Tantalum Oxynitride Thin Films Research Articles

Electronic, Optical, and Epsilon Near-Zero Response in Magnetron-Sputtered Tantalum Oxynitride Thin Films

Electronic, Optical, and Epsilon Near-Zero Response in Magnetron-Sputtered Tantalum Oxynitride Thin Films

On the chemistry, photocatalytical, and corrosion behavior of co-sputtered tantalum and titanium oxynitride thin films

Direct current magnetron co-sputtered titanium and tantalum based oxynitride coatings (TaTiON) were analyzed in terms of their chemistry, surface morphology, surface energy, photocatalytic activity, and corrosion resistance. The variable parameter for the deposition was the applied current on each target, changing between 0.75A and 0.25A for the Ta target, and from 0.25A to 0.75 A for the Ti target, to obtain a total current of 1A. Reference single-sputtered samples (TaON and TiON) were deposited under identical conditions. It was observed that a higher degree of oxidation occurred in the samples deposited with higher current on the Ti target, while nitriding and oxynitriding processes occurred only on the surfaces of the films containing Ta. In terms of surface roughness, the co-sputtered coatings exhibited significantly smaller values, compared to the single-sputtered coatings. The highest photodegradation efficiency was registered for the co-sputtered sample which contains the highest N concentration. The corrosion rate, obtained from electrochemical tests, varies in a rather large domain, as function of the chemical species in the coatings.

Microstructure and electrical property of tantalum oxynitride thin films prepared using high-power impulse reactive magnetron sputtering

Ta-N thin films were prepared on glass and Al2O3 substrates using high-power impulse reactive magnetron sputtering. A Ta target was used and sputtered using Ar/N2 two gasses mixture. The phase structures, microstructures and electrical properties of Ta-N thin film with different powers and annealing temperatures were investigated. The results showed that an amorphous structure existed in the as-deposited Ta-N films at 500 W, and some crystalline phases (TaN, Ta2N and β-Ta) were observed in as-deposited films at 1500 W and 2500 W. The crystallization phase did not change when the annealing temperature ranged from room temperature up to 500 °C. When the sputtering power increased to 2500 W, TaN, Ta2N and β-Ta crystalline phases coexisted in the as-deposited films. However, Ta-N films deposited at 2500 W and annealed at 500 °C in N2 exhibited resistivity of ∼460 μΩ-cm with −93 ppm °C−1 temperature coefficient of resistance.

Spectroscopic study on amorphous tantalum oxynitride thin films prepared by reactive gas-timing RF magnetron sputtering

The amorphous tantalum oxynitride (TaOxNy) thin films were prepared on silicon (100) substrates by magnetron sputtering system with different techniques of conventional reactive sputtering and reactive gas-timing (RGT). The films were studied via spectroscopic ellipsometry (SE) measured in the range of 0.75–5.0 eV with 0.025 eV interval at 70° incident angle, and the optical model based on Tauc-Lorentz function was constructed to extract the properties of the films. The SE results indicated that all prepared films were grown homogeneously and show different optical properties upon their deposition conditions and techniques. The optical properties of film prepared by conventional reactive sputtering were close to the tantalum oxide film (TaO). The refractive index and optical band gap (Eg) of RGT samples changed with the oxygen timing and correlated with the change of oxygen and nitrogen concentration of the films. In addition, the morphologies, crystallinities, atomic concentrations and distributions of nitrogen atoms in the films analyzed by field-emission scanning electron microscopy, glazing-incident X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy are also discussed.

-TaON thin films: production by reactive magnetron sputtering and the question of non-stoichiometry

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-of-flight elastic recoil detection analysis, x-ray photoelectron spectroscopy and spectroscopic ellipsometry. The composition and the partial pressure of the reactive atmosphere (N2 + O2) have been varied in order to find conditions suitable for the -TaON phase production. As prepared thin films are amorphous and annealing at °C is necessary to promote crystallization. We discuss the role of N2 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 -TaON films increases with more N2 or O2 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 -TaOxNy crystallites with x > y .

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

Tantalum oxynitride thin films have been deposited by reactive magnetron sputtering, using a fixed proportion reactive gas mixture (85% N2 + 15% O2). To produce the films, the partial pressure of the mixture in the working atmosphere was varied. The characteristics of the produced films were analyzed from three main perspectives and correspondent correlations: the study of the bonding states in the films, the efficiency of photo-degradation, and the antibacterial/antibiofilm capacity of the coatings against Salmonella. X-ray Photoelectron Spectroscopy results suggest that nitride and oxynitride features agree with a constant behavior relative to the tantalum chemistry. The coatings deposited with a higher reactive gas mixture partial pressure exhibit a significantly better antibiofilm capacity. Favorable antibacterial resistance was correlated with the presence of dominant oxynitride contributions. The photocatalytic ability of the deposited films was assessed by measuring the level of degradation of an aqueous solution containing methyl orange, with or without the addition of H2O2, under UV or VIS irradiation. Degradation efficiencies as high as 82% have been obtained, suggesting that tantalum oxynitride films, obtained in certain configurations, are promising materials for the photodegradation of organic pollutants (dyes).

Examination of various characteristics for sputtered tantalum oxide-nitride thin films deposited at various oxygen flowrates

ABSTRACTTantalum oxynitride thin films were prepared by reactive sputtering. The argon and nitrogen flow rate were kept stable whereas oxygen flow rate was incremented periodically. The effect of oxygen flow rate on various properties of tantalum oxynitride thin films is reported in this research paper. XRD patterns of tantalum oxynitride thin films displayed peaks commonly as for nano-crystalline materials. Surface topography observed to be smooth and exhibited smaller grain structure. Wettability test showed promising results for hydrophobicity. Wear test was done on uncoated and coated tantalum oxynitride thin films on 10 mm diameter cylindrical pins of brass and mild steel.

On the structural, morphological and electrical properties of tantalum oxy nitride thin films by varying oxygen percentage in reactive gases plasma

Tantalum oxy nitride (Ta-ON) thin films possess unique properties due to combined beneficial aspects of tantalum nitride and tantalum oxide. In the present work, Ta-ON thin films are synthesized using energetic ions and electrons beams emanated from the hot and decaying plasma in dense plasma focus (DPF) device. Oxygen percentage in the reactive gas admixture [O/(O+N)]% is varied from 10 to 60 for thin film synthesis. Influence of oxygen percentage on structural, morphological, compositional and electrical properties of thin films is also analyzed. Increase of oxygen percentage in the gas admixture (upto 40%) resulted in transformation of thin film from tantalum nitride to tantalum oxy nitride; however; higher oxygen percentages (≥ 50%) caused amorphization in synthesized thin film. Morphological analysis revealed that pure nitrogen environment yields the granular structure of film in nano-meter range whereas escalation of grains is observed with the increase in oxygen percentage. Cross sectional SEM showed better film growth rate at lower oxygen percentages. Compositional profiles exhibited improvement of oxygen content in thin film by increasing oxygen percentage in the admixture. The electrical resistivity of films shifted from conducting (for 0% oxygen) to semiconducting-insulating (for 60% oxygen) material range for maximum oxygen percentage.

Fabrication of TaOxNy thin films by reactive ion beam-assisted ac double magnetron sputtering for optical applications

Tantalum oxynitride (TaOxNy) thin films have been deposited by reactive ion beam-assisted ac double magnetron sputtering. Thin films deposited by this method are known to have high mechanical durability and adhesion. A controlled variation of the refractive index of these optical coatings has been achieved through a systematic control of the oxygen and nitrogen gases present in the chamber during the film deposition. This method offers a rapid and economical way of fabricating interference and gradient index coatings used in many optical applications. To show the potential of this deposition method, a Bragg mirror stack was made with twenty alternating layers of oxygen-rich (high x) and nitrogen-rich (high y) TaOxNy thin films.

Tantalum nitride films integrated with transparent conductive oxide substrates via atomic layer deposition for photoelectrochemical water splitting.

Tantalum nitride, Ta3N5, is one of the most promising materials for solar energy driven water oxidation. One significant challenge of this material is the high temperature and long duration of ammonolysis previously required to synthesize it, which has so far prevented the use of transparent conductive oxide (TCO) substrates to be used which would allow sub-bandgap light to be transmitted to a photocathode. Here, we overcome this challenge by utilizing atomic layer deposition (ALD) to directly deposit tantalum oxynitride thin films, which can be fully converted to Ta3N5via ammonolysis at 750 °C for 30 minutes. This synthesis employs far more moderate conditions than previous reports of efficient Ta3N5 photoanodes. Further, we report the first ALD of Ta-doped TiO2 which we show is a viable TCO material that is stable under the relatively mild ammonolysis conditions employed. As a result, we report the first example of a Ta3N5 electrode deposited on a TCO substrate, and the photoelectrochemical behavior. These results open the door to achieve efficient overall water splitting using a Ta3N5 photoanode.

Multiphase Structure of Tantalum Oxynitride TaOxNy Thin Films Deposited by Reactive Magnetron Sputtering

This work deals with the structure and the microstructure of tantalum oxynitride thin films deposited by reactive magnetron sputtering. The local structures of amorphous as-prepared thin films are investigated using the pair distribution function (PDF) technique based on total X-ray scattering experiments. The corresponding annealed thin films are analyzed using conventional θ–θ X-ray diffraction technique and full-pattern fitting methods. Rutherford backscattering and X-ray photoelectron spectrometries are used in conjunction with X-ray techniques. As-prepared thin films are nanostructured. The PDF signal is coming from small structural units below 10 A in diameter, which only maintain nearest-neighbor order and with a composition changing gradually from TaN to δ-TaON and Ta2O5 as the oxygen content in the reactive gas increases. On the other hand, the annealed thin films consist of a mixture of separate crystalline phases with refined cell parameters consistent with the formation of TaN (Fm–3m), β-TaON ...

Composition and structure variation for magnetron sputtered tantalum oxynitride thin films, as function of deposition parameters

Tantalum oxynitride thin films were produced by magnetron sputtering. The films were deposited using a pure Ta target and a working atmosphere with a constant N2/O2 ratio. The choice of this constant ratio limits the study concerning the influence of each reactive gas, but allows a deeper understanding of the aspects related to the affinity of Ta to the non-metallic elements and it is economically advantageous. This work begins by analysing the data obtained directly from the film deposition stage, followed by the analysis of the morphology, composition and structure. For a better understanding regarding the influence of the deposition parameters, the analyses are presented by using the following criterion: the films were divided into two sets, one of them produced with grounded substrate holder and the other with a polarization of −50V. Each one of these sets was produced with different partial pressure of the reactive gases P(N2+O2). All the films exhibited a O/N ratio higher than the N/O ratio in the deposition chamber atmosphere. In the case of the films produced with grounded substrate holder, a strong increase of the O content is observed, associated to the strong decrease of the N content, when P(N2+O2) is higher than 0.13Pa. The higher Ta affinity for O strongly influences the structural evolution of the films. Grazing incidence X-ray diffraction showed that the lower partial pressure films were crystalline, while X-ray reflectivity studies found out that the density of the films depended on the deposition conditions: the higher the gas pressure, the lower the density. Firstly, a dominant β-Ta structure is observed, for low P(N2+O2); secondly a fcc-Ta(N,O) structure, for intermediate P(N2+O2); thirdly, the films are amorphous for the highest partial pressures. The comparison of the characteristics of both sets of produced TaNxOy films are explained, with detail, in the text.

Structure dependent resistivity and dielectric characteristics of tantalum oxynitride thin films produced by magnetron sputtering

The main purpose of this work is to present and to interpret the change of electrical properties of TaxNyOz thin films, produced by DC reactive magnetron sputtering. Some parameters were varied during deposition: the flow of the reactive gases mixture (N2 and O2, with a constant concentration ratio of 17:3); the substrate voltage bias (grounded, −50V or −100V) and the substrate (glass, (100) Si or high speed steel). The obtained films exhibit significant differences. The variation of the deposition parameters induces variations of the composition, microstructure and morphology. These differences cause variation of the electrical resistivity essentially correlated with the composition and structural changes. The gradual decrease of the Ta concentration in the films induces amorphization and causes a raise of the resistivity. The dielectric characteristics of some of the high resistance TaxNyOz films were obtained in the samples with a capacitor-like design (deposited onto high speed steel, with gold pads deposited on the dielectric TaxNyOz films). Some of these films exhibited dielectric constant values higher than those reported for other tantalum based dielectric films.

Structural and ellipsometric study on tailored optical properties of tantalum oxynitride films deposited by reactive sputtering

Oxynitride materials, which offer the possibility of merging oxide and nitride properties, are increasingly studied for this reason. This paper focuses on assessing the optical properties of tantalum oxynitride thin films deposited by pure tantalum target sputtering in an Ar/O2/N2 reactive atmosphere. First, by changing the oxygen to reactive gas flow rate ratio, and using thermal post-treatment, we deposited films with elemental compositions studied by Rutherford backscattering spectroscopy, ranging from a nitride (close to Ta3N5) to an oxide (close to Ta2O5) with various structures analyzed by x-ray diffraction. Their optical properties were investigated in depth by spectroscopic ellipsometry and UV-visible spectroscopy. For the ellipsometry investigation, we propose a model combining the Tauc–Lorentz law and additional Lorentz oscillator: the first contribution is linked to a semi-conductor or insulator film matrix, and the second one to the presence of conductive TaN crystals. Ellipsometry thus appears as a powerful tool to investigate complex materials such as tantalum oxynitrides. Moreover, we demonstrated that using this deposition method we were able to finely tune the film refractive index from 3.4 to 2.0 (at 1.96 eV) and the optical band gap, specifically from 1.3 to 2.7 eV.

Tantalum oxynitride thin films: Mechanical properties and wear behavior dependence on growth conditions

Tantalum oxynitride (TaNxOy) thin films were produced by magnetron sputtering. This work analyzes and compares the mechanical properties and the wear behavior of the films, taking into account the differences promoted by changes in composition and structure, caused by the variation of the partial pressure of the reactive gases (P(N2+O2)) and by the polarization of the substrate holder.Besides the change in composition, the variation of P(N2+O2) causes significant changes in the morphology and structure of the films. Those produced with low P(N2+O2) evidence a higher crystallinity and, in these conditions, the films exhibit hardness around 20GPa. Films produced with higher P(N2+O2) exhibit higher O content, are amorphous and the hardness is significantly lower.The substrate bias does not influence the adhesion of the films to the high speed steel substrate, but influences the mechanical properties, particularly the hardness, at low P(N2+O2) regime. Films with higher crystallinity exhibit higher hardness, but in the low P(N2+O2) regime, those who were produced with polarization are harder. Although some dependence may be established for set B films, the hardness is not as influent on the wear resistance of the TaNxOy films as the friction coefficient.

High-Mobility Electron Conduction in Oxynitride: Anatase TaON

We report on a new route for synthesizing metastable anatase tantalum oxynitride (TaON) in thin film form on lattice-matched (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) single crystals by using nitrogen plasma assisted pulsed laser deposition. Epitaxial stress from the substrate stabilized the anatase structure without the need for doping an impurity, such as Sc or Mg, which is required in conventional bulk synthesis by ammonolysis. X-ray diffraction measurements and cross-sectional transmission electron microscope (TEM) observations demonstrated the growth of phase-pure anatase TaON thin films with the epitaxial relationships (001)TaON ∥ (001)LSAT and [100]TaON ∥ [100]LSAT. A high growth temperature (≥750 °C) and a balanced supply of oxygen and nitrogen are crucial for obtaining high-quality anatase TaON thin films. The films grown at 800 °C exhibited good n-type conduction with a resistivity of ∼1 × 10–2 Ω cm. The source of the carrier electrons was likely anion vacancies. The Hall mobility of anatase TaON (∼17 cm2 V–1 s–1 at 300 K) is comparably high to that of anatase TiO2, which is a well-known oxide semiconductor with the same crystal structure and d0 electronic configuration. The bandgap and refractive index of anatase TaON thin films were 2.37 eV and approximately 3.0, respectively, in the visible region.

Development of tantalum oxynitride thin films produced by PVD: Study of structural stability

The purpose of this work is to study the evolution of the structure and of the thermal stability of a group of tantalum oxynitride thin films, prepared by magnetron sputtering, under the influence of vacuum annealing, up to a temperature of 800°C.When varying the partial pressure of the reactive gases (PO2+N2), during the deposition process, the films change from a structure with a combination of poorly developed crystallites of the tetragonal β-Ta and of the face centred cubic (fcc) Ta(O,N) phases, for the films deposited with low PO2+N2, to a quasi-amorphous structure, for the films deposited with highest pressures. For intermediate pressures, the films reveal the presence of the fcc-Ta(O,N) structure. This structure corresponds to O atoms substituting some of the N atoms on the fcc-TaN structure and/or N atoms substituting O atoms of the fcc-γ-TaO structure.When subjected to the thermal annealing at 700°C or higher, the film produced with lowest partial pressure revealed a remarkable structural change. New diffraction peaks appear and can only be attributed to a sub-stoichiometric hexagonal tantalum nitride structure. The film did not reveal any signs of delamination or cracks after all annealing temperatures. The two films produced with highest partial pressure proved to be the most stable. Structurally, they maintain the amorphous structure after all the annealing treatments and, in addition, no cracks or delamination were detected.

Properties of tantalum oxynitride thin films produced by magnetron sputtering: The influence of processing parameters

The main purpose of this work is to present and to interpret the change of structure and physical properties of tantalum oxynitride (TaNxOy) thin films, produced by dc reactive magnetron sputtering, by varying the processing parameters. A set of TaNxOy films was prepared by varying the reactive gases flow rate, using a N2/O2 gas mixture with a concentration ratio of 17:3. The different films, obtained by this process, exhibited significant differences. The obtained composition and the interpretation of X-ray diffraction results, shows that, depending on the partial pressure of the reactive gases, the films are: essentially dark grey metallic, when the atomic ratio (N + O)/Ta < 0.1, evidencing a tetragonal β-Ta structure; grey-brownish, when 0.1 < (N + O)/Ta < 1, exhibiting a face-centred cubic (fcc) TaN-like structure; and transparent oxide-type, when (N + O)/Ta > 1, evidencing the existence of Ta2O5, but with an amorphous structure. These transparent films exhibit refractive indexes, in the visible region, always higher than 2.0.The wear resistance of the films is relatively good. The best behaviour was obtained for the films with (N + O)/Ta ≈ 0.5 and (N + O)/Ta ≈ 1.3.

Effect of the rapid thermal annealing on the structure and optical properties of TaOxNy thin films deposited by reactive magnetron sputtering

Tantalum oxynitride thin films are deposited by radio-frequency magnetron sputtering using a pure tantalum target under argon/oxygen/nitrogen gas mixture. The argon flow is kept constant while the oxygen and nitrogen flows are changed simultaneously in a way to keep constant the total flow of these reactive gases. We succeed to deposit TaOxNy films with stoichiometry ranging between those of TaN and Ta2O5. All films are deposited at room temperature without any biasing. A thermal annealing in a RTA furnace was applied to all the films in a nitrogen atmosphere. A phase transition was detected by XRD investigations and SEM scanning from as deposited to annealed films, noticing the crystallisation of all films which depends on the composition of each film.

Potential of TaO&lt;sub&gt;X&lt;/sub&gt;N&lt;sub&gt;Y&lt;/sub&gt; Thin Films Deposited by Reactive Sputtering as Antireflective Coatings: Composition and Optical Properties

Tantalum oxynitride thin films are deposited by radio-frequency magnetron sputtering using a pure tantalum target under argon/oxygen/nitrogen gas mixture. The argon flow is kept constant while the oxygen and nitrogen flows are changed simultaneously in a way to keep constant the total flow of these reactive gases. We succeed to deposit TaOxNyfilms with stoichiometry ranging between those of TaN and Ta2O5. All films are deposited at room temperature and are amorphous. Spectroscopic ellipsometry and UV-visible spectrometry investigations show a direct relation between the optical properties and the stoichiometry of the films. In particular, the results show a variation of the refractive index from pure tantalum nitride-like films (3.76) to tantalum pentoxyde-like films (2.1), which confirms the possibility to deposit graded antireflective coatings with tantalum oxynitride.