Staff directory José Manuel Caicedo Roque

José Manuel Caicedo Roque

Research Engineer
Nanomaterials Growth Unit



  • Antisite Defects and Chemical Expansion in Low-damping, High-magnetization Yttrium Iron Garnet Films

    Santiso, J; Garcia, C; Romanque, C; Henry, L; Bernier, N; Bagues, N; Caicedo, JM; Valvidares, M; Sandiumenge, F Chemnanomat; 2023. 10.1002/cnma.202200495.

  • Enhanced Thermoelectric Properties of Misfit Bi2Sr2-xCaxCo2Oy: Isovalent Substitutions and Selective Phonon Scattering

    Chatterjee, A; Banik, A; El Sachat, A; Roque, JMC; Padilla-Pantoja, J; Torres, CS; Biswas, K; Santiso, J; Chavez-Angel, E Materials (Basel); 16 (4): 1413. 2023. 10.3390/ma16041413.

  • Tunable Molecular Electrodes for Bistable Polarization Screening

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


  • Effects of exsolution on the stability and morphology of Ni nanoparticles on BZY thin films

    Jennings D., Ricote S., Santiso J., Caicedo J., Reimanis I. Acta Materialia; 228 (117752) 2022. 10.1016/j.actamat.2022.117752. IF: 8.203

    Yttria doped barium zirconate (BZY) is of interest for use as a catalyst support material, supporting exsolved Ni nanoparticles. Exsolution has been hypothesized to impart catalytic nanoparticles with exceptional resistance to particle coarsening, a known degradation mechanism in catalysts. However, the mechanisms and kinetics of Ni nanoparticle coarsening in BZY are unknown. This work analyzes the kinetics of the coarsening of exsolved Ni nanoparticles on epitaxial BZY thin films at three temperatures (600, 700, and 800 ∘C) over a time span of 150 h. It is demonstrated that Ni coarsening transitions from an Ostwald ripening process to particle migration and coalescence after Ni particles reach a critical size. The coarsening behavior of BZY/Ni is shown to be dependent on the BZY surface orientation, with Ni particles on (111) oriented thin films coarsening the least. The preferred orientation relationships between Ni and BZY on (100), (110), and (111) oriented films are determined. Additionally, the morphology of Ni particles produced through exsolution and thin film dewetting are compared, showing that the socketing behavior and interfacial energy are independent of the Ni particle preparation method. © 2022

  • Role of pO2 and film microstructure on the memristive properties of La2NiO4+δ/LaNiO3−δ bilayers

    Maas K., Wulles C., Caicedo Roque J.M., Ballesteros B., Lafarge V., Santiso J., Burriel M. Journal of Materials Chemistry A; 10 (12): 6523 - 6530. 2022. 10.1039/d1ta10296f. IF: 12.732

    LaNiO3/La2NiO4 bilayers deposited at varying pO2 conditions resulted in remarkable differences in film microstructure and cell parameters, directly affecting the electrical behaviour of Pt/LaNiO3/La2NiO4/Pt devices. The devices deposited at low pO2 showed the largest memristance. We propose this is due to the formation of a p-type Schottky contact between LaNiO3 and La2NiO4, where the extent of its carrier depletion width can be modulated by the electric-field induced drift of interstitial oxygen ions acting as mobile acceptor dopants in La2NiO4 © 2022 The Royal Society of Chemistry

  • Tailored nano-columnar La2NiO4cathodes for improved electrode performance

    Stangl A., Riaz A., Rapenne L., Caicedo J.M., De Dios Sirvent J., Baiutti F., Jiménez C., Tarancón A., Mermoux M., Burriel M. Journal of Materials Chemistry A; 10 (5): 2528 - 2540. 2022. 10.1039/d1ta09110g. IF: 12.732

    La2NiO4 is a very promising cathode material for intermediate and low temperature solid oxide cell applications, due to its good electronic and ionic conductivity, together with its high oxygen exchange activity with a low activation energy. Oxygen incorporation and transport in La2NiO4 (L2NO4) thin films are limited by surface reactions. Hence, tailoring the morphology is expected to lead to an overall improvement of the electrode performance. We report the growth of nano-architectured La2NiO4 thin film electrodes by Pulsed Injection Metal Organic Chemical Vapour Deposition (PI-MOCVD), achieving vertically gapped columns with a multi-fold active surface area, leading to much faster oxygen exchange. This nano-columnar structure is rooted in a dense bottom layer serving as a good electronic and ionic conduction pathway. The microstructure is tuned by modification of the growth temperature and characterised by SEM, TEM and XRD. We studied the effect of surface activity by electrical conductivity relaxation measurements in fully dense and nano-columnar La2NiO4 thin films of various thicknesses grown on several different single crystal substrates. Our results demonstrate that the increased surface area, in combination with the opening of different surface terminations, leads to a significant enhancement of the total exchange activity in our films with an optimized nano-architectured microstructure. This journal is © The Royal Society of Chemistry.


  • Carbon Incorporation in MOCVD of MoS2Thin Films Grown from an Organosulfide Precursor

    Schaefer C.M., Caicedo Roque J.M., Sauthier G., Bousquet J., Hébert C., Sperling J.R., Pérez-Tomás A., Santiso J., Del Corro E., Garrido J.A. Chemistry of Materials; 33 (12): 4474 - 4487. 2021. 10.1021/acs.chemmater.1c00646. IF: 9.811

    With the rise of two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors and their prospective use in commercial (opto)electronic applications, it has become key to develop scalable and reliable TMD synthesis methods with well-monitored and controlled levels of impurities. While metal-organic chemical vapor deposition (MOCVD) has emerged as the method of choice for large-scale TMD fabrication, carbon (C) incorporation arising during MOCVD growth of TMDs has been a persistent concern-especially in instances where organic chalcogen precursors are desired as a less hazardous alternative to more toxic chalcogen hydrides. However, the underlying mechanisms of such unintentional C incorporation and the effects on film growth and properties are still elusive. Here, we report on the role of C-containing side products of organosulfur precursor pyrolysis in MoS2 thin films grown from molybdenum hexacarbonyl Mo(CO)6 and diethyl sulfide (CH3CH2)2S (DES). By combining in situ gas-phase monitoring with ex situ microscopy and spectroscopy analyses, we systematically investigate the effect of temperature and Mo(CO)6/DES/H2 gas mixture ratios on film morphology, chemical composition, and stoichiometry. Aiming at high-quality TMD growth that typically requires elevated growth temperatures and high DES/Mo(CO)6 precursor ratios, we observed that temperatures above DES pyrolysis onset (â 600 °C) and excessive DES flow result in the formation of nanographitic carbon, competing with MoS2 growth. We found that by introducing H2 gas to the process, DES pyrolysis is significantly hindered, which reduces carbon incorporation. The C content in the MoS2 films is shown to quench the MoS2 photoluminescence and influence the trion-To-exciton ratio via charge transfer. This finding is fundamental for understanding process-induced C impurity doping in MOCVD-grown 2D semiconductors and might have important implications for the functionality and performance of (opto)electronic devices. ©

  • Direct Visualization of Anti-Ferroelectric Switching Dynamics via Electrocaloric Imaging

    Vales-Castro P., Vellvehi M., Perpiñà X., Caicedo J.M., Jordà X., Faye R., Roleder K., Kajewski D., Perez-Tomas A., Defay E., Catalan G. Advanced Electronic Materials; 7 (12, 2100380) 2021. 10.1002/aelm.202100380. IF: 7.295

    The large electrocaloric coupling in PbZrO3 allows using high-speed infrared imaging for visualizing anti-ferroelectric switching dynamics via the associated temperature change. It is found that in ceramic samples of homogeneous temperature and thickness, switching is fast due to the generation of multiple nucleation sites, with devices responding in the millisecond range. By introducing gradients of thickness, however, it is possible to change the dynamics to propagation limited, whereby a single-phase boundary sweeps across the sample like a cold front, at a speed of ≈20 cm s−1. Additionally, introducing thermostatic temperature differences between two sides of the sample enables the simultaneous generation of a negative electrocaloric effect on one side and a positive one on the other, yielding a Janus-like electrocaloric response. © 2021 Wiley-VCH GmbH

  • Origin of large negative electrocaloric effect in antiferroelectric PbZr O3

    Vales-Castro P., Faye R., Vellvehi M., Nouchokgwe Y., Perpiñà X., Caicedo J.M., Jordà X., Roleder K., Kajewski D., Perez-Tomas A., Defay E., Catalan G. Physical Review B; 103 (5, 054112) 2021. 10.1103/PhysRevB.103.054112. IF: 4.036

    We have studied the electrocaloric response of the archetypal antiferroelectric PbZrO3 as a function of voltage and temperature in the vicinity of its antiferroelectric-paraelectric phase transition. Large electrocaloric effects of opposite signs, ranging from an electrocooling of -3.5 K to an electroheating of +5.5K, were directly measured with an infrared camera. We show by calorimetric and electromechanical measurements that the large negative electrocaloric effect comes from an endothermic antiferroelectric-ferroelectric switching, in contrast to dipole destabilization of the antiparallel lattice, previously proposed as an explanation for the negative electrocaloric effect of antiferroelectrics. © 2021 American Physical Society.

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

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

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

  • Pulsed laser deposition of epitaxial non-doped PbTiO3 thin films from Pbo-TiO2 mosaic targets

    Sakai J., Roque J.M.C., Vales-Castro P., Padilla-Pantoja J., Sauthier G., Santiso J. Coatings; 11 (6, 662) 2021. 10.3390/coatings11060662. IF: 2.881

    PbTiO3 (PTO) suffers from difficulty in preparing high-density robust bulk ceramics, which in turn has been a bottleneck in thin films growth with physical vapor deposition (PVD) methods. In the present work, we prepared non-doped PTO thin films by a pulsed laser deposition (PLD) method with either a single PTO target or a mosaic target consisting of PbO and TiO2 pie-shaped pieces. On the PTO single target, laser irradiation caused selective ablation of Pb, resulting in Tirich cone-shaped pillar structure on the surface, whereas the irradiated surface of PbO and TiO2 pieces was smoother. Epitaxial PTO films deposited on SrTiO3 (001) substrates from the pie-chart targets with PbO:TiO2 areal ratio from 3:5 to 5:3 resulted in composition, crystallinity, flatness, and ferroelectric properties almost independent of the areal ratio. The averaged composition of each film was close to stoichiometric, suggesting a compositional self-control mechanism. For growing epitaxial and high-quality non-doped PTO films, a PbO-TiO2 pie-chart target is advantageous in easiness of handling and stable surface structure. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

  • Strong strain gradients and phase coexistence at the metal-insulator transition in VO2 epitaxial films

    Rodríguez L., Sandiumenge F., Frontera C., Caicedo J.M., Padilla J., Catalán G., Santiso J. Acta Materialia; 220 (117336) 2021. 10.1016/j.actamat.2021.117336. IF: 8.203

    The proximity of a thermodynamic triple point and the formation of transient metastable phases may result in complex phase and microstructural trajectories across the metal-insulator transition in strained VO2 films. A detailed analysis using in-situ synchrotron X-ray diffraction unveils subtle fingerprints of this complexity in the structure of epitaxial films. During phase transition the low-temperature monoclinic M1 phase is constrained along the {111}R planes by the coexisting high-temperature R phase domains, which remain epitaxially clamped to the substrate. This geometrical constraint induces counteracting local stresses that result in a combined tilt and uniaxial in-plane compression of M1 domains, and a concomitant anomalous cR-axis elongation. This mechanism progressively transforms the M1 phase into the transitional triclinic phase (T), and ultimately into the monoclinic M2 phase, generating strong strain and tilt gradients that remain frozen after the complete transformation of the R phase upon cooling to RT. The transformation path of VO2 films, the complex competition between stable and metastable VO2 polymorphs and its impact on the structure of the low temperature monoclinic state, provide essential insights for understanding the electronic and mechanical properties of the films at the nanoscale, as well as to control their use in functional devices. © 2021

  • The effect of Ni and Fe on the decomposition of yttrium doped barium zirconate thin films

    Jennings D., Ricote S., Caicedo J.M., Santiso J., Reimanis I. Scripta Materialia; 201 (113948) 2021. 10.1016/j.scriptamat.2021.113948. IF: 5.611

    Transition metal dopants like Ni and Fe are known to influence the densification and microstructure evolution of yttrium doped barium zirconate (BZY), and understanding their behavior impacts the use of BZY in applications like protonic ceramic fuel cells and catalysts. This work investigates the effects of Ni and Fe on the evolution of BZY thin films in high temperature (1175°C), reducing environments, where BZY faceting and decomposition is observed. It is shown that the addition of Ni promotes film decomposition, whereas Fe prevents decomposition. The effects of the dopants on film decomposition are consistent with thermodynamic predictions that indicate the addition of Fe to the B-site of the perovskite structure diminishes the Gibbs free energy change for decomposition. © 2021


  • Control of lateral composition distribution in graded films of soluble solid systems A1-xBx by partitioned dual-beam pulsed laser deposition

    Sakai J., Roque J.M.C., Vales-Castro P., Padilla-Pantoja J., Sauthier G., Catalan G., Santiso J. Coatings; 10 (6, 540) 2020. 10.3390/COATINGS10060540. IF: 2.436

    Lateral compositionally-graded thin films are powerful media for the observation of phase boundaries aswell as for high-throughputmaterials exploration.We herein propose amethod to prepare epitaxial lateral compositionally-graded films using a dual-beampulsed laser deposition (PLD)method with two targets separated by a partition. Tuning the ambient pressure and the partition-substrate gap makes it possible to control of the gradient length of the deposits at the small sizes (≤ 10 mm) suitable for commercial oxide single crystal substrates. A simple Monte Carlo simulation qualitatively reproduced the characteristic features of the lateral thickness distribution. To demonstrate this method, we prepared (1-x)PbTiO3-xPbZrO3 and (1-x)LaMnO3-xLa0.6Sr0.4MnO3 films with lateral composition gradient widths of 10 and 1 mm, respectively, with the partitioned dual PLD. © 2020 by the authors.

  • Large thermoelectric power variations in epitaxial thin films of layered perovskite GdBaCo2O5.5±δwith a different preferred orientation and strain

    Chatterjee A., Chavez-Angel E., Ballesteros B., Caicedo J.M., Padilla-Pantoja J., Leborán V., Sotomayor Torres C.M., Rivadulla F., Santiso J. Journal of Materials Chemistry A; 8 (38): 19975 - 19983. 2020. 10.1039/d0ta04781c. IF: 11.301

    This work describes the growth of thin epitaxial films of the layered perovskite material GdBaCo2O5.5±δ(GBCO) on different single crystal substrates SrTiO3(STO), (LaAlO3)0.3(Sr2TaAlO6)0.7(LSAT) and LaAlO3(LAO) as an approach to study changes in the thermoelectric properties by means of the induced epitaxial strain. In addition to strain changes, the films grow with considerably different preferred orientations and domain microstructures: GBCO films on STO are purelyc-axis oriented (c⊥) with an average 0.18% in-plane tensile strain; GBCO on LSAT is composed of domains with a mixed orientation (c‖andc⊥) with an average 0.71% in-plane compressive strain; while on LAO it isb-axis oriented (c‖) with an average 0.89% in-plane compressive strain. These differences result in important cell volume changes, as well as in the orthorhombicity of thea-bplane of the GBCO structure, which in turn induce a change in the sign and temperature dependence of the thermopower, while the electrical conductivity remains almost unchanged. In general, compressively strained films show negativeSthermopower (n-type) while tensile strained films show a positiveS(p-type) at low temperatures, probing the adaptive nature of the GdBaCo2O5.5±δcompound. These results point to the spontaneous generation of oxygen vacancies to partially accommodate the epitaxial stress as the main cause for this effect. © The Royal Society of Chemistry 2020.

  • Revealing Strain Effects on the Chemical Composition of Perovskite Oxide Thin Films Surface, Bulk, and Interfaces

    van den Bosch C.A.M., Cavallaro A., Moreno R., Cibin G., Kerherve G., Caicedo J.M., Lippert T.K., Doebeli M., Santiso J., Skinner S.J., Aguadero A. Advanced Materials Interfaces; 7 (2, 1901440) 2020. 10.1002/admi.201901440. IF: 4.948

    Understanding the effects of lattice strain on oxygen surface and diffusion kinetics in oxides is a controversial subject that is critical for developing efficient energy storage and conversion materials. In this work, high-quality epitaxial thin films of the model perovskite La0.5Sr0.5Mn0.5Co0.5O3− δ (LSMC), under compressive or tensile strain, are characterized with a combination of in situ and ex situ bulk and surface-sensitive techniques. The results demonstrate a nonlinear correlation of mechanical and chemical properties as a function of the operation conditions. It is observed that the effect of strain on reducibility is dependent on the “effective strain” induced on the chemical bonds. In-plain strain, and in particular the relative BO length bond, is the key factor controlling which of the B-site cation can be reduced preferentially. Furthermore, the need to use a set of complimentary techniques to isolate different chemically induced strain effects is proven. With this, it is confirmed that tensile strain favors the stabilization of a more reduced lattice, accompanied by greater segregation of strontium secondary phases and a decrease of oxygen exchange kinetics on LSMC thin films. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Bipolar “table with legs” resistive switching in epitaxial perovskite heterostructures

    Bagdzevicius S., Boudard M., Caicedo J.M., Mescot X., Rodríguez-Lamas R., Santiso J., Burriel M. Solid State Ionics; 334: 29 - 35. 2019. 10.1016/j.ssi.2019.01.027. IF: 2.886

    We report the experimental investigation of bipolar resistive switching with “table with legs” shaped hysteresis switching loops in epitaxial perovskite GdBaCo 2 O 5+δ /LaNiO 3 bilayers deposited by pulsed laser deposition. The possibility of varying the resistivity of GdBaCo 2 O 5+δ by changing its oxygen content allowed engineering this perovskite heterostructure with controlled interfaces creating two symmetric junctions. It has been proved that the resistance state of the device can be reproducibly varied by both continuous voltage sweeps and by electrical pulses. The symmetric devices show slightly non-symmetric resistance profiles, which can be explained by a valence change resistive switching model, and presented promising multilevel properties required for novel memories and neuromorphic computing. © 2019

  • Superposition of interface and volume type resistive switching in perovskite nanoionic devices

    Bagdzevicius S., Boudard M., Caicedo J.M., Rapenne L., Mescot X., Rodríguez-Lamas R., Robaut F., Santiso J., Burriel M. Journal of Materials Chemistry C; 7 (25): 7580 - 7592. 2019. 10.1039/c9tc00609e. IF: 6.641

    The microelectronics industry is currently searching for reliable redox-based resistive switching (RS) memories which are filament-free, scale with the electrode size and do not require a high voltage electroforming step. Interface and volume type switching devices are the most promising memristors to achieve these challenging requirements, both for ReRAM (Resistive Random-Access Memories) non-volatile memory and neuromorphic computing applications. Here RS was investigated for the first time in nanoionic memristors based on GdBaCo2O5+δ (GBCO), an oxide with high oxygen mobility. Non-filamentary and non-volatile reproducible RS was obtained when GBCO is sandwiched between Ag and LaNiO3 (LNO) electrodes. The observed bipolar RS could be successfully induced both by voltage sweeps and by pulses, showing asymmetric clock-wise hysteretic R(V) characteristics at room temperature. The temperature dependence of two independent devices in high and low resistance states (HRS and LRS) revealed a gradual decrease of the resistance difference between the two states on cooling from room temperature to 150 K and its increase below 100 K. Similarly, the R(V) switching curves obtained at low temperature showed the disappearance of the hysteresis at 150 K and its reappearance at lower temperatures. The superposition of volume and interface type RS mechanisms have proven to be responsible for the observed non-volatile change of the remnant resistance. The volume-type RS was related to the variation of the GBCO resistivity due to a change in oxygen content. The interface-type RS, on the other hand, was associated to the created electronic and ionic conduction barrier between GBCO and the LNO bottom electrode. © 2019 The Royal Society of Chemistry.


  • An in operando study of chemical expansion and oxygen surface exchange rates in epitaxial GdBaCo2O5.5 electrodes in a solid-state electrochemical cell by time-resolved X-ray diffraction

    Chatterjee A., Caicedo J.M., Ballesteros B., Santiso J. Journal of Materials Chemistry A; 6 (26): 12430 - 12439. 2018. 10.1039/c8ta02790k. IF: 9.931

    This report explores the fundamental characteristics of epitaxial thin films of a mixed ionic electronic conducting GdBaCo2O5.5±δ (GBCO) material with a layered perovskite structure, relevant for use as an active electrode for the oxygen reduction and evolution reactions in electrochemical devices. Time-resolved X-ray diffraction in combination with voltage step chrono-amperometric measurements in a solid state electrochemical cell provides a deeper insight into the chemical expansion mechanism in the GBCO electrode. The chemical expansion coefficient along the c-axis, αc, shows a negative value upon the compound oxidation contrary to standard perovskite materials with disordered oxygen vacancies. Chemical expansion also shows a remarkable asymmetry from αc = -0.037 to -0.014 at δ < 0 and δ > 0, respectively. This change in chemical expansion is an indication of a different mechanism of the structural changes associated with the variable Co cation oxidation state from Co2+ → Co3+ → Co4+. Since redox reactions are dominated by oxygen surface exchange between the GBCO electrode and gas atmosphere, monitoring the time response of the structural changes allows for direct determination of oxygen reduction and evolution reaction kinetics. The reaction kinetics are progressively slowed down upon reduction in the δ < 0 oxygen stoichiometry region, while they maintain a high catalytic activity in the δ > 0 region, in agreement with the structural changes and the electronic carrier delocalization when crossing δ = 0. This work validates the time-resolved XRD technique for fast and reversible measurements of electrode activity in a wide range of oxygen non-stoichiometry in a solid-state electrochemical cell operating under realistic working conditions. © 2018 The Royal Society of Chemistry.