Physics

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A detailed study of the formation of β-FeSi 2 films by ion-beam mixing of Fe/Si bilayers with noble gas ions is presented. Fe films of 35-50 nm deposited on Si (100) were irradiated with 80-700 keV Ar, Kr, or Xe ions in a wide temperature interval, from room temperature to 600 °C. The structures were analyzed by Rutherford backscattering spectroscopy, x-ray diffraction, conversion electron Mössbauer spectroscopy, elastic recoil detection analysis, cross-section high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. Already after Xe irradiation at 300 °C the whole Fe layer is transformed to a mixture of Fe 3 Si, ε-FeSi, and β-FeSi 2 phases. At 400-450 °C, a unique, layer by layer growth of β-FeSi 2 starting from the surface was found. A full transformation of 35 nm Fe on Si to a 105 nm β-FeSi 2 layer was achieved by irradiation with 205 keV Xe to 2×10 16 ions/cm 2 , at a temperature of 600 °C. The fully ion-beam grown layers exhibit a pronounced surface roughness, but a sharp interface to Si. This structure is assigned to a growth of β-FeSi 2 grains in a local surrounding of interdiffused silicon. Rapid diffusion of silicon to the surface was observed during all ion irradiations. Single-phase β-FeSi 2 layers were also synthesized by vacuum annealing for 2 h at 600 °C of 35 nm Fe/Si bilayers premixed with Xe at 450 °C. In this case, the layers form with a smoother surface topography. It is concluded that ion-beam mixing can be used successfully for growth of β-FeSi 2 layers at moderate temperatures, either directly or combined with postirradiation annealing. © 2001 American Institute of Physics.

World University root node

(SoNS) School of Natural Sciences

Fulltext

Journal of Applied Physics

Growth of β-Fesi 2 films via noble-gas ion-beam mixing of Fe/Si bilayers

The effect of 835 MeV Kr irradiation at 90 K on a stable icosahedral quasicrystal (Al65Cu25Fe5V5) is discussed here. A Kr-beam of this energy was chosen in order to keep the stopping power ∼1300 eV/Å in accordance with our previous work [Nucl. Instrum. Meth. B, 156 (1999) 201], while increasing the travelled path in which strong electronic excitations occur (≫sample thickness). The ratio ρ(φ)/ρ(0) {resistivity at fluence φ/resistivity at zero fluence} of quasicrystal goes through oscillatory changes, up to ∼1 × 1012 ions/cm2 where this ratio drops considerably. The ex situ XRD on the irradiated samples however shows the evidence of degradation of the structure after a critical fluence of 1 × 1011 ions/cm2. From the ex situ XRD measurements, this degradation does not seem to increase with further fluence up to φ = 1 × 1013 ions/cm2. © 2001 Elsevier Science Ltd. All rights reserved.

Solid State Communications

The observation of oscillatory behaviour in swift heavy ion irradiated quasicrystals

Thermally induced epitaxial crystallization of thin a-SiO2 films represents a promising procedure for removing the ion-beam damage induced during the fabrication of integrated optical devices. In this paper we report on the crystallization of a-SiO2 films deposited on single crystalline α-quartz substrates, investigated by means of Rutherford backscattering spectrometry in channeling geometry (RBS-C). The epitaxial crystallization was achieved by means of a novel three-step procedure which uses high-fluence Cs+-ion doping of the films and subsequent annealing in air at 800-900°C. Similarly, amorphous SiO2 layers, created by the ion irradiation of α-quartz samples, were epitaxially regrown after alkali post-implantation and annealing, thus demonstrating that the regrowth is independent of the production history of the amorphous film. Optical spectroscopy in the range 300-1100 nm showed the good optical properties of the regrown layer. © 2001 Elsevier Science B.V.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Ion beam doping and epitaxial regrowth of α-quartz

The irradiation effects in Ni3N/Si bilayers induced by 100–700 keV Xe ions at fluences up to 4 × 1016ions/cm2 were investigated at 80 K and room temperature. The element depth profiles were measured via Rutherford backscattering (Ni, Si) and resonant nuclear reaction (N) analysis, the phase formation at the interface via x-ray diffraction, and the surface roughness by atomic force microscopy. The observed dissociation and preferential sputtering of Ni3N followed by nitrogen out-diffusion were related to the small binding energy of this compound. Mixing at the Ni3N/Si interface occurs via a combination of diffusion and reaction controlled transport processes and the interface broadening varies in second order with the ion fluence. At higher ion fluences, the formation of NiSi2 and Si3N4 phases at the interface was found. © 2001 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Xenon irradiation of Ni3N/Si bilayers: Surface roughening and interface mixing and reactions

Magnetic moment measurements of picosecond states generally make use of the huge transient magnetic fields which fast nuclei experience during their passage through a ferromagnetic foil. Based on the Recoil Distance Transient Field (RDTF) method previously pioneered by the Göttingen group, we propose the Doppler Shift Transient Field (DSTF) method to measure g-factors of short-lived high-spin states excited in a heavy ion fusion reaction at a high recoil velocity. This method can be used whenever the state is populated by fast discrete feeder transitions γ2. By measuring the Larmor precession of the decay γ-ray γ1 with a gate set on the Doppler shifted tail of γ2, one selects events of high recoil velocity (= high transient field) and avoids, to a large extent, the uncertainties of delayed side and cascade feedings inherent in heavy-ion fusion reactions. Estimates are given for the DSTF precessions in 102Cd and 74Br. © 2002 Kluwer Academic Publishers.

Hyperfine Interactions

Magnetic moment measurement of short lived states via the Doppler Shift Transient Field method

In the framework of SUSYQM extended to deal with non-Hermitian Hamiltonians, we analyze three sets of complex potentials with real spectra, recently derived by a potential algebraic approach based upon the complex Lie algebra sl(2, C). This extends to the complex domain the well-known relationship between SUSYQM and potential algebras for Hermitian Hamiltonians, resulting from their common link with the factorization method and Darboux transformations. In the same framework, we also generate for the first time a pair of elliptic partner potentials of Weierstrass type, one of them being real and the other imaginary and PT symmetric. The latter turns out to be quasiexactly solvable with one known eigenvalue corresponding to a bound state. When the Weierstrass function degenerates to a hyperbolic one, the imaginary potential becomes PT nonsymmetric and its known eigenvalue corresponds to an unbound state.

International Journal of Modern Physics A

Generating complex potentials with real eigenvalues in supersymmetric quantum mechanics

The article reports on the Xe ion beam irradiation studies of Ni3N/Al bilayers at 80 K. The ion-induced modifications were monitored by Rutherford backscattering (RBS), resonant nuclear reaction analysis (RNRA), X-ray diffraction (XRD) and atomic force microscopy (AFM). We found preferential loss of nitrogen from the surface region of the Ni3N top layers. The surface roughness ΔσS and the interface broadening variance Δσint2 increase linearly with the Xe ion fluence Φ. The experimental mixing rate of Δσ2/Φ = 1.8 nm4 is explained by considering an enhancement of ballistic mixing due to chemical reactions at the interface. © 2001 Elsevier Science B.V.

Heavy ion irradiation induced effects in Ni3N/Al bilayers

This paper presents results on the direct synthesis of the β-FeSi2 phase by ion beam mixing of Fe/Si bilayers with Xe ions. The influence of the substrate temperature, ion fluence and energy on the growth of this phase was investigated using Rutherford backscattering (RBS), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). Complete growth of single-phase β-FeSi2 was achieved by 205 keV Xe ion irradiation to a fluence of 2 × 1016 ions/cm2 at 600°C. We propose a two-step reaction mechanism involving thermal and ion beam energy deposition. © 2001 Elsevier Science B.V.

Synthesizing single-phase β-FeSi2 via ion beam irradiations of Fe/Si bilayers

On the lattice fermions paired and then composed with precise phases are the lattice bosons. We construct rules for deforming the underlying algebra that keep unchanged the boson interpretation. These deformations alter the phases of the fermion pairs. The solutions of the deformed algebra are the pair-phase excitations of the lattice bosons. We find these eigenstates of the Dirac Hamiltonian of fermions with mass. The gauge interactions are shown to excite the k-deformed modes. © 2001 Published by Elsevier Science B.V.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Algebraic bosonisation: The case of the Dirac fermion

The effect of pure electronic excitations (by ∼ 835 MeV Kr irradiation) on a stable icosahedral quasicrystal is compared with the effect of electronic excitations combined with the nuclear collisions (by 100 MeV Ni irradiation) occurring in a similar quasicrystal. The critical stopping power was kept at 1300 eV/Å for both the experiments. Under the pure electronic excitations, the R(Φ))/R(0) [ratio of resistance at fluence Φ and the resistance on the same piece with zero fluence) of quasicrystal goes through oscillatory changes, until at ∼ 1 × 1012 ions/cm2 where this ratio drops considerably. The ex-situ XRD on the irradiated sample does show the evidence of degradation of the structure. In contrast, the Ni-irradiated sample shows an increase in resistivity after a critical fluence of 2.5 × 1013 ions/cm2, which remains constant for higher fluences. Corresponding defect annihilation effects are observed in the XRD of Ni-irradiated samples.