CONICET | Buscador de Institutos y Recursos Humanos

In recent years, the modification of Ti/TiO2 substrates by metal nanoparticles (NP´s) has received considerable attention due to its importance in nanoscale systems applications [1]. Consequently, the knowledge of interactions between metal NP´s and the used support has an essential importance to predict the shape and size of the deposited structures. Investigations of TiO2 surfaces are being carried out in a wide range of surrounding environments, from ultra-high vacuum (UHV) to those that involve the contact with aqueous solutions, where variations in the surface electronic structure induced by the different experimental conditions are compared, and clear trends are observed. Modifications by metal deposition and/or adsorption/desorption of species from a solution, affect the interface properties and the chemical reactions. Peres et al. [2], have studied the WF of multilayer electrodes by Kelvin probe force microscopy (KPFM) in air, performing WF measurements on well characterized commercial indium tin oxide (ITO) samples tocalibrate the tip. They subsequently have performed measurements on TiO2/Ag/TiO2, SOx/Ag/SOx, and ZnS/Ag/ZnS samples, obtaining reliable results. We have used a similar procedure to study the deposition of Ag and Ag-Co on Ti/TiO2 samples by KPFM under ambient pressure and temperature conditions. The Ag and Co NP´s were either spontaneously (sp) formed or electrodeposited (ed) onto Ti/TiO2 samples. Clear differences in the surfaces topography were found depending on which deposition methodology was used. In the case of TiO2/Ag, for the sp a sort of plate-like structures of approximately 200-500 nm are formed over the upmost surface of the sample. For the ed one, well defined spherical NP´s with diameters ranging between 100-150 nm are obtained. For TiO2/Ag-Co, a similar stripped morphology resembling the bare substrate is observed for the sp. In the ed region, a similar plated-like surface as the TiO2/Ag sp is obtained, with the presence of smaller NP´s in the range of approx. 50 nm of diameter.We performed WF measurements on well characterized Pt(111) samples (5.37 eV) and used them as a calibration method to characterize the tip WF, considering the contact potential difference (CPD) related directly to the WF differences between the tip and the sample. Using this calibrated tip, we subsequently performed the WF measurements over different samples. First, a bare TiO2 surface (5.35 eV) was measured in order to compare the obtained value with those found for the modified surfaces. Based on the CPD value for the TiO2/Ag-Co region, an increase of 0.2 eV with respect to the bare TiO2WF was found. Additionally, considering the CPD value obtained for the TiO2/Ag region, a decrease of 0.15 eV compared to the bare TiO2WF was found. KPFM proved to be a useful tool to characterize changes in the substrate WF´s after they have been modified. Studies by SEM and EPMA were also carried out for the same samples. It could be demonstrated by EPMA that for TiO2/Ag samples, indeed the observed NP´s correspond to Ag. In the TiO2/Ag-Co case, it seems that the NP´s amount was below the detection limit of the technique, so no traces of them were observed.