| 1. |
- Darmastuti, Zhafira
(författare)
-
SiCFET gassensors : theory, developent, and applications to flue gas cleaning processes in power plants
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental and health concerns lead to stricter regulations on power plant emission. Sensors play an important role, not only as part of the process control to ensure that the effluent stays under the regulated values, but also to increase the pollution removal efficiency and to decrease the reagent consumption.Previous studies, on the use of SiC based Field Effect Transistors (FET) as NH3 sensors in Tekniska Verken power plants and as CO sensors for the control of the domestic boilers, have shown promising results. Moreover, these sensors can withstand high temperature operation and are considerably cheaper than most conventional sensors used in power plants. The price of the sensors enable the installation of multiple sensors in one flue gas duct section, which lead to better monitoring of the flue gas uniformity. Based on that argument, this study is performed to determine whether it is possible to expand the possible application of SiC-FET sensors for the detection of other pollutants emitted by power plants. This thesis reports the characterization and performance testing of SiC-FET sensors towards other selected air pollutants: H2S, methanol as a product of CO2 hydrogenation, and SO2.The study is performed by I-V characterization of the sensors toward the test gas in different background gases and studies of the detection mechanism. Detection mechanism studies include DRIFT spectroscopy, mass spectroscopy, and theoretical study of the surface reaction with Density Functional Theory (DFT).Ir-gate SiC-FET sensors at 350oC show a very high sensitivity to H2S. The large response reduces the possibility of cross-sensitivity from other gases. Pt-gate sensors offer very fast response with decent response magnitude at 200oC for methanol. The presence of oxygen improves the response to methanol, which is favorable for the leak detection application. Besides oxygen, the influence of hydrogen, propene, and water vapor is also observed in the experiment with methanol. The detection mechanism and different sensing behavior of Pt and Ir gates are illustrated with model reaction mechanisms on the surface of the metals. Sensor characterization has been performed for SO2 with several catalytic metal gates: Pt, Ir, Cu, and Au. The results suggest that a single sensor with any of Pt, Ir, Cu, and Au gates is able to detect the presence of SO2 in the air or nitrogen background. However, they are unable to measure different SO2 concentration. Moreover, the response level to SO2 is so small, that it will probably disappear if there is any other gas present in the mixture.
|
|
| 2. |
- Bur, Christian
(författare)
-
Selectivity Enhancement of Gas Sensitive Field Effect Transistors by Dynamic Operation
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas sensitive field effect transistors based on silicon carbide, SiC-FETs, have been applied to various applications mainly in the area of exhaust and combustion monitoring. So far, these sensors have normally been operated at constant temperatures and adaptations to specific applications have been done by material and transducer platform optimization.In this thesis, the methodology of dynamic operation for selectivity enhancement is systematically developed for SiC-FETs. Temperature cycling, which is well known for metal oxide gas sensors, is transferred to SiC-FETs. Additionally, gate bias modulation is introduced increasing the performance further.The multi-dimensional sensor data are evaluated by use of pattern recognition mainly based on multivariate statistics. Different strategies for feature selection, crossvalidation, and classification methods are studied.After developing the methodology of dynamic operation, i.e., applying the virtual multi-sensor approach on SiC-FETs, the concept is validated by two different case studies under laboratory conditions: Discrimination of typical exhaust gases and quantification of nitrogen oxides in a varying background is presented. Additionally, discrimination and quantification of volatile organic compounds in the low parts-perbillion range for indoor air quality applications is demonstrated. The selectivity of SiC-FETs is enhanced further by combining temperature and gate bias cycled operation. Stability is increased by extended training.
|
|
| 3. |
- Darmastuti, Zhafira
(författare)
-
SiC-FET Gas Sensors Developed for Control of the Flue Gas Desulfurization System in Power Plants Experimental and Modeling : Experimental and Modeling
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electricity and power generation is an essential part of our life. However, powergeneration activities also create by-products (such as sulphur oxides, nitrogen oxides,carbon monoxide, etc), which can be dangerous when released to the atmosphere.Sensors, as part of the control system, play very vital role for the fluegas cleaning processes in power plants. This thesis concerns the development ofSilicon Carbide Field Effect Transistor (SiC-FET) gas sensors as sensors for sulfurcontaining gases (SO2 and H2S) used as part of the environmental control systemin power plants. The works includes sensor deposition and assembly, sensinglayer characterization, operation mode development, performance testing of thesensors in a gas mixing rig in the laboratory and field test in a desulfurization pilotunit, and both experimental and theoretical studies on the detection mechanismof the sensors.The sensor response to SO2 was very small and saturated quickly. SO2 is a verystable gas and therefore reaction with other species requires a large energy input.SO2 mostly reacts with the catalyst through physisorption, which results in lowresponse level. Another problem was that once it finally reacted with oxygen andadsorbed on the surface of the catalyst in form of a sulfate compound, it is desorbedwith difficulty. Therefore, the sensor signal saturated after a certain timeof exposure to SO2. Different gate materials were tested in static operation (Pt,Ir, Au), but the saturation phenomena occurred in all three cases. Dynamic sensoroperation using temperature cycling and multivariate data analysis could mitigatethis problem. Pt-gate sensors were operated at several different temperatures in acyclic fashion. One of the applied temperatures was chosen to be very high for ashort time to serve as cleaning step. This method was also termed the virtual multisensor method because the data generated could represent the data from multiplesensors in static operation at different temperatures. Then, several features of thesignal, such as mean value and slope, were extracted and processed with multivariatedata analysis. Linear Discrimination Analysis (LDA) was chosen since itiiiallows controlled data analysis. It was shown that it was possible to quantify SO2with a 2-step LDA. The background was identified in the first step and SO2 wasquantified in the second step. Pt sensors in dynamic operation and 2-step LDAevaluation has also demonstrated promising results for SO2 measurement in thelaboratory as well as in a desulfurization pilot unit. For a commercial sensor, algorithmhave to be developed to enable on-line measurement in real time.It was observed that Ir-gate sensors at 350oC were very sensitive to H2S. The responseobtained by Ir sensors to H2S was almost five times larger than that of Ptsensors, which might be due to the higher oxygen coverage of Ir. Moreover, Irsensors were also more stable with less drift during the operation as a result ofhigher thermal stability. However, the recovery time for Ir sensors was very long,due to the high desorption energy. Overall, the Ir sensors performed well whentested for a leak detection application (presence of oxygen and dry environment).The geothermal application, where heat is extracted from the earth, requires thesensor to be operated in humid condition in the absence (or very low concentration)of oxygen, and this poses a problem. Temperature cycle operation and smartdata evaluation might also be an option for future development.Along with the sensor performance testing, a study on the detection mechanismwas also performed for SO2 sensor, both experimentally and theoretically. The experimentincluded the study of the species formed on the surface of the catalystwith DRIFT (diffuse reflectance infrared frourier transform) spectroscopy and theanalysis of the residual gas with mass spectroscopy. Explanatory investigation ofthe surface reactions was performed using quantum-chemical calculations. Theoreticalcalculations of the infrared (IR) vibration spectra was employed to supportthe identification of peaks in the DRIFT measurement. Based on the study on theresidual gas analysis and quantum-chemical calculations, a reaction mechanismfor the SO2 molecule adsorption on the sensor surface was suggested.
|
|
| 4. |
- Fashandi, Hossein, 1984-
(författare)
-
Novel Layered and 2D Materials for Functionality Enhancement of Contacts and Gas Sensors
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chemical gas sensors are widely-used electronic devices for detecting or measuring the density levels of desired gas species. In this study, materials with established or potential applications for gas sensors are treated. For the case of high-temperature applications (≈ 600 °C), semiconductor-based gas sensors suffer from rapid oxidation of the metallic ohmic contacts, the same cause-of-failure as for the general case of high-temperature semiconductor electronics. 4H-SiC is an ideal semiconductor for high-temperature applications. Ti3SiC2 is a known ohmic contact to 4H-SiC with the known two-step synthesis process of post-annealing of pre-deposited Ti/Al multilayers or sputter-deposition of Ti3SiC2 films at > 900 °C. Here, sputter-deposition of Ti on 4H-SiC at > 900 °C is presented as a novel single-step method for the synthesis of Ti3SiC2 ohmic contacts, based on a concurrent reaction between sputter-deposited Ti and 4HSiC. Ti3SiC2, similar to any other known ohmic contact, degrade rapidly in high-temperature oxidizing ambient. To try to overcome this obstacle, noble metal diffusion into Ti3SiC2 has been s studied with the goal to retain ohmic properties of Ti3SiC2 and harnessing oxidation resistivity of noble metals. A novel exchange intercalation between Ti3SiC2 and Au is discovered which results in the almost complete exchange of Si with Au giving rise to novel Ti3AuC2 and Ti3Au2C2. Ti3IrC2 is also synthesized through exchange intercalation of Ir into Ti3Au2C2. All the aforementioned phases showed ohmic properties to 4H-SiC. This technique is also studied based on Ti2AlC and Ti3AlC2 resulting in the synthesis of novel Ti2Au2C and Ti3Au2C2, respectively. Using Ti3AuC2 and an Au/IrOx capping layer, an ohmic contact was manufactured, which maintained ohmic properties and showed no structural defects after 1000 h of aging at 600 °C air.Ti3SiC2 is a member of a large family of materials known as Mn+1AXn phases. While exchange reactions of Si (or Al) planes in Ti3SiC2 (Ti2AlC and Ti3AlC2) is presented here, a world-wide research already exists on chemical removal of the same atomic planes from different Mn+1AXn phases and the synthesis of Mn+1Xn sheets known as MXenes. I performed a theoretical study regarding simulation of electronic and structural properties of more than120 different possible MXene phases. The results show that some MXene phases, when terminated by particular gas species, turn into Dirac materials. That is, they possess massless Dirac fermions with different properties compared to graphene such as higher number of Dirac points at the Fermi level, giant spin orbit splitting, and preserved 2D-type electronic properties by extending the dimensionality. The general substantial change of the electronic properties of MXenes under different gas adsorption configurations stands out and can thus be harnessed for sensing applications.Growth of monolayer iron oxide on porous Pt sensing layers is another novel approach used in this study for applying the unique properties of 2D materials for gas sensors. A low temperature shift in CO oxidation characteristics is presented. The approach is similar to that previously reported using bulk single crystal Pt substrate, the latter being an unrealistic model for sensors and catalysts. Monolayer-coated Pt sensing layers were fabricated as the metal component of a metal oxide semiconductor (MOS) capacitor device, whereby the electrical response of the MOS device could be used to map out the catalytic properties of the sensing layer. The monolayer-coated Pt surface showed to be stable with retained improved catalytic properties for > 200 h. The MOS device measurements are here utilized as a handy method for in-situ monitoring of the surface chemical properties of the monolayer-coated Pt and the approach is highly functional for use and characterization of monolayer coatings of widely used sensingor catalytic layers.
|
|
| 5. |
- Andersson, Sandra, 1978-
(författare)
-
Validation of antibodies for tissue based immunoassays
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In situ protein detection in human tissues using antibodies reveals the cellular protein localization, and affinity-based proteomic studies can help to discover proteins involved in the development of diseases. However, antibodies often suffer from cross-reactivity, and the lack of positive and negative tissue controls for uncharacterized proteins complicates the mapping of the proteome. The aim of this thesis is thus to improve the methodology for validating antibodies used for immunostaining on formalin-fixed paraffin-embedded tissues.Two of the papers include comparisons between mRNA-expression and immunostaining of corresponding protein. In paper I, ISH and IHC staining patterns were compared on consecutive TMA-slides. The study of well-characterized genes showed that ISH could be used for validation of antibodies. ISH was further used for antibody evaluation, and could validate four out of nine antibodies showing potentially interesting staining patterns. In paper III, transcriptomic data generated by RNA-sequencing were used to identify tissue specific expression in lymphohematopoietic tissues. An increased expression in one or more of these tissues compared to other tissue types was seen for 693 genes, and these were further compared to the staining patterns of corresponding proteins in tissues.Antibody labeling is necessary for many immunoassays. In paper II, two techniques for antibody-biotinylation were compared, aiming to find a stringent labeling method for antibodies used for immunostaining on TMAs. The ZBPA-method, binding specifically to Fc-part of antibodies, was found to be superior to the Lightning Link-biotinylation kit targeting amine groups, since labeling of amine groups on stabilizing proteins in the antibody buffer causes unspecific staining.The localization of the estrogen receptor beta (ERβ) in human normal and cancer tissues was studied in paper IV. Thorough evaluation of 13 antibodies using positive and negative control cell lines showed that only one antibody, PPZ0506, is specific for ERβ in all three immunoassays used. Contradictory to previously published data, tissue profiling using PPZ0506 showed that ERβ is expressed in a limited number of normal and cancer tissues.In conclusion, the present investigations present tools for validation of antibodies used for large-scale studies of protein expression in tissues.
|
|
