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Löfdahl, Mikael
Publications (9 of 9) Show all publications
Wingbrant, H., Svenningstorp, H., Salomonsson, P., Kubinski, D., Visser, J. H., Löfdahl, M. & Lloyd Spetz, A. (2005). Using a MISiC-FET sensor for detecting NH3 in SCR systems. IEEE Sensors Journal, 5(5), 1099-1105
Open this publication in new window or tab >>Using a MISiC-FET sensor for detecting NH3 in SCR systems
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2005 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 5, p. 1099-1105Article in journal (Refereed) Published
Abstract [en]

One way to decrease the emitted levels of NOx from diesel engines is to add NH3 in the form of urea to the exhausts after combustion. NH3 will react with NOx in the catalytic converter to form N2 and water, which is called selective catalytic reduction (SCR). The amount of NH3 added may be regulated through closed-loop control by using an NH3 sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH3. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N2O and NO2, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH3 in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH3 in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH3 response was slightly decreased by a background level of NO2.

Keywords
Ammonia, field-effect transistor (FET) sensor, iridium, platinum, selective catalytic reduction (SCR)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13408 (URN)10.1109/JSEN.2005.854489 (DOI)
Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
Andersson, M., Ljung, P., Mattsson, M., Löfdahl, M. & Lloyd Spetz, A. (2004). Investigations on the possibilities of a MISiCFET sensor system for OBD and combustion control utilizing different catalytic gate materials. Topics in catalysis, 30-31(1), 365-368
Open this publication in new window or tab >>Investigations on the possibilities of a MISiCFET sensor system for OBD and combustion control utilizing different catalytic gate materials
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2004 (English)In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 30-31, no 1, p. 365-368Article in journal (Refereed) Published
Abstract [en]

Different catalytic materials, like Pt and Ir, applied as gate contacts on metal insulator silicon carbide field effect transistors — MISiCFET—facilitate the manufacture of gas sensor devices with differences in selectivity, devices which due to the chemical stability and wide band gap of SiC are suitable for high temperature applications. The combination of such devices in a sensor system, utilizing multivariate analysis/modeling, have been tested and some promising results in respect of monitoring a few typical exhaust and flue gas constituents, in the future aiming at on board diagnostics (OBD) and combustion control, have been obtained.

Keywords
platinum, iridium, sensor system, field effect sensors, SiC, OBD, combustion control, car exhaust, flue gases
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13092 (URN)10.1023/B:TOCA.0000029776.18603.74 (DOI)
Available from: 2008-04-01 Created: 2008-04-01 Last updated: 2017-12-13Bibliographically approved
Nakagomi, S., Takahashi, M., Kokubun, Y., Unéus, L., Savage, S., Wingbrant, H., . . . Lloyd-Spets, A. (2004). Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode. Materials Science Forum, 457-460, 1507-1510
Open this publication in new window or tab >>Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode
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2004 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 457-460, p. 1507-1510Article in journal (Refereed) Published
Abstract [en]

The drain current-voltage (I-d-V-D) characteristics of a chemical gas sensor based on a catalytic metal insulator silicon carbide field effect transistor (SiC-FET) were measured in H-2 or O-2 ambient while applying negative substrate bias, V-sub, at temperatures up to 600degreesC. An increase in the negative V-sub gives rise to an increase of the drain voltage at a given drain current level, which can be used to adjust the device baseline. In addition, we found that the difference in drain voltage between H-2 and O-2 ambient at a given drain current level (the gas response to H-2) increases for an increased negative substrate bias. By modifying an equation for the drain current in a SIT (static induction transistor), the influence of substrate bias on the amplification factors, mu and eta, was estimated using the temperature dependence of the I-d-V-D characteristics. From this, the effect of substrate bias on the gas response to hydrogen was calculated. It was clarified that the increase in the gas response caused by the negative substrate bias is due to a substrate bias dependence of the amplification factor of the short channel device.

Keywords
gas sensor, catalytic gate, substrate bias, buried channel, JFET, SIT, high temperature
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48313 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Enander, K., Dolphin, G., Löfdahl, M., Lundström, I., Liedberg, B. & Baltzer, L. (2002). Designed, folded polypeptides as functional units in surface-based biosensors - versatile scaffolds connecting recognition and reporting. In: Europtrode VI,2002.
Open this publication in new window or tab >>Designed, folded polypeptides as functional units in surface-based biosensors - versatile scaffolds connecting recognition and reporting
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2002 (English)In: Europtrode VI,2002, 2002Conference paper, Published paper (Refereed)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-42431 (URN)64022 (Local ID)64022 (Archive number)64022 (OAI)
Note
oral presentationAvailable from: 2009-10-10 Created: 2009-10-10
Löfdahl, M., Eriksson, M., Johansson, M. & Lundström, I. (2002). Difference in hydrogen sensitivity between Pt and Pd field-effect devices. Journal of Applied Physics, 91(7), 4275
Open this publication in new window or tab >>Difference in hydrogen sensitivity between Pt and Pd field-effect devices
2002 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 7, p. 4275-Article in journal (Refereed) Published
Abstract [en]

[No abstract available]

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47053 (URN)10.1063/1.1448874 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Enander, K., Dolphin, G., Löfdahl, M., Lundström, I., Liedberg, B. & Baltzer, L. (2002). Helix-loop-helix polypeptides as scaffolds for designed biosensing surfaces. In: 6th World Congress on Biosensors,2002.
Open this publication in new window or tab >>Helix-loop-helix polypeptides as scaffolds for designed biosensing surfaces
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2002 (English)In: 6th World Congress on Biosensors,2002, 2002Conference paper, Published paper (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-43338 (URN)73561 (Local ID)73561 (Archive number)73561 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Wingbrant, H., Unéus, L., Andersson, M., Cerda, J., Savage, S., Svenningstorp, H., . . . Lloyd-Spets, A. (2002). MISiCFET chemical sensors for applications in exhaust gases and flue gases. Materials Science Forum, 433-4, 953-956
Open this publication in new window or tab >>MISiCFET chemical sensors for applications in exhaust gases and flue gases
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-4, p. 953-956Article 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 choice of silicon carbide as the semiconductor material allows the sensor to operate at high temperatures, for more than 6 months in flue gases at 300degreesC and for at least three days at 700degreesC. The chemical inertness of silicon carbide and a buried gate design 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. Here we show that sensors with a porous platinum or iridium gate show different temperature ranges for NH3 detection. 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 metals, combustion, exhaust gases, field effect transistor, flue gases, gas sensor, high temperature, SCR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48564 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Löfdahl, M., Utaiwasin, C., Carlsson, A., Lundström, I. & Eriksson, M. (2001). Gas response dependence on gate metal morphology of field-effect devices. Sensors and actuators. B, Chemical, 80(3), 183-192
Open this publication in new window or tab >>Gas response dependence on gate metal morphology of field-effect devices
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2001 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 80, no 3, p. 183-192Article in journal (Refereed) Published
Abstract [en]

The dependence of the gas response on the gate metal morphology of field-effect gas sensors has been investigated in a new systematic way by using a scanning light pulse technique (SLPT) together with fabrication of metal gates where the metal morphology is continuously varied over the gate area. With the SLPT the local gas response at different points of the gate area can be measured. Furthermore, a mass spectrometric local gas sampling technique has been applied in combination with the local gas response measurements, which gives complementary information about the surface chemistry and how it changes with the morphology of the metal gate. Three different gate metals, Pd, Pt and Ir, have been studied by analysing the morphology and the gas response to five different gases, H2, NH3, C2H5OH, C2H4 and CH3CHO. Morphological aspects such as crack coverage, concentration of cracks and the length of the crack boundary, have been calculated from acquired scanning electron microscopy (SEM) images. Different possible response mechanisms are discussed in order to explain the observed responses and to understand the role of the morphology and the choice of the catalytic metal. Only in the case of ammonia a direct correlation between the morphological aspects, e.g. crack coverage, and the response was found. For Pd large changes in the local water pressure close to the metal gate surface have been measured at different parts of the metal gate by using the local gas sampling technique and a correlation is observed with the simultaneously measured gas response. Of the response mechanisms discussed in this contribution only a dissociative mechanism, where hydrogen atoms trapped at the interface between the metal gate and the insulator gives the response of the device, is consistent with all obtained results. © 2001 Elsevier Science B.V. All rights reserved.

Keywords
Field-effect gas sensors, Ir, Pd, Pt, Scanning light pulse technique
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47208 (URN)10.1016/S0925-4005(01)00886-3 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Löfdahl, M., Eriksson, M. & Lundström, I. (2000). Chemical images. Sensors and actuators. B, Chemical, 70(1-3), 77-82
Open this publication in new window or tab >>Chemical images
2000 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 70, no 1-3, p. 77-82Article in journal (Refereed) Published
Abstract [en]

Chemical sensors can be used to generate a vast amount of information about the emissions from bio- and chemical processes, from food and bacteria and from a number of products. These emissions are either wanted or should be avoided. Wolfgang Gopel was one of those who recognized early the large potential of chemical sensor arrays and different modes of operation of a given sensor. We describe how large area field effect devices, with catalytic metal gates, can be used for the construction of a response image of a gaseous emission. More specifically, we discuss the new possibilities obtained through the use of catalytic metals with a gradient in thickness. Some basic features of such sensing surfaces are demonstrated and, finally, time-dependent response images from aging meat are used to demonstrate the potential of the method used. It is based on a scanning light pulse technique (SLPT) which measures local polarization or work function changes in two dimensions and, e.g. a sensing surface consisting of bands of different catalytic metals with a gradient in thickness.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47551 (URN)10.1016/S0925-4005(00)00562-1 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
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