Direct observation of hydration of TiO₂ on Ti using electrochemical AFM: Freely corroding versus potentiostatically held

Hydration of titanium/titanium oxide surfaces under freely corroding and potentiostatically held conditions has been characterized using electrochemical atomic force microscopy (EC AFM). In contrast to conventional high vacuum techniques, AFM enables measurement of morphological surface structure in the in situ hydrated state. Electrochemical probes in the imaging environment further enable acquisition of electrical characteristics during AFM imaging. Experiments were performed on etched, electropolished commercially pure titanium. As noted by direct observation and corroborated by power spectral density (Fourier analysis) measurements, oxide domes cover the titanium surface and grow laterally during hydration. Applied potential altered the growth rate. Under open circuit potential conditions, growth proceeded approximately six times faster than under a -1 V applied voltage (1098 ± 52 nm²/min ± versus 184.84 ± 19 nm²/min). Film growth increased electrical resistance and lowered interfacial capacitance based on step polarization impedance spectroscopy tests.