$ \newcommand{\bt}{\beta} \bt$ -TaON thin films: production by reactive magnetron sputtering and the question of non-stoichiometry

Abstract

In this work we report on the structure, morphology, composition, chemical bonding and optical properties of tantalum oxynitride (Ta-O-N) thin films prepared by reactive direct current magnetron sputtering. The films have been investigated by grazing incidence x-ray diffraction, x-ray reflectivity, grazing incidence small angle x-ray scattering, time-offlight elastic recoil detection analysis, x-ray photoelectron spectroscopy and spectroscopic ellipsometry. The composition and the partial pressure of the reactive atmosphere (N 2 + O 2 ) have been varied in order to find conditions suitable for the β-TaON phase production. As prepared thin films are amorphous and annealing at T a 800 °C is necessary to promote crystallization. We discuss the role of N 2 gas on the kinetics of sputtered particles and its influence on the oxidation rate and porosity of the growing film. The anion composition in Ta-O-N films strongly depends on the reactive gas condition during the deposition. We found that the O/N ratio in β-TaON films increases with more N 2 or O 2 gas in the chamber, whereas the corresponding absorption onset and valence band maximum show a blue shift of up to 0.5 eV. These results were related to the non-stoichiometry in β-TaO x N y crystallites with x > y .

Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films

“…For oxygen flow to increase to higher than 0.25 sccm, the oxynitride starts to form. Gaussian fit yields very complicated crystal structures with a large number of crystal planes (TaON, ICCD PDF 70-1193 and 71-0178) [37,38]. The signature peaks for tantalum oxynitrides are (-1,1,1), (1,1,1), and the tri-peaks are (0,0,2), (0,2,0), (2,0,0).…”

Combinatorial Approach for Single-Crystalline TaON Growth: Epitaxial β-TaON (100)/α-Al2O3 (012)

“…Tantalum oxynitride with a monoclinic crystal structure (β-TaON) is a very attractive material for this photocatalytic application. , β-TaON has a band gap of 2.5 eV, which is within the visible part of the solar spectrum. The valence band maximum (VBM) and conduction band minimum (CBM) of this material are optimally positioned with respect to the reduction and oxidation potentials of the water-splitting reaction. ,, …”

“…For efficiency, our material development process combined a compositional spread in the synthesis step with high-throughput measurements of the produced phases. − Machine learning-based big data techniques were used to convert a large set of experimental data into actionable small clusters. − In the process of trying to grow a β-TaON thin film, the stoichiometry (O/N) is crucial to obtaining the preferred phase . Instead of realizing and optimizing the O/N ratio from a large set of individual thin-film samples, we deposited a lateral compositional graded thin-film sample using multitarget PLD .…”