Student Abstracts: Materials Sciences at PNNL

CRYSTAL LATTICE INTERFACE ANALYSIS OF SRTIO3/SI USING ION BEAM TECHNIQUES. EVAN ADAMS (Whitman College, Walla Walla, WA 99362) THEVA THEVUTHASAN (Pacific Northwest National Laboratory, Richland, WA 99352) .
The understanding of metal oxides has become increasing more important in recent years because silicon dioxide (SiO2) will soon reach its operational limit in the semiconductor industry. Strontium titanate (SrTiO3) is considered a strong candidate in the search for SiO2's replacement due to the similar high dielectric properties it shares with SiO2. Single crystal SrTiO3 (100) was grown in Motorola labs and the stability of the film was studied with respect to temperature. SrTiO3/Si was annealed in three different environments: vacuum, oxygen, and hydrogen. The film's crystalline structure was analyzed with Rutherford backscattering spectroscopy (RBS) including channeling, nuclear reaction analysis (NRA), and X-ray photoelectron spectroscopy (XPS) at Pacific Northwest National Laboratory (PNNL). The channeling measurements discovered a disordering of crystal at the interface between the film and substrate. This corresponds with the reported idea that an amorphous silicate layer was produced at the intersection of the two layers. When the sample is annealed in either a vacuum or hydrogen environments the interface seems to become more disordered as oxygen migrates through the sample. But when heated in an oxygen environment overall crystalline quality seems to improve and the interface becomes more ordered. This suggests that the silicate layer is more thermodynamically stable than the SrTiO3 film and that oxygen will diffuse to the interface. This diffusion creates an oxygen deficiency that disrupts the rest of the film, unless the oxygen is supplied in the environment.

Initial Characterization of a Silicon-Based System (Gubka) for the Treatment and Disposal of Aqueous Waste. ANN BAKER (Washington State University, Tri-Cities, WA 99352) NANCY FOSTER-MILLS (Pacific Northwest National Laboratory, Richland, WA 99352) .
Russian scientists have developed a new porous material called gubka, which is produced using the hollow glass microspheres recovered from fly ash, a waste product of coal combustion. Russian researchers have reported using gubka to treat and immobilize hazardous wastes as well as using it as a catalyst for methane oxidation. The purpose of our research was to determine if gubka could be used to increase the evaporation rate of water, to determine how temperature affects the evaporation rate of water (with and without gubka), and to determine the feasibility of using gubka as a platform to store and/or treat waste. Measured rates based on the exposed geometric surface area (g/sec/mm2) showed no significant difference between samples with and without gubka. Evaporation rates of water increased with increasing temperature with no significant difference in the rates between samples with and without gubka. Salt loading studies were designed to determine the feasibility of using gubka as a platform for waste storage. Gubka was etched with hot acid to form holes in the microspheres. After the gubka was etched, it held 5-10% of its weight in salt, which is lower than published values. Improvements in the etching procedure should lead to improvements in the storage capacity of gubka.

Electro-Spark Deposition. TIMOTHY CHIN (University of Washington, Seattle, WA 98195) ROGER N. JOHNSON (Pacific Northwest National Laboratory, Richland, WA 99352) .
Electro Spark Deposition, or ESD, is a pulsed-arc microwelding process. ESD can be used between virtually any electrically conductive materials. It creates a metallurgically bonded coating of an electrode material on a substrate material. Coatings of Stellite 21 on 4340 steel were sent for evaluation from Advanced Surfaces and Processes, Inc. (Forest Grove, OR). Microhardness testing was conducted on the raw electrode materials and coatings to see if there was any effect of the ESD process on the hardness of a material. Microhardness testing on the substrate was conducted to determine if there was a heat-affected zone (HAZ) present, and, if there was, how much it affected the hardness and what the depth of the HAZ was. HAZ's were present in most coatings. The HAZ's only lowered the hardness by 50 to 100HK and did not extend much further than 10mm from the coating/substrate interface.

Low temperature synthesis of silicon and titanium nitrides & Thin film deposition on silicon wafers. ELIZABETH FRANZ (Whitman College, Walla Walla, WA 99362) JEROME BIRNBAUM (Pacific Northwest National Laboratory, Richland, WA 99352) .
Due to its physical and chemical inertness, silicon nitride is ideal for such applications as catalyst and sensor support. In this experiment, low temperature nitride synthesis by photolysis was attempted on (CH3)3SiN3, [(CH3)2N]2Si(CH3)2, [(C2H5)2N]4Zr, [(C2H5)2N]4Ti, and [(CH3)2N]4Ti. UV-vis spectra were taken for each of the chemicals, and their extinction coefficients at 254 and 300 nm were determined. The chemicals were then photolysed under 254 nm light for at least 15 hours. 1H and 13C NMR showed significant consumption of each of the chemicals. The products of photolysis have yet to be determined. A carbon chain is usually present between a silicon wafer and the functional group when a film is deposited on a wafer. In this experiment we attempted to attach a thin film of (-CF3) groups to silicon wafers. The wafers were hydroxylated and soaked in 0.5% (CF3CO)2O. The thickness and contact angle were then recorded. Wafers were the photolysed for 30 minutes under 254 nm light, their thickness and contact angle measured, and XPS was performed on the wafers. XPS showed a low content of fluorine, in agreement with low contact angle and thickness measurements to indicate that the film deposition was unsuccessful.

Synthesis of CdS Nanocrystals in Surfactants. CHRISTINA FREYMAN (Georgia Tech, Atlanta, GA 30332) S.K. SUNDARAM (Pacific Northwest National Laboratory, Richland, WA 99352) .
CdS nanocrystals were prepared in the micelle of two surfactants, a hydroxylated poly(syrene-b-butifiene-b-syrene) [SBS] and a commercially produced surfactant, Igepal in three different chain lengths. The synthesis of the SBS was difficult demonstrating the need for a surfactant that can be used as is. The surfactants were dissolved in toluene and hexane to produce micelles formed by the insoluble ends of the molecule. Then these solutions were loaded with Cd2+ and S2- ions both in an aqueous method and an anhydrous method to produce CdS nanocrystals in the micelles. The solutions produced were analyzed with FTIR, UV-vis, and TEM. The anhydrous loading of the solution produced more uniform solutions. FTIR confirmed the hydroxylation of the SBS and the interaction between the OH function groups and the Cd2+ ions. TEM confirmed UV-vis adsorption edge particle size calculation of about 4 nanometers in both the hydroxylated SBS solution and the Igepal solutions.

Precipitation of Barium Tantalates From Borosilicate Glass. DOUG GLINIAK (University of Washington, Seattle, WA 98125) S.K. SUNDARAM (Pacific Northwest National Laboratory, Richland, WA 99352) .
Barium tantalates are typically materials used for microwave applications as dielectric resonators. BaMg1/3Ta2/3O3 is particularly attractive as a possible material to be used in the millimeter wave frequency range due to a combination of suitable dielectric constant [e=10], and low tangential loss [tan(d)=1.00x10-4], which can theoretically outperform alumina as the current leader according to the fundamental attenuation equation [1] in the 30-300GHz frequency range. Many variables are yet to be uncovered and these results are only a preliminary indication of possible low heat formation precipitation of the barium tantalite family from a borosilicate glass. Current results have successfully precipitated out Ba1/2TaO3 and BaTa2O6, both having perovskite crystal structures belonging respectively to tetragonal and orthorhombic systems. Ba(Mg1/3Ta2/3)O3 precipitation did not form within the borosilicate glass with stoichiometric concentrations up to 70mol%, indicating possible thermodynamic stability problems with Ba1/2TaO3 and BaTa2O6 forming prematurely to exclude Mg within the growth of the perovskite structure.

Ruthenium Partitioning Between Simulated Waste Glass and Spinel. JEREMY HOLBROOK (Western Washington University, Bellingham, WA 98225) S.K. SUNDARAM (Pacific Northwest National Laboratory, Richland, WA 99352) .
Extensive research has led to the consensus opinion of vitrification as the best suited technology for the disposal of nuclear wastes. Crystals such as spinel (MgAl2O4) form in the glass melts. These crystals settle at the bottom of electrically heated melter. Noble metals present in the waste will also precipitate from the melt and settle. These elements dissolve into the spinel lattice, forming a conductive layer and short-circuiting the electrodes, leading to potential failure. The main objectives of this study are: 1) study the interaction of Ruthenium with spinel and 2) evaluate Tungsten as a noble metals surrogate. Ruthenium was chosen because it is a commonly observed end product in melter tests. A simulated Hanford waste glass, MS-7, was used. Spinels were cut into pieces and a hole of 3 mm diameter and 2 mm depth was drilled into them. The basic glass was melted and ground into a powder. Then, 5 wt.% each of Ru, RuO2, W and WO3 was added to make four testing glasses. The test glass powder was packed into the hole in the spinel. Test temperatures were 900 and 1000ºC. Test durations were: 7, 15, 19, and 23 hours. The samples were then cut at the melt line, polished, and used for Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). Results obtained were as follows: 1. There was significant interaction between the spinel and the melt. 2. An interfacial region exists between the melt and the spinel. 3) Interfacial region was populated by crystals of the dopants (Ru and W). Future work proposed includes: 1) quantitative testing of interfacial kinetics and 2) effect of the chemical composition and the spinel stoichiometry.

Microstructural Analysis of the Mechanisms for Intergranular Stress Corrosion Cracking in Austenitic Type 304 Stainless Steels. ANTONIO NISSEN (Sacramento City College, Sacramento, CA 95822) DR. STEPHEN M. BRUEMMER (Pacific Northwest National Laboratory, Richland, WA 99352) .
The phenomena of Intergranular Stress Corrosion Cracking (IGSCC) is believed to be caused by one of two very distinct mechanisms: slip dissolution (oxidation) or hydrogen embrittlement. Two different tests are being performed on Type 304 SS: one using a statically loaded U-bend sample in corrosive solutions of 100 ppm NaF, 100 ppm NaCl, and 100 ppm Na2S2O3 and the other using a statically loaded U-bend sample electrochemically polarized, in a solution of H2SO4 to isolate anodic (dissolution) or cathodic (hydrogen) reactions. The purpose is to produce "classic cracks" for each IGSCC mechanism and to assess solution impurity effects. Resulting IGSCC crack characteristics will be recorded using optical metallography, scanning electron microscopy (SEM), and finally transmission electron microscopy (TEM) of cross-section samples. The Type 304 SS metal was heated to create a "sensitized" microstructure causing carbide precipitates and chromium depletion to form at internal grain boundaries. This microstructure is very susceptible to IGSCC. As of the printing of this paper, IGSCC tests are still in progress. Cracks have initiated on the NaCl solution samples with others showing signs of advanced pitting and surface degradation. Completion, of these tests, is expected to require another 2-4 weeks with a journal publication planned after characterization work is complete.

Biodegradable Deicing Fluid for the U.S. Air Force. ANNA OSTERGAARD (Columbia Basin College, Pasco, Wa 99301) KEVIN SIMMONS (Pacific Northwest National Laboratory, Richland, WA 99352) .
Deicing fluid is a very important necessity for flying airplanes in unfair weather conditions. These fluids, which are mostly composed of a chemical called glycol, are sprayed onto the airplanes wings to increase airflow across the wings and decrease the level of ice that forms from the cold air. During the winter months, when weather conditions are more frequent, there is a high demand for deicing fluid. Right now, the present deicer is harmful to the environment, especially at the rate they are used. This project is geared towards finding a more "Economically and Environmentally Friendly" fluid that performs the exactly same way as the present deicer.

Comparative Study of Cicadellidae Utilizing Optical and Electron Microscopy: Practical Considerations. AMY REDELL (Washington State University-Tri-Cities, Richland, WA 99352) JAMES S. YOUNG (Pacific Northwest National Laboratory, Richland, WA 99352) .
The invention of the light microscope in 1590 opened the door to the microscopic world. This microscope magnified objects up to 30 times their original size. In the 1930's another prospect began to open: the submicroscopic world as viewed by the electron microscope. The electron microscope utilized the much shorter wavelength of the electron. Using the electron microscope, another thousand-fold increase in magnification was made possible, accompanied by a parallel increase in resolution. There are benefits and limitations to all methods of microscopy. Resolution, depth of field, contrast formation, and illumination source are just four areas of concern. Using a compound, stereoscopic, and scanning electron microscope, micrographs were compared to illustrate these four attributes. The micrographs show the depth of field limitation characteristic of lighted microscopy. At 50x magnification, both microscopes displayed problems with depth of field and resolution. The SEM, however, demonstrated clear depth of field at 20,000x magnification. These results show that there is a strong need for all areas of microscopy. No single technique is without limitations. However, the future of electron microscopy is promising. It is a future goal to have the routine capability of imaging living systems at high resolution. Electron microscopy is expected to continue to meet the submicroscopic imaging needs of science and medicine.

Studies Toward Solid/Solid Interaction. BRIAN TRUE (Washington State University, Pullman, Wa 99163) KEVIN SIMMONS (Pacific Northwest National Laboratory, Richland, WA 99352) .
Laser light is a concern in the military today due to it potentially being hazardous to the eyes of military personnel and equipment. In an effort to eliminate this problem a number of separate attempts have been made to refract laser light in a medium. One attempt was using a polymer/solvent pair and the other using a solid/solvent pair. The polymer/solvent pair was synthesized using a polyphosphazene polymer with a specific index. The solid/solvent pair used two different plastics with known refractive indices, Methacrylate-Styrene Copolymer and Styrene-Acrylonitrile, dissolved in trichloroethane. The optical limiting concept is based upon the Christiansen-Shelyubskii filter. The idea is to match the indices of the two materials to the fourth decimal place. If the refractive indices of these materials do match the laser light will be negated.

Studies Toward Solid/Solid Interaction. CANDICE WILLMON (Lewis-Clark State College, Lewiston, ID 83501) WILLIAM D SAMUELS (Pacific Northwest National Laboratory, Richland, WA 99352) .
Laser light is a concern in the military today due to it potentially being hazardous to the eyes of military personnel and equipment. In an effort to eliminate this problem a number of separate attempts have been made to refract laser light in a medium. One attempt was using a polymer/solvent pair and the other using a solid/solvent pair. The polymer/solvent pair was synthesized using a polyphosphazene polymer with a specific index. The solid/solvent pair used two different plastics with known refractive indices, Methacrylate-Styrene Copolymer and Styrene-Acrylonitrile, dissolved in trichloroethane. The optical limiting concept is based upon the Christiansen-Shelyubskii filter. The idea is to match the indices of the two materials to the fourth decimal place. If the refractive indices of these materials do match the laser light will be negated.