Ta2O5 Films Research Articles

A comparative study of TiO2, Ta2O5 and Nb2O5 coated Ti6Al4V titanium alloy for biomedical applications

Refractory metal oxides such as titanium dioxide (TiO2), tantalum oxide (Ta2O5), and niobium oxide (Nb2O5) coated-titanium and its alloys for medical applications have recently gained significant attention due to their remarkable properties, including high hardness, strong chemical inertness, and excellent biocompatibility. However, comparative studies among them remain scarce. In this study, thin films of Ta2O5, Nb2O5, and TiO2 were deposited on Ti6Al4V titanium alloy using radio frequency sputtering technology. Their properties were comparably evaluated through a series of tests, including scratching, nanoindentation, friction and wear, potentiodynamic polarization, and cell cultivation experiments. The results revealed that all three coatings, with a thickness of approximately 2.6–2.8 μm, exhibited an amorphous columnar growth pattern with dense surfaces resembling cauliflower. The bonding force of the TiO2 coating exceeds 50 N, which is 26.2 times and 14.5 times greater than that of Ta2O5 and Nb2O5, respectively. Furthermore, all coated samples demonstrate superior wear resistance, corrosion resistance, and biocompatibility compared to bare Ti6Al4V. Among the coatings, TiO2 showed the best performance, followed by Ta2O5, while Nb2O5 exhibited the least favorable performance. These findings revealed the performance differences among the three ceramic coatings on Ti6Al4V samples and offer valuable insights for further research and the selection of coatings to enhance the properties of Ti6Al4V titanium alloy for biomedical applications.

High-performance Ta₂O₅ films prepared by plasma ion-assisted deposition for low-absorption optics

High-performance Ta₂O₅ films prepared by plasma ion-assisted deposition for low-absorption optics

Fabrication of ultra-high-Q Ta2O5 microdisks by photolithography-assisted chemo-mechanical etching

Tantalum pentoxide (Ta2O5) is widely recognized as a promising material platform for photonic integration. This is primarily attributed to its exceptional properties including large bandgap of 3.8 eV, broad transparency window ranging from 300 nm to 8000 nm, high nonlinear refractive index of ∼7.2 × 10−19 m2/W, low optical loss, moderate refractive index of 2.05, low intrinsic material stress, compatibility with CMOS technology, and high solubility for rare-earth ions. However, dry etching of Ta2O5 is challenging and typically results in sidewall roughness with substantial scattering losses. Here, we report on fabrication of a high-Q whispering gallery mode (WGM) microdisk with a diameter of 120 µm and a loaded Q factor of 1.92 × 106 by femtosecond laser photolithography assisted chemo-mechanical etching (PLACE) on amorphous Ta2O5 film. Thanks to the suppression of sidewall scattering, the loaded Q factor is two orders of magnitude higher than the best reported value in dispersion engineered Ta2O5 microresonators.

INFLUENCE OF THE NANOSTRUCTURE OF TANTALUM OXIDE ON THE FLARE CHARACTER OF ITS ELECTROLUMINESCENCEWITH ANODIC-ELECTROLYSIS FORMATION IN CHEMICALLY PURE WATER

Theoretical and experimental studies were carried out to identify the reasons for the flash nature of the combustion of electroluminescence (EL) of tantalum oxide (Ta2O5), formed in chemically pure (distilled) water during high-voltage anodization of 1700 s. Nonlinear growth of the Ta2O5 film during this time was established, and a polychrome effect was discovered for its thicknesses from 150 ± 28 nm to 820 ± 80 nm. At the same time, EL ignition begins at an oxide thickness of 390 ± 74 nm, which corresponds to an anodization time of 78 ± 15 s, and from 968 ± 185 s until the end of this process, bright EL flashes are observed. Their luminosity can reach 2.8·10–3 lm/m2. It is shown that the cause of the outbreaks is explosive processes in dynamically changing Ta2O5 pores ranging in size from tens of nanometers to several micrometers and containing gas-discharge plasma from various products of electro- and plasma-chemical reactions with a temperature of the order of 12000 K, created due to Joule heating by the flowing current. It has been established that the formation of the plasma itself occurs as a result of electrical breakdown in pores, the field strength in which can reach the order of 3·108 V/m or more.

Oxidation behavior and atomic structural transition of size-selected coalescence-resistant tantalum nanoclusters

Herein a series of size-selected Ta N (N = 147, 309, 561, 923, 1415, 2057, 6525, 10 000, 20 000) clusters are generated using a gas-phase condensation cluster beam source equipped with a lateral time-of-flight mass-selector. Aberration-corrected scanning transmission electron microscopy (AC-STEM) imaging reveals good thermal stability of Ta N clusters in this study. The oxidation-induced amorphization is observed from AC-STEM imaging and further demonstrated through x-ray photoelectron spectroscopy and energy-dispersive spectroscopy. The oxidized Ta predominantly exists in the +5 oxidation state and the maximum spontaneous oxidation depth of the Ta cluster is observed to be 5 nm under prolonged atmosphere exposure. Furthermore, the size-dependent sintering and crystallization processes of oxidized Ta N clusters are observed with an in situ heating technique, and eventually, ordered structures are restored. As the temperature reaches 1300 °C, a fraction of oxidized Ta309 clusters exhibit decahedral and icosahedral structures. However, the five-fold symmetry structures are absent in larger clusters, instead, these clusters exhibit ordered structures resembling those of the crystalline Ta2O5 films. Notably, the sintering and crystallization process occurs at temperatures significantly lower than the melting point of Ta and Ta2O5, and the ordered structures resulting from annealing remain well-preserved after six months of exposure to ambient conditions.

Development of highly sensitive and solar blind surface acoustic wave UV-C photodetector based on the In2O3/Ta2O5 nano-heterojunction and its interface electronics

A highly sensitive surface acoustic wave (SAW) ultraviolet-C (UV-C) sensor based on In2O3/Ta2O5 nano-heterojunctions and its interface electronics was developed to detect solar blind corona discharge near high voltage power lines. The SAW sensor, based on pristine In2O3 nanoparticles, exhibits a weaker and slower response to UV-C light. To improve the response to deep UV light, In2O3 nanoparticles/Ta2O5 heterojunctions were formed by depositing Ta2O5 films of different thicknesses (2–10 nm) around the In2O3 nanoparticles via atomic layer deposition (ALD) on the cavity between two interdigital transducers (IDTs) in the SAW delay line. The experimental results show a significantly enhanced sensor response towards UV-C light, which is attributed to a high surface-to-volume ratio, an inhibited recombination rate of the photogenerated electron-hole pairs on the surface of the sensing material owing to Ta2O5 conformal coverage, and well-matched energy bandgap engineering. An empirical mechanism was proposed to elucidate the enhanced sensing behavior of the heterostructure. To observe the frequency shifts in real-time on a PC display, portable interface electronics were developed on a single printed circuit board (PCB) for the SAW UV-C sensor, eliminating the effect of frequency shifts caused by ambient temperature and humidity changes. The sensor characteristics were evaluated based on the size and annealing conditions of the In2O3 nanoparticles and the thickness of the decorated Ta2O5, and the scientific and technical causes and analysis of the results were thoroughly investigated. In the selectivity test, the fabricated sensor exhibited a strong response to a UV-C light beam with a sensitivity of 368.3 (ppm (μW/cm2)−1 at 254 nm, and its spectral response to UV-C light was 3.3 times higher than that under UV-A 365 nm light.

Modulation of electrical properties of sputtered Ta2O5 films by variation of RF power and substrate temperature

Dielectric thin films are important building blocks of microelectronic devices, and hence, research on the development of high-k dielectric thin films has drawn tremendous research interest. In this research, thin films of tantalum oxide (Ta2O5), a high-k dielectric material, are deposited on the Si substrate by the radio frequency (RF) magnetron sputtering technique. During the deposition of Ta2O5 thin film, the sputtering parameters such as sputtering power and substrate temperature were systematically varied, and post-deposition structural, morphological, and electrical properties of sputtered Ta2O5 films are studied by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscope, capacitance–voltage (C-V) and current–voltage (I-V) measurement techniques. The annealed Ta2O5 thin film at the temperature of 900 °C for 1 h possesses polycrystalline nature with β—phase orthorhombic crystal structure. The film deposited at 150 W and substrate temperature at room temperature has shown comparatively lower surface roughness, which depicts the energy, and mobility of adatoms greatly influenced by RF power and substrate temperature. With the increase in sputtering power, the oxide charge density (Qox) is found to increase. On the other hand, Qox is found to decrease with the increase in substrate temperature. The film deposited at RF power of 150 W and substrate temperature of 300 °C is found to be of high dielectric constant, low oxide and interface charge density, and lower leakage current.

In Operando Near‐Field Optical Investigation of Memristive Ta2O5 Thin Film Devices with a Graphene Top Electrode

AbstractResistive switching devices based on metal oxides are candidates for nonvolatile memory storage. They often rely on the valence change mechanism, the field‐induced movement of donor ions leading to nanoscale conductive paths in filamentary‐type devices. Devices usually consist of a transition metal oxide like Ta2O5 sandwiched between two metal electrodes. Critical parameters of the devices, such as cycle‐to‐cycle variability, Roff/Ron ratio, and endurance depend on the morphology and composition of the filaments. However, investigating filaments on the nanoscale is cumbersome, and commonly applied techniques such as conductive atomic force or transmission electron microscopy require delaminating the metal top electrode, inhibiting in operando investigations over many switching cycles. Here, the authors use infrared scattering‐type scanning near‐field optical microscopy (s‐SNOM) to investigate resistive switching in Ta2O5 films with a graphene top electrode in operando and reveal individual filaments on the device level. By selecting an appropriate illumination frequency, the authors can trace the evolution of filaments and the joule heating‐induced retraction of the top electrode until device failure. s‐SNOM promises a deeper understanding of resistive switching devices’ microscopic switching behavior and applies to a wide range of resistive switching oxides, such as HfO2, SrTiO3, and SiO2.

Structural, optical and mechanical properties of Ti-doped Ta2O5 films for PV glass covers

Ti doped Ta2O5 thin films (TTO) with uniform thickness were prepared on photovoltaic glass substrates by DC and RF magnetron co-sputtering with different target powers. The surface morphology and microstructure of the films were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM). The composition of the films was analyzed by X-ray photoelectron spectroscopy. The optical parameters of the films were measured by UV–visible spectrophotometer. The hardness and Young 's modulus of the coating were tested by nanoindentation. XPS analysis shows that the main components of TTO films are TiO2 and Ta2O5. SEM and AFM results show that the surface of the TTO film is smooth and flat, with uniform elemental distribution and nanometer roughness. The SEM cross-sectional morphology shows that the TTO film presents a dense columnar structure growth. The TEM results show that the TTO films do not show bright diffraction rings and mainly exhibit an amorphous phase structure dominated by Ta2O5. The optical test results show that the maximum transmittance of TTO film can reach 94.59 %. The transmittance of TTO films shows a decreasing trend with increasing sputtering power of the target, while the opposite is true for reflectance and refractive index. The optical band gap of the TTO films is between 4.12 eV and 4.42 eV. The mechanical test results show that the hardness of the TTO film can reach up to 9.53 Gpa. The hardness of TTO film increases with the increase of target power. The H/E and H3/E2 values indicate that Ti doped Ta2O5 films are favourable for improving the resistance to plastic deformation of the films. Comprehensive analyses show that Ti doped Ta2O5 films can have both excellent optical and mechanical properties. TTO films can provide a valuable reference for the study of PV glass protective layer.

Exceptional Hole-Selective Properties of Ta2O5 Films via Sn4+ Doping for High Performance Silicon Heterojunction Solar Cells.

Carrier-selective passivating contacts using transition metal oxides (TMOs) have attracted great attention for crystalline silicon (c-Si) heterojunction solar cells recently. Among them, tantalum oxide (Ta2O5) exhibits outstanding advantages, such as a wide bandgap, good surface passivation, and a small conduction band offset with c-Si, which is typically used as an electron-selective contact layer. Interestingly, it is first demonstrated that solution-processed Ta2O5 films exhibit a high hole selectivity, which blocks electrons and promotes hole transport simultaneously. Through the ozone pre-treatment of Ta2O5/p-Si interface and optimization of the film thickness (≈9nm), the interfacial recombination is suppressed and the contact resistivity is reduced from 178.0 to 29.3mΩcm2. Moreover, the Sn4+ doping increases both the work function and oxygen vacancies of the film, contributing to the improved hole-selective contact performance. As a result, the photoelectric conversion efficiencies of Ta2O5/p-Si heterojunction solar cells are significantly improved from 14.84% to 18.47%, with a high thermal stability up to 300°C. The work has provided a feasible strategy to explore new features of TMOs for carrier-selective contact applications, that is, bipolar carrier transport properties.

Enhanced self-driven ultraviolet photodetection performance of high-k Ta2O5/GaN heterostructure

Recently, high-k dielectric oxide-based MIS type ultraviolet (UV) photodetectors (PDs) have engrossed the researchers in the area of optoelectronics owing to their superior properties. The current work focuses on the preparation of symmetric interdigitated Au electrodes on Ta2O5/GaN heterojunction and to check its functioning as a photosensor in UV region. The impact of post-annealing procedure on the bandgap, crystalline quality, surface morphology and chemical composition has been investigated using UV-VIS, XRD, AFM and XPS techniques, respectively. The evaluated optical bandgaps from the Tauc's plots for the Ta2O5 films ranging from 4.52 eV to 4.92 eV. XRD analysis showed the formation of an orthorhombic phase after post-annealing temperature of 700 °C. The post-annealed Ta2O5 film surface morphology comprises prearranged atomic clusters with spherical shapes. The XPS exploration revealed the occurrence of the Ta5+ state and confirmed the formation of Ta2O5 phase. Photodetection parameters of the designed Au/Ta2O5/GaN MIS BB PDs are studied using I–V, responsivity and temporal responses as a function of the post-annealing process. At 0 V bias, with the illumination of 310 nm UV light, the 800 °C post-annealed MIS PD device exhibited peak responsivity of 212 mA/W, external quantum efficiency (EQE) of 86.8 % and detectivity of 1.5 × 1013 Jones. Further, under self-driven mode with 350 nm light illumination, the 800 °C post-annealed UV PD device generated faster rise and fall times of 90 ms and 790 ms, respectively. The post-annealed Au/Ta2O5/GaN heterostructure PD device demonstrates improved photoresponsivity, EQE and rise/fall times compared with the as-deposited PD device. This remarkable improvement in the photodetection performance is attributed to the best band configuration of the Ta2O5/GaN heterostructure because of substantial post-annealing process and facilitating broadband absorption from UV-C to A region with quicker generation, separation and transportation of photogenerated charge carriers. Consequently, the current research work emphasizes the significance of the combination of UV sensing Ta2O5 high-k oxide and n-GaN materials to serve the future necessities of the photodetection technology under self-driven mode i.e., without any external bias.

Study on microstructure, optical and tribological properties of self-formed Ta oxide films

Ta2O5 films were deposited on glass and silicon substrates by magnetron sputtering with different power. The microstructure of Ta2O5 films was studied by XRD, SEM, EDS, XPS and AFM. The mechanical and tribological properties of Ta2O5 thin films were studied by ultraviolet–visible spectrophotometer, nanoindentation and friction and wear tester. The sputtering power has a significant effect on the surface morphology of Ta2O5 films. The transmittance of the film decreases with the increase of sputtering power. The optical band gap of the film fluctuates with the change of sputtering power. This is related to the packing density of the sputtered particles and the oxygen vacancies in the film. The wear forms of Ta2O5 films prepared under different sputtering power conditions are mainly fatigue wear and adhesive wear. The optical properties of Ta2O5 films are more sensitive to the change of sputtering power. Ta2O5 films with good optical and tribological properties can be obtained under appropriate process conditions.

Tribological behaviors of tantalum prepared by SPS under different loads

PurposeTantalum is a kind of metal material with moderate hardness, high ductility, small thermal expansion coefficient, excellent corrosion resistance and outstanding biocompatibility. The purpose of this study is that its tribological performance could be tested and analyzed so as to use it in different fields.Design/methodology/approachThe friction resistance of a-Ta under dry friction conditions was tested at different roads. The relationships between load and friction coefficient, wear rate and two-dimensional shape of wear scars were studied.FindingsThe stable Ta2O5 film with lubrication effect was generated in the process of friction. And, the larger the test load, the more Ta2O5 would be generated.Originality/valueThis work lays a theoretical foundation for tantalum as an excellent wear-resistant material.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2023-0047/

Sol-gel prepared amorphous Ta2O5 thin film for application in high LIDT antireflection coating and UV photodetection

In this report, a sol–gel method has been developed using tantalum ethoxide to produce homogenous thin films of amorphous Ta2O5 for application in optical coating for high power laser as well as photodetection in the UV range. Morphology, stoichiometry, optical properties, short range atomic structure and valence band have been investigated at various annealing temperature up to 500 °C. A large valence band onset of 3.5 ± 0.20 eV has been measured for the film annealed at 500 °C, ensuring hole blockage through the film and electron selective transport. Extended X-ray absorption fine structure (EXAFS) study has revealed the Ta–O bond distance to be 1.85 Å for as-deposited film, which increased with annealing and approached the crystallographic value. The sol-gel prepared Ta2O5 film has been used as antireflection (AR) coating on silicon and fused silica (FS) substrates. 99.4% transmission with a LIDT of 20 J/cm2 @6 ns at 1064 nm is obtained for Ta2O5/SiO2 AR coatings on FS. Using these sol-gel films, Ta2O5/Si vertical heterojunction photodetectors have been fabricated, which exhibited a responsivity of 560 mA/W, external quantum efficiency of 213%, and specific detectivity ∼1 × 1012 Jones at −1 V bias voltage and 325 nm illumination wavelength.

Resistive switching behaviors of oxygen-rich TaOx films prepared by reactive magnetron sputtering

ABSTRACT In this work, Ta2O5 films were first deposited on Si substrates by reactive magnetron sputtering of a Ta metal target at various substrate temperatures, RF powers and sputtering pressures. The crystal characteristics of these films can be effectively tailored by controlling the sputtering process. Based on the optimized process parameters, tantalum oxide (TaOx) films with different oxygen component content were sputtered on ITO buffered Si substrates and comparatively investigated. The results show that the film with Ta/TaOx/ITO structure has a resistance switching (RS) behavior and its conduction mechanism is closely related to the O2-/O concentration related to the oxygen partial pressure at the dielectric layer and electrode interface. This study provides an in-depth understanding of the component/structure design and structure-activity relationship for high-performance TaOx-based resistive memory.

Determination of stress in thin films using micro-machined buckled membranes

In this work, optical profilometry and finite-element simulations are applied on buckled micromachined membranes for the stress analysis of ion-beam-sputtered Ta2O5 and SiO2 thin films. Layers with different thicknesses are grown on silicon substrates, and then several membranes with different geometries are manufactured with standard microsystem technologies; due to a high level of films’ compressive stress, buckled membranes are obtained. Thermally grown silica membranes are also produced for comparison. The residual stress values are determined by comparing the measured and simulated deflections of the membranes. The average stress state of Ta2O5 thin films is found to be −209 MPa. The SiO2 thin films are in a higher compressive stress state whose average value is −576 MPa. For comparison, the average stress in thermal SiO2 thin layers grown at 1130°C is found equal to −321 MPa, in good agreement with the literature.

Crystal growth in amorphous films of tantalum pentoxide

Amorphous films are formed on substrates at room temperature in the process of pulsed laser sputtering of Ta target in an oxygen atmosphere. Electron beam irradiation causes their crystallization with the formation of Ta2O5 crystals with hexagonal lattice. Electron microscope investigation, including “in situ” and video recording methods, revealed the following crystallization modes in different regions of the same amorphous film of Ta2O5. 1. Island polymorphous crystallization. 2. Interjacent crystallization mode. 3. Layer polymorphous crystallization mode. The presence of three different crystallization modes is explained by the phenomenon of polyamorphism in amorphous films.

Microstructure, hardness and wear resistance of AlCoCrFeNiTax (x = 0, 0.1, 0.3) high-entropy alloys enhanced by laser remelting and Ta addition

Laser remelting (LR) treatment was used to regulate the microstructure of AlCoCrFeNiTax high-entropy alloys prepared by vacuum arc melting, and the microstructure and properties of the alloys before and after LR treatment were analyzed. The original AlCoCrFeNiTax alloys have typical dendritic morphology and the addition of Ta element promoted the formation of a Laves phase, gradually changing the alloys from two phase (BCC + B2) to three phase (BCC + B2 + Laves phase). After LR treatment, the grains were significantly refined, elemental segregation was alleviated, and a dense remelting layer with a thickness of 1200–1600 µm was formed on the surface of the alloy. In addition, the hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment, mainly caused by the combined effects of solution strengthening, second phase strengthening and fine grain strengthening. At the same time, the corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution is significantly improved by a stable Ta2O5 and TaO2 passivation films and the formation of a dense uniform remelting layer.

Effect of ionic oxygen concentration on properties of SiO2 and Ta2O5 monolayers deposited by ion beam sputtering

Optical thin films with ultralow absorption loss are crucial for high-precision optical systems. The ionic oxygen concentration and oxygen flow rate play decisive roles in the absorption loss of the film. We prepared SiO2 and Ta2O5 monolayers using a double-ion beam sputtering (DIBS) deposition system and studied the effects of different ionic oxygen concentrations and oxygen flow rates on the optical constants, weak absorption, –OH defects, and dispersion energy parameters. The results show that the oxygen flow slightly affects the weak absorption of SiO2 films, while a higher ionic oxygen concentration facilitates the reduction of the absorption loss of SiO2 films, resulting in fewer –OH defects. A higher ionic oxygen concentration decreases the refractive index of the Ta2O5 films. The relatively low lattice permittivity of the Ta2O5 films may be attributed to the argon bubbles wrapped in the film. Annealing can reduce the absorption of the film but cannot improve its surface roughness. A Ta2O5/SiO2 high-reflection film was produced with an optimal ionic oxygen concentration and oxygen flow rate, with the lowest absorption loss for both materials. The weak absorption attained 1.4 ppm, playing a significant role in improving the performance of the high-power and high-precision optical systems.

Tantalum pentoxide (Ta2O5 and Ta2O5-x)-based memristor for photonic in-memory computing application

Photonic in-memory computing exhibits promising potential to address the inherent limitations of traditional von Neumann architecture. In this study, we demonstrate a tantalum pentoxide (Ta2O5 and Ta2O5−x)-based memristor as a non-volatile memory for photonic in-memory computing functions. The active layer of the memristor on a heavily doped N-Si substrate comprises two films of Ta2O5 and Ta2O5−x with a size of 3 × 3 µm2 of which roughness root-mean-square values are 1.25 nm and 1.59 nm, respectively. A controllable electrical behavior transition from write-once-read-many-times (WORM) memory to resistive random-access memory (RRAM) is achieved by changing the depositional sequence. Benefitting from the visible light response, the in situ photonic Boolean logic operations (“AND/OR”) are achieved in the RRAM device by mixing the light and electric signals, and the power consumption of an “AND” or “OR” operation consumes 4.503 nJ and 4.526 nJ, respectively, proving the superior photonic in-memory computing potential. The basic logic “IMPLICATION” operation is implemented by performing electrical regulation in a circuit with two RRAM devices connected in parallel. Finally, a 5 × 5 RRAM array is developed and thereafter, the array-level logic for image processing applications is realized. The proposed tantalum pentoxide-based memristors possess great potential in constructing efficient in-memory computing architectures.