G. Teowee

Sol—gel derived coatings on glass

Abstract Sol—gel processing is a versatile method for depositing oxide based coatings on a variety of substrates in an economical manner. The present review will consider coatings deposited on glass, and will discuss a number of representative applications for such coatings, namely anti-reflection coatings, transparent conducting coatings, anti-static coatings, fluorinated coatings, coatings incorporating active dye molecules and ferroelectric coatings.

Sol-Gel Science and Technology: Current State and Future Prospects

This paper addresses the current state and future prospects of sol-gel processing. It summarizes responses to a questionnaire received from more than four dozen leaders of the sol-gel community. Overall, the respondents remain quite sanguine about the future prospects for the field, and with numerous areas where sol-gel processing can provide unique capabilities and novel materials. The present authors acknowledge this potential, but argue that its achievement will depend upon greatly increased involvement of the sol-gel community with applications, and carrying out a much larger fraction of sol-gel research in the context of applications.

The Future of Sol-Gel Science and Technology

This paper addresses the future prospects for sol-gel processing. It includes responses from nearly two dozen leading practitioners of the sol-gel art, who were kind enough to answer a questionnaire about the present state and future directions of the field. Overall, the prospects appear quite bright; but achievement of anything like the full potential of the method will require greatly increased interaction between sol-gel specialists and device technologists.

Crystallization of gel-derived glasses

Abstract The crystallization behaviors of gels, gel-derived glasses and melted glasses are reviewed, and comparisons are effected among the observed behaviors. These comparisons are related to the behavior expected on the basis of models for the nucleation frequency and crystal growth rate, as well as the anticipated differences in material characteristics among gels and the two types of glasses. Different temperature regimes are identified where different comparisons between melted and gel-derived materials are expected. It is concluded that a need exists for more definitive, detailed data on the crystallization behavior of gel-derived materials.

User controllable photochromic (UCPC) devices

A novel class of photochromic devices is described which allows the user control over the photochromic response of the device. The ability to limit the photochromic response of the device under illumination potentially allows the use of these devices in applications where traditional photochromics are excluded today. User controllable photochromic devices are described in terms of their general materials, properties, construction and performance.

Sol-gel synthesis of optical thin films and coatings

Sol-gel methods offer a number of notable advantages for the synthesis of optical films and coatings. Areas of potential or actual application of this technology range from single layer and multilayer antireflection coatings to embossed planar waveguides and organic-modified oxide materials. The most notable advantages of these wet chemical nethods will be surveyed, as will progress achieved to date in a number of the most attractive representative areas. The technical bases for the success/failure in each case will be considered. Also to be discussed will be the prospects - in both the near-term and long-term - of future developments in the sol-gel synthesis of optical films, as well as the principal technical hurdles which must be overcome in order that such synthesis methods may achieve more widespread use in the future. Finally, a comparison will be made between the microstructures and characteristics of films and coatings deposited using sol-gel methods with those deposited from the vapor phase. In all cases, use will be made of recent advances in our laboratory in the subject area.

Electro-optic properties of sol-gel derived PZT and PLZT thin films

Abstract Ferroelectric(FE) films exhibit interesting electro-optic (EO) properties and are utilized in devices used for second harmonic generation, spatial light modulators and optical switches. These films typically yield large values of linear and quadratic electro-optic coefficients. Solgel derived FE films namely PZT 53 47 and PLZT 28/0/100 were prepared on conductive glass substrates. 0.5M precursor solutions based on the appropriate stoichiometric amounts of lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated on the substrates. They were the fired to 600C to crystallize them into single phase perovskite films. Top Au Pd electrodes were deposited to form the top contacts for the capacitors. The refractive indices, extinction coefficients, linear and quadratic coefficients of the films were obtained using multiangle reflection ellipsometry. These parameters were then used to calculate the linear and quadratic electro-optic coefficients of the films. The quadratic EO coefficients of PLZT 28/0/100 and PZT 53 47 films were measured to be 0.07 and 0.38 × 10−16 m2/V2 respectively while the linear electrooptic coefficients of PLZT 28/0/100 and PZT 53 47 were found to be 59 and 315 pm/V respectively, with the reff value for PZT 53 47 the highest among reported ferroelectric films in literature.

New optical materials by wet chemical processing

Wet chemical processing of ceramics, glasses and inorganic-organic hybrids for optical applications is rapidly developing. The present review focuses on optical films obtained by wet chemical processing, with emphasis on recent developments in ferroelectric and magneto-optic films, rare earth lasers and surface patterned films. Where appropriate, the subject matter is illustrated with recent results from our laboratories.

Optical properties of sol-gel-derived PZT thin films

A series of sol-gel derived PT-based films, including PT, PZ, PZT, PLT, PLZ and PLZT, was prepared on platinized Si, fused SiO2 and Corning 7059 substrates. These films were fired at 400 - 700 C for 30 mins. The phase assembly and development were dependent on the precursor chemistries, processing and choice of substrates. The presence of Zr impacted significantly on the crystallization behavior, PbO loss and cracking behavior of the films. Crystallization was severely retarded, especially in Zr-containing PZT films when deposited on amorphous substrates compared to crystalline Pt substrates. Amorphous and crystalline PZT films can be utilized for passive and active optical applications. Waveguiding was achieved in an amorphous PZT 53/47 and a crystalline PLT 28 films and gave attenuation losses of 1.0 and 1.4 dB/cm respectively which represent the lowest values reported to date. The optical properties of the films were investigated using ellipsometry, UV-VIS transmission spectroscopy and waveguide loss measurements. Depending on composition and processing conditions, PZT films (2500 A thick) with refractive indices of 1.60 to 2.33 and absorption edges of 2900 - 3100 A can be obtained. It was ascertained that the resulting interfacial reaction layers between the films and substrates affected considerably the optical properties of thinner films (< 2000 A).

Piezoelectric properties of sol-gel derived ZnO thin films

Abstract ZnO films exhibit a wide range of interesting material properties. Recently, ZnO films have been studied for sensing applications based on their piezoelectric and pyroelectric behaviors. Reported literature values of piezoelectric and pyroelectric coefficients of ZnO films are in the range of 11–12 pm/V and 1.0–1.4 nC/cm2-K Respectively. In this study, the piezoelectric properties of sol-gel derived ZnO thin films were measured. These films were prepared on platinized Si wafers and fired to temperatures ranging from 550°C to 750°C. Multiple spincoating was performed with an intermediate firing at 400°C between coatings to obtain films up to 6000 A thick. Top Pt electrodes were sputtered to form monolithic capacitors. XRD indicated that the films consisted of crystalline wurtzite at firing temperature as low as 400°C, and that the c-axis orientation increased with increasing firing temperature. A dielectric constant of 10 was obtained, while piezoelectric characterization indicated d33 values as l...