Staff directory Neus Domingo Marimón

Neus Domingo Marimón

Senior Researcher
Oxide Nanophysics



  • Tunable Molecular Electrodes for Bistable Polarization Screening

    Spasojevic, I; Santiso, J; Caicedo, JM; Catalan, G; Domingo, N Small; 2023. 10.1002/smll.202207799.


  • Progress on Emerging Ferroelectric Materials for Energy Harvesting, Storage and Conversion

    Wei X.-K., Domingo N., Sun Y., Balke N., Dunin-Borkowski R.E., Mayer J. Advanced Energy Materials; 12 (24, 2201199) 2022. 10.1002/aenm.202201199.

    Since the discovery of Rochelle salt a century ago, ferroelectric materials have been investigated extensively due to their robust responses to electric, mechanical, thermal, magnetic, and optical fields. These features give rise to a series of ferroelectric-based modern device applications such as piezoelectric transducers, memories, infrared detectors, nonlinear optical devices, etc. On the way to broaden the material systems, for example, from three to two dimensions, new phenomena of topological polarity, improper ferroelectricity, magnetoelectric effects, and domain wall nanoelectronics bear the hope for next-generation electronic devices. In the meantime, ferroelectric research has been aggressively extended to more diverse applications such as solar cells, water splitting, and CO2 reduction. In this review, the most recent research progress on newly emerging ferroelectric states and phenomena in insulators, ionic conductors, and metals are summarized, which have been used for energy storage, energy harvesting, and electrochemical energy conversion. Along with the intricate coupling between polarization, coordination, defect, and spin state, the exploration of transient ferroelectric behavior, ionic migration, polarization switching dynamics, and topological ferroelectricity, sets up the physical foundation ferroelectric energy research. Accordingly, the progress in understanding of ferroelectric physics is expected to provide insightful guidance on the design of advanced energy materials. © 2022 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH.

  • Voltage control of magnetism with magneto-ionic approaches: Beyond voltage-driven oxygen ion migration

    De Rojas J., Quintana A., Rius G., Stefani C., Domingo N., Costa-Krämer J.L., Menéndez E., Sort J. Applied Physics Letters; 120 (7, 070501) 2022. 10.1063/5.0079762. IF: 3.791

    Magneto-ionics is an emerging field in materials science where voltage is used as an energy-efficient means to tune magnetic properties, such as magnetization, coercive field, or exchange bias, by voltage-driven ion transport. We first discuss the emergence of magneto-ionics in the last decade, its core aspects, and key avenues of research. We also highlight recent progress in materials and approaches made during the past few years. We then focus on the "structural-ion"approach as developed in our research group in which the mobile ions are already present in the target material and discuss its potential advantages and challenges. Particular emphasis is given to the energetic and structural benefits of using nitrogen as the mobile ion, as well as on the unique manner in which ionic motion occurs in CoN and FeN systems. Extensions into patterned systems and textures to generate imprinted magnetic structures are also presented. Finally, we comment on the prospects and future directions of magneto-ionics and its potential for practical realizations in emerging fields, such as neuromorphic computing, magnetic random-access memory, or micro- and nano-electromechanical systems. © 2022 Author(s).


  • Deconvolution of Phonon Scattering by Ferroelectric Domain Walls and Point Defects in a PbTiO3Thin Film Deposited in a Composition-Spread Geometry

    Bugallo D., Langenberg E., Ferreiro-Vila E., Smith E.H., Stefani C., Batlle X., Catalan G., Domingo N., Schlom D.G., Rivadulla F. ACS Applied Materials and Interfaces; 13 (38): 45679 - 45685. 2021. 10.1021/acsami.1c08758. IF: 9.229

    We present a detailed analysis of the temperature dependence of the thermal conductivity of a ferroelectric PbTiO3 thin film deposited in a composition-spread geometry enabling a continuous range of compositions from ∼25% titanium deficient to ∼20% titanium rich to be studied. By fitting the experimental results to the Debye model we deconvolute and quantify the two main phonon-scattering sources in the system: ferroelectric domain walls (DWs) and point defects. Our results prove that ferroelectric DWs are the main agent limiting the thermal conductivity in this system, not only in the stoichiometric region of the thin film ([Pb]/[Ti] ≈ 1) but also when the concentration of the cation point defects is significant (up to ∼15%). Hence, DWs in ferroelectric materials are a source of phonon scattering at least as effective as point defects. Our results demonstrate the viability and effectiveness of using reconfigurable DWs to control the thermal conductivity in solid-state devices. © 2021 American Chemical Society.

  • Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains

    Spasojevic I., Verdaguer A., Catalan G., Domingo N. Advanced Electronic Materials; 8 (6, 2100650) 2021. 10.1002/aelm.202100650. IF: 7.295

    The switching dynamics of ferroelectric polarization under electric fields depends on the availability of screening charges in order to stabilize the switched polarization. In ferroelectrics, thin films with exposed surfaces investigated by piezoresponse force microscopy (PFM), the main source of external screening charges is the atmosphere and the water neck, and therefore relative humidity (RH) plays a major role. Here, it is shown how the dynamic writing of domains in BaTiO3 thin films changes by varying scanning speeds in the range of RH between 2.5% and 60%. The measurements reveal that the critical speed for domain writing, which is defined as the highest speed at which electrical writing of a continuous stripe domain is possible, increases non-monotonically with RH. Additionally, the width of line domains shows a power law dependence on the writing speed, with a growth rate coefficient decreasing with RH. The size of the written domains at a constant speed as well as the creep-factor μ describing the domain wall kinetics follow the behavior of water adsorption represented by the adsorption isotherm, indicating that the screening mechanism dominating the switching dynamics is the thickness and the structure of adsorbed water structure and its associated dielectric constant and ionic mobility. © 2021 The Authors. Advanced Electronic Materials published by Wiley-VCH GmbH.

  • Local and correlated studies of humidity-mediated ferroelectric thin film surface charge dynamics

    Gaponenko I., Musy L., Domingo N., Stucki N., Verdaguer A., Bassiri-Gharb N., Paruch P. npj Computational Materials; 7 (1, 163) 2021. 10.1038/s41524-021-00615-4. IF: 12.241

    Electrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. We analyse the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorisation, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh–Nagumo reaction–diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis. © 2021, The Author(s).

  • Mechanical reading of ferroelectric polarization

    Stefani C., Langenberg E., Cordero-Edwards K., Schlom D.G., Catalan G., Domingo N. Journal of Applied Physics; 130 (7, 0059930) 2021. 10.1063/5.0059930. IF: 2.546

    Flexoelectricity is a property of dielectric materials whereby they exhibit electric polarization induced by strain gradients; while this effect can be negligible at the macroscale, it can become dominant at the nanoscale, where strain gradients can turn out to be tremendous. Previous works have demonstrated that flexoelectricity coupled with piezoelectricity enables the mechanical writing of ferroelectric polarization. When considering ferroelectric materials with out-of-plane polarization, the coupling of piezoelectricity with flexoelectricity can insert a mechanical asymmetry to the system and enable the distinction of oppositely polarized domains, based on their nanomechanical response. Using atomic force microscopy and, more specifically, contact resonance techniques, the coupling of flexoelectricity to piezoelectricity can be exploited to mechanically read the sign of ferroelectric polarization in a non-destructive way. We have measured a variety of ferroelectric materials, from a single crystal to thin films, and domains that are polarized down always appear to be stiffer than oppositely polarized domains. In this article, we demonstrate experimentally that the phenomenon is size-dependent and strongly enhanced when the dimension of the material is reduced to nanoscale in thin films. Ultimately, we demonstrate how the sensitivity in mechanical reading of ferroelectric polarization can be improved by appropriately tuning the mechanical stiffness of the cantilevers. © 2021 Author(s).

  • Non-linear nanoscale piezoresponse of single ZnO nanowires affected by piezotronic effect

    Lozano H., Catalán G., Esteve J., Domingo N., Murillo G. Nanotechnology; 32 (2, 025202) 2021. 10.1088/1361-6528/abb972. IF: 3.874

    Zinc oxide (ZnO) nanowires (NWs) as semiconductor piezoelectric nanostructures have emerged as material of interest for applications in energy harvesting, photonics, sensing, biomedical science, actuators or spintronics. The expression for the piezoelectric properties in semiconductor materials is concealed by the screening effect of the available carriers and the piezotronic effect, leading to complex nanoscale piezoresponse signals. Here, we have developed a metal-semiconductor-metal model to simulate the piezoresponse of single ZnO NWs, demonstrating that the apparent non-linearity in the piezoelectric coefficient arises from the asymmetry created by the forward and reversed biased Schottky barriers at the semiconductor-metal junctions. By directly measuring the experimental I-V characteristics of ZnO NWs with conductive atomic force microscope together with the piezoelectric vertical coefficient by piezoresponse force microscopy, and comparing them with the numerical calculations for our model, effective piezoelectric coefficients in the range d 33eff ∼ 8.6 pm V-1-12.3 pm V-1 have been extracted for ZnO NWs. We have further demonstrated via simulations the dependence between the effective piezoelectric coefficient d 33eff and the geometry and physical dimensions of the NW (radius to length ratio), revealing that the higher d 33eff is obtained for thin and long NWs due to the tensor nature proportionality between electric fields and deformation in NW geometries. Moreover, the non-linearity of the piezoresponse also leads to multiharmonic electromechanical response observed at the second and higher harmonics that indeed is not restricted to piezoelectric semiconductor materials but can be generalized to any type of asymmetric voltage drops on a piezoelectric structure as well as leaky wide band-gap semiconductor ferroelectrics. © 2020 IOP Publishing Ltd.

  • Oxidation processes at the surface of BaTiO3 thin films under environmental conditions

    Spasojevic I., Sauthier G., Caicedo J.M., Verdaguer A., Domingo N. Applied Surface Science; 565 (150288) 2021. 10.1016/j.apsusc.2021.150288. IF: 6.707

    Dissociation and adsorption of water on ferroelectric oxide surfaces play important role in the processes of screening and switching dynamics of ferroelectric polarization, as well as in catalytic processes which can be additionally coupled with light, temperature or vibration stimuli. In this work, we present XPS study of ferroelectric BaTiO3thin films and determine the entanglement between surface chemistry, polarization direction and stability, by observing changes upon time exposure to environmental conditions, heating in O2atmosphere and irradiation in vacuum. We devote special attention to Ba 3d spectral region and identify two different oxidation states of O atoms in the compounds of Ba. While this second specie was generally attributed to Ba in surface compounds where it has different oxygen coordination than in the bulk, based on the XPS results of oxygen annealed thin films, we demonstrate that this so far neglected component, corresponds to barium peroxide (BaO2) and identify it as important active specie for the study of screening mechanisms closely related with catalytic activity present in this ferroelectric material. Finally, we report on chemically assisted polarization switching in thin films induced by heating in vacuum or exposure to X-Ray radiation due to the formation of positive surface electric field created by oxygen or electron vacancies, respectively. © 2021 The Authors


  • Mechanical Softness of Ferroelectric 180° Domain Walls MECHANICAL SOFTNESS of FERROELECTRIC 180 DEGREE ... STEFANI CHRISTINA et al.

    Stefani C., Ponet L., Shapovalov K., Chen P., Langenberg E., Schlom D.G., Artyukhin S., Stengel M., Domingo N., Catalan G. Physical Review X; 10 (4, 041001) 2020. 10.1103/PhysRevX.10.041001. IF: 12.577

    Using scanning probe microscopy, we measure the out-of-plane mechanical response of ferroelectric 180° domain walls and observe that, despite separating domains that are mechanically identical, the walls appear mechanically distinct-softer-compared to the domains. This effect is observed in different ferroelectric materials (LiNbO3, BaTiO3, and PbTiO3) and with different morphologies (from single crystals to thin films), suggesting that the effect is universal. We propose a theoretical framework that explains the domain wall softening and justifies that the effect should be common to all ferroelectrics. The lesson is, therefore, that domain walls are not only functionally different from the domains they separate, but also mechanically distinct. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the ""Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

  • Self-Pixelation Through Fracture in VO2 Thin Films

    Laura Rodríguez, Elena del Corro, Michele Conroy, Kalani Moore, Felip Sandiumenge, Neus Domingo, José Santiso, Gustau Catalan Acs Applied Electronic Materials; 2 (5): 1433 - 1439. 2020. 10.1021/acsaelm.0c00199. IF: 0.000

  • Strain-Engineered Ferroelastic Structures in PbTiO3 Films and Their Control by Electric Fields

    Langenberg E., Paik H., Smith E.H., Nair H.P., Hanke I., Ganschow S., Catalan G., Domingo N., Schlom D.G. ACS Applied Materials and Interfaces; 12 (18): 20691 - 20703. 2020. 10.1021/acsami.0c04381. IF: 8.758

    We study the interplay between epitaxial strain, film thickness, and electric field in the creation, modification, and design of distinct ferroelastic structures in PbTiO3 thin films. Strain and thickness greatly affect the structures formed, providing a two-variable parameterization of the resulting self-assembly. Under applied electric fields, these strain-engineered ferroelastic structures are highly malleable, especially when a/c and a1/a2 superdomains coexist. To reconfigure the ferroelastic structures and achieve self-assembled nanoscale-ordered morphologies, pure ferroelectric switching of individual c-domains within the a/c superdomains is essential. The stability, however, of the electrically written ferroelastic structures is in most cases ephemeral; the speed of the relaxation process depends sensitively on strain and thickness. Only under low tensile strain - as is the case for PbTiO3 on GdScO3 - and below a critical thickness do the electrically created a/c superdomain structures become stable for days or longer, making them relevant for reconfigurable nanoscale electronics or nonvolatile electromechanical applications. Copyright © 2020 American Chemical Society.

  • Temperature-independent giant dielectric response in transitional BaTiO3 thin films

    Everhardt A.S., Denneulin T., Grünebohm A., Shao Y.-T., Ondrejkovic P., Zhou S., Domingo N., Catalan G., Hlinka J., Zuo J.-M., Matzen S., Noheda B. Applied Physics Reviews; 7 (1, 011402) 2020. 10.1063/1.5122954. IF: 17.054

    Ferroelectric materials exhibit the largest dielectric permittivities and piezoelectric responses in nature, making them invaluable in applications from supercapacitors or sensors to actuators or electromechanical transducers. The origin of this behavior is their proximity to phase transitions. However, the largest possible responses are most often not utilized due to the impracticality of using temperature as a control parameter and to operate at phase transitions. This has motivated the design of solid solutions with morphotropic phase boundaries between different polar phases that are tuned by composition and that are weakly dependent on temperature. Thus far, the best piezoelectrics have been achieved in materials with intermediate (bridging or adaptive) phases. But so far, complex chemistry or an intricate microstructure has been required to achieve temperature-independent phase-transition boundaries. Here, we report such a temperature-independent bridging state in thin films of chemically simple BaTiO3. A coexistence among tetragonal, orthorhombic, and their bridging low-symmetry phases are shown to induce continuous vertical polarization rotation, which recreates a smear in-transition state and leads to a giant temperature-independent dielectric response. The current material contains a ferroelectric state that is distinct from those at morphotropic phase boundaries and cannot be considered as ferroelectric crystals. We believe that other materials can be engineered in a similar way to contain a ferroelectric state with gradual change of structure, forming a class of transitional ferroelectrics. Similar mechanisms could be utilized in other materials to design low-power ferroelectrics, piezoelectrics, dielectrics, or shape-memory alloys, as well as efficient electro- and magnetocalorics. © 2020 Author(s).


  • Converse flexoelectricity yields large piezoresponse force microscopy signals in non-piezoelectric materials

    Abdollahi A., Domingo N., Arias I., Catalan G. Nature Communications; 10 (1, 1266) 2019. 10.1038/s41467-019-09266-y. IF: 11.878

    Converse flexoelectricity is a mechanical stress induced by an electric polarization gradient. It can appear in any material, irrespective of symmetry, whenever there is an inhomogeneous electric field distribution. This situation invariably happens in piezoresponse force microscopy (PFM), which is a technique whereby a voltage is delivered to the tip of an atomic force microscope in order to stimulate and probe piezoelectricity at the nanoscale. While PFM is the premier technique for studying ferroelectricity and piezoelectricity at the nanoscale, here we show, theoretically and experimentally, that large effective piezoelectric coefficients can be measured in non-piezoelectric dielectrics due to converse flexoelectricity. © 2019, The Author(s).

  • Ferroelectric Domain Walls in PbTiO3 Are Effective Regulators of Heat Flow at Room Temperature

    Langenberg E., Saha D., Holtz M.E., Wang J.-J., Bugallo D., Ferreiro-Vila E., Paik H., Hanke I., Ganschow S., Muller D.A., Chen L.-Q., Catalan G., Domingo N., Malen J., Schlom D.G., Rivadulla F. Nano Letters; 19 (11): 7901 - 7907. 2019. 10.1021/acs.nanolett.9b02991. IF: 12.279

    Achieving efficient spatial modulation of phonon transmission is an essential step on the path to phononic circuits using "phonon currents". With their intrinsic and reconfigurable interfaces, domain walls (DWs), ferroelectrics are alluring candidates to be harnessed as dynamic heat modulators. This paper reports the thermal conductivity of single-crystal PbTiO3 thin films over a wide variety of epitaxial-strain-engineered ferroelectric domain configurations. The phonon transport is proved to be strongly affected by the density and type of DWs, achieving a 61% reduction of the roomerature thermal conductivity compared to the single-domain scenario. The thermal resistance across the ferroelectric DWs is obtained, revealing a very high value (≈5.0 × 10-9 K m2 W-1), comparable to grain boundaries in oxides, explaining the strong modulation of the thermal conductivity in PbTiO3. This low thermal conductance of the DWs is ascribed to the structural mismatch and polarization gradient found between the different types of domains in the PbTiO3 films, resulting in a structural inhomogeneity that extends several unit cells around the DWs. These findings demonstrate the potential of ferroelectric DWs as efficient regulators of heat flow in one single material, overcoming the complexity of multilayers systems and the uncontrolled distribution of grain boundaries, paving the way for applications in phononics. Copyright © 2019 American Chemical Society.

  • Periodicity-Doubling Cascades: Direct Observation in Ferroelastic Materials

    Everhardt A.S., Damerio S., Zorn J.A., Zhou S., Domingo N., Catalan G., Salje E.K.H., Chen L.-Q., Noheda B. Physical Review Letters; 123 (8, 087603) 2019. 10.1103/PhysRevLett.123.087603. IF: 9.227

    Very sensitive responses to external forces are found near phase transitions. However, transition dynamics and preequilibrium phenomena are difficult to detect and control. We have observed that the equilibrium domain structure following a phase transition in ferroelectric and ferroelastic BaTiO3 is attained by halving of the domain periodicity multiple times. The process is reversible, with periodicity doubling as temperature is increased. This observation is reminiscent of the period-doubling cascades generally observed during bifurcation phenomena, and, thus, it conforms to the "spatial chaos" regime earlier proposed by Jensen and Bak [Phys. Scr. T 9, 64 (1985)PHSTER0281-184710.1088/0031-8949/1985/T9/009] for systems with competing spatial modulations. © 2019 American Physical Society.

  • Signal enhancement on gold nanoparticle-based lateral flow tests using cellulose nanofibers

    Quesada-González D., Stefani C., González I., de la Escosura-Muñiz A., Domingo N., Mutjé P., Merkoçi A. Biosensors and Bioelectronics; 141 (111407) 2019. 10.1016/j.bios.2019.111407. IF: 9.518

    Lateral flow paper-based biosensors merge as powerful tools in point-of-care diagnostics since they are cheap, portable, robust, selective, fast and easy to use. However, the sensitivity of this type of biosensors is not always as high as required, often not permitting a clear quantification. To improve the colorimetric response of standard lateral flow strips (LFs), we have applied a new enhancement strategy that increases the sensitivity of LFs based on the use of cellulose nanofibers (CNF). CNF penetrate inside the pores of LFs nitrocellulose paper, compacting the pore size only in the test line, particularly near the surface of the strip. This modification retains the bioreceptors (antibodies) close to the surface of the strips, and thus further increasing the density of selectively attached gold nanoparticles (AuNPs) in the top part of the membrane, in the test line area, only when the sample is positive. This effect boosts in average a 36.6% the sensitivity of the LFs. The optical measurements of the LFs were carried out with a mobile phone camera whose imaging resolution was improved by attaching microscopic lens on the camera objective. The characterization of CNF into paper and their effect was analyzed using atomic force microscope (AFM) and scanning electron microscope (SEM) imaging techniques. © 2019 Elsevier B.V.

  • Surface charged species and electrochemistry of ferroelectric thin films

    Domingo N., Gaponenko I., Cordero-Edwards K., Stucki N., Pérez-Dieste V., Escudero C., Pach E., Verdaguer A., Paruch P. Nanoscale; 11 (38): 17920 - 17930. 2019. 10.1039/c9nr05526f. IF: 6.970

    The combination of scanning probe microscopy and ambient pressure X-ray photoelectron spectroscopy opens up new perspectives for the study of combined surface chemical, electrochemical and electromechanical properties at the nanoscale, providing both nanoscale resolution of physical information and the chemical sensitivity required to identify surface species and bulk ionic composition. In this work, we determine the nature and evolution over time of surface chemical species obtained after water-mediated redox reactions on Pb(Zr0.2,Ti0.8)O3 thin films with opposite as-grown polarization states. Starting with intrinsically different surface chemical composition on the oppositely polarized films (as a result of their ferroelectric-dominated interaction with environmental water), we identify the reversible and irreversible electrochemical reactions under an external electric field, distinguishing switching and charging events. We find that while reversible ionic displacements upon polarization switching dominate screening in the bulk of the sample, polarization dependent irreversible redox reactions determine surface chemical composition, which reveals itself as a characteristic fingerprint of the ferroelectric polarization switching history. © 2019 The Royal Society of Chemistry.

  • Water adsorption, dissociation and oxidation on SrTiO 3 and ferroelectric surfaces revealed by ambient pressure X-ray photoelectron spectroscopy

    Domingo N., Pach E., Cordero-Edwards K., Pérez-Dieste V., Escudero C., Verdaguer A. Physical Chemistry Chemical Physics; 21 (9): 4920 - 4930. 2019. 10.1039/c8cp07632d. IF: 3.567

    Water dissociation on oxides is of great interest because its fundamental aspects are still not well understood and it has implications in many processes, from ferroelectric polarization screening phenomena to surface catalysis and surface chemistry on oxides. In situ water dissociation and redox processes on metal oxide perovskites which easily expose TiO 2 -terminated surfaces, such as SrTiO 3 , BaTiO 3 or Pb(Zr,Ti)O 3 , are studied by ambient pressure XPS, as a function of water vapour pressure. From the analysis of the O1s spectrum, we determine the presence of different types of oxygen based species, from hydroxyl groups, either bound to Ti 4+ and metal sites or lattice oxygen, to different peroxide compounds, and propose a model for the adsorbate layer composition, valid for environmental conditions. From the XPS analysis, we describe the existing surface redox reactions for metal oxide perovskites, occurring at different water vapour pressures. Among them, peroxide species resulting from surface oxidative reactions are correlated with the presence of Ti 4+ ions, which are observed to specifically promote surface oxidation and water dissociation as compared to other metals. Finally, surface peroxidation is enhanced by X-ray beam irradiation, leading to a higher coverage of peroxide species after beam overexposure and by ferroelectric polarization, demonstrating the enhancement of the reactivity of the surfaces of ferroelectric materials due to the effect of internal electric fields. © 2019 the Owner Societies.


  • Interfacial Engineering of Metal Oxides for Highly Stable Halide Perovskite Solar Cells

    Mingorance A., Xie H., Kim H.-S., Wang Z., Balsells M., Morales-Melgares A., Domingo N., Kazuteru N., Tress W., Fraxedas J., Vlachopoulos N., Hagfeldt A., Lira-Cantu M. Advanced Materials Interfaces; 5 (22, 1800367) 2018. 10.1002/admi.201800367. IF: 4.834

    Oxides employed in halide perovskite solar cells (PSCs) have already demonstrated to deliver enhanced stability, low cost, and the ease of fabrication required for the commercialization of the technology. The most stable PSCs configuration, the carbon-based hole transport layer-free PSC (HTL-free PSC), has demonstrated a stability of more than one year of continuous operation partially due to the dual presence of insulating oxide scaffolds and conductive oxides. Despite these advances, the stability of PSCs is still a concern and a strong limiting factor for their industrial implementation. The engineering of oxide interfaces functionalized with molecules (like self-assembly monolayers) or polymers results in the passivation of defects (traps), providing numerous advantages such as the elimination of hysteresis and the enhancement of solar cell efficiency. But most important is the beneficial effect of interfacial engineering on the lifetime and stability of PSCs. In this work, the authors provide a brief insight into the recent developments reported on the surface functionalization of oxide interfaces in PSCs with emphasis on the effect of device stability. This paper also discusses the different binding modes, their effect on defect passivation, band alignment or dipole formation, and how these parameters influence device lifetime. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Local Piezoelectric Behavior of Potassium Sodium Niobate Prepared by a Facile Synthesis via Water Soluble Precursors

    Senes N., Iacomini A., Domingo N., Enzo S., Mulas G., Cuesta-Lopez S., Garroni S. Physica Status Solidi (A) Applications and Materials Science; 215 (16, 1700921) 2018. 10.1002/pssa.201700921. IF: 1.795

    Due to the ever-increasing restrictions connected to the use of toxic lead-based materials, the developing of lead-free piezoceramics has become one of the most urgent tasks. In this context, potassium sodium niobate materials (KNN) have attracted a lot of interest as promising candidates due to their excellent piezo properties. For this reason, many efforts have been addressed to optimize the synthesis process now suffering by several drawbacks including the high volatilization of potassium and sodium at the conventional high temperature treatments and the use of expensive metal precursors. To overcome these issues, a new modified Pechini method to synthesize single phase K0.5Na0.5NbO3 powders, from water soluble metal precursors, is presented. Microstructural and structural parameters are characterized by X-ray diffraction (XRD). Depending on the amount of citric acid added to the starting reagents, two pure single-phase K0.5Na0.5NbO3 (2 g citric acid) and K0.3Na0.7NbO3 (0.2 g citric acid), respectively, are obtained with a good crystallinity at a moderate temperature of 500 °C. The piezo responses of the as calcined systems are tested by piezoresponse force microscopy (PFM). K0.5Na0.5NbO3 exhibits a much higher response with respect to the other phase, which relates to the larger crystallinity and to the chemical composition. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Domain wall magnetoresistance in BiFeO3 thin films measured by scanning probe microscopy

    Domingo N., Farokhipoor S., Santiso J., Noheda B., Catalan G. Journal of Physics Condensed Matter; 29 (33, 334003) 2017. 10.1088/1361-648X/aa7a24. IF: 2.678

    We measure the magnetotransport properties of individual 71° domain walls in multiferroic BiFeO3 by means of conductive-atomic force microscopy (C-AFM) in the presence of magnetic fields up to one Tesla. The results suggest anisotropic magnetoresistance at room temperature, with the sign of the magnetoresistance depending on the relative orientation between the magnetic field and the domain wall plane. A consequence of this finding is that macroscopically averaged magnetoresistance measurements for domain wall bunches are likely to underestimate the magnetoresistance of each individual domain wall. © 2017 IOP Publishing Ltd.

  • Ferroelectrics as Smart Mechanical Materials

    Cordero-Edwards K., Domingo N., Abdollahi A., Sort J., Catalan G. Advanced Materials; 29 (37, 1702210) 2017. 10.1002/adma.201702210. IF: 19.791

    The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact-resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO3) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Lateral Magnetically Modulated Multilayers by Combining Ion Implantation and Lithography

    Menéndez E., Modarresi H., Petermann C., Nogués J., Domingo N., Liu H., Kirby B.J., Mohd A.S., Salhi Z., Babcock E., Mattauch S., Van Haesendonck C., Vantomme A., Temst K. Small; 13 (11, 1603465) 2017. 10.1002/smll.201603465. IF: 8.643

    The combination of lithography and ion implantation is demonstrated to be a suitable method to prepare lateral multilayers. A laterally, compositionally, and magnetically modulated microscale pattern consisting of alternating Co (1.6 µm wide) and Co-CoO (2.4 µm wide) lines has been obtained by oxygen ion implantation into a lithographically masked Au-sandwiched Co thin film. Magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an effective positive giant magnetoresistance (GMR) behavior at room temperature. Conversely, anisotropic magnetoresistance and GMR contributions are distinguished at low temperature (i.e., 10 K) since the O-implanted areas become exchange coupled. This planar GMR is principally ascribed to the spatial modulation of coercivity in a spring-magnet-type configuration, which results in 180° Néel extrinsic domain walls at the Co/Co-CoO interfaces. The versatility, in terms of pattern size, morphology, and composition adjustment, of this method offers a unique route to fabricate planar systems for, among others, spintronic research and applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Production of biofunctionalized MoS2 flakes with rationally modified lysozyme: A biocompatible 2D hybrid material

    Siepi M., Morales-Narváez E., Domingo N., Monti D.M., Notomista E., Merkoçi A. 2D Materials; 4 (3, 035007) 2017. 10.1088/2053-1583/aa7966. IF: 6.937

    Bioapplications of 2D materials embrace demanding features in terms of environmental impact, toxicity and biocompatibility. Here we report on the use of a rationally modified lysozyme to assist the exfoliation of Mos2 bulk crystals suspended in water through ultrasonic exfoliation. The design of the proposed lysozyme derivative provides this exfoliated 2D-materail with both, hydrophobic groups that interact with the surface of Mos2 and hydrophilic groups exposed to the aqueous medium, which hinders its re-Aggregation. This approach, clarified also by molecular docking studies, leads to a stable material (ζ-potential, 27 ?} 1 mV) with a yield of up to 430 μg ml-1. The bio-hybrid material was characterized in terms of number of layers and optical properties according to different slots separated by diverse centrifugal forces. Furthermore the obtained material was proved to be biocompatible using human normal keratinocytes and human cancer epithelial cells, whereas the method was demonstrated to be applicable to produce other 2D materials such as graphene. This approach is appealing for the advantageous production of high quality Mos2 flakes and their application in biomedicine and biosensing. Moreover, this method can be applied to different starting materials, making the denatured lysozyme a promising bio-Tool for surface functionalization of 2D materials. © 2017 IOP Publishing Ltd.


  • Conductance of Threading Dislocations in InGaAs/Si Stacks by Temperature-CAFM Measurements

    Couso C., Iglesias V., Porti M., Claramunt S., Nafría M., Domingo N., Cordes A., Bersuker G. IEEE Electron Device Letters; 37 (5, 7422696): 640 - 643. 2016. 10.1109/LED.2016.2537051. IF: 2.528

    The stacks of III-V materials, grown on the Si substrate, that are considered for the fabrication of highly scaled devices tend to develop structural defects, in particular threading dislocations (TDs), which affect device electrical properties. We demonstrate that the characteristics of the TD sites can be analyzed by using the conductive atomic force microscopy technique with nanoscale spatial resolution within a wide temperature range. In the studied InGaAs/Si stacks, electrical conductance through the TD sites was found to be governed by the Poole-Frenkel emission, while the off-TDs conductivity is dominated by the thermionic emission process. © 1980-2012 IEEE.

  • Ferroelectric Domain Structures in Low-Strain BaTiO3

    Everhardt A.S., Matzen S., Domingo N., Catalan G., Noheda B. Advanced Electronic Materials; 2 (1, 1500214) 2016. 10.1002/aelm.201500214. IF: 0.000

    Epitaxial strain in ferroelectric films offers the possibility to enhance the piezoelectric performance utilizing low crystal symmetries and high density of domain walls. Ferroelectric BaTiO3 has been predicted to order in a variety of phases and domain configurations when grown under low strain on low mismatched substrates, but little experimental evidence of that region of the phase diagram exist. Here, epitaxial BaTiO3 thin films are grown on NdScO3 substrates under ≈0.1% strain. A monoclinic ca1/ca2 phase, with 90° periodic in-plane domain configuration and small additional out-of-plane component of polarization, is stabilized at room temperature and investigated using piezoelectric force microscopy and X-ray diffraction. Above 50 °C, this phase is transformed into an a/c phase with alternating in-plane and out-of-plane polarizations and forming zigzag domain walls between up-polarized and down-polarized superdomains. Both types of domain patterns are highly anisotropic, giving rise to very long domain walls. Above 130 °C, the paraelectric phase is observed. The occurrence of a phase transition close to room temperature, a low symmetry ca1/ca2 phase, and the formation of periodic domains make of this material a promising candidate for high piezoelectric response. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Freezing the Nonclassical Crystal Growth of a Coordination Polymer Using Controlled Dynamic Gradients

    Rubio-Martinez M., Imaz I., Domingo N., Abrishamkar A., Mayor T.S., Rossi R.M., Carbonell C., deMello A.J., Amabilino D.B., Maspoch D., Puigmartí-Luis J. Advanced Materials; : 8150 - 8155. 2016. 10.1002/adma.201506462. IF: 18.960

    An experiment was conducted to show that diffusion-limited and kinetically controlled growth regimes occurring in microfluidic devices can provide valuable insights into crystallization processes. The microfluidic channels employed in this study were structured in PDMS master form fabricated by standard photolithographic techniques. Before attaching the cured and structured PDMS mould to a glass coverslip through plasma activation, inlet holes connecting the microfluidic channels were punched with a Biopsy puncher. The cross-sectional dimensions of the microchannels were 50 μm into 50 μm for the four input microchannels, and 250 μm into 50 μm for the main reactor channel. The total length of the main reactor channel was 9 mm. Data were indexed, integrated, and scaled using HKL2000 software. The H atoms were included in theoretical positions but not refined. The low max value was due to the data collection process, which was performed in the BM16 line with only a phi scan. The structure was solved by direct methods using the program SHELXS-97. The AFM results suggest that the early stage isolated seeds organize at a single level and in a perpendicular fashion, leading to the final plate-like crystalline morphologies observed in bulk and at an FFR of 0.1.

  • Identification of HIV-1–Based Virus-like Particles by Multifrequency Atomic Force Microscopy

    González-Domínguez I., Gutiérrez-Granados S., Cervera L., Gòdia F., Domingo N. Biophysical Journal; 111 (6): 1173 - 1179. 2016. 10.1016/j.bpj.2016.07.046. IF: 3.632

    Virus-like particles (VLPs) have become a promising platform for vaccine production. VLPs are formed by structural viral proteins that inherently self-assemble when expressed in a host cell. They represent a highly immunogenic and safe vaccine platform, due to the absence of the viral genome and its high protein density. One of the most important parameters in vaccine production is the quality of the product. A related bottleneck in VLP-based products is the presence of cellular vesicles as a major contaminant in the preparations, which will require the set up of techniques allowing for specific discrimination of VLPs from host vesicular bodies. In this work novel, to our knowledge, multifrequency (MF) atomic force microscopy (AFM) has permitted full structural nanophysical characterization by its access to the virus capsid of the HIV-based VLPs. The assessment of these particles by advanced amplitude modulation-frequency modulation (AM-FM) viscoelastic mapping mode has enhanced the imaging resolution of their nanomechanical properties, opening a new window for the study of the biophysical attributes of VLPs. Finally, the identification and differentiation of HIV-based VLPs from cellular vesicles has been performed under ambient conditions, providing, to our knowledge, novel methodology for the monitoring and quality control of VLPs. © 2016 Biophysical Society

  • Monolithic integration of room-temperature multifunctional BaTiO 3 -CoFe 2 O 4 epitaxial heterostructures on Si(001)

    Scigaj M., Dix N., Gázquez J., Varela M., Fina I., Domingo N., Herranz G., Skumryev V., Fontcuberta J., Sánchez F. Scientific Reports; 6 ( 31870) 2016. 10.1038/srep31870. IF: 5.228

    The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe 2 O 4 /BaTiO 3 bilayers are integrated with Si(001) using LaNiO 3 /CeO 2 /YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature. © The Author(s) 2016.

  • Piezoelectric Templates - New Views on Biomineralization and Biomimetics

    Stitz N., Eiben S., Atanasova P., Domingo N., Leineweber A., Burghard Z., Bill J. Scientific Reports; 6 ( 26518) 2016. 10.1038/srep26518. IF: 5.228

    Biomineralization in general is based on electrostatic interactions and molecular recognition of organic and inorganic phases. These principles of biomineralization have also been utilized and transferred to bio-inspired synthesis of functional materials during the past decades. Proteins involved in both, biomineralization and bio-inspired processes, are often piezoelectric due to their dipolar character hinting to the impact of a template's piezoelectricity on mineralization processes. However, the piezoelectric contribution on the mineralization process and especially the interaction of organic and inorganic phases is hardly considered so far. We herein report the successful use of the intrinsic piezoelectric properties of tobacco mosaic virus (TMV) to synthesize piezoelectric ZnO. Such films show a two-fold increase of the piezoelectric coefficient up to 7.2 pm V-1 compared to films synthesized on non-piezoelectric templates. By utilizing the intrinsic piezoelectricity of a biotemplate, we thus established a novel synthesis pathway towards functional materials, which sheds light on the whole field of biomimetics. The obtained results are of even broader and general interest since they are providing a new, more comprehensive insight into the mechanisms involved into biomineralization in living nature.

  • Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

    Golvano-Escobal I., Gonzalez-Rosillo J.C., Domingo N., Illa X., López-Barberá J.F., Fornell J., Solsona P., Aballe L., Foerster M., Surinãch S., Baró M.D., Puig T., Pané S., Nogués J., Pellicer E., Sort J. Scientific Reports; 6 ( 30398) 2016. 10.1038/srep30398. IF: 5.228

    Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.

  • Water Affinity and Surface Charging at the z-Cut and y-Cut LiNbO3 Surfaces: An Ambient Pressure X-ray Photoelectron Spectroscopy Study

    Cordero-Edwards K., Rodríguez L., Calò A., Esplandiu M.J., Pérez-Dieste V., Escudero C., Domingo N., Verdaguer A. Journal of Physical Chemistry C; 120 (42): 24048 - 24055. 2016. 10.1021/acs.jpcc.6b05465. IF: 4.509

    Polarization dependence of water adsorption and desorption on LiNbO3 surfaces was demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under near-ambient conditions. Positive and negative (0001) faces (z-cut) of the same crystal were compared for the same temperature and pressure conditions. Our results indicate a preferential adsorption on the positive face of the crystal with increasing water pressure and also higher desorption temperature of the adsorbed molecular water at the positive face. Adsorption measurements on the (1100) face (y-cut) showed also strong affinity to water, as observed for the z-cut positive surface. We found a direct relation between the capacity of the surface to discharge and/or to screen surface charges and the affinity for water of each face. XPS spectra indicate the presence of OH groups at the surface for all the conditions and surfaces measured. © 2016 American Chemical Society.


  • Enhanced conduction and ferromagnetic order at (100)-type twin walls in L a0.7 S r0.3Mn O3 thin films

    Balcells L., Paradinas M., Baguès N., Domingo N., Moreno R., Galceran R., Walls M., Santiso J., Konstantinovic Z., Pomar A., Casanove M.-J., Ocal C., Martínez B., Sandiumenge F. Physical Review B - Condensed Matter and Materials Physics; 92 (7, 075111) 2015. 10.1103/PhysRevB.92.075111. IF: 3.736

    There is increasing evidence supporting the strong potential of twin walls in ferroic materials as distinct, spatially tunable, functional elements in future electronic devices. Here, we report an increase of about one order of magnitude in conductivity and more robust magnetic interactions at (100)-type twin walls in La0.7Sr0.3MnO3 thin films. The nature and microscopic origin of such distinctive behavior is investigated by combining conductive, magnetic, and force modulation scanning force microscopies with transmission electron microscopy techniques. Our analyses indicate that the observed behavior is due to a severe compressive strained state within an ∼1nm slab of material centered at the twin walls, promoting stronger Mn 3d-O2p orbital overlapping leading to a broader bandwidth and enhanced magnetic interactions. © 2015 American Physical Society.

  • Giant reversible nanoscale piezoresistance at room temperature in Sr2IrO4 thin films

    Domingo N., López-Mir L., Paradinas M., Holy V., Železný J., Yi D., Suresha S.J., Liu J., Rayan Serrao C., Ramesh R., Ocal C., Martí X., Catalan G. Nanoscale; 7 (8): 3453 - 3459. 2015. 10.1039/c4nr06954d. IF: 7.394

    Layered iridates have been the subject of intense scrutiny on account of their unusually strong spin-orbit coupling, which opens up a narrow bandgap in a material that would otherwise be a metal. This insulating state is very sensitive to external perturbations. Here, we show that vertical compression at the nanoscale, delivered using the tip of a standard scanning probe microscope, is capable of inducing a five orders of magnitude change in the room temperature resistivity of Sr2IrO4. The extreme sensitivity of the electronic structure to anisotropic deformations opens up a new angle of interest on this material, with the giant and fully reversible perpendicular piezoresistance rendering iridates as promising materials for room temperature piezotronic devices. This journal is © The Royal Society of Chemistry.

  • Persistence of ferroelectricity above the Curie temperature at the surface of Pb(Z n1/3 N b2/3) O3-12%PbTi O3

    Domingo N., Bagués N., Santiso J., Catalan G. Physical Review B - Condensed Matter and Materials Physics; 91 (9, 094111) 2015. 10.1103/PhysRevB.91.094111. IF: 3.736

    Relaxor-based ferroelectrics have been known for decades to possess a relatively thick surface layer ("skin") that is distinct from its interior. Yet while there is consensus about its existence, there are controversies about its symmetry, phase stability, and origin. In an attempt to clarify these issues, we have examined the surface layer of PZN-12%PT. While the bulk transitions from a ferroelastically twinned tetragonal ferroelectric state with in-plane polarization to a cubic paraphase at Tc=200C, the skin layer shows a robust labyrinthine nanodomain structure with out-of-plane polarization that persists hundreds of degrees above the bulk Curie temperature. Cross-sectional transmission electron microscopy analysis shows that the resilience of the skin's polarization is correlated with a compositional imbalance: lead vacancies at the surface are charge-compensated by niobium enrichment; the excess of Nb5+ - a small ion with d0 orbital occupancy - stabilizes the ferroelectricity of the skin layer. © 2015 American Physical Society.

  • Revealing water films structure from force reconstruction in dynamic AFM

    Calò A., Domingo N., Santos S., Verdaguer A. Journal of Physical Chemistry C; 119 (15): 8258 - 8265. 2015. 10.1021/acs.jpcc.5b02411. IF: 4.772

    The structure of water films in contact with surfaces has direct implications in many important interfacial processes, from biology to climatology, as well as in ice nucleation. Here we report on the detection of individual ice-like water layers adsorbed on surfaces in ambient conditions. Reconstructed force profiles obtained in amplitude modulation atomic force microscopy (AM-AFM) on top of (111) BaF2 surfaces, with a lattice constant close to the distance of facing water molecules in hexagonal ice (Ih), showed characteristic oscillations in the attractive regime with a periodicity of 3.7 Å. This distance matches the thickness of a bilayer of Ih ice and is absent in force profiles on (111) CaF2 surfaces, which show a different lattice parameter. A thickness of 2.6 Å is measured for the first water layer in contact with the surface, corresponding to a high-density liquid film structure predicted from calculations in the literature. Our results indicate that, although epitaxial Ih growth of the first water layer on BaF2 crystals is not observed, the matching of the lattice parameter between Ih and BaF2 does induce a strong ordering of the water films and the formation of ice-like structures, even at room temperature. © 2015 American Chemical Society.

  • Spectroscopy Methods for Molecular Nanomagnets

    Baker M.L., Blundell S.J., Domingo N., Hill S. Structure and Bonding; 164: 231 - 291. 2015. 10.1007/430_2014_155.

    This chapter provides a detailed overview of some of the primary spectroscopic methods that have contributed to the current understanding of molecular nanomagnets (MNs). These include: electron paramagnetic resonance (EPR); optical spectroscopy, including magnetic and X-ray magnetic circular dichroism (MCD/XMCD); inelastic neutron scattering (INS); and muon spin rotation (μ +SR). For each technique, a historical survey of the most important discoveries is provided, up to and including the most recent developments. Each section gives an introduction to the theoretical principles underpinning the techniques, as well as a description of experimental requirements and protocols. A common theme among the described spectroscopies is the fact that state-of-the-art measurements typically have to be performed at major research facilities such as synchrotrons (terahertz EPR and XMCD), high magnetic field laboratories (EPR), and accelerator facilities or reactors (INS and μ +SR). Details of such facilities are given where appropriate. Forefront issues that are addressed in the chapter include: the fundamental properties of both mono- and poly-nuclear single-molecule magnets (SMMs); the deployment of MNs in quantum information processing applications; the addressing of individual magnetic molecules on surfaces or in devices; the probing of spin dynamics in MNs using EPR, INS, and μ +SR; and studies of long-range magnetic ordering in MN crystals. An extensive list of references is provided. The chapter is intended for physicists, chemists, and materials scientists, particularly junior researchers who are just starting work in the field. © 2015 Springer-Verlag Berlin Heidelberg.

  • Threading dislocations in III-V semiconductors: Analysis of electrical conduction

    Iglesias V., Porti M., Couso C., Wu Q., Claramunt S., Nafría M., Miranda E., Domingo N., Bersuker G., Cordes A. IEEE International Reliability Physics Symposium Proceedings; 2015-May (7112788): CD41 - CD46. 2015. 10.1109/IRPS.2015.7112788.

    The implementation of devices with high mobility substrates requires growing III-V semiconductors over the underlying silicon substrates. However, due to the lattice mismatch, III-V materials tend to develop a significant density of structural defects, which may affect the device electrical characteristics. In this study, Threading Dislocation (TD) defects, which may propagate through the III-V layers, were studied using Conductive Atomic force Microscopy (CAFM). This technique is shown to be effective for identification and analysis at the nanoscale of the pre- and post-electrically stressed TD. The TD conduction studied at different temperatures (T) is shown to be consistent with the Poole-Frenkel (PF) emission process. © 2015 IEEE.