V2O3(0001)Surface Termination: Phase Equilibrium

Abstract

Complementary but independent medium-energy and low-energy ion scattering studies of the (0001) surfaces of V 2 O 3 films grown on Pd(111), Au(111) and Cu 3 Au(100) reveal a reconstructed full O 3 -layer termination creating a VO 2 surface trilayer. This structure is fully consistent with previous calculations based on thermodynamic equilibrium at the surface during growth, but contrasts with previous suggestions that the surface termination comprises a complete monolayer of vanadyl (V=O) species.

The structure of epitaxial V2O3 films and their surfaces: A medium energy ion scattering study

“…Finally, we may ask whether, for these materials, the surface structure predicted to be in thermodynamic equilibrium with the gas phase under the preparation conditions of temperature and oxygen partial pressure is actually observed. In particular, previous studies of the (0001) faces of α-Al 2 O 3 [2,3,4] and Cr 2 O 3 [5,6,7,8,9] have indicated that is largely the case [10], but that for V 2 O 3 it is not (e.g. [10,11,12,13,14,15]).…”

Carbon Dioxide Adsorption on V2O3(0001)

“…There is some fine structure especially in the feature around 1300 cm −1 which points towards a number of slightly different adsorption states, but there are no indications that the states are significantly different for CO 2 on the oxide which contains mainly 18 O and the one prepared with 16 O, which may be viewed as an indication that it is not carbonate which is formed on the surface since this would involve a bond of CO 2 to surface oxygen. Another observation that points into the same direction is that CO 2 does not react with the vanadyl terminated surface, for which only molecular adsorption is found (see Fig.…”

“…Crossley and King [33] have treated the frequency shifts of molecular vibrations in isotopic mixtures for the case of 13 CO and 12 CO on Pt(111) theoretically and measured the molecular vibrational energies with IRAS, finding a downward shift of the 12 CO band in the isotopic mixture, similar to what we find for the V= 16 O vanadyl vibration. A point to note is that the intensities of the V= 16 O and V= 18 O vanadyl vibrations in the bottom spectra in Fig. 3 are not proportional to the concentrations of 16 O and 18 O in the oxide layer since there is an intensity transfer from the low energy band to the high energy band [33][34][35][36].…”

“…In this context especially the interaction with carbon dioxide as discussed later in this text has to be considered. Therefore the oxide layer contained a mixture of the oxygen isotopes 18 O and 16 O which is the origin of the two vanadyl vibrations at 1000 and 1034 cm −1 in the spectra of the vanadyl terminated surfaces in Fig. 3.…”

“…Guided mainly by the presence of an intense vanadyl induced feature in vibrational spectra [10,11] is was concluded that the surface should be terminated by a layer of vanadyl groups. This was questioned some years ago by studies which reported that the surface should be terminated by a quasi-hexagonal oxygen layer [18][19][20]. A later I/V-LEED (LEED = low energy electron diffraction; I/V-LEED = LEED intensity analysis) study could show that the initial picture of a vanadyl terminated surface is probably correct [21,22] and therefore we will use the term 'vanadyl terminated' throughout this text.…”