Ta Ions Research Articles

The electron cyclotron resonance coupled to laser ion source for charge state enhancement experiment: Production of high intensity ion beams by means of a hybrid ion source

The experiment concerning the ECLISSE method (ECR ion source coupled to a laser ion source for charge state enhancement) has been carried out by coupling a laser ion source (LIS) to the superconducting electron cyclotron resonance source (SERSE) electron cyclotron resonance (ECR) ion source with the goal to obtain intense beams of highly charged ions (cw or pulsed mode) from metal samples, especially from refractory elements. The coupling efficiency of the ion beam produced by the LIS with the ECR plasma was remarkable and the measured beam intensities were quite high. The maximum charge states, obtained with a good reproducibility, were 38+ for Ta and 41+ for Au. The highest current was obtained for 25+ and 28+ for Ta and Au ions, respectively, and it was in both cases of the order of some tens of microampere, i.e., higher than the current obtained from SERSE with other methods (i.e., evaporation and sputtering). The ion beam stability and reproducibility were both acceptable. The possibility to get a further enhancement of the available charge states was limited by charge exchange processes connected with the target ablation. The main features of the LNS facility based on a Nd:YAG (yag, yttrium aluminum garnet) laser (0.9J∕9ns, laser power densities <5×1010W∕cm2) and on the SERSE superconducting ECRIS working in single frequency mode (18GHz) will be shown in the following. The analysis of the results and the way to get rid of the existing limits will be also presented and discussed.

Changes in electronic structure upon lithium insertion reaction into the A-site-deficient perovskite-type oxides, Gd 1/3TaO 3: Part 1. XAS measurements

Electrochemical behavior and the variation of electronic structure upon lithium insertion into the A-site-deficient perovskite oxide, Gd 1/3TaO 3, have been studied by X-ray absorption spectroscopy (XAS). During electrochemical lithium insertion, Gd L III-edge and Ta L I-edge XAS revealed that Gd ion did not contribute the charge compensation, while Ta ion reduced its oxidation state. Furthermore, the changes in O K-edge spectra with electrochemical lithium insertion were clearly observed, indicating that O ions also contribute to the electron-transfer reaction.

Influence of the Ta doping on the peritectic transformation of YBaCuO superconductor

In this work we present a systematic study of the influence of Ta doping on the YBa 2Cu 3O 7− δ (Y123) high T c superconductor. The results reveal that Ta ion substitutes the yttrium site in the lattice and the stoichiometry can be represented by Y 1− x Ta x Ba 2Cu 3O y in the interval 0⩽ x⩽0.08. The differential thermal analysis curves show displacement of the peritectic temperature from 1020 °C in x=0 to 950 °C in x=0.08. These significant displacements in the peritectic line suggest that the material can be textured at lower temperature compared with pure Y123. The results show that a second phase of the YTa 1.6Ba 3.5Cu 0.7O y composition segregates within of the grain. This fact suggests this phase can act as pinning center. All the results indicate that Ta content does not change the onset and offset of the superconducting transition temperature. The X-ray diffraction data show that textured material presents only peaks related to the reflections (0 0 l) and the excellent preferential orientation is confirmed by rocking curve which presented FWHM ∼0.2°.

Nonlinear optical response of Ta nanoparticles embedded in insulators by 60 keV negative ion implantation

Linear and nonlinear optical properties of Ta nanoparticle composites, fabricated by negative ion implantation, were studied in the visible range. Negative Ta ions of 60 keV were implanted into amorphous SiO 2 and crystalline TiO 2 with a total fluence of 3 × 10 16 ions/cm 2. Spheres of Ta particles of 10–40 nm in diameter are distributed near the surface in amorphous SiO 2. Optical absorption evidently indicated a surface plasmon peak around 2 eV and the peak resulted from formation of nanoparticles embedded in the matrices. The plasmon peak shifted depending on the refractive index of the substrates. Laser-induced transient absorption was measured with the technique of pump-probe femtosecond spectroscopy. The transient absorption of the Ta nanoparticle composite in SiO 2 recovered in several picoseconds due to energy transfer from the excited electrons to the lattice via the electron–phonon interaction. The transient response was comparable to that of the noble metals. The electron–phonon coupling was evaluated by the two-temperature model and the coupling constant yielded a value of g=3.1×10 18 W/m 3 K. The Ta nanoparticle composite has the advantage of greater thermal stability in comparison with Cu nanoparticle composites.

Charge-energy distribution of Ta ions from plasmas produced by 1ω and 3ω frequencies of a high-power iodine laser

The high-power iodine laser system PALS (λ0=1.315 μm at the fundamental laser frequency, 1ω, and λ1/3=0.438 μm at the third harmonic frequency, 3ω), with a maximum laser intensity IL of up to about 3×1016 W/cm2, was used to generate highly charged Ta ions. Maximum ion charge states slightly above z=50+ were determined by using an electrostatic ion energy analyzer and the maximum energy of emitted ions, estimated from the ion collector signals, was even higher than Ei=22 MeV, as determined by track detectors. Charge-state distributions, as well as charge-energy distributions were evaluated for both 1ω and 3ω laser frequencies. The focus position with regard to the target surface (in addition to the focus spot size) determines not only the laser power density deposited and the amount of produced ions, but it also directly influences the mechanisms of ion generation. Highly charged ions with the charge states above 50+ can be generated either by using a sufficiently high laser intensity (about 1×1016 W/cm2) or, at lower laser intensities (IL>2×1014 W/cm2), in the case where the conditions for the relativistic self-focusing are met.

Tribological properties changes of H13 steel induced by MEVVA Ta ion implantation*1

Tribological properties changes of H13 steel induced by MEVVA Ta ion implantation*1

Theoretical study of structural and electronic properties ofβ−Ta2O5andδ−Ta2O5

Using density functional theory within the local density approximation (LDA) and generalized gradient approximation (GGA), we discuss the relative stability of the orthorhombic (or the $\ensuremath{\beta})$ phase and the hexagonal (or the $\ensuremath{\delta})$ phase of tantalum pentoxide. We find that, both LDA and GGA pseudopotential calculations favor the $\ensuremath{\delta}$ phase, whereas spin-orbit all-electron calculations favor the $\ensuremath{\beta}(\ensuremath{\delta})$ phase within the LDA (GGA); however, the all-electron energy differences are too small to be significant. The spin-orbit coupling has a significant effect on the band gaps and the band gap is indirect (direct) in the $\ensuremath{\delta}(\ensuremath{\beta})$ phase. The chemical bonding between Ta and oxygen ions is of a mixed type (mainly ionic but partly covalent).

Tribological properties changes of H13 steel induced by MEVVA Ta ion implantation

The tribological properties of Ta-implanted H13 steel was studied using a metal vapor vacuum arc (MEVVA) ion source. The doses of Ta and C ions implanted on H13 steel were 5×1017 and 2×1017cm−2, respectively. The extraction voltages were 48kV for Ta implantation and 30kV for C implantation. Rutherford backscattering spectrum (RBS) was used to measure the surface composition of the samples implanted. The observation of phase induced by Ta, C implantation was carried out by grazing-angle X-ray diffraction (GXRD). The wear test of the implanted surface revealed that Ta+C dual implantation reduced the wear of the implanted steel by nearly a factor of 2. This wear mechanism of the Ta-implanted steel was compared with that of Ti implantation.

Co-existence of ferroelectricity and ferromagnetism in 1.4 nmSrBi2Ta2O11 film

In pseudo-tetragonal strontium bismuth tantalate,SrBi2Ta2O9 (SBT), with two formula units per unit cell, bismuth oxide{(Bi2O2)2+} layers alternate with double strontium tantalate perovskite layers{(SrTa2O7)2−}.A unit cell of SBT is truncated to form a sub-cell or film, of compositionSrBi2Ta2O11,which is 1.4 nm thick and comprised of a bottom(BiO2)1+ layer, acentral (SrTa2O7)2− layerand a top (BiO2)1+ layer. Using spin-polarized first-principles calculations, it is found that thisSrBi2Ta2O11 film is multi-ferroic, magnetoelectric, i.e. it simultaneously exhibits ferroelectricand ferromagnetic characteristics. When Ta ions are collectively displaced in theab plane and in the [110] direction, the calculated double potential energy well, with a depth of−3.1 eV/unit cell at a Ta off-centre displacement of 0.032 nm, reflects the ferroelectric character. Thecalculated spin-polarized electronic structure reveals that ferromagnetism stems, not fromthe d electrons of the Ta ions, but predominantly from the unpaired p electrons ofthe O ions. The O ions in the Sr–O layer have the largest magnetic moment of1.32 μB. Specifically,the ferromagnetic character is mediated by the unoccupied states of the Sr 5p band above the Fermilevel, EF.These states provide a mechanism for the double exchange or hopping of highly localizedO 2p (majority) spins between adjacent O ions located on both sides of the Sr ion.

Structural and electronic properties of SBT in FEDREAM devices

In the present study, we performed first-principles modeling of calculation on electricity behavior of ferroelectric strontium bismuth tantalate (SBT). Different cluster models were chosen for the discussion of the influence of atomic coordination on the atomic valence configuration, atomic charge, and bond order etc. in the DV-Xα calculations. This allowed us to understand size effects of cluster on the electronic structure of SBT. The results of first-principles calculations of the electronic structure in SrBi 2Ta 2O 9 (SBT) were reported. The electronic density distribution indicates density of states induced local levels within the gap, and finds significant hybridization between metal d states and the O 2p–Ta 5d and Ta 6s state. The charge of Sr is transferred to the oxygen atom, the bonding between them was nearly ionic bonding. The calculated electronic structure of SBT indicates that the absence of an energy gap in the vicinity of the fermi level stems from lowering of the Sr orbital energies due to its lower electro-negativity relative to Ta and Bi ions, and significant hybridization between Ta, Bi and O ions. The calculated total densities of states were in agreement with the reported X-ray photoemission spectroscopy data.

Ordering in (La,Sr)(Al,Ta)O3 substrates

(La, Sr)(Al, Ta)O3 (LSAT) has recently received increased attention as a substrate for the deposition of various oxide films. LSAT is usually considered as having a perovskite structure. However, the exact atomic structure of LSAT is not yet well known and has received little attention up to now. In this paper, a series of studies using x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometry were conducted to determine the atomic structure of LSAT. It was found that LSAT consists of two types of domains: one with a simple cubic perovskite structure (disordered with a = 0.3868 nm) and the other with a face-centered-cubic structure (ordered with a = 0.773 nm). Computer image simulation of high-resolution lattice images suggests that the ordered structure is due to ordering of the Al and Ta ions.

Formation of TaSi 2 and associated fractal growth on Si surface upon high current pulsed Ta-ion implantation

Using a metal vapor vacuum arc ion source, tantalum ion implantation was conducted to synthesize TaSi 2 phases on silicon wafers, and the continuous and stable TaSi 2 layers were directly obtained with neither external heating nor post-annealing. Interestingly, under some specific conditions, the formed TaSi 2 grains organized themselves in a fractal pattern featuring self-similarity. The mechanism of the TaSi 2 formation as well as the growth of the fractal pattern is discussed in terms of the temperature rise caused by the energetic Ta ions beam heating effect and the dose adjustment during high current pulsed Ta-ion implantation far from equilibrium.

Characteristics of ion emission from plasma produced by high-energy short-wavelength (438 nm) laser radiation

Efficient production of highly charged (z>45) high-energy (up to ∼20 MeV) Ta ions by the interaction of a short-wavelength subnanosecond laser pulse with a solid target has been demonstrated by experimental studies of ion emission from plasma generated by the PALS high-energy short-wavelength (3ω0) iodine laser system (⩽0.25 kJ, 0.4 ns, 0.438 μm, ⩽1016 W cm−2) in Prague. The plasma was investigated by means of ion diagnostics based on the time-of-flight method, i.e. ion collectors (ICs) and an electrostatic ion-energy analyser equipped with a windowless electron multiplier serving as an ion current detector. Five ICs were located at different angles with respect to the target normal. The existence of fast highly charged ions, as well as thermal and slow ions, has now been demonstrated for plasma produced by short-wavelength high-energy laser pulses, as it previously was for long-wavelength lasers

Nonlinear optical properties of metal nanoparticle composites for optical applications

Optical absorption and nonlinear optical response were investigated for nanoparticle composites in amorphous SiO 2 fabricated by negative Ta ion implantation at 60 keV. X-ray photoelectron spectroscopy was used to identify Ta and the oxide formation in the matrix. Optical absorption clearly indicated a surface plasmon peak at 2.2 eV and the peak resulted from formation of nanoparticles embedded in the matrix. The measured absorption was compared with calculated ones, evaluated by Maxwell-Garnett theory. Nonlinear absorption was measured with a pump-probe method using a femtosecond laser system. The pumping laser transiently bleached the surface plasmon band and lead to the nonlinearity. The transient response recovered in several picoseconds and behaved in terms of electron dynamics in metallic nanoparticles. The Ta nanoparticle composite is one of the promising candidates for nonlinear optical materials with good thermal stability.

Effects of Superlattice Ordering and Ceramic Microstructure on the Microwave Q Factor of Complex Perovskite-Type Oxide Ba(Zn1/3Ta2/3)O3

Effects of superlattice ordering and ceramic microstructure on the microwave dielectric properties of complex perovskite-type oxide Ba(Zn1/3Ta2/3)O3 polycrystalline ceramics are studied. The superlattice ordering ratio was controlled by the sintering time at 1350°C. The superlattice ordering of Zn and Ta ions on B sites increased with increasing sintering time until 80h and reached a saturated value of 80%. However, the microwave Q factor of the samples showed a large variation of the same magnitude of the superlattice ordering ratio. This result suggests that the microwave Q factor of Ba(Zn1/3Ta2/3)O3 ceramics depends not only on the superlattice ordering but also on the ceramic microstructure.

Formation of low resistivity alpha Ta by ion beam sputtering

The properties of tantalum thin film prepared by ion beam sputtering with Xe ions (0.6–1.5 KV) have been investigated. β-Ta thin films with high resistivity (170 μΩ cm) on Si substrate were obtained without Cr underlayer. With Cr underlayer, however, a body-centered-cubic phase (bcc) α-Ta thin film with low resistivity (20 μΩ cm) has been successfully obtained at room temperature. The experimental results indicate that the Cr underlayer plays an important role in α-Ta formation and that the critical thickness of Cr is 20 Å. Properties of α-Ta are also influenced by Ta thickness and ion beam deposition process conditions. α-Ta with lower resistivity was achieved by using approximate beam energy of 1000 eV and beam current of 150 mA. X-ray diffraction analysis indicates that changes in resistivity can be attributed to changes in microstructure that is influenced by the ion beam conditions.

Synthesis, crystal structure, and magnetic properties of ordered perovskites Sr 2LnTaO 6 (Ln = lanthanides)

A series of Sr 2LnTaO 6 (Ln=lanthanides except for La, Ce, and Pr) has been prepared by a standard ceramic method and their crystal structure has been determined by powder X-ray diffraction using the Rietveld analysis method. The crystal symmetry of their oxides is monoclinic (space group P2 1/ n) with an ordered arrangement of Ln and Ta ions. Magnetic susceptibility measurements show that these compounds are paramagnetic down to 5 K. The 151 Eu Mössbauer spectrum for Sr 2EuTaO 6 indicates that the Eu ion is in the trivalent state. The symmetry of the Eu site is distorted from the octahedral symmetry, and its spin–orbit coupling constant is determined to be 342 cm −1. In the Yb compound, the energy levels in the octahedral crystal field splitting are determined to be E Γ 7− Γ 6 =1324 and E Γ 8− Γ 6 =391 cm −1 by calculating the magnetic susceptibility.

Fast ion emission from the plasma produced by the PALS laser system

This paper presents the results of studies of fast ion emission from the multiply charged high-Z number plasma generated using the PALS high-energy iodine laser system (⩽1.2 kJ, 0.4 ns) at the PALS Research Center in Prague. The properties of the emitted ion streams were investigated using ion collectors located at various angles with respect to the target normal and an electrostatic energy analyser. The x-ray emission from the plasma was measured using semiconductor detectors. Different groups of ions (slow, thermal and fast) were observed in the ion collector signals. Ion current densities higher than 80 mA cm−2 at ∼1 m from the target were demonstrated. The charge velocity distribution, ion current density and angular distribution of ion charge emission, as well as total charge and average ion energy were obtained from these signals. Using the electrostatic ion-energy analyser, the emission of highly charged heavy ions (Ta52+, Ag38+) with energies up to 7 MeV for Ta ions was demonstrated. The dependence of ion stream parameters on the experimental conditions is discussed. We also report the results of preliminary experiments on the direct implantation of laser-produced ions into various materials.

Angular distribution of ions emitted from Nd:YAG laser-produced plasma

Angular distribution of ion currents emitted from laser-produced plasmas are reported for a Nd:YAG laser with intensities lower than 1×1010 W/cm2. This distributions are strongly peaked along the normal to the target surface for Cu, Sn, Ta, W, Au, and Pb ion streams, independent of the incidence angle of the irradiated target. For Al, Ni, and Nb the main axis tends to decline to about −10°. The comparison of fits of Gaussian function and cosP(α−α0)+y0 to the experimental data verified the formal equivalency of both the functions. Fitted values of the FWHM and of the exponent P are compared for all the elements used. The angular distribution of mean ion velocity 〈v〉 and ion kinetic energy 〈E〉 are presented.

Preparation and Luminescent Characteristics of Phosphate-Based Phosphors

In order to search new phosphors for plasma display panel(PDP), phosphate hosts which has a host excitation band at around 150nm were prepared and their luminescent properties were investigated. In the preparation of <TEX>$YPO_4: Eu\; and\; (Y,Gd)PO_4: Eu$</TEX> phosphors, the effect of oxide and oxalate starting materials on prepared phosphors were compared in terms of relative emission intensities and particle characteristics. The results showed that oxalate starting materials gave better performance in emission intensities and smaller size and more round shape phosphors which would be more applicable for high resolution display. Additionally, Gd, V, Nb and Ta ions were doped to <TEX>$YPO_4:Eu$</TEX> and the luminescent properties of the resulant solid solutions were investigated to find efficient sensitizer. Among these ions, Gd, V and Nb ions increased the emission intensities of parent phosphor to around 10%. While Nb ion gave the best result in emission intensities, CIE color coordinate were improved by doping V ion into <TEX>$YPO_4:Eu$</TEX> phosphor to give x=0.6523, y=0.3406 compared to commercial sample.