Physics

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Shiv Nadar University

This study deals with structural and optical properties of β-FeSi2 layers produced by direct ion beam mixing of Fe/Si bilayers with Xe ions. By irradiation of 35 nm Fe on Si, at 600 °C with 205 keV Xe to 2 × 1016 ions/cm2, the formation of ~ 105 nm single-phase β-FeSi2 layers was achieved. Their structures were analyzed by Rutherford backscattering spectroscopy. X-ray diffraction, conversion electron Mössbauer spectroscopy, high resolution transmission electron microscopy, and photo-absorption. The structural analyses revealed that the β-FeSi2 layers grow in the form of irregularly shaped crystal grains, with a pronounced surface morphology, but with a rather sharp silicide/silicon interface. The grains that originate from the interface are epitaxially oriented relative to the Si(100) substrate. Optical absorption, as compared with that in β-FeSi2 layers produced by ion beam synthesis or co-sputter deposition, indicates a direct band gap of 0.92 eV. A pronounced surface roughness of the ion beam mixed layers yielded photo-absorption approximately three times higher as compared with the other two sets of samples. The band gap stays nearly constant over the temperature range from 80 to 295 K. This is tentatively assigned to a high degree of structural disorder and stress induced in the ion beam mixed β-FeSi2 layers. © 2002 Elsevier Science B.V. All rights reserved.

World University root node

(SoNS) School of Natural Sciences

Surface and Coatings Technology

Structural and optical properties of β-FeSi2 layers grown by ion beam mixing

We discuss certain features of pseudo-Hermiticity and weak pseudo-Hermiticity conditions and point out that, contrary to a recent claim, there is no inconsistency if the correct orthogonality condition is used for the class of pseudo-Hermitian, PT symmetric Hamiltonians of the type Hβ = [p + iβv(x)]2/2m + V (x). © 2002 Elsevier Science B.V. All rights reserved.

Fulltext

Physics Letters, Section A: General, Atomic and Solid State Physics

Pseudo-Hermiticity, weak pseudo-Hermiticity and η-orthogonality condition

We analyze a set of three PT-symmetric complex potentials, namely harmonic oscillator, generalized Pöschl-Teller and Scarf II, all of which reveal a double series of energy levels along with the corresponding superpotential. Inspired by the fact that two superpotentials reside naturally in order-two parasupersymmetry (PSUSY) and second-derivative supersymmetry (SSUSY) schemes, we complexify their frameworks to successfully account for the three potentials.

International Journal of Modern Physics A

Complexified PSUSY and SSUSY interpretations of some PT-symmetric Hamiltonians possessing two series of real energy eigenvalues

Effect of 100 MeV58Ni+8 ion irradiation on the electrical transport behaviour of Al-Cu-Fe quasicrystalline thin films have been investigated by in situ and ex situ resistivity measurements. The quasicrystalline thin films grown by indirect heating, electron-beam and flash evaporation methods have been used for this purpose. The fluence of 100 MeV58Ni+8 beam is varied from 1 × 109 to 1 × 1013 particles/cm2. A small oscillatory variation of resistivity up to a critical fluence of 5×1012 particles/cm2 is observed in all the samples. A rapid decrease in resistivity is observed at a fluence of 1 × 1013 particles/cm2 for all the quasicrystalline thin films. These thin films also show negative temperature coefficient of resistivity similar to that of unirradiated quasicrystalline thin films. The results of simulation for resistivity versus temperature (unirradiated and irradiated at fluence 1 × 1013 particles/cm2) support the observed behaviour of resistivity with temperature. © 2002 Elsevier Science Ltd. All rights reserved.

Vacuum

Effect of irradiation by 100 MeV58Ni+8 ion on quasicrystalline thin films

Solid phase epitaxial regrowth of α-quartz amorphized by ion implantation of dopants appears to be an attractive method for processing this optoelectronically important material. In an attempt to optimize solid phase epitaxy of α-quartz, we have studied the case of 50 keV 23Na ion implantation and annealing in an 18O atmosphere at 500-850 °C. The damage profiles were monitored by means of Rutherford backscattering-channeling, while the out-diffusion of the implanted 23Na and the 16O ⇔ 18O exchange in the near-surface layers were investigated using the time-of-flight Elastic Recoil Detection analysis technique. As in the case of Cs-irradiated quartz, full epitaxial recrystallization was observed to occur for Na-irradiated quartz, however, at the lower temperature of approximately 650 °C (vs. 875 °C for Cs). Based on these observations, Na appears to offer a good compromise between a low recrystallization temperature (required to avoid oxidation of the dopants) and full recrystallization of the matrix. © 2002 Elsevier Science B.V. All rights reserved.

Epitaxial recrystallization of amorphized α-quartz after sodium ion implantation and oxygen annealing

Solid phase epitaxial regrowth of the amorphized layer in α-quartz induced by Rb ion implantations has been studied by thermal annealing in air at 800-1200 K. The Rb+ ions were implanted at 175 keV to fluences of 1.0 × 1016-3.4 × 1016 ions/cm2. The damage profiles and Rb depth distributions were measured by Rutherford backscattering and channeling spectroscopy. Complete epitaxial recrystallization was achieved for the samples implanted with 2.5 × 1016 Rb/cm2 after a 1 h annealing in air at 1173 K. The regrowth process occurs in two steps and has activation energies of EaL = 0.6 ± 0.1 and EaH = 3.6 ± 0.4 eV. The recrystallization rate was found to increase for increasing implanted Rb fluence. The results are discussed by considering the topological structures and network connectivity of SiO2. © 2002 Elsevier Science B.V. All rights reserved.

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

Epitaxial recrystallization of Rb-irradiated α-quartz during thermal annealing in air

Thin ribbons of stable icosahedral quasicrystal Al65Cu20Fe15 were irradiated with swift heavy ion (SHI) beam of 170 million electron volt (MeV) 58Ni+12 in high and clean vacuum environment at a temperature of 80 K to study the modification of its properties. Dynamic variation of resistance was studied on-line during and after irradiation for the first time, to understand the effect of SHI. The resistance decreased sharply at the time of incidence of ion beam due to creation of a large number of charge carriers by intense ionization by SHI and did oscillate around a mean value during irradiation due to defect creation and annihilation. The resistance increased rapidly just after the beam was stopped from its mean value during irradiation. The quasicrystalline peaks of the XRD data on these samples irradiated by SHI, were prominent till the ion beam fluence of 5 × 1012 particles/cm2, but the peak height consistently decreased with increasing fluence after a fluence of 1012 particles/cm2. © 2001 Elsevier Science Ltd. All rights reserved.

Materials Research Bulletin

Modification of icosahedral quasicrystal Al65Cu20Fe15 by 170-MeV 58Ni+12 beam

We construct two commuting sets of creation and annihilation operators for the PT-symmetric oscillator. We then build coherent states of the latter as eigenstates of such annihilation operators by employing a modified version of the normalization integral that is relevant to PT-symmetric systems. We show that the coherent states are normalizable only in the range (0, 1) of the underlying coupling parameter α.

Modern Physics Letters A

Creation and annihilation operators and coherent states for the PT-symmetric oscillator

We consider a PT-symmetric partner to Khare-Mandal's recently proposed non-Hermitian potential with complex eigen-values. Our potential, which is quasi-exactly solvable, is shown to possess only real eigenvalues. © 2001 Elsevier Science B.V. All rights reserved.

A PT-symmetric QES partner to the Khare-Mandal potential with real eigenvalues

The continuity equation relating the change in time of the position probability density to the gradient of the probability current density is generalized to PT-symmetric quantum mechanics. The normalization condition of eigenfunctions is modified in accordance with this new conservation law and illustrated with some detailed examples.