The scanning Kelvin probe (SKP) is a versatile tool for the investigation of surface related processes. The SKP distinguishes itself due to extremely sensitive detection of variations in surface potential induced by chemical reactions on the surface of the specimen (e. g. corrosion of metals) but also by physical interactions with the atmosphere close to the sample (e. g. adsorption of a thin water film). These prerequisites show the need for the establishment and preservation of stable environmental conditions for measurements with the SKP. This fact was the starting point for the present thesis. The aim was to modify a SKP system available at the Institute for Chemical Technology of Inorganic Materials (Johannes Kepler University Linz) in terms of system stability and further development to be able to address a larger variety of scientific questions. Therefore several tests and measurements on various sample surfaces have been run to evaluate critical parameters to be able to define a number of meaningful modifications concerning the setup itself which have been implemented consecutively. First of all, a closed measurement chamber with an indium tin oxide (ITO) coated openable glass viewport was mounted along with sensors to monitor temperature, humidity and oxygen content within the chamber. Furthermore a climate regulation gadget for establishment of either dry or humid conditions as well as gas atmospheres, depending on the scientific question, was attached. For further stabilization vibration dampers and a housing of the whole system which can be thermally regulated were applied. To determine the lateral resolution of the SKP depending on the tip diameter as well as the tip-sample distance several measurements systematically varying these parameters along with deriving a mathematical expression by the method of images has been performed resulting in an equation so that the real probed spot size can be easily calculated.
As already mentioned in the title, the investigation of thin film material libraries is one of the main topics. A material library usually consists of two or more substances, in this case metals, which are deposited on a substrate from two or more different sources covering a wide range of different compounds by exhibiting a gradient in composition. Various techniques were used for deposition, mainly thermal evaporation and sputter deposition usually followed by investigations using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and SKP techniques. Cu-Zn as well as Cu-Ni-oxide material libraries were produced using a self-modified direct current (DC) sputtering system. By SKP measurements a distinct compositional zone (Cu-14 at% Ni to Cu-19 at% Ni) was identified for the Cu-Ni-oxide system having unique surface related features. The surface structure shows a drastic change which goes along with an increased corrosion stability shown by dissolution experiments (0.1 M HCl) using a flow type scanning droplet cell microscope (FT-SDCM). The ability of Cu having an electro catalytic effect on the formaldehyde oxidation was examined on a Cu-Pd material library produced by co-sputter deposition. For the compositional zone Cu-7.5 at.% Pd the maximum oxidation current was identified and exactly in this region SKP investigation showed minimum surface potential. Two more combinatorial material libraries produced via thermal evaporation (AlCu-Ni and Mn-Si) were analysed in the same manner. For the AlCu-Ni library SKP measurement showed a discrete range (from AlCu-7 at.% Ni to AlCu-13 at.% Ni) with a drastic and focused drop in surface potential for which the Ni concentration showed to be the key parameter for the stability. For a Mn-Si material library dependency of higher manganese silicide formation as well as oxide formation connected to water content in the annealing atmosphere (ranging from 510 to 12500 ppm), SKP scans revealed the ability to detect the starting point of oxide growth with respect to water content in the atmosphere. For the sample annealed at lowest water content (510 ppm) it was found that the influence of Si content on the measured potential is dominating the Mn influence until an amount of Mn-Si 50 at.% is reached resulting in a sudden and significant elevation of potential (around 600 mV).
Finally investigations concerning hydrogen mobility in metals were performed. Therefore a specially designed electrochemical cell was used to evolve hydrogen on one side of a metal sheet and detect potential changes on the other side of the sample by SKP. Alternatively, the sample was loaded followed by SKP evaluation on the same side of the specimen. Several sample setups and metals (palladium and steel) were explored for hydrogen diffusion studies, depending on electrochemical loading cycles, and models for hydrogen removal from the exit side were derived. For the steel sample electrochemical loading of the specimen for 3.5 hours was performed followed by consecutive SKP area scans over the whole circular loading spot for several hours and assessment of equipotential planes. Finally dependency of hydrogen diffusion coefficient on rolling direction of the steel was proved. A Pd sample was utilized to define the influence of variations in humidity and in oxygen content which have an impact on the calibration for hydrogen detection. Therefore in situ SKP measurement on the exit side of the Pd foil for varying humidity and oxygen contents in the measurement chamber was connected to different hydrogen loading cycles as described before.
One more field of research is the ability of the Kelvin probe to detect shifts in the Fermi levels of semiconductors upon illumination which showed a critical minimum layer thickness. For investigation thin film libraries of Fe2O3 (thickness gradient 0 50 nm) were chosen. Threshold values of 20 nm thickness for Fe2O3 and 30 nm for ZnO were identified above which increasing layer thickness does not result in any significant changes in surface voltage scanned by SKP.
All in all it was shown that the accuracy of the scanning Kelvin probe depends on the environmental conditions which were stabilized realizing several measures. Various fields of research were addressed showing the ability of the SKP to provide additional information for interpretation of measurement data in a quick and easy way.