Ox Thin Films Research Articles

Surface and Electrical Characterization of Non-Stoichiometric Semiconducting Thin-Film Coatings Based on Ti-Co Mixed Oxides Obtained by Gas Impulse Magnetron Sputtering

This article presents a detailed investigation of non-stoichiometric (Ti,Co)Ox thin films prepared using the Gas Impulse Magnetron Sputtering (GIMS) technique. The films were prepared with various Co contents (3 at.%, 19 at.%, 44 at.%, and 60 at.%) and characterized for their material composition, microstructure, and electrical properties. The films exhibited an ohmic behavior with linear current-voltage (I-V) characteristics, and their resistivity values ranged from approximately 10−3 to 104 Ω·cm. The highest resistivity was observed in the film with 3 at.% Co content. Thermoelectric measurements revealed that all of the prepared films displayed n-type semiconducting properties, with the Seebeck coefficient (S) tending close to zero. The resistivity of the films decreased as the temperature increased, affirming their semiconducting nature. The activation energy (Ea) values, determined using the Arrhenius formula, ranged from 0.0058 eV to 0.267 eV, with the highest Ea observed for films containing 3 at.% Co. Additionally, the films’ surface topography and microstructure were examined through Atomic Force Microscopy (AFM) and optical profiler techniques. The results showed that the films had smooth, crack-free surfaces with remarkable homogeneity. The surface diversification decreased with the increase in cobalt in the (Ti,Co)Ox films.

Reverse Engineering Analysis of Optical Properties of (Ti,Cu)Ox Gradient Thin Film Coating

Analysis of the optical properties of a gradient (Ti,Cu)Ox thin film is presented in this paper. The thin film was prepared using reactive co-sputtering of Ti and Cu targets. The desired elemental concentration profiles of Cu and Ti versus the thin film thickness were obtained by changing the power delivered to the magnetron equipped with Cu, while the powering of the magnetron equipped with the Ti target was maintained at a constant level during the film deposition. Optical properties were analysed using the reverse engineering method, based on simultaneously measured optical transmittance and reflectance. Detailed microstructure analysis performed using transmission electron microscopy investigations revealed that the thin film consisted of at least four areas with different structural properties. Finding a satisfying fit of theoretical to experimental data required taking into account the heterogeneity in the material composition and microstructure in relation to the depth in the prepared gradient thin film. On the basis of the built equivalent layer stack model, the composition profile and porosity at the cross-section of the prepared gradient film were evaluated, which agreed well with the obtained elemental and microscopy studies.

Hydrogen Gas Sensing Properties of Mixed Copper-Titanium Oxide Thin Films.

Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. In this work, mixed copper-titanium oxide ((CuTi)Ox) thin films with various copper concentrations (0-100 at.%), deposited by magnetron sputtering and annealed at 473 K, were investigated as a prospective hydrogen gas sensing material. Scanning electron microscopy was applied to determine the morphology of the thin films. Their structure and chemical composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The prepared films were nanocrystalline mixtures of metallic copper, cuprous oxide, and titanium anatase in the bulk, whereas at the surface only cupric oxide was found. In comparison to the literature, the (CuTi)Ox thin films already showed a sensor response to hydrogen at a relatively low operating temperature of 473 K without using any extra catalyst. The best sensor response and sensitivity to hydrogen gas were found in the mixed copper-titanium oxides containing similar atomic concentrations of both metals, i.e., 41/59 and 56/44 of Cu/Ti. Most probably, this effect is related to their similar morphology and to the simultaneous presence of Cu and Cu2O crystals in these mixed oxide films. In particular, the studies of surface oxidation state revealed that it was the same for all annealed films and consisted only of CuO. However, in view of their crystalline structure, they consisted of Cu and Cu2O nanocrystals in the thin film volume.

P-type (CuTi)Ox Thin Films Deposited by Magnetron Co-Sputtering and Their Electronic and Hydrogen Sensing Properties

Thin films of copper oxide (CuxO), titanium oxide (TiOx), and several mixtures of copper and titanium oxides ((CuTi)Ox) were deposited using magnetron sputtering. X-ray diffraction analysis of the as-deposited TiOx thin film revealed the presence of TiO crystallites, while in the case of (CuTi)Ox with the lowest amount of copper, metallic Cu crystallites were found. In the case of (Cu0.77Ti0.23)Ox and CuxO thin films, characteristic peaks for metallic copper and copper oxides were observed in their diffractograms. It was found that post-process annealing at 473 K considerably affects the microstructure of (CuTi)Ox thin films. After annealing, anatase phase was observed in (Cu0.23Ti0.77)Ox and (Cu0.41Ti0.59)Ox thin films. In turn, the (Cu0.77Ti0.23)Ox and CuxO films were formed only in the copper oxide phase. The (Cu0.77Ti0.23)Ox film annealed at 473 K showed the best opto-electronic performance, as it had the highest transmission and the lowest resistivity. However, the greatest advantage of this thin film was the p-type semiconducting behavior, which was the strongest of all of the thin films in this work, as indicated by the measurement of the Seebeck coefficient. All deposited thin films were sensitive to hydrogen exposure, while the best sensor response of 10.9 was observed for the (Cu0.77Ti0.23) Ox thin film annealed at 473 K.

Influence of annealing on selected properties of mixed copper and titanium oxides

This work presents an investigation of the effects of post-process annealing on the morphologyof mixed copper and titanium oxides and on their electrical and hydrogen sensing properties. (CuTi)Oxthin films were deposited by magnetron sputtering on amorphous silica and ceramic substrates withinterdigitated electrodes. In addition, post-process thermal treatment was applied at the temperaturesof 200C and 250C.The transformation of the thin film structure during the thermal oxidation process was studied byX-ray diffraction, while the morphology of the thin films was determined using an optical profilometer.Current-voltage and thermoelectric characteristics were measured to determine electrical properties,from which the resistance and conduction type were determined. The post-treatment (CuTi)Ox thinfilms exhibited hole-type conduction and, additionally, strongly responded to hydrogen atmosphere.Keywords: electronics, hydrogen gas sensors, mixed copper and titanium oxides, thin films, magnetronsputtering

Investigation of a memory effect in a Au/(Ti-Cu)Ox-gradient thin film/TiAlV structure.

This paper presents the results of the analysis of resistive switching properties observed in a Au/(Ti–Cu)Ox/TiAlV structure with a gradient distribution of Cu and Ti along the (Ti–Cu)Ox thin film thickness. Thin films were prepared via multisource reactive magnetron co-sputtering. The programmed profile of the pulse width modulation coefficient during sputtering of the Cu target allowed us to obtain the designed gradient U-shape profile of the Cu concentration in the deposited thin film. Electrical measurements of the Au/(Ti–Cu)Ox/TiAlV structure showed the presence of nonpinched hysteresis loops in the voltage–current plane testifying a resistive switching behavior. Results of optical, X-ray, and ultraviolet photoelectron spectroscopy measurements allowed us to elaborate the scheme of the bandgap alignment of the prepared thin films with respect to the Au and TiAlV electrical contacts. Detailed structure and elemental profile investigations allowed us to conclude about the possible mechanism for the observed resistive switching mechanism.

Properties of Metallic and Oxide Thin Films Based on Ti and Co Prepared by Magnetron Sputtering from Sintered Targets with Different Co-Content.

In this work, selected properties of metallic and oxide thin films based on titanium and cobalt were described. Thin-film coatings were prepared using the magnetron sputtering method. The deposition was carried out from sintered targets with different Co-content (2 at.%, 12 at.% and 50 at.%). The relation between the Ti–Co target composition and the Co-content in the metallic and oxide films was examined. There was 15–20% more cobalt in the films than in the target. Moreover, the deposition rate under neutral conditions (in Ar plasma) was even 10-times higher compared to oxidizing Ar:O2 (70:30) plasma. A comprehensive analysis of the structural properties (performed with GIXRD and SEM) revealed the amorphous nature of (Ti,Co)Ox coatings, regardless of the cobalt content in the coating. The fine-grained, homogenous microstructure was observed, where cracks and voids were identified only for films with high Co-content. Optical studies have shown that these films were well transparent (60% ÷ 80%), and the amount of cobalt in the target from which they were sputtered had a significant impact on the decrease in the transparency level, the slight shift of the absorption edge position (from 279 nm to 289 nm) as well as the decrease in their optical band gap energy (from 3.13 eV to 1.71 eV). Electrical studies have shown that in (Ti,Co)Ox thin films, a unipolar memristive-like effect can be observed. The occurrence of such effects has not been reported so far in the case of TiO2 coatings with the addition of Co.

Substrate-Dependent Growth Behavior of Atomic-Layer-Deposited Zinc Oxide and Zinc Tin Oxide Thin Films for Thin-Film Transistor Applications

The growth behaviors and electrical performances of semiconducting ZnO, SnO2, and (Zn,Sn)Ox thin films, grown by atomic layer deposition (ALD) using O3 as the oxygen source, were studied. A signifi...

Formation and Properties of Amorphous Multi-Component (CrFeMoNbZr)Ox Thin Films

In this work, a new multi-component (CrFeMoNbZr)Ox system was developed. The thin films presented dual-phase amorphous structures, comprising a dominant amorphous alloy phase and a small amount of an amorphous oxide phase. The thin films showed higher hardness and better corrosion resistance than a commercial Zr-based alloy. The combined properties of high hardness and superior corrosion-resistance make the amorphous thin film a candidate for coating materials on commercial Zr-based alloys for engineering applications.

Influence of post-process annealing temperature on structural, optical, mechanical and corrosion properties of mixed TiO2[sbnd]WO3 thin films

The paper focuses on the comparative studies on the structural, optical, corrosion and mechanical properties of TiO2, WO3 and mixed TiO2WO3, i.e. (Ti0.68W0.32)Ox and (Ti0.41W0.59)Ox thin film coatings. Oxide thin films were prepared from WO3 and Ti3O5 pellets by electron beam evaporation method and were additionally annealed at 600 °C and 800 °C using tubular furnace. The microstructure of prepared coatings was analysed using scanning electron microscopy and X-ray diffraction. The transparency of as-deposited thin films was high, while annealing caused significant decrease of the transmission of TiO2 and WO3 coatings. In the case of mixed oxides such post-process treatment did not cause severe change of the optical properties. The corrosion properties of the thin films were examined by an analysis of the voltammetric curves, while mechanical properties were determined by nanoidentation measurements. The hardness of the (Ti0.41W0.59)Ox film was approx. 3.42 GPa, but after annealing at 800 °C it increased to Hit = 14.6 GPa. Preparation of the mixed titanium-tungsten oxidethin films caused a decrease of the electrochemical activity. The Ti6Al4V substrate coated with (Ti0.41W0.59) Oxthin filmannealed at 800 °C exhibited the best corrosion properties among stprepared thin-film coatings.

Cu0.78Sn0.12Mn0.1Ox Thin Films as a Photocatalytic Material under Visible Light

AbstractThis work investigates the feasibility of using an earth‐abundant and eco‐friendly Cu0.78Sn0.12Mn0.1Ox thin film as a catalyst for photodegradation applications under visible light. The thin film was deposited by e‐beam evaporation using the pallet formed using CuO, SnO2, and MnO2 powders as raw materials. The photocurrent response and performance as a catalyst of Methyl Orange (MO) dye photodegradation was optimized by varying the oxide composition to tune band gap and the use of post‐annealing at 500 °C for 3 hr in air to obtain crystalline structure of Cu0.78Sn0.12Mn0.1Ox thin films for higher photoconductivity. The band gap, conduction band energy level, and valence band energy level of the crystalline Cu0.78Sn0.12Mn0.1Ox oxide thin film were characterized to be 2.3 eV, −4.4 eV and −6.7 eV to vacuum, respectively. The stable photocurrent response with an intensity of ∼42 uA/cm2 at an applied voltage of −0.4 V under filtered 150 W Xe‐lamp visible light illumination could be achieved, which is higher than previous works even with lower power and thinner materials. Besides, the feasibility of Cu0.78Sn0.12Mn0.1Ox thin film for MO photodegradation under the visible light has also been demonstrated, though the rate constant still needs further improvement.

The effect of post-process annealing on optical and electrical properties of mixed HfO2\u2013TiO2 thin film coatings

In this paper a comparison of electrical and optical properties of mixed hafnium-titanium oxides is described. Thin films were deposited with the use of the magnetron co-sputtering method. For further analysis (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox coatings, which were amorphous directly after the deposition process, were chosen,. Moreover, post-process annealing was also performed in order to compare the electrical and optical properties of amorphous and nanocrystalline thin films with the same material composition. It was found that the phase transition from amorphous to orthorhombic HfTiO4 occurred in the case of (Hf0.52Ti0.48)Ox coating at 650 °C. In turn, the phase transition to TiO2-anatase was observed at the temperature of 600 °C in the case of (Hf0.29Ti0.71)Ox thin film. The leakage current for both amorphous coatings was in the range of 10−7–10−8 A/cm2. After additional annealing and phase transition, the leakage current slightly decreased for (Hf0.29Ti0.71)Ox thin film, while in the case of (Hf0.52Ti0.48)Ox sample the resistance switching effect was observed. The dielectric constant was equal to 24 and 25 for amorphous (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox films, respectively. However, after the phase transition it decreased to 15 for (Hf0.52Ti0.48)Ox and increased to 51 for (Hf0.29Ti0.71)Ox film. The results of optical studies showed that amorphous thin films were well transparent in a visible light range with an average transparency of ca. 85%. After the phase transition to HfTiO4-orthorhombic and TiO2-anatase, a slight decrease in the transparency level by 3% and a redshift of the cut-off wavelength was observed. Moreover, additional annealing caused small changes of the optical band gap energy, refractive index and extinction coefficient.

Analysis of electrical properties of forward-to-open (Ti,Cu)Ox memristor rectifier with elemental gradient distribution prepared using (multi)magnetron co-sputtering process

The paper presents a discussion on memristive-like properties observed in metal/semiconducting-oxide/metal structure containing a semiconducting (TixCu1-x)Ox thin film with asymmetrical elemental Cu distribution over the thin film thickness. The thin film was prepared using a combinatorial multi-magnetron sputtering process. Based on current-to-voltage electrical investigations, a sharp forward-to-open rectifying behaviour was observed with a hysteresis loop in the forward bias conditions only. Detailed structure and elemental profile investigations allowed to propose explanation of observed type of resistive transition.

Evaluation of characteristics in VOx microbolometer fabricated by MOD on Si3N4/SiO2 membrane

AbstractVOx thin films were fabricated on Si3N4/SiO2/Si substrates by firing precursor films, which were fabricated by metal‐organic decomposition (MOD), with a reduced pressure. Resistance‐temperature (R‐T) characteristics of the films indicating the phase transition from metal to insulator with about 4 orders of resistance change specified with VO2 (M) were obtained. Furthermore, the films fabricated with a firing temperature of 580‐600°C had temperature coefficient of resistance (TCR) of −2.8 to −2.9 %/K at room temperature. After fabricating VOx microbolometers with 40 × 10 μm2 using the films on Si3N4/SiO2/Si substrates, Si with a thickness of about 340 μm was etched using Deep‐RIE and XeF2 vapor etching from the backside of the substrate. Then, the VOx microbolometer was completed on Si3N4/SiO2 membrane. The VOx microbolometer on Si3N4/SiO2 membrane had a high DC sensitivity of 2310 W−1, which was about 15 times higher than that of the microbolometer on the Si3N4/SiO2/Si substrate.

Memristive properties of transparent oxide semiconducting (Ti,Cu)Ox-gradient thin film

The paper presents the results of the analysis of memristive properties observed in (Ti,Cu)-oxide thin film with gradient distribution of elements, prepared using the multi-source reactive magnetron co-sputtering process. The performed electrical measurements showed the presence of pinched hysteresis loops in the voltage–current plane for direct and alternating current bipolar periodic signal stimulation. Investigations performed using a transmission electron microscope equipped with an energy dispersive spectrometer showed that the elemental composition at the cross section of the thin film was very well correlated with the gradient V-shaped profile of the powering of the magnetron source equipped with a Cu target. The prepared samples were transparent in the visible part of optical radiation. The obtained results showed that the prepared gradient (Ti,Cu)Ox thin film could be an interesting alternative to the conventional multilayer stack construction of memristive devices, which makes them a promising material for manufacturing transparent memory devices for transparent electronics.

Inductive Effect of Nd for Ni3+ Stabilization in NdNiO3 Synthesized by Reactive DC Cosputtering

This work focus on the oxidation states of nickel in NdNiO3, Nd2NiO4, and NiOx thin films deposited by reactive magnetron sputtering. Thin films with a high Ni3+ content have been reached in the ternary oxides using a soft subsequent annealing in air. In order to understand the presence of Ni3+ oxidation state, the present work establishes a comparative study between the NiOx and Nd–Ni–Ox thin films deposited at room temperature in reactive conditions using different oxygen partial pressures. Crystallographic phases have been systematically identified by X-ray diffraction showing crystallized NiOx and amorphous thin films in the case of Ni and Nd cosputtering. The ionization state of Ni ions has been tracked by X-ray photoelectron spectroscopy. Analyses confirm the presence of Ni2+ in NiOx films whereas Ni3+ is systematically observed in Nd–Ni–Ox films highlighting the key role of Nd element during the deposition. The electron donor character of Nd3+ on Ni3+ via O 2p states by an inductive effect is clearly evidenced. This effect is strengthened by a strong difference in electronegativity between the rare earth (Re) and the transition metal (M). This concept is enlarged and faced with other ReMO3 perovskites, and their thermodynamic stability is discussed.

Comparison of structural, mechanical and corrosion properties of (Ti0.68W0.32)Ox and (Ti0.41W0.59)Ox thin films, deposited on TiAlV surface by electron beam evaporation

In this paper, comparative studies of the structural, mechanical and corrosion properties of TiO2-WO3 thin films, with different contents of WO3, have been investigated. The thin films were formed using the electron beam evaporation method, on the Ti6Al4V surface. After the deposition process both thin films were additionally annealed at 1073 K in a computer-controlled Nabertherm tubular furnace in an ambient atmosphere. The structural characteristics of the thin films obtained, before and after the annealing process, were examined using SEM and XRD measurements. The mechanical properties of the coatings were determined by nanoindentation measurements. The corrosion properties of the thin films were determined by an analysis of the voltammetric curves. The results obtained show that the layer with the higher content of tungsten – (Ti0.41W0.59)Ox annealed at 1073 K is characterised by the best mechanical and corrosion properties from all tested samples. The hardness obtained for this sample was equal to 14.9 GPa, and was about four times higher than the value obtained for the same sample before the annealing process, and almost one and half times higher than the value obtained for the annealed sample with a lower content of tungsten. In addition, the value of corrosion current density for this sample was equal to 6.02 ∙ 10− 9 A/cm2 and was lower than the value obtained for the same sample before the annealing process. This indicates that after the annealing process the mechanical and corrosion properties of the (Ti0.41W0.59)Ox thin film improved, as compared with the layer with the lower content of tungsten, for which the corrosion properties after the annealing process degraded.

Analysis of surface properties of semiconducting (Ti,Pd,Eu)Ox thin films

In this paper an analysis of the surface properties of (Ti,Pd,Eu)O

Perspectives of development of TCO and TOS thin films based on (Ti-Cu)oxide composites

Abstract The present paper contains a short discussion on possibilities and difficulties connected with fabrication of transparent oxide conductors and semiconductors for the use in transparent electronics. As an example the method of preparation of mixed (Ti-Cu)Ox thin films using multi-magnetron co-sputtering method together with basic research of their structure, optical and electrical properties have been presented. By selection of the magnetrons' powering conditions, thin films with different Cu/Ti chemical compositions were prepared. Structure investigations using x-ray diffraction method did not reveal any crystalline phases in fabricated samples. However, further investigations using x-ray photoelectron spectroscopy allowed determination that the films were composed from the mixture of TiO 2 and Cu 2 O phases. Electrical studies revealed that prepared thin films were semiconducting with p -type of electrical conduction. Increasing Cu amount in the thin films resulted in decreasing of their resistivity from ~ 10 5 Ωcm to ~ 10 − 2 Ωcm but simultaneously the transparency dropped from about 80% to 40% in the visible wavelength range.

Investigation of structural, optical and micro-mechanical properties of (NdyTi1−y)Ox thin films deposited by magnetron sputtering

Abstract TiO2 and (NdyTi1 − y)Ox thin films were deposited by reactive magnetron sputtering process from mosaic Ti–Nd targets and characterised by X-ray diffraction (XRD), Raman optical spectroscopy and nanoindentation technique. XRD measurements revealed that as-prepared titanium dioxide and TiO2 thin films with 4 and 7 at.% of Nd had nanocrystalline rutile structure, while coatings with larger amount of Nd were amorphous. Raman spectroscopy investigations showed that the increase of the neodymium concentration caused amorphisation of the coatings and hindered their crystal growth. All as-prepared coatings were transparent in the visible wavelength range with a transmittance of approximately 80%. The refractive index and extinction coefficient of the thin films gradually decreased with the increase of the neodymium concentration. Micro-mechanical properties, i.e. hardness and elastic modulus, were determined using traditional load-controlled nanoindentation testing and continuous stiffness measurements. The highest hardness and elastic modulus values were obtained for thin films with 7 at.% of Nd and were approximately 14.8 GPa and 166.3 GPa, respectively.