Anita Lloyd-Spetz

Oxide growth on SiC(0 0 0 1) surfaces

The oxidation of 6H SiC(0 0 0 1) surfaces is studied by high resolution photoelectron spectroscopy. We compare the oxides formed by HF dip, by room temperature treatment in ozone, and by thermal oxidation in air at 1000 °C, respectively. We find a stable intermediate layer in all investigated systems which differs from the bulk oxide that is stable up to 1200 °C. Our data suggest that the growth of the SiO2 layer proceeds via that intermediate silicate layer.

Response of metal–insulator–silicon carbide sensors to different components in exhaust gases

The effects of different components in simulated car exhaust gases on silicon carbide based field effect sensors are studied using a two-level factorial design. Strong effects are observed for H-2, ...

Multi-transduction of molecular recognition events in metalloporphyrin layers

Besides the design and synthesis of appropriate molecular recognition systems, the development of chemical sensors requires a careful selection of the transducer to allow conversion of the chemical interaction into an exploitable electric signal. Metalloporphyrins, which are characterized by manifold of interactions of different strength and selectivity, provide a good example of the complexity of such an issue. In this paper, an example of the different ways to capture interactions occurring in a metalloporphyrin layer is presented. In particular, the properties of mass (quartz microbalance) and surface potential transducers (field effect transistor) are illustrated. Results suggest that field effect transistors are more suitable to preserve the interactions magnitude scale than to maintain the original selectivity of the molecular recognition system.

Oxygen absorption effect on the sensitivity and material stability of ZnO nanostructured films

In this work the effect of ambient influence on the electrical conductivity of ZnO films has been studied. Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range 300-500degC. A dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturation with time. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposed undoped ZnO films revealed high sensitivity for oxygen content change in the ambience, therefore they have been further processed for gas sensor fabrication.

Multiparametric light-assisted silicon device transduction of molecular recognition events

The contemporaneous measurement of different physical properties of a chemical sensing layer is expected to provide a general increase of selectivity. The application of this concept generally requires the use of multiple devices. In this paper, the measurement of optical and electric properties of one sensing layer with a single device is presented. The surface potential and optical sensitivities of a field effect transistor are utilized to develop a multi-parametric sensor able to evaluate, at the same time, changes in the electric dipole and in the optical absorbance of a metalloporphyrin layer. The properties of the multiparametric approach are illustrated with an example aimed at recognizing different gases and vapours.

FET Transduction of Electric Dipole Changes in Organic Layers

Modern chemistry makes possibile the production of artificial receptors endowed with interaction sites specific towards selected analytes. To fabricate chemical sensors a transducer able to preserve the selectivity of such sensing layers is requested. We demonstrate the Field Effect Transistors (FET) coated by metalloporphyrins emphasizes the coordination of analytes with the sensing molecules with respect to the weakest forces that tend to cancel the selectivity. Molecular simulations show that coordination of gases such as carbon monoxide and nitric oxide greatly change the porphyrin electric dipole both in magnitude and direction inducing a large FET signal shift.