Conformal Patterning of an Infrared Sensory Array on Planar and Nonplanar Surfaces
D. A. Payne,* E. A. Mikalsen, in collaboration with R. G. Nuzzo and R. Brandman in the Department of Chemistry
Defense Advanced Research Projects Agency (In cooperation with the Materials Research Laboratory)

This study is involved with the development of thin-film materials for high-resolution infrared detectors. Soft lithographic methods, including micromolding in capillaries (MIMIC) and mediated monolayer patterning by microcontact printing (mCP), are under investigation for the selective deposition of solution-derived oxide thin films. Our approach is to develop soft lithographic methods and sol-gel deposition processes to integrate infrared sensory arrays on both planar and nonplanar surfaces. Materials under investigation include pyroelectric lead zirconium titanate and barium titanate and semiconducting vanadium pentoxide. The radiation sensors and temperature bolometers operate on the thermally stimulated pyroelectric current or temperature coefficient of resistivity.

Crystal Growth, Structure, and Properties of Ferroelectric SrBi2Ta2O9
D. A. Payne,* X. Lu, P. Han
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with Materials Research Laboratory)

Recently, SrBi2Ta2O9 (SBT) has been recognized as a leading candidate material for practical nonvolatile ferroelectric memory applications. However, its exact structure and intrinsic properties are not well understood. This research is directed at solving this problem. Crystals as thick as 1.5 mm have been grown. The structure was refined by using TEM and x-ray diffraction methods. Reliable data on electrical, thermal, and elastic properties were obtained. The study also provided a plausible explanation on the excellent resistance to fatigue for SBT.

Densification and Stress Development in Sol-Gel-derived PZT Coatings
D. A. Payne,* R. J. Ong, in collaboration with L. H. Allen
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Sol-gel-derived PZT thin layers deposited on silicon were examined for their shrinkage behavior using in situ ellipsometry. Correlating densification data with thermal analysis (DTA, TGA), the effect of pyrolysis and crystallization on layer shrinkage is observed as experimental parameters such as layer thickness and substrate type were varied. The resulting stresses in the coating are measured as a function of heat treatment by a laser reflectance technique and related to associated densification phenomena and substrate/layer thermal expansion mismatch.

Development of Barrier Coatings for Metal Halide Lamps
H. H. Chen,* Z. M. Wu
APL Engineered Materials, Ltd.

The purpose of this project is to carry out initial and feasibility studies leading to the potential development of quartz arc tube inner wall barrier coatings by thin-film deposition method(s) to be used in metal halide lamps. Specific tasks include: (1) MOCVD coating of a selected group of oxide films and (2) characterizing coatings prior to as well as after testing to assess the quality of the coatings using XRD, SEM, optical microscopy and other techniques.

Effects of Atmospheric Moisture on the Structure of Sol-Gel Thin Layers
D. A. Payne,* E. A. Mikalsen, K. L. Holverson
Defense Advanced Research Projects Agency (In cooperation with the Materials Research Laboratory)

This study investigates the structural consequences of atmospheric moisture during the spin coating deposition process in PZT thin layers. Film thickness, density, and refractive index are effected through variations in the film deposition conditions. In polymers gels, hydrolysis and condensation reactions prescribe the structure during spin coating. By controlling the atmospheric moisture during the spin coating process, we can investigate the effect on film density and uniformity, crystallization behavior, and dielectric, ferroelectric, and optical properties. The sensitivity of difference chemical routes to atmospheric moisture is also under investigation.

Electrical Properties of Grain Boundaries in Manganese Ferrite
G. P. Wirtz*
University of Illinois

Minor amounts of CaO and SiO2 are being added to MnFe2O4 to study their effects on the electrical transport properties of the ferrite. The additives are concentrated in the grain boundaries, which is believed to produce high-resistance grain boundaries, surrounding more conductive grains, thus reducing eddy current losses at high frequencies in the ferrite. It is also found that the concentration of dopant in the grain boundary prevents decomposition of the ferrite in oxidizing atmospheres, thus maintaining the stoichiometry of the high-resistance ferrite. Impedance spectroscopy, thermogravimetry, and electrochemical cell measurements are being used in the study.

Fabrication and Characterization of Ferroelectric Thin Films by the MOCVD Method
H. H. Chen,* C. H. Lin, P. Friddle, A. Daga, C. Macaluso
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

This work encompasses the fabrication and characterization of ferroelectric thin films fabricated by metal-organic chemical vapor deposition (MOCVD) techniques. For infrared detector applications, we grow Pb(Sc0.5Ta0.5)O3-PbT:O3 (PSTT) thin films and perform noise, blackbody responsivity, and spectral response and frequency response measurements. The PSTT detectors' performance will be compared with commercial state-of-the-art pyroelectric detectors. The ultimate goal of this work is to develop a room-temperature infrared radiation detector. We base our work on the ferroelectric PSTT system and a novel detection approach which utilizes both the ferroelectric and the pyroelectric properties. We also fabricate other perovskite thin films and multilayers such as PT, PZT, and BST on various types of substrates and investigate the structure-property-processing relationships.

Functionally Graded Metal Oxide Thin Films
D. A. Payne,* E. A. Mikalsen, R. J. Ong
Defense Advanced Research Projects Agency (In cooperation with the Materials Research Laboratory)

This study is involved with the development of solution-derived ferroelectric thin layers integrated on platinized silicon for the improvement of pyroelectric, plezoelectric, and dielectric properties. Successive amorphous layers of various PZT compositions are deposited and densified through spin coating followed by heating to 300?C. A graded ferroelectric structure is obtained after low-temperature crystallization below 700?C. In addition, modified routes for chemical precursors are currently under investigation.

Ionic Transport in Composite Electrolytes
J. Kieffer,* R. B. Rao, E. Guilbert
National Science Foundation, DMR 93-15779 REU

Composites consisting of organic polymers and inorganic glassy phases are developed for use as electrolyte materials. The organic polymer contains the charge-carrying species and acts as the conducting phase, whereas the inorganic glass provides mechanical stability. High ionic conductivities can be achieved with this constellation because the conducting phase can be maintained above the glass transition temperature. The electrolytes are synthesized via a sol-gel process. This project is concerned with controlling the structure at the nanoscale to optimize component performance. The electrolytes synthesized in the laboratory are characterized using impedance spectroscopy, small-angle x-ray scattering, and thermal analysis.

Oxide Thin Films for Electronic and Optical Applications
H. H. Chen,* S. W. Lee, J. Finch, H. R. Chen
U.S. Department of Energy, DE-FG02-96ER45439; Nippon Steel Co. Gift (In cooperation with the Materials Research Laboratory)

The primary objective of this research is to produce oxide thin films for electronic applications. One example is a flammable gas sensor using SnO2 and the other is Ta2Os as dielectric material or thermal barrier. These oxide thin films are grown by the MOCVD technique. Microstructural analysis is also carried out on the grown films using XRD, SEM, TEM, AES, and XPS. Sensing tests are done for SnO2 using resistivity measurements with reducing gases such as H2, alcohol, etc. Dielectric constant, C-V, optical transmittance, and film conductance measurements are made. Models are suggested to explain the measured electrical and optical properties.

Preparation and Characterization of Ta2O5-TiO2 Ceramics
D. A. Payne,* S. Hemjinda
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

We have been successful in preparing higher dielectric constant (KB) tantalum oxide based ceramics for possible applications in the next generation of DRAMs and VLSI gate oxides. Results show that the properties were significantly influenced by small substitutions of TiO2. For example, 0.944Ta2O5-0.056TiO2 had a K=189 with tand=0.01 (at 1 MHz), a significant improvement over Ta2O5 alone (K=35, tand=0.008). The structure of titania modified tantalum oxide was monoclinic. Increasing titania additions led to a lowering of the orthorhombic-monoclinic phase transformation temperature from 1360?C to 1200?C (e.g., for 0.92Ta2O5-0.0.8TiO2). The study shows promising future applications for Ta2O5-TiO2 based ceramics as new dielectric materials. Work in progress includes measurements of electrical properties, such as resistivity, leakage-current density, and band-gap energy, as a function of service conditions.

Single Crystals and Thin Films of Doped Rare Earth Manganese Perovskites
D. A. Payne,* B. A. Clothier
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Rare earth manganese perovskites doped with divalent cations, such as Ca, Sr, Ba, and Pb, have been shown to exhibit greatly enhanced magnetoresistive properties when compared with metallic heterolayers. Improved magnetoresistive behavior is greatly desired for sensor applications, such as magnetic read heads, or advanced computer memories, such as MRAM cells. Current research is concerned with the electronic behavior and morphological characterization of doped rare earth manganese perovskite single crystals. Resulting candidate materials are deposited by low-temperature solution processing and self-assembled patterning to form integrated structures for devices.

Synthesis and Characterization of Perovskite Pb(Zn1{Nb2{)O3-PbTiO3 Ceramics
D. A. Payne,* P. Han, Z. Xu
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Composition near the morphotropic phase boundary in the solid solution of Pb(Zn1{Nb2{)O3-PbTiO3 (PZN)-PbTiO3 (PT) system display ultrahigh piezoelectric coefficients, strain levels, and electromechanical coupling. This superior piezoelectric property has only been realized in single crystals. In this research, ultrahigh pressure forming will be used to synthesize PZN-PT ceramics with 100% perovskite structure. Transformation from the pychlore to preovskite phase as a function of synthesis conditions will be studied by XRD. Analytical TEM will be used to study microstructure development for different synthesis conditions. Particular attention will be directed to investigation of synthesis conditions, microstructure development, and piezoelectric property relationships.

Transmission Electron Microscopy Studies of Incommensuration in Modified High Zr Content Lead Zirconate Titanate Perovskites
D. A. Payne,* Z. Xu
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Lead zirconate titanate (PZT) perovskite materials are of considerable technological importance, particularly with regard to physical properties such as pyro- and piezoelectricity and electric field-induced antiferroelectric-to-ferroelectric phase switching. A systematic study of the effects of temperature, Sn- and La-substituents, and Zr/Ti ratio on the evolution of incommensurate phases in high Zr-content PZT is carried out by hot- and cold-stage TEM. Particular attention is paid to the possible development of 1/x[110] incommensurate modulations and to the resul-tant influence on the macroscopic properties. The pur-pose of this investigation is to obtain a fundamental understanding of microstructure-property relationships for electroceramics.