Search

Implanting photoactive ions into quartz or silica is a simple and efficient way to tune the luminescence light used for various optoelectronic applications. However, such ion implantation damages or even destroys the crystalline order in quartz. We report here on cathodoluminescence of α-quartz after 175 keV Rb-ion implantation and epitaxial growth when annealing the samples in air or 18 O 2. In the cathodoluminescence spectra taken at room temperature, five bands were identified. In addition to three intrinsic bands at 2.40, 2.79, and 4.30 eV, which are related to the quartz and/or silica matrix, two strong violet sub-bands at 3.25 and 3.65 eV were observed, which appear to be strongly correlated with the presence of alkali ions and/or the degree of epitaxy of the matrix. Their properties and origin are discussed in relation to similar bands observed after Ba, Ge, and Na ion implantation. [ABSTRACT FROM AUTHOR]

The neutron-deficient nucleus68As was populated at high spin in two experiments using the reaction40Ca(32S, 3pn) at beam energies of 105 and 95 MeV. A self-supporting and a gold-backed, highly enriched40Ca target were used. Gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The68As level scheme was considerably extended, especially at negative parity and many previous spin-parity assignments were confirmed or rejected. The total-Routhian-surface (TRS) calculations find shape coexistence and ? softness for the negative- and positive-parity states, respectively. [ABSTRACT FROM AUTHOR]

In the course of a systematic investigation of heavy ion-irradiated Fe/Si layers, we have studied atomic transport and phase formation induced by 22-keV14N2+ ion implantation in57Fe(30 nm)/Si bilayers at high fluences. We report here results obtained by Rutherford backscattering spectroscopy, X-ray diffraction, and conversion electron Mössbauer spectroscopy after implantation and post-implantation annealing treatments. The irradiations caused little sputtering, but significant interface mixing. During implantation, iron nitrides, but no silicides were formed, even at the highest nitrogen fluence of 2×1017 ions/cm2. When heating these samples in vacuo up to 700 °C, the iron-rich phases e-Fe3N and ?'-Fe4N were produced. Starting at 600 °C the silicide phase ß-FeSi2 was also identified. [ABSTRACT FROM AUTHOR]

Crystalline and ion-beam-amorphized silicon samples were irradiated with a pulsed nanosecond excimer laser in a pure hydrogen atmosphere. The hydrogen concentration was determined via the [SUP1] H([SUP15]N,αβ)[SUP12]C nuclear reaction. In the case of crystalline silicon, hydrogen incorporation into the sample surface was found to be well above the hydrogen solubility limit at thermodynamic equilibrium. The hydrogen depth profiles perfectly matched the damage profiles measured via Rutherford backscattering channeling spectroscopy. For the preamorphized silicon samples, the laser treatment resulted in epitaxial recrystallization of the amorphous top layer, but the hydrogen uptake was found to be negligible in that case. The experimental data were compared with the results of thermodynamic simulations of the laser-gas-material interaction. [ABSTRACT FROM AUTHOR]

Silicide formation and ion beam mixing of Fe/Si bilayers due to Ar-, Xe- and Au-ion irradiations at room and liquid-nitrogen temperatures were investigated. For the study of silicide phase formation, the Fe/Si bilayers were irradiated with 100-keV Ar[SUP+], 250-keV Xe[SUP+], 700-keV Xe[SUP2+] or 400-keV Au[SUP+] ions at fluences of 1 × 10[SUP15] to 2 × 10[SUP16] ions/cm[SUP2]. The influence of the ion-charge state on the mixing process was studied in Fe/Si by 100-keV Ar[SUP8+]-ion implantation, in addition to the corresponding irradiations with singly charged ions at the same energy. Changes in the samples were analyzed by Rutherford backscattering spectroscopy, conversion electron Mössbauer spectroscopy, X-ray diffraction and atomic force microscopy. Pronounced structural changes and the intermixing of the components at the Fe/Si interfaces were measured as a function of the ion species, ion fluence and sample temperature. A linear correlation between the interface broadening and the fluence was observed for all the cases. Mössbauer analysis with enriched [SUP57]Fe layers revealed the onset of phase formation out of the solid solution. In order to interpret the mixing rates in this most general case, we considered mixing through thermal local or global spikes and compound formation. The highly charged Ar[SUP8+]-ion irradiation produced a higher athermal mixing rate compared to singly charged Ar[SUP+] ions, and this result could not be explained by the above models. [ABSTRACT FROM AUTHOR]

The known level energies, electromagnetic moments and decay probabilities of high-spin states in the N = 46 isotones 86Zr, 87Nb, 88Mo, 89Tc, and 90Ru are interpreted within the shell model. The single-particle space was truncated to the p1/2 and g9/2 orbits (relative to the 88Sr core) and the single-particle energies and empirical two-body matrix elements derived by Gross and Frenkel were used in the calculations. Based on the generally good success of this approach, energies and decay properties of the yrast spectra in 90Ru and 91Rh are predicted. [ABSTRACT FROM AUTHOR]

Subpicosecond lifetimes of high spin states in the rotational nuclei 73Se, 74Se and 74Br have been measured using the 58Ni +19F compound reaction and the Doppler Shift Attenuation method. Six EUROBALL Cluster detectors arranged in cube geometry allowed us to select the relevant transitions in γγ coincidence mode. The high counting statistics achieved in this setup also facilitated the determination of average sidefeeding times, which were found to agree rather well with the results of Monte-Carlo calculations of the particle and γ-ray evaporation process. The deduced quadrupole strengths and deformations are compared with the results of previous measurements and the predictions of Cranked Shell Model calculations. In 74Br, a large and constant prolate deformation of β2= 0.37(1) was found for the presumed 4+ and 3− two-quasiparticle bands. [ABSTRACT FROM AUTHOR]

The magnetic moments of the 12+ and 11− yrast states in 94Ru and of the 25/2−, 29/2+, and 35/2+ levels in 95Rh have been measured via the IMPAD technique. The nuclei were produced in the reaction 58Ni +40Ca and recoil-implanted into polarized Ni and Fe hosts. The g-factors were deduced from the measured time-integral Larmor precessions. The comparison between the experimental results and large-scale shell model calculations suggests that the 12+ and 11− states in 94Ru and the 25/2− level in 95Rh are pure proton states whereas the 29/2+ and 35/2+ states in 95Rh contain a neutron excitation across the N=50 shell gap. This interpretation supports the conclusion drawn from recent lifetime measurements. [ABSTRACT FROM AUTHOR]

Perturbed angular correlation (PAC) experiments with implanted 111In tracers have recently been used to investigate magnetic phase transitions in metal oxides. Here we report on PAC measurements for 111Cd in polycrystalline Fe3O4 in the neighborhood of the Verwey phase transition (TV≈ 120 K). Perturbed angular correlation spectra were taken for implanted 111In probes at temperatures between 9 and 850 K. The two observed Larmor frequencies are attributed to the two possible cation sites in the cubic inverse spinel lattice. For T > 120 K, the temperature dependence of both Larmor frequencies follows a Curie–Weiss power law ωL(T)/ ωL(0)=(1-T/TN)β, with the parameters TN=848(2) K and β= 0.392(2). At the Verwey temperature we find a rapid change of both Larmor frequencies, with ωL1 increasing from 178(2) MHz at 120 K to 191(4) MHz at 100 K, and ωL2 decreasing from 173(4) MHz to 151(5) MHz. The Verwey transition also affects the widths of the frequency distributions, which more or less double below TV. This possibly indicates the presence of several components with Larmor frequencies similar to those found in the previous Mössbauer data, or for electronic after-effects correlated with the semiconductivity of magnetite below TV. [ABSTRACT FROM AUTHOR]

Ag/Fe bilayers in which a submonolayer of 111In had been deposited in the Fe layer at a distance of x=0–17 nm from the interface, were irradiated at 80 K with 450 keV Xe ions to a fluence of 3 and 6⋅ 1015 ions/cm2. Perturbed Angular Correlation spectroscopy was used to monitor the microsurrounding of the 111In tracers and to identify the radiation-induced defects. The fraction of tracer atoms being transported into the Ag layer cannot be explained by ballistic mixing, but is reproduced when assuming local thermal spikes to develop. The diffusion of 111In into the Ag layer can be modeled if the local spikes have an average diameter of some 5 nm. [ABSTRACT FROM AUTHOR]

The Au–In equilibrium phase diagram exhibits a large number of intermetallic phases which have recently been explored via perturbed angular correlation spectroscopy, using alloyed and/or diffused 111In probes. In the present work we report on the phase transition from Au7In3 (hexagonal, γ'-phase) to Au9In4 (γ-brass phase) induced via Xe- or Ar-ion implantations at 80 K. We compare the hyperfine parameters with those obtained in thermal equilibrium and after quenching, and argue that ion beam mixing and fast cooling in the condensation phase of thermal (local) spikes are the predominant mechanisms to interpret our findings. [ABSTRACT FROM AUTHOR]

The electric hyperfine interaction of ion beam implanted 111In and 111Cd probe atoms in sapphire (Al2O3) single crystals has been investigated using perturbed angular correlation spectroscopy. For both probe atoms the same distinctive electric field gradient was found, indicating that nearly all the implanted probe atoms form a stable substitutional configuration in the temperature range between 77 K and 873 K on the aluminum sublattice. A comparative study between 111In and 111Cd-measurements points to a dynamic interaction initiated by the electron-capture of 111In(EC)111Cd similar to In2O3 and La2O3. Size and orientation of the EFG are discussed in comparison to experimental results in Cr2O3 single crystals. [ABSTRACT FROM AUTHOR]

Segregation of In in Fe-based alloys containing 0.11–2.12 at.% In has been studied by measuring the perturbed angular correlations of γ-rays emitted in the nuclear decay of 111In. The probe atoms were introduced into the alloys by either adding the carrier-free 111In during melting or via ion implantation. Ageing of the samples at elevated temperatures followed by a slow cooling to room temperature allowed us to determine the upper limit of the solubility at room temperature, S(300 K)≤ 30 at. ppm. This value is far below the one reported in the published phase diagram. Quenching of the samples in water from 973–1373 K resulted in the determination of the indium solubility in iron at these elevated temperatures. [ABSTRACT FROM AUTHOR]

We report on the results of Perturbed Angular Correlation measurements in polycrystalline (Co1-xInx)1-δO samples (x = 0.04 and 0.8 at.%) using ion-implanted 111In tracers. The temperature and the oxygen activity (adjusted via a CO/CO2 mixture) were chosen in such a way as to be able to observe defect trapping and detrapping in thermal equilibrium. The results are compared with those obtained for (Co1-xInx)1-δO (x= 0.04 at.%) rapidly cooled to 350 K and for CoO. [ABSTRACT FROM AUTHOR]

The temperature dependence of the hyperfine parameters in SrHfO3 powder samples has been investigated by means of Perturbed Angular Correlation spectroscopy using implanted 111In probes. Three quadrupole interactions have been established, with the largest fraction showing a pronounced dynamic interaction. We assign this fraction to 111In / 111Cd probe atoms on substitutional Hf sites. The temperature dependence of the dynamic interaction has been associated to the Pnma↔Imma phase transition at ∼700 K. We discuss the results in relation to those obtained for 181Hf / 111Ta-probes in AHfO3 (A=Ba, Sr, Ca) and for 111In / 111Cd-probes in PbZrO3 and BaTiO3. [ABSTRACT FROM AUTHOR]

In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and still fair agreement for most measured B(M1) and B(E2) values. [ABSTRACT FROM AUTHOR]