Ordered Fe(II)Ti(IV)O₃ Mixed Monolayer Oxide on Rutile TiO₂(011)

Abstract

Oxide monolayers supported or intermixed with an oxide support are potential nanocatalysts whose properties are determined by the interplay with the support. For fundamental studies of monolayer oxides on metal oxide supports, well-defined systems are needed, but so far, the synthesis of monolayer oxides with long-range order on single-crystal oxide surfaces is rare. Here, we show by a combination of scanning tunneling microscopy, photoemission spectroscopy, and density functional theory (DFT)-based computational analysis that the rutile TiO2(011) surface supports the formation of an ordered mixed FeTiO3 monolayer. Deposition of iron in a slightly oxidizing atmosphere (10(-8) Torr O2) and annealing to 300 °C results in a well-ordered surface structure with Fe in a 2+ charge state and Ti in a 4+ charge states. Low-energy ion scattering suggests that the cation surface composition is close to half Fe and half Ti. This surface is stable in ultrahigh vacuum to annealing temperatures of 300 °C before the iron is reduced. DFT simulations confirm that a surface structure with coverage of 50% FeO units is stable and forms an ordered structure. Although distinct from known bulk phases of the iron-titanium oxide systems, the FeTiO3 monolayer exhibits some resemblance to the ilmenite structure, which may suggest that a variety of different mixed oxide phases (of systems that exist in a bulk ilmenite phase) may be synthesized in this way on the rutile TiO2(011) substrate.

Fe(II)Ti(IV)O3 mixed oxide monolayer at rutile TiO2(011): Structures and reactivities

“…Among these structures, the one illustrated in Fig. 1(d) is also the one reported in our previous work of the experimental measurement of this mixed oxide surface [31], which has obvious similarity with the ilmenite (012) surface. Interestingly, in the current work, by using improved optimization algorithm, we actually located several structures that are more stable, which even have no obvious ilmenite features.…”

“…In addition, small amount of iron impurities in anatase or rutile TiO 2 have been reported previously to segregate to the surface by vacuum annealing, but no ordered mixed oxide layer at the surface was formed [29,30]. Very recently, we have reported an ordered Fe/Ti mixed oxide surface layer on the rutile TiO 2 (011) surface through combined experimental and computational studies [31], and a preliminary structural model based on the ilmenite surface has been proposed to describe the atomic configuration of the mixed oxide layer.…”

“…In particular, the GA method was used for generating structures and helping us to obtain a large set of possible metastable and global minimum structures, which may even provide information on surface evolution. On the basis of the previous experimental measurement regarding the composition of the Fe-Ti mixed oxide monolayer, we constructed the surface by adding two FeO units in each 2×1 rutile TiO 2 (011) surface cell [31]. In other words, the Fe(II)Ti(IV)O 3 mixed oxide monolayer actually consists of 1/2 ML of Fe(II)O oxide with respect to the exposed TiO 2 surface units on the original surface.…”

Epitaxial corundum-VTiO3 thin films grown on c-cut sapphire

“…Interestingly the TiVO3 O-2p band appears at significantly (~1eV) lower binding energy than both Ti2O3 and V2O3 reference spectra. In fact the O-2p binding energy onset is more similar to that of ntype TiO2, whose spectrum 54 is also shown for comparison in Fig. 7.…”

Two-Dimensional Iron Tungstate: A Ternary Oxide Layer With Honeycomb Geometry

“…2D phases of ternary oxides have only recently been discovered, which feature fascinating structural behavior 30 − 32 and show promise for nanocatalysis applications. 33 The 2D iron tungstate phase described here is synthesized via a solid-state reaction of (WO 3 ) 3 clusters with a FeO monolayer on a Pt(111) surface and has been characterized by a variety of surface analytical techniques, including X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and temperature-programmed desorption (TPD), combined with first-principles density functional theory (DFT) analysis, thus achieving a thorough understanding of its structural and electronic properties. The bulk iron tungstate phase, ferberite (FeWO 4 ), which is the pure end member of natural wolframite (Fe x Mn 1– x WO 4 ) minerals, is a promising material with potential applications in photocatalysis, battery electrodes, photoluminescence, magnetism, and multiferroics.…”