Ruthenium(IV)oxide (RuO₂) is a material used for various purposes. It acts as a catalytic agent in several reactions, for example oxidation of carbon monoxide. Furthermore, it is used as gate material in gas sensors. In this work theoretical and computational studies were made on adsorbed molecules on RuO₂ (110) surface, in order to follow the chemistry on the molecular level. Density functional theory calculations of the reactions on the surface have been performed. The calculated reaction and activation energies have been used as input for thermodynamic and kinetics calculations. A surface phase diagram was calculated, presenting the equilibrium composition of the surface at different temperature and gas compositions. The kinetics results are in line with the experimental studies of gas sensors, where water has been produced on the surface, and hydrogen is found at the surface which is responsible for the sensor response.

Gas sensitive metal/metal-oxide field effect transistors based on silicon carbide were used to study the sensor response to benzene (C₆H₆) at the low parts per billion (ppb) concentration range. A combination of iridium and tungsten trioxide was used to develop the sensing layer. Highsensitivity to 10 ppb C₆H₆ was demonstrated during several repeated measurements at a constant temperature from 180 to 300 °C. The sensor performance was studied also as a function of the electrical operating point of the device, i.e., linear, onset of saturation, and saturation mode. Measurements performed in saturation mode gave a sensor response up to 52 % higher than those performed in linear mode.

High-temperature iridium-gated field effect transistors based on silicon carbide have been used for sensitive detection of specific volatile organic compounds (VOCs) in concentrations of health concern, for indoorair quality monitoring and control. Formaldehyde, naphthalene, and benzene were studied as hazardous VOCs at parts per billion (ppb) down to sub-ppb levels. The sensor performance and characteristics were investigated at a constant temperature of 330° C and at different levels of relative humidity up to 60 %, showing good stability and repeatability of the sensor response, and excellent detection limits in the sub-ppb range.

Gas sensitive field effect transistors based on silicon carbide, SiC-FETs, have been studied for indoor air quality applications. The selectivity of the sensors was increased by temperature cycled operation, TCO, and data evaluation based on multivariate statistics. Discrimination of benzene, naphthalene, and formaldehyde independent of the level of background humidity is possible by using shape describing features as input for Linear Discriminant Analysis, LDA, or Partial Least Squares – Discriminant Analysis, PLS-DA. Leave-one-out cross-validation leads to a correct classification rate of 90 % for LDA, and for PLS-DA a classification rate of 83 % is achieved. Quantification of naphthalene in the relevant concentration range, i.e. 0 ppb to 40 ppb, was performed by Partial Least Squares Regression and a combination of LDA with a second order polynomial fit function. The resolution of the model based on a calibration with three concentrations was approximately 8 ppb at 40 ppb naphthalene for both algorithms.

Hence, the suggested strategy is suitable for on demand ventilation control in indoor air quality application systems.

Automobile exhaust gas emissions are causing serious damage to urban air quality in and around major cities of the world, which demands continuous monitoring of exhaust emissions. The chief components of automobile exhaust include carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons. Indium zirconate (InZrOx) and gold/indium zirconate (Au/InZrOx) composite nanopowders are believed to be interesting materials to detect these substances. To this end, characterization and gas sensing properties of InZrOx and Au/InZrOx composite nanopowders are discussed. InZrOx nanoparticles with In/Zr atomic ratio of 1.00 (+/- 0.05) are synthesized via pH-controlled co-precipitation of In and Zr salts in aqueous ammonia. Gold (Au) nanoparticles are subsequently deposited on InZrOx using an in situ sacrificial Au electrolysis procedure. The products are characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The gas sensing performance of Au/InZrOx composite nanopowder is studied by depositing a thick powder film on interdigitated electrode structures patterned on SiC substrate to facilitate high temperature operation. The resistivity of the Au/InZrOx layer is the sensor signal, and the sensors could be operated at 500-600 A degrees C, which is a suitable temperature range for engine exhaust measurements. The control sensing measurements reveal that Au/InZrOx composite nanopowder exhibits higher response towards 2-20 % O-2 gas as compared to pristine InZrOx nanoparticles. Further studies show that when applied to exhaust gases such as CO and nitric oxide (NO), the response of Au/InZrOx sensors is significantly higher towards NO in this temperature range. Thus, sensor performance characteristics of Au/InZrOx composite nanopowder are promising in terms of their applications in automobile exhaust emission control.

Experiments were performed both in the laboratory and a desulfurization pilot unit in order to improve the SiC-FET sensor performance using two-step data evaluation. In both cases, a porous Pt-gate enhancement type SiC-FET was utilized in a temperature cycled operation (TCO). Liner Discriminant Analysis (LDA) was chosen as the method for multivariate data analysis. Hierarchical methods with two-step LDA worked quite well in the laboratory tests with SO2 concentrations varied from 25-200 ppm. The same data evaluation was also applied to tests in the desulfurization pilot unit, with higher gas flow and a larger SO2 concentration range (up to 5000 ppm). The results from the SO2 quantification showed a significantly improved fit to corresponding reference instrument (FTIR) values.