Evidence for structural transition in crystalline tantalum pentoxide films grown by RF magnetron sputtering

Abstract

We investigate the effect of annealing temperature on the crystalline structure and physical properties of tantalum-pentoxide films grown by radio frequency magnetron sputtering. For this purpose, several tantalum films were deposited and the Ta2O5 crystalline phase was induced by exposing the samples to heat treatments in air in the temperature range from (575 to 1000) • C. Coating characterization was performed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and UV-VIS spectroscopy. By X-ray diffraction analysis we found that a hexagonal Ta2O5 phase generates at temperatures above 675 • C. As the annealing temperature raises, we observe peak sharpening and new peaks in the corresponding diffraction patterns indicating a possible structural transition from hexagonal to orthorhombic. The microstructure of the films starts with flake-like structures formed on the surface and evolves, as the temperature is further increased, to round grains. We found out that, according to the features exhibited in the corresponding spectra, Raman spectroscopy can be sensitive enough to discriminate between the orthorhombic and hexagonal phases of Ta2O5. Finally, as the films crystallize the magnitude of the optical band gap increases from 2.4 eV to the typical reported value of 3.8 eV.arXiv:1704.05514v1 [cond-mat.supr-con]

Tantalum Oxynitride Thin Films: Assessment of the Photocatalytic Efficiency and Antimicrobial Capacity

“…The UV-Vis spectra were also used to find the type of energy transition and the optical band gap of the Ta species, using the Tauc plots, considering that the optical absorption coefficient α depends on the photon energy ( hν ) according to Equation (2):ln(αhυ)=lnα0+n×ln(hυ−Eg) where α 0 is the band tailing parameter and n is the power factor of the transition mode (for direct allowed transitions, n = 0.5, for the forbidden transitions n = 1.5, while for indirect allowed transitions, n = 2). To determine the type of transitions for each type of film, ln( αhν ) was plotted as a function of n · ln( hν − E g ), giving (for a certain region of the spectrum) a straight line with the slope equal to the power factor n [41]. By plotting ( αhν ) 1/2 , or (αhν) 2 , as a function of the photon energy, for indirect or direct transitions, respectively, the resulting dependency will have a linear part, whose intersection with the hν axis gives the values for the optical band gap energy, E g (eV) [42].…”

Influence of post-deposition annealing on the chemical states of crystalline tantalum pentoxide films

“…It is evident that F1273 exhibits a series of small reflections along the whole pattern that match the reference pattern PDF 025-0922. It is important to underline that so far there has not been a consensus regarding the spatial symmetry of these two phases, and, due to the overlapping of several peaks, one cannot rule out the coexistence of both phases 21,[29][30][31][32][33][34][35][36] .…”

Thermal, mechanical and γ‐ray shielding properties of micro‐ and nano‐Ta2O5 loaded DGEBA epoxy resin composites

“…The intensity of this peak decreased with filler addition and distinct peaks of Ta 2 O 5 fillers have appeared in XRD spectra of both micro and nanocomposites. The sharp characteristic peaks at 2θ = 22.84°, 28.40°, 36.74°, 46.75°, 50.70°, 55.68°, 58.44°, and 63.87° correspond to (001), (1110), (1111), (002), (2151), (1112), (2200), and (2221) planes, respectively of orthorhombic phase of β‐Ta 2 O 5 (PDF 00–025‐0922 with lattice parameters a = 6.1980 Å, b = 40.2900 Å, c = 3.8880 Å, and α = β = γ = 90° for the spatial group P2 1 2 1 2) 27,28 . The XRD peaks of nanocomposites were observed to be slightly broader and less sharp compared to their micro counterparts denoting the increase in lattice strain and decrease in crystallinity of the samples.…”