Ta Foil Research Articles

Mechanical property improvement of diffusion bonded ZrCx joints by chemical homogenization using Ta as the interlayer

In the present study, a transition metal Ta foil was used as the interlayer to diffusion bond ZrCx ceramics. A needle-like ζ-Ta4C3-x phase was initially formed at the interface and could be effectively dissolved into the base ceramic by reasonably tuning the bonding temperature and holding time, resulting in a chemically homogeneous joint when diffusion bonded at 1600 °C for 1 h under 20 MPa pressure. The composition of the homogeneous joints was composed of ZrCx(Ta), which is very similar to the base ceramic. The ζ-Ta4C3-x phase was found beneficial to the mechanical property of the joints due to its mechanically interlocking effect and the ability to absorb the propagation energy of microcracks. The chemically homogeneous joint had comparable four-point bending strength and nano-indentation hardness with that of the base ceramic, indicating that chemical homogenization of the joint has great potential to enhance the mechanical property of the ZrCx joints.

Preparation, optical properties, room temperature ferromagnetism, and mechanism of ordered nanotube-like tantalum oxide films

Physical property changes caused by defects have recently attracted significant attention due to their potential applications in sensors, spintronic devices, and multifunctional memory. Due to their numerous surface defects, this study fabricated ordered Ta2O5 nanotube (NT) thin films on Ta foil through an anodization technique. Then, the oxygen bubble model was applied to explain the formation of NTs from the perspective of lattice orientation. Furthermore, this study investigated influence of anodization duration and annealing treatment on the crystal structure, optical properties, and magnetic behavior. Notably, room-temperature ferromagnetism was observed in the as-prepared Ta2O5 NTs for the first time. After annealing in an argon atmosphere, the band gap of the sample decreased, accompanied by an increase in ferromagnetism. The underlying mechanism for this phenomenon was elucidated using a hydrogen-like impurity model. Consequently, this study on the magnetism of Ta2O5 NTs holds excellent potential for expanding their application in spin electronic devices.

Impact of Scattering Foil Composition on Electron Energy Distribution in a Clinical Linear Accelerator Modified for FLASH Radiotherapy: A Monte Carlo Study.

This study investigates how scattering foil materials and sampling holder placement affect electron energy distribution in electron beams from a modified medical linear accelerator for FLASH radiotherapy. We analyze electron energy spectra at various positions-ionization chamber, mirror, and jaw-to evaluate the impact of Cu, Pb-Cu, Pb, and Ta foils. Our findings show that close proximity to the source intensifies the dependence of electron energy distribution on foil material, enabling precise beam control through material selection. Monte Carlo simulations are effective for designing foils to achieve desired energy distributions. Moving the sampling holder farther from the source reduces foil material influence, promoting more uniform energy spreads, particularly in the 0.5-10 MeV range for 12 MeV electron beams. These insights emphasize the critical role of tailored material selection and sampling holder positioning in optimizing electron energy distribution and fluence intensity for FLASH radiotherapy research, benefiting both experimental design and clinical applications.

New microfocus source based on a betatron for hard X-rays imaging

The paper reports experimental results demonstrating some properties of microfocus radiation generated in narrow internal silicon (Si) and tantalum (Ta) targets of the B-18 betatron with electron energy of 18 MeV. The targets were 50-μm- and 8-μm-thick Si crystals and a 13-μm-thick Ta foil oriented with a goniometer along the inner electron beam. The results showed strong dependence of the radiation beam shape on the orientation of the target relative to the electron beam, and on the target material. The resolution and contrast dependences of the Duplex IQI standard wire pair images on the position of the pairs in the radiation beam and on the target material are shown. The obtained results revealed the role of absorption and refraction of radiation in generation of magnified images of plastic and metal plate edges. Radiation generated in the Ta target showed high detection sensitivity for narrow gaps and thin inclusions in steel thickness.

X-ray Induced Electric Currents in Anodized Ta2O5: Towards a Large-Area Thin-Film Sensor.

We investigated the characteristics of radiation-induced current in nano-porous pellet and thin-film anodized tantalum exposed to kVp X-ray beams. We aim at developing a large area (≫cm2) thin-film radiation sensor for medical, national security and space applications. Large area (few cm2) micro-thin Ta foils were anodized and coated with a counter electrode made of conductive polymer. In addition, several types of commercial electrolytic porous tantalum capacitors were assembled and prepared for irradiation with kVp X-rays. We measured dark current (leakage) as well as transient radiation-induced currents as a function of external voltage bias. Large transient currents (up to 50 nA) under X-ray irradiation (dose rate of about 3 cGy/s) were measured in Ta2O5 capacitors. Small nano-porous Ta and large-area flat Ta foil capacitors show similar current-voltage characteristic curve after accounting for different X-ray attenuation in capacitor geometry. The signal is larger for thicker capacitor oxide. A non-negligible signal for null external voltage bias is observed, which is explained by fast electron production in Ta foils. Anodized tantalum is a promising material for use in large-area, self-powered radiation sensors for X-ray detection and for energy harvesting.

Effect of irradiation on grain size and texture in Mo and Ta films

Implantation of heavy ions into metal matrices leads to the creation of a high concentration of radiation defects. X-ray diffraction studies of Mo and Ta foils implanted with 57Fe ions have been carried out. It is shown that the implantation of Fe ions does not significantly affect the lattice parameters. It has been established that irradiation leads to broadening of diffraction lines and a decrease in the size of crystal grains. The Mo and Ta foils with {100} orientation are found to be highly textured. Irradiation with Fe ions has no noticeable effect on the texture. However, subsequent annealing at a temperature of 700°С weakens the texture on the irradiated side for Mo and Ta foils without affecting the texture of the nonirradiated side.

Role of Surface Chemistry of Ta Metal Foil on the Growth of GaN Nanorods by Laser Molecular Beam Epitaxy and Their Field Emission Characteristics.

This study investigates the influence of surface nitridation of Ta metal foil substrates on the growth of GaN nanorods using the laser molecular beam epitaxy (LMBE) technique and the field emission characteristics of the grown GaN nanorod ensemble. Surface morphology examinations underscore the pivotal role of Ta foil nitridation in shaping the dimensions and densities of GaN nanorods. Bare Ta foil fosters the formation of high-density, vertically self-aligned GaN nanorods at a growth temperature of 700 °C. Furthermore, the density of these nanorods is directly related to the duration of Ta foil nitridation, with increased duration leading to a reduced nanorod density. X-ray Photoelectron Spectroscopy (XPS) studies reveal that the transition of the Ta foil surface from tantalum oxide to tantalum nitride during nitridation emerges as a crucial factor influencing GaN nanorod growth. Photoluminescence (PL) spectroscopy at ambient temperature reveals a strong near-band-edge (NBE) emission peak with negligible defect-related peaks, displaying the high optical quality of the GaN nanorods. The highly dense vertically aligned GaN nanorod ensemble growth without Ta prenitridation exhibits the most favorable field emission performance, featuring a turn-on field of 2.1 V/μm, a field enhancement factor of 2480, and a stable long-term operation at the emission current density of 2.26 mA/cm2. This study advances the understanding of the role of the surface chemistry of metal foil in determining GaN nanorod growth and opens up exciting possibilities for tailoring advanced optoelectronic devices for specific application requirements.

Microstructure and mechanical property of bonding zones between Ta foil and steel plate fabricated by explosive welding

This work aims to produce a thorough comprehension concerning microstructure related properties of the joint interface between Ta foil and steel plate fabricated by explosive welding. For this, a self-developed explosive welding configuration was employed to join Ta foil and steel plate, and different microscopic methods were adopted to investigate its microstructures and mechanical properties. It was found that the Ta/Fe interface was featured by regular wavy structures with a well-defined amplitude and period. The melted zones were mainly observed within the vortex structures, and occasionally at the Ta/Fe interfaces, which were formed by intense mixing of participating metals. The EBSD analyses revealed a diversity of the grain structures near the Ta/Fe interface, such as formation of the curved and elongated grains in Ta matrix, and fine equiaxed and columnar grains in Fe matrix. Especially, several adiabatic shear bands (ASBs) characterized by small equiaxed grains were found in Fe matrix, which were due to stress wave concentration in the narrow paths, and the materials in these zones underwent a recrystallization process. Finally, the nanoindentation results revealed inhomogenous mechanical behaviors in the bonding zones, which could be well related to the changes of microstructure and chemical composition.

Carbon Contamination Prevention during Spark Plasma Sintering.

Carbon contamination from graphite molds during spark plasma sintering (SPS) considerably affects the properties of the sintered materials, especially transparent ceramics. Herein, transparent Y3Al5O12 (YAG) ceramics were prepared via SPS using Mo and Ta foils, separately and in tandem, as protective barriers against carbon contamination. The effects of Ta and Mo foils on the transparency and microstructure of the ceramics, and their protection mechanisms were studied. Experimental results show that a reaction layer formed at the Ta-YAG interface with a YTaO4-Al2O3 eutectic composition suppresses carbon penetration into the ceramic, increasing its transparency. By contrast, Mo foils, when used as protective barriers, allow carbon diffusion into the ceramic, resulting in the formation of nonuniform microstructural features. However, it does not form a reactive layer and, hence, is removed easily from the YAG surface. Multilayered Ta-Mo barrier exhibits improved outcomes if the Ta thickness is more than ∼100 μm. This behavior is attributed to the interior diffusion-blocking mechanism of Ta. Similar optical performance was demonstrated by both approaches. The results prove that carbon contamination in SPS-derived samples can be effectively prevented. Additionally, this study reports on a novel strategy of bonding oxide ceramics to metals by adding a Ta layer at the joint interface.

Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

We report a novel approach in producing and characterizing enriched isotopic selenium-82 (82Se) thin films with trigonal hexagonal crystal structure (t-82Se), the most thermodynamically stable form of the element. The obtained t-82Se thin films are used as targets in accelerator based nuclear structure experiments. Several 82Se thin films with thicknesses around 5 mg/cm2 (10.4 μm) were deposited on 5 mg/cm2 (3 μm) tantalum (Ta) foils by vacuum evaporation-condensation method. The condensed 82Se films exhibit unstable amorphous structure (a-82Se), therefore were converted to t-82Se by means of an appropriate vacuum heat treatment developed in the target laboratory of IFIN-HH. After the thermal treatment, the microstructure, morphology and composition of the 82Se films were evaluated before and after the vacuum thermal treatment using Fourier Transform Raman Spectroscopy (FT-Raman), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. Furthermore, an in-beam γ-spectroscopy experiment performed at the 9-MV tandem accelerator of IFIN-HH confirmed that the thermally treated t-82Se films possess high durability and high purity with no detectable contamination and no mass loss.

Tantalum oxynitride nanotube film arrays for unconventional nanostructured photo-electrodes active with visible light

Tantalum-oxy-nitride nanotubes (TaOxNy NTs) ordered in 1D were successfully synthesized through controlled anodic oxidation of metallic Ta foils followed by high-temperature annealing under NH3 flow to prepare unconventional nanostructured photo-electrodes active with visible light. For the synthesis, a two-step anodization process was adopted: i) the first step in ethylene glycol with 0.33 % NH4F and 3 % H2O, ii) the second step in H2SO4 (98 %) with 1 % HF and 4 % H2O, by applying different voltages and anodization times. Scanning Electron Microscopy integrated with Energy Dispersive X-ray spectroscopy (SEM-EDX) revealed the NTs length ranging from 2 to 5 µm, and the inner tube diameter from 20 to 100 nm, in good correlation with the synthesis parameters. The N-content (from 2.7 % to 19.1 %) was dependent on the nitridation temperature (from 500° to 900°C), and the conversion of bare Ta2O5 into TaOxNy strongly influenced the absorption in the visible region with a bandgap shift from 4.0 to 2.1 eV, respectively. Photo-electrochemical and catalytic performances were evaluated with chronoamperometric measurements and tests in different photo-reactions using AM 1.5 G simulated sunlight: (i) degradation of methylene blue (MB), (ii) ethanol gas-phase photo-reforming and (iii) bias-assisted photoelectrochemical water splitting. The TaOxNy NTs film-type electrode obtained by nitriding at 800 °C showed the highest photocurrent value (0.1 mA∙cm-2), and the highest rates of MB degradation (k1 of 0.0189 min-1) and H2 photo-production.

Experimental study of medical isotopes 62,64Cu and 68Ga production using intense picosecond laser pulse

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which copper-62, 64 (62,64Cu) and gallium-68 (68Ga) are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments that generate these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center in Mianyang. High-charge ( ∼ 40 nC) MeV electron (e− ) beams were generated with 100 terawatts, picosecond laser pulses. The e− beams were then impinged on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung x-rays and medical isotopes 62,64Cu and 68Ga, respectively. The characteristic emissions of the produced 62,64Cu and 68Ga were detected off-line , and the production yields of 62,64Cu and 68Ga were obtained to be of the order of 106 per laser shot. For electrons with energy higher than 8 MeV, the dependence of isotope production efficiency (per e− ) on electron temperature () is investigated through Geant4 simulations. It is found that the production efficiency increases with the . At ∼ 10 MeV, the values are 10−4 for 62Cu and 2 × 10 − 5 for 68Ga, respectively. The prospect of producing the medical isotopes 62,64Cu and 68Ga are further evaluated using a table-top femtosecond laser system of high repetition. With a repetition rate of 100 Hz, their activity is expected to reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical isotopes with an all-optical, high-repetition laser system.

An Ultra‐Thin, Ultra‐High Capacitance Density Tantalum Capacitor for 3D Packaging

AbstractAlthough embedded capacitors have been applied and researched for many years, their large‐scale application still faces challenges such as low capacitance density, high thickness, high cost, and incompatibility with integrated processes. In this work, a breakthrough has been made in the fabrication of ultra‐thin tantalum (Ta) capacitors with ultra‐high capacitance density that can be used for 3D packaging. The key to these excellent performances is the application of Ta foil with nano‐porous structure to the anode of the capacitor. The Ta foil with high specific surface area (SSA) is successfully prepared by direct current pulse etching. At a current density of 15 mA cm−2, a pulse frequency of 50 Hz, and a duty cycle of 30%, the SSA of Ta foil is increased by 76 times after etching in an electrolyte with 0.01 v% TOA for 30 min. Based on this, Ta capacitors with a form factor of less than 40 µm, showing a capacitance density of 750 nF mm−2 and a leakage current of less than 2.1 × 10−7 A at 8 V is successfully fabricated. To the best of the authors’ knowledge, this is the highest capacitance density reported to date for the mentioned form factors.

The anomalous annealing hardening behaviors in commercial pure Tantalum foil

Annealing softening phenomenon is usually observed in pure metals. However, in this study, the anomalous annealing hardening behavior is found in commercial pure Tantalum (Ta) foil. When the cold-rolled Ta foils are annealed at a temperature lower than 700 °C, both the yield strength and ductility gradually increase with the rise in annealing temperature, resulting in an anomalous "low-temperature annealing hardening" phenomenon. The yield strength of Ta foils annealed at 700 °C reaches the maximum value of about 750 MPa. This phenomenon in Ta foil is closely related with the shear bands and the pinning behavior between interstitial atoms and dislocations. When annealing temperature is higher than 700 °C, the yield strength decreases. When annealing temperature exceeds 900 °C, recrystallization occurs in Ta foil. Anomalous yield point phenomenon appears in the recrystallization foils during stretching, which is also related with the pinning of dislocations by interstitial atoms. As annealing temperature further increases, the volume fraction of surface grains gets larger. And {112}<111> slip systems are preferred over {110}<111> slip systems in the surface grains.

An integrated system for user-friendly X-ray intensity attenuation in a wide energy range

For undulator hard X-ray beamlines of a wide energy range, the beam intensity control is often needed to regulate the photon flux impinging on delicate detectors. Despite the capability of state-of-the-art X-ray pixel detectors being greatly advanced recently, the frontier undulator beamlines in synchrotron facilities often carry outstanding photon fluxes that are sometimes too high for certain measurements. Here, we report a developed protocol that allows intensity attenuation of an X-ray beam in the 4-23 keV energy range with flexible attenuation factors; a prototype is installed and tested on the 13A biological small-angle X-ray scattering beamline of the 3 GeV Taiwan Photon Source (TPS) of the National Synchrotron Radiation Research Center, Hsinchu, Taiwan. The intensity attenuation system is modified from a commercially available pneumatically actuated, vacuum-type precision X-ray attenuator of ADC ABS-300; the system provides beam attenuation factors covering 8 orders of intensity attenuation for an X-ray beam in 4-23 keV. This was achieved with selected combinations of 10 sets of metal foils comprising different thicknesses of Al, Ti, Cu, and Ta foils. A user-friendly protocol is established to automatically compare a subscribed attenuation factor with all the possible attenuation factors from the 1024 combinations of the 10 sets of foils in the X-ray energy used, and determine a set of the metal foils having a best-matched attenuation factor. Calculation of beam intensity attenuations with the selected foils is coded with Python and integrated into the Experimental Physics and Industrial Control System (EPICS). The input of an attenuation factor is done through a graphical display of the attenuator system based on the Control System Studio (CSS). The developed X-ray beam attenuation system provides a convenient and intuitive beam intensity control and has the potential to be adopted in future beamlines.

Thickness Dependency of Battery Anode Properties in Multilayer Graphene.

With the development of practical thin-film batteries, multilayer graphene (MLG) is being actively investigated as an anode material. Therefore, research on determining a technique to fabricate thick MLG on arbitrary substrates at low temperatures is essential. In this study, we formed an MLG with controlled thickness at low temperatures using a layer exchange (LE) technique and evaluated its anode properties. The LE technique enabled the formation of a uniform MLG with a wide range of thicknesses (25-500 nm) on Ta foil. The charge/discharge characterization using coin-type cells revealed that the total capacity, which corresponded to Li intercalation into the MLG interlayer, increased with increasing MLG thickness. In contrast, cross-sectional transmission electron microscopy showed a metal oxide formed at the MLG/Ta interface during annealing, which had small Li capacity. MLG with sufficient thickness (500 nm) exhibited an excellent Coulombic efficiency and capacity retention compared to bulk graphite formed at high temperatures. These results have led to the development of inexpensive and reliable rechargeable thin-film batteries.

Wire-based directed energy deposition of NiTiTa shape memory alloys: Microstructure, phase transformation, electrochemistry, X-ray visibility and mechanical properties

Wire and arc additive manufacturing (WAAM) technology was used for the fabrication of NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) for the first time, using commercialy available NiTi wire and Ta foil as the feedstock materials. The addition of Ta significantly increased the phase transformation temperatures, leading to a room-temperature microstructure composed of both B19′ martensite and B2 austenite, and (Ti,Ta)2Ni precipitates distributed at the grain boundaries. Compared with the WAAM fabricated NiTi counterpart, the corrosion potential (Ecorr) of the NiTiTa material increased from − 0.55 to − 0.44 V, while the corrosion current density (Icorr) decreased from 1.90 × 10−6 to 4.2 × 10−7 A/cm2. The X-ray brightness increased from 19.6 to 56.4 %. These results indicate that the addition of Ta can enhance the corrosion resistance and X-ray visibility of NiTiTa parts. Furthermore, the WAAM fabricated NiTiTa material was able to retain a stable superelastic response under 10 loading-unloading cycles, highlighting the great potential application value in the biomedical field. Our work provides an innovative method for additively manufacturing NiTi-based multi-component SMAs through WAAM.

A key factor in determining the effectiveness of etchants for electrochemical surface enlargement of Ta foil for electrolytic capacitor

For electrochemical etching, it is often assumed intuitively that the high specific surface area (SSA) is largely dependent on the aggressiveness of the corrosive agent. Today, however, we present a different perspective. In this study, we combine theoretical calculations and electrochemical experiments to fully understand the mechanisms of Cl- and Br- in the three stages of the tantalum (Ta) pitting process, including passivation film breakdown, Ta anodic dissolution and re-passivation. The results show that both Cl- and Br- cause the breakdown of the passivation film and the dissolution of Ta atoms, with the former having a more pronounced effect. However, MD simulations show that the re-passivation of Ta occurs only in Br- containing media but not in Cl- containing media. This means that Ta is protected by adsorption of dissolved oxygen while being destroyed by Br-, but is only dissolved in NaCl solution. The same result is observed in our electrochemical experiments. In addition, the specific capacity of etched Ta foil in NaBr solution is as high as 325μF/cm2 while it is only 48μF/cm2 in NaCl. It is precisely the protective rather than the destructive effect of the etchant that is more important for obtaining high SSA.

Thermo analytical characterization of tantalum oxide in the process for the development of tantalum nitride photoelectrodes

Thermogravimetric analysis and differential scanning calorimetry techniques were used to estimate the kinetic parameters of the oxidation of a tantalum metallic foil in the Ta3N5 photoelectrodes preparation process. Model-free methods were used to determine the pre-exponential and activation energy of the Arrhenius equation related to the tantalum oxidation. The obtained kinetic model considers the existence of two independent oxidation events: [A→FnB] and [C→AnD→AnE].X-ray powder diffraction analysis was used to identify the crystalline phases present in each sample. The sample oxidized at 5 °C·min−1 (500 °C), contained two tantalum oxide polymorphs, Ta4O (25 ± 5) % and Ta2O (25 ± 2) %, and metallic tantalum showing a cubic structure. All the remaining samples presented a monophasic Ta2O5 with orthorhombic unit cells which showed a similar cell volume, but crystallite size increased with the temperature.The heating rate used in the oxidation of the Ta foils was verified to influence the photoelectrochemical performance of the prepared Ta3N5 photoelectrodes. Samples prepared with increasing heating rates evidenced a shift in onset potential towards higher potentials, and a more pronounced dark current. For the considered nitridation conditions of 8 h at 850 °C, the highest photocurrent performance was obtained with a heating rate of 5 °C·min−1 to 700 °C.

Joining of Al2O3 ceramic to Cu using refractory metal foil

Joining of Al 2 O 3 ceramic to Cu has been conducted with Ag-26.7Cu-4.5Ti braze and refractory metal (W or Ta) foil. The interfacial microstructure in the joint with W foil is similar to that with Ta foil. The joining region in the joint consists of a reaction zone, braze zone I, refractory metal layer and braze zone II. The reaction zone of Cu 3 Ti 3 O with a thickness of about 5 μm develops close to Al 2 O 3 side due to the reactions of Ti and Cu in the braze with Al 2 O 3 substrate. The braze zones I and II are mainly composed of Ag- and Cu-based solid solutions. For the joint with W foil, the adsorption of Ti at the braze/W interfaces followed by the Ti diffusion into W foil occurs, whilst slight dissolution and diffusion of Ta into the brazes take place in the joint with Ta foil. The average shear strengths of joints with W and Ta foils are much higher than those without refractory metal foil, indicating the contribution of the refractory metal foil to the improvement of joint mechanical strength. Introduction of refractory metal foil in Al 2 O 3 /Cu joining is beneficial for the shift of joint residual stress distribution and the decrease of stress concentration in the joint since the coefficient of thermal expansion (CTE) of refractory metal layer approximately approaches that of Al 2 O 3 . Furthermore, a slight thickness increase of the Cu 3 Ti 3 O reaction zone in the joint with refractory metal foil may also give rise to the joint strength promotion.