Piezo-generated charge mapping revealed through Direct Piezoelectric Force Microscopy

While piezoelectrics and ferroelectrics are playing a key role in many everyday applications, there are still a number of open questions related to the physics of those materials. In order to foster the understanding of piezoelectrics and ferroelectric and pave the way to future applications, the nanoscale characterization of these materials is essential. In this light, we have developed a novel AFM based mode that obtains a direct quantitative analysis of the piezoelectric coefficient d33. This nanoscale tool is capable of detecting and reveal piezo-charge generation through the direct piezoelectric effect at the surface of the piezoelectric and ferroelectric materials. We report the first nanoscale images of the charge generated in a thick single crystal of Periodically Poled Lithium Niobate (PPLN) and a Bismuth Ferrite (BiFO3) thin film by applying a force and recording the current produced by the materials. The quantification of both d33 coefficients for PPLN and BFO are 13 +- 2 pC/N and 46 +- 7 pC/N respectively, in agreement with the values reported in the literature. This new mode can operate simultaneously with PFM mode providing a powerful tool for the electromechanical and piezo-charge generation characterization of ferroelectric and piezoelectric materials

Preparation of macroporous epitaxial quartz films on silicon by chemical solution deposition

International audienceThis work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step process based on the preparation of a sol in a one-pot synthesis which is followed by the deposition of a gel film on Si(100) substrates by evaporation induced self-assembly using the dip-coating technique and ends with a thermal treatment of the material to induce the gel crystallization and the growth of the quartz film. The formation of a silica gel is based on the reaction of a tetraethyl orthosilicate and water, catalyzed by HCl, in ethanol. However, the solution contains two additional components that are essential for preparing mesoporous epitaxial quartz films from these silica gels dip-coated on Si. Alkaline earth ions, like Sr2+ act as glass melting agents that facilitate the crystallization of silica and in combination with cetyl trimethylammonium bromide (CTAB) amphiphilic template form a phase separation responsible of the macroporosity of the films. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth

Growth of 1D- oxide nanostructures

International audienceOne-dimensional (1D) oxide materials are anisotropic nanocrystals with large aspect ratios (length/diameter). Typically, they display diameters of 1–200 nm and lengths up to several tens of micrometers. Given their specific shape, 1D oxides are found in the literature under different names: nanowires, nanorods, nanotubes, nanobelts, nanofibers, whiskers, etc. To date, different approaches have been proposed to achieve 1D growth of oxides with different degrees of control over the growth process. These approaches are based on (i) taking advantage of the inherent anisotropic crystallographic structure of certain solids to promote the 1D growth, (ii) using organic additives or surfactants to kinetically control the oriented attachment of some crystallographic facets of a seed to finally form 1D nanostructures, (iii) using hard or soft templates (with 1D porosity) to directly grow nanowires and/or nanotubes, or (iv) controlling the condition of supersaturation to modify the tendency of seed to growth. Multinary oxides, also named functional complex oxides, are materials that contain two or more metals in a precise ratio. The preparation of these oxides is to date a key challenge in materials science development

Ferromagnetic 1D oxide nanostructures grown from chemical solutions in confined geometries

International audienceThis review summarizes the capabilities and recent developments of nanoporous polymeric template systems directly supported on different substrates for the confined growth of epitaxial ferromagnetic complex oxides 1D nanostructures. In particular, we describe the versatility and potentiality of chemical solutions combined with track-etched polymers to synthesize i) vertical polycrystalline La0.7Sr0.3MnO3 nanorods on top of single crystal perovskites, ii) single crystalline manganese based octahedral molecular sieves (OMS) nanowires on silicon substrates, and iii) the epitaxial directional growth of single crystal OMS nanowires when grown on top of fluorite-type substrates. The influence of the distinct growth parameters on the nanostructural evolution of the resulting nanostructures and their magnetic properties is further discussed in detail

Electronic and Magnetic Structure of LaSr-2x4 Manganese Oxide Molecular Sieve Nanowires

International audienceIn this study we combine scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and electron magnetic chiral dichroism (EMCD) to get new insights into the electronic and magnetic structure of LaSr-2×4 manganese oxide molecular sieve nanowiresintegrated on a silicon substrate. These nanowires exhibit ferromagnetism with strongly enhanced Curie temperature (Tc> 500 K), and we show that the new crystallographic structure of these LaSr-2×4nanowires involves spin orbital coupling and a mixed-valence Mn3+/Mn4+, which is a mustfor the ferromagnetic ordering to appear

Chiral habit selection on nanostructured epitaxial quartz films

International audienceUnderstanding the crystallization of enantiomorphically pure systems can be relevant to diverse fields such as the study of the origins of life or the purification of racemates. Here we report on polycrystalline epitaxial thin films of quartz on Si substrates displaying two distinct types of chiral habits that never coexist in the same film. We combine Atomic Force Microscopy (AFM) analysis and computer-assisted crystallographic calculations to make a detailed study of these habits of quartz. By estimating the surface energies of the observed crystallites we argue that the films are enantiomorphically pure and we briefly outline a possible mechanism to explain the habit and chiral selection in this system

Structural and magnetic study of La0.7Sr0.3MnO3 nanotubes grown from chemical solutions in confined geometries

26-30 Mai 2014International audienceCompared with solid nanowires [1], metal oxide tubular nanostructures have attracted significant research interest because of their large specific surface areas, very narrow inner pores, and enhanced surface catalytic properties. Furthermore, 1D nanotubes (NTs) have showed improved performance in gas sensors, field-emission, photovoltaics, and batteries. However, the development of facile, mild and effective approaches for generating size controllable 1D NTs of complex oxides remains a significant challenge. We demonstrate that self standing La0.7Sr0.3MnO3 (LSMO) NTs with diameters ranging from 80 to 200nm can be successfully synthesized by template assisted chemical solution deposition using nanoporous anodized alumina membranes of varying pore size. The template synthetic strategy provides almost monodisperse size distribution in the fabricated NT dimensions. A sol-gel based polymer precursor route was used allowing a good control of the viscosity and stability of the precursor solution, which are crucial parameters for template aided synthesis. The porous membranes were filled with the precursor solution and subsequently heated at high temperature (700-900°C) for phase formation. We prove that the synthesized LSMO NTs are polycrystalline and ferromagnetic with a Curie temperature above 350K. These 1D nanostructures are good candidates to study the magnetic properties of reduced dimensionality systems. [1] A. Carretero-Genevrier et al. Chem.Soc.Rev. 10.1039/C3CS60288E (2013

Soft chemistry integration of ferromagnetic La0.7Sr0.3MnO3 on silicon

11-15 mai 2015International audienceno abstrac

Chemical solution growth of La0.7Sr0.3MnO3 nanotubes in confined geometries

International audienceSelf-standing La0.7Sr0.3MnO3 nanotubes with outer diameter ranging from 100 - 200 nm have been successfully synthesized by template assisted chemical solution deposition using nanoporous anodized alumina membranes of varying pore size. This template synthetic strategy provides rather monodisperse size distributed nanotubes. A sol-gel based polymer precursor route was used to fill the porous membranes and a subsequent heat treatment (700-1000ºC) enabled the phase formation and crystallization of the nanotubes. A good control over viscosity, stoichiometry and stability of the precursor solution were identified as crucial parameters for the template aided synthesis. The synthesized La0.7Sr0.3MnO3 nanotubes are polycrystalline and ferromagnetic with a Curie temperature of 350 K. Control over the nanowall thickness is attained by varying template filling time which is corroborated by magnetic moment results

Thin epitaxial quartz films with tunable textures on silicon.

9-13 March 2015International audienceThe integration of quartz on silicon in thin film form is appealing for its prospective applications in sensing and electronics. For instance, this could be used to make oscillators with higher resonance frequencies, in new electromechanical devices or mass sensors showing improved detection limits. We have recently reported the epitaxial growth of quartz films on silicon following a soft-chemistry approach1. The aim of this contribution is to discuss in detail the mechanisms of this synthesis. The films are obtained by the crystallization of amorphous silica films prepared by chemical solution deposition. Two key components of the solution are Sr2+, acting as catalyst for the crystallization of silica, and amphipilic templates playing the role of structuring agents and assisting in the crucial phase separation of the catalyst. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth. The films are piezoelectric and can be tailored to be dense or to present an ordered porosity with pore diameters ranging from a few tenths of nanometer to the micron scale