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G. Serrano, B. Bonanni, T. Kosmala, M. Di Giovannantonio, U. Diebold, K. Wandelt, C. Goletti:
"In situ scanning tunneling microscopy study of Ca-modified rutile TiO₂(110) in bulk water";
Beilstein Journal of Nanotechnology, 6 (2015), 438 - 443.

Despite the rising technological interest in the use of calcium-modified TiO2 surfaces in biomedical implants, the Ca/TiO2 interface
has not been studied in an aqueous environment. This investigation is the first report on the use of in situ scanning tunneling
microscopy (STM) to study calcium-modified rutile TiO2(110) surfaces immersed in high purity water. The TiO2 surface was
prepared under ultrahigh vacuum (UHV) with repeated sputtering/annealing cycles. Low energy electron diffraction (LEED)
analysis shows a pattern typical for the surface segregation of calcium, which is present as an impurity on the TiO2 bulk. In situ
STM images of the surface in bulk water exhibit one-dimensional rows of segregated calcium regularly aligned with the [001]
crystal direction. The in situ-characterized morphology and structure of this Ca-modified TiO2 surface are discussed and compared
with UHV-STM results from the literature. Prolonged immersion (two days) in the liquid leads to degradation of the overlayer,
resulting in a disordered surface. X-ray photoelectron spectroscopy, performed after immersion in water, confirms the presence of
calcium.