We achieved parallel nanoscale patterning of ferroelectric complex oxides by pulsed laser deposition through a nanostencil ͑i.e., through a pattern of apertures in a thin free-standing membrane͒. Ordered arrays of nanostructured barium titanate ͑BaTiO 3 ͒ were obtained onto different substrates in a single deposition step, at room temperature, replicating accurately the aperture patterns in the stencil membrane. After a postdeposition annealing treatment, x-ray diffraction pattern showed a nanocrystalline BaTiO 3 structure close to the perovskite cubic phase with grains 30-35 nm in size. Their local ferroelectric properties were detected using piezoresponse force microscopy.

There is an increasing interest in developing and characterizing multifunctional materials, as they exhibit rich physical and chemical properties and offer exciting opportunities, for example, to miniaturize integrated devices and extend the potential of establishing nanoarchitecture concepts. [ 1 , 2 ] In this context, multiferroic materials [ 3 ] which combine two or more ferroic functionalities are promising for applications in fi elds such as spintronics and non-volatile data storage. [ 4 ] As recently demonstrated [ 5 ] ferromagnetic-ferroelectric multiferroics can be advantageously used to encode the information in electric polarization and magnetization giving rise to a four logic state memory. The coupling between magnetic and electrical properties leads to additional versatility for related devices, such as electric fi eld-controlled magnetic data storage. [ 6 ] The recent emergence of Bi-based double perovskite thin fi lms, such as Bi 2 FeCrO 6 (BFCO) [7][8][9] and Bi 2 CoMnO 6 , [ 10 ] with strong magnetic behavior at room temperature, create opportunities to practically apply multiferroics. In competition with rival technologies, downscaling the feature size of multifunctional materials is an important step to achieve very high-density memory devices. [ 11 , 12 ] However, conventional patterning and lithography techniques applied to these materials with complex multiphase structure often damage or induce changes in stoichiometry, affecting the quality (and thus the properties) of the as-grown fi lm.Non-conventional patterning techniques, such as microcontact printing, [ 13 ] nanoimprint, [ 14 ] and nanostencil patterning, [ 15 , 16 ] are being increasingly explored. Compared to traditional methods (e.g., electron-beam lithography and focused ion beam lithography), they are simpler, faster and even cheaper. In addition, they offer a better process fl exibility and compatibility with several applications, [ 13 ] as they do not require post-deposition etching processes.Here we demonstrate the controlled epitaxial growth by pulsed laser deposition (PLD) of ordered arrays of sub-micrometer BFCO multiferroic structures on niobium-doped SrTiO 3 (Nb-STO) substrates, through a nanostencil, i.e., a shadow mask with nanometer-scale features. We show that the asgrown structures retain their room temperature multifunctional (ferroelectric and magnetic) character even at submicrometer dimensions. Our work represents an important step towards the successful integration of nanometer-scale multiferroic elements in current microelectronics and future nanoelectronics.Growth through a nanostencil allows a simpler parallel and resist-free patterning of complex oxides (as opposed to resistbased methods; see Experimental Section). To obtain large arrays (square millimeters) of multiferroic BFCO nano structures we fi rst optimized the PLD parameters to obtain stoichiometric, epitaxial BFCO multiferroic thin fi lms on single crystal STO substrates, [ 7 , 17 ] and under conditions compatible with stencil technology (e.g....

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Elastic modulus evolution and behaviour of Si/Mullite/BSAS-based environmental barrier coatings exposed to high temperature in water vapour environment Cojocaru, C. V.; Kruger, S. E.; Moreau, C.; Lima, R. S. Submitted May 14, 2010; in revised form October 22, 2010) Si-based ceramics (e.g., SiC and Si 3 N 4 ) are known as promising high-temperature structural materials in various components where metals/alloys reached their ultimate performances (e.g., advanced gas turbine engines and structural components of future hypersonic vehicles). To alleviate the surface recession that Si-based ceramics undergo in a high-temperature environmental attack (e.g., H 2 O vapor), appropriate refractory oxides are engineered to serve as environmental barrier coatings (EBCs). The current stateof-the-art EBCs multilayer system comprises a silicon (Si) bond coat, mullite (3Al 2 O 3 AE2SiO 2 ) interlayer and (1 2 x)BaOAExSrOAEAl 2 O 3 AE2SiO 2 ,0 £ x £ 1 (BSAS) top coat. In this article, the role of hightemperature exposure (1300°C) performed in H 2 O vapor environment (for time intervals up to 500 h) on the elastic moduli of air plasma sprayed Si/mullite/BSAS layers deposited on SiC substrates was investigated via depth-sensing indentation. Laser-ultrasonics was employed to evaluate the E values of as-sprayed BSAS coatings as an attempt to validate the indentation results. Fully crystalline, crack-free, and near-crack-free as-sprayed EBCs were engineered under controlled deposition conditions. The absence of phase transformation and stability of the low elastic modulus values (e.g.,~60-70 GPa) retained by the BSAS top layers after harsh environmental exposure provides a plausible explanation for the almost crack-free coatings observed. The relationships between the measured elastic moduli of the EBCs and their microstructural behavior during the high-temperature exposure are discussed.

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