Electrochemical Monitoring of the Formation of Self Organized Monolayers: Octadecylphosphonic Acid on Anodically Grown Titanium Dioxide

Abstract

(1486.6 eV; 300W) as excitation source. High resolution spectra were recorded using a pass energy of 23.5 eV, with a resolution of 0.1 eV, using the binding energy of the bulk TiO2 peak to correct the spectra for charging. 3. Results and discussion 3. 1 Coverage and kinetics of the self assembly Impedance spectroscopy offers the possibility to investigate the electronic and electrochemical behavior of compact oxide layers as such or functionalized with organic monolayers. In order to screen the influence of the TiO2 substrate in impedance response and to establish a maximum contrast between coated and uncoated surfaces, we measured the impedance of the system coated and uncoated as a function of the applied potential at a constant frequency of 1000 Hz, 100 Hz, 10 Hz and 1 Hz (Fig. 1a) and impedance spectra at 0 V vs. Ag/AgCl (Fig. 1b). From Figure 1 and considering that annealed TiO2 behaves as a n-type semiconductor it is shown that changing the potential from the flatband potential ~ 0.725 V 23) to more positive potentials leads to a widening of the space charge layer in the n-type TiO2 and thus the impedance increases. At potentials higher than 0.3 V the whole oxide layer is depleted and the impedance levels to a constant value. High negative voltages