Oxide Nanophysics Group

Group Leader: Gustau Catalán

Publications

2018

  • A Solar Transistor and Photoferroelectric Memory

    Pérez-Tomás A., Lima A., Billon Q., Shirley I., Catalan G., Lira-Cantú M. Advanced Functional Materials; 28 (17, 1707099) 2018. 10.1002/adfm.201707099.

    This study presents a new self-powered electronic transistor concept “the solar transistor.” The transistor effect is enabled by the functional integration of a ferroelectric-oxide thin film and an organic bulk heterojunction. The organic heterojunction efficiently harvests photon energy and splits photogenerated excitons into free electron and holes, and the ferroelectric film acts as a switchable electron transport layer with tuneable conduction band offsets that depend on its polarization state. This results in the device photoconductivity modulation. All this (i.e., carrier extraction and poling) is achieved with only two sandwiched electrodes and therefore, with the role of the gating electrode being taken by light. The two-terminal solar-powered phototransistor (or solaristor) thus has the added advantages of a compact photodiode architecture in addition to the nonvolatile functionality of a ferroelectric memory that is written by voltage and nondestructively read by light. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Flexoelectricity in antiferroelectrics

    Vales-Castro P., Roleder K., Zhao L., Li J.-F., Kajewski D., Catalan G. Applied Physics Letters; 113 (13, 132903) 2018. 10.1063/1.5044724.

    Flexoelectricity (coupling between polarization and strain gradients) is a property of all dielectric materials that has been theoretically known for decades, but only relatively recently it has begun to attract experimental attention. As a consequence, there are still entire families of materials whose flexoelectric performance is unknown. Such is the case of antiferroelectrics: materials with an antiparallel but switchable arrangement of dipoles. These materials are expected to be flexoelectrically relevant because it has been hypothesised that flexoelectricity could be linked to the origin of their antiferroelectricity. In this work, we have measured the flexoelectricity of two different antiferroelectrics (PbZrO3 and AgNbO3) as a function of temperature, up to and beyond their Curie temperature. Although their flexocoupling shows a sharp peak at the antiferroelectric phase transition, neither flexoelectricity nor the flexocoupling coefficients are anomalously high, suggesting that it is unlikely that flexoelectricity causes antiferroelectricity. © 2018 Author(s).


  • Flexoelectricity in Bones

    Vasquez-Sancho F., Abdollahi A., Damjanovic D., Catalan G. Advanced Materials; 30 (9, 1705316) 2018. 10.1002/adma.201705316.

    Bones generate electricity under pressure, and this electromechanical behavior is thought to be essential for bone's self-repair and remodeling properties. The origin of this response is attributed to the piezoelectricity of collagen, which is the main structural protein of bones. In theory, however, any material can also generate voltages in response to strain gradients, thanks to the property known as flexoelectricity. In this work, the flexoelectricity of bone and pure bone mineral (hydroxyapatite) are measured and found to be of the same order of magnitude; the quantitative similarity suggests that hydroxyapatite flexoelectricity is the main source of bending-induced polarization in cortical bone. In addition, the measured flexoelectric coefficients are used to calculate the (flexo)electric fields generated by cracks in bone mineral. The results indicate that crack-generated flexoelectricity is theoretically large enough to induce osteocyte apoptosis and thus initiate the crack-healing process, suggesting a central role of flexoelectricity in bone repair and remodeling. © 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.

    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


  • Substrate Dependence of the Freezing Dynamics of Supercooled Water Films: A High-Speed Optical Microscope Study

    Pach E., Rodriguez L., Verdaguer A. Journal of Physical Chemistry B; 122 (2): 818 - 826. 2018. 10.1021/acs.jpcb.7b06933.

    The freezing of supercooled water films on different substrates was investigated using a high-speed camera coupled to an optical microscope, obtaining details of the freezing process not described in the literature before. We observed the two well known freezing stages (fast dendritic growth and slow freezing of the water liquid left after the dendritic growth), but we separated the process into different phenomena that were studied separately: two-dimensional dendrite growth on the substrate interface, vertical dendrite growth, formation and evolution of ice domains, trapping of air bubbles and freezing of the water film surface. We found all of these processes to be dependent on both the supercooling temperature and the substrate used. Ice dendrite (or ice front) growth during the first stage was found to be dependent on thermal properties of the substrate but could not be unequivocally related to them. Finally, for low supercooling, a direct relationship was observed between the morphology of the dendrites formed in the first stage, which depends on the substrate, and the roughness and the shape of the surface of the ice, when freezing of the film was completed. This opens the possibility of using surfaces and coatings to control ice morphology beyond anti-icing properties. © 2017 American Chemical Society.


  • Wide and ultra-wide bandgap oxides: Where paradigm-shift photovoltaics meets transparent power electronics

    Pérez-Tomás A., Chikoidze E., Jennings M.R., Russell S.A.O., Teherani F.H., Bove P., Sandana E.V., Rogers D.J. Proceedings of SPIE - The International Society for Optical Engineering; 10533 ( 105331Q) 2018. 10.1117/12.2302576.

    Oxides represent the largest family of wide bandgap (WBG) semiconductors and also offer a huge potential range of complementary magnetic and electronic properties, such as ferromagnetism, ferroelectricity, antiferroelectricity and high-temperature superconductivity. Here, we review our integration of WBG and ultra WBG semiconductor oxides into different solar cells architectures where they have the role of transparent conductive electrodes and/or barriers bringing unique functionalities into the structure such above bandgap voltages or switchable interfaces. We also give an overview of the state-of-the-art and perspectives for the emerging semiconductor β- Ga2O3, which is widely forecast to herald the next generation of power electronic converters because of the combination of an UWBG with the capacity to conduct electricity. This opens unprecedented possibilities for the monolithic integration in solar cells of both self-powered logic and power electronics functionalities. Therefore, WBG and UWBG oxides have enormous promise to become key enabling technologies for the zero emissions smart integration of the internet of things. © Copyright 2018 SPIE.


2017

  • Cryogenic characterisation and modelling of commercial SiC MOSFETs

    Woodend L.J., Gammon P.M., Shah V.A., Pérez-Tomás A., Li F., Hamilton D.P., Myronov M., Mawby P.A. Materials Science Forum; 897 MSF: 557 - 560. 2017. 10.4028/www.scientific.net/MSF.897.557. IF: 0.399

    Two commercial 1.2 kV SiC MOSFETs have been extensively characterised from 30 to 320 K. The temperature dependence of their I/V characteristics, threshold voltage, and breakdown voltage has been examined and are presented in this paper. Overall, the measured characteristics of both devices demonstrate very similar temperature dependencies and it is shown that below ~100 K any further decrease in temperature has little effect on any of the tested characteristics. Increasing temperature beyond 100 K results in a decrease in drain current for a given drain-source and gatesource voltage, a decrease in threshold voltage, and an increase in breakdown voltage. Successful attempts have been made to model the results of these tests by applying theories found in the literature. © 2017 Trans Tech Publications, Switzerland.


  • 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.


  • Epitaxial Growth of SrTiO3 Films on Cube-Textured Cu-Clad Substrates by PLD at Low Temperature Under Reducing Atmosphere

    Padilla J.A., Xuriguera E., Rodríguez L., Vannozzi A., Segarra M., Celentano G., Varela M. Nanoscale Research Letters; 12 (1, 226) 2017. 10.1186/s11671-017-1997-9. IF: 2.833

    The growth of epitaxial {001}<100> SrTiO3 (STO) on low-cost cube-textured Cu-based clad substrate at low temperature was carried out by means of pulsed laser deposition (PLD). STO film was deposited in one step under a reducing atmosphere (5% H2 and 95% Ar mixture) to prevent the oxidation of the metal surface. The optimization of PLD parameters leads to a sharpest biaxial texture at a temperature as low as 500 °C and a thickness of 500 nm with a (100) STO layer. The upper limit of highly textured STO thickness was also investigated. The maximum thickness which retains the best quality {001}<100> texture is 800 nm, since the texture is preserved not only through the layer but also on the surface. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements showed that STO films are continuous, dense, and smooth with very low roughness (between 5 and 7 nm). This paper describes the development of STO layer by means of PLD in absence of oxygen throughout the process, suggesting an alternative and effective method for growing highly {001}<100> textured STO layer on low-cost metal substrates. © 2017, The Author(s).


  • 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


  • Functional oxide as an extreme high-k dielectric towards 4H-SiC MOSFET incorporation

    Russell S.A.O., Jennings M.R., Dai T., Li F., Hamilton D.P., Fisher C.A., Sharma Y.K., Mawby P.A., Pérez-Tomás A. Materials Science Forum; 897 MSF: 155 - 158. 2017. 10.4028/www.scientific.net/MSF.897.155. IF: 0.399

    MOS Capacitors are demonstrated on 4H-SiC using an octahedral ABO3 ferroic thin-film as a dielectric prepared on several buffer layers. Five samples were prepared: ABO3 on SiC, ABO3 on SiC with a SiO2 buffer (10 nm and 40 nm) and ABO3 on SiC with an Al2O3 buffer (10nm and 40 nm). Depending on the buffer material the oxide forms in either the pyrochlore or perovskite phase. A better lattice match with the Al2O3 buffer yields a perovskite phase with internal switchable dipoles. Hysteresis polarization-voltage loops show an oxide capacitance of ~ 0.2 μF/cm2 in the accumulation region indicating a dielectric constant of ~120. © 2017 Trans Tech Publications, Switzerland.


  • Heteroepitaxial Beta-Ga2O3 on 4H-SiC for an FET with Reduced Self Heating

    Russell S.A.O., Perez-Tomas A., McConville C.F., Fisher C.A., Hamilton D.P., Mawby P.A., Jennings M.R. IEEE Journal of the Electron Devices Society; 5 (4, 7932063): 256 - 261. 2017. 10.1109/JEDS.2017.2706321. IF: 3.141

    A method to improve thermal management of ${\beta }$ -Ga2O3 FETs is demonstrated here via simulation of epitaxial growth on a 4H-SiC substrate. Using a recently published device as a model, the reduction achieved in self-heating allows the device to be driven at higher gate voltages and increases the overall performance. For the same operating parameters an 18% increase in peak drain current and 15% reduction in lattice temperature are observed. Device dimensions may be substantially reduced without detriment to performance and normally off operation may be achieved. © 2013 IEEE.


  • Hidden Magnetic States Emergent under Electric Field, in A Room Temperature Composite Magnetoelectric Multiferroic

    Clarkson J.D., Fina I., Liu Z.Q., Lee Y., Kim J., Frontera C., Cordero K., Wisotzki S., Sanchez F., Sort J., Hsu S.L., Ko C., Aballe L., Foerster M., Wu J., Christen H.M., Heron J.T., Schlom D.G., Salahuddin S., Kioussis N., Fontcuberta J., Marti X., Ramesh R. Scientific Reports; 7 (1, 15460) 2017. 10.1038/s41598-017-13760-y. IF: 4.259

    The ability to control a magnetic phase with an electric field is of great current interest for a variety of low power electronics in which the magnetic state is used either for information storage or logic operations. Over the past several years, there has been a considerable amount of research on pathways to control the direction of magnetization with an electric field. More recently, an alternative pathway involving the change of the magnetic state (ferromagnet to antiferromagnet) has been proposed. In this paper, we demonstrate electric field control of the Anomalous Hall Transport in a metamagnetic FeRh thin film, accompanying an antiferromagnet (AFM) to ferromagnet (FM) phase transition. This approach provides us with a pathway to "hide" or "reveal" a given ferromagnetic region at zero magnetic field. By converting the AFM phase into the FM phase, the stray field, and hence sensitivity to external fields, is decreased or eliminated. Using detailed structural analyses of FeRh films of varying crystalline quality and chemical order, we relate the direct nanoscale origins of this memory effect to site disorder as well as variations of the net magnetic anisotropy of FM nuclei. Our work opens pathways toward a new generation of antiferromagnetic - ferromagnetic interactions for spintronics. © 2017 The Author(s).


  • High-Temperature Electrical and Thermal Aging Performance and Application Considerations for SiC Power DMOSFETs

    Hamilton D.P., Jennings M.R., Perez-Tomas A., Russell S.A.O., Hindmarsh S.A., Fisher C.A., Mawby P.A. IEEE Transactions on Power Electronics; 32 (10, 7776925): 7967 - 7979. 2017. 10.1109/TPEL.2016.2636743. IF: 7.151

    The temperature dependence and stability of three different commercially-available unpackaged SiC Dmosfets have been measured. On-state resistances increased to 6 or 7 times their room temperature values at 350 °C. Threshold voltages almost doubled after tens of minutes of positive gate voltage stressing at 300 °C, but approached their original values again after only one or two minutes of negative gate bias stressing. Fortunately, the change in drain current due to these threshold instabilities was almost negligible. However, the threshold approaches zero volts at high temperatures after a high temperature negative gate bias stress. The zero gate bias leakage is low until the threshold voltage reduces to approximately 150 mV, where-after the leakage increases exponentially. Thermal aging tests demonstrated a sudden change from linear to nonlinear output characteristics after 24-100 h air storage at 300 °C and after 570-1000 h in N2 atmosphere. We attribute this to nickel oxide growth on the drain contact metallization which forms a heterojunction p-n diode with the SiC substrate. It was determined that these state-of-the-art SiC mosfet devices may be operated in real applications at temperatures far exceeding their rated operating temperatures. © 1986-2012 IEEE.


  • 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


  • On the persistence of polar domains in ultrathin ferroelectric capacitors

    Zubko P., Lu H., Bark C.-W., Martí X., Santiso J., Eom C.-B., Catalan G., Gruverman A. Journal of Physics Condensed Matter; 29 (28, 284001) 2017. 10.1088/1361-648X/aa73c3. IF: 2.678

    The instability of ferroelectric ordering in ultra-thin films is one of the most important fundamental issues pertaining realization of a number of electronic devices with enhanced functionality, such as ferroelectric and multiferroic tunnel junctions or ferroelectric field effect transistors. In this paper, we investigate the polarization state of archetypal ultrathin (several nanometres) ferroelectric heterostructures: epitaxial single-crystalline BaTiO3 films sandwiched between the most habitual perovskite electrodes, SrRuO3, on top of the most used perovskite substrate, SrTiO3. We use a combination of piezoresponse force microscopy, dielectric measurements and structural characterization to provide conclusive evidence for the ferroelectric nature of the relaxed polarization state in ultrathin BaTiO3 capacitors. We show that even the high screening efficiency of SrRuO3 electrodes is still insufficient to stabilize polarization in SrRuO3/BaTiO3/SrRuO3 heterostructures at room temperature. We identify the key role of domain wall motion in determining the macroscopic electrical properties of ultrathin capacitors and discuss their dielectric response in the light of the recent interest in negative capacitance behaviour. © 2017 IOP Publishing Ltd.


  • P-type beta-gallium oxide: A new perspective for power and optoelectronic devices

    Chikoidze E., Fellous A., Perez-Tomas A., Sauthier G., Tchelidze T., Ton-That C., Than Huynh T., Phillips M., Russell S., Jennings M., Berini B., Jomard F., Dumont Y. Materials Today Physics; 3: 118 - 126. 2017. 10.1016/j.mtphys.2017.10.002.

    Wide-bandgap semiconductors (WBG) are expected to be applied to solid-state lighting and power devices, supporting a future energy-saving society. Here we present evidence of p-type conduction in the undoped WBG β-Ga2O3. Hole conduction, established by Hall and Seebeck measurements, is consistent with findings from photoemission and cathodoluminescence spectroscopies. The ionization energy of the acceptor level was measured to be 1.1eV above the valence band edge. The gallium vacancy was identified as a possible acceptor candidate based on thermodynamic equilibrium Ga2O3 (crystal) – O2 (gas) system calculations (Kroger theory) which revealed a window without oxygen vacancy compensation. The possibility of fabricating large diameter wafers of β-Ga2O3 of p and n type nature, provides new avenues for high power and deep UV-optoelectronic devices.


  • Physical characterisation of 3C-SiC(001)/SiO2 interface using XPS

    Li F., Vavasour O., Walker M., Martin D.M., Sharma Y., Russell S., Jennings M., Pérez-Tomás A., Mawby P.A. Materials Science Forum; 897 MSF: 151 - 154. 2017. 10.4028/www.scientific.net/MSF.897.151. IF: 0.399

    Normally-on MOSFETs were fabricated on 3C-SiC epilayers (Si face) using high temperature (1300 °C) wet oxidation. XPS analysis found little carbon at the MOS interface yet the channel mobility (60 cm2/V.s) is considerably low. Si suboxides (SiOx, x<2) exist at the wet oxidised 3C-SiC/SiO2 interface, which may act as interface traps and degrade the conduction performance. © 2017 Trans Tech Publications, Switzerland.


  • 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.


2016

  • 3C-SiC Transistor with Ohmic Contacts Defined at Room Temperature

    Li F., Sharma Y., Walker D., Hindmarsh S., Jennings M., Martin D., Fisher C., Gammon P., Pérez-Tomás A., Mawby P. IEEE Electron Device Letters; 37 (9, 7518645): 1189 - 1192. 2016. 10.1109/LED.2016.2593771. IF: 2.528

    Among all SiC polytypes, only 3C-SiC has a cubic structure and can be hetero-epitaxial grown on large area Si substrate, thus providing an alternative choice for fabricating cheap wide bandgap power devices. Here, we present a low resistivity (~3 × 10-5Ω cm2) ohmic contact formed by directly depositing a Ti/Ni metal stack on n-type 3C-SiC without any extra annealing. For the first time, 3C-SiC lateral MOSFETs with asdeposited ohmic contacts were fabricated, and it turned out not only the ohmic contact is free from any interface voids, but also a higher field-effect mobility value (~80 cm2/V · s) was achieved compared with the annealed devices. © 1980-2012 IEEE.


  • A flexoelectric microelectromechanical system on silicon

    Bhaskar U.K., Banerjee N., Abdollahi A., Wang Z., Schlom D.G., Rijnders G., Catalan G. Nature Nanotechnology; 11 (3): 263 - 266. 2016. 10.1038/nnano.2015.260. IF: 35.267

    Flexoelectricity allows a dielectric material to polarize in response to a mechanical bending moment and, conversely, to bend in response to an electric field. Compared with piezoelectricity, flexoelectricity is a weak effect of little practical significance in bulk materials. However, the roles can be reversed at the nanoscale. Here, we demonstrate that flexoelectricity is a viable route to lead-free microelectromechanical and nanoelectromechanical systems. Specifically, we have fabricated a silicon-compatible thin-film cantilever actuator with a single flexoelectrically active layer of strontium titanate with a figure of merit (curvature divided by electric field) of 3.33MV â '1, comparable to that of state-of-the-art piezoelectric bimorph cantilevers. © 2016 Macmillan Publishers Limited.


  • Above-Bandgap Photovoltages in Antiferroelectrics

    Pérez-Tomás A., Lira-Cantú M., Catalan G. Advanced Materials; 28 (43): 9644 - 9647. 2016. 10.1002/adma.201603176. IF: 18.960

    The closed circuit photocurrent and open circuit photovoltage of antiferroelectric thin films were characterized both in their ground (antipolar) state and in their polarized state. A sharp transition happens from near zero to large photovoltages as the polarization is switched on, consistent with the activation of the bulk photovoltaic effect. The AFE layers have been grown by a solution processing method (sol?gel synthesis followed by spin coating deposition) onto fluorine-doped tin oxide (FTO), a transparent conducting oxide with low sheet resistance and a higher resilience to high-temperature processing than indium tin oxide and a standard for solar cells such as organometal trihalide perovskites. Light absorption confirmed that the PZO films are, as expected, wide-band gap semiconductors with a gap of 3.7.8 eV and thus highly absorbing in the near-ultraviolet range. On a virgin sample, there is no shortcircuit photocurrent, consistent with the antipolar nature of the ground state. As an external bias voltage is applied, the current remains negligible until suddenly, at the coercive voltage, a spike is observed, corresponding to the transient displacement current caused by the onset of polarization.


  • 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.


  • Enhanced flexoelectric-like response in oxide semiconductors

    Narvaez J., Vasquez-Sancho F., Catalan G. Nature; 538 (7624): 219 - 221. 2016. 10.1038/nature19761. IF: 38.138

    Flexoelectricity is a property of all dielectric materials whereby they polarize in response to deformation gradients such as those produced by bending. Although it is generally thought of as a property of dielectric insulators, insulation is not a formal requirement: in principle, semiconductors can also redistribute their free charge in response to strain gradients. Here we show that bending a semiconductor not only generates a flexoelectric-like response, but that this response can in fact be much larger than in insulators. By doping single crystals of wide-bandgap oxides to increase their conductivity, their effective flexoelectric coefficient was increased by orders of magnitude. This large response can be explained by a barrier-layer mechanism that remains important even at the macroscale, where conventional (insulator) flexoelectricity otherwise tends to be small. Our results open up the possibility of using semiconductors as active ingredients in electromechanical transducer applications. © 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.


  • 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


  • Flexoelectric MEMS: Towards an electromechanical strain diode

    Bhaskar U.K., Banerjee N., Abdollahi A., Solanas E., Rijnders G., Catalan G. Nanoscale; 8 (3): 1293 - 1298. 2016. 10.1039/c5nr06514c. IF: 7.760

    Piezoelectricity and flexoelectricity are two independent but not incompatible forms of electromechanical response exhibited by nanoscale ferroelectrics. Here, we show that flexoelectricity can either enhance or suppress the piezoelectric response of the cantilever depending on the ferroelectric polarity and lead to a diode-like asymmetric (two-state) electromechanical response. © 2016 The Royal Society of Chemistry.


  • 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


  • Improved channel mobility by oxide nitridation for n-channel MOSFET on 3C-SiC(100)/Si

    Li F., Sharma Y.K., Jennings M.R., Pérez-Tomás A., Shah V.A., Rong H., Russell S.A.O., Martin D.M., Mawby P.A. Materials Science Forum; 858: 667 - 670. 2016. 10.4028/www.scientific.net/MSF.858.667. IF: 0.000

    In this work we studied the gate oxidation temperature and nitridation influences on the resultant 3C-SiC MOSFET forward characteristics. Conventional long channel lateral MOSFETs were fabricated on 3C-SiC(100) epilayers grown on Si substrates using five different oxidation processes. Both room temperature and high temperature (up to 500K) forward IV performance were characterised, and channel mobility as high as 90cm2/V.s was obtained for devices with nitrided gate oxide, considerable higher than the ones without nitridation process (~70 cm2/V.s). © 2016 Trans Tech Publications, Switzerland.


  • 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.


  • Performance and stability of mixed FAPbI3(0.85)MAPbBr3(0.15) halide perovskite solar cells under outdoor conditions and the effect of low light irradiation

    Reyna Y., Salado M., Kazim S., Pérez-Tomas A., Ahmad S., Lira-Cantu M. Nano Energy; 30: 570 - 579. 2016. 10.1016/j.nanoen.2016.10.053. IF: 11.553

    We demonstrate for the first time, the real lifetime response of mixed halide perovskite solar cells (PSCs) for >1000 h under outdoor conditions and the exceptional photoresponse observed at low-light intensities attributed to the ionic-electronic nature of the material. The investigated devices were fabricated by utilizing mixed perovskites containing formamidinium (FA) and methylammonium (MA) cations, in a one step solution-process method through a solvent engineering approach. The devices’ architecture is FTO/TiO2 (blocking layer) TiO2 (mesoporous)/FAPbI3(0.85)MAPbBr3(0.15)/Spiro-OMeTAD/Au. Notably, low short circuit current (Jsc) was observed at low light intensities (<50 W/m2) together with high open circuit potential build-up, which resulted in high PCEs. This response is in agreement with a “double electronic-ionic transport” model of the halide perovskite where the ionic component dominates at low light intensities and the electronic component dictates at high light irradiances. Our results highlight the exceptional stability of mixed MA/FA mesoscopic PSCs when operated for >1000 h under real outdoor conditions and the strong ionic component observed at low light irradiation. © 2016 Elsevier Ltd


  • 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.


2015

  • Dielectric relaxation in YMnO3 single crystals

    Adem U., Mufti N., Nugroho A.A., Catalan G., Noheda B., Palstra T.T.M. Journal of Alloys and Compounds; 638: 228 - 232. 2015. 10.1016/j.jallcom.2015.02.207. IF: 2.999

    We have investigated the origin of the dielectric relaxation in YMnO3 single crystals. Two distinct dielectric relaxation features were observed at low (200≤T≤373K) and high (300≤T≤450K) temperatures. Analysis of our detailed frequency, electrode and thickness dependent dielectric measurements and ac conductivity data as well as the use of single crystals allow us to get a comprehensive picture of these relaxations. The low temperature relaxation is attributed to the Maxwell-Wagner type effects originating from the dipoles at the surface while the high temperature one is suggested to originate from hopping of charge carriers resulting from the second ionization of oxygen vacancies. © 2015 Elsevier B.V. All rights reserved.


  • Electrical activation of nitrogen heavily implanted 3C-SiC(1 0 0)

    Li F., Sharma Y., Shah V., Jennings M., Pérez-Tomás A., Myronov M., Fisher C., Leadley D., Mawby P. Applied Surface Science; 353: 958 - 963. 2015. 10.1016/j.apsusc.2015.06.169. IF: 2.711

    A degenerated wide bandgap semiconductor is a rare system. In general, implant levels lie deeper in the band-gap and carrier freeze-out usually takes place at room temperature. Nevertheless, we have observed that heavily doped n-type degenerated 3C-SiC films are achieved by nitrogen implantation level of ∼6 × 1020 cm-3 at 20 K. According to temperature dependent Hall measurements, nitrogen activation rates decrease with the doping level from almost 100% (1.5 × 1019 cm-3, donor level 15 meV) to ∼12% for 6 × 1020 cm-3. Free donors are found to saturate in 3C-SiC at ∼7 × 1019 cm-3. The implanted film electrical performances are characterized as a function of the dopant doses and post implantation annealing (PIA) conditions by fabricating Van der Pauw structures. A deposited SiO2 layer was used as the surface capping layer during the PIA process to study its effect on the resultant film properties. From the device design point of view, the lowest sheet resistivity (∼1.4 mΩ cm) has been observed for medium doped (4 × 1019 cm-3) sample with PIA 1375 °C 2 h without a SiO2 cap. Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.


  • 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.


  • Ferroelectrics: Negative capacitance detected

    Catalan G., Jimenez D., Gruverman A. Nature Materials; 14 (2): 137 - 139. 2015. 10.1038/nmat4195. IF: 36.503

    [No abstract available]


  • Four-state ferroelectric spin-valve

    Quindeau A., Fina I., Marti X., Apachitei G., Ferrer P., Nicklin C., Pippel E., Hesse D., Alexe M. Scientific Reports; 5 ( 9749) 2015. 10.1038/srep09749. IF: 5.578

    Spin-valves had empowered the giant magnetoresistance (GMR) devices to have memory. The insertion of thin antiferromagnetic (AFM) films allowed two stable magnetic field-induced switchable resistance states persisting in remanence. In this letter, we show that, without the deliberate introduction of such an AFM layer, this functionality is transferred to multiferroic tunnel junctions (MFTJ) allowing us to create a four-state resistive memory device. We observed that the ferroelectric/ferromagnetic interface plays a crucial role in the stabilization of the exchange bias, which ultimately leads to four robust electro tunnel electro resistance (TER) and tunnel magneto resistance (TMR) states in the junction.


  • Fracture toughening and toughness asymmetry induced by flexoelectricity

    Abdollahi A., Peco C., Millán D., Arroyo M., Catalan G., Arias I. Physical Review B - Condensed Matter and Materials Physics; 92 (9, 094101) 2015. 10.1103/PhysRevB.92.094101. IF: 3.736

    Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity in fracture: the resistance to fracture increases as structural size decreases, and it becomes asymmetric with respect to the sign of polarization. The latter phenomenon manifests itself in a range of intermediate sizes where piezo- and flexoelectricity compete. In BaTiO3 at room temperature, this range spans from 0.1 to 50 nm, a typical thickness range for epitaxial ferroelectric thin films. © 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.


  • High-Temperature (1200–1400°C) Dry Oxidation of 3C-SiC on Silicon

    Sharma Y.K., Li F., Jennings M.R., Fisher C.A., Pérez-Tomás A., Thomas S., Hamilton D.P., Russell S.A.O., Mawby P.A. Journal of Electronic Materials; 44 (11): 4167 - 4174. 2015. 10.1007/s11664-015-3949-4. IF: 1.798

    In a novel approach, high temperatures (1200–1400°C) were used to oxidize cubic silicon carbide (3C-SiC) grown on silicon substrate. High-temperature oxidation does not significantly affect 3C-SiC doping concentration, 3C-SiC structural composition, or the final morphology of the SiO2 layer, which remains unaffected even at 1400°C (the melting point of silicon is 1414°C). Metal-oxide-semiconductor capacitors (MOS-C) and lateral channel metal-oxide-semiconductor field-effect-transistors (MOSFET) were fabricated by use of the high-temperature oxidation process to study 3C-SiC/SiO2 interfaces. Unlike 4H-SiC MOSFET, there is no extra benefit of increasing the oxidation temperature from 1200°C to 1400°C. All the MOSFET resulted in a maximum field-effect mobility of approximately 70 cm2/V s. © 2015, The Minerals, Metals & Materials Society.


  • In-plane tunnelling field-effect transistor integrated on Silicon

    Fina I., Apachitei G., Preziosi D., Deniz H., Kriegner D., Marti X., Alexe M. Scientific Reports; 5 ( 14367) 2015. 10.1038/srep14367. IF: 5.578

    Silicon has persevered as the primary substrate of microelectronics during last decades. During last years, it has been gradually embracing the integration of ferroelectricity and ferromagnetism. The successful incorporation of these two functionalities to silicon has delivered the desired non-volatility via charge-effects and giant magneto-resistance. On the other hand, there has been a numerous demonstrations of the so-called magnetoelectric effect (coupling between ferroelectric and ferromagnetic order) using nearly-perfect heterostructures. However, the scrutiny of the ingredients that lead to magnetoelectric coupling, namely magnetic moment and a conducting channel, does not necessarily require structural perfection. In this work, we circumvent the stringent requirements for epilayers while preserving the magnetoelectric functionality in a silicon-integrated device. Additionally, we have identified an in-plane tunnelling mechanism which responds to a vertical electric field. This genuine electroresistance effect is distinct from known resistive-switching or tunnel electro resistance.


  • Large Flexoelectric Anisotropy in Paraelectric Barium Titanate

    Narvaez J., Saremi S., Hong J., Stengel M., Catalan G. Physical Review Letters; 115 (3, 037601) 2015. 10.1103/PhysRevLett.115.037601. IF: 7.512

    The bending-induced polarization of barium titanate single crystals has been measured with an aim to elucidate the origin of the large difference between theoretically predicted and experimentally measured flexoelectricity in this material. The results indicate that part of the difference is due to polar regions (short-range order) that exist above TC and up to T∗≈200-225°C. Above T∗, however, the flexovoltage coefficient still shows an unexpectedly large anisotropy for a cubic material, with (001)-oriented crystals displaying 10 times more flexoelectricity than (111)-oriented crystals. Theoretical analysis shows that this anisotropy cannot be a bulk property, and we therefore interpret it as indirect evidence for the theoretically predicted but experimentally elusive contribution of surface piezoelectricity to macroscopic bending-induced polarization. © 2015 American Physical Society. © 2015 American Physical Society.


  • Mechanical tuning of LaAlO3/SrTiO3 interface conductivity

    Sharma P., Ryu S., Burton J.D., Paudel T.R., Bark C.W., Huang Z., Ariando, Tsymbal E.Y., Catalan G., Eom C.B., Gruverman A. Nano Letters; 15 (5): 3547 - 3551. 2015. 10.1021/acs.nanolett.5b01021. IF: 13.592

    In recent years, complex-oxide heterostructures and their interfaces have become the focus of significant research activity, primarily driven by the discovery of emerging states and functionalities that open up opportunities for the development of new oxide-based nanoelectronic devices. The highly conductive state at the interface between insulators LaAlO3 and SrTiO3 is a prime example of such emergent functionality, with potential application in high electron density transistors. In this report, we demonstrate a new paradigm for voltage-free tuning of LaAlO3/SrTiO3 (LAO/STO) interface conductivity, which involves the mechanical gating of interface conductance through stress exerted by the tip of a scanning probe microscope. The mechanical control of channel conductivity and the long retention time of the induced resistance states enable transistor functionality with zero gate voltage. © 2015 American Chemical Society.


  • Nanomechanics of flexoelectric switching

    Očenášek J., Lu H., Bark C.W., Eom C.B., Alcalá J., Catalan G., Gruverman A. Physical Review B - Condensed Matter and Materials Physics; 92 (3, 035417) 2015. 10.1103/PhysRevB.92.035417. IF: 3.736

    We examine the phenomenon of flexoelectric switching of polarization in ultrathin films of barium titanate induced by a tip of an atomic force microscope (AFM). The spatial distribution of the tip-induced flexoelectricity is computationally modeled both for perpendicular mechanical load (point measurements) and for sliding load (scanning measurements), and compared with experiments. We find that (i) perpendicular load does not lead to stable ferroelectric switching in contrast to the load applied in the sliding contact load regime, due to nontrivial differences between the strain distributions in both regimes: ferroelectric switching for the perpendicular load mode is impaired by a strain gradient inversion layer immediately underneath the AFM tip; while for the sliding load regime, domain inversion is unimpaired within a greater material volume subjected to larger values of the mechanically induced electric field that includes the region behind the sliding tip; (ii) beyond a relatively small value of an applied force, increasing mechanical pressure does not increase the flexoelectric field inside the film, but results instead in a growing volume of the region subjected to such field that aids domain nucleation processes; and (iii) the flexoelectric coefficients of the films are of the order of few nC/m, which is much smaller than for bulk BaTiO3 ceramics, indicating that there is a "flexoelectric size effect" that mirrors the ferroelectric one. ©2015 American Physical Society.


  • Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor

    Pérez-Tomás A., Catalàn G., Fontserè A., Iglesias V., Chen H., Gammon P.M., Jennings M.R., Thomas M., Fisher C.A., Sharma Y.K., Placidi M., Chmielowska M., Chenot S., Porti M., Nafría M., Cordier Y. Nanotechnology; 26 (11, 115203) 2015. 10.1088/0957-4484/26/11/115203. IF: 3.821

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids>1 A mm-1) to be defined (0.5 A mm-1 at 300 C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current. © 2015 IOP Publishing Ltd.


  • 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.


  • Prospect for antiferromagnetic spintronics

    Marti X., Fina I., Jungwirth T. IEEE Transactions on Magnetics; 51 (4, 7109970) 2015. 10.1109/TMAG.2014.2358939. IF: 1.386

    Exploiting both spin and charge of the electron in electronic micordevices has lead to a tremendous progress in both basic condensed-matter research and microelectronic applications, resulting in the modern field of spintronics. Current spintronics relies primarily on ferromagnets while antiferromagnets (AFMs) have traditionally played only a supporting role. Recently, antiferromagnets have been revisited as potential candidates for the key active elements in spintronic devices. In this paper, we review approaches that have been employed for reading, writing, and storing information in AFMs. © 1965-2012 IEEE.


  • 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.


2014

  • Anisotropic magnetoresistance in an antiferromagnetic semiconductor

    Fina, I.; Marti, X.; Yi, D.; Liu, J.; Chu, J.H.; Rayan-Serrao, C.; Suresha, S.; Shick, A.B.; Ž elezný, J.; Jungwirth, T.; Fontcuberta, J.; Ramesh, R. Nature Communications; 5 2014. 10.1038/ncomms5671. IF: 10.742


  • Chemical strain and oxidation-reduction kinetics of epitaxial thin films of mixed ionic-electronic conducting oxides determined by x-ray diffraction

    Moreno, R.; Zapata, J.; Roqueta, J.; Bagués, N.; Santiso, J. Journal of the Electrochemical Society; 161 (11): F3046 - F3051. 2014. 10.1149/2.0091411jes. IF: 2.859


  • Electrocatalytic tuning of biosensing response through electrostatic or hydrophobic enzyme-graphene oxide interactions

    Baptista-Pires, L.; Pérez-López, B.; Mayorga-Martinez, C.C.; Morales-Narváez, E.; Domingo, N.; Esplandiu, M.J.; Alzina, F.; Torres, C.M.S.; Merkoçi, A. Biosensors and Bioelectronics; 61: 655 - 662. 2014. 10.1016/j.bios.2014.05.028. IF: 6.451


  • Improved performance of 4H-SiC PiN diodes using a novel combined high temperature oxidation and annealing process

    Fisher, C.A.; Jennings, M.R.; Sharma, Y.K.; Hamilton, D.P.; Gammon, P.M.; Pérez-Tomás, A.; Thomas, S.M.; Burrows, S.E.; Mawby, P.A. IEEE Transactions on Semiconductor Manufacturing; 27 (3): 443 - 451. 2014. 10.1109/TSM.2014.2336701. IF: 0.977


  • On the Schottky barrier height lowering effect of Ti3SiC2 in ohmic contacts to p-type 4H-SiC

    C. A. Fisher; M. R. Jennings; Y. K. Sharma; A. Sanchez; D. Walker; P. M. Gammon; A. Pérez-Tomás; S. M. Thomas; S. E. Burrows; P. A. Mawby International Journal of Fundamental Physical Sciences (IJFPS); 4 (3): 95 - 100. 2014. 10.14331/ijfps.2014.330071. IF: 0.000


  • Origin of the enhanced flexoelectricity of relaxor ferroelectrics

    Narvaez, J.; Catalan, G. Applied Physics Letters; 104 (16) 2014. 10.1063/1.4871686. IF: 3.515


  • Room-temperature negative capacitance in a ferroelectric-dielectric superlattice heterostructure

    Gao, W.; Khan, A.; Marti, X.; Nelson, C.; Serrao, C.; Ravichandran, J.; Ramesh, R.; Salahuddin, S. Nano Letters; 14 (10): 5814 - 5819. 2014. 10.1021/nl502691u. IF: 12.940


  • Spectroscopy methods for molecular nanomagnets

    Baker, M.L.; Blundell, S.J.; Domingo, N.; Hill, S. Structure and Bonding; 164: 231 - 292. 2014. 10.1007/430-2014-155. IF: 1.836


  • Spintronic functionality of BiFeO3domain walls

    Lee, J.H.; Fina, I.; Marti, X.; Kim, Y.H.; Hesse, D.; Alexe, M. Advanced Materials; 26 (41): 7078 - 7082. 2014. 10.1002/adma.201402558. IF: 15.409


  • Tailoring the interfacial magnetic anisotropy in multiferroic field-effect devices

    Preziosi, D.; Fina, I.; Pippel, E.; Hesse, D.; Marti, X.; Bern, F.; Ziese, M.; Alexe, M. Physical Review B - Condensed Matter and Materials Physics; 90 (12) 2014. 10.1103/PhysRevB.90.125155. IF: 3.664


2013

  • Anisotropic 18O tracer diffusion in epitaxial films of GdBaCo2O5+δ cathode material with different orientations

    Zapata, J.; Burriel, M.; García, P.; Kilner, J.A.; Santiso, J. Journal of Materials Chemistry A; 1: 7408 - 7414. 2013. 10.1039/c3ta10749c. IF: 6.108


  • Chemical strain kinetics induced by oxygen surface exchange in epitaxial films explored by time-resolved X-ray diffraction

    Moreno, R.; García, P.; Zapata, J.; Roqueta, J.; Chaigneau, J.; Santiso, J. Chemistry of Materials; 25: 3640 - 3647. 2013. 10.1021/cm401714d. IF: 8.238


  • Flexoelectric effect in solids

    Zubko, P.; Catalan, G.; Tagantsev, A.K. Annual Review of Materials Research; 43: 387 - 421. 2013. 10.1146/annurev-matsci-071312-121634. IF: 16.179


  • Local properties of the surface layer(s) of BiFeO3 single crystals

    Domingo, N.; Narvaez, J.; Alexe, M.; Catalan, G. Journal of Applied Physics; 113 2013. 10.1063/1.4801974. IF: 2.210


  • Surface screening of written ferroelectric domains in ambient conditions

    Segura, J.J.; Domingo, N.; Fraxedas, J.; Verdaguer, A. Journal of Applied Physics; 113 2013. 10.1063/1.4801983. IF: 2.210


  • Thickness scaling of ferroelastic domains in PbTiO3 films on DyScO3

    Nesterov, O.; Matzen, S.; Magen, C.; Vlooswijk, A.H.G.; Catalan, G.; Noheda, B. Applied Physics Letters; 103 2013. 10.1063/1.4823536. IF: 3.794


2012

  • Advances on structuring, integration and magnetic characterization of molecular nanomagnets on surfaces and devices

    Domingo, N.; Bellido, E.; Ruiz-Molina, D. Chemical Society Reviews; 41: 258 - 302. 2012. 10.1039/c1cs15096k.


  • Controlled positioning of nanoparticles on graphene by noninvasive AFM lithography

    Bellido, E.; Ojea-Jiménez, I.; Ghirri, A.; Alvino, C.; Candini, A.; Puntes, V.; Affronte, M.; Domingo, N.; Ruiz-Molina, D. Langmuir : the ACS journal of surfaces and colloids; 28: 12400 - 12409. 2012. 10.1021/la3023419.


  • Domain wall nanoelectronics

    Catalan, G.; Seidel, J.; Ramesh, R.; Scott, J.F. Reviews of Modern Physics; 84: 119 - 156. 2012. 10.1103/RevModPhys.84.119.


  • Elastic and anelastic relaxations in the relaxor ferroelectric Pb(Mg 1/3Nb 2/3)O 3: I. Strain analysis and a static order parameter

    Carpenter, M.A.; Bryson, J.F.J.; Catalan, G.; Howard, C.J. Journal of Physics Condensed Matter; 24 2012. 10.1088/0953-8984/24/4/045901.


  • Elastic and anelastic relaxations in the relaxor ferroelectric Pb(Mg 1/3Nb 2/3)O 3: II. Strainorder parameter coupling and dynamic softening mechanisms

    Carpenter, M.A.; Bryson, J.F.J.; Catalan, G.; Zhang, S.J.; Donnelly, N.J. Journal of Physics Condensed Matter; 24 2012. 10.1088/0953-8984/24/4/045902.


  • Magnetotransport at domain walls in BiFeO 3

    He, Q.; Yeh, C.-H.; Yang, J.-C.; Singh-Bhalla, G.; Liang, C.-W.; Chiu, P.-W.; Catalan, G.; Martin, L.W.; Chu, Y.-H.; Scott, J.F.; Ramesh, R. Physical Review Letters; 108 2012. 10.1103/PhysRevLett.108.067203.


  • Mechanical Writing of Ferroelectric Polarization

    Lu, H. ; Bark, C.W.; Esque de los Ojos, D.; Alcala, J. ; Eom, C. B.; Catalan, G. ; Gruverman, A. SCIENCE; 336 (6077): 59 - 61. 2012. DOI: 10.1126/science.1218693.


  • Structural, spectroscopic, magnetic and electrical characterization of Ca-doped polycrystalline bismuth ferrite, Bi 1xCa xFeO 3x/2 (x0.1)

    Sardar, K.; Hong, J.; Catalan, G.; Biswas, P.K.; Lees, M.R.; Walton, R.I.; Scott, J.F.; Redfern, S.A.T. Journal of Physics Condensed Matter; 24 2012. 10.1088/0953-8984/24/4/045905.


  • Structuration and integration of magnetic nanoparticles on surfaces and devices

    Bellido, E.; Domingo, N.; Ojea-Jiménez, I.; Ruiz-Molina, D. Small; 8: 1465 - 1491. 2012. 10.1002/smll.201101456.


  • Surface phase transitions in BiFeO 3 below room temperature

    Jarrier, R.; Marti, X.; Herrero-Albillos, J.; Ferrer, P.; Haumont, R.; Gemeiner, P.; Geneste, G.; Berthet, P.; Schülli, T.; Cevc, P.; Blinc, R.; Wong, S.S.; Park, T.-J.; Alexe, M.; Carpenter, M.A.; Scott, J.F.; Catalan, G.; Dkhil, B. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.184104.


2011

  • Flexoelectric rotation of polarization in ferroelectric thin films.

    Catalan, G. ; Lubk, A.; Vlooswijk, A. H. G.; Snoeck, E.; Magen, C. ; Janssens, A.; Rispens, G.; Rijnders, G.; Blank, D. H. A.; Noheda, B. Nature Materials; 10: 963. 2011. .


  • Skin layer of BiFeO3 single crystals

    Martí, X.; Ferrer, P.; Herrero-Albillos, J.; Narvaez, J.; Holy, V.; Barrett, N.; Alexe, M.; Catalan, G. Physical Review Letters; 106 2011. 10.1103/PhysRevLett.106.236101.


2010

  • Comment on "Nanometer resolution piezoresponse force microscopy to study deep submicron ferroelectric and ferroelastic domains" [Appl. Phys. Lett. 94, 162903 (2009)]----NO ES ARTICULO

    Vlooswijk, A.H.G.; Catalan, G.; Noheda, B. Applied Physics Letters; 97 2010. 10.1063/1.3467005.


  • Electric-field control of the metal-insulator transition in ultrathin NdNiO3 films

    Scherwitzl, R.; Zubko, P.; Lezama, I.G.; Ono, S.; Morpurgo, A.F.; Catalan, G.; Triscone, J.-M. Advanced Materials; 22: 5517 - 5520. 2010. 10.1002/adma.201003241.


  • Influence of the microstructure on the high-temperature transport properties of GdBaCo2O5.5+δ epitaxial films

    Burriel, M.; Casas-Cabanas, M.; Zapata, J.; Tan, H.; Verbeeck, J.; Solís, C.; Roqueta, J.; Skinner, S.J.; Kilner, J.A.; Van Tendeloo, G.; Santiso, J. Chemistry of Materials; 22: 5512 - 5520. 2010. 10.1021/cm101423z.


  • Interface exchange coupling in Co nanoparticles dispersed in a Mn matrix

    Binns, C. ; Domingo, N. ; Testa, A.M.; Fiorani, D. ; Trohidou, K.N. ; Vasilakaki, M ; Blackman, J.A.; Asaduzzaman, A.M.; Baker, S.; Roy, M.; Peddis, D. Journal of Physics Condensed Matter; 22: 436005 - 6 paginas. 2010. 10.1088/0953-8984/22/43/436005.


  • Landau theory of domain wall magnetoelectricity

    Daraktchiev, M.; Catalan, G.; Scott, J.F. Physical Review B - Condensed Matter and Materials Physics; 81 2010. 10.1103/PhysRevB.81.224118.


  • Metal-radical chains based on polychlorotriphenylmethyl radicals: Synthesis, structure, and magnetic properties

    Roques, N.; Domingo, N.; Maspoch, D.; Wurst, K.; Rovira, C.; Tejada, J.; Ruiz-Molina, D.; Veciana, J. Inorganic Chemistry; 49: 3482 - 3488. 2010. 10.1021/ic100037z.


  • Neutron diffraction study of the BiFeO3 spin cycloid at low temperature

    Herrero-Albillos, J.; Catalan, G.; Rodriguez-Velamazan, J.A.; Viret, M.; Colson, D.; Scott, J.F. Journal of Physics Condensed Matter; 22: 256001 - 256005. 2010. 10.1088/0953-8984/22/25/256001.


  • The β-to-γ transition in BiFeO 3: A powder neutron diffraction study

    Arnold, D.C.; Knight, K.S.; Catalan, G.; Redfern, S.A.T.; Scott, J.F.; Lightfoot, P.; Morrison, F.D. Advanced Functional Materials; 20: 2116 - 2123. 2010. 10.1002/adfm.201000118.


  • The flexoelectricity of barium and strontium titanates from first principles

    Hong, J.; Catalan, G.; Scott, J.F.; Artacho, E. Journal of Physics Condensed Matter; 22 2010. 10.1088/0953-8984/22/11/112201.


2009

  • Domains in Ferroelectric Nanodots

    A. Schilling; D. Byrne; G. Catalan; K. G. Webber; Y. A. Genenko; G. S. Wu; J. F. Scott; J. M. Gregg Nano Letters; 9: 3359. 2009. .


  • Effect of chemical substitution on the Néel temperature of multiferroic Bi1¿xCaxFeO3

    G. Catalan; K. Sardar; N. S. Church; J. F. Scott; R. J. Harrison; S. A. T. Redfern Physical Review B; 79: 212415. 2009. 10.1103/PhysRevB.79.212415.


  • Effect of wall thickness on the ferroelastic domain size of BaTiO3

    G. Catalan; I. Lukyanchuk; A. Schilling; J. M. Gregg; J. F. Scott Journal of Materials Science; 44: 5307. 2009. 10.1007/s10853-009-3554-0.


  • Elastic and electrical anomalies at low-temperature phase transitions in BiFeO3

    S. A. T. Redfern; Can Wang; J. W. Hong; G. Catalan; J. F. Scott Journal of Physics Condensed Matter; 20: 452205. 2009. 10.1088/0953-8984/20/45/452205.


  • Epitaxial TbMnO3 thin films on SrTiO3 substrates: a structural study

    C. J. M. Daumont; D. Mannix; S. Venkatesan; G. Catalan; D. Rubi; B. J. Kooi; J. Th. M. De Hosson; B. Noheda Journal of Physics Condensed Matter; 21: 182001. 2009. 10.1088/0953-8984/21/18/182001.


  • Origin of ferroelastic domains in free-standing single-crystal ferroelectric films

    I. A. Luk¿yanchuk; A. Schilling; J.M. Gregg; G. Catalan; J.F. Scott Physical Review B; 79: 144111. 2009. 10.1103/PhysRevB.79.144111.


  • Particle-size dependence of magnetization relaxation in Mn12 crystals

    Domingo, N.; Luis, F.; Nakano, M.; Muntó, M.; Gómez, J.; Chaboy, J.; Ventosa, N.; Campo, J.; Veciana, J.; Ruiz-Molina, D. Physical Review B - Condensed Matter and Materials Physics; 79 2009. 10.1103/PhysRevB.79.214404.


  • Physics and applications of BiFeO3

    G. Catalan; J. F. Scott Advanced Materials; 21: 2463 - 2485. 2009. 10.1002/adma.200802849.


2008

  • Conduction at domain walls in oxide multiferroics

    J. Seidel; L. W. Martin; Q. He; Q. Zhan; Y.-H. Chu; A. Rother; M. E. Hawkridge; P. Maksymovych; P. Yu; M. Gajek; N. Balke; S. V. Kalinin; S. Gemming; H. Lichte; F. Wang; G. Catalan; J. F. Scott; N. A. Spaldin; J. Orenstein; R. Ramesh Nature Materials; 8: 229 - 234. 2008. 10.1038/nmat2373.


  • Conformal oxide coating of carbon nanotubes

    S. Kawasaki; G. Catalan; H. J. Fan; M. M. Saad; J. M. Gregg; M. A. Correa-Duarte; J. Rybczynski; F. D. Morrison; T. Tatsuta; O. Tsuji; and J. F. Scott Applied Physics Letters; 92 (5): 53109. 2008. 10.1063/1.2841710.


  • Fractal walls and domain size scaling in thin films of multiferroic BiFeO3

    G. Catalan; H. Béa; S. Fusil; M. Bibes; P. Paruch; A. Barthélémy; and J. F. Scott Physical Review Letters; 100: 27602. 2008. 10.1103/PhysRevLett.100.027602.


  • Landau Theory of Multiferroic Domain Walls

    M. Daraktchiev; G. Catalan; J. F. Scott Ferroelectrics; 375: 122 - 131. 2008. 10.1080/00150190802437969.


  • Progress in perovskite nickelate research

    G. Catalan Phase Transitions; 81: 729. 2008. 10.1080/01411590801992463.


  • ß phase and ¿-ß metal-insulator transition in multiferroic BiFeO3

    R. Palai; R. S. Katiyar; H. Schmid; P. Tissot; S. J. Clark; J. Robertson; S. A. Redfern; G. Catalan; J. F. Scott Physical Review B - Condensed Matter and Materials Physics; 77: 14110. 2008. 10.1103/PhysRevB.77.014110.


  • Solution-process coating of vertical ZnO nanowires with ferroelectrics

    S. Kawasaki; H. J. Fan; G. Catalan; F. D. Morrison; T. Tatsuta; O. Tsuji; J. F Scott Nanotechnology; 19: 375302. 2008. 10.1088/0957-4484/19/37/375302.


2007

  • First-row transition-metal complexes based on a carboxylate polychlorotriphenylmethyl radical: Trends in metal-radical exchange interactions

    Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Hernández, J.M.; Lloret, F.; Tejada, J.; Rovira, C.; Veciana, J. Inorganic Chemistry; 46: 1627 - 1633. 2007. 10.1021/ic061815x.


  • Structural and magnetic modulation of a purely organic open framework by selective guest inclusion

    Maspoch, D.; Domingo, N.; Roques, N.; Wurst, K.; Tejada, J.; Rovira, C.; Ruiz-Molina, D.; Veciana, J. Chemistry - A European Journal; 13: 8153 - 8163. 2007. 10.1002/chem.200700353.


2005

  • An unusually stable trinuclear manganese(II) complex bearing bulk carboxylic radical ligands

    Maspoch, D.; Gómez-Segura, J.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Rovira, C.; Tejada, J.; Veciana, J. Inorganic Chemistry; 44: 6936 - 6938. 2005. 10.1021/ic050977a.


  • Carboxylic-substituted polychlorotriphenylmethyl radicals, new organic building-blocks to design nanoporous magnetic molecular materials

    Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Tejada, J.; Rovira, C.; Veciana, J. Comptes Rendus Chimie; 8: 1213 - 1225. 2005. 10.1016/j.crci.2005.02.020.


  • Coexistence of ferro- and antiferromagnetic interactions in a metal-organic radical-based (6,3)-helical network with large channels

    Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Hernández, J.-M.; Vaughan, G.; Rovira, C.; Lloret, F.; Tejada, J.; Veciana, J. Chemical Communications; : 5035 - 5037. 2005. 10.1039/b505827a.


  • Hydrogen-bonded self-assemblies in a polychlorotriphenylmethyl radical derivative substituted with six meta-carboxylic acid groups

    Roques, N.; Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Tejada, J.; Rovira, C.; Veciana, J. Chemical Communications; : 4801 - 4803. 2005. 10.1039/b508952b.


2004

  • A Robust Nanocontainer Based on a Pure Organic Free Radical

    Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Tejada, J.; Rovira, C.; Veciana, J. Journal of the American Chemical Society; 126: 730 - 731. 2004. 10.1021/ja038988v.


  • A robust purely organic nanoporous magnet

    Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Vaughan, G.; Tejada, J.; Rovira, C.; Veciana, J. Angewandte Chemie - International Edition; 43: 1828 - 1832. 2004. 10.1002/anie.200353358.


  • Chiral, single-molecule nanomagnets: Synthesis, magnetic characterization and natural and magnetic circular dichroism

    Gerbier, P.; Domingo, N.; Gómez-Segura, J.; Ruiz-Molina, D.; Amabilino, D.B.; Tejada, J.; Williamson, B.E.; Veciana, J. Journal of Materials Chemistry; 14: 2455 - 2460. 2004. 10.1039/b403062a.


  • Magnetism of isolated Mn12 single-molecule magnets detected by magnetic circular dichroism: Observation of spin tunneling with a magneto-optical technique

    Domingo, N.; Williamson, B.E.; Gómez-Segura, J.; Gerbier, Ph.; Ruiz-Molina, D.; Amabilino, D.B.; Veciana, J.; Tejada, J. Physical Review B; 69: 524051 - 524054. 2004. .


  • Open-shell channel-like salts formed by the supramolecular assembly of a tricarboxylated perchlorotriphenylmethyl radical and a [Co(bpy) 3]2+ cation

    Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Vaughan, G.; Domingo, N.; Tejada, J.; Rovira, C.; Veciana, J. CrystEngComm; 6: 573 - 578. 2004. 10.1039/b410810h.