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Shiv Nadar University

(SoNS) School of Natural Sciences

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

Physics

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

In this paper, a novel approach is described for the a priori prediction of protein retention in ion exchange systems. Quantitative structure retention relationship (QSRR) models based on a genetic algorithm/partial least squares approach were developed using experimental chromatographic data in concert with molecular descriptors computed using protein crystal structures. The resulting QSRR models were well-correlated, with cross-validated r2 values of 0.938 and 0.907, and the predictive power of these models was demonstrated using proteins not included in the derivation of the models. Importantly, these models were able to predict selectivity reversals observed with two different stationary phase materials. To our knowledge, this is the first published example of predictive QSRR models of protein retention based on crystal structure data.

Chemistry

Analytical Chemistry

Prediction of protein retention in ion-exchange systems using molecular descriptors obtained from crystal structure

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

We construct representations of certain direct limit Lie groups G=lim Gn via direct limits of Zuckerman derived functor modules of the groups Gn. We show such direct limits exist when the degree of cohomology can be held constant, and discuss some examples for the groups Sp(p,<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>∞</mo></math>) and SO(2p,<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>∞</mo></math>), relating to the discrete series and ladder representations. We show that our examples belong to the "admissible" class of Ol'shanskii, and also discuss the globalizations of the Harish-Chandra modules obtained by the derived functor construction. The representations constructed here are the first ones in cohomology of non-zero degree for direct limits of non-compact Lie groups.&nbsp;

Mathematics

Journal of Lie Theory

Direct Limits of Zuckerman Derived Functor Modules

The hepatitis E virus (HEV) is the causative agent of hepatitis E, an acute form of viral hepatitis. The biology and pathogenesis of HEV remain poorly understood. We have used in vitro binding assays to show that the HEV ORF3 protein (pORF3) binds to a number of cellular signal transduction pathway proteins. This includes the protein tyrosine kinases Src, Hck, and Fyn, the p85α regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cγ, and the adaptor protein Grb2. A yeast two-hybrid assay was used to further confirm the pORF3-Grb2 interaction. The binding involves a proline-rich region in pORF3 and the src homology 3 (SH3) domains in the cellular proteins. Competition assays and computer-assisted modeling was used to evaluate the binding surfaces and interaction energies of the pORF3-SH3 complex. In pORF3-expressing cells, pp60src was found to associate with an 80-kDa protein, but no activation of the Src kinase was observed in these cells. However, there was increased activity and nuclear localization of ERK in the pORF3-expressing cells. These studies suggest that pORF3 is a viral regulatory protein involved in the modulation of cell signaling. The ORF3 protein of HEV appears to be the first example of a SH3 domain-binding protein encoded by a virus that causes an acute and primarily self-limited infection.

Life Sciences

Journal of Biological Chemistry

The ORF3 Protein of Hepatitis E Virus Binds to Src Homology 3 Domains and Activates MAPK

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.