Staff directory María José Esplandiu Egido

Publications

2018

  • Impact of the: In situ rise in hydrogen partial pressure on graphene shape evolution during CVD growth of graphene

    Gebeyehu Z.M., Arrighi A., Costache M.V., Sotomayor-Torres C.M., Esplandiu M.J., Valenzuela S.O. RSC Advances; 8 (15): 8234 - 8239. 2018. 10.1039/c7ra13169k.

    Exposing graphene to a hydrogen post-etching process yields dendritic graphene shapes. Here, we demonstrate that similar dendritic structures can be achieved at long growth times without adding hydrogen externally. These shapes are not a result of a surface diffusion controlled growth but of the competing backward reaction (etching), which dominates the growth dynamics at long times due to an in situ rise in the hydrogen partial pressure. We have performed a systematic study on the growth of graphene as a function of time to identify the onset and gradual evolution of graphene shapes caused by etching and then demonstrated that the etching can be stopped by reducing the flow of hydrogen from the feed. In addition, we have found that the etching rate due to the in situ rise in hydrogen is strongly dependent on the confinement (geometrical confinement) of copper foil. Highly etched graphene with dendritic shapes was observed in unconfined copper foil regions while no etching was found in graphene grown in a confined reaction region. This highlights the effect of the dynamic reactant distribution in activating the in situ etching process during growth, which needs to be counteracted or controlled for large scale growth. © The Royal Society of Chemistry 2018.


  • Unraveling the Operational Mechanisms of Chemically Propelled Motors with Micropumps

    Esplandiu M.J., Zhang K., Fraxedas J., Sepulveda B., Reguera D. Accounts of Chemical Research; 51 (9): 1921 - 1930. 2018. 10.1021/acs.accounts.8b00241.

    ConspectusThe development of effective autonomous micro- and nanomotors relies on controlling fluid motion at interfaces. One of the main challenges in the engineering of such artificial machines is the quest for efficient mechanisms to power them without using external driving forces. In the past decade, there has been an important increase of man-made micro- and nanomotors fueled by self-generated physicochemical gradients. Impressive proofs of concept of multitasking machines have been reported demonstrating their capabilities for a plethora of applications. While the progress toward applications is promising, there are still open questions on fundamental physicochemical aspects behind the mechanical actuation, which require more experimental and theoretical efforts. These efforts are not merely academic but will open the door for an efficient and practical implementation of such promising devices.In this Account, we focus on chemically driven motors whose motion is the result of a complex interplay of chemical reactions and (electro)hydrodynamic phenomena. A reliable study of these processes is rather difficult with mobile objects like swimming motors. However, pumps, which are the immobilized motor counterparts, emerge as simple manufacturing and well-defined platforms for a better experimental probing of the mechanisms and key parameters controlling the actuation.Here we review some recent studies using a new methodology that has turned out to be very helpful to characterize micropump chemomechanics. The aim was to identify the redox role of the motor components, to map the chemical reaction, and to quantify the relevant electrokinetic parameters (e.g., electric field and fluid flow). This was achieved by monitoring the velocity of differently charged tracers and by fluorescence imaging of the chemical species involved in the chemical reaction, for example, proton gradients. We applied these techniques to different systems of interest. First, we probed bimetallic pumps as counterparts of the pioneering bimetallic swimmers. We corroborated that fluid motion was due to a self-generated electro-osmotic mechanism driven by the redox decomposition of H2O2. In addition, we analyzed by simulations the key parameters that yield an optimized operation. Moreover, we accomplished a better assessment of the importance of surface chemistry on the metal electrochemical response, highlighting its relevance in controlling the redox role of the metals and motion direction.Second, we focused on metallic and semiconductor micropumps to analyze light-controlled motion mechanisms through photoelectrochemical decomposition of fuels. These pumps were driven by visible light and could operate using just water as fuel. In these systems, we found a very interesting competition between two different mechanisms for fluid propulsion, namely, light-activated electro-osmosis and light-insensitive diffusio-osmosis, stemming from different chemical pathways in the fuel decomposition. In this case, surface roughness becomes a pivotal parameter to enhance or depress one mechanism over the other.These examples demonstrate that pumps are practical platforms to explore operating mechanisms and to quantify their performance. Additionally, they are suitable systems to test novel fuels or motor materials. This knowledge is extensible to swimmers providing not only fundamental understanding of their locomotion mechanisms but also useful clues for their design and optimization. © 2018 American Chemical Society.


2017

  • Photochemically Activated Motors: From Electrokinetic to Diffusion Motion Control

    Zhang K., Fraxedas J., Sepulveda B., Esplandiu M.J. ACS Applied Materials and Interfaces; 9 (51): 44948 - 44953. 2017. 10.1021/acsami.7b15855. IF: 7.504

    Self-propelled micro/nanomotors that can transform chemical energy from the surrounding environment into mechanical motion are cutting edge nanotechnologies with potential applications in biomedicine and environmental remediation. These applications require full understanding of the propulsion mechanisms to improve the performance and controllability of the motors. In this work, we demonstrate that there are two competing chemomechanical mechanisms at semiconductor/metal (Si/Pt) micromotors in a pump configuration under visible light exposure. The first propulsion mechanism is driven by an electro-osmotic process stemmed from a photoactivation reaction mediated by H2O2, which takes place in two separated redox reactions at the Si and Pt interfaces. One reaction involves the oxidation of H2O2 at the silicon side, and the other the H2O2 reduction at the metal side. The second mechanism is not light responsive and is triggered by the redox decomposition of H2O2 exclusively at the Pt surface. We show that it is possible to enhance/suppress one mechanism over the other by tuning the surface roughness of the micromotor metal. More specifically, the actuation mechanism can be switched from light-controlled electrokinetics to light-insensitive diffusio-osmosis by only increasing the metal surface roughness. The different actuation mechanisms yield strikingly different fluid flow velocities, electric fields, and light sensitivities. Consequently, these findings are very relevant and can have a remarkable impact on the design and optimization of photoactivated catalytic devices and, in general, on bimetallic or insulating-metallic motors. © 2017 American Chemical Society.


2016

  • Key parameters controlling the performance of catalytic motors

    Esplandiu M.J., Afshar Farniya A., Reguera D. Journal of Chemical Physics; 144 (12, 124702) 2016. 10.1063/1.4944319. IF: 2.894

    The development of autonomous micro/nanomotors driven by self-generated chemical gradients is a topic of high interest given their potential impact in medicine and environmental remediation. Although impressive functionalities of these devices have been demonstrated, a detailed understanding of the propulsion mechanism is still lacking. In this work, we perform a comprehensive numerical analysis of the key parameters governing the actuation of bimetallic catalytic micropumps. We show that the fluid motion is driven by self-generated electro-osmosis where the electric field originates by a proton current rather than by a lateral charge asymmetry inside the double layer. Hence, the surface potential and the electric field are the key parameters for setting the pumping strength and directionality. The proton flux that generates the electric field stems from the proton gradient induced by the electrochemical reactions taken place at the pump. Surprisingly the electric field and consequently the fluid flow are mainly controlled by the ionic strength and not by the conductivity of the solution, as one could have expected. We have also analyzed the influence of the chemical fuel concentration, electrochemical reaction rates, and size of the metallic structures for an optimized pump performance. Our findings cast light on the complex chemomechanical actuation of catalytic motors and provide important clues for the search, design, and optimization of novel catalytic actuators. © 2016 AIP Publishing LLC.


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

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

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


2015

  • Elucidation of the wettability of graphene through a multi-length-scale investigation approach

    Amadei C.A., Lai C.-Y., Esplandiu M.J., Alzina F., Vecitis C.D., Verdaguer A., Chiesa M. RSC Advances; 5 (49): 39532 - 39538. 2015. 10.1039/c5ra04397b. IF: 3.840

    Univocal conclusions around the wettability of graphene exposed to environmental conditions remain elusive despite the recent efforts of several research groups. The main discrepancy rests on the question of whether a graphene monolayer (GML) is transparent or not to water and more generally what the role is that the substrate plays in determining the degree of wetting of the GML. In this work, we investigate the water transparency of GML by means of a multi-length-scale approach. We complement traditional static contact angle measurements and environmental scanning electron microscopy experiments with atomic force microscopy based force spectroscopy to assess the role that intermolecular interactions play in determining the wetting of GML. To gain deeper insight into the wetting transparency issue, we perform experiments on inert metals, such as gold and platinum, covered or not covered by GML. The comparison of the results obtained for different systems (i.e. GML covered and uncovered inert metals), provides unambiguous evidence that supports the non-wetting transparency theory of GML. This work aims to assist the development of technologies based on graphene-water interaction, such as graphitic membranes for water separation processes. © The Royal Society of Chemistry 2015.


  • Silicon-Based Chemical Motors: An Efficient Pump for Triggering and Guiding Fluid Motion Using Visible Light

    Esplandiu M.J., Afshar Farniya A., Bachtold A. ACS Nano; 9 (11): 11234 - 11240. 2015. 10.1021/acsnano.5b04830. IF: 12.881

    We report a simple yet highly efficient chemical motor that can be controlled with visible light. The motor made from a noble metal and doped silicon acts as a pump, which is driven through a light-activated catalytic reaction process. We show that the actuation is based on electro-osmosis with the electric field generated by chemical reactions at the metal and silicon surfaces, whereas the contribution of diffusio-osmosis to the actuation is negligible. Surprisingly, the pump can be operated using water as fuel. This is possible because of the large - Potential of silicon, which makes the electro-osmotic fluid motion sizable even though the electric field generated by the reaction is weak. The electro-hydrodynamic process is greatly amplified with the addition of reactive species, such as hydrogen peroxide, which generates higher electric fields. Another remarkable finding is the tunability of silicon-based pumps. That is, it is possible to control the speed of the fluid with light. We take advantage of this property to manipulate the spatial distribution of colloidal microparticles in the liquid and to pattern colloidal microparticle structures at specific locations on a wafer surface. Silicon-based pumps hold great promise for controlled mass transport in fluids. © 2015 American Chemical Society.


2014

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

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


  • Sequential tasks performed by catalytic pumps for colloidal crystallization

    Afshar Farniya, A.; Esplandiu, M.J.; Bachtold, A. Langmuir : the ACS journal of surfaces and colloids; 30 (39): 11841 - 11845. 2014. 10.1021/la503118t. IF: 4.384


  • Synthesis of polydopamine at the femtoliter scale and confined fabrication of Ag nanoparticles on surfaces

    Guardingo, M.; Esplandiu, M.J.; Ruiz-Molina, D. Chemical Communications; 50 (83): 12548 - 12551. 2014. 10.1039/c4cc02500h. IF: 6.718


2013

  • Imaging the proton concentration and mapping the spatial distribution of the electric field of catalytic micropumps

    Farniya, A.A.; Esplandiu, M.J.; Reguera, D.; Bachtold, A. Physical Review Letters; 111 2013. 10.1103/PhysRevLett.111.168301. IF: 7.943


  • Ultrasensitive force detection with a nanotube mechanical resonator

    Moser, J.; Güttinger, J.; Eichler, A.; Esplandiu, M.J.; Liu, D.E.; Dykman, M.I.; Bachtold, A. Nature Nanotechnology; 8: 493 - 496. 2013. 10.1038/nnano.2013.97. IF: 31.170


2012

  • A simple approach for DNA detection on carbon nanotube microelectrode arrays

    Pacios, M.; Yilmaz, N.; Martín-Fernández, I.; Villa, R.; Godignon, P.; Del Valle, M.; Bartrolí, J.; Esplandiu, M.J. Sensors and Actuators, B: Chemical; 162: 120 - 127. 2012. 10.1016/j.snb.2011.12.048.


  • Asymmetric Hybrid Silica Nanomotors for Capture and Cargo Transport: Towards a Novel Motion-Based DNA Sensor

    Simmchen, J. ; Baeza, A.; Ruiz, D. ; Esplandiu, M. J.; Vallet-Regí, M. Small; 8 (13): 2053 - 2059. 2012. .


  • Asymmetric hybrid silica nanomotors for capture and cargo transport: Towards a novel motion-based DNA sensor

    Simmchen, J.; Baeza, A.; Ruiz, D.; Esplandiu, M.J.; Vallet-Regí, M. Small; 8: 2053 - 2059. 2012. 10.1002/smll.201101593.


  • Novel Approach for Energy Spectrum Probing in Semiconducting Quantum Dots

    Drojek, Z.; Wasik, M. ; Esplandiu, M.J. ; Bachtold, A. Acta Physica Polonica A; 122: 321. 2012. .


2010

  • Electrostatic and hydrophobic interactions of the ODN adsorption process on carbon nanotubes

    Carot, M.; García, C.; Esplandiu, M.J.; Toressi, R.; Giacomelli, C. Journal of Physical Chemistry C; 114: 4459 - 4465. 2010. .


  • Impedimetric genosensing of DNA polymorphism correlated to cystic fibrosis: A comparison among different protocols and electrode surfaces

    Bonanni, A.; Esplandiu, M.J.; Del Valle, M. Biosensors and Bioelectronics; 26: 1245 - 1251. 2010. .


  • Massive manufacture and characterization of single-walled carbon nanotube field effect transistors

    Martin-Fernandez, I.; Sansa, M.; Esplandiu, M.J.; Lora-Tamayo, E.; Perez-Murano, F.; Godignon, P. Microelectronic Engineering; 87: 1554 - 1556. 2010. 10.1016/j.mee.2009.11.026.


  • Strategies for the optimization of carbon nanotube/polymer ratio in composite materials: Applications as voltammetric sensors

    Olivé-Monllau, R.; Esplandiu, M.J.; Baeza, M. ; Céspedes, F.; Bartroli, J. Sensors and Actuators, B: Chemical; 146: 356 - 360. 2010. .


2009

  • Electron counting spectroscopy of CdSe quantum dots

    Zdrojek, M.; Esplandiu, M.J.; Barreiro, A.; Bachtold, A. Physical Review Letters; 102 2009. 10.1103/PhysRevLett.102.226804.


2007

  • Detecting individual electrons using a carbon nanotube field-effect transistor

    Gruneis, A.; Esplandiu, M.J.; Garcia-Sanchez, D.; Bachtold, A. Nano Letters; 7: 3766 - 3769. 2007. 10.1021/nl072243w.


  • Mechanical detection of carbon nanotube resonator vibrations

    Garcia-Sanchez, D.; San Paulo, A.; Esplandiu, M.J.; Perez-Murano, F.; Forró, L.; Aguasca, A.; Bachtold, A. Physical Review Letters; 99 2007. 10.1103/PhysRevLett.99.085501.