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Garcia-Abuin A.,ETSE | Garcia-Abuin A.,University of Santiago de Compostela | Gomez-Diaz D.,ETSE | Gomez-Diaz D.,University of Santiago de Compostela | And 4 more authors.
Indian Journal of Chemical Technology | Year: 2015

The influence of surfactants upon sulfur dioxide chemical absorption in a bubble column reactor has been analysed. This kind of substances (surfactants) can cause important influences over mass transfer processes due the amphiphilic behaviour of these compounds. This kind of behaviour produces the accumulation of surfactants at the gas-liquid interface influencing upon mass transfer processes. Different alkalis have been used to enhance sulfur dioxide transfer by the chemical reaction with absorbed gas in the liquid phase. The high gas solubility and gas absorption rate causes the surfactant presence to have a low influence upon sulfur dioxide absorption under some experimental conditions. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.


Placidi M.,IMB CNM | Perez-Tomas A.,IMB CNM | Zielinski M.,NOVASiC | Godignon P.,IMB CNM | And 4 more authors.
Journal of Micromechanics and Microengineering | Year: 2010

Here, we report on a comparison between two different insulated substrates, semi-insulated silicon (SIS) and silicon-on-insulator (SOI), used for the growth of 3C-SiC for electrostatic-based mechanical resonators able to operate at high temperatures. The epitaxial growth of monocrystalline 3C-SiC films in these starting materials is first described and the main encountered problems are discussed. Structural and morphological characterization of the SiC layers is then performed using an optical microscope, a scanning electron microscope, an atomic force microscope and x-ray diffraction. Raman spectroscopy is also used to study the residual stress. Then, innovative lateral electrostatic SiC resonators using these materials are fabricated and electrically tested. Globally, devices using a SOI substrate allowed electrical sensing without any associated circuitry. Temperature measurements of the electrical resonance up to 200 °C are also performed and demonstrate that SiC on SOI is a promising material for a new generation of a harsh-environment-resistant micro-electro-mechanical system. © 2010 IOP Publishing Ltd.


Fontsere A.,IMB CNM CSIC | Perez-Tomas A.,IMB CNM CSIC | Placidi M.,IMB CNM CSIC | Llobet J.,IMB CNM CSIC | And 9 more authors.
Applied Physics Letters | Year: 2012

The gate leakage current of AlGaN/GaN (on silicon) high electron mobility transistor (HEMT) is investigated at the micro and nanoscale. The gate current dependence (25-310 °C) on the temperature is used to identify the potential conduction mechanisms, as trap assisted tunneling or field emission. The conductive atomic force microscopy investigation of the HEMT surface has revealed some correlation between the topography and the leakage current, which is analyzed in detail. The effect of introducing a thin dielectric in the gate is also discussed in the micro and the nanoscale. © 2012 American Institute of Physics.


Fontsere A.,IMB CNM CSIC | Perez-Toms A.,IMB CNM CSIC | Placidi M.,IMB CNM CSIC | Llobet J.,IMB CNM CSIC | And 10 more authors.
Applied Physics Letters | Year: 2011

As GaN technology continues to gain popularity, it is necessary to control the ohmic contact properties and to improve device consistency across the whole wafer. In this paper, we use a range of submicron characterization tools to understand the conduction mechanisms through the AlGaN/GaN ohmic contact. Our results suggest that there is a direct path for electron flow between the two dimensional electron gas and the contact pad. The estimated area of these highly conductive pillars is around 5 of the total contact area. © 2011 American Institute of Physics.


Fontsere A.,IMB CNM CSIC | Perez-Tomas A.,IMB CNM CSIC | Placidi M.,IMB CNM CSIC | Llobet J.,IMB CNM CSIC | And 12 more authors.
Nanotechnology | Year: 2012

AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents. © 2012 IOP Publishing Ltd.


Wahab H.F.,University of Strathclyde | Katebi R.,University of Strathclyde | Villanova R.,ETSE
2012 20th Mediterranean Conference on Control and Automation, MED 2012 - Conference Proceedings | Year: 2012

This paper deals with five existing nonlinear estimators (filters), which include Extended Kalman Filter (EKF), Extended H-infinity Filter (EHF), State Dependent Filter (SDF), State Dependent H-Infinity Filter (SDHF) and Unscented Kalman Filter (UKF) that are formulated and implemented to estimate unmeasured states of a typical biological wastewater system. The performance of these five estimators of different complexities, behaviour and advantages are demonstrated and compared via nonlinear simulations. This study shows promising application of UKF for monitoring and control of the process variables, which are not directly measurable. © 2012 IEEE.


Perez-Tomas A.,Catalan Institute of Nanoscience and Nanotechnology | Catalan G.,Catalan Institute of Nanoscience and Nanotechnology | Catalan G.,Catalan Institution for Research and Advanced Studies | Fontsere A.,ALBA Synchrotron | And 13 more authors.
Nanotechnology | Year: 2015

The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids>1 A mm-1) to be defined (0.5 A mm-1 at 300 C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current. © 2015 IOP Publishing Ltd.


Placidi M.,IMB CNM | Perez-Tomas A.,IMB CNM | Godignon P.,IMB CNM | Mestres N.,ICMAB | And 3 more authors.
Materials Science Forum | Year: 2010

In this study, a SiC on insulator growth is optimized, in order to electrically isolate the active structural layer towards the substrate. High quality single crystalline SiC was grown on SOI and SIS substrates. Smooth surface, low stress and bowing, confirmed by microscopy techniques, SEM, AFM, X-Ray diffraction and Raman spectroscopy, have been obtained. SiC electrostatic resonators on insulated substrates were also fabricated, and electrically driven. These results demonstrate that this material is very promising for MEMS application requiring isolation from the substrate and operation in harsh ambient. © (2010) Trans Tech Publications, Switzerland.


Taboada-Puig R.,E.T.S.E. | Lu-Chau T.,E.T.S.E. | Eibes G.,E.T.S.E. | Moreira M.T.,E.T.S.E. | And 2 more authors.
Biotechnology Progress | Year: 2011

The objective of this study was to investigate the enzymatic generation of the Mn3+-malonate complex and its application to the process of oxidizing several organic compounds. The experimental set-up consisted of an enzymatic reactor coupled to an ultrafiltration membrane, providing continuous generation of Mn3+-malonate from a reaction medium containing versatile peroxidase (an enzyme produced by Bjerkandera adusta strain BOS55), H2O2, MnSO4, and malonate. The effluent of the enzymatic reactor was introduced into a batch-stirred reactor to oxidize three different classes of compounds: an azo dye (Orange II), three natural and synthetic estrogens, and a polycyclic aromatic hydrocarbon (anthracene). The enzymatic reactor provided the Mn3+ complex under steady-state conditions, and this oxidative species was able to transform the three classes of xenobiotics considerably (90-99%) with negligible loss of activity. © 2011 American Institute of Chemical Engineers (AIChE).

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