In situ scanning tunneling microscopy study of Ca-modified rutile TiO2(110) in bulk water

G. Serrano, B. Bonanni, T. Kosmala, M. Di Giovannantonio, U. Diebold, K. Wandelt, C. Goletti

Department of Physics, Università degli Studi di Roma "Tor Vergata", 00133 Rome, Italy
Institut für Physikalische und Theoretische Chemie, 53115 Bonn, Germany
Istituto di Struttura della Materia (ISM), Consiglio Nazionale delle Ricerche (CNR), 00133 Rome, Italy
Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria

Beilstein J. Nanotechnol. 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.

Corresponding author: Giulia Serrano. Reprints also available from Ulrike Diebold (diebold at iap_tuwien_ac_at).

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