Effects of damage rate on Cu precipitation in Fe–Cu model alloys under neutron irradiation

The formation of Cu precipitates and point defect clusters was investigated in two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, irradiated at 573?K at three different damage rates, namely 3.8?×?10^?10, 1.5?×?10^?8 and 5?×?10^?8?dpa (displacements per atom)/s, up to about 1.6?×?10^?2?dpa. Results of positron annihilation experiments indicated that Cu precipitates were formed in these irradiations with different damage rates. The growth of Cu precipitates does not increase monotonously with increasing irradiation dose, but it rather depends on the nucleation and growth of microvoids. It is also clear that the nucleation and growth of microvoids are influenced by the irradiation dose rate.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

In situ study of self-ion irradiation damage in W and W–5Re at 500 °C

In situ self-ion irradiations (150?keV?W⁺) have been carried out on W and W–5Re at 500?°C, with doses ranging from 10¹⁶ to 10¹⁸ W⁺m^?2 (～1.0?dpa). Early damage formation (10¹⁶W⁺m^?2) was observed in both materials. Black–white contrast experiments and image simulations using the TEMACI software suggested that vacancy loops were formed within individual cascades, and thus, the loop nucleation mechanism is likely to be ‘cascade collapse’. Dynamic observations showed the nucleation and growth of interstitial loops at higher doses, and that elastic loop interactions may involve changes in loop Burgers vector. Elastic interactions may also promote loop reactions such as absorption or coalescence or loop string formation. Loops in both W and W–5Re remained stable after annealing at 500?°C. One-dimensional hopping of loops (b?=?1/2 ?111>) was only seen in W. At the final dose (10¹⁸W⁺m^?2), a slightly denser damage microstructure was seen in W–5Re. Both materials had about 3–4?×?10¹⁵ loops m^?2. Detailed post-irradiation analyses were carried out for loops of size???4?nm. Both b?=?1/2 ?111? (～75%) and b?= ?100> (～25%) loops were present. Inside–outside contrast experiments were performed under safe orientations to determine the nature of loops. The interstitial-to-vacancy loop ratio turned out close to unity for 1/2 ?111? loops in W, and for both 1/2 ?111? and ?100? loops in W–5Re. However, interstitial loops were dominant for ?100? loops in W. Re seemed to restrict loop mobility, leading to a smaller average loop size and a higher number density in the W-Re alloy.     

Spectroscopic study of the formation of excited strontium ions upon interaction of electrons with metastable atoms

The interaction of electrons with metastable Sr atoms, as a result of which the latter are simultaneously ionized and excited, is investigated experimentally. The magnitudes of the interaction cross sections (reaching ≈5 × 10^?20 m² for the 5² S _1/2-3² P _3/2 transition in Sr II) and their energy dependences are determined. Possible mechanisms of this interaction are discussed.     

Formation of doubly charged negative ions under the conditions of the resonant electron capture by fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C₆₀F _n (n = 36, 48) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C₆₀F ₃₆ ^2? and C₆₀F ₄₈ ^2? are estimated to be about 1.1 × 10^?24 and 1.5 × 10^?24 m² at their maximum-yield energies of 2.0 and 1.6 eV, respectively.     

Ion bombardment induced phase transformations and inert gas mobility in the semiconductors Ge,Si, and GaAs

Abstract

The present study contributes some new aspects to the general understanding of the ion implantation behaviour of 3 common semiconductor materials, and of diffusion processes in these materials. Single crystals of Si, Ge, and GaAs were bombarded with Kr- or Xe-ions at energies of 40 or 500 keV and doses between 10¹¹ and 2 × 10¹⁶ ions/cm². Gas release measurements and Rutherford scattering of 1 MeV He⁺-ions combined with channeling were used to study bombardment damage (amorphization) and inert gas diffusion. At low bombardment doses (10¹¹ ions/cm²) and energy (40 keV), no damage was observed and the gas release was compatible with volume diffusion resembling Group I and VIII behaviour. Hence, the pre-exponential terms, D ₀, were low (range 10-^5±1 cm² sec^?1) and the activation enthalpies, Δ H, were much lower than those of self-diffusion or of diffusion of Group III and V elements. The Δ H's for gas diffusion followed the relation Δ H = (1.05±0.1) × 10^?3 T_m eV with the melting point, T_m , in °K. The mechanism of gas mobility might be the Turnbull dissociative mechanism. Rutherford scattering and channeling data indicated that part of the gas occupied lattice sites.

At higher doses, the bombarded layers turned amorphous. Channeling experiments showed a coincidence in temperatures for a gas release process different from the above one of volume diffusion, and recrystallization of the disordered layer to the single crystalline state. Both processes occurred in the temperature range 0.60 to 0.65 T_m . The gas release indicated a (partial) single jump character with implied Δ H's following the relation Δ H = (2.1±0.1) × 10^?3 T_m eV. Contrary to previous results on oxides, this new gas release occurred at temperatures near to those or even above those of volume diffusion of the gas.

Due to the easy formation of an amorphous layer it was difficult to observe the retarded release (trapping of gas) that has been found in many materials at high gas and damage concentrations. However, in a separate series of experiments with 500 keV Kr-ions, a release retarded with respect to volume diffusion of the gas was observed in Si and Ge.     

Absolute intensity measurements of the CO2 bands 401III←000 and 411III←010

The absolute intensities of the transitions 401_III←000 and 411_III←010 of CO₂ have been measured from spectra obtained under high resolution. Both the vibration-rotation line intensities and the integrated band intensities are reported. The rotationless transition moment of 401_III←000 is deduced and a vibration-rotation interaction factor F(m) = 1+(4.92×10^?4)m+(4.4×10^?7)m² is determined. The values obtained are: S_Band(401_III←000) = (25.54±0.22)×10^?5 cm^?2atm_{(293 K)}^?1, |R₀₀₀^401_III| = (1.87±0.02)×10^?4D, and S_Band(411_III←010) = (1.83±0.13)×10^?5 cm^?2atm_{(293 K)}^?1.     

Spectroscopic studies of a plasma temperature and radiation standard based on a wall-stabilized arc

The absolute determination of the axial temperature (12,000 K ≤ T ≤ 14,500 K, 0.9×10²³ m^-3 ≤ N_e ≤2.5×10^-3 m^-3 of a 3 mm bore wall-stabilized arc operating in argon at 1.75×10⁵ Pa is described using spectroscopic techniques both in the visible and vacuum u.v. spectral regions. Computer simulation techniques to predict the line wing correction for the A(I) line at 430 nm and a detailed study of sources of systematic error have been applied. The reproducibility of the temperature results and the establishment of LTE demonstrates the suitability of the source as a plasma temperature and radiation standard. A detailed study of the Stark broadening of H_β and the comparison of the experimental profiles with the theories of Kepple and Griem and Vidal, Cooper and Smith has shown the former giving N_e values some 11% lower and the latter 1% higher than the pure argon diagnostics at N_e ? 2 × 10²³ m^-3. New values for the argon transition probabilities of two lines and continuum factors at two wavelengths are presented.     

Ne(I) spectral lines from a Ne-O2 d.c. glow discharge

Measurements have been made of intensities of the spectral lines emitted from an Ne-O₂ d.c. discharge with small discharge current (1–4 mA) under the following conditions: gas pressures of 2 and 3 torr and oxygen partial pressures (P₀₂) up to 0.1 torr. All of the Ne(I) line intensities observed decrease when O₂ is added. The Ne(I) λ5852 line (1s₂-2p₁) has been studied in detail as a representative example. The population density of the 2p₁ level of neon has been obtained from the intensity measurements as a function of P₀₂. The energy-distribution function of electrons has been determined using Druyvesteyn's method in order to calculate the population density for a corona model. The high-energy tail of the measured distribution function is markedly reduced when O₂ is added. It is shown that inelastic collisions of electrons with O₂ produce large energy losses for the electrons. These cause a decrease in population density of the 2p₁ level when O₂ is added. The population density of the 2p₁ level at a gas pressure of 2 torr is 1.2×10⁴ cm^-3 in pure neon and 5.2×10² cm^-3 in an Ne-O₂ mixture (P₀₂ = 0.01 torr). The electron densities and average electron energies are 3.5×10⁸ cm^-3 and 8.7 eV and 1.7×10⁸ cm^-3 and 5.3 eV, respectively, for the specified two cases.     

Self-luminescence of several fluorite-structure halides doped with curium or berkelium

The self-luminescence emission spectra of several fluorite-structure halides doped with 0.1 cation % ²⁴⁴Cm or ²⁴⁹Bk were measured in the range 14 × 10⁵ to 50 × 10⁵ m^-1 (200–700 nm) between 295 and 600 K. The hosts studied included CaF₂, SrF₂, BaF₂, and SrCl₂ (for Cm) and BaF₂ and SrCl₂ (for Bk). The room-temperature spectra of the Cm-doped samples all have relatively sharp peaks at approximately 16.5 × 10⁵ m^-1 and broad, asymmetric bands with maxima near 35 × 10⁵ m^-1 (fluorides) or 28 × 10⁵ m^-1 (SrCl₂). The sharp peaks are attributed to the Cm dopant and are stable to at least 600 K, while the broad bands appear to be associated with host anion centers and disappear on sample heating. The room-temperature spectrum of Bk-doped BaF₂ also displays an anion- related band at 35 × 10⁵ m^-1, while that of Bk-doped SrCl₂ has both an anion band at 28 × 10⁵ m^-1 and a peak at 19 × 10⁵ m^-1 (believed to be an additional host effect). The luminescence intensity of all samples decreased with room-temperature storage, but could be partially restored by annealing.     

Experimental investigation of excitation of argon metastables by an electron swarm in argon nitrogen gas mixtures

Excitation of argon metastable levels (4³ P ₂+4³ P ₀) in a nonselfsustained discharge in Ar(≧99%)+N₂(≦1%) gas mixtures has been investigated by measuring N₂ second positive group which is the result of excitation transfer from Ar metastables to N₂ molecules. The method is based on the assumption, experimentally verified, that addition of small quantities of N₂ do not change markedly the probability of Ar excitation. The obtained excitation coefficients for production of Ar ^m in theE/N range (20–70)×10^?21Vm² are (3.5–13)×10^?22m² with an estimated uncertainty of ±50%. Simultaneously, excitation coefficients for direct excitation of nitrogenC-state by swarm electrons in Ar-N₂ mixtures have been obtained. A comparison of nitrogen spectra excited by electrons and by argon metastables showed significant differences in relative population of vibrational and rotational levels of the N₂(C ³ Π _U state in these two cases.     

Nucleation kinetics for gold deposited onto mica substrates

The nucleation behavior of gold deposited under ultra high vacuum conditions onto cleaved mica substrates has been measured over the temperature range 270–450 °C at impingement fluxes of 6 × 10¹³ and 8 × 10¹² atoms cm^?2sec^?1. A step-kinetic technique was used wherein separate substrate areas were exposed for successively longer times to the vapor beam from a thermal source. The deposits were examined in a high resolution electron microscope. For mica cleaved in situ in UHV, the variation in number density of nuclei with time of exposure to the atom beam revealed that nucleation occurred rapidly on preferred sites which were exhausted within the first few seconds of exposure. After the initial saturation, nucleation appeared to occur randomly over the rest of the surface. The number density of preferred sites increased with decreasing temperature indicating that a spectrum of preferred sites of varying degrees of potency were active. The random nucleation rates could by analyzed satisfactorily using the atomistic model for nucleation. A critical sized nucleus consisting of one atom is consistent with the data. The characteristic energy for nucleation (2ΔG_des ?ΔG_sd), was found to be 1.1 eV. Nucleation behavior on mica substrates cleaved in air did not indicate the presence of active preferred sites, but nucleation was more rapid.     

Covalent distribution of spin in V2O3:O17 nuclear resonance

O¹⁷ nuclear magnetic resonance has been observed in metallic V₂O₃ with frequency shifts from (?0.10 ± 0.02)-(?0.05 ± 0.02) per cent between 170 and 460°K respectively, a linewidth of 37 ± 5 oe and spin-lattice relaxation rate 1/T₁ ≈ 60 sec^?1 at 296°K. From these quantities, covalency parameters f_s/2S = ? 0.35 × 10^?3 and ?_π/2S ≈ ? 0.07 are calculated. One of the two vanadium 3d electrons in the antiferromagnetic state below the 170°K metal-insulator transition is inferred to lie in a non-magnetic state, while covalent charge transfer augments the spin moment of the other 3d electron to the observed 1.2 μ_B.     

Charge transfer reaction of multi-charged oxygen ions with O2

The rate of transfer of electrons from O₂ to O²⁺ and O³⁺ has been measured at energies ? 2 eV using a stored ion technique. The rate for O²⁺ is k = 1.0(0.3) × 10^?9 cm³/s and for O³⁺, k = 2.5(0.3) × 10^?9 cm³/s, compared to calculated Langevin rates of 1.8 × 10^?9 cm³/s and 2.7 × 10^?9 cm³/s respectively.     

Measured collisional radiative coefficients of the 4p groups of the argon I and argon II systems

We determine the r¹ (p) coefficients of the argon I 4p ¹P₁ state (2p₂ with Paschen notation) with the λ = 696.5 nm line and of the argon II 4p ²D_{$\text{5}\text{2}$} state with the λ = 488.0 nm line in a highly ionized, low temperature (T_{e = 3?4 eV}), magnetically confined (0.2 T) plasma of a hollow cathode arc with electron densities n_e between 10¹⁹ and 10²⁰ m^?3. The neutral density n₀ is 10¹⁹ m^?3 or less. The r¹ (4p) values are (6 ± 2) × 10^?5 for argon I and (5 ± 2) × 10^?4 for argon II.     

Search for a Neutrino with a Mass of 0.01–1.0 MeV in Beta Decays of <Superscript>144</Superscript>Ce–<Superscript>144</Superscript>Pr Nuclei

Spectra of electrons from beta decays of ¹⁴⁴Ce–¹⁴⁴Pr nuclei have been measured and analyzed in order to find a contribution from a heavy neutrino. For the neutrino with the mass m_νH in the interval of 150–350 keV, a new upper bound |U_eH|² ≤ (2?5) × 10^?3 at 90% C.L. has been found for the mixing parameter.     

Measurements of gf-values for FeI lines

Iron atoms were formed in an all-glass shock tube from mixtures of Fe(CO)₅ in Ar. Observations of the reflected shock region have led to the following gf-values (within ±20 per cent) for selected low-excitation lines of multiplet 13: 1·05 × 10^-4 for the line at 6280·620 A, 1·70 × 10^-4 at 6358·690 A, and 6·70 × 10^-5 at 6498·950 A. The following results (within ±30 per cent) were obtained for gf-values of high-excitation lines belonging to multiplets 1032, 843 and 928, respectively: 1·05 × 10^-1 for the line at 5187·92 A, 3·00 × 10^-1 at 5242·50 A, and 1·10 × 10^-1 at 5379·58 A. The new measurements correspond to an increase of the more recently accepted f-number scale by about a factor of two.Curves of growth for the strong, high-excitation lines have been used to determine half-widths for collision broadening of Fe by the gas mixture existing under equilibrium conditions. The most frequent collision partners are argon atoms and electrons. At room temperature, the broadening coefficient is 0·15 cm^-1 at 1 atm, which is about five times larger than the values normally observed in nonreactive collisions, but is appreciably smaller than the line-widths expected for hydrogen-atom broadening of iron lines.Particular care was exercised in these investigations in order to define the gas composition in the reflected-shock region. Large systematic errors were encountered when a conventional static mixing procedure was used in place of a dynamic procedure, which is required for adequate composition control of strongly-adsorbed gases [Fe(CO)₅] in a large excess of inert diluent (Ar). The consistency of our observations was demonstrated by showing that, although measured intensity-time data were strongly affected, final estimates for gf-values were not influenced by the following systematic variations in experimental technique: changes in the mole ratio of Fe(CO)₅ to Ar produced by temperature alterations in the liquid Fe(CO)₅-bath which served as an equilibrium source for Fe(CO)₅; changes in the flow rate of Ar through the isothermal Fe(CO)₅ supply source; changes in the volume of the liquid Fe(CO)₅ supply source; admixture of excess CO to the Ar which served as carrier gas for Fe(CO)₅; changes in the slit functions; changes in the concentration of the dominant collision partners for the iron atoms.     

Investigation of the effect of resonant environment (Mössbauer screen) on the observed half-life of the 119m1Sn isomer (E = 23.8 keV, T 1/2 ∼ 18 ns)

In order to analyze the effect of resonant environment on the γ decay of excited nuclei, the half-life of the ^119m1Sn isomer (E = 23.8 keV, T _1/2 ～ 18 ns), which appears from the decay of the ^119m2Sn state (E = 89 keV, T _1/2 ～ 293 d), has been measured by the e-γ coincidence method on samples consisting of the mixture of tin oxides containing the ¹¹⁹Sn stable nucleus and ^119m2Sn radioactive nuclei with various values of the ¹¹⁹SnO₂/^119m2SnO₂ ratio. For the samples, where this ratio is equal to 6.2 × 10⁴, 1.2 × 10⁶, 6.5 × 10⁶, and 1.7 × 10⁷, the half-life T _1/2is equal to 18.69(2), 18.71(2), 18.91(5), and 19.43(4) ns, respectively. For the reference sample (a metal with a ¹¹⁹Sn/^119m2Sn ratio of 1.5 × 10⁵), the value T _1/2 = 18.68(6) ns is obtained.     

Quantitative analysis of blistering upon annealing of hydrogen-ion-implanted diamond single crystals

Local blistering observed upon high-temperature annealing of natural diamond single crystals implanted by 350-keV hydrogen ions with a dose of 12 × 10¹⁶ cm^?2 is studied. Based on room-temperature measurements, Griffith cracking criterion, and gas law, model quantitative calculations of blister size (R _j = (0.361?5.568) × 10^?3 m, V _j = (307?9695) × 10^?18 m³) and the amount of molecules in a blister (n _j = (0.448?10.95) × 10¹³) are carried out for the first time. At room temperature, T ₁ = 293 K, the amount of local elastic stresses σ_ij in the upper layer of the diamond is counterbalanced by (inner) hydrogen pressure P _ij of the (σ _j1 = P _j1 = (2.968?6.439) × 10⁷ Pa). At annealing temperature T ₂ = 1693 K, the hydrogen pressure rises to P _j2 = (0.1717?0.8750) GPa. Under subsequent annealing at a still higher temperature, T ₃ = 1743 K, the pressure in the blisters might be expected to grow to P _j3 = (0.1747?0.9010) GPa; however, some of blisters collapse and thin diamond slices flake away.     

Effect of MeV electron irradiation on the free volume of polyimide

The free volume of the microvoids in the polyimide samples, irradiated with 6 MeV electrons, was measured by the positron annihilation technique. The free volume initially decreased the virgin value from ～13.70 to ～10.98 Å³ and then increased to ～18.11 Å³ with increasing the electron fluence, over the range of 5?×?10¹⁴ – 5?×?10¹⁵ e/cm². The evolution of gaseous species from the polyimide during electron irradiation was confirmed by the residual gas analysis technique. The polyimide samples irradiated with 6 MeV electrons in AgNO₃ solution were studied with the Rutherford back scattering technique. The diffusion of silver in these polyimide samples was observed for fluences >2?×?10¹⁵ e/cm², at which microvoids of size ≥3 Å are produced. Silver atoms did not diffuse in the polyimide samples, which were first irradiated with electrons and then immersed in AgNO₃ solution. These results indicate that during electron irradiation, the microvoids with size ≥3 Å were retained in the surface region through which silver atoms of size ～2.88 Å could diffuse into the polyimide. The average depth of diffusion of silver atoms in the polyimide was ～2.5 μm.