HAADF STEM and Ab Initio Calculations Investigation of Anatase TiO2/LaAlO3 Heterointerface

The understanding of the origin of a two-dimensional electron gas (2DEG) at the surface of anatase TiO2 remains a challenging issue. In particular, in TiO2 ultra-thin films, it is extremely difficult to distinguish intrinsic effects, due to the physics of the TiO2, from extrinsic effects, such as th...

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Published inApplied sciences Vol. 12; no. 3; p. 1489
Main Authors Islam, Mahabul, Rajak, Piu, Knez, Daniel, Chaluvadi, Sandeep Kumar, Orgiani, Pasquale, Rossi, Giorgio, Dražić, Goran, Ciancio, Regina
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.02.2022
Subjects
2DEG
aberration-corrected scanning transmission electron microscopy
Anatase
anatase TiO2
Density functional theory
DFT calculations
Electron gas
heterointerfaces
Image transmission
Interfaces
Lasers
oxygen vacancies
Scanning transmission electron microscopy
Substrates
Thin films
Titanium dioxide
Titanium oxides
Transmission electron microscopy
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Summary:The understanding of the origin of a two-dimensional electron gas (2DEG) at the surface of anatase TiO2 remains a challenging issue. In particular, in TiO2 ultra-thin films, it is extremely difficult to distinguish intrinsic effects, due to the physics of the TiO2, from extrinsic effects, such as those arising from structural defects, dislocations, and the presence of competing phases at the film/substrate interface. It is, therefore, mandatory to unambiguously ascertain the structure of the TiO2/substrate interface. In this work, by combining high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), density functional theory calculations, and multislice image simulations, we have investigated the nature of strainless anatase TiO2 thin films grown on LaAlO3 substrate. In particular, the presence of oxygen vacancies in anatase TiO2 has been proved to stabilize the formation of an extra alloy layer, Ti2AlO4, by means of interface rearrangement. Our results, therefore, elucidate why the growth of anatase TiO2 directly on LaAlO3 substrate has required the deposition of a TiOx extra-layer to have a 2DEG established, thus confirming the absence of a critical thickness for the TiO2 to stabilize a 2DEG at its surface. These findings provide fundamental insights on the underlying formation mechanism of the 2DEG in TiO2/LAO hetero-interfaces to engineer the 2DEG formation in anatase TiO2 for tailored applications.
ISSN:2076-3417
2076-3417
DOI:10.3390/app12031489