Piezo-generated charge mapping revealed through direct piezoelectric force microscopy

Piezo-generated charge mapping revealed through direct piezoelectric force microscopy

A. GomezM. GichA. Carretero-GenevrierT. Puig & X. Obradors Nature Communications 8, Article number: 1113 (2017) doi:10.1038/s41467-017-01361-2 

While piezoelectric and ferroelectric materials play a key role in many everyday applications, there are still a number of open questions related to their physics. To enhance our understanding of piezoelectrics and ferroelectrics, nanoscale characterization is essential. Here, we develop an atomic force microscopy based mode that obtains a direct quantitative analysis of the piezoelectric coefficient d33. We report nanoscale images of piezogenerated charge in a thick single crystal of periodically poled lithium niobate (PPLN), a bismuth ferrite (BiFO3) thin film, and lead zirconate titanate (PZT) by applying a force and recording the current produced by these materials. The quantification of d33coefficients for PPLN (14 ± 3 pC per N) and BFO (43 ± 6 pC per N) is in agreement with the values reported in the literature. Even stronger evidence of the reliability of the method is provided by an equally accurate measurement of the significantly larger d33 of PZT.

Competition between Polar and Nonpolar Lattice Distortions in Oxide Quantum Wells: New Critical Thickness at Polar Interfaces

Competition between Polar and Nonpolar Lattice Distortions in Oxide Quantum Wells: New Critical Thickness at Polar Interfaces

J. Gazquez, M. Stengel, R. Mishra, M. Scigaj, M. Varela, M. A. Roldan, J. Fontcuberta, F. Sánchez, and G. Herranz. Phys. Rev. Lett. 119, 106102 – Published 7 September 2017. DOI: https://doi.org/10.1103/PhysRevLett.119.106102

Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO3/SrTiO3 system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO3 structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO3/SrTiO3 system and for the general quest towards nanoscale control of material properties.

Probing localized strain in solution-derived YBa2Cu3O7−δ nanocomposite thin films

Roger Guzman, Jaume Gazquez, Bernat Mundet, Mariona Coll, Xavier Obradors, and Teresa Puig. Phys. Rev. Materials. DOI: 10.1103/PhysRevMaterials.1.024801

Enhanced pinning due to nanoscale strain is unique to the high-Tc cuprates, where pairing may be modified with lattice distortion. Therefore a comprehensive understanding of the defect landscape is required for a broad range of applications. However, determining the type and distribution of defects and their associated strain constitutes a critical task, and for this aim, real-space techniques for atomic resolution characterization are necessary. Here, we use scanning transmission electron microscopy (STEM) to study the atomic structure of individual defects of solution-derived YBa2Cu3O7 (YBCO) nanocomposites, where the inclusion of incoherent secondary phase nanoparticles within the YBCO matrix dramatically increases the density of Y1Ba2Cu4O8 (Y124) intergrowths, the commonest defect in YBCO thin films. The formation of the Y124 is found to trigger a concatenation of strain-derived interactions with other defects and the concomitant nucleation of intrinsic defects, which weave a web of randomly distributed nanostrained regions that profoundly transform the vortex-pinning landscape of the YBCO nanocomposite thin films.

Novel Fe3O4@GNF@SiO2 nanocapsules fabricated through the combination of an in situ formation method and SiO2 coating process for magnetic resonance imaging

Novel Fe3O4@GNF@SiO2 nanocapsules fabricated through the combination of an in situformation method and SiO2 coating process for magnetic resonance imaging

Changyong Lu,* Stefania Sandoval, Teresa Puig, Xavier Obradors, Gerard Tobias, Josep Rosa and Susagna Ricart. RSC Adv., 2017, 7, 24690. DOI: 10.1039/c7ra04080f

An in situ approach for the synthesis of Fe3O4 nanoparticles combined with a SiO2 coating process was employed to prepare Fe3O4@GNF@SiO>2 nanocapsules. Graphitised nanofibres (GNF) were initially filled with iron(III) acetylacetonate, and used as a precursor for the synthesis of ultrasmall Fe3O4 nanoparticles (4.6 nm in diameter) inside the cavities of GNF (Fe3O4@GNF) with a high density. By using a silica coating process, Fe3O4@GNF@SiO>2 nanocapsules were obtained. The presence of the silica shell not only prevented leakage of the nanoparticles from inside the GNF but also protected the magnetite nanoparticles from dissolution, even in harsh acidic conditions. Furthermore, the silica coating resulted in an increased dispersability of the nanocomposites in water. Magnetic resonance imaging (MRI) studies indicate relatively high Image ID:c7ra04080f-t1.gif relaxivities for Fe3O4@GNF nanocomposites and Fe3O4@GNF@SiO>2 nanocapsules revealing the potential application of these hybrid materials for bioimaging. Therefore, the coating of filled GNF with silica is as an excellent strategy for the protection of encapsulated payloads.

Hybrid YBa2Cu3O7 Superconducting–Ferromagnetic Nanocomposite Thin Films Prepared from Colloidal Chemical Solutions

Hybrid YBa2Cu3O7 Superconducting–Ferromagnetic Nanocomposite Thin Films Prepared from Colloidal Chemical Solutions

Elena Bartolomé, Pablo Cayado, Eduardo Solano,Cristian Mocuta, Susagna Ricart, Bernat Mundet, Marionna Coll, Jaume Gázquez, Alexander Meledin, Gustaaf van Tendeloo, Manuel Valvidares, Javier Herrero-Martín, Pierluigi Gargiani, Eric Pellegrin, Cesar Magén, Teresa Puig, Xavier Obradors. Adv. Electron. Mater. 2017, 1700037. DOI: 10.1002/aelm.201700037

High Tc superconductor–ferromagnetic heterostructures constitute an appealing playground to study the interplay between flux vortices and magnetic moments. Here, the capability of a solution-derived route to grow hybrid YBa2Cu3O7-ferromagnetic nanocomposite epitaxial thin films from preformed spinel ferrite (MFe2O4, M = Mn, Co) nanoparticles (NPs) is explored. The characterization, performed using a combination of structural and magnetic techniques, reveals the complexity of the resulting nanocomposites. Results show that during the YBCO growth process, most of the NPs evolve to ferromagnetic double-perovskite (DP) phases (YBaCu2−xyFexCoyO5/YBaCoFeO5), while a residual fraction of preformed ferrite NPs may remain in the YBCO matrix. Magnetometry cycles reflect the presence of ferromagnetic structures associated to the DPs embedded in the superconducting films. In addition, a superparamagnetic signal that may be associated with a diluted system of ferromagnetic clusters around complex defects has been detected, as previously observed in standard YBCO films and nanocomposites. The hybrid nanocomposites described in this work will allow studying several fundamental issues like the nucleation of superconductivity and the mechanisms of magnetic vortex pinning in superconducting/ferromagnetic heterostructures.

Untangling surface oxygen exchange effects in YBa2Cu3O6+x thin films by electrical conductivity relaxation

P. CayadoC. F. Sánchez-Valdés,  A. Stangl,  M. Coll,  P. Roura,  A. Palau,  T. Puig  and  X. Obradors*. Phys. Chem. Chem. Phys., 2017,19, 14129-14140. DOI: 0.1039/C7CP01855J0.1039/C7CP01855J
The kinetics of oxygen incorporation (in-diffusion process) and excorporation (out-diffusion process), in YBa2Cu3O6+x (YBCO) epitaxial thin films prepared using the chemical solution deposition (CSD) methodology by the trifluoroacetate route, was investigated by electrical conductivity relaxation measurements. We show that the oxygenation kinetics of YBCO films is limited by the surface exchange process of oxygen molecules prior to bulk diffusion into the films. The analysis of the temperature and oxygen partial pressure influence on the oxygenation kinetics has drawn a consistent picture of the oxygen surface exchange process enabling us to define the most likely rate determining step. We have also established a strategy to accelerate the oxygenation kinetics at low temperatures based on the catalytic influence of Ag coatings thus allowing us to decrease the oxygenation temperature in the YBCO thin films.

Unveiling the Nucleation and Coarsening Mechanisms of Solution-Derived Self-Assembled Epitaxial Ce0.9Gd0.1O2–y Nanostructures

Albert Queraltó*, María de la Mata, Jordi Arbiol, Ruben Hühne∥, Xavier Obradors, and Teresa Puig. Cryst. Growth Des., 2017, 17 (2), pp 504–516. DOI: 10.1021/acs.cgd.6b01358


Self-assembling approaches based on chemical solution deposition (CSD) are ideal methods for the cost-effective production of epitaxial nanostructures with high throughput. Therefore, an in-depth investigation of the nucleation and coarsening processes involved in the self-assembly of nanostructures is mandatory to achieve a good control over nanostructure shape, dimensions, and orientation. Heteroepitaxial Ce0.9Gd0.1O2-y (CGO) is an ideal model system to unveil the underlying nanostructure development mechanisms in addition to their promising properties for catalysis, gas sensors, and ionic conductivity. Rapid thermal annealing furnaces have been used to study separately the thermodynamic and kinetic nucleation and coarsening mechanisms of self-assembled CGO isotropic and anisotropic nanostructures based on strain-engineering and surface energies control. Different CGO nanoislands are obtained: isotropic (001)CGO nanodots are grown on (001)-oriented Y2O3:ZrO2 (YSZ) and LaAlO3 (LAO) substrates, whereas (011)LAO substrates promote the growth of elongated (011)CGO nanowires. HRTEM and RHEED analyses are used to study the early stages of nucleation, as well as the shape and interfacial structure of CGO nanostructures. A systematic study with the heating ramp, annealing temperature and time, and strain in combination with thermally activated theoretical models provides information on the nucleation behavior, nucleation barriers, and atomic diffusion coefficients along in-plane and out-of-plane island orientations. Highly anisotropic atomic diffusion constants have been shown to be at the origin of the high aspect ratios of some of the nanostructures. Overall, our study provides a general method for the evaluation of nucleation and coarsening of multiple CSD-derived oxide nanostructures and understanding the shape development by combining thermodynamic and kinetic approaches.

Superconducting YBa2Cu3O7–δ Nanocomposites Using Preformed ZrO2 Nanocrystals: Growth Mechanisms and Vortex Pinning Properties

keukeleere_et_al-2016-advanced_electronic_materials Katrien De Keukeleere, Pablo Cayado, Alexander Meledin, Ferran Vallès, Jonathan De Roo, Hannes Rijckaert, Glenn Pollefeyt, Els Bruneel, Anna Palau, Mariona Coll, Susagna Ricart, Gustaaf Van Tendeloo, Teresa Puig, Xavier Obradors, Isabel Van Driessche. Advanced Electronic Materials. DOI: 10.1002/aelm.201600161 Although high temperature superconductors are promising for power applications, the production of low-cost coated conductors with high current densities—at high magnetic fields—remains challenging. A superior superconducting YBa2Cu3O7–δ nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs’ stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7–δ, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density JC of 5 MA cm−2 at 77 K in self-field. Importantly, this new approach results in a smaller magnetic field decay of JC(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7–δ nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7–δ nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications.

One-Step Route to Iron Oxide Hollow Nanocuboids by Cluster Condensation: Implementation in Water Remediation Technology

Lluís BalcellsCarlos Martínez-Boubeta*José Cisneros-FernándezKonstantinos SimeonidisBernat BozzoJudith Oró-SoleNúria BaguésJordi ArbiolNarcís Mestres, and Benjamín Martínez*. ACS Appl. Mater. Interfaces, 2016, 8 (42), pp 28599–28606. DOI: 10.1021/acsami.6b08709


The fabrication procedure of hollow iron oxide nanoparticles with a large surface to volume ratio by a single-step gas condensation process at ambient temperature is presented. Fe clusters formed during the sputtering process are progressively transformed into hollow cuboids with oxide shells by the Kirkendall mechanism at the expense of oxygen captured inside the deposition chamber. TEM and Raman spectroscopy techniques point to magnetite as the main component of the nanocuboids; however, the magnetic behavior exhibited by the samples suggests the presence of FeO as well. In addition, these particles showed strong stability after several months of exposure to ambient conditions, making them of potential interest in diverse technological applications. In particular, these hierarchical hollow particles turned out to be very efficient for both As(III) and As(V) absorption (326 and 190 mg/g, respectively), thus making them of strong interest for drinking water remediation.

Ultrafast Epitaxial Growth Kinetics in Functional Oxide Thin Films Grown by Pulsed Laser Annealing of Chemical Solutions

cm-2016-01968a_0008 Albert Queraltó*Angel Pérez del PinoMaría de la MataJordi ArbiolMar TristanyXavier Obradors, and Teresa Puig; Chem. Mater., 2016, 28 (17), pp 6136–6145. DOI: 10.1021/acs.chemmater.6b01968 The crystallization process and physical properties of different functional oxide thin films (Ce0.9Zr0.1O2-y, LaNiO3, Ba0.8Sr0.2TiO3, and La0.7Sr0.3MnO3) on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) are studied by pulsed laser annealing (PLA). A Nd:YAG laser source (λ = 266 nm, 10 Hz and τ ∼ 3 ns) is employed to crystallize chemical solution deposited (CSD) amorphous/nanocrystalline films under atmospheric conditions. We provide new insight on the influence of photochemical and photothermal interactions on the epitaxial crystallization kinetics of oxide thin films during the transformation from amorphous/polycrystalline material (i.e., atomic diffusion, epitaxial growth rates, and activation energies of nucleation and crystallization). The epitaxial growth is investigated by varying the laser fluence and the applied number of pulses. The morphology, structure, and epitaxial evolution of films are evaluated by means of atomic force and transmission electron microscopies and X-ray diffraction. Highly epitaxial oriented films of 20–40 nm in thickness are obtained by PLA. The crystallization kinetics of laser treatments is determined to be orders of magnitude faster than thermal treatments with similar activation energies (1.5–4.1 eV), mainly due to the large temperature gradients inducing modified atomic diffusion mechanisms derived mainly from photothermal interactions, as well as a minor contribution of photochemical effects. The fast heating rates achieved by PLA also contribute to the fast epitaxial growth due to reduced coarsening of polycrystalline material. The measurement of the physical properties (electrical resistivity and magnetism) of laser processed CSD films has revealed significantly good functionalities, close to those of thermally grown films, but with much shorter processing times.

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