Physics

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Shiv Nadar University

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Applied Physics Letters

Structural and electrical properties of silicon dioxide layers with embedded germanium nanocrystals grown by molecular beam epitaxy

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 + , 250-keV Xe + , 700-keV Xe 2+ or 400-keV Au + ions at fluences of 1 × 10 15 to 2 × 10 16 ions/cm 2 . The influence of the ion-charge state on the mixing process was studied in Fe/Si by 100-keV Ar 8+ -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 57 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 8+ -ion irradiation produced a higher athermal mixing rate compared to singly charged Ar + ions, and this result could not be explained by the above models.

Applied Physics A: Materials Science and Processing

Ion-beam mixing in Fe/Si bilayers by singly and highly charged ions: Evolution of phases, spike mechanism and possible effects of the ion-charge state

Potential algebras are extended from Hermitian to non-Hermitian Hamiltonians and shown to provide an elegant method for studying the transition from real to complex eigenvalues for a class of non-Hermitian Hamiltonians associated with the complex Lie algebra A1.

Institute of Physics Conference Series

Non-Hermitian Hamiltonians with real and complex eigenvalues: An sl(2,C) approach

By exploiting the hidden algebraic structure of the Schrödinger Hamiltonian, namely the sl(2), we propose a unified approach of generating both exactly solvable and quasi-exactly solvable potentials. We obtain, in this way, two new classes of quasi-exactly solvable systems one of which is of periodic type while the other hyperbolic.

Journal of Physics A: Mathematical and General

A unified treatment of exactly solvable and quasi-exactly solvable quantum potentials

Thin Fe and Ta layers of 30-45 nm thickness, deposited via magnetron sputtering on Si (1 0 0) substrates, were bombarded at room temperature with 100 keV Ar1+ or Ar8+ or with 250 keV Xe1+ or Xe19+ ions in order to test the influence of the ion charge state on the surface sputtering and interface mixing. The samples were characterized by means of Rutherford backscattering at 0.9-3.0 MeV α-particle energy, time-of-flight elastic recoil detection analysis with a 53 MeV 127I10+ beam and atomic force microscopy. No influence of the charge state on the sputtering and athermal mixing rate was observed in the case of the Ta/Si system. However, in the case of the Fe/Si system, the ion charge was observed to have an influence on the mixing rate. © 2003 Elsevier Science B.V. All rights reserved.

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

Ion beam mixing in Fe/Si and Ta/Si bilayers: Possible effects of ion charges

A study on a vertically correlated submonolayer (VCSML) InAs/GaAs quantum-dot (QD) heterostructure was presented. The Tagaki-Taupin equations were used to simulate the high resolution x-ray diffraction (HRXRD) (004) rocking curve. The simulation was achieved assuming that indium-rich VCSML QDs are embedded in a quantum well (QW) with lower indium content and an observed QD coverage of 10%.

Structure and optical anisotropy of vertically correlated submonolayer InAs/GaAs quantum dots

In order to investigate the swift heavy-ion-induced mixing of nitride coatings we have irradiated Ni3N films on SiO2-, Si 3N4-, SiC- and Si-substrates with Ar, Kr, Xe and Au ions of energies ranging from 90 to 350 MeV, for which electronic energy loss dominates. The Ni-concentration profiles at the interfaces before and after irradiation were determined by means of Rutherford backscattering spectrometry with 900 keV He2+ ions. In all the cases, strong mixing occurred as soon as a material-dependent threshold Sec in the electronic stopping power Se was exceeded. The mixing rate exhibits a squared scaling k = Δσ2/Φ = η2 (Se - Sec)2 and estimation of the effective diffusion constant indicates interdiffusion in molten ion tracks. The threshold value Sec depends on the substrate material and seems to be determined by its melting point and specific heat. © 2003 Published by Elsevier Ltd.

Radiation Measurements

Interface mixing in Ni3N/SiX bilayers induced by swift heavy ions

We report a systematic search for electrical signature of defect clusters in ion-implanted silicon using Deep Level Transient Spectroscopy (DLTS) and related capacitance transient measurements. We show that slow carrier capture dynamics among energy broadened multiple states and occurrence of capture induced metastable states are some of the distinctive hall marks of cluster related trap levels. Isothermal transient spectroscopy is shown to be appropriate for recognition of these features.

Proceedings of SPIE - The International Society for Optical Engineering

Carrier dynamics at deep traps in ion implanted silicon: Possible signature of defect clusters

In this paper, we present a systematic structural study on the (Al1-xGex)65Cu10+yMn25-y alloy system. The emphasis of the work is to understand the effect of Ge concentration on the occurrence, growth and morphology of the quasicrystalline phases in the system, as we move from Cu/Mn ratio of 20:15 to 10:25 in order to span the varied electronic behavior (as shown in the literature) of this quaternary system. Throughout the series, coexistence of icosahedral and decagonal phases has been observed. To the best of our knowledge, these are the first observations of their type in the alloy system (AlGe) CuMn. © 2002 Elsevier Science B.V. All rights reserved.

Materials Letters

Structural studies of (Al1-xGex)65Cu10+yMn25-y (0≤x≤0.4, 0≤y≤10)

In this paper, we report the formation of stable icosahedral Al-Cu-Fe quasicrystalline thin films by thermal vapor deposition techniques (indirect heating and e-beam heating) from a single source. Deposition of these films by a single-source indirect heating method, in the stable icosahedral phase, is reported for the first time. A direct comparison between the two different heating methods has been made. The final compositions of the prepared films with desired properties were found to be Al62.9Cu24.6Fe12.5 (indirect heating method) and Al63.1Cu24.5Fe12.4 (e-beam method), respectively. The resistivities of the films prepared by both methods were ∼2000 μΩ cm at room temperature and ∼ 4000 μΩ cm at 10 K. © 2002 Elsevier Science Ltd. All rigts reserved.