Robert J. Walko

Porous Optical Composites

Previous studies have shown that sol-gel matrices are excellent low temperature hosts for various optically-active materials, both organic and inorganic. Optical properties of these composites depend upon such factors as the structure of the matrix and size, shape, and degree of dispersion of the optically-active phase. We discuss factors that control the shrinkage and clarity of silicate aerogel host matrices and report on novel composites in which the optical properties are controlled by solid-vapor and/or solid-liquid reactions within the host matrix.

Development of Standards for Characterization of Cathodoluminescence Efficiency

Cathodoluminescence (CL) characterization in a demountable vacuum chamber is an important benchmarking tool for flat- panel display phosphors and screens. The proper way to perform these measurement is to minimize the effects of secondary electrons, excite the phosphor/screen with a uniform beam profile, and maintain a clean vacuum environment. CL measurements are important for preliminary evaluation and lifetesting of phosphor powders and screens prior to incorporation into the FPD. A survey of many CL characterization systems currently in use revealed the myriad of spectroradiometers, colorimeters, electron guns, vacuum pumps, mass spectrometers, etc. that introduce many avenues for error that are often difficult to isolate. A preliminary round-robin experiment was coordinated by Sandia and involved five other research groups. The purpose of this experiment was to obtain an indication of equipment capabilities and instrument variations, as well as reliability and consistency of results. Each group was asked to measure the luminance and chromaticity coordinates of a Y3Al2Ga3O12:Tb pellet and calculate the luminous efficiency. Pellets were chosen in order to reduce errors associated with processing and handling of powders or screens. Some of the data reported in this experiment were in good agreement, while others differed significantly. Determining sources of error in CL measurements is an ongoing effort. By performing this experiment, we were able to identify some of the causes of error and develop a characterization protocol for display phosphors.

The potential of vacuum microelectronics for space reactor applications

Matrixed field emission devices have been fabricated using a modification of standard integrated circuit fabrication techniques. The emtter‐to‐gate spacing is fixed by the thickness of a deposited oxide and not by photolithograpnic techniques. Functioning triodes have been fabricated using this deposited oxide spacer spproach. Measured emission current to a collector electrically and physically separated from the matrixed emission array follows Fowler‐Nordheim behavior. Modeling of the potential field near the emitter and gate structures as well as the emitted electron trajectories with a two‐dimensional, Poisson solver, finite‐differnce code was used to evaluate and improve field emission structures.