Retention of surface structure causes lower density in atomic layer deposition of amorphous titanium oxide thin films

Size effects and structural modifications in amorphous TiO 2 films deposited by atomic layer deposition (ALD) were investigated. As with the previously investigated ALD-deposited Al 2 O 3 system we found that the film's structure and properties are strongly dependent on its thickness, but here,...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2021-03, Vol.23 (11), p.66-6612
Main Authors: Rich, Benjamin B, Etinger-Geller, Yael, Ciatto, Gianluca, Katsman, Alexander, Pokroy, Boaz
Format: Article
Language:English
Subjects:
Aluminum oxide
Atomic layer epitaxy
Corundum
Density
Size effects
Surface layers
Surface structure
Thin films
Titanium dioxide
Titanium oxides
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Summary:Size effects and structural modifications in amorphous TiO 2 films deposited by atomic layer deposition (ALD) were investigated. As with the previously investigated ALD-deposited Al 2 O 3 system we found that the film's structure and properties are strongly dependent on its thickness, but here, besides the significant change in the density of the films there is also a change in their chemical state. The thin near-surface layer contained a significantly larger amount of Ti +3 species and oxygen vacancies relative to the sample's bulk. We attribute this change in chemistry to the ALD specific deposition process wherein each different atomic species is deposited in turn, thereby forming a "corundum-like" structure of the near-surface layer resembling that found in the Al 2 O 3 system. This, combined with the fact that each deposited layer starts out as a surface layer and maintains the surface structure over the next several following deposition cycles, is responsible for the overall decrease in the film density. This is the first time this effect has been shown in detail for TiO 2 , expending the previously discovered phenomenon to a new system and demonstrating that while similar effects occur, they can present in different ways for oxide systems with different structures and symmetries. Size effects were investigated in thin amorphous TiO 2 ALD films. Significant changes in film density and Ti +3 /Ti +4 species ratio were discovered; this was attributed to surface reconstruction and formation of oxygen vacancies during the ALD process.
ISSN:1463-9076
1463-9084
DOI:10.1039/d1cp00341k