grain boundaries.

Thirty-seven layer optical filter from polymerized solgel solutions.

The feasibility of making multilayer optical filters using polymerized solgel solutions was demonstrated. Theoretical modeling was done to determine the expected optical response of multilayer coatings with various index profiles to select a coating design which was achievable using current technology and which would demonstrate the effectiveness of the method. The selected design consisted of a multilayer film whose index profile approximated a sine function, simulating the rugate concept for maximum reflection at 1.5 microm using a silicon substrate. Samples were prepared with 21, 29, and 37 layers. Agreement between the actual and the predicted optical performance of these films was good, showing that this method can be used to produce optical coatings having complicated index profiles.

Characterization of plasma-deposited and dip-coated films for critical optical applications.

Two types of coatings were evaluated with respect to their suitability for optical applications in which low scattering is required. The plasma-deposition technique produces dense pinhole-free films of refractory materials from a glow discharge plasma at typical substrate temperatures of 200-300 degrees C. Plasma-deposited films of SiO(2) and Si(3)N(4), produced from reactions of SiH(4) with N(2)O and NH(3), respectively, were evaluated in this study. SiO(2) films were also produced from metal-organic precursor solutions using dipping and spinning application techniques followed by pyrolysis at 600 degrees C. Coatings were deposited on the highest quality substrates available, which were characterized prior to deposition so that the effects of the coatings could be separated from those of the substrates. Nomarski microscopy, surface profiling, total integrated scattering, ellipsometry, and photon backscattering techniques were used for characterization. The properties of these coatings and information on how the quality depends on coating conditions are reported in this paper.

Assessment of degree of poling in 0–3 piezoelectric composites by X-ray methods

Abstract This paper describes the use of X-ray pole figures to determine the degree of preferential orientation induced by poling of 0-3 piezoelectric composites. By comparing pole figures and 2θ scans of the same samples, we demonstrate that the pole figure technique is superior to conventional 2θ X-ray scans because it is capable of recording diffraction from many orientations of the sample with respect to the incident X-ray beam instead of just one. Samples poled at higher fields have a greater degree of orientation, as do those with large, multidomain particles. It is also shown that poling of the composites is nonuniform through the thickness of the samples.