Abstract
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.
Highlights
Metal oxide surfaces (in particular titanium dioxide (TiO2) surfaces) covered by an alkaline-earth-metal overlayer have been investigated in recent years in experiments [1,2,3,4,5] and theoretical studies [6], considering applications ranging from nanotechnology [7] to gas sensing [8], as well as catalysis [9] and biomedicine [10,11]
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(110) surface was prepared in ultrahigh vacuum (UHV) with sputtering/ annealing cycles, as described in detail in the Experimental section, and the surface quality was examined using Low energy electron diffraction (LEED)
Summary
Metal oxide surfaces (in particular titanium dioxide (TiO2) surfaces) covered by an alkaline-earth-metal overlayer have been investigated in recent years in experiments [1,2,3,4,5] and theoretical studies [6], considering applications ranging from nanotechnology [7] to gas sensing [8], as well as catalysis [9] and biomedicine [10,11]. 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.
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