Contact free potential mapping by vibrating capacitor
The contact free vibrating capacitor method is a valuable tool for investigating the surface potentials of solid surfaces. The purpose of the present article is to summarize the theory and capabilities of the vibrating capacitor method, especially scanning vibrating capacitor pictures in the electronics. After a brief review some results will be discussed, such as a contact potential map taken from a printed circuit board, a surface potential map from a biased ceramic thick film circuit and some results from silicon solid state devices and solar cells. Potential maps contain a lot of information concerning the surface conditions, included the inhomogeneities of the technology, bias and other additional excitation. These potential maps may help in the development, quality control and defect analysis
Chemical imaging by direct methods
Chemical imaging is a very old principle of analysis. It has been used for many millions of years in biological tasting and smelling systems. Artificial versions of chemical imaging are traditional paper chromatography and the pH indicator strip used in chemical analysis, which directly result in real (visible) chemical images. In a recent article the indirect and direct chemical imaging methods are introduced, especially the evaluation methods for gas sensitive surfaces by direct pixelizing of the surface and interface potential changes. The scanned light pulse technique (SLPT) and the scanning vibrating capacitor are very effective tools for the chemical mapping of the surfaces. These methods are sensitive for the interface or surface potential shifts (adsorption induced work function shifts) respectively, that depend on the composition of adsorbed layers. Advantages and disadvantages, some technical limits, theory, practice and some results are discussed, too.
Study of adsorption of oxygen on β-Al2O3 + Au and β-Al2O3 + Pt
Abstract To improve the understanding of the electrochemical effects observed on an original potentiometric gas sensor, interactions of oxygen with the device were investigated. This gas sensor is made of a solid electrolyte (treated Na-β-alumina) associated with two metallic electrodes (gold and platinum) located in the same gas mixture. Adsorption of charged oxygen species, considered responsible for the electrical response developed by the sensor, was investigated by work function measurements. Results showed that charged oxygen species only form on partially gold or platinum covered solid electrolyte. Comparison of these results with those obtained in a previous calorimetric study of interactions between oxygen and the same materials suggests the existence of at least two different oxygen species adsorbed on the surface of the sensitive element. The first one, located on the solid electrolyte surface, is neutral and characterized by an endothermal reaction of formation. The second one is charged and probably produced at the gas/solid electrolyte/metallic electrode interface. A mechanism based on the concept of “three phase boundary” and similar to the “reverse spillover” phenomenon is proposed to account for the adsorption of these oxygen species.