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The article presents the results of studies of the features and regularities of high-intensity nitrogen ion implantation into titanium using repetitively-pulsed beams with high average power densities. It is shown that the method of low-energy high-intensity nitrogen ion implantation at current densities of 180, 140, 60, and 10 mA/cm2 makes it possible to obtain wide ion-doped layers in titanium. The regularities of changes in both thickness and elemental composition of ion-doped layers depending on the ion current density have been established. It has been established that a wide diffusion layer is observed at ion current densities from 60 to 180 mA/cm2. Nitrogen concentration in the diffusion layer increases with an increase in the ion current density. The article presents the transmission electron microscopy data showing that the modified layers at a depth of 10 μm consist of α-Ti, in the volume of which nanosized particles of δ-TiN with average size of 15.4 nm crystallize. [ABSTRACT FROM AUTHOR]

Motion of point defects is a fundamental process that governs microstructure and properties of materials. Here, we examine the near-surface and grain boundary cavity swelling depth profiles in neutron- and ion-irradiated simple metals (Cu, Ni, and Fe-Cr) and investigate diffusional broadening of implanted Ni ions in Fe-Cr alloys. Vacancy migration energies and radiation-enhanced diffusion were experimentally estimated. Cavity denuded zone widths near planar sinks are shown to be dependent on temperature, damage rate, balance of point defects and sinks, and vacancy migration energies. An enhanced cavity swelling zone adjacent to the void-denuded zone was observed in specimens with low to moderate sink strength and interpreted as evidence of 1D gliding interstitial clusters. Radiation-enhanced diffusional broadening of implanted Ni ions (at 400–550 °C) in Fe and Fe-Cr was up to 250 nm toward the surface, which leads to a much broader near-peak-damage region where cavity swelling is suppressed. Diffusional broadening of implanted ions is calculated to be similarly pronounced for self-ion irradiations, particularly near the peak and higher swelling temperature regimes. Adequately high ion energies (∼8–15 MeV) are recommended for ion-irradiation studies to provide a sufficiently broad midrange safe analysis region with minimized surface and injected ion effects.

The radiation enhanced diffusion (RED) of three key fission products in SiC: cesium, europium, and strontium was investigated following ion irradiation at a damage rate of 4.6 × 10-4 dpa s-1 at temperatures between 900° C and 1100° C. The radiation enhancement of diffusion was as large as 107 at 900° C, and dropped to a value of 1 by 1300° C for all but cesium grain boundary diffusion. Strontium and cesium exhibited several orders of magnitude enhancement for both mechanisms. Europium enhancement was greatest at 900° C, but dropped to the thermal rates at 1100° C for both mechanisms. The trends in the RED mechanism correlated well with the point defect concentrations suggesting that both carbon and silicon vacancy concentrations are important for fission product diffusion. These constitute the first radiation-enhanced diffusion measurements of strontium, cesium and europium in SiC.

A method for calculating diffusion coefficients DFe and DCr and interdiffusion coefficient in an irradiated Fe–Cr alloy is proposed. The substitution of the values of the self-diffusion coefficient of iron into Darken's equation refined by Manning, which are determined with allowance for the radiation enhanced diffusion and the formation of vI and iI complexes (v is a vacancy, i is a self-interstitial atom, and I is an impurity atom), makes it possible to obtain the temperature and concentration dependences of DFe, DCr, and D at various rates of generation of radiation point defects (dpa/s). [ABSTRACT FROM AUTHOR]

[Display omitted] • Texture formation in NC Ni under self-ion irradiation at 250–550 °C was studied using EBSD. • Irradiation at 250 °C strengthens the as-deposited <1 0 0> texture by ion beam mixing at GBs. • Irradiation-induced recrystallization occurs at 350 °C, downward shifting of 100 °C relative to thermal. • At 350 °C, 450 °C, irradiation enhances the thermally-induced texture, <1 1 1> by radiation enhanced diffusion. • Thermally-activated texture reversal occurred at 550 °C and irradiation enhances this <1 0 0> texture. The application of nickel coatings on structural materials in molten salt reactors for corrosion resistance is being researched. For corrosion resistance, the coatings must have specific texture and grain boundary characteristics that withstand irradiation. While most reported results concern textural changes caused by room-temperature irradiation, research in the thermally-assisted regime, which is the operating temperature range of nuclear reactors, is limited. In this study, we investigate the effect of 1.4 MeV Ni+ ion irradiation on the texture, recrystallization, and grain boundary characteristics of nanocrystalline Ni at temperatures ranging from 250 °C to 550 °C. Thermal activation at 350 °C and 450 °C results in partially and fully recrystallized microstructures, respectively. A concurrent decrease of <1 0 0>//ED and evolution of <1 1 1>//ED, as well as minor orientations that reduces surface energy, are detected up to 450 °C; nevertheless, textural reversal is found at higher temperatures. Irradiation accelerated the recrystallization kinetics, resulting in a fully recrystallized microstructure at temperatures 100 °C lower. Irradiation at temperatures above 350 °C increased the thermally-induced texture; at 250 °C, this trend reversed. Calculated radiation-enhanced diffusion (RED) coefficients at 250 °C revealed that ion mixing drives the growth of <1 0 0> by consuming <1 1 1> orientations. Conversely, the increasing RED contribution at higher temperatures strengthens the thermally-induced textures. [ABSTRACT FROM AUTHOR]

Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing. [ABSTRACT FROM AUTHOR]

The radiation enhanced diffusion (RED) of three key fission products in SiC: cesium, europium, and strontium was investigated following ion irradiation at a damage rate of 4.6 × 10 −4 dpa s −1 at temperatures between 900° C and 1100° C. The radiation enhancement of diffusion was as large as 10 7 at 900° C, and dropped to a value of 1 by 1300° C for all but cesium grain boundary diffusion. Strontium and cesium exhibited several orders of magnitude enhancement for both mechanisms. Europium enhancement was greatest at 900° C, but dropped to the thermal rates at 1100° C for both mechanisms. The trends in the RED mechanism correlated well with the point defect concentrations suggesting that both carbon and silicon vacancy concentrations are important for fission product diffusion. These constitute the first radiation-enhanced diffusion measurements of strontium, cesium and europium in SiC. [ABSTRACT FROM AUTHOR]

Single crystal UO 2 thin films with Nd as tracer elements in the film mid-plane have been grown on yttria-stabilized zirconia (YSZ) substrates. The films were irradiated with 1.8 MeV Kr + ions in the temperature range from 400 °C to 1113 °C, where an evident enhanced diffusion was found in UO 2 . The temperature dependent measurements have shown an activation energy of 0.56 ± 0.04 eV below 800 °C, and 1.9 ± 0.3 eV above 900 °C. The rate-dependent measurements have shown a linear dependence on the radiation flux, which indicates radiation enhanced diffusion (RED) is in the sink limited kinetics regime. Comparison of the RED results between UO 2 and CeO 2 has shown significant differences, which indicates that CeO 2 used as UO 2 surrogate may be questioned in terms of cation diffusion. [ABSTRACT FROM AUTHOR]

Abstract: B diffusion in crystalline Ge is investigated under equilibrium and non-equilibrium conditions in a large temperature range (200–800°C), in order to discriminate the role of self-interstitials (Is) and the energy barriers involved in the microscopic mechanism of B migration. To this aim, we copiously furnished Is by 200 or 300keV H+ irradiation, and performed a direct comparison with B diffusion in thermal conditions at the same temperature (T). The diffused profiles of B were simulated assuming the kick-out model, and the extracted parameters (migration length, λ, and formation rate of mobile B, g) indicated that the B diffusion is always mediated by Is showing different features at low and high T regimes. For T lower than 600°C the thermal generation of Is is negligible and the only barrier to g (measured to be ∼0.1eV) is due to the Is migration and B mobile formation. At T higher than 600°C, the thermal generation of Is starts to overcome the Is supply from the irradiation, and the activation energy of g increases to 3.0–3.5eV. The migration length in the low-T regime has the largest value (∼20nm), while it decreases down to 1–2nm by increasing T, showing a negative activation energy of ∼−0.64eV, compatible with a dissociation process which stops the diffusion event. In this regard, we observed that the mobile B migration length depends only on T, regardless of the point defects concentration. These results and the energy barriers measurements contribute to a further comprehension of the B diffusion and point defects in crystalline Ge. [Copyright &y& Elsevier]

Abstract: It has been known for a long time that the maximum areal density of inert gases that can be retained in solids after ion implantation is significantly lower than expected if sputter erosion were the only limiting factor. The difference can be explained in terms of the idea that the trapped gas atoms migrate towards the surface in a series of detrapping–trapping events so that reemission takes place well before the receding surface has advanced to the original depth of implantation. Here it is shown that the fluence dependent shift and shape of implantation profiles, previously determined by Rutherford backscattering spectrometry (RBS), can be reproduced surprisingly well by extending a simple retention model originally developed to account only for the effect of surface recession by sputtering (‘sputter approximation’). The additional migration of inert gas atoms is formally included by introducing an effective shift parameter Y eff as the sum of the sputtering yield Y and a relocation efficiency Ψ rel. The approach is discussed in detail for 145keV Xe+ implanted in Si at normal incidence. Y eff was found to increase with increasing fluence, to arrive at a maximum equivalent to about twice the sputtering yield. At the surface one needs to account for Xe depletion and the limited depth resolution of RBS. The (high-fluence) effect of implanted Xe on the range distributions is discussed on the basis of SRIM calculations for different definitions of the mean target density, including the case of volume expansion (swelling). To identify a ‘range shortening’ effect, the implanted gas atoms must be excluded from the definition of the depth scale. The impact-energy dependence of the relocation efficiency was derived from measured stationary Xe concentrations. Above some characteristic energy (∼20keV for Ar, ∼200keV for Xe), Y exceeds Ψ rel. With decreasing energy, however, Ψ rel increases rapidly. Below 2–3keV more than 90% of the reemission of Ar and Xe is estimated to be due to bombardment induced relocation and reemission, only the remaining 10% (or less) can be attributed to sputter erosion. The relocation efficiency is interpreted as the ‘speed’ of radiation enhanced diffusion towards the surface. The directionality of diffusion is attributed to the gradient of the defect density on the large-depth side of the damage distribution where most of the implanted rare gas atoms come to rest. Based on SRIM calculations, two representative parameters are defined, the peak number of lattice displacements, N d,m, and the spacing, △z r,d, between the peaks of the range and the damage distributions. Support in favour of rapid rare gas relocation by radiation enhanced diffusion is provided by the finding that the relocation efficiencies for Ar and Xe, which vary by up to one order of magnitude, scale as , independent to the implantation energy (10–80keV Ar, 10–500keV Xe), within an error margin of only±15%. The parameter k contains the properties of the implanted rare gas atoms. A recently described computer simulation model, which assumed that the pressure established by the implanted gas drives reemission, is shown to reproduce measured Xe profiles quite well, but only at that energy at which the fitting parameter of the model was determined (140keV). Using the same parameter at other energies, deviations by up to a factor of four are observed. [Copyright &y& Elsevier]

Abstract: About 10MeV helium and 120MeV neon implantations were used for the local lifetime control of silicon power diodes with subsequent annealing at 200°C. DLTS measurements show that the concentration ratio between VO(–/0) pairs and divacancies after the implantation of neon is close to one in agreement with the data published for other heavy ions. The implantation dose to achieve the same point at the technology curve of the diodes under test was found about 10 times lower for the neon compared to helium. The radiation enhanced diffusion (RED) of platinum at 725°C was evaluated both for the enhancement by implantation of helium and neon. The electrical parameters of silicon diodes (carrier lifetime, voltage drop, leakage current and reverse recovery) were compared. One order lower implantation dose of the neon compared to that of the helium was found necessary to obtain the same improvement of electrical parameters. The RED of Pt using the neon implantation was found functional in a similar way to that of the helium. The reduction of carrier lifetime, which would be normally sufficient for robust diodes, was found for the doses of neon at about 1×1013 cm−2. However, the simultaneous increase of background doping concentration at the end of range of neon, which increases electric field, was found responsible for the decreased static breakdown voltage, decreased turn-off ruggedness and increased leakage current. [Copyright &y& Elsevier]

Abstract: Ta/Si interfaces were systematically studied concerning ion beam mixing effects. Tantalum was evaporated on silicon of (100) and (111) orientation using the molecular beam epitaxy (MBE) method. The samples were then irradiated with 1.85MeV and 6MeV Ar, 90keV O and 90keV C. Rutherford backscattering spectroscopy (RBS) was used to examine mixing effects. Atomic force microscopy (AFM) was applied for investigating the surface roughness. Ballistic mixing, radiation enhanced diffusion and thermal spike effects were found in both systems. Si substrates of the orientation (100) led to smaller mixing rates at the Ta/Si interface as compared to Si(111). [Copyright &y& Elsevier]

Abstract: A mass transfer model for metal ion implantation into a metal target at elevated temperatures has been built up based on transport of ions in matter and radiation enhanced diffusion. It is used to calculate concentration-depth profiles and compositional changes of the implanted species. The ion implantation at elevated temperatures was simulated by a dynamic Monte Carlo (MC) method, which takes into account a local saturation in the crystalline target by using a maximum atomic fraction allowed in the matrix. For the diffusion process, the transport of the implanted species was obtained from the diffusion equations for the implanted species and nonequilibrium vacancies. The radiation enhanced diffusion coefficient was obtained by taking into account linear annealing of the defects. A nonequilibrium vacancy source function and surface sputtering were introduced into the diffusion equations. Concentration-depth profiles of Cr, Fe and Ni ions implanted into Al at a temperature range from 200 to 510°C were calculated. The calculated results principally were consistent with measured concentration-depth profiles obtained by Rutherford backscattering spectroscopy (RBS). In some cases deviations occur, which are discussed. [Copyright &y& Elsevier]

Systematic ion beam mixing experiments have been performed on Ta/SiO2 and Ta/Si interfaces. Tantalum was evaporated on silicon and SiO2/silicon substrates by means of molecular beam epithaxy. Samples were subsequently irradiated with 500 keV Si, 100 keV C and 100 keV O ions to different ionic fluences. The irradiated samples were studied by Rutherford backscattering spectrometry (RBS) to obtain the depth profiles and the interdiffusion parameters at the interfaces. Atomic force microscopy (AFM) was used to examine the surface roughness before and after irradiation. Ballistic mixing was found in both systems. Additional contributions to diffusion parameters were thermal spike effects (Ta/Si) and chemical reactions (Ta/SiO2). Radiation enhanced diffusion was found to be the dominant process above room temperature in both systems. [Copyright &y& Elsevier]

We report on the diffusion of Bi, Er and Eu in the photoresist S1813. The implantation of Bi into the resist at low energies (E=20 keV) and fluences (Φ=1012 cm−2) allowed us to minimize both radiation damage and cluster formation. The impurity redistribution in the samples annealed between 100 and 300 °C was determined using the Rutherford backscattering technique. The results for Bi indicate regular thermal diffusion with an activation energy of Ea=680 meV. At higher fluences, the trapping in radiation-induced defects influence the migration behavior. However, the activation energy is hardly influenced (650 meV for implanted Bi at 5 × 1012 cm−2). Both the lanthanides Er and Eu implanted into the resist at fluences of 5 × 1012 and 1013 at/cm2 show quite a similar behavior as Bi implanted at the highest fluence with similar values for the activation energy (Ea(Eu)=525 meV and Ea(Er)=530 meV). [Copyright &y& Elsevier]

The TRIUMF-ISAC facility target stations were designed for ISOL target irradiations with up to 100 μA proton beam currents. Since beginning operation in 1998, ISAC irradiation currents have progressively increased from initial values of ∼1 μA to present levels of up to 40 μA on refractory metal foil targets. In addition, refractory carbide targets have operated at currents of up to 15 μA for extended periods. The 1–40 μA operational regime is achieved by tailoring each target to the thermal requirements dictated by material properties such as beam power deposition, thermal conductivity and maximum operating temperature of the target material. The number of heat shields on each target can be varied in order to match the effective emissivity of the target surface for the required radiative power dissipation.Targets of different thickness, surface area and volume have been investigated to study the effect of diffusion and effusion delays on the yield of radioisotopes. For yields of short-lived products, believed to be dominated by diffusion delays, a consistent nonlinear increase of yield as a function of proton current has been observed. The nonlinear dependence is consistent with expectations from radiation enhanced diffusion. [Copyright &y& Elsevier]

A two-dimensional model of doping of the active regions in semiconductor devices by means of ion implantation and thermal annealing is stated and analyzed. Radiation enhanced diffusion of impurity atoms during high temperature implantation of hydrogen ions is also considered. An economic finite difference method for solving the obtained system of diffusion equations is developed and numerical computations of the diffusion processes are carried out. [Copyright &y& Elsevier]

In this study, BSi cluster ions of 77 keV and B monomer ions of 22 keV were respectively implanted into silicon wafers at room temperature and geometrically tilted. Rapid thermal annealing of the as-implanted specimens at 1050 °C for 25 s was also employed. The results revealed that all the as-implanted and as-annealed range parameters (Rp, ΔRp, γ, β and ΔRt) of the BSi cluster ion implantation are smaller than those of the B monomer ion implantation. The as-annealed range parameters are larger than the as-implanted ones for both the BSi cluster ion and the B monomer ion implantations mainly due to radiation enhanced diffusion (RED) effects. RED effects also tend to drive boron atoms out-diffusion towards the specimen surface. However, the SiO2 layer at the surface acts as a diffusion barrier by which it traps boron atoms nearby. The existence of larger amounts of defects explains the presence of a more pronounced accumulation of out-diffused boron atoms in the as-annealed boron depth profile of the BSi cluster ion implantation compared to that of the B monomer ion implantation. [Copyright &y& Elsevier]

Atomic transport in ion beam mixed Co/Pt and Pd/Au bilayer systems have been studied from the shifts of maker layers in Rutherford backscattering spectroscopy. Thin layers (1 nm) of marker (Pd for Co/Pt and Ni for Pd/Au) were embedded as markers at each interfaces. 80 keV Ar+ was used to irradiate the marker samples at the temperature range between 90 and 600 K. The Co/Pt system shows isotropic atomic transport (JCo/JPt∼1.1) at low temperatures and anisotropic atomic transport (JCo/JPt∼5.0) at high temperatures. Meanwhile, the Pd/Au system shows near isotropic atomic transport (JPd/JAu∼1.2) at all temperatures examined. These results were discussed in terms of the activation energies for the normal impurity diffusion, cohesive energy difference, and the vacancy migration energy. Atomic transport in thermal spike regime is closely related with the activation energy for normal impurity diffusion. In radiation enhanced diffusion regime, the cohesive energy and/or the vacancy migration energy plays a dominant role for the atomic transport. [Copyright &y& Elsevier]

• Measured steady state sputter yields for Mo, Ru, Pd, W targets under oxygen ion bombardment at energy range 50–500 eV. • Ion induced oxides have similar states as atomic O exposed metals but with larger oxide thickness. • Oxide thickness from ions larger than range of ion transport from TRIDYN simulations. • External diffusion algorithm models diffusive transport of oxygen freed from oxide upon ion bombardment. • Radiation enhanced diffusion from ion bombardment explains oxide thicknesses formed at near-threshold ion energies. Transition metals used in semiconductor, photolithography and fusion applications interact with low energy oxygen ions. Understanding erosion, the nature of the formed oxide and depth of oxygen transport is necessary in mitigating unexpected performance of sensors, optics or plasma facing components. Oxide formation is governed by both the ion–target combination and the incident ion energy. We study the interaction of the transition metals molybdenum, ruthenium, palladium and tungsten, with oxygen ions in the energy region of 50–500 eV. Near-threshold sputtering of metals was experimentally measured and compared to predictions by the Monte Carlo code TRIDYN. Compositional changes and oxide thicknesses following sputtering were measured using Angle resolved X-ray photoelectron spectroscopy and subsequently compared to limiting oxide formed by atomic oxygen exposures. Sputter yields in some cases (ruthenium) were found to be sensitive to ion beam impurities such as ozone (< 1% of background gas) leading to chemical sputtering. Ion induced oxide thicknesses (for molybdenum and tungsten) were found to be larger than those predicted by ballistic transport where sputtering is balanced by implantation. It is hypothesized that radiation enhanced diffusion of free oxygen leads to thicker oxide films at low ion energies. [ABSTRACT FROM AUTHOR]