Staff directory

Jordi Arbiol Cobos

ICREA Research Professor and Group Leader
jordi.arbiol(ELIMINAR)@icn2.cat
Advanced Electron Nanoscopy

Publications

2017

  • Charge Transfer Characterization of ALD-Grown TiO2 Protective Layers in Silicon Photocathodes

    Ros C., Andreu T., Hernández-Alonso M.D., Penelas-Pérez G., Arbiol J., Morante J.R. ACS Applied Materials and Interfaces; 9 (21): 17932 - 17941. 2017. 10.1021/acsami.7b02996.

    A critical parameter for the implementation of standard high-efficiency photovoltaic absorber materials for photoelectrochemical water splitting is its proper protection from chemical corrosion while remaining transparent and highly conductive. Atomic layer deposited (ALD) TiO2 layers fulfill material requirements while conformally protecting the underlying photoabsorber. Nanoscale conductivity of ALD TiO2 protective layers on silicon-based photocathodes has been analyzed, proving that the conduction path is through the columnar crystalline structure of TiO2. Deposition temperature has been explored from 100 to 300 °C, and a temperature threshold is found to be mandatory for an efficient charge transfer, as a consequence of layer crystallization between 100 and 200 °C. Completely crystallized TiO2 is demonstrated to be mandatory for long-term stability, as seen in the 300 h continuous operation test. © 2017 American Chemical Society.


  • Inorganic photocatalytic enhancement: Activated RhB Photodegradation by surface modification of SnO2 Nanocrystals with V2 O5-like species

    Epifani M., Kaciulis S., Mezzi A., Altamura D., Giannini C., Díaz R., Force C., Genç A., Arbiol J., Siciliano P., Comini E., Concina I. Scientific Reports; 7 ( 44763) 2017. 10.1038/srep44763.

    SnO2 nanocrystals were prepared by precipitation in dodecylamine at 100 °C, then they were reacted with vanadium chloromethoxide in oleic acid at 250 °C. The resulting materials were heat-treated at various temperatures up to 650 °C for thermal stabilization, chemical purification and for studying the overall structural transformations. From the crossed use of various characterization techniques, it emerged that the as-prepared materials were constituted by cassiterite SnO2 nanocrystals with a surface modified by isolated V(IV) oxide species. After heat-treatment at 400 °C, the SnO2 nanocrystals were wrapped by layers composed of vanadium oxide (IV-V mixed oxidation state) and carbon residuals. After heating at 500 °C, only SnO2 cassiterite nanocrystals were obtained, with a mean size of 2.8 nm and wrapped by only V2 O5-like species. The samples heat-treated at 500 °C were tested as RhB photodegradation catalysts. At 10-7 M concentration, all RhB was degraded within 1 h of reaction, at a much faster rate than all pure SnO2 materials reported until now. © The Author(s) 2017.


  • Low-Temperature Growth of Axial Si/Ge Nanowire Heterostructures Enabled by Trisilane

    Hui H.Y., De La Mata M., Arbiol J., Filler M.A. Chemistry of Materials; 29 (8): 3397 - 3402. 2017. 10.1021/acs.chemmater.6b03952.

    Axial Si/Ge heterostructure nanowires, despite their promise in applications ranging from electronics to thermal transport, remain notoriously difficult to synthesize. Here, we grow axial Si/Ge heterostructures at low temperatures using a Au catalyst with a combination of trisilane and digermane. This approach yields, as determined with detailed electron microscopy characterization, arrays of epitaxial Si/Ge nanowires with excellent morphologies and purely axial composition profiles. Our data indicate that heterostructure formation can occur via the vapor-liquid-solid or vapor-solid-solid mechanism. These findings highlight the importance of precursor chemistry in semiconductor nanowire synthesis and open the door to Si/Ge nanowires with programmable quantum domains. © 2017 American Chemical Society.


  • Polybenzoxazine-Derived N-doped Carbon as Matrix for Powder-Based Electrocatalysts

    Barwe S., Andronescu C., Masa J., Ventosa E., Klink S., Genç A., Arbiol J., Schuhmann W. ChemSusChem; 10 (12): 2653 - 2659. 2017. 10.1002/cssc.201700593.

    In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long-term operation of particle- and especially powder-based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near-zero shrinkage and high residual-char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (KmMnx[Co(CN)6]y⋅n H2O) embedded in a bisphenol A and aniline-based pBO led to the formation of a N-doped carbon matrix modified with MnxCoyOz nanocubes. The obtained electrocatalyst exhibits high efficiency toward the oxygen evolution reaction (OER) and more importantly a stable performance for at least 65 h. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Probing the surface reactivity of nanocrystals by the catalytic degradation of organic dyes: The effect of size, surface chemistry and composition

    Piella J., Merkoçi F., Genç A., Arbiol J., Bastús N.G., Puntes V. Journal of Materials Chemistry A; 5 (23): 11917 - 11929. 2017. 10.1039/c7ta01328k.

    We herein present a comprehensive study on how the catalytic performance and reusability of Au nanocrystals (NCs) are affected by systematic variations of crystal size, surface coating and composition. The reductions of different organic dyes (4-nitrophenol, rhodamine B and methylene blue) by borohydride ions were used as model catalytic reactions. The catalytic performance of the Au NCs ranged between 3.6 to 110 nm was found to be dependent on crystal size, indicating that Au surface atoms have a distinct size-dependent reactivity in this reaction. Similarly, the catalytic performance was found to be strongly dependent on the nature of the coating molecule, obtaining lower catalytic activities for molecules strongly bound to the Au surface. Finally, the catalytic performance was found to be dependent on the chemical composition of the NC (Au, Ag, Pt) and the model dye used as a testing system, with the highest degradation rate found for methylene blue, followed by 4-nitrophenol and rhodamine B. We believe that this study provides a better understanding of the catalytic performance of Au NCs upon controlled modifications of the structural and morphological parameters, and a working environment that can be used to facilitate the selection of the optimum NC size, coating molecule and evaluation system for a particular study of interest. © 2017 The Royal Society of Chemistry.


  • Solution-based synthesis and processing of Sn- and Bi-doped Cu3SbSe4 nanocrystals, nanomaterials and ring-shaped thermoelectric generators

    Liu Y., García G., Ortega S., Cadavid D., Palacios P., Lu J., Ibáñez M., Xi L., De Roo J., López A.M., Martí-Sánchez S., Cabezas I., Mata M.D.L., Luo Z., Dun C., Dobrozhan O., Carroll D.L., Zhang W., Martins J., Kovalenko M.V., Arbiol J., Noriega G., Song J., Wahnón P., Cabot A. Journal of Materials Chemistry A; 5 (6): 2592 - 2602. 2017. 10.1039/c6ta08467b.

    Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystals (NCs) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu3SbSe4 (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopy, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes, which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times. © The Royal Society of Chemistry.


  • Surface-Guided Core-Shell ZnSe@ZnTe Nanowires as Radial p-n Heterojunctions with Photovoltaic Behavior

    Oksenberg E., Martí-Sánchez S., Popovitz-Biro R., Arbiol J., Joselevich E. ACS Nano; 11 (6): 6155 - 6166. 2017. 10.1021/acsnano.7b02199.

    The organization of nanowires on surfaces remains a major obstacle toward their large-scale integration into functional devices. Surface-material interactions have been used, with different materials and substrates, to guide horizontal nanowires during their growth into well-organized assemblies, but the only guided nanowire heterostructures reported so far are axial and not radial. Here, we demonstrate the guided growth of horizontal core-shell nanowires, specifically of ZnSe@ZnTe, with control over their crystal phase and crystallographic orientations. We exploit the directional control of the guided growth for the parallel production of multiple radial p-n heterojunctions and probe their optoelectronic properties. The devices exhibit a rectifying behavior with photovoltaic characteristics upon illumination. Guided nanowire heterostructures enable the bottom-up assembly of complex semiconductor structures with controlled electronic and optoelectronic properties. © 2017 American Chemical Society.


  • Ultrathin High Surface Area Nickel Boride (NixB) Nanosheets as Highly Efficient Electrocatalyst for Oxygen Evolution

    Masa J., Sinev I., Mistry H., Ventosa E., de la Mata M., Arbiol J., Muhler M., Roldan Cuenya B., Schuhmann W. Advanced Energy Materials; 7 (17, 1700381) 2017. 10.1002/aenm.201700381.

    The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high-surface area nickel boride (NixB) nanosheets as a low-cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm−2 at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V at 20 mA cm−2 when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X-ray absorption fine-structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni-B under OER conditions, owing to a Ni-B core@nickel oxyhydroxide shell (Ni-B@NiOxH) structure, and increase in disorder of the NiOxH layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Unveiling the nucleation & coarsening mechanisms of solution-derived self-Assembled epitaxial Ce0.9Gd0.1O2-yNanostructures

    Queralto A., De La Mata M., Arbiol J., Hühne R., Obradors X., Puig T. Crystal Growth and Design; 17 (2): 504 - 516. 2017. 10.1021/acs.cgd.6b01358.

    Self-Assembling approaches based on chemical solution deposition (CSD) are ideal methods for the cost-effective production of epitaxial nanostructures with high throughput. Therefore, an in-depth investigation of the nucleation and coarsening processes involved in the self-Assembly of nanostructures is mandatory to achieve a good control over nanostructure shape, dimensions, and orientation. Heteroepitaxial Ce0.9Gd0.1O2-y (CGO) is an ideal model system to unveil the underlying nanostructure development mechanisms in addition to their promising properties for catalysis, gas sensors, and ionic conductivity. Rapid thermal annealing furnaces have been used to study separately the thermodynamic and kinetic nucleation and coarsening mechanisms of self-Assembled CGO isotropic and anisotropic nanostructures based on strain-engineering and surface energies control. Different CGO nanoislands are obtained: isotropic (001)CGO nanodots are grown on (001)-oriented Y2O3:ZrO2(YSZ) and LaAlO3 (Lao) substrates, whereas (011)Lao substrates promote the growth of elongated (011)CGO nanowires. HRTEM and RHEED analyses are used to study the early stages of nucleation, as well as the shape and interfacial structure of CGO nanostructures. A systematic study with the heating ramp, annealing temperature and time, and strain in combination with thermally activated theoretical models provides information on the nucleation behavior, nucleation barriers, and atomic diffusion coefficients along in-plane and out-of-plane island orientations. Highly anisotropic atomic diffusion constants have been shown to be at the origin of the high aspect ratios of some of the nanostructures. Overall, our study provides a general method for the evaluation of nucleation and coarsening of multiple CSD-derived oxide nanostructures and understanding the shape development by combining thermodynamic and kinetic approaches. ©2016 American Chemical Society.


2016

  • Co-Cu Nanoparticles: Synthesis by Galvanic Replacement and Phase Rearrangement during Catalytic Activation

    Nafria R., Genç A., Ibáñez M., Arbiol J., Ramírez De La Piscina P., Homs N., Cabot A. Langmuir; 32 (9): 2267 - 2276. 2016. 10.1021/acs.langmuir.5b04622.

    The control of the phase distribution in multicomponent nanomaterials is critical to optimize their catalytic performance. In this direction, while impressive advances have been achieved in the past decade in the synthesis of multicomponent nanoparticles and nanocomposites, element rearrangement during catalyst activation has been frequently overseen. Here, we present a facile galvanic replacement-based procedure to synthesize Co@Cu nanoparticles with narrow size and composition distributions. We further characterize their phase arrangement before and after catalytic activation. When oxidized at 350 °C in air to remove organics, Co@Cu core-shell nanostructures oxidize to polycrystalline CuO-Co3O4 nanoparticles with randomly distributed CuO and Co3O4 crystallites. During a posterior reduction treatment in H2 atmosphere, Cu precipitates in a metallic core and Co migrates to the nanoparticle surface to form Cu@Co core-shell nanostructures. The catalytic behavior of such Cu@Co nanoparticles supported on mesoporous silica was further analyzed toward CO2 hydrogenation in real working conditions. © 2016 American Chemical Society.


  • Demonstrating the steady performance of iron oxide composites over 2000 cycles at fast charge-rates for Li-ion batteries

    Sun Z., Madej E., Genç A., Muhler M., Arbiol J., Schuhmann W., Ventosa E. Chemical Communications; 52 (46): 7348 - 7351. 2016. 10.1039/c6cc00168h.

    The feasibility of using iron oxides as negative electrode materials for safe high-power Li-ion batteries is demonstrated by the carbon-coated FeOx/CNT composite synthesized by controlled pyrolysis of ferrocene, which delivered a specific capacity retention of 84% (445 mA h g-1) after 2000 cycles at 2000 mA g-1 (4C). © 2016 The Royal Society of Chemistry.


  • Disentangling Epitaxial Growth Mechanisms of Solution Derived Functional Oxide Thin Films

    Queraltó A., de la Mata M., Arbiol J., Obradors X., Puig T. Advanced Materials Interfaces; 3 (18, 1600392) 2016. 10.1002/admi.201600392.

    This study investigates the mechanisms of epitaxial development and functional properties of oxide thin films (Ce0.9Zr0.1O2− y, LaNiO3, and Ba0.8Sr0.2TiO3) grown on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) by the chemical solution deposition approach. Rapid thermal annealing furnaces are very powerful tools in this study providing valuable information of the early stages of nucleation, the kinetics of epitaxial film growth, and the coarsening of nanocrystalline phases. Advanced transmission electron microscopies, X-ray diffraction, and atomic force microscopy are employed to investigate the film microstructure and morphology, microstrain relaxation, and epitaxial crystallization. This study demonstrates that the isothermal evolution toward epitaxial film growth follows a self-limited process driven by atomic diffusion, and surface and interface energy minimization. All investigated oxides experience a transformation from the polycrystalline to the epitaxial phase. This study unequivocally evidences that the film thickness highly influences the epitaxial crystallization rate due to the competition between heterogeneous and homogeneous nucleation barriers and the fast coarsening of polycrystalline grains as compared to epitaxial growth. The investigated films possess good functional properties, and this study successfully confirms an improvement at long annealing times that can be correlated with grain boundary healing processes. Thick epitaxial films can be crystallized by growing sequential individual epitaxial layers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Enhanced Activity and Acid pH Stability of Prussian Blue-type Oxygen Evolution Electrocatalysts Processed by Chemical Etching

    Han L., Tang P., Reyes-Carmona A., Rodríguez-García B., Torréns M., Morante J.R., Arbiol J., Galan-Mascaros J.R. Journal of the American Chemical Society; 138 (49): 16037 - 16045. 2016. 10.1021/jacs.6b09778.

    The development of upscalable oxygen evolving electrocatalysts from earth-abundant metals able to operate in neutral or acidic environments and low overpotentials remains a fundamental challenge for the realization of artificial photosynthesis. In this study, we report a highly active phase of heterobimetallic cyanide-bridged electrocatalysts able to promote water oxidation under neutral, basic (pH < 13), and acidic conditions (pH > 1). Cobalt-iron Prussian blue-type thin films, formed by chemical etching of Co(OH)1.0(CO3)0.5·nH2O nanocrystals, yield a dramatic enhancement of the catalytic performance toward oxygen production, when compared with previous reports for analogous materials. Electrochemical, spectroscopic, and structural studies confirm the excellent performance, stability, and corrosion resistance, even when compared with state-of-the-art metal oxide catalysts under moderate overpotentials and in a remarkably large pH range, including acid media where most cost-effective water oxidation catalysts are not useful. The origin of the superior electrocatalytic activity toward water oxidation appears to be in the optimized interfacial matching between catalyst and electrode surface obtained through this fabrication method. © 2016 American Chemical Society.


  • Enhanced thermoelectric performance of solution-derived bismuth telluride based nanocomposites via liquid-phase Sintering

    Zhang C., de la Mata M., Li Z., Belarre F.J., Arbiol J., Khor K.A., Poletti D., Zhu B., Yan Q., Xiong Q. Nano Energy; 30: 630 - 638. 2016. 10.1016/j.nanoen.2016.10.056.

    Bismuth telluride based thermoelectric materials show great promise in electricity generation from waste heat and solid-state refrigeration, but improving their conversion efficiency with economical approaches for widespread use remains a challenge. An economical facile bottom-up approach has been developed to obtain nanostructured powders, which are used to build bulk thermoelectric materials. Using excess tellurium as sacrificial additive to enable liquid-phase sintering in the spark plasma sintering process, the lattice and bipolar contributions to the thermal conductivity are both greatly reduced without compromising too much the power factor, which leads to the achievement of high figure of merit (ZT) in both n-type and p-type bismuth telluride based nanocomposites. The ZT values are 1.59±0.16 for p-type Bi0.5Sb1.5Te3 and 0.98±0.07 for n-type Bi2Te2.7Se0.3 at 370 K, which are significantly high for bottom-up approaches. These results demonstrate that solution-chemistry approaches as facile, scalable and low-energy-intensive ways to achieve nanopowders, combined with liquid-phase sintering process, can open up great possibilities in developing high-performance low-price thermoelectric bulk nanocomposites. © 2016 Elsevier Ltd


  • Fe3O4@NiFexOy Nanoparticles with Enhanced Electrocatalytic Properties for Oxygen Evolution in Carbonate Electrolyte

    Luo Z., Martí-Sànchez S., Nafria R., Joshua G., De La Mata M., Guardia P., Flox C., Martínez-Boubeta C., Simeonidis K., Llorca J., Morante J.R., Arbiol J., Ibáñez M., Cabot A. ACS Applied Materials and Interfaces; 8 (43): 29461 - 29469. 2016. 10.1021/acsami.6b09888.

    The design and engineering of earth-abundant catalysts that are both cost-effective and highly active for water splitting are crucial challenges in a number of energy conversion and storage technologies. In this direction, herein we report the synthesis of Fe3O4@NiFexOy core-shell nanoheterostructures and the characterization of their electrocatalytic performance toward the oxygen evolution reaction (OER). Such nanoparticles (NPs) were produced by a two-step synthesis procedure involving the colloidal synthesis of Fe3O4 nanocubes with a defective shell and the posterior diffusion of nickel cations within this defective shell. Fe3O4@NiFexOy NPs were subsequently spin-coated over ITO-covered glass and their electrocatalytic activity toward water oxidation in carbonate electrolyte was characterized. Fe3O4@NiFexOy catalysts reached current densities above 1 mA/cm2 with a 410 mV overpotential and Tafel slopes of 48 mV/dec, which is among the best electrocatalytic performances reported in carbonate electrolyte. © 2016 American Chemical Society.


  • High-performance thermoelectric nanocomposites from nanocrystal building blocks

    Ibáñez M., Luo Z., Genç A., Piveteau L., Ortega S., Cadavid D., Dobrozhan O., Liu Y., Nachtegaal M., Zebarjadi M., Arbiol J., Kovalenko M.V., Cabot A. Nature Communications; 7 ( 10766) 2016. 10.1038/ncomms10766.

    The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom-up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS-Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS-Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K.


  • Mn3O4@CoMn2O4-CoxOy Nanoparticles: Partial Cation Exchange Synthesis and Electrocatalytic Properties toward the Oxygen Reduction and Evolution Reactions

    Luo Z., Irtem E., Ibánez M., Nafria R., Martĺ-Sánchez S., Genç A., De La Mata M., Liu Y., Cadavid D., Llorca J., Arbiol J., Andreu T., Morante J.R., Cabot A. ACS Applied Materials and Interfaces; 8 (27): 17435 - 17444. 2016. 10.1021/acsami.6b02786.

    Mn3O4@CoMn2O4 nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one-pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn3O4 NPs. Selecting the proper cobalt precursor, the nucleation of CoxOy crystallites at the Mn3O4@CoMn2O4 surface could be simultaneously promoted to form Mn3O4@CoMn2O4-CoxOy NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn3O4@CoMn2O4-CoxOy NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 V at -3 mA·cm-2 and a small Tafel slope of 52 mV·dec-1 for ORR, and overpotentials of 0.31 V at 10 mA·cm-2 and a Tafel slope of 81 mV·dec-1 for OER, thus outperforming commercial Pt-, IrO2-based and previously reported transition metal oxides. This cation-exchange-based synthesis protocol opens up a new approach to design novel heterostructured NPs as efficient nonprecious metal bifunctional oxygen catalysts. © 2016 American Chemical Society.


  • One-pot polyol synthesis of highly monodisperse short green silver nanorods

    Patarroyo J., Genç A., Arbiol J., Bastús N.G., Puntes V. Chemical Communications; 52 (73): 10960 - 10963. 2016. 10.1039/c6cc04796c.

    Green silver nanorods (Ag NRs) of a low aspect ratio (2.8) have been produced in high yields via an optimized, simple, and robust one-pot polyol method in the presence of tannic acid, which favors the nucleation of decahedral seeds needed for the production of monodisperse Ag NRs. These Ag NRs were further used as sacrificial templates to produce Au hollow nanostructures via galvanic replacement reaction with HAuCl4 at room temperature. © 2016 The Royal Society of Chemistry.


  • Orientation symmetry breaking in self-assembled Ce1-: XGdxO2- y nanowires derived from chemical solutions

    Queraltó A., De La Mata M., Martínez L., Magén C., Gibert M., Arbiol J., Hühne R., Obradors X., Puig T. RSC Advances; 6 (99): 97226 - 97236. 2016. 10.1039/c6ra23717g.

    Understanding the growth mechanisms of nanostructures obtained from chemical solutions, a high-throughput production methodology, is essential to correlate precisely the growth conditions with the nanostructures' morphology, dimensions and orientation. It is shown that self-organized (011)-oriented Ce0.9Gd0.1O2-y (CGO) nanowires having a single in-plane orientation are achieved when an anisotropic (011)-LaAlO3 (LAO) substrate is chosen. STEM and AFM images of the epitaxial nanowires reveal the (001)CGO[0-11](011)LAO[100] growth orientation, with the enlargement occurring along the [0-11]CGO direction with (111) lateral facets. The chosen substrate allowed us to study a unique case where the resulting biaxial strain is isotropic, while the dissimilar lateral surface energies are the key factor to obtain an energetically imbalanced and non-degenerated nanowire configuration. Rapid Thermal Annealing (RTA) has allowed sorting of experimental nucleation from coarsening and analysis of the kinetic phenomena of the nanowires. A thermodynamic driving force is shown to exist for a continuous elongation of the nanowires while the coarsening rates are found to be strongly temperature dependent and so kinetic effects are the key factors to control the size and density of the self-organized nanowire system. A remarkably fast nanowire growth rate (14-40 nm min-1) is observed, which we associate with a high atomic mobility probably linked to a high concentration of oxygen vacancies, as detected by XPS. These nanowires are envisaged as model systems pushing forward the study of low energetic and highly oxygen deficient {111} lateral facets useful for catalysis, gas sensors and ionic conductivity applications. © 2016 The Royal Society of Chemistry.


  • Orientationally Ordered Silicon Nanocrystal Cuboctahedra in Superlattices

    Yu Y., Lu X., Guillaussier A., Voggu V.R., Pineros W., De La Mata M., Arbiol J., Smilgies D.-M., Truskett T.M., Korgel B.A. Nano Letters; 16 (12): 7814 - 7821. 2016. 10.1021/acs.nanolett.6b04006.

    Uniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices. © 2016 American Chemical Society.


  • Pd2Sn [010] nanorods as a highly active and stable ethanol oxidation catalyst

    Luo Z., Lu J., Flox C., Nafria R., Genç A., Arbiol J., Llorca J., Ibáñez M., Morante J.R., Cabot A. Journal of Materials Chemistry A; 4 (42): 16706 - 16713. 2016. 10.1039/c6ta06430b.

    The development of highly active, low cost and stable electrocatalysts for direct alcohol fuel cells remains a critical challenge. While Pd2Sn has been reported as an excellent catalyst for the ethanol oxidation reaction (EOR), here we present DFT analysis results showing the (100) and (001) facets of orthorhombic Pd2Sn to be more favourable for the EOR than (010). Accordingly, using tri-n-octylphosphine, oleylamine (OLA) and methylamine hydrochloride as size and shape directing agents, we produced colloidal Pd2Sn nanorods (NRs) grown in the [010] direction. Such Pd2Sn NRs, supported on graphitic carbon, showed excellent performance and stability as an anode electrocatalyst for the EOR in alkaline media, exhibiting 3 times and 10 times higher EOR current densities than that of Pd2Sn and Pd nanospheres, respectively. We associate this improved performance with the favourable faceting of the NRs. © 2016 The Royal Society of Chemistry.


  • Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs

    Meyns M., Perálvarez M., Heuer-Jungemann A., Hertog W., Ibáñez M., Nafria R., Genç A., Arbiol J., Kovalenko M.V., Carreras J., Cabot A., Kanaras A.G. ACS Applied Materials and Interfaces; 8 (30): 19579 - 19586. 2016. 10.1021/acsami.6b02529.

    Cesium lead halide (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) offer exceptional optical properties for several potential applications but their implementation is hindered by a low chemical and structural stability and limited processability. In the present work, we developed a new method to efficiently coat CsPbX3 NCs, which resulted in their increased chemical and optical stability as well as processability. The method is based on the incorporation of poly(maleic anhydride-alt-1-octadecene) (PMA) into the synthesis of the perovskite NCs. The presence of PMA in the ligand shell stabilizes the NCs by tightening the ligand binding, limiting in this way the NC surface interaction with the surrounding media. We further show that these NCs can be embedded in self-standing silicone/glass plates as down-conversion filters for the fabrication of monochromatic green and white light emitting diodes (LEDs) with narrow bandwidths and appealing color characteristics. © 2016 American Chemical Society.


  • Scalable Heating-Up Synthesis of Monodisperse Cu2ZnSnS4 Nanocrystals

    Shavel A., Ibáñez M., Luo Z., De Roo J., Carrete A., Dimitrievska M., Gencì A., Meyns M., Pérez-Rodríguez A., Kovalenko M.V., Arbiol J., Cabot A. Chemistry of Materials; 28 (3): 720 - 726. 2016. 10.1021/acs.chemmater.5b03417.

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals (NCs), with quasi-spherical shape, were prepared by a facile, high-yield, scalable, and high-concentration heat-up procedure. The key parameters to minimize the NC size distribution were efficient mixing and heat transfer in the reaction mixture through intensive argon bubbling and improved control of the heating ramp stability. Optimized synthetic conditions allowed the production of several grams of highly monodisperse CZTS NCs per batch, with up to 5 wt % concentration in a crude solution and a yield above 90%. © 2016 American Chemical Society.


  • Surface Hydrogen Enables Subeutectic Vapor-Liquid-Solid Semiconductor Nanowire Growth

    Sivaram S.V., Hui H.Y., De La Mata M., Arbiol J., Filler M.A. Nano Letters; 16 (11): 6717 - 6723. 2016. 10.1021/acs.nanolett.6b01640.

    Vapor-liquid-solid nanowire growth below the bulk metal-semiconductor eutectic temperature is known for several systems; however, the fundamental processes that govern this behavior are poorly understood. Here, we show that hydrogen atoms adsorbed on the Ge nanowire sidewall enable AuGe catalyst supercooling and control Au transport. Our approach combines in situ infrared spectroscopy to directly and quantitatively determine hydrogen atom coverage with a "regrowth" step that allows catalyst phase to be determined with ex situ electron microscopy. Maintenance of a supercooled catalyst with only hydrogen radical delivery confirms the centrality of sidewall chemistry. This work underscores the importance of the nanowire sidewall and its chemistry on catalyst state, identifies new methods to regulate catalyst composition, and provides synthetic strategies for subeutectic growth in other nanowire systems. © 2016 American Chemical Society.


  • Synergistic effects in 3D honeycomb-like hematite nanoflakes/branched polypyrrole nanoleaves heterostructures as high-performance negative electrodes for asymmetric supercapacitors

    Tang P.-Y., Han L.-J., Genç A., He Y.-M., Zhang X., Zhang L., Galán-Mascarós J.R., Morante J.R., Arbiol J. Nano Energy; 22: 189 - 201. 2016. 10.1016/j.nanoen.2016.02.019.

    Rational assembly of unique branched heterostructures is one of the facile techniques to improve the electrochemical figure of merit of materials. By taking advantages of hydrogen bubbles dynamic template, hydrothermal method and electrochemical polymerization, branched polypyrrole (PPy) nanoleaves decorated honeycomb-like hematite nanoflakes (core-branch Fe2O3@PPy) are fabricated. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and scanning transmission electron microscopy in high angle annular dark field mode with electron energy loss spectroscopy were combined to elucidate the mechanisms underlying formation and morphogenesis evolution of core-branch Fe2O3@PPy heterostructures. Benefiting from the stability of honeycomb-like hematite nanoflakes and the high conductivity of PPy nanoleaves, the resultant core-branch Fe2O3@PPy exhibits an ultrahigh capacitance of 1167.8 F g-1 at 1 A g-1 in 0.5 M Na2SO4 aqueous solution. Moreover, the assembled bi-metal oxides asymmetric supercapacitor (Fe2O3@PPy//MnO2) gives rise to a maximum energy density of 42.4 W h kg-1 and a maximum power density of 19.14 kW kg-1 with an excellent cycling performance of 97.1% retention after 3000 cycles at 3 A g-1. These performance features are superior than previous reported iron oxide/hydroxides based supercapacitors, offering an important guideline for future design of advanced next-generation supercapacitors. © 2016 Elsevier Ltd.


  • The Ethylhexanoate Route to Metal Oxide Nanocrystals: Synthesis of CoO Nanooctahedra from CoII2-Ethylhexanoate

    Epifani M., Tang P.-Y., Genç A., Morante J.R., Arbiol J., Díaz R., Wicker S. European Journal of Inorganic Chemistry; 2016 (24): 3963 - 3968. 2016. 10.1002/ejic.201600511.

    CoO nanocrystals were prepared by solvothermal processing of Co 2-ethylhexanoate in oleylamine at 250 °C. The obtained products, identified as CoO by X-ray diffraction, had an octahedral shape, as seen by transmission electron microscopy, reflecting the cubic symmetry of the CoO crystallographic phase. The materials were converted into the Co3O4phase after heat treatment at 400 °C. The nanocrystal evolution was investigated by FTIR spectroscopy. It was concluded that weak oleylamine bonding to the nanocrystal surface during the synthesis step favored the exchange with 2-ethylhexanoato ligands, and that the interplay between the two ligands favored the kinetic control of the growth, resulting in the finally observed octahedral morphology. The Co3O4phase obtained from the heat treatment at 400 °C was used to process chemoresistive sensors, which were able to detect ethanol under dry and humid conditions (0 and 50 % r.h. H2O at 25 °C) at low temperatures (100 °C). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Thermoelectric properties of semiconductor-metal composites produced by particle blending

    Liu Y., Cadavid D., Ibáñez M., Ortega S., Martí-Sánchez S., Dobrozhan O., Kovalenko M.V., Arbiol J., Cabot A. APL Materials; 4 (10, 104813) 2016. 10.1063/1.4961679.

    In the quest for more efficient thermoelectric material able to convert thermal to electrical energy and vice versa, composites that combine a semiconductor host having a large Seebeck coefficient with metal nanodomains that provide phonon scattering and free charge carriers are particularly appealing. Here, we present our experimental results on the thermal and electrical transport properties of PbS-metal composites produced by a versatile particle blending procedure, and where the metal work function allows injecting electrons to the intrinsic PbS host. We compare the thermoelectric performance of composites with microcrystalline or nanocrystalline structures. The electrical conductivity of the microcrystalline host can be increased several orders of magnitude with the metal inclusion, while relatively high Seebeck coefficient can be simultaneously conserved. On the other hand, in nanostructured materials, the host crystallites are not able to sustain a band bending at its interface with the metal, becoming flooded with electrons. This translates into even higher electrical conductivities than the microcrystalline material, but at the expense of lower Seebeck coefficient values. © 2016 Author(s).


  • Tuning the Plasmonic Response up: Hollow Cuboid Metal Nanostructures

    Genç A., Patarroyo J., Sancho-Parramon J., Arenal R., Duchamp M., Gonzalez E.E., Henrard L., Bastús N.G., Dunin-Borkowski R.E., Puntes V.F., Arbiol J. ACS Photonics; 3 (5): 770 - 779. 2016. 10.1021/acsphotonics.5b00667.

    We report the fine-tuning of the localized surface plasmon resonances (LSPRs) from ultraviolet to near-infrared by nanoengineering the metal nanoparticle morphologies from solid Ag nanocubes to hollow AuAg nanoboxes and AuAg nanoframes. Spatially resolved mapping of plasmon resonances by electron energy loss spectroscopy (EELS) revealed a homogeneous distribution of highly intense plasmon resonances around the hollow nanostructures and the interaction, that is, hybridization, of inner and outer plasmon fields for the nanoframe. Experimental findings are accurately correlated with the boundary element method (BEM) simulations demonstrating that the homogeneous distribution of the plasmon resonances is the key factor for their improved plasmonic properties. As a proof of concept for these enhanced plasmonic properties, we show the effective label free sensing of bovine serum albumin (BSA) of single-walled AuAg nanoboxes in comparison with solid Au nanoparticles, demonstrating their excellent performance for future biomedical applications. © 2016 American Chemical Society.


  • Twin-Induced InSb Nanosails: A Convenient High Mobility Quantum System

    De La Mata M., Leturcq R., Plissard S.R., Rolland C., Magén C., Arbiol J., Caroff P. Nano Letters; 16 (2): 825 - 833. 2016. 10.1021/acs.nanolett.5b05125.

    Ultra narrow bandgap III-V semiconductor nanomaterials provide a unique platform for realizing advanced nanoelectronics, thermoelectrics, infrared photodetection, and quantum transport physics. In this work we employ molecular beam epitaxy to synthesize novel nanosheet-like InSb nanostructures exhibiting superior electronic performance. Through careful morphological and crystallographic characterization we show how this unique geometry is the result of a single twinning event in an otherwise pure zinc blende structure. Four-terminal electrical measurements performed in both the Hall and van der Pauw configurations reveal a room temperature electron mobility greater than 12 000 cm2·V-1·s-1. Quantized conductance in a quantum point contact processed with a split-gate configuration is also demonstrated. We thus introduce InSb "nanosails" as a versatile and convenient platform for realizing new device and physics experiments with a strong interplay between electronic and spin degrees of freedom. © 2016 American Chemical Society.


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

    Queraltó A., Pérez Del Pino A., De La Mata M., Arbiol J., Tristany M., Obradors X., Puig T. Chemistry of Materials; 28 (17): 6136 - 6145. 2016. 10.1021/acs.chemmater.6b01968.

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


  • UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

    Lähnemann J., Den Hertog M., Hille P., De La Mata M., Fournier T., Schörmann J., Arbiol J., Eickhoff M., Monroy E. Nano Letters; 16 (5): 3260 - 3267. 2016. 10.1021/acs.nanolett.6b00806.

    We have characterized the photodetection capabilities of single GaN nanowires incorporating 20 periods of AlN/GaN:Ge axial heterostructures enveloped in an AlN shell. Transmission electron microscopy confirms the absence of an additional GaN shell around the heterostructures. In the absence of a surface conduction channel, the incorporation of the heterostructure leads to a decrease of the dark current and an increase of the photosensitivity. A significant dispersion in the magnitude of dark currents for different single nanowires is attributed to the coalescence of nanowires with displaced nanodisks, reducing the effective length of the heterostructure. A larger number of active nanodisks and AlN barriers in the current path results in lower dark current and higher photosensitivity and improves the sensitivity of the nanowire to variations in the illumination intensity (improved linearity). Additionally, we observe a persistence of the photocurrent, which is attributed to a change of the resistance of the overall structure, particularly the GaN stem and cap sections. As a consequence, the time response is rather independent of the dark current. © 2016 American Chemical Society.


2015

  • Cu2ZnSnS4-Ag2S Nanoscale p-n Heterostructures as Sensitizers for Photoelectrochemical Water Splitting

    Yu X., Liu J., Genç A., Ibáñez M., Luo Z., Shavel A., Arbiol J., Zhang G., Zhang Y., Cabot A. Langmuir; 31 (38): 10555 - 10561. 2015. 10.1021/acs.langmuir.5b02490.

    A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled composition. We report a detailed study of the formation of such CZTS-Ag2S nanoheterostructures and of their photocatalytic properties. When compared to pure CZTS, the use of nanoscale p-n heterostructures as light absorbers for photocatalytic water splitting provides superior photocurrents. We associate this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We believe this and other type-II nanoheterostructures will open the door to the use of CZTS, with excellent light absorption properties and made of abundant and environmental friendly elements, to the field of photocatalysis. © 2015 American Chemical Society.


  • Cu2ZnSnS4-PtM (M = Co, Ni) Nanoheterostructures for Photocatalytic Hydrogen Evolution

    Yu X., An X., Genç A., Ibáñez M., Arbiol J., Zhang Y., Cabot A. Journal of Physical Chemistry C; 119 (38): 21882 - 21888. 2015. 10.1021/acs.jpcc.5b06199.

    We report the synthesis and photocatalytic and magnetic characterization of colloidal nanoheterostructures formed by combining a Pt-based magnetic metal alloy (PtCo, PtNi) with Cu2ZnSnS4 (CZTS). While CZTS is one of the main candidate materials for solar energy conversion, the introduction of a Pt-based alloy on its surface strongly influences its chemical and electronic properties, ultimately determining its functionality. In this regard, up to a 15-fold increase of the photocatalytic hydrogen evolution activity was obtained with CZTS-PtCo when compared with CZTS. Furthermore, two times higher hydrogen evolution rates were obtained for CZTS-PtCo when compared with CZTS-Pt, in spite of the lower precious metal loading of the former. Besides, the magnetic properties of the PtCo nanoparticles attached to the CZTS nanocrystals were retained in the heterostructures, which could facilitate catalyst purification and recovery for its posterior recycling and/or reutilization. © 2015 American Chemical Society.


  • Electron Bottleneck in the Charge/Discharge Mechanism of Lithium Titanates for Batteries

    Ventosa E., Skoumal M., Vazquez F.J., Flox C., Arbiol J., Morante J.R. ChemSusChem; 8 (10): 1737 - 1744. 2015. 10.1002/cssc.201500349.

    The semi-solid flow battery (SSFB) is a promising storage energy technology featured by employing semi-solid fluid electrodes containing conductive additive and active Li-ion battery materials. The state of art anode material for SSFB is Li4Ti5O12 (LTO). This work shows that LTO improves drastically the performance in fluid electrode via hydrogen annealing manifesting the importance of the electrical conductivity of the active material in SSFBs. On the other hand, the properties of fluid electrodes allow the contributions of ionic and electrical resistance to be separated in operando. The asymmetric overpotential observed in Li4Ti5O12 and TiO2 is proposed to originate from the so-called electron bottleneck mechanism based on the transformation from electrically insulator to conductor upon (de-)lithiation, or vice versa, which should be considered when modelling, evaluating or designing advanced materials based on Li4Ti5O12, TiO2 or others with insulating-conducting behavior materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


  • Enhanced reactivity of high-index surface platinum hollow nanocrystals

    González E., Merkoçi F., Arenal R., Arbiol J., Esteve J., Bastús N.G., Puntes V. Journal of Materials Chemistry A; 4 (1): 200 - 208. 2015. 10.1039/c5ta07504a.

    The precise morphological control of the surface of inorganic nanocrystals (NCs) is critical for the understanding of the unique properties of the materials at the nanoscale and useful in a wide range of applications, such as catalysis, where the development of highly active and low-cost materials represents a landmark for the development of industrial technologies. Here we show how combining solid state chemistry and colloidal synthesis allows us to prepare exotic materials, in particular, PtAg@Pt single-crystal hollow NCs with high-index planes synthesized at room temperature by controlled corrosion of silver templates, which minimize Pt consumption and maximize surface reactivity. © The Royal Society of Chemistry 2016.


  • High aspect ratio gold nanorods grown with platinum seeds

    Varón M., Arbiol J., Puntes V.F. Journal of Physical Chemistry C; 119 (21): 11818 - 11825. 2015. 10.1021/acs.jpcc.5b01263.

    Using Au chloride as precursor, Pt nanocrystals as seeds, ascorbic acid as a reducer, and CTAB as surfactant and complexing agent, extremely long Au nanorods have been grown. The influence of different parameters such as the composition of the seeds, the amount of Pt, or the type of Pt present in solution has been analyzed. These large Au NRs have been exhaustively characterized by (S)TEM, SEM and optical microscopy as well as UV-vis spectroscopy and their morphology correlated with the growth mechanism. © 2015 American Chemical Society.


  • High yield of gaas nanowire arrays on si mediated by the pinning and contact angle of Ga

    Russo-Averchi E., Vukajlovic Plestina J., Tütüncüoglu G., Matteini F., Dalmau-Mallorquí A., De La Mata M., Rüffer D., Potts H.A., Arbiol J., Conesa-Boj S., Fontcuberta I. Morral A. Nano Letters; 15 (5): 2869 - 2874. 2015. 10.1021/nl504437v.

    GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfill this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work, we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90°, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon. © 2015 American Chemical Society.


  • High-yield synthesis and optical properties of g-C3N4

    Yuan Y., Zhang L., Xing J., Utama M.I.B., Lu X., Du K., Li Y., Hu X., Wang S., Genc A., Dunin-Borkowski R., Arbiol J., Xiong Q. Nanoscale; 7 (29): 12343 - 12350. 2015. 10.1039/c5nr02905h. IF: 7.394

    Graphitic carbon nitride (g-C3N4), a metal-free semiconductor with a band gap of 2.7 eV, has received considerable attention owing to its fascinating photocatalytic performances under visible-light. g-C3N4 exhibits high thermal and chemical stability and non-toxicity such that it has been considered as the most promising photocatalyst for environmental improvement and energy conservation. Hence, it is of great importance to obtain high-quality g-C3N4 and gain a clear understanding of its optical properties. Herein, we report a high-yield synthesis of g-C3N4 products via heating of high vacuum-sealed melamine powder in an ampoule at temperatures between 450 and 650°C. Using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the chemical composition and crystallization of the as-produced g-C3N4 are demonstrated. A systematic optical study of g-C3N4 is carried out with several approaches. The optical phonon behavior of g-C3N4 is revealed by infrared and Raman spectroscopy, and the emission properties of g-C3N4 are investigated using photoluminescence (PL) spectroscopy, while the photocatalytic properties are explored by the photodegradation experiment. This journal is © The Royal Society of Chemistry.


  • Long-lived excitons in GaN/AlN nanowire heterostructures

    Beeler M., Lim C.B., Hille P., Bleuse J., Schörmann J., De La Mata M., Arbiol J., Eickhoff M., Monroy E. Physical Review B - Condensed Matter and Materials Physics; 91 (20, 205440) 2015. 10.1103/PhysRevB.91.205440.

    GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts. © Published by the American Physical Society.


  • Phonon Engineering in Isotopically Disordered Silicon Nanowires

    Mukherjee S., Givan U., Senz S., Bergeron A., Francoeur S., De La Mata M., Arbiol J., Sekiguchi T., Itoh K.M., Isheim D., Seidman D.N., Moutanabbir O. Nano Letters; 15 (6): 3885 - 3893. 2015. 10.1021/acs.nanolett.5b00708.

    The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires 28Six30Si1-x with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure 29Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of 28Si and 30Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in 28Six30Si1-x nanowires behave remarkably differently from those in 29Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed 28Six30Si1-x nanowires is ∼30% lower than that of isotopically pure 29Si nanowires in agreement with theoretical predictions. (Figure Presented). © 2015 American Chemical Society.


  • Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy

    Schuster F., Hetzl M., Weiszer S., Garrido J.A., De La Mata M., Magen C., Arbiol J., Stutzmann M. Nano Letters; 15 (3): 1773 - 1779. 2015. 10.1021/nl504446r.

    In this work the position-controlled growth of GaN nanowires (NWs) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can be seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks are structured by electron beam lithography which allows the fabrication of perfectly homogeneous GaN NW arrays with different diameters and distances. While the wurtzite NWs are found to be Ga-polar, N-polar nucleation leads to the formation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 °C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nanowire to nanotube growth by employing a highly competitive growth regime. © 2015 American Chemical Society.


  • Resonant tunnelling features in a suspended silicon nanowire single-hole transistor

    Llobet J., Krali E., Wang C., Arbiol J., Jones M.E., Pérez-Murano F., Durrani Z.A.K. Applied Physics Letters; 107 (22, 223501) 2015. 10.1063/1.4936757.

    Suspended silicon nanowires have significant potential for a broad spectrum of device applications. A suspended p-type Si nanowire incorporating Si nanocrystal quantum dots has been used to form a single-hole transistor. Transistor fabrication uses a novel and rapid process, based on focused gallium ion beam exposure and anisotropic wet etching, generating <10 nm nanocrystals inside suspended Si nanowires. Electrical characteristics at 10 K show Coulomb diamonds with charging energy ∼27 meV, associated with a single dominant nanocrystal. Resonant tunnelling features with energy spacing ∼10 meV are observed, parallel to both diamond edges. These may be associated either with excited states or hole-acoustic phonon interactions, in the nanocrystal. In the latter case, the energy spacing corresponds well with reported Raman spectroscopy results and phonon spectra calculations. © 2015 AIP Publishing LLC.


  • Size and aspect ratio control of Pd2Sn nanorods and their water denitration properties

    Luo Z., Ibáñez M., Antolín A.M., Genç A., Shavel A., Contreras S., Medina F., Arbiol J., Cabot A. Langmuir; 31 (13): 3952 - 3957. 2015. 10.1021/la504906q.

    Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration. © 2015 American Chemical Society.


  • Strain-induced spatially indirect exciton recombination in zinc-blende/wurtzite CdS heterostructures

    Li D., Liu Y., de la Mata M., Magen C., Arbiol J., Feng Y., Xiong Q. Nano Research; 8 (9): 3035 - 3044. 2015. 10.1007/s12274-015-0809-8.

    Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properties of hetero-structures consisting of different crystalline phases in the same CdS nanobelts. The strained portion was found to produce an additional emission peak on the low-energy side that was blueshifted with increasing strain. Furthermore, the additional emission peak obeyed the Varshni equation with temperature and exhibited the band-filling effect at high excitation power. This new emission peak may be attributed to spatially indirect exciton recombination between different crystalline phases of CdS. First-principles calculations were performed based on the spatially indirect exciton recombination, and the calculated and experimental results agreed with one another. Strain proved to be capable of enhancing the anti-Stokes emission, suggesting that the efficiency of laser cooling may be improved by strain engineering. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.


  • Surface modification of TiO2 nanocrystals by WOx coating or wrapping: Solvothermal synthesis and enhanced surface chemistry

    Epifani M., Diaz R., Force C., Comini E., Manzanares M., Andreu T., Gencc A., Arbiol J., Siciliano P., Faglia G., Morante J.R. ACS Applied Materials and Interfaces; 7 (12): 6898 - 6908. 2015. 10.1021/acsami.5b00632. IF: 6.723

    TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in the presence of W chloroalkoxide, with W/Ti nominal atomic concentration (Rw) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 °C for thermal stabilization and sensing device processing. For R0.16, the as-prepared materials were constituted by an anatase core surface-modified by WOx monolayers. This structure persisted up to 500 °C, without any WO3 phase segregation. For Rw up to R0.64, the anatase core was initially wrapped by an amorphous WOx gel. Upon heat treatment, the WOx phase underwent structural reorganization, remaining amorphous up to 400 °C and forming tiny WO3 nanocrystals dispersed into the TiO2 host after heating at 500 °C, when part of tungsten also migrated into the TiO2 structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compared with pure TiO2 and WO3 analogously prepared. They showed that even the simple surface modification of the TiO2 host resulted in a 3 orders of magnitude response improvement with respect to pure TiO2. © 2015 American Chemical Society.


  • Towards defect-free 1-D GaAs/AlGaAs heterostructures based on GaAs nanomembranes

    Tutuncuoglu G., De La Mata M., Deiana D., Potts H., Matteini F., Arbiol J., Fontcuberta I Morral A. Nanoscale; 7 (46): 19453 - 19460. 2015. 10.1039/c5nr04821d. IF: 7.394

    We demonstrate the growth of defect-free zinc-blende GaAs nanomembranes by molecular beam epitaxy. Our growth studies indicate a strong impact of As4 re-emission and shadowing in the growth rate of the structures. The highest aspect ratio structures are obtained for pitches around 0.7-1 μm and a gallium rate of 1 Å s-1. The functionality of the membranes is further illustrated by the growth of quantum heterostructures (such as quantum wells) and the characterization of their optical properties at the nanoscale. This proves the potential of nanoscale membranes for optoelectronic applications. © 2015 The Royal Society of Chemistry.


  • What do you do, titanium? Insight into the role of titanium oxide as a water oxidation promoter in hematite-based photoanodes

    Monllor-Satoca D., Bärtsch M., Fàbrega C., Genç A., Reinhard S., Andreu T., Arbiol J., Niederberger M., Morante J.R. Energy and Environmental Science; 8 (11): 3242 - 3254. 2015. 10.1039/c5ee01679g. IF: 20.523

    Hematite (α-Fe2O3) is a promising photoanode in solar water splitting devices with a set of intrinsic limitations that lessen its maximum performance; among the methods used for improving its photoactivity, titanium doping has witnessed an intensive research during recent years. However, the origin of the Ti-induced enhancement remains elusive to date with the lack of a systematic mechanistic study. In this contribution, we prepared mesoporous hematite (host)-titania (guest) composite films by mixing the respective preformed nanoparticles obtained by a non-aqueous sol-gel route in a wide range of loading levels (0-20 mol%) up to the solid state solubility limits of both components. Voltammetric and impedance measurements were performed observing an optimum 10% doping, with a 15-fold photocurrent increase (up to 1.3 mA cm-2 at 1.23 VRHE) and a 100-fold decrease in the charge transfer resistance. The roles of surface states and charge donor (dopant) densities were also assessed, assuming a charge transfer mechanism through hole trapping at surface states and its isoenergetic transfer to water; an optimum 10-15% doping range was obtained similarly to photocurrent, where the maximum overlapping between surface and water states is prevalent. Finally, HR-TEM and EELS measurements were employed to detect the presence of pseudobrookite and titania phases (20% doping), evincing that hematite-pseudobrookite heterojunctions have a beneficial cascade of charge transfers but titania-pseudobrookite heterojunctions depict a deleterious "hole mirror" mechanism that prevents water photooxidation. Tailoring the combined effect of donor states (conductivity), phase coexistence (solubility), heterojunctions (energetics) and surface states (kinetics) in the composite paves the way for understanding the mechanism of other dopant-induced changes and could be extended to further photoactive materials. © 2015 The Royal Society of Chemistry.


2014

  • Enabling electromechanical transduction in silicon nanowire mechanical resonators fabricated by focused ion beam implantation

    Llobet, J.; Sansa, M.; Gerbolés, M.; Mestres, N.; Arbiol, J.; Borrisé, X.; Pérez-Murano, F. Nanotechnology; 2014. 10.1088/0957-4484/25/13/135302. IF: 3.672


  • Programmed iron oxide nanoparticles disintegration in anaerobic digesters boosts biogas production

    Casals, E.; Barrena, R.; García, A.; González, E.; Delgado, L.; Busquets-Fité, M.; Font, X.; Arbiol, J.; Glatzel, P.; Kvashnina, K.; Sánchez, A.; Puntes, V. Small; 10 (14): 2801 - 2808. 2014. 10.1002/smll.201303703. IF: 7.514


2013

  • Spontaneous formation of hollow cobalt oxide nanoparticles by the Kirkendall effect at room temperature at the water-air interface

    Varón, M.; Ojea-Jimenez, I.; Arbiol, J.; Balcells, L.; Martínez, B.; Puntes, V.F. Nanoscale; 5: 2429 - 2436. 2013. 10.1039/c2nr32657d. IF: 6.233


2012

  • Citrate-Coated Gold Nanoparticles As Smart Scavengers for Mercury(II) Removal from Polluted Waters

    Ojea-Jiménez, I.; López, X.; Arbiol, J.; Puntes, V. ACS Nano; 6: 2253 - 2260. 2012. .


  • Synthesis of co-organosilane-Au nanocomposites via a controlled interphasic reduction

    Ojea-Jiménez, I.; Lorenzo, J.; Rebled, J.M.; Sendra, J.; Arbiol, J.; Puntes, V. Chemistry of Materials; 24: 4019 - 4027. 2012. 10.1021/cm300757j.


2011

  • Carving at the nanoscale: Sequential galvanic exchange and Kirkendall growth at room temperature

    González, E.; Arbiol, J.; Puntes, V.F. SCIENCE; 334: 1377 - 1380. 2011. 10.1126/science.1212822.


  • Pt nanocrystal evolution in the presence of Au(iii)-salts at room temperature: Spontaneous formation of AuPt heterodimers

    Lim, S.I.; Varon, M.; Ojea-Jiménez, I.; Arbiol, J.; Puntes, V. Journal of Materials Chemistry; 21: 11518 - 11523. 2011. 10.1039/c1jm10313j.


2010

  • Exploring the limitations of the use of competing reducers to control the morphology and composition of Pt and PtCo nanocrystals

    Lim, S.I.; Varón, M.; Ojea-Jiménez, I.; Arbiol, J.; Puntes, V. Chemistry of Materials; 22: 4495 - 4504. 2010. 10.1021/cm101436p.


  • Size-dependent passivation shell and magnetic properties in antiferromagnetic/ferrimagnetic core/shell MnO nanoparticles

    Lopez-Ortega, A.; Tobia, D.; Winkler, E.; Golosovsky, I.V.; Salazar-Alvarez, G.; Estrade, S.; Estrader, M.; Sort, J.; González, M.A.; Suriñach, S.; Arbiol, J.; Peiró, F.; Zysler, R.D.; Baro, M.D.; Nogués, J. Journal of the American Chemical Society; 132: 9398 - 9407. 2010. 10.1021/ja1021798.


  • Synthesis of platinum cubes, polypods, cuboctahedrons, and raspberries assisted by cobalt nanocrystals

    Lim, S.I.; Ojea-Jiménez, I.; Varon, M.; Casals, E.; Arbiol, J.; Puntes, V. Nano Letters; 10: 964 - 973. 2010. 10.1021/nl100032c.