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Ekedahl, Lars-Gunnar
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Publications (10 of 42) Show all publications
Briand, D., Wingbrant, H., Sundgren, H., Van, d. S., Ekedahl, L.-G., Lundström, I. & De, R. N. .. (2003). Modulated operating temperature for MOSFET gas sensors: Hydrogen recovery time reduction and gas discrimination. Sensors and actuators. B, Chemical, 93(1-3)
Open this publication in new window or tab >>Modulated operating temperature for MOSFET gas sensors: Hydrogen recovery time reduction and gas discrimination
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2003 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 93, no 1-3, p. 276-285Conference paper, Published paper (Other academic)
Abstract [en]

This communication presents a modulated mode of operation for MOSFET gas sensors. A low-power micromachined device allows pulsing the temperature of MOSFET gas sensors with a time constant less than 100ms. Modulating the temperature during the gas exposure modifies the kinetics of the gas reactions with the sensing film. The way the sensor response is modified by the temperature modulation depends on the sensor "history", on the nature of the surrounding gaseous atmosphere, and on the type of materials used as catalytic sensing film. Pulsing the temperature up just after the gas exposure can reduce the recovery time for specific applications, such as for hydrogen detection. Cycling the temperature can allow the discrimination between different gas mixtures. Discrimination was shown for gaseous mixtures of hydrogen and ammonia in air. The results obtained indicate that a "smart" combination of sample and temperature profile could be used to expand the information content in the sensor response. © 2003 Elsevier Science B.V. All rights reserved.

Keywords
Gas sensor, Low-power, MOSFET, Temperature modulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46546 (URN)10.1016/S0925-4005(03)00230-2 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Johnson, H., Karlsson, O., Winqvist, F., Krantz-Rulcker, C. & Ekedahl, L.-G. (2003). Predicting microbial growth in pulp using an electronic tongue. Nordic Pulp & Paper Research Journal, 18(2), 134-140
Open this publication in new window or tab >>Predicting microbial growth in pulp using an electronic tongue
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2003 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 2, p. 134-140Article in journal (Refereed) Published
Abstract [en]

This paper describes how an electronic tongue based on pulsed voltammetry over noble metal electrodes can be used as an instrument to predict the amount of microorganisms in pulp during their growth cycle. The electronic tongue consists of a sensor body and a PC, which is used to control a potentiostat which applies the voltammetric large amplitude pulsed voltammetry (LAPV)-waveform across the sensor electrodes, and to collect the data of the resulting current. The sensor body is constructed of four noble metal electrodes, a stainless steel electrode as counterelectrode, and an Ag/AgCl reference electrode. This arrangement works as a standard three-electrode voltammetry system. Principal component analysis (PCA) and partial least squares (PLS) multivariate prediction methods are used to extract information from the data and to aid interpretation. It is shown that PLS-models of the voltammetric signals from this sensor array predicts the reference methods, viable count using Petrifilm(TM) aerobic total counts, with good accuracy (root mean square error of prediction (RMSEP) 9% of maximum value or 20% in a lower region corresponding to 500-1000 colony forming units) and adenosine triphosphate (ATP)-measurements with lower accuracy (10% of maximum value or 55% in a lower region). Since the precision of this method of detection is on a level with the viable count method, this method can be considered superior where short response times or the possibility of on-line measurement are of value.

Keywords
pulp, microbiology, electronic tongue, voltammetry, multivariate data analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48600 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2018-08-02
Nakagomi, S., Shinobu, H., Unéus, L., Lundström, I., Ekedahl, L.-G., Yakimova, R., . . . Lloyd-Spets, A. (2002). Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions. In: Materials Science Forum, Vols. 389-393. Paper presented at ICSCRM2001 (pp. 1423-1426). , 389-3
Open this publication in new window or tab >>Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions
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2002 (English)In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1423-1426Conference paper, Published paper (Refereed)
Abstract [en]

Schottky diode gas sensors were fabricated on top of the epitaxial layer grown by three different methods, purchased from Cree Research Inc., by hot wall CVD, or by sublimation at a high growth rate. The epitaxial layers have different thickness and doping. The current-voltage characteristics of the gas sensors were compared in different gas ambient during operation in the high temperature region. The temperature dependence of the series resistance of the diodes revealed two types of carrier scattering mechanisms, impurity scattering for the sublimation epitaxial layer at 300-400degreesC and at 400-600degreesC, lattice scattering for all diodes. The ideality factor of the diode fabricated on the Cree substrate is higher than others. The higher ideality factor gives rise to a larger forward voltage change for a change in gas ambient. The amount of change in barrier height caused by a change in the ambient gas is almost the same for the three types of diodes. The value of the barrier height of the diode grown by the sublimation method is lower than for the others, which gives a higher reverse saturation current at temperatures above 400degreesC. The largest saturation current also shows the largest current change when switching between different gas atmospheres.

Keywords
epitaxial layers, gas sensors, high temperature, resistance, scattering, Schottky diodes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48832 (URN)
Conference
ICSCRM2001
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2014-10-08
Lloyd-Spets, A., Unéus, L., Svenningstorp, H., Wingbrant, H., Harris, C., Salomonsson, P., . . . Savage, S. (2002). MISiCFET chemical gas sensors for high temperature and corrosive environment applications. Materials Science Forum, 389-3, 1415-1418
Open this publication in new window or tab >>MISiCFET chemical gas sensors for high temperature and corrosive environment applications
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 389-3, p. 1415-1418Article in journal (Refereed) Published
Abstract [en]

A chemical gas sensor based on a silicon carbide field effect transistor with a catalytic gate metal has been under development for a number of years. The buried gate design allows the sensor to operate at high temperatures, routinely up to 600degreesC and for at least three days at 700degreesC. The chemical inertness of silicon carbide makes it a suitable sensor technology for applications in corrosive environments such as exhaust gases and flue gases from boilers. The selectivity of the sensor devices is established through the choice of type and structure of the gate metal as well as the operation temperature. In this way NH3 sensors with low cross sensitivity to NOx have been demonstrated as potential sensors for control of selective catalytic reduction (SCR) of NOx by urea injection into diesel exhausts. The hardness of the silicon carbide makes it for example more resistant to water splash at cold start of a petrol engine than existing technologies, and a sensor which can control the air to fuel ratio, before the exhaust gases are heated, has been demonstrated. Silicon carbide sensors are also tested in flue gases from boilers. Efficient regulation of the combustion in a boiler will decrease fuel consumption and reduce emissions.

Keywords
ammonia, catalytic metal, combustion, FETs, flue gases, gas sensors, high temperature, SCR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48830 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Unéus, L., Nakagomi, S., Linnarsson, M., Jensen, M., Svensson, B., Yakimova, R., . . . Lloyd-Spets, A. (2002). The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures. In: Materials Science Forum, Vols. 389-393. Paper presented at ICSCRM2001 (pp. 1419-1422). , 389-3
Open this publication in new window or tab >>The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
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2002 (English)In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1419-1422Conference paper, Published paper (Refereed)
Abstract [en]

We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.

Keywords
annealing, gas sensors, high temperature, hydrogen diffusion, Schottky diodes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48831 (URN)
Conference
ICSCRM2001
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2014-10-08
Amandusson, H., Ekedahl, L.-G. & Dannetun, H. (2001). Alcohol dehydrogenation over Pd versus PdAg membranes. Applied Catalysis A: General, 217(1-2), 157-164
Open this publication in new window or tab >>Alcohol dehydrogenation over Pd versus PdAg membranes
2001 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 217, no 1-2, p. 157-164Article in journal (Refereed) Published
Abstract [en]

The dehydrogenation of methanol and ethanol and the subsequent permeation of hydrogen through Pd and Pd70Ag30 membranes, respectively, have been studied. In order to keep a continuous hydrogen permeation rate, oxygen needs to be added to the alcohol supply. Without oxygen, the decomposition products will form a contaminating layer on the upstream membrane surface. The extraction of hydrogen from ethanol is six times more effective through a Pd70Ag30 membrane than through a pure Pd membrane (at optimum conditions). For methanol, the hydrogen permeation is 30% larger through a Pd70Ag30 membrane than through a membrane of pure Pd. The increased hydrogen permeation yield through Pd70Ag30 compared to Pd can be attributed mainly to a lower upstream consumption of hydrogen due to water formation, but also to an increased conversion of the alcohol in the presence of oxygen. © 2001 Elsevier Science B.V.

Keywords
Ethanol, Hydrogen, Membrane, Methanol, Palladium, Silver
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47269 (URN)10.1016/S0926-860X(01)00591-9 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Svenningstorp, H., Widén, B., Salomonsson, P., Ekedahl, L.-G., Lundström, I., Tobias, P. & Lloyd-Spets, A. (2001). Detection of HC in exhaust gases by an array of MISiC sensors. Sensors and actuators. B, Chemical, 77(1-2), 177-185
Open this publication in new window or tab >>Detection of HC in exhaust gases by an array of MISiC sensors
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2001 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 77, no 1-2, p. 177-185Article in journal (Refereed) Published
Abstract [en]

Future legislations for car emissions make direct measurements in exhaust gases of hydrocarbon (HC) as well as CO and NOx interesting. Robust sensors that can stand the high temperature and rough environment in the exhaust gases are needed. Silicon carbide has the advantage of being a chemically very inert material, which, due to its high band gap, is a semiconductor even at temperatures around 800°C. Catalytic metal insulator silicon carbide Schottky diode sensors respond to gases like H2, HC, NOx in exhaust gases. The choice of catalytic metal, structure of the metal, and the operation temperature determines the response pattern to different gases. Here we will demonstrate that an array of different MISiC sensors to some extent predicts the HC concentration in gasoline exhaust gases. Chemometric methods are used for the evaluation of the signals. © 2001 Elsevier Science B.V.

Keywords
Exhaust gases, Field effect, Gas sensors, Hydrocarbons, Silicon carbide
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47351 (URN)10.1016/S0925-4005(01)00690-6 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Salomonsson, A., Eriksson, M., Ekedahl, L.-G. & Dannetun, H. (2001). Hydrogen ad- and absorption on Pt-SiO2-Si structures. In: : . Paper presented at ECOSS-20, Poland, Sept.
Open this publication in new window or tab >>Hydrogen ad- and absorption on Pt-SiO2-Si structures
2001 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67437 (URN)
Conference
ECOSS-20, Poland, Sept
Available from: 2011-04-12 Created: 2011-04-12 Last updated: 2016-07-08
Johansson, M. & Ekedahl, L.-G. (2001). Hydrogen adsorbed on palladium during water formation studied with palladium membranes. Applied Surface Science, 173(1-2), 122-133
Open this publication in new window or tab >>Hydrogen adsorbed on palladium during water formation studied with palladium membranes
2001 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 173, no 1-2, p. 122-133Article in journal (Refereed) Published
Abstract [en]

The amount of hydrogen adsorbed on palladium during water formation has been studied by measurements of the rate at which hydrogen permeates a palladium membrane. The water formation and hydrogen permeation rates were measured simultaneously for palladium membranes exposed to a hydrogen-oxygen-argon mixture on one side and to pure argon on the other side. Investigations were carried out for the temperatures 100, 150 and 200 °C at a total pressure of 760 Torr. If the rates are plotted as a function of a, where a = pH(2)/(pH(2)+pO(2)), pH(2) and pO(2) are the pressures of hydrogen and oxygen at the palladium surface, respectively, it is found that, at 100 °C, a peak occurs in the water formation rate at amax˜0.2. The palladium surface is dominated by hydrogen for a>amax and is hydrogen deficient for a>amax. This is consistent with a rate limiting step for the water forming reaction where adsorbed hydrogen is one of the reactants. It is also concluded that the heat of adsorption for hydrogen on the palladium surface is significantly lower than previously derived from experiments made under ultrahigh vacuum conditions.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47431 (URN)10.1016/S0169-4332(00)00894-1 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Amandusson, H., Ekedahl, L.-G. & Dannetun, H. (2001). Hydrogen permeation through surface modified Pd and PdAg membranes. Journal of Membrane Science, 193(1), 35-47
Open this publication in new window or tab >>Hydrogen permeation through surface modified Pd and PdAg membranes
2001 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 193, no 1, p. 35-47Article in journal (Refereed) Published
Abstract [en]

The hydrogen permeation through surface modified Pd and Pd70Ag30 membranes has been studied at temperatures between 100 and 350°C. Silver has been evaporated on Pd and Pd70Ag30 foils with a thickness of 25µm in order to study the role of the surface composition in comparison with the membrane bulk composition. The Pd70Ag30-based membranes display the largest permeation rates at temperatures below 200°C, while Pd membranes with 20Å silver evaporated on the upstream side show the largest permeation rates above 200°C. There are, consequently, different rate limiting processes above and below 200°C: at temperatures below 200°C, the bulk diffusion through the membrane is rate limiting, while at temperatures above 200°C, the influence of the surface composition starts to become significant. It has further been concluded that a sharp silver concentration gradient from the surface to the bulk is important for the hydrogen permeation rate at temperatures above 200°C. Adding oxygen to the hydrogen supply will almost totally inhibit the hydrogen permeation rate when a pure Pd membrane surface is facing the upstream side, while for silver-containing surfaces the presence of oxygen has almost no effect. On a clean Pd surface, oxygen effectively consumes adsorbed hydrogen in a water forming reaction. With Ag on the surface, no water formation is detected. Co-supplied CO inhibits the permeation of hydrogen in a similar manner on all studied membrane surfaces, independent of surface silver content. © 2001 Elsevier Science B.V. All rights reserved.

Keywords
Hydrogen, Oxygen, Palladium, Permeation, Silver
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47235 (URN)10.1016/S0376-7388(01)00414-8 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
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