Widely Tuneable Composition and Crystallinity of Graded Na1+xTaO3±δ Thin Films Fabricated by Chemical Beam Vapor Deposition

Abstract

Combinatorial approach has been widely recognized as a powerful strategy to develop new-higher performance materials and shed the light on the stoichiometry-dependent properties of known systems. Herein, we take advantage of the unique features of chemical beam vapor deposition to fabricate compositionally graded Na1+xTaO3±δ thin films with −0.6 < x < 0.5. Such a varied composition was enabled by the ability of the employed technique to deliver and combine an extensive range of precursors flows over the same deposition area. The film growth occurred in a complex process, where precursor absolute flows, flow ratios, and substrate temperature played a role. The deviation of the measured Na/Ta ratios from those predicted by flow simulations suggests that a chemical-reaction limited regime underlies the growth mechanism and highlights the importance of the Ta precursor in assisting the decomposition of the Na one. The crystallinity was observed to be strongly dependent on its stoichiometry. High under-stoichiometries (e.g., Na0.5TaO3−δ) compared to NaTaO3 were detrimental for the formation of a perovskite framework, owing to the excessive amount of sodium vacancies and oxygen vacancies. Conversely, a well-crystallized orthorhombic perovskite structure peculiar of NaTaO3 was observed from mildly under-stoichiometric (e.g., Na0.9TaO3−δ) to highly over-stoichiometric (e.g., Na1.5TaO3+δ) compositions.

Efficient Optimization of High‐Quality Epitaxial Lithium Niobate Thin Films by Chemical Beam Vapor Deposition: Impact of Cationic Stoichiometry

“…The presented approach is easily scalable to mass production as deposition has been already demonstrated for substrates of 450 mm in diameter for other materials. [ 35,65 ]…”

“…The presented approach is easily scalable to mass production as deposition has been already demonstrated for substrates of 450 mm in diameter for other materials. [35,65] Further film improvement will be investigated in next experiments by exploring lower deposition temperatures (below 450 °C) with further recrystallization either by rapid thermal annealing or by laser assisted or post-deposition irradiation.…”

SrTiO3 thin film photoanodes fabricated by combinatorial chemical beam vapour deposition: intricate connection between elemental composition and thin films' properties

“…In this respect, we already demonstrated the use of CBVD for the growth of combinatorial NaTaO 3 perovskite thin films, with a controlled cationic Na/Ta ratio gradient, as well as double-cation doped NaTaO 3 . 27…”

“…In this respect, we already demonstrated the use of CBVD for the growth of combinatorial NaTaO 3 perovskite thin lms, with a controlled cationic Na/Ta ratio gradient, as well as doublecation doped NaTaO 3 . 27 In this paper, we leverage the combinatorial Chemical Beam Vapour Deposition (CBVD) approach to grow graded Sr x Ti y O z thin lms and elucidate the relationship between composition and local physico-chemical properties, particularly photoelectrochemical performances. We discuss the interplay between cationic Sr/Ti ratios and crystalline structures, optical properties, and photo-anodic behaviours under ultraviolet light illumination.…”