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The synthesis of nanosized metal–organic frameworks (NMOFs) is requisite for their application as injectable drug delivery systems (DDSs) and other biorelevant purposes. Herein, we have critically examined the role of different synthetic parameters leading to the production of UiO-66 crystals smaller than 100 nm. Of note, we demonstrate the co-modulator role conferred by halide ions, not only to produce NMOFs with precise morphology and size, but also to significantly improve the reaction yield. The resulting NMOFs are highly crystalline and exhibit sustained colloidal stability in different biologically relevant media. As a proof of concept, these NMOFs were loaded with Rhodamine 6G (R6G), which remained trapped in most common biologically relevant media. When incubated with living mammalian cells, the R6G-loaded NMOFs were efficiently internalized and did not impair cell viability even at relatively high doses. The authors acknowledge the financial support of the MCIN/AEI (PID2019-108624RB-I00, RYC-2017-23457, RYC-2019-028238-I), the Xunta de Galicia (ED431F 2017/02, ED431F 2020/11, 2021-CP090, Centro Singular de Investigación de Galicia Accreditation 2019–2022, ED431G 2019/03), the European Union (European RegionalDevelopment Fund – ERDF; H2020-MSCA-ITN grant agreement no. 860942; H2020-FET-Open grant agreement no. 899612; H2020-ICT grant agreement no. 10101694 and INTERREG V-A Spain–Portugal, project 0624_2IQBIONEURO_6_E), and the European Research Council (starting grant no. 950421). M.C.-M. thanks the AEI (FPU19/03155). The authors are grateful for the use of RIAIDT-USC analytical facilities. SI

We use an original water-based chemical method to grow pure epitaxial BiFeO3 (BFO) ultra-thin films with excellent piezoelectric properties. Particularly, we show that this novel chemical route produces higher natural ferroelectric domain size distribution and coercive field compared to similar BFO films grown by physical methods. Moreover, we measured the d33 piezoelectric coefficient of 60 nm thick BFO films by a direct approach, using Direct Piezoelectric Force Microscopy (DPFM). As a result, first piezo-generated charge maps of a very thin BFO layer were obtained applying this novel technology. We also performed a comparative study of the d33 coefficients between standard PFM analysis and DPFM microscopy showing similar values i.e. 17 pm V−1 and 22 pC N−1, respectively. Finally, we proved that the directionality of the piezoelectric effect in BFO ferroelectric thin films is preserved at low thickness dimensions demonstrating the potential of chemical processes for the development of low cost functional ferroelectric and piezoelectric devices., A. C.-G. and J. M. V.-F. acknowledge the financial support from the French Agence Nationale de la Recherche (ANR) and project Q-NOSS ANR-16-CE09-0006-01. J. G. acknowledges the Ramon y Cajal program (RYC-2012-11709). The research leading to these results has received funding from the European Union Seventh Framework Programme under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative–I3). This project has received funding from the EU-H2020 research and innovation Programme under grant agreement No 654360 having benefitted from the access provided by ICMAB-CSIC in Barcelona within the framework of the NFFA-Europe. ICMAB acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496) Transnational Access Activity.

Oxide spinels of general formula AB2O4 (A = Mg2+, Fe2+; B = Al3+, Cr3+, etc.) constitute one of the most abundant crystalline structures in mineralogy. In this structure, cations distribute among octahedral and tetrahedral sites, according to their size and the crystal-field stabilization energy. The cationic arrangement determines the mechanical, magnetic, and transport properties of the spinel and can be influenced by external parameters like temperature, pressure, or epitaxial stress in the case of thin films. Here, we report a progressive change in the sign of the Poisson ratio, ν, in thin films of CoFe2O4, defining a smooth crossover from auxetic (ν < 0) to non-auxetic (ν > 0) behavior in response to epitaxial stress and temperature. Microstructural and magnetization studies, as well as ab initio calculations, demonstrate that such unusual elastic response is actually due to a progressive redistribution of Co2+ among the octahedral and tetrahedral sites of the spinel structure. The results presented in this work clarify a long standing controversy about the magnetic and elastic properties of Co-ferrites and are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures., This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2016-80762-R and MAT2017-82970-C2-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, No. ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187–SPICOLOST.

We use an original water-based chemical method to grow pure epitaxial BiFeO3 (BFO) ultra-thin films with excellent piezoelectric properties. Particularly, we show that this novel chemical route produces higher natural ferroelectric domain size distribution and coercive field compared to similar BFO films grown by physical methods. Moreover, we measured the d33 piezoelectric coefficient of 60 nm thick BFO films by a direct approach, using Direct Piezoelectric Force Microscopy (DPFM). As a result, first piezo-generated charge maps of a very thin BFO layer were obtained applying this novel technology. We also performed a comparative study of the d33 coefficients between standard PFM analysis and DPFM microscopy showing similar values i.e. 17 pm V-1 and 22 pC N-1, respectively. Finally, we proved that the directionality of the piezoelectric effect in BFO ferroelectric thin films is preserved at low thickness dimensions demonstrating the potential of chemical processes for the development of low cost functional ferroelectric and piezoelectric devices.

Chemical solution methods for thin-film deposition constitute an affordable alternative to high-vacuum physical technologies, like Sputtering, Pulsed Laser Deposition (PLD) or Molecular Beam Epitaxy (MBE). Particularly, chemical methods have proven to be very suitable for producing functional films over large areas, especially in the relatively thick range, from >100 nm to microns. Also, their versatile ability to synthesize different types of materials, i.e. carbides, silicides, pnictides, oxides or chalcogenides, makes them very attractive for a wide range of applications and studies. However, problems with surface/interface roughness, control of stoichiometry in multicationic or precisely-doped materials, and a lack of accurate control of the thickness in the thin limit range (

Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO3 thin film on Si(001) is explored. It is found that the ferroelectric polarization can be reversed, and resistive switching can be measured, upon a mechanical load in epitaxial BaTiO3−δ/La0.7Sr0.3MnO3/SrTiO3/Si columnar nanostructures. A flexoelectric effect is found, stemming from substantial strain gradients that can be created with moderate loads. Simultaneously, mechanical effects on the local conductivity can be used to modulate a nonvolatile resistive state of the BaTiO3−δ heterostructure. As a result, three different configurations of the system become accessible on top of the usual voltage reversal of polarization and resistive states.

A solar heat shield coating featuring the combination of plasmonic nanostructures in silica-based insulating materials has been developed and tested under conditions resembling natural sunlight exposure. Our results when implementing this coating on standard glazing reveal a blocking efficiency higher than 40%, compatible with a notable preservation of visible light transmittance above 75%. This strategy is (i) cost-effective, as only requires minute amounts of absorbent material in order to obtain the desired effect; (ii) straightforward, because no particular ordering of the plasmon resonators is needed onto the glass substrate; (iii) eco-friendly, as no metal leaching is observed once the gold is encapsulated; and (iv) retrofit-capable, given the fact that these nanostructures can be easily incorporated onto pre-installed glazing. All of these features emphasize the great potential of this approach in the search of more sustainable technologies for the fenestration industry.

Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO

We report the fabrication of epitaxial Y3Fe5O12 (YIG) thin films on Gd3Ga5O12 (111) using a chemical solution method. Cubic YIG is a ferrimagnetic material at room temperature, with excellent magneto-optical properties, high electrical resistivity, and a very narrow ferromagnetic resonance, which makes it particularly suitable for applications in filters and resonators at microwave frequencies. But these properties depend on the precise stoichiometry and distribution of Fe3+ ions among the octahedral/tetrahedral sites of a complex structure, which hampered the production of high-quality YIG thin films by affordable chemical methods. Here we report the chemical solution synthesis of YIG thin films, with excellent chemical, crystalline, and magnetic homogeneity. The films show a very narrow ferromagnetic resonance (long spin relaxation time), comparable to that obtained from high-vacuum physical deposition methods. These results demonstrate that chemical methods can compete to develop nanometer-thick YIG films with the quality required for spintronic devices and other high-frequency applications., This work was supported by the Ministry of Science of Spain (Projects No. MAT2016-80762-R, MAT2017-82970-C2-R, and No. MAT2014-51982-C2), the Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia (ED431F 2016/008, and Centro Singular de Investigación de Galicia Accreditation 2016–2019, ED431G/09), the European Regional Development Fund (ERDF), and the Aragón Regional Government through Projects E26. The microscopy works have been conducted in the Laboratorio de Microscopías Avanzadas (LMA) at Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza. The authors acknowledge the LMA-INA for offering access to their instruments and expertise. Pilar Jiménez-Cavero acknowledges Spanish MECD for support through FPU program (Reference No. FPU014/02546).

We report magnetic and electronic transport measurements across epitaxial bilayers of ferromagnetic insulator LaCoO3 and half-metallic ferromagnet La2/3Sr1/3MnO3 (LCO/LSMO: 3.5 nm/20 nm) fabricated by a chemical solution method. The I–V curves at room temperature and 4K measured with conducting atomic force microscopy (CAFM) on well-defined patterned areas exhibit the typical features of a tunneling process. The curves have been fitted to the Simmons model to determine the height (φ) and width (s) of the insulating LCO barrier. The results yield φ = 0.40 ± 0.05 eV (0.50 ± 0.01 eV) at room temperature (4K) and s = 3 nm, in good agreement with the structural analysis. Our results demonstrate that this chemical method is able to produce epitaxial heterostructures with the quality required for this type of fundamental studies and applications.

We report the synthesis of high quality epitaxial bilayers of LaMnO 3 /LaCoO 3 (LCO/LMO) on (001) LaAlO 3 , by spin-coating of a polymeric aqueous solutions. The bilayer shows a very large increase of the magnetization coercive field (≈ 3000%) with respect to the isolated LMO or LCO films. We suggest that the origin of this effect is a strong Mn 4 + –O–Co 2 + exchange interaction at the interface. Our results demonstrate that a simple chemical method is able to produce high quality epitaxial heterostructures in which interfacial effects can modify substantially the properties of the individual layers.

We report the synthesis of epitaxial bilayers of ultrathin La0.92MnO3/LaCoO3 (LMO/LCO) on SrTiO3 (STO) by polymer solution deposition. We have achieved an excellent control over the thickness (from ∼4 to ∼20 nm) and roughness of the films, which allows the fabrication of the sharp interfaces required for their functionality. We suggest that the large increase in the coercive field observed in the bilayer with respect to isolated films of LMO or LCO is due to a strong ferromagnetic Mn–O–Co superexchange interaction at the interface. Our results demonstrate that abrupt interfaces can be obtained in epitaxial multilayers by a simple and affordable chemical deposition technique, with the quality required for fundamental studies or highly demanding applications.

International audience; The technological impact of combining substrate technologies with the properties of functional advanced oxide ceramics is colossal given its relevant role in the development of novel and more efficient devices. However the precise control of interfaces and crystallization mechanisms of dissimilar materials at the nanoscale needs to be further developed. As an example, the integration of hybrid structures of high quality epitaxial oxide films and nanostructures on silicon as remains extremely challenging because these materials present major chemical, structural and thermal differences. This book chapter describes the main promising strategies that are being used to accommodate advanced oxide nanostructured ceramics on different technological substrates via chemical solution deposition approaches. We will focus on novel examples separated in two main sections: (i) epitaxial ceramic nanomaterials entirely performed by soft chemistry, such as nanostructured piezoelectric quartz thin films on silicon or 1D complex oxide nanostructures epitaxially grown on silicon, and (ii) ceramic materials prepared by combining soft chemistry and physical techniques, such as epitaxial perovskite oxide thin films on silicon using the combination of soft chemistry and Molecular Beam Epitaxy (MBE). Consequently, this chapter will cover cutting-edge strategies based on the potential of combining epitaxial growth and chemical solution deposition to develop oxide ceramics nanomaterials with novel structures and improved physical properties.

et al., The suitability of a particular material for use in magnetic devices is determined by the process of magnetization reversal/relaxation, which in turn depends on the magnetic anisotropy. Therefore, designing new ways to control magnetic anisotropy in technologically important materials is highly desirable. Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic ferromagnet LaSrMnO (LSMO) is determined by the proximity to thermodynamic equilibrium conditions during growth. We performed a series of x-ray diffraction and ferromagnetic resonance (FMR) experiments in two different sets of samples: the first corresponds to LSMO thin-films deposited under tensile strain on (0 0 1) SrTiO by pulsed laser deposition (PLD; far from thermodynamic equilibrium); the second were deposited by a slow chemical solution deposition (CSD) method, under quasi-equilibrium conditions. Thin films prepared by PLD show fourfold in-plane magnetic anisotropy, with an overimposed uniaxial term. However, the uniaxial anisotropy is completely suppressed in the CSD films. This change is due to a different rotation pattern of MnO octahedra to accommodate epitaxial strain, which depends not only on the amplitude of tensile stress imposed by the STO substrate, but also on the growth conditions. Our results demonstrate that the nature and magnitude of the magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during thin-film deposition., This work was supported by the European Research Council (ERC StG-259082, 2DTHERMS), Xunta de Galicia (2012-Projet No. CP072) and by the Ministry of Science of Spain (Project No. MAT2013-44673-R). JMVF also acknowledges the same organization for an FPI grant. EW and JM thank UNCuyo Argentina for Grant No C011.

High quality epitaxial thin films of LaCoO3 on SrTiO3 have been prepared by spin-coating of a metal/polymeric aqueous solution. The films (≈ 17 nm) are homogeneous and smooth over large areas. The characteristic low-spin (LS) state is replaced by a higher spin configuration of Co(III), due to strain-induced distortions of the CoO6 octahedra, introducing a ferromagnetic interaction and negative magnetoresistance below TC = 85 K. This simple chemical method produces the high-quality films required for either fundamental studies or applications, similar to physical deposition techniques.

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructures This research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2010-16157 & MAT2013-44673-R) and Xunta de Galicia (2012-CP071). J.M.V-F acknowledges the MINECO for support with a PhD grant of the FPI program SI

Hole-doping into the Mott insulator LaMnO3 results in a very rich magneto-electric phase diagram, including colossal magnetoresistance and different types of charge and orbital ordering. On the other hand, LaMnO3 presents an important catalytic activity for oxygen reduction, which is fundamental for increasing the efficiency of solid-oxide fuel cells and other energy-conversion devices. In this work, we report the chemical solution (water-based) synthesis of high-quality epitaxial thin films of LaMnO3, free of defects at square-centimeter scales, and compatible with standard microfabrication techniques. The films show a robust ferromagnetic moment and large magnetoresistance at room temperature. Through a comparison with films grown by pulsed laser deposition, we show that the quasi-equilibrium growth conditions characteristic of this chemical process can be exploited to tune new functionalities of the material.

We report magnetic and electronic transport measurements across epitaxial bilayers of ferromagnetic insulator LaCoO3 and half-metallic ferromagnet La2/3Sr1/3MnO3 (LCO/LSMO: 3.5 nm/20 nm) fabricated by a chemical solution method. The I-V curves at room temperature and 4K measured with conducting atomic force microscopy (CAFM) on well-defined patterned areas exhibit the typical features of a tunneling process. The curves have been fitted to the Simmons model to determine the height (φ) and width (s) of the insulating LCO barrier. The results yield φ = 0.40 ± 0.05 eV (0.50 ± 0.01 eV) at room temperature (4K) and s = 3 nm, in good agreement with the structural analysis. Our results demonstrate that this chemical method is able to produce epitaxial heterostructures with the quality required for this type of fundamental studies and applications.

We report the synthesis of polycrystalline films of La1-xCaxMnO3 in Si (111) by Polymer Assisted Deposition (PAD). An aqueous solution polyethyleneimine (PEI) and different metal ions stabilized with EDTA, was spin coated on hydrophilized Si substrates and subsequently annealed under different atmospheres. Homogeneous, dense polycrystalline films are obtained at optimized conditions of 950 ºC under flowing O2. The morphology and magnetic properties of the samples are compared with films obtained by Pulsed Laser Deposition.

We propose a novel route for optimizing the thermoelectric power of a polaronic conductor, independent of its electronic conductivity. This mechanism is exemplified here in thin-films of La2NiO4+δ. Tensile stress induced by epitaxial growth on SrTiO3 doubles the thermoelectric power of ≈15 nm thick films relative to ≈90 nm films, while the electronic conductivity remains practically unchanged. Epitaxial strain influences the statistical contribution to the high temperature thermopower, but introduces a smaller correction to the electronic conductivity. This mechanism provides a new way for optimizing the high temperature thermoelectric performance of polaronic conductors This work was supported by the European Research Council (ERC StG-259082, 2DTHERMS), and Ministerio de Economía y Competitividad of Spain through the project MAT2010-16157, and a Ph.D. grant of the FPI program (J.M.V.-F.) SI

Ferroelectric oxides have attracted much attention due to their wide range of applications, particularly in electronic devices such as nonvolatile memories and tunnel junctions. As a result, the monolithic integration of these materials into silicon technology and their nanostructuration to develop alternative cost-effective processes are among the central points in the current technology. In this work, we used a chemical route to obtain nanowire thin films of a novel Sr1+δMn8O16 (SMO) hollandite-type manganese oxide on silicon. Scanning transmission electron microscopy combined with crystallographic computing reveals a crystal structure comprising hollandite and pyrolusite units sharing the edges of their MnO6 octahedra, resulting in three types of tunnels arranged along the c axis, where the ordering of the Sr atoms produces natural symmetry breaking. The novel structure gives rise to ferroelectricity and piezoelectricity, as revealed by local direct piezoelectric force microscopy measurements, which confirmed the ferroelectric nature of the SMO nanowire thin films at room temperature and showed a piezoelectric coefficient d33 value of 22 ± 6 pC N−1. Moreover, we proved that flexible vertical SMO nanowires can be harvested providing an electrical output energy through the piezoelectric effect, showing excellent deformability and high interface recombination. This work indicates the possibility of engineering the integration of 1D manganese oxides on silicon, a step which precedes the production of microelectronic devices., A. C.-G., C. J., R. G.-B. and J. M. V.-F. acknowledge the financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (No. 803004) and the French Agence Nationale de la Recherche (ANR), project Q-NOSS ANR ANR-16-CE09-0006-01. This project has received funding from the EU-H2020 research and innovation program under grant agreement no 654360 having benefitted from the access provided by ICMAB-CSIC in Barcelona within the framework of the NFFA-Europe Transnational Access Activity. This project has received funding from the European's Union Horizon 2020 research and innovation programme under Grant No. 823717-ESTEEM3, the Spanish Ministry of Economy and Competitivity through Project MAT2017-82970-C2-2-R, and the Aragon Regional Government through Project No. E13_20R (with European Social Fund). We acknowledge SOLEIL for provision of synchrotron radiation facilities, and we would like to thank Pierre Fertey for assistance in using beamline Cristal. J. G. also acknowledges the Ramon y Cajal program (RYC-2012-11709). The authors thank D. Montero for providing the FEGSEM images. N. M. acknowledges the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa FUNFUTURE (CEX2019-000917-S) and SUMATE (RTI2018-095853-B-C21) projects, co-financed by the European Regional Development Fund. The FEGSEM instrumentation was facilitated by the Institut des Matériaux de Paris Centre (IMPC FR2482). The authors thank Frederic Pichot for his expertise and advice during the nanowire lithographic process. The STEM microscopy work was conducted in the Laboratorio de Microscopias Avanzadas (LMA) at Instituto de Nanociencia de Aragon (INA) at the University of Zaragoza.

Catalysts typically lose effectiveness during operation, with much effort invested in stabilising active metal centres to prolong their functional lifetime for as long as possible. In this study palladium nanoparticles (PdNP) supported inside hollow graphitised carbon nanofibers (GNF), designated as PdNP@GNF, opposed this trend. PdNP@GNF exhibited continuously increasing activity over 30000 reaction cycles when used as an electrocatalyst in the hydrogen evolution reaction (HER). The activity of PdNP@GNF, expressed as the exchange current density, was always higher than activated carbon (Pd/C), and after 10000 cycles PdNP@GNF surpassed the activity of platinum on carbon (Pt/C). The extraordinary durability and self-improving behaviour of PdNP@GNF was solely related the unique nature of the location of the palladium nanoparticles, that is, at the graphitic step-edges within the GNF. Transmission electron microscopy imaging combined with spectroscopic analysis revealed an orchestrated series of reactions occurring at the graphitic step-edges during electrocatalytic cycling, in which some of the curved graphitic surfaces opened up to form a stack of graphene layers bonding directly with Pd atoms through Pd−C bonds. This resulted in the active metal centres becoming effectively hardwired into the electrically conducting nanoreactors (GNF), enabling facile charge transport to/from the catalytic centres resulting in the dramatic self-improving characteristics of the electrocatalyst This work has received financial support from the Republic of Turkey Ministry of National Education (fellowship for M.A.), the Ministry of Science of Spain (Projects No. RTI2018-101097-A-I00, EIN2019-103246 and RyC-2016-20258 for M.G-L.), the European Research Council (ERC) (Starting Investigator Grant (NANOCOMP-679124) for M.G-L), the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09; convenio colaboracion 2018-AD006), the European Union (European Regional Development Fund – ERDF) and Engineering and Physical Sciences Research Council (EPSRC) SI