Lepidocrocite-like structure of the TiO2 monolayer grown on Ag(100)

Abstract

Titanium oxide ultrathin films were grown on Ag(100) by evaporation of titanium in an O(2) atmosphere. The growth of the oxide films was monitored by means of XPS. The Ti2p XPS spectra indicate the formation of films with a TiO(2) stoichiometry in the whole range of coverages studied here. The STM results show that titania films appear to grow as islands of uniform thickness up to the completion of the first layer. Up to the formation of one complete monolayer, a (5 × 1) LEED pattern is observed. This pattern can be interpreted as a coincidence mesh and the lattice parameters of the oxide layer are very close to those of TiO(2) films with a lepidocrocite-like structure. However, the STM images show a long-range coincidence between the periodicity of the oxide film and that of the substrate along the short side of the oxide unit cell revealing that this lattice parameter is not exactly equal to that of the substrate. Above the monolayer coverage, additional spots become visible in the LEED pattern which can be interpreted in terms of the unit cell of rutile (110). The structural determination was carried out for the monolayer of titania by means of XPD and LEED intensity analysis. The results of these investigations demonstrate that the titania monolayer has a lepidocrocite-like structure. The DFT calculations carried out for the titania monolayer show the higher stability of the lepidocrocite structure with respect to other structures derived from crystallographic planes of bulk TiO(2) phases. Moreover, these calculations allow us to determine the oxide-substrate interface energy as well as to clarify the effect of the strain on the stability of the oxide layer.

Transition from Reconstruction toward Thin Film on the (110) Surface of Strontium Titanate

“…Excluding the trench structure, the STM images are similar to published data for lepidocrocite titania nanosheets. 24 − 26 …”

“…At higher coverages ( > 4 monolayers) the STM images suggest a transition to a metallic structure closer to lepidocrocite titania nanosheets. 24 − 26 We suspect there are misfit dislocations at the buried interface although the exact Ti atom distribution below the outermost layer accessible to STM imaging is unclear so we will not speculate further here.…”

Reducible Oxides as Ultrathin Epitaxial Films

“…Interestingly, DFT provided also information about the electronic properties of the film, showing that the O 2p and Cu 4sp states overlap and that the film does not show an insulating behaviour because of an upshift of the O 2p bands and a downshift of the Ti 4s states, compared to the case of the ideal unsupported films. A TiO 2 lepidocrocite-like structure was instead obtained at submonolayer coverage when the substrate used for the growth was Ag(100) [66]. Again, LEED, XPD and STM experiments results were compared with the results of DFT calculations.…”

Density functional theory study of TiO2/Ag interfaces and their role in memristor devices

“…38 Recently, a monolayer TiO 2 film with lepidocrocite structure grown on Ag(100) has been reported. 39 On the theoretical side, Lopez and Norskov 40 studied the Au(111)/TiO 2 (110) rutile interface, which implies a large modification of the lattice parameter of gold metal in order to create a commensurate interface. Since Ag(111) is the most stable Ag surface and it is also the surface which offers the better lattice mismatch, this configuration has been used as a starting point for our study of the Ag(111)/TiO 2 (110) rutile interface; the Ag(111) slab has been compressed by 7% in the (111) direction and expanded by the same amount in However, due to the large lattice mismatch, when the structure is relaxed, unphysical distortions occur in the metal phase.…”