Staff directory

Jose Antonio Garrido Ariza

ICREA Research Professor and Group Leader
joseantonio.garrido(ELIMINAR) - Tel. +34937374648
Advanced Electronic Materials and Devices



  • Frequency response of electrolyte-gated graphene electrodes and transistors

    Drieschner S., Guimerà A., Cortadella R.G., Viana D., Makrygiannis E., Blaschke B.M., Vieten J., Garrido J.A. Journal of Physics D: Applied Physics; 50 (9, 095304) 2017. 10.1088/1361-6463/aa5443.

    The interface between graphene and aqueous electrolytes is of high importance for applications of graphene in the field of biosensors and bioelectronics. The graphene/electrolyte interface is governed by the low density of states of graphene that limits the capacitance near the Dirac point in graphene and the sheet resistance. While several reports have focused on studying the capacitance of graphene as a function of the gate voltage, the frequency response of graphene electrodes and electrolyte-gated transistors has not been discussed so far. Here, we report on the impedance characterization of single layer graphene electrodes and transistors, showing that due to the relatively high sheet resistance of graphene, the frequency response is governed by the distribution of resistive and capacitive circuit elements along the graphene/electrolyte interface. Based on an analytical solution for the impedance of the distributed circuit elements, we model the graphene/electrolyte interface both for the electrode and the transistor configurations. Using this model, we can extract the relevant material and device parameters such as the voltage-dependent intrinsic sheet and series resistances as well as the interfacial capacitance. The model also provides information about the frequency threshold of electrolyte-gated graphene transistors, above which the device exhibits a non-resistive response, offering an important insight into the suitable frequency range of operation of electrolyte-gated graphene devices. © 2017 IOP Publishing Ltd.

  • GaN surface states investigated by electrochemical studies

    Winnerl A., Garrido J.A., Stutzmann M. Applied Physics Letters; 110 (10, 101602) 2017. 10.1063/1.4977947.

    We present a systematic study of electrochemically active surface states on MOCVD-grown n-type GaN in aqueous electrolytes using cyclic voltammetry and impedance spectroscopy over a wide range of potentials and frequencies. In order to alter the surface states, the GaN samples are either etched or oxidized, and the influence of the surface treatment on the defect-mediated charge transfer to the electrolyte is investigated. Etching in HCl removes substoichiometric GaOx, and leads to a pronounced density of electrochemically active surface states. Oxidation effectively removes these surface states. © 2017 Author(s).


  • Flexible graphene transistors for recording cell action potentials

    Blaschke B.M., Lottner M., Drieschner S., Calia A.B., Stoiber K., Rousseau L., Lissourges G., Garrido J.A. 2D Materials; 3 (2, 025007) 2016. 10.1088/2053-1583/3/2/025007. IF: 9.611

    Graphene solution-gated field-effect transistors (SGFETs) are a promising platform for the recording of cell action potentials due to the intrinsic high signal amplification of graphene transistors. In addition, graphene technology fulfills important key requirements for in-vivo applications, such as biocompability, mechanical flexibility, as well as ease of high density integration. In this paper we demonstrate the fabrication of flexible arrays of graphene SGFETs on polyimide, a biocompatible polymeric substrate. We investigate the transistor's transconductance and intrinsic electronic noise which are key parameters for the device sensitivity, confirming that the obtained values are comparable to those of rigid graphene SGFETs. Furthermore, we show that the devices do not degrade during repeated bending and the transconductance, governed by the electronic properties of graphene, is unaffected by bending. After cell culture, we demonstrate the recording of cell action potentials from cardiomyocyte-like cells with a high signal-to-noise ratio that is higher or comparable to competing state of the art technologies. Our results highlight the great capabilities of flexible graphene SGFETs in bioelectronics, providing a solid foundation for in-vivo experiments and, eventually, for graphene-based neuroprosthetics. © 2016 IOP Publishing Ltd.

  • High surface area graphene foams by chemical vapor deposition

    Drieschner S., Weber M., Wohlketzetter J., Vieten J., Makrygiannis E., Blaschke B.M., Morandi V., Colombo L., Bonaccorso F., Garrido J.A. 2D Materials; 3 (4, 045013) 2016. 10.1088/2053-1583/3/4/045013. IF: 9.611

    Three-dimensional (3D) graphene-based structures combine the unique physical properties of graphene with the opportunity to get high electrochemically available surface area per unit of geometric surface area. Several preparation techniques have been reported to fabricate 3D graphene-based macroscopic structures for energy storage applications such as supercapacitors. Although reaserch has been focused so far on achieving either high specific capacitance or high volumetric capacitance, much less attention has been dedicated to obtain high specific and high volumetric capacitance simultaneously. Here, we present a facile technique to fabricate graphene foams (GF) of high crystal quality with tunable pore size grown by chemical vapor deposition. We exploited porous sacrificial templates prepared by sintering nickel and copper metal powders. Tuning the particle size of the metal powders and the growth temperature allow fine control of the resulting pore size of the 3D graphene-based structures smaller than 1 μm. The as-produced 3D graphene structures provide a high volumetric electric double layer capacitance (165 mF cm-3). High specific capacitance (100 Fg-1) is obtained by lowering the number of layers down to single layer graphene. Furthermore, the small pore size increases the stability of these GFs in contrast to the ones that have been grown so far on commercial metal foams. Electrodes based on the as-prepared GFs can be a boost for the development of supercapacitors, where both low volume and mass are required. © 2016 IOP Publishing Ltd.

  • Suppression of Photoanodic Surface Oxidation of n-Type 6H-SiC Electrodes in Aqueous Electrolytes

    Sachsenhauser M., Walczak K., Hampel P.A., Stutzmann M., Sharp I.D., Garrido J.A. Langmuir; 32 (6): 1637 - 1644. 2016. 10.1021/acs.langmuir.5b04376. IF: 3.993

    The photoelectrochemical characterization of silicon carbide (SiC) electrodes is important for enabling a wide range of potential applications for this semiconductor. However, photocorrosion of the SiC surface remains a key challenge, because this process considerably hinders the deployment of this material into functional devices. In this report, we use cyclic voltammetry to investigate the stability of n-type 6H-SiC photoelectrodes in buffered aqueous electrolytes. For measurements in pure Tris buffer, photogenerated holes accumulate at the interface under anodic polarization, resulting in the formation of a porous surface oxide layer. Two possibilities are presented to significantly enhance the stability of the SiC photoelectrodes. In the first approach, redox molecules are added to the buffer solution to kinetically facilitate hole transfer to these molecules, and in the second approach, water oxidation in the electrolyte is induced by depositing a cobalt phosphate catalyst onto the semiconductor surface. Both methods are found to effectively suppress photocorrosion of the SiC electrodes, as confirmed by atomic force microscopy and X-ray photoelectron spectroscopy measurements. The presented study provides straightforward routes to stabilize n-type SiC photoelectrodes in aqueous electrolytes, which is essential for a possible utilization of this material in the fields of photocatalysis and multimodal biosensing. © 2016 American Chemical Society.

  • Surface State Mediated Electron Transfer Across the N-Type SiC/Electrolyte Interface

    Sachsenhauser M., Sharp I.D., Stutzmann M., Garrido J.A. Journal of Physical Chemistry C; 120 (12): 6524 - 6533. 2016. 10.1021/acs.jpcc.5b11569. IF: 4.509

    Understanding the mechanisms of charge transfer across the semiconductor/electrolyte interface is a basic prerequisite for a variety of practical applications. In particular, electrically active surface states located in the semiconductor band gap are expected to play an important role, but direct experimental evidence of surface states has proven to be challenging, and further experimental studies are required to verify their influence on the exchange of charge carriers between semiconductor and electrolyte. Due to its wide band gap, chemical stability, and controllable surface termination, silicon carbide (SiC) provides an excellent model system for this purpose. In this report, we provide a fundamental electrochemical study of n-type 6H-SiC and 4H-SiC electrodes in aqueous electrolytes containing the ferricyanide/ferrocyanide redox couple. Cyclic voltammetry and impedance spectroscopy measurements are performed over a wide range of potentials to determine the energetic positions of the SiC band edges and to investigate the electron-transfer kinetics between SiC and the ferricyanide molecules. For both polytypes, a broad distribution of surface states with energy levels close to the conduction band is found to mediate electron transfer, resulting in deviations of the observed charge transport characteristics from the predictions of well-established models. Moreover, a detailed evaluation of the impedance data allows for explicit correlation of the charge-transfer resistance associated with the ferricyanide reduction reaction with the potential-dependent distribution of surface states. In addition to the relevance of our studies for advancing the implementation of SiC in biosensing, electrocatalytic, and photocatalytic applications, the presented methodology can also be adopted for fundamental electrochemical investigations of other semiconductor electrodes. (Figure Presented). © 2016 American Chemical Society.

  • α,ω -dihexyl-sexithiophene thin films for solution-gated organic field-effect transistors

    Schamoni H., Noever S., Nickel B., Stutzmann M., Garrido J.A. Applied Physics Letters; 108 (7, 073301) 2016. 10.1063/1.4942407. IF: 3.142

    While organic semiconductors are being widely investigated for chemical and biochemical sensing applications, major drawbacks such as the poor device stability and low charge carrier mobility in aqueous electrolytes have not yet been solved to complete satisfaction. In this work, solution-gated organic field-effect transistors (SGOFETs) based on the molecule α,ω-dihexyl-sexithiophene (DH6T) are presented as promising platforms for in-electrolyte sensing. Thin films of DH6T were investigated with regard to the influence of the substrate temperature during deposition on the grain size and structural order. The performance of SGOFETs can be improved by choosing suitable growth parameters that lead to a two-dimensional film morphology and a high degree of structural order. Furthermore, the capability of the SGOFETs to detect changes in the pH or ionic strength of the gate electrolyte is demonstrated and simulated. Finally, excellent transistor stability is confirmed by continuously operating the device over a period of several days, which is a consequence of the low threshold voltage of DH6T-based SGOFETs. Altogether, our results demonstrate the feasibility of high performance and highly stable organic semiconductor devices for chemical or biochemical applications. © 2016 AIP Publishing LLC.


  • 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. IF: 13.592

    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.

  • Role of grain boundaries in tailoring electronic properties of polycrystalline graphene by chemical functionalization

    Seifert M., Vargas J.E.B., Bobinger M., Sachsenhauser M., Cummings A.W., Roche S., Garrido J.A. 2D Materials; 2 (2, 024008) 2015. 10.1088/2053-1583/2/2/024008. IF: 0.000

    Grain boundaries, inevitably present in chemical vapor deposited graphene, are expected to have considerable impact on the development of graphene-based hybrid materials with tailored material properties.Wedemonstrate here the critical role of polycrystallinity on the chemical functionalization of graphene comparing ozone-induced oxidation with remote plasma hydrogenation.Weshow that graphene oxidation and hydrogenation occur in two consecutive stages upon increasing defect density: an initial step in which surface-bound functional groups are generated, followed by the creation of vacancies. Remarkably, we find that hydrogenation yields homogeneously distributed defects while ozone-induced defects are preferentially accumulated at the grain boundaries eventually provoking local cracking of the structure. Supported by quantum simulations, our experimental findings reveal distinct electronic transport regimes depending on the density and distribution of induced defects on the polycrystalline graphene films. Our findings highlight the key role played by grain boundaries during graphene functionalization, and at the same time provide a novel perspective to tailor the properties of polycrystalline graphene. © 2015 IOP Publishing Ltd.

  • Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

    Ferrari A.C., Bonaccorso F., Fal'ko V., Novoselov K.S., Roche S., Bøggild P., Borini S., Koppens F.H.L., Palermo V., Pugno N., Garrido J.A., Sordan R., Bianco A., Ballerini L., Prato M., Lidorikis E., Kivioja J., Marinelli C., Ryhänen T., Morpurgo A., Coleman J.N., Nicolosi V., Colombo L., Fert A., Garcia-Hernandez M., Bachtold A., Schneider G.F., Guinea F., Dekker C., Barbone M., Sun Z., Galiotis C., Grigorenko A.N., Konstantatos G., Kis A., Katsnelson M., Vandersypen L., Loiseau A., Morandi V., Neumaier D., Treossi E., Pellegrini V., Polini M., Tredicucci A., Williams G.M., Hee Hong B., Ahn J.-H., Min Kim J., Zirath H., Van Wees B.J., Van Der Zant H., Occhipinti L., Di Matteo A., Kinloch I.A., Seyller T., Quesnel E., Feng X., Teo K., Rupesinghe N., Hakonen P., Neil S.R.T., Tannock Q., Löfwander T., Kinaret J. Nanoscale; 7 (11): 4598 - 4810. 2015. 10.1039/c4nr01600a. IF: 7.394

    We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field. © The Royal Society of Chemistry 2015.