Publications

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The mechanisms governing D loss in ErD2 films with and without a Mo diffusion barrier on kovar substrates were studied between 200 and 600 °C via in-situ Ion Beam Analysis (IBA). Significant intermixing between kovar and Er was observed above 450°C and between kovar and ErD2 above 500 °C. The D loss mechanism in ErD2 films was found to change from intermixing between kovar and ErD2 at low temperatures (< 500 °C) to thermal decomposition at higher temperatures (> 500 °C). Diffusion between kovar and ErD2 was measured isothermally at 500 and 550 °C. An activation energy of 2.1 eV and a pre-exponential factor of 0.071 cm2/s were determined. Diffusion between the kovar components and ErD2 film was inhibited by depositing a 200 nm Mo diffusion barrier between the kovar substrate and the ErD2 film. The processing of the Mo diffusion barrier was shown to impact its performance. Intermixing between the kovar / Mo / ErD2 stack becomes significant between 500 and 550 °C with a sputter deposited Mo diffusion barrier and between 550 and 600 °C for an electron-beam evaporated Mo diffusion barrier. Copyright © 2009 ASM International® All rights reserved.

Activation energies for the intermixing reaction of textured metal-metal multilayer thin films have been determined using X-ray diffraction analysis. Kinetic data were collected utilizing an area detector so as to reduce intensity bias from changes in out-of-plane texture during the intermixing reaction. Activation energies for Al/Pt, Ni/Ti, and Co/Al metal-metal multilayer thin films have been determined as 95.4(2) kJ/mol, 201(13) kJ/mol, and 247(19) kJ/mol, respectively. © 2009 International Centre for Diffraction Data.

{sm_bullet}Mixing from some thermal process steps thought to drive H,D,T loss - This does not appear to be a problem with the Mo/Er occluder stacks {sm_bullet}Diffusion barriers investigated to prevent mixing

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The stress evolution during electrodeposition of NiMn from a sulfamate-based bath was investigated as a function of Mn concentration and current density. The NiMn stress evolution with film thickness exhibited an initial high transitional stress region followed by a region of steady-state stress with a magnitude that depended on deposition rate, similar to the previously reported stress evolution in electrodeposited Ni [S. J. Hearne and J. A. Floro, J. Appl. Phys. 97, 014901-1 (2005)]. The incorporation of increasing amounts of Mn resulted in a linear increase in the steady-state stress at constant current density. However, no significant changes in the texture or grain size were observed, which indicates that an atomistic process is driving the changes in steady-state stress. Additionally, microstrain measured by ex situ x-ray diffraction increased with increasing Mn content, which was likely the result of localized lattice distortions associated with substitutional incorporation of Mn and/or increased twin density.

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Protein microtubules (MTs) 25 nm in diameter and tens of micrometers long have been used as templates for the biomimetic mineralization of FeOOH. Exposure of MTs to anaerobic aqueous solutions of Fe{sup 2+} buffered to neutral pH followed by aerial oxidation leads to the formation of iron oxide coated MTs. The iron oxide layer was found to grow via a two-step process: initially formed 10-30 nm thick coatings were found to be amorphous in structure and comprised of several iron-containing species. Further growth resulted in MTs coated with highly crystalline layers of lepidocrocite with a controllable thickness of up to 125 nm. On the micrometer size scale, these coated MTs were observed to form large, irregular bundles containing hundreds of individually coated MTs. Iron oxide grew selectively on the MT surface, a result of the highly charged MT surface that provided an interface favorable for iron oxide nucleation. This result illustrates that MTs can be used as scaffolds for the in-situ production of high-aspect-ratio inorganic nanowires.

Two-dimensional proportional detectors with their faster data collection, large dynamic range, and more available information than point or linear proportional detectors make them ideal for microdiffraction analysis. The unique capabilities of these detectors coupled with a rotating anode source, capillary optics, and a variety of accessories allow for a wide range of applications.

Palmierite (K2Pb(SO4)2) has been prepared via a chemical synthesis method. Intensity differences were observed when X-ray powder data from the newly synthesized compound were compared to the published powder diffraction card (PDF) 29-1015 for Palmierite. Investigation of these differences indicated the possibility of preferred orientation and/or chemical inhomogeneity affecting intensities, particularly those of the basal (00l) reflections. Annealing of the Palmierite was found to reduce the effects of preferred orientation. Electron microprobe analysis confirmed K:Pb:S as 2:1:2 for the for the annealed Palmierite powder. Subsequent least-squares refinement and Rietveld analysis of the annealed powder showed peak intensities very close to that of a calculated Palmierite pattern (based on single crystal data), yet substantially higher than many of the PDF 29-1015 published intensities. Further investigation of peak intensity variation via calculated patterns suggested that the intensity discrepancies between the annealed sample and those found in PDF 29-1015 were potentially due to chemical variation in the K2Pb(SO4)2 composition. X-ray powder diffraction and crystal data for Palmierite are reported for the annealed sample. Palmierite is trigonal/hexagonal with unit cell parameters a = 5.497(1) Å, c = 20.864(2) Å, space group R-3m(166), and Z=3. © 2007 International Centre for Diffraction Data.

Magnesium vanadates are potentially important catalytic materials for the conversion of alkanes to alkenes via oxidative dehydrogenation. However, little is known about the active sites at which the catalytic reactions take place. It may be possible to obtain a significant increase in the catalytic efficiency if the effects of certain material properties on the surface reactions could be quantified and optimized through the use of appropriate preparation techniques. Given that surface reactivity is often dependent upon surface structure and that the atomic level structure of the active sites in these catalysts is virtually unknown, we desire thin film samples consisting of a single magnesium vanadate phase and a well defined crystallographic orientation in order to reduce complexity and simplify the study of active sites. This report describes the use of reactive RF sputter deposition to fabricate very highly oriented, stoichiometric Mg{sub 3}(VO{sub 4}){sub 2} thin films, and subsequent studies of the reactivity of these films under reaction conditions typically found during oxidative dehydrogenation. We demonstrate that the synthesis methods employed do in fact result in stoichiometric films with the desired crystallographic orientation, and that the chemical behavior of the films closely approximates that of bulk, high surface area Mg{sub 3}(VO{sub 4}){sub 2} powders. We further use these films to demonstrate the effects of oxygen vacancies on chemical behavior, demonstrate that surface composition can vary significantly under reaction conditions, and obtain the first evidence for structure sensitivity in Mg{sub 3}(VO{sub 4}){sub 2} catalysts.

An overall trend toward smaller electronic packages and devices makes it increasingly important and difficult to obtain meaningful diffraction information from small areas. X-ray micro-diffraction, electron back-scattered diffraction (EBSD) and Kossel are micro-diffraction techniques used for crystallographic analysis including texture, phase identification and strain measurements. X-ray micro-diffraction primarily is used for phase analysis and residual strain measurements. X-ray micro-diffraction primarily is used for phase analysis and residual strain measurements of areas between 10 {micro}m to 100 {micro}m. For areas this small glass capillary optics are used for producing a usable collimated x-ray beam. These optics are designed to reflect x-rays below the critical angle therefore allowing for larger solid acceptance angle at the x-ray source resulting in brighter smaller x-ray beams. The determination of residual strain using micro-diffraction techniques is very important to the semiconductor industry. Residual stresses have caused voiding of the interconnect metal which then destroys electrical continuity. Being able to determine the residual stress helps industry to predict failures from the aging effects of interconnects due to this stress voiding. Stress measurements would be impossible using a conventional x-ray diffractometer; however, utilizing a 30{micro}m glass capillary these small areas are readily assessable for analysis. Kossel produces a wide angle diffraction pattern from fluorescent x-rays generated in the sample by an e-beam in a SEM. This technique can yield very precise lattice parameters for determining strain. Fig. 2 shows a Kossel pattern from a Ni specimen. Phase analysis on small areas is also possible using an energy dispersive spectrometer (EBSD) and x-ray micro-diffraction techniques. EBSD has the advantage of allowing the user to observe the area of interest using the excellent imaging capabilities of the SEM. An EDS detector has been used for simultaneous element identification which enhances phase identification of unknowns. The x-ray area detector also allows for rapid microstructure information including crystallite orientation and size by directly observing the diffraction rings. These techniques allow for small area analysis that in the past would have been difficult if not impossible to obtain. The future development in x-ray optics and the use of synchrotron sources will allow for the potential of nondestructive submicron x-ray diffraction analysis.