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Articles you may be interested inThermoelectric properties of epitaxial ScN films deposited by reactive magnetron sputtering onto MgO(001) substrates J. Appl. Phys. 113, 153704 (2013); 10.1063/1.4801886Influence of working gas pressure on structure and properties of WO 3 films reactively deposited by rf magnetron sputtering J.Influence of the target-substrate distance on the properties of indium tin oxide films prepared by radio frequency reactive magnetron sputtering Microstructural evolution and Poisson ratio of epitaxial ScN grown on TiN(001)/MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition ScN layers, 180 nm thick, were grown on MgO͑001͒ substrates at 750°C by ultra-high-vacuum reactive magnetron sputter deposition in pure N 2 discharges. N/Sc ratios, determined by Rutherford backscattering spectroscopy, were 0.98Ϯ0.02. X-ray diffraction -2 scans and pole figures combined with plan-view and cross-sectional transmission electron microscopy showed that the films are strongly textured, both in plane and along the growth direction, and have a columnar microstructure with an average column width near the film surface of 30Ϯ5 nm. During nucleation and the early stages of film growth, the layers consist of approximately equal volume fractions of 002-and 111-oriented grains. However, preferred orientation evolves toward a purely 111 texture within Ӎ40 nm as the 002 grains grow out of existence in a kinetically limited competitive growth mode. 002 grains exhibit local cube-on-cube epitaxy with an orientation relationship (001) ScN ʈ (001) MgO and ͓010͔ ScN ʈ ͓010͔ MgO while 111 grains have a complex fourfold 90°-rotated in-plane preferred orientation in which strained ScN triangular ͕111͖ surface unit cells exhibit local epitaxy with square MgO unit cells yielding the orientation relationship (111) ScN ʈ (001) MgO , ͓110͔ ScN ʈ ͓110͔ MgO , and ͓112͔ ScN ʈ ͓110͔ MgO . Room-temperature electrical resistivity is 1.2 ϫ10 4 ⍀ cm while d/dT was found to be negative, indicating semiconducting behavior, with varying from 1.6ϫ10 4 ⍀ cm at 80 K to 1.1ϫ10 4 ⍀ cm at 400 K. Optical absorption coefficients ranged from 1ϫ10 4 cm Ϫ1 at 1.5 eV to 2.6ϫ10 5 cm Ϫ1 at 3.5 eV with a well-defined edge corresponding to a direct transition at 2.37Ϯ0.05 eV.

CeO2 films with thicknesses ranging from 8.8 to 199 nm were grown on Al2O3 (1102) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO2 (001) planes parallel to the Al2O3 (1102) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10–90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (111)-facets. High-quality YBa2Cu3O7−δ (YBCO) thin films were deposited directly onto the CeO2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO2 layer. Postdeposition ex situ annealing was carried out on two CeO2 films and evaluated by AFM. Upon annealing samples at 930 °C, a relatively smooth morphology without facets was obtained. Annealing films at 800 °C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.

Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O2 gas mixtures at substrate temperatures ranging from 650 to 850 °C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1Ti0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of ∼300 nm, the typical dielectric constants as measured at ∼77 K and 1 MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films.

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In 2012, the National Science Foundation (NSF) created a new cross-directorate initiativeSustainable Chemistry, Engineering, and Materials (SusChEM)within its Science, Engineering and Education for Sustainability (SEES) portfolio. SusChEM aims to support the discovery of new science and engineering that will provide humanity with a safe, stable, and sustainable supply of chemicals and materials sufficient to meet future global demand. While NSF has historically supported research in this area, the SusChEM effort elevates this interest to a priority. In particular, NSF will support the discovery of new science and engineering that will (1) improve the harvesting and processing of natural resources, (2) develop replacement and substitute chemicals and materials for those that are scarce, toxic, and/or expensive, (3) extend the lifetime of materials through improved durability, (4) reduce energy consumption through improved catalysis, and (5) discover low-energy means of recycling, repurposing, recovering, and reusing chemicals and materials. This article provides an overview of the sustainability challenges that the mathematical, physical, and geological science and engineering communities are well poised to address and presents the National Science Foundation's vision of the SusChEM initiative.

Single and multiple layers of self-assembled InAs quantum dots (QDs) produced by the indium-flush technique have been studied by transmission electron microscopy (TEM) in an effort to develop techniques to reproducibly grow QDs of uniform size and shape. To monitor the changes in QD dimensions, plan-view samples of capped single layers were studied as well as cross-sectional samples of QDs in multiple layers and stacks. The changes in the observed round- and square-shaped QD images under various plan-view TEM imaging conditions, as well as the contrast reversal in the center of QD images viewed in cross-section are modeled using the many-beam Bloch-wave approach, including strain. The sizes and shapes of the QDs are determined through the interpretation of the observed (primarily strain) contrast in plan-view and the observed (primarily atomic number) contrast in cross-sectional TEM.

Na0.5K0.5NbO3 thin films have been deposited onto textured polycrystalline Pt80Ir20 substrates using radio frequency magnetron sputtering. Films were grown in off- and on-axis positions relative to the target at growth temperatures of 500–700 °C and sputtering pressures of 1–7 Pa. The deposited films were found to be textured, displaying a mixture of two orientations (001) and (101). Films grown on-axis showed a prefered (001) orientation, while the off-axis films had a (101) orientation. Scanning electron microscopy showed that the morphology of the films was dependent on the substrate position and sputtering pressure. The low-frequency (10 kHz) dielectric constants of the films were found to be in the range of approximately 490–590. Hydrostatic piezoelectric measurements showed that the films were piezoelectric in the as-deposited form with a constant up to 14.5 pC/N.