Joan Daniel Prades

University of Barcelona, Barcino, Catalonia, Spain

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Publications (104)304.41 Total impact

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    ABSTRACT: One dimensional (1D) nanostructures offer a promising path towards a highly efficient heating and temperature control in integrated microsystems. The so called self-heating effect can be used to modulate the response of solid state gas sensor devices. In this work, efficient self-heating was found to occur at random networks of nanostructured systems with similar power requirements than in highly ordered systems (e.g. individual nanowires, where its thermal efficiency attributed to the small dimensions of the objects). Infrared thermography and Raman spectroscopy were used to map the temperature profiles of films based on random arrangements of carbon nanofibers during self-heating occurrence. Both techniques demonstrate consistently that heating concentrates in small regions, the here-called “hot-spots”. Correlating dynamic temperature mapping with electrical measurements, we also observed that these minute hot-spots rule the resistance values observed macroscopically. A physical model of a random network of 1D resistors helped us to explain this observation. The model shows that, for a given random arrangement of 1D nanowires, current spreading though the network ends up defining a set of spots that dominate both the electrical resistance and the power dissipation. Such highly localized heating explains the high power savings observed in larger nanostructured systems. This understanding opens a path to design highly efficient self-heating systems, based on random or pseudo-random distributions of 1D nanostructures.
    No preview · Article · Feb 2016 · Nanoscale
  • O. Monereo · O. Casals · J.D. Prades · A. Cirera
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    ABSTRACT: The usual operation of a conductometric sensor device requires of an external energy source (i.e. an embedded heater). In the last years, the Joule effect in the sensing material, the so called self-heating effect, offered and alternative method to provide this energy: the probing current (or voltage) applied to measure the sensor signal also serves to heat up the sensor active film. Here, evidences of self-heating effects occurring on large arrays of nanostructures fabricated with low-cost methods are provided. The methodology is proven to be suitable to sense gases (humidity, NH3 and NO2) with low-powered heater-free devices.
    No preview · Article · Dec 2015 · Procedia Engineering
  • O. Monereo · O. Casals · J.D. Prades · A. Cirera
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    ABSTRACT: Sensor signal instability and drift are still unresolved challenges in conductometric gas sensors. Here, the use of self-heating effect to operate a gas sensor in a pulsed temperature modulation mode (pulsed self-heating operation) is presented as an effective method to enhance signal stability and reduce consumption figures down to a few μW. The sensor operation temperature was pulsed periodically between two levels, obtaining two different sensing states from one single device driven with self-heating, i.e. free of heater. The signal differences between both operating points correlated well with gas concentrations and displayed no drift. This methodology is exemplified with a thorough study of the response of carbon nanofibers to humidity. Specifically, after analyzing the influence of the pulse characteristics (i.e. temperature variation, pulse period and pulse duty cycle) on the sensor performance, thumb rules to select suitable pulsing conditions are provided. The methodology is successfully extended to other target gases, such as NO2 and NH3. Finally, its implementation in a real-time sensing system with low computational requirements is demonstrated and discussed in detail.
    No preview · Article · Nov 2015 · Sensors and Actuators B Chemical
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    ABSTRACT: Dielectrophoretic alignment is found to be a simple and efficient method to deposit the solution prepared ZnO nanowires onto micro hot plate substrates. Due to the strong surface effects, positive temperature coefficient for resistance was encountered with ZnO nanowires in the high temperature range (>250 °C). The response to ammonia (NH3) was evaluated in isothermal and temperature-pulsed operation mode; the relative higher response observed in the latter case demonstrates that the use of this methodology is a good strategy to improve the performance of metal oxide sensors based on nanomaterials. Here, we evaluate the response to NH3 and qualitatively describe the sensing mechanism in temperature-pulsed mode, highlighting the main differences compared to the standard isothermal methodology.
    No preview · Article · Nov 2015 · Sensors and Actuators B Chemical
  • Borja Martinez · Marius Monton · Ignasi Vilajosana · Joan Daniel Prades
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    ABSTRACT: Low-energy technologies in the Internet of Things (IoTs) era are still unable to provide the reliability needed by the industrial world, particularly in terms of the wireless operation that pervasive deployments demand. While the industrial wireless performance has achieved an acceptable degree in communications, it is no easy task to determine an efficient energy-dimensioning of the device in order to meet the application requirements. This is especially true in the face of the uncertainty inherent in energy harvesting. Thus, it is of utmost importance to model and dimension the energy consumption of the IoT applications at the pre-deployment or pre-production stages, especially when considering critical factors, such as reduced cost, life-time, and available energy. This paper presents a comprehensive model for the power consumption of wireless sensor nodes. The model takes a system-level perspective to account for all energy expenditures: communications, acquisition and processing. Furthermore, it is based only on parameters that can empirically be quantified once the platform (i.e., technology) and the application (i.e., operating conditions) are defined. This results in a new framework for studying and analyzing the energy life-cycles in applications, and it is suitable for determining in advance the specific weight of application parameters, as well as for understanding the tolerance margins and tradeoffs in the system.
    No preview · Article · Oct 2015 · IEEE Sensors Journal
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    ABSTRACT: The prevailing design approaches of semiconductor gas sensors struggle to overcome most of their current limitations such as poor selectivity, and high power consumption. Herein, a new sensing concept based on devices that are capable of detecting gases without the need of any external power sources required to activate interaction of gases with sensor or to generate the sensor read out signal. Based on the integration of complementary functionalities (namely; powering and sensing) in a singular nanostructure, self-sustained gas sensors will be demonstrated. Moreover, a rational methodology to design organic surface functionalization that provide high selectivity towards single gas species will also be discussed. Specifically, theoretical results, confirmed experimentally, indicate that precisely tuning of the sterical and electronic structure of sensor material/organic interfaces can lead to unprecedented selectivity values, comparable to those typical of bioselective processes. Finally, an integrated gas sensor that combine both the self-powering and selective detection strategies in one single device will also be presented.
    No preview · Conference Paper · Sep 2015
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    ABSTRACT: The integration of one dimensional (1D) nanostructures of non-industry-standard semiconductors in functional devices following bottom-up approaches is still an open challenge that hampers the exploitation of all their potential. Here, we present a simple approach to integrate metal oxide nanowires in electronic devices based on controlled dielectrophoretic positioning together with proof of concept devices that corroborate their functionality. The method is flexible enough to manipulate nanowires of different sizes and compositions exclusively using macroscopic solution-based techniques in conventional electrode designs. Our results show that fully functional devices, which display all the advantages of single-nanowire gas sensors, photodetectors, and even field-effect transistors, are thus obtained right after a direct assembly step without subsequent metallization processing. This paves the way to low cost, high throughput manufacturing of general-purpose electronic devices based on non-conventional and high quality 1D nanostructures driving up many options for high performance and new low energy consumption devices.
    Full-text · Article · Jun 2015 · Sensors and Actuators B Chemical
  • S Illera · J D Prades · A Cirera · A Cornet
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    ABSTRACT: We present a theoretical model that explains the optoelectronic response of nanodevices based on large quantum dot (QD) arrays. The model is grounded on rate equations in the self-consistent field regime and it accurately describes the most important part of the system: the tunnel junctions. We demonstrate that the ratio between the optical terms and the transport rates determines the final device response. Furthermore, we showed that to obtain a net photocurrent the QD has to be asymmetrically coupled to the leads.
    No preview · Article · May 2015 · Journal of Physics Conference Series
  • S. Illera · J. D. Prades · A. Cirera
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    ABSTRACT: The role of different charge transport mechanisms in Si / Si O 2 structures has been studied. A theoretical model based on the Transfer Hamiltonian Formalism has been developed to explain experimental current trends in terms of three different elastic tunneling processes: (1) trap assisted tunneling; (2) transport through an intermediate quantum dot; and (3) direct tunneling between leads. In general, at low fields carrier transport is dominated by the quantum dots whereas, for moderate and high fields, transport through deep traps inherent to the SiO 2 is the most relevant process. Besides, current trends in Si / Si O 2 superlattice structure have been properly reproduced.
    No preview · Article · May 2015 · Journal of Applied Physics
  • O. Monereo · J.D. Prades · A. Cirera
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    ABSTRACT: Herein, we prove that self-heating effects occur in sensor films made of randomly oriented nanoparticles (electro-sprayed, drop-casted and paint-brushed films of carbon nanofibers). A 2-point calibration method, reliable enough to overcome the lack of reproducibility of low cost fabrication methods, is also proposed. Self-heating operation makes possible reaching temperatures up to 250 °C with power consumptions in the range of tens of mW. For certain low-temperature applications (<100 °C) typical power consumptions are as low as tens of μW. The method is suitable to modulate the response towards gases, such as humidity, NH3 or NO2. This approach overcomes the complex fabrication requirements of previous self-heating investigations and opens the door to use this effect in cost-effective devices.
    No preview · Article · Feb 2015 · Sensors and Actuators B Chemical
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    ABSTRACT: The integration of one dimensional (1D) nanostructures of non-industry-standard semiconductors in functional devices following bottom-up approaches is still an open challenge that hampers the exploitation of all their potential. Here, we present a simple approach to integrate metal oxide nanowires in electronic devices based on controlled dielectrophoretic positioning together with proof of concept devices that corroborate their functionality. The method is flexible enough to manipulate nanowires of different sizes and compositions exclusively using macroscopic solution-based techniques in conventional electrode designs. Our results show that fully functional devices, which display all the advantages of single-nanowire gas sensors, photodetectors, and even field-effect transistors, are thus obtained right after a direct assembly step without subsequent metallization processing. This paves the way to low cost, high throughput manufacturing of general-purpose electronic devices based on non-conventional and high quality 1D nanostructures driving up many options for high performance and new low energy consumption devices.
    No preview · Article · Jan 2015 · Sensors and Actuators B Chemical
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    ABSTRACT: Low power consumption and reliable selectivity are the two main requirements for gas sensors to be applicable in mobile devices. The high flexibility of organic surface modifications in terms of functional groups, as well as their steric and electronic structures might possibly enable the targeted design of various specific gas sensors. Since illumination with light in the visible range is sufficient to facilitate gas-desorption processes for fast response and recovery processes of SAM modified gas sensors, the organic groups furthermore ensure a sensing operation without the need of external thermal or UV-light energy that is usually required for the activation of the metal oxide surface of traditional gas sensor systems and consume a major fraction of the total required energy in conventional sensor systems.
    Full-text · Article · Oct 2014 · Advanced Materials
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    ABSTRACT: We describe a low-power, easy-to-use and portable device for measuring the electrochemical impedance of different types of biosensors. The measurement technique is based on the direct synthesis of sinusoidal signals followed by a Discrete-time Fourier Transform (DFT) analysis, carried out by an integrated electronic stage that excites and collects the sample response. This technique provides excellent signal-to-noise ratio, high sensibility to small variations in the sensor impedance and high accuracy and reliability. The device was tested studying the response at different frequencies of a gold microelectrode, which was manufactured by means of a combination of soft lithography tools, enabling us to monitorize the antibody-antigen concentration of Interleukin-10 (IL-10). Our custom design permits to expand the current range down to the pA, with accuracy better than 1%, and to optimize the power consumption to reach figures under 150 µW per measurement.
    Full-text · Conference Paper · Sep 2014
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    ABSTRACT: Copper (II) oxide (CuO) is a metal oxide suitable for developing solid state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between gas molecules and this metal oxide is still limited. Here, individual CuO nanowires were evaluated as ammonia (NH3) and hydrogen sulphide (H2S) sensors, validating the p-type character of this semiconductor. The working principle behind their performance was qualitatively modeled and it was concluded that adsorbed oxygen at the surface plays a key role necessary to explain the experimental data. Compared to their counterparts of SnO2 nanowires, an appreciable sensitivity enhancement to NH3 for concentrations below 100 ppm was demonstrated.
    Full-text · Article · Aug 2014 · Applied Surface Science
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    Full-text · Dataset · Mar 2014
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    ABSTRACT: An appropriate way of realizing property nanoengineering in complex quaternary chalcogenide nanocrystals is presented for Cu2CdxSnSey(CCTSe) polypods. The pivotal role of the polarity in determining morphology, growth, and polytypic branching mechanism is demonstrated. Polarity is considered to be responsible for the formation of an initial seed that takes the form of a tetrahedron with four cation-polar facets. Size and shape confinement of the intermediate pentatetrahedral seed is also attributed to polarity as their external facets are anion-polar. The final polypod extensions also branch out as a result of cation-polarity-driven mechanism. Aberration-corrected scanning transmission electron microscopy is used to identify stannite cation ordering, while ab initio studies are used to show the influence of cation ordering/distortion, stoichiometry, and polytypic structural change on the electronic band structure.
    Full-text · Article · Feb 2014 · ACS Nano
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    ABSTRACT: 3D single crystalline well aligned GaN-InGaN rod arrays are fabricated by selective area growth (SAG) metal-organic vapor phase epitaxy (MOVPE) for visible light water splitting. Epitaxial InGaN layer grows successfully on 3D GaN rods to minimize defects within the GaN-InGaN heterojunctions. The indium concentration (In ~ 0.30 ± 0.04) is rather homogeneous in InGaN shells along the radial and longitudinal directions. The growing strategy allows to tune the band gap of the InGaN layer in order to match the visible absorption with the solar spectrum as well as to align the semiconductor bands close to the water redox potentials to achieve high efficiency. The relation between structure, surface and photoelectrochemical property of GaN-InGaN is explored by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), current-voltage and open circuit potential (OCP) measurements. The epitaxial GaN-InGaN interface, pseudomorphic InGaN thin films, homogeneous and suitable indium concentration and defined surface orientation are properties demanded for systematic study and efficient photoanodes based on III-Nitride heterojunctions.
    Full-text · Article · Feb 2014 · ACS Applied Materials & Interfaces
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    ABSTRACT: Organic–inorganic hybrid gas sensors can offer outstanding performance in terms of selectivity and sensitivity towards single gas species. The enormous variety of organic functionalities enables novel flexibility of active sensor surfaces compared to commonly used pure inorganic materials, but goes along with an increase of system complexity that usually hinders a predictable sensor design. In this work, an ultra-selective NO2 sensor is realized based on self-assembled monolayer (SAM)-modified semiconductor nanowires (NWs). The crucial chemical and electronic parameters for an effective interaction between the sensor and different gas species are identified using density functional theory simulations. The theoretical findings are consistent with the experimentally observed extraordinary selectivity and sensitivity of the amine-terminated SnO2 NW towards NO2. The energetic position of the SAM–gas frontier orbitals with respect to the NW Fermi level is the key to ensure or impede an efficient charge transfer between the NW and the gas. As this condition strongly depends on the gas species and the sensor system, these insights into the charge transfer mechanisms can have a substantial impact on the development of highly selective hybrid gas sensors.
    Full-text · Article · Feb 2014 · Advanced Functional Materials
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    ABSTRACT: In this work, bottom-up devices based on individual monocrystalline SnO2 nanowires (NWs) were fabricated using FIB nanolithography on top of suspended microhotplates, with integrated heater and interdigitated microelectrodes. The electrical characterisation of such devices in the presence of different gases show that devices with improved gas sensing properties can be fabricated.
    Full-text · Article · Dec 2013
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    ABSTRACT: Microelectromechanical systems (MEMS) with integrated heaters, originally designed for the readout of the resistance of metal oxide (MOX) layers, were configured to observe surface ionisation (SI) gas signals. Interdigital platinum (Pt) electrodes on top of the dielectric membranes acted as ion emitting layers while flat-plate counter electrodes, positioned at a short distance above them, were used for the current readout. In this work, we show that this device configuration leads to SI responses orders of magnitude higher than those previously reported for thin-film, flat-plate devices and fully comparable to the performance of parallel-nanowire devices (PNDs). The high ionisation efficiency of our MEMS devices, which are suitable for large-scale production and further integration steps, is attributed to the electric field enhancement that takes place at the sharp edges of the Pt electrodes.
    Full-text · Article · Dec 2013 · Sensors and Actuators B Chemical

Publication Stats

1k Citations
304.41 Total Impact Points

Institutions

  • 2007-2015
    • University of Barcelona
      • Department of Electronics
      Barcino, Catalonia, Spain
    • Ecole des Métiers de l'Environnement (EME)
      Bruz, Brittany, France
  • 2009-2013
    • IREC Catalonia Institute for Energy Research
      • Department of Advanced Materials for Energy
      Sant Adrià de Besòs, Catalonia, Spain