Thick Ta Research Articles

Towards sub-10 nm spatial resolution by tender X-ray ptychographic coherent diffraction imaging

As the first experiment at BL10U in NanoTerasu, tender X-ray ptychographic coherent diffraction imaging (PCDI) was conducted using a photon energy of 3.5 keV. The ptychographic diffraction patterns from a 200 nm thick Ta test chart and a micrometer-sized particle of sulfurized polymer were collected. Subsequently, phase images were reconstructed with resolutions of sub-20 nm and sub-50 nm, respectively. In the near future, tender X-ray PCDI with sub-10 nm resolution is anticipated to potentially revolutionize the visualization of nanoscale structures and chemical states in various functional materials composed of light elements.

Exploring nanoscale metallic multilayer Ta/Cu films: Structure and some insights on deformation and strengthening mechanisms

Nanoscale metallic multilayer (NMM) films are systems offering insight into the role of interfaces in metal plasticity, deformation, and strengthening mechanisms. Magnetron sputtering was used to fabricate the Ta/Cu NMM films with a periodicity (equal Ta and Cu layer thickness) from 6 to 80 nm, and with the structure exhibiting immiscible tetragonal β-Ta and face-centred cubic Cu phases. Transmission electron microscopy and X-ray diffraction analyses revealed that, irrespective of the period, all films manifested a polycrystalline structure. The growth direction of both Cu and Ta layers was found to be along 〈001〉 β-Ta || 〈111〉 Cu directions, with the crystallite size constrained by the layer thickness. The studies showed that the Ta/Cu NMMs exhibited compressive residual macro-stress and flow strength, and enhanced elastic recovery at the periodicity of ≤12 nm. Activation volume V⁎ value of 11 to 20 b3 as determined from the indentation creep test under a constant load, may indicate a mixed deformation mechanism. This mechanism likely involves the emission of dislocations from the incoherent Ta/Cu interfaces, as well as the formation of screw dislocations within Cu grains. The high-load indentation test, TEM studies, and the rCLS model collectively demonstrate that all NMM films predominantly undergo plastic deformation. This plastic deformation primarily occurs within the soft Cu layer, while the propagation of dislocations across the incoherent interface is largely excluded.

Medial arch instability/internal foot overload association with non-insertional Achilles tendinopathy and the ‘Zone of Conflict Theory’

BackgroundNon insertional Achilles tendinopathy [AT] is a degenerative condition that is prevalent in runners. 30% have no preceding history and many runners do not develop AT. Overuse, pronation, and compromised blood supply are hypothesised as causal. The exact precipitant is still unknown. The link between medial arch instability and AT has not been made. The purpose of this study was to investigate the association between spring ligament (SL) laxity and first ray (FRI) instability, and the presence of (AT). MethodsEthical approval was obtained. Patients were identified from hospital databases for unilateral AT, allowing the opposite unaffected foot to be used as an internal control. SL laxity was measured using the lateral translation score and FRI was measured using a modified digital Klauemeter. Ultrasound was used to assess the tendoachilles [TA] in affected vs unaffected legs. Results17 patients were recruited with a mean age of 55.6 and mean body mass index (BMI) of 33.3. The average symptom duration was 3.62 years. There were 12 left feet and 5 right feet. There was no statistical difference in dorsiflexion angles for the TA or the gastrocnemius. All Beighton scores < 5. Lateral translation scores, FRI scores and TA thickness was significantly greater in AT feet [p < 0.05]. More affected feet had Tibialis posterior tendon pain (TP) [p < 0.05]. ConclusionsFeet with AT exhibit higher lateral translation scores and greater FRI compared to healthy feet, and combined with previous literature evidence, suggests alteration of the subtalar axis alters force moments that may lead to an intrinsic overload of the TA, when the foot enters a "zone of conflict". Medial arch instability, in particular SL laxity and FRI, may contribute to the development of non-insertional AT and treatment of this with early arch support may prevent progressive degeneration.

Lifetime measurement of the Ex = 2485.3 keV level of 25Al populated through 24Mg(p,γ)25Al resonance reaction

Results of our experimental study of the 24Mg(p,γ)25Al resonance reaction at E=plab223 keV are presented. The proton beam energy is varied from 220 to 265 keV. An evaporated Mg target with thick Ta backing is used. We remeasure a mean lifetime of τ=6.04−2.65+3.03 fs for the E=x2485.3 keV level of 25Al, using Doppler shift attenuation (DSA) method. Three most successfully used empirical effective interactions developed for the sd shell by Wildenthal (w), Chung-Wildenthal (cw) and Preedom-Wildenthal (pw), are utilized to calculate energy spectra, spectroscopic factors, beta decay properties, transition probabilities and the lifetime of the resonance state in 25Al within the framework of nuclear shell model. The theoretical results agree reasonably well with the experimental data. However, a detailed study for each set to identify the most preferred interaction for this nucleus is performed. Calculated lifetimes using two of the interactions (w, cw) agree better with the central value of the experimental lifetime of the resonance state measured in the present work.

Optimization of target system for the production of 99Mo via 100Mo(γ,n)99Mo reaction

With an increase of stopping operation of nuclear reactors worldwide, the supply of medical 99Mo becomes difficult and thus many efforts have been made to find an alternative. A process based on an electron linear accelerator (linac) system and a100Mo target via the 100Mo (γ,n)99Mo reaction receives a lot of attention due to the relatively low level of co-produced impurities. This process has been recently developed at the Institute of Modern Physics (IMP) and the Monte Carlo simulation was used to optimize the target system before operating pilot irradiation experiments. First, tungsten and tantalum, as mostly used converter materials, were tested. The yield of 99Mo was evaluated with respect to the converter thickness and the electron beam energy by means of Geant4 simulations. Besides, the specific activity of 99Mo produced from one-stage approach (100Mo target without a converter) and two-stage approach (100Mo target with a converter) was compared when varying the testing conditions. The two-stage approach was selected for the experiment due to the higher specific activity of produced 99Mo at all tested conditions. A target consisting of a 10 mm thickness of the 100Mo tablets and a 2.4 mm thick Ta converter was irradiated for 40 h (50 MeV with 0.2 μA). The Geant4-calculated specific activity of generated 99Mo at the end of bombardment agreed well with the experimental value, which proved high level of accuracy of the Geant4 simulation. In future studies, the Geant4 simulation will be used to optimize the production process when using high power linac system.

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.

Yield of residues produced in 6Li reaction on Ta: A comparative analysis for 183Os

The present work reports an analysis of the production yield of residues from the 6Li ＋ 181Ta reaction in a low-energy regime. The experimental yield of 183gOs, 183mOs, 182Os, 183Re, 183Ta, 182m2Ta, and 180Ta have been measured in the 27–43 MeV energy window and compared with equilibrium and pre-equilibrium model calculations under the framework of the nuclear reaction model code, EMPIRE-3.2.2. The maximum yield measured for 183gOs is 80.5 ± 14.9 MBq/C at 40.2 MeV energy in a 2.3 mg/cm2 thick Ta target corresponding to a cross-section of 360.1 ± 34.4 mb from the 181Ta(6Li,4n)183Os reaction and that for 183Re is 1.36 ± 0.4 MBq/C at 42.75 MeV in a 2.4 mg/cm2 thick target. The model estimations agree well with the experimental yields of 183gOs and 183Re. The possible production of stable residues has been estimated using the model-predicted cross-section in the studied energy range. A comparison of production yields of 183m,gOs from 6Li- and 7Li-induced reaction on Ta demonstrates the 6Li reaction as a better candidate. Thick target yields have been evaluated for Os and Re isotopes.

Impact of supporting substrate on the measured neutron yields from natLi (p, n) system: A case study with natC and natTa stopping targets

Abstract The high energy neutron generation facilities worldwide uses the Li(p,n) system for production of the quasi mono-energetic neutrons from epithermal to few hundreds of MeV. Among the facilities either self-standing thick Li target or Li foil supported on a target assembly is used. In case of a supported Li target, either low or high mass supporting substrates like Al, C, Au, Ta etc. can be used. However, the neutron emission from the supporting substrate can interfere with the Li(p,n) reaction neutrons. In the present study neutron yields from a thin natural Li target supported on the thick natural Ta (high Z) and C (low Z) targets were measured at incident proton energies between 8-20 MeV. The proton irradiation of targets were performed at the Pelletron accelerator Facility, Mumbai and the emitted neutrons were measures at both forward (0°) and lateral (90°) directions with respect to the incident beam. The neutron yield was estimated using the CR-39 detectors and dual scintillator based active neutron spectrometer. A neutron dose equivalent (NDE) meter was also used to measure the neutron ambient dose equivalent at the measurement point. Experimentally measured neutron yields and ambient neutron dose equivalent estimates indicated higher Li(p,n) neutron yield with carbon as the supporting substrate. This is due to fewer self-emissions from natC compared to natTa target. Carbon supporting substrate also ensures improved spectral features of the Li(p,n) emission neutrons and lesser neutron fluence around the source location. This ensures efficient implementation of radiation protection practices with carbon target due to lower neutron fluence around the source compared to tantalum target. Carbon is a favorable supporting substrate compared to high Z- metal targets like Ta for emission neutron studies on Li target at proton energies between 8-20 MeV.

Neutron spectrometry and dosimetry using a multi-shell Single Sphere Neutron Spectrometer with thermo-luminescent and optically stimulated luminescent detectors

A portable neutron spectrometer with concentric multi-shell moderating assembly and TL, OSL detectors has been validated with standard neutron reference fields to generate the neutron spectra and estimate the ambient dose equivalents, H*(10). Further, the system has been used in the mixed neutron–gamma radiation fields at accelerator facility. The neutron fluence and the ambient dose equivalent estimates were verified using the standard reference neutron fields, viz. 241Am-Be, 252Cf, D-T neutron sources. The system was then employed in the accelerator radiation environment to measure the neutron spectral yield from the interactions of 15 and 20 MeV protons with a thick natural Ta target. The results were compared with those obtained from FLUKA simulations. A conventional neutron dose equivalent meter was also used to verify the ambient dose equivalent estimated from the spectrometric measurements. The reproducibility of the neutron spectra and dose values were found to be satisfactory, thereby encouraging the implementation of the portable single sphere neutron spectrometer in complex radiation environment around particle accelerators. Present studies demonstrate the measurements with the in-house built spectrometer for neutron energies up to 20 MeV.

Chemical mechanical planarization for Ta-based superconducting quantum devices

We report on the development of a chemical mechanical planarization (CMP) process for thick damascene Ta structures with pattern feature sizes down to 100 nm. This CMP process is the core of the fabrication sequence for scalable superconducting integrated circuits at a 300 mm wafer scale. This work has established the elements of various CMP-related design rules that can be followed by a designer for the layout of circuits that include Ta-based coplanar waveguide resonators, capacitors, and interconnects for tantalum-based qubits and single flux quantum circuits. The fabrication of these structures utilizes a 193 nm optical lithography along with 300 mm process tools for dielectric deposition, reactive ion etch, wet-clean, CMP, and in-line metrology—all tools typical for a 300 mm wafer CMOS foundry. Theprocess development was guided by measurements of the physical and electrical characteristics of the planarized structures. Physical characterization such as atomic force microscopy across the 300 mm wafer surface showed that local topography was less than 5 nm. Electrical characterization confirmed low leakage at room temperature, and less than 12% within wafer sheet resistance variation for damascene Ta line widths ranging from 100 nm to 3 μm. Run-to-run reproducibility was also evaluated. Effects of process integration choices including the deposited thickness of Ta are discussed.

Optimization of converter and bremsstrahlung characteristics for object irradiation

The four-layer converter consisting of Ta+H2O(2 mm)+Fe(2 mm)+Pb is considered. The influence of the Ta and Pb layers thicknesses on the penetration power of bremsstrahlung (BR) produced by 7.5 MeV electrons in the converter has been studied. The average BR energy increases with increase of Ta and Pb layers thickness due to the absorption of low-energy photons in Ta and Pb. Absorbed doses in an object caused by a single element of a small size converter (SEC) are calculated by the Monte Carlo method. The total absorbed doses in the object are determined by summing the doses from the SEC placed along the extended converter. The densities of the electron beam along the converter are determined for two- and four-sided irradiation of objects of given sizes, which provide the minimum Dose Uniformity Ratio (DUR) magnitudes. The polyethylene thickness is shown to be by the factor 1.6 larger in the case of four-sided irradiation by electron beam with optimal density and DUR < 1.5 than in the case of two-sided irradiation.

Maximizing spin Hall magnetoresistance in heavy metal/crystalline metallic ferromagnet multilayers with opposite spin Hall angles.

Interconversion between charge and spin through spin-orbit coupling at a heavy metal (HM)/ferromagnet (FM) interface plays a key role in determining the amplitude of spin Hall magnetoresistance (SMR), which might maximally facilitate its applications in novel electronics. In this study, annealed NiFe films grown on MgO (100) substrates capped with Pt and Ta are reported to exhibit a maximum SMR. When the measuring temperature is reduced, the SMR rises and is significantly larger in crystalline NiFe than in amorphous NiFe. Another physical process for the negative SMR in Ta(dTa)/Pt(3 nm)/annealed NiFe samples is attributed to the interfacial spin-orbit coupling (ISOC) driven spin current (Js) generation and its reciprocal effects. Moreover, spin accumulation is enhanced at Pt(3 nm)/annealed NiFe interfaces after capping with a Ta layer, which functions as a spin sink in a certain thinner thickness range. With the cooperative interaction of choosing the proper Ta's thickness and annealing NiFe layers, the maximum SMR is obtained. Our results pave the way for rational interface engineering to enhance SMR for developing high-efficiency spintronic devices.

Role of Spin Transport through the β-Ta/Co20Fe60B20 Interface on its Ultrafast Demagnetization: Implications for Ultra-High-Speed Spin-Orbitronic Devices

Femtosecond laser-induced spin manipulation has fueled intense interest but understanding its underlying microscopic mechanisms in complex systems such as nonmagnet (NM)/ferromagnet (FM) heterostructures having strong spin-orbit effect is still at its infancy. Here, we report on the ultrafast demagnetization, remagnetization, and damping study in β-Ta(t nm)/Co20Fe60B20(d nm)/SiO2(2 nm) thin-film heterostructures by systematically varying both the Ta and Co20Fe60B20 thicknesses. Based on experimental results, we have established a direct relationship between the variation of the demagnetization rate and the Gilbert damping constant, indicating interface spin transport as the prevailing mechanism for both the ultrafast demagnetization and the damping. At higher thicknesses (t ≥ 7 nm) of β-Ta, the spin accumulation coefficient is found to be ∼0.24 eV, which is about 1.8 times less than its value in the lower thickness regime (t < 7 nm). These results will have important implications toward the evolution of ultra-high-speed spin-orbitronic devices.

Ta thickness effect on field-free switching and spin–orbit torque efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer

Current induced spin–orbit torque (SOT) switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications. In this work, we systematically investigated the effect of Ta thickness on the magnetic properties, field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer with perpendicular magnetic anisotropy. We found that both the anisotropy field and coercivity increase with increasing Ta thickness from 0.15 nm to 0.4 nm. With further increase of Ta thickness to 0.5 nm, two-step switching is observed, indicating that the two magnetic layers are magnetically decoupled. Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness. Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for the β DL decrease as the Ta spacer thickness increases. The studied structure with the incorporation of a CoFeB layer is able to realize field-free switching in the strong ferromagnetic coupling region, which may contribute to the further development of magnetic tunnel junctions for better memory applications.

All-Optical study of Gilbert damping and spin orbit torque in Ta/CoFeB/SiO2 heterostructures

Pure spin-current induced spin–orbit torque in a magnetic layer can externally control its magnetization dynamics including Gilbert damping. Here, we demonstrate control over Gilbert damping (Δα) in Substrate/β-Ta(t)/CoFeB(3 nm)/SiO2(2 nm) heterostructures with widely varying Ta thickness (3 ≤ t ≤ 20 nm) having stable β-phase using all-optical time-resolved magneto-optical Kerr effect. The pure spin-current due to the spin Hall effect in β-Ta exerts both damping-like and field-like spin–orbit torque to the CoFeB layer. We estimate the damping-like-torque efficiency over a wide range of t with and without Joule heating. In both cases, we obtained a remarkably high-value of damping-like-torque efficiency (ξDL) ∼ 0.40, suggesting that Joule heating has a negligible effect on the Δα. However, the modulation of precession frequency mainly originates from the Joule heating where contributions from field-like-torque and Oersted field are negligible. The high-value of ξDL and its stability over a wide-range of t will be key ingredients for future energy-efficient spintronic and magnonic devices.

Improvement of textured AlCu with Ta underlayer on LiNbO3 substrate

Improving the lifetime of surface acoustic wave filters requires reduction of electromigration effects. We report on the growth mechanism of AlCu2% films deposited by the e-beam physical vapor deposition technique. The state of the art shows that the introduction of an underlayer that alters the surface free energy can change a film’s growth mode or improve the earliest stages of film formation. In this work, this will be achieved by using an ultra-thin (&amp;lt;5 nm) Ta underlayer between the LiNbO3 substrate and the AlCu2% film. The effects of the Ta underlayer on the microstructure of AlCu2%/LiNbO3 films are investigated. An increase in the surface energy of the LiNbO3 substrate is observed with the addition of a 1.3 nm thick Ta underlayer. The crystalline quality of the AlCu2% thin film with a Ta underlayer is measured using XRD techniques. A post-deposition heat processing technique is also used to recrystallize the films. The AlCu2%/1.3Ta/LiNbO3 film annealed at 250 °C improved the electrode quality with the increase of 16% of the grain size.

Diffraction enhanced imaging utilizing a laser produced x-ray source.

Image formation by Fresnel diffraction utilizes both absorption and phase-contrast to measure electron density profiles. The low spatial and spectral coherence requirements allow the technique to be performed with a laser-produced x-ray source coupled with a narrow slit. This makes it an excellent candidate for probing interfaces between materials at extreme conditions, which can only be generated at large-scale laser or pulsed power facilities. Here, we present the results from a proof-of-principle experiment demonstrating an effective ∼2 μm laser-generated source at the OMEGA Laser Facility. This was achieved using slits of 1 ×30μm2 and 2 ×40μm2 geometry, which were milled into 30 μm thick Ta plates. Combining these slits with a vanadium He-like 5.2keV source created a 1D imaging system capable of micrometer-scale resolution. The principal obstacles to achieving an effective 1 μm source are the slit tilt and taper-where the use of a tapered slit is necessary to increase the alignment tolerance. We demonstrate an effective source size by imaging a 2 ± 0.2 μm radius tungsten wire.

Spin-wave nonreciprocity and formation of lateral standing spin waves in CoFeB/Ta/NiFe meander-shaped films

Studying the spin-wave (SW) propagation in 3D periodic structures opens new possibilities for joining functional units placed on the different layers of the magnonic circuitry. In the path toward 3D magnonics, the main challenge is the fabrication of large-scale 3D magnetic structures with nanometric precision control of geometry and material composition. In this work, we study the dependence on the Ta spacer thickness of the magnonic band structure, measured by Brillouin light scattering spectroscopy, of CoFeB/Ta/NiFe meander-shaped bilayers fabricated on pre-patterned Si substrate with thickness steps of 50 nm. Both propagating and stationary SW modes are observed. While the frequency of the dispersive mode slightly depends on the Ta spacer thickness, the frequency position of the three stationary modes in the lowest frequency range of the spectra significantly increases by increasing the Ta thickness. Micromagnetic calculations indicate that each of the three stationary modes is composed of a doublet of modes whose frequency separation, within each doublet, increases by increasing the mode frequency. The origin of this frequency separation is ascribed to the dynamic dipolar coupling between the magnetic layers that generate a significant frequency nonreciprocity of counterpropagating SWs. For these reasons, the investigated structures offer potential application as the nonreciprocal versatile interconnections performing the frequency selective regimes of signal propagation in magnonic circuits.

Atomistic simulations of mechanical response of a heterogeneous fcc/bcc nanolayered composite

Molecular dynamics simulations are performed to study the mechanical properties and deformation mechanisms of a heterogeneous face-centered cubic/ body-centered cubic Cu/Ta nanolayered composite under uniaxial tension and compression. The results show that the stress–strain curves exhibit two main yield points in tension while only one yield point during compression, and the deformation primarily experiences three stages. The first stage is linearly elastic at small strains, followed by the nucleation and propagation of dislocations and stacking faults in the Cu layers, and eventually the Ta layers yield to plastic deformation. The yield of the specimen is mainly determined by the dislocation evolution in the hard phase (i.e. Ta layers), which leads to a sharp drop in the stress–strain curve. We show that the heterogeneous nanolayered composite exhibits a good deformation compatibility during compression but an obvious deformation incompatibility between Cu and Ta layers in tension. The temperature effect is also systematically investigated. It is revealed that the yield of the specimen at higher temperature depends only on the dislocation evolution in the thick Ta layers, and the yield strengths in tension and compression both decrease with the increasing temperature. In particular, our computations show that high temperature can significantly suppress the dislocation activities in the Cu layers during deformation, which results in a lower dislocation density of the Cu layers compared with that of the Ta layers and thus causing an incompatible fashion among the constituent layers.

OPTIMIZATION OF BREMSSTRAHLUNG CHARACTERISTICS FOR IRRADIATING THICK OBJECTS

The characteristics of bremsstrahlung (BS) irradiated at different angles from a three-layer converter made of Ta, water, and Fe, the electron energy is 7.5 MeV, was investigated. It is shown that Ta thickness increasing leads to increasing of Eav – the average energy of BS, but Eav decrease with increasing BS emitted angle relative to the electron trajectory. It is shown that the depth-dose distribution of the irradiated polyethylene depends on both the incident angle on the surface and the spectral composition of BS. For double-side irradiation, the maximum object thickness depends on the BS angle interval at a fixed dose inhomogeneity DUR. The use of BS filters made of heavy materials was proposed for irradiation of materials requiring high depth-dose uniformity (small DUR values).