Tantalum Films Research Articles

On the origin of the metastable β-Ta phase stabilization in tantalum sputtered thin films

Despite extensive studies since the 1960s, the exact mechanisms underlying phase formation of metastable tetragonal beta-Tantalum (β-Ta) structure commonly found in magnetron sputtered tantalum films have not yet been unraveled. Here, we combine in situ and real-time multiple beam optical stress sensor (MOSS) during sputter-deposition of Ta films together with ex situ X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) to gain insights into the early growth stages and interface properties. The nucleation conditions were varied by depositing films on different buffer layers, either amorphous (a-Si, a-SiOx, a-SiNx) or crystalline (c-Mo), as well as changing the substrate temperature (Ts = 300–750 K). The influence of the mean deposited energy, in the range of 25–83 eV/atom, as calculated from Monte Carlo simulations, on the resulting stress state and phase formation was also investigated by varying the Ar working pressure (0.12–0.75 Pa) and substrate bias voltage (0 to −190 V). It is shown that the nucleation step is decisive for the stabilization of β-Ta phase on amorphous layers. After the initial formation of an interfacial amorphous Ta(Si) alloyed layer, β-Ta nuclei form due to interface energy minimization and grow columnar with a strong [001] fiber-texture. No transition to the equilibrium bcc alpha-phase (α-Ta) was found with increasing film thickness or variation of the deposited energy. The results are interpreted based on a thermodynamic description of nucleation and growth theory. Such rationale also qualitatively supports experimental findings of α-Ta phase selection with the assistance of substrate heating or by by-passing the nucleation stage upon direct growth in registry on crystalline Mo (110) seed layers.

Microstructure, mechanical and tribological properties of TaCN composite films

Tantalum and carbon nitride films, with varied power of the carbon target were synthesised by multi-target magnetron sputtering. The microstructure, mechanical and tribological properties of TaCN films were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, nano-indentation, nano-scratch, and a high temperature ball-on-disc tribometer. X-ray diffraction reveals that these films exhibit face centred cubic and base centred orthorhombic crystal structures, regardless of the power of the carbon target. At 50 W, the hardness, critical loads for cohesive failure (Lc1) and critical loads for adhesive failure (Lc2) of these films reach a maximum, 28·6 GPa, 4·52 N and 8·1 N, respectively, while at 80 W, the lowest average friction coefficient and wear rate of TaCN films are obtained, measured as 0·36 and 2·91×10−7 mm2 N−1, respectively.

Corrosion behaviour and adhesion properties of sputtered tantalum coating on Ti6Al4V substrate

Abstract Tantalum coating on Ti6Al4V substrate was prepared by sputtering and the mechanical and corrosion performance of the tantalum coating was investigated. In addition to the normal structure of a sole tantalum film on the substrate, a buffer layer of titanium was first deposited on the substrate in a hope to improve the film adhesion. XRD examination shows that the Ta coatings exhibit a α/β dual-phase structure. Both the sole Ta coating and the Ta coating with a Ti buffer layer increased the apparent hardness of the surface of the Ti6Al4V substrate significantly. The compressive residual stress of the Ta/Ti of the order of 0.9 GPa is noticeably reduced comparing to 1.2 GPa of the sole Ta coating, resulting in an improved adhesion between the coating-substrate interface. The hydrophobicity of the Ti6Al4V surface after Ta coating also increased, which is believed to help in protein absorption and enhance lubrication. The corrosion current density of the Ta coated Ti6Al4V decreased from 2.0 × 10 − 8 to 3.4 × 10 − 9 A·cm − 2 (at high scan rates) comparing to the uncoated Ti6Al4V substrate. The mechanisms of the improved corrosion current density by the Ta coating and the enhancement of mechanical bonding of the Ta coating by a Ti buffer layer are further discussed.

Development of a New Neuro-Endoscope Cylinder for Safer Neuro-Endoscopic Surgery

<i>Objective</i>:Successful endoscopic surgery for intracerebral hemorrhage has previously been hampered by impaired visualization during the operation to remove the clot, leading to a relatively low removal efficiency for hematomas. However, in multiple case series, intracerebral hematomas have been reported to be removed using endoscopic visualization. Although using tubular retractors in cranial surgery is one technique to gain access to deep-seated lesions, it is difficult to confirm the depth of the retractor's sheath in the surgical field using only the outer sheath. We built various-sized cylinders, developed by the Japan Science and Technology Agency's(JST)program for revitalization promotion, with scales that are visible during both endoscopic and radiographic procedures. We report the use of these cylinders in clinical cases. <i>Method and Results</i>:The JST-developed cylinders benefit from new techniques for plating and tantalum film implantation used to form tubes made of fluorinated ethylene propylene. We successfully removed various hematomas using these cylinders, as we were able to clearly visualize the border of the brain parenchyma and the depth of the hematoma using the cylinder. <i>Conclusion</i>:Cylinders with visible scales for both endoscopic and radiographic uses developed by the JST programs may provide greater patient safety during endoscopic surgery. We next plan to improve the hardness, length, and smoothness of the groove on the cylinder.

Yielding of tantalum at strain rates up to 109 s−1

We have used a 45 μJ laser pulse to accelerate the free surface of fine-grained tantalum films up to peak velocities of ∼1.2 km s−1. The films had thicknesses of ∼1–2 μm and in-plane grain widths of ∼75–150 nm. Using ultrafast interferometry, we have measured the time history of the velocity of the surface at different spatial positions across the accelerated region. The initial part of the histories (assumed to correspond to the “elastic precursor” observed previously) exhibited measured strain rates of ∼0.6 to ∼3.2 × 109 s−1 and stresses of ∼4 to ∼22 GPa. Importantly, we find that elastic amplitudes exhibit little variation with strain rate for a constant peak surface velocity, even though, via covariation of the strain rate with peak surface velocity, they vary with strain rate. Furthermore, by comparison with data obtained at lower strain rates, we find that amplitudes are much better predicted by peak velocities rather than by either strain rate or sample thickness.

Phase tailoring of tantalum thin films deposited in deep oscillation magnetron sputtering mode

The effect of energetic ion bombardment on the properties of tantalum thin films was investigated. To achieve such energetic ion bombardment during the process the Ta thin films were deposited by deep oscillation magnetron sputtering (DOMS), an ionized physical vapor deposition technique related to high power impulse magnetron sputtering. The peak power was between 49 and 130kW and the substrate was silicon at room temperature and ground potential. The directionality and the energy of the depositing species was controlled by changing the ionization fraction of the Ta species arriving at the substrate at different peak powers. In this work, the surface morphology (AFM), microstructure (SEM), structure (XRD) and hardness and Young's modulus (nanoindentation) of the films were characterized. The ion energy distributions (IEDs) were measured using an electrostatic quadrupole ion energy and mass spectrometer (HIDEN EQP 300). The IEDs showed that the DOMS process applies a very energetic (up to 120eV) ion bombardment on the growing tantalum films. Therefore, with such conditions it was possible to deposit pure α-Ta (of 2μm of thickness) without the use of additional equipment, i.e., without substrate bias or substrate heating. Conditions are therefore significantly different than in previous works, offering a much simpler and cheaper solution to up-scale for industrial operation.

Evaluation of residual stress in sputtered tantalum thin-film

The influence of deposition conditions on the residual stress of sputtered tantalum thin-film has been evaluated in the present study. Films have been deposited by DC magnetron sputtering and curvature measurement method has been employed to calculate the residual stress of the films. Transitions of tantalum film stress from compressive to tensile state have been observed as the sputtering pressure increases. Also, the effect of annealing process at temperature range of 90–300°C in oxygen ambient on the residual stress of the films has been studied. The results demonstrate that the residual stress of the films that have been deposited at lower sputtering pressure has become more compressive when annealed at 300°C. Furthermore, the impact of exposure to atmospheric ambient on the tantalum film stress has been investigated by monitoring the variation of the residual stress of both annealed and unannealed films over time. The as-deposited films have been exposed to pure Argon energy bombardment and as result, a high compressive stress has been developed in the films.

Effect of process pressure on biocompatibility of nanostructured tantalum film deposited on AISI316L stainless steel by PACVD

Effect of process pressure on biocompatibility of nanostructured tantalum film deposited on AISI316L stainless steel by PACVD

Synthesis of thin tantalum films by magnetron sputtering

A technique for the synthesis of thin (of about 1 nm) continuous tantalum films on the surface of insulating (sapphire) or conducting (n-GaAs) substrates by magnetron sputtering of a thick (of about 10 nm) film with subsequent etching in argon plasma to the needed thickness is proposed. The conditions of deposition of films and their etching rate are determined. It is demonstrated that the obtained films remain continuous down to a thickness of about 1 nm.

Retraction of "Fabrication of Tantalum and Nitrogen Codoped ZnO (Ta, N-ZnO) Thin Films Using the Electrospay: Twin Applications as an Excellent Transparent Electrode and a Field Emitter".

ADVERTISEMENT RETURN TO ISSUEPREVRetractionNEXTORIGINAL ARTICLEThis notice is a retraction.Retraction of “Fabrication of Tantalum and Nitrogen Codoped ZnO (Ta, N-ZnO) Thin Films Using the Electrospay: Twin Applications as an Excellent Transparent Electrode and a Field Emitter”Khalid Mahmood, Seung Bin Park*, and Hyung Jin SungCite this: ACS Appl. Mater. Interfaces 2015, 7, 46, 26005Publication Date (Web):November 12, 2015Publication History Published online12 November 2015Published inissue 25 November 2015https://doi.org/10.1021/acsami.5b10101Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1520Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (108 KB) Get e-Alerts Get e-Alerts

The behavior of tantalum under ultrashort loads induced by femtosecond laser

We studied the shock-wave and ablation phenomena in tantalum films of submicron thicknesses irradiated by femtosecond laser pulses. The single-shot spectral interferometry was used for continuous diagnostics of movement in a picosecond range both the frontal and rear surfaces of a sample. Measured displacement histories were converted into surface velocity histories. As a result, the new data on shear and tensile strength have been obtained for solid and molten tantalum at strain rate ∼ 109 s-1.

Formation of porous α tantalum in films

Ta—Cd alloys in the form of coatings with up to 66.2 at % Cd are fabricated for the first time by ion-plasma sputtering and the subsequent codeposition of ultradispersed Ta and Cd particles. At a concentration higher than 44.0 at % Cd, tetragonal β-Ta transforms into bcc α-Ta. Beginning from 74.4 at %, cadmium forms its hexagonal lattice and tantalum in the coatings is represented by an amorphous phase. During vacuum heat treatment at 700–750°C, cadmium evaporates from the binary tantalum—cadmium system containing more than 74.4 at % Cd, and a porous tantalum coating with a well-developed surface forms. Tantalum in the coating is represented by various flakelike crystallites, and tantalum in the near-surface layer mainly has a globular shape. A comparison of the specific surface areas of a tantalum film and the porous tantalum coating, which is performed by the BET method, demonstrates that the specific surface area increases by 277.5 m2/g Ta. Our results can be applied to other binary systems having similar properties.

The effect of vacuum annealing on the microstructure, mechanical and electrical properties of tantalum films

The microstructure, mechanical and electrical properties of vacuum annealed tantalum films were studied. X-ray diffraction spectra confirmed the presence of mixed (α and β) phases in the as-deposited Ta films. After vacuum annealing (at 750°C for 1h), the metastable β-phase was completely transformed to stable α-phase. The grain size increased (from 35±3nm to 92±3nm) with the increase in annealing temperature. The mixed (α and β) phases resulted in higher hardness and higher Young's modulus. The film annealed at 750°C for 1h exhibited lower resistivity (52±4μΩ-cm), lower hardness (H=10.4±1.3GPa) and lower Young's modulus (Y=185±5GPa) as compared to the as-deposited and annealed (at temperature<750°C) films. This is attributed to the phase transformation from β to α at an annealing temperature of 750°C.

Resistive switching in a few nanometers thick tantalum oxide film formed by a metal oxidation

Resistive switching in a Cu/Ta2O5/Pt structure that consisted of a few nanometer-thick Ta2O5 film was demonstrated. The Ta2O5 film with thicknesses of 2–5 nm was formed with a combination of Ta metal film deposition and neutral oxygen particle irradiation at room temperature. The device exhibited a bipolar resistive switching with a threshold voltage of 0.2 V and multilevel switching operation.

Interplay of electron correlations and localization in disordered β-tantalum films: Evidence from dc transport and spectroscopic ellipsometry study

We report the dc transport (5 K ≲ T ≲ 380 K) and spectroscopic ellipsometry (0.8 eV ≤ hν ≤ 8.5 eV, T ≃ 300 K) study of β-Ta films prepared by rf sputtering deposition as a function of their thickness in the range 2.5 nm ≲ d ≲ 200 nm. The dc transport of the β-Ta films with a thickness d ≳ 25 nm is characterized by negative temperature coefficient of resistivity (TCR) caused by localization effects peculiar of highly disordered metals. Their dielectric function spectra display non-metallic-like behavior due to the presence of the pronounced band at 2 eV. We found that with increasing TCR absolute value, specifying elevated degree disorder, the optical spectral weight (SW) of free charge carriers decreases. The associated SW is recovered in the range of Mott-Hubbard transitions, indicating the mechanism of localization enhancement by electronic correlations in disordered metals.

Signature of Cooper pairs in the non-superconducting phases of amorphous superconducting tantalum films

We have studied the magnetic field or disorder induced insulating and metallic phases in amorphous Ta superconducting thin films. The evolution of the nonlinear transport in the insulating phase exhibits a non-monotonic behavior as the magnetic field is increased. We suggest that this observation could be evidence of the presence of localized Cooper pairs in the insulating phase. As the metallic phase intervenes the superconducting and insulating states in Ta films, this result further reveals that Cooper pairs also exist in the metallic ground state.

Hydrogen gas sensors using a thin Ta2O5 dielectric film

A capacitive-type hydrogen gas sensor with a MIS (metal-insulator-semiconductor) structure was investigated for high-temperature applications. In this work, a tantalum oxide (Ta2O5) layer of tens of nanometers in thickness formed by oxidizing tantalum film in rapid thermal processing (RTP) was exploited with the purpose of sensitivity improvement. Silicon carbide (SiC), which is good even at high temperatures over 500 °C, was used as the substrate. We fabricated sensors composed of Pd/Ta2O5/SiC, and the dependences of the capacitance response properties and the I-V characteristics on the hydrogen concentration were analyzed from the temperature range of room temperature to 500 °C. As a result, our hydrogen sensor showed promising performance with respect to the sensitivity and the adaptability at high temperature.

Nucleation of fcc Ta when heating thin films

Thin tantalum films have been studied during in situ heating in a transmission electron microscope. Diffraction patterns from the as-deposited films were typical of amorphous materials. Crystalline grains were observed to form when the specimen was annealed in situ at 450 °C. Particular attention was addressed to the formation and growth of grains with the face-centered cubic (fcc) crystal structure. These observations are discussed in relation to prior work on the formation of fcc Ta by deformation and during thin film deposition.

On interlayer stability and high-cycle simulator performance of diamond-like carbon layers for articulating joint replacements.

Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the orthopaedic field, layer performance, stability and adhesion in physiologically relevant setups are crucial and not consistently investigated. In vitro wear testing as well as adequate corrosion tests of interfaces and interlayers are of great importance to verify the long term stability of DLC coated load bearing implants in the human body. DLC coatings were deposited on articulating lumbar spinal disks made of CoCr28Mo6 biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer, tantalum films were deposited by magnetron sputtering. Wear tests of coated and uncoated implants were performed in physiological solution up to a maximum of 101 million articulation cycles with an amplitude of ±2° and −3/+6° in successive intervals at a preload of 1200 N. The implants were characterized by gravimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and cross section scanning electron microscopy (SEM) analysis. It is shown that DLC coated surfaces with uncontaminated tantalum interlayers perform very well and no corrosive or mechanical failure could be observed. This also holds true in tests featuring overload and third-body wear by cortical bone chips present in the bearing pairs. Regarding the interlayer tolerance towards interlayer contamination (oxygen), limits for initiation of potential failure modes were established. It was found that mechanical failure is the most critical aspect and this mode is hypothetically linked to the α-β tantalum phase switch induced by increasing oxygen levels as observed by X-ray diffraction (XRD). It is concluded that DLC coatings are a feasible candidate for near zero wear articulations on implants, potentially even surpassing the performance of ceramic vs. ceramic.

Investigation of the Young's modulus and thermal expansion of amorphous titania-doped tantala films.

The current generation of advanced gravitational wave detectors utilize titania-doped tantala/silica multilayer stacks for their mirror coatings. The properties of the low-refractive-index silica are well known; however, in the absence of detailed direct measurements, the material parameters of Young's modulus and coefficient of thermal expansion (CTE) of the high refractive index material, titania-doped tantala, have been assumed to be equal to values measured for pure tantala coatings. In order to ascertain the true values necessary for thermal noise calculations, we have undertaken measurements of Young's modulus and CTE through the use of nanoindentation and thermal-bending measurements. The measurements were designed to assess the effects of titania-doping concentration and post-deposition heat-treatment on the measured values in order to evaluate the possibility of optimizing material parameters to further improve thermal noise in the detector. Young's modulus measurements on pure tantala and 25% and 55% titania-doped tantala show a wide range of values, from 132 to 177 GPa, which are dependent on both titania concentration and heat-treatment. Measurements of CTE give values of (3.9±0.1)×10⁻⁶ K⁻¹ and (4.9±0.3)×10⁻⁶ K⁻¹ for 25% and 55% titania-doped tantala, respectively, without dependence on post-deposition heat-treatment.