Anomalous behavior in temporal evolution of ripple wavelength under medium energy Ar+-ion bombardment on Si: A case of initial wavelength selection

We have studied the early stage dynamics of ripple patterns on Si surfaces, in the fluence range of 1-3 x 10(18) ions cm(-2), as induced by medium energy Ar+-ion irradiation at room temperature. Under our experimental conditions, the ripple evolution is found to be in the linear regime, while a clear decreasing trend in the ripple wavelength is observed up to a certain time (fluence). Numerical simulations of a continuum model of ion-sputtered surfaces suggest that this anomalous behavior is due to the relaxation of the surface features of the experimental pristine surface during the initial stage of pattern formation. The observation of this hitherto unobserved behavior of the ripple wavelength seems to have been enabled by the use of medium energy ions, where the ripple wavelengths are found to be order(s) of magnitude larger than those at lower ion energies.The authors are thankful to D. P. Datta from National Institute of Science Education and Research (NISER), Bhubaneswar, for his support and discussion at various stages of this work. R.C. acknowledges funding by MINECO (Spain) through Grant Nos. FIS2012-38866-C05-01 and FIS2015-66020-C2-1-P. S.K.G. acknowledges local support by Universidad Carlos III de Madrid during a short-term visit

Fabrication of Germanium-on-insulator in a Ge wafer with a crystalline Ge top layer and buried GeO2 layer by Oxygen ion implantation

The paper reports fabrication of Germanium-on-Insulator (GeOI) wafer by Oxygen ion implantation of an undoped single crystalline Ge wafer of orientation (100). Oxygen ions of energy 200 keV were implanted. The implanted wafer was subjected to Rapid Thermal Annealing to 650 C. The resulting wafer has a top crystalline Ge layer of 220 nm thickness and Buried Oxide layer (BOX) layer of good quality crystalline Germanium oxide with thickness around 0.62 micron. The crystalline BOX layer has hexagonal crystal structure with lattice constants close to the standard values. Raman Spectroscopy, cross-sectional HRTEM with SAED and EDS established that the top Ge layer was recrystallized during annealing with faceted crystallites. The top layer has a small tensile strain of around +0.4\% and has estimated dislocation density of 2.7 x 10^{7}cm^{-2}. The thickness, crystallinity and electrical characteristics of the top layer and the quality of the BOX layer of GeO_{2} are such that it can be utilized for device fabrication

Ion beam generated surface ripples: new insight in the underlying mechanism

A new hydrodynamic mechanism is proposed for the ion beam induced surface patterning on solid surfaces. Unlike the standard mechanisms based on the ion beam impact generated erosion and mass redistribution at the free surface (proposed by Bradley-Harper (BH) and its extended theories), the new mechanism proposes that the ion beam induced saltation and creep processes, coupled with incompressible solid flow in amorphous layer, leads to the formation of ripple patterns at the amorphous/crystalline (a/c) interface and hence at the free surface. Ion beam stimulated solid flow inside the amorphous layer controls the wavelength, where as the amount of material transported and re-deposited at a/c interface control the amplitude of ripples. The new approach is verified by designed experiments and supported by the discrete simulation method.Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1206.082

Synthesis of Pt nanoparticles and their burrowing into Si due to synergistic effects of ion beam energy losses

We report the synthesis of Pt nanoparticles and their burrowing into silicon upon irradiation of a Pt-Si thin film with medium-energy neon ions at constant fluence (1.0 x 10(17) ions/cm(2)). Several values of medium-energy neon ions were chosen in order to vary the ratio of the electronic energy loss to the nuclear energy loss (S-e/S-n) from 1 to 10. The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). A TEM image of a cross section of the film irradiated with S-e/S-n = 1 shows approximate to 5 nm Pt NPs were buried up to approximate to 240 nm into the silicon. No silicide phase was detected in the XRD pattern of the film irradiated at the highest value of S-e/S-n. The synergistic effect of the energy losses of the ion beam (molten zones are produced by S-e, and sputtering and local defects are produced by S-n) leading to the synthesis and burrowing of Pt NPs is evidenced. The Pt NP synthesis mechanism and their burrowing into the silicon is discussed in detail

Role of surface composition in morphological evolution of GaAs nano-dots with low-energy ion irradiation

The surface chemistry of GaAs (100) with 50-keV Ar(+) ion beam irradiation at off-normal incidence has been investigated in order to elucidate the surface nano-structuring mechanism(s). Core level and valence band studies of the surface composition were carried out as a function of fluences, which varied from 1 × 10(17) to 7 × 10(17) ions/cm(2). Core-level spectra of samples analyzed by X-ray photoelectron spectroscopy confirmed the Ga enrichment of the surface resulting in bigger sized nano-dots. Formation of such nano-dots is attributed to be due to the interplay between preferential sputtering and surface diffusion processes. Valence band measurement shows that the shift in the Fermi edge is higher for Ga- rich, bigger sized nano-dots due to the partial oxide formation of Ga. ‘One-dimensional power spectral density’ extracted from atomic force micrographs also confirms the significant role of surface diffusion in observed nano-structuring

Design of a Compact Hybrid Undulator for the THz Radiation Facility of Delhi Light Source (DLS)

A compact Free Electron Laser (FEL) facility to produce coherent THz radiation is in the development stage at Inter-University Accelerator Centre (IUAC), New Delhi, India [1-3]. The facility is named the Delhi Light Source (DLS). It is planned to produce an 8-MeV electron beam from a photo-cathode RF gun, and the electron beam will be injected into a compact undulator to generate the radiation. To produce THz radiation in the range of 0.15 to 3.0 THz, the electron beam energy and the undulator gap will be varied from 4 to 8 MeV and 20 to 45 mm, respectively. The variable-gap undulator of 1.5-m length will consist of NdFeB magnets with vanadium permendur poles. The magnet design and dimensions are optimised by using code 3D RADIA [4]. The detailed design of the compact hybrid undulator is presented in this paper

Enhancement of superconducting parameters of MgB2 by low energy carbon ion implantation

The aim of work is to study the effects of carbon ion implantation on enhancement of superconducting properties of MgB2. Pure MgB2 bulk samples are irradiated by carbon ion beam of energy 40 keV (beam current 1 mu A) at different fluences. After irradiation, there is enhancement in superconducting properties viz., critical current density (J(c)), critical magnetic field (H-c2), comparing to pristine sample. Estimated with Ginzburg-Landau theory method at zero kelvin, the critical magnetic field H-c2(0) for irradiated sample shows an increase of 47 T than that of 38 T reported for pristine sample. There is also a four times increase in J(c) after implantation. Improvement in grain connectivity with ion fluence is found in surface morphological studies. Raman spectroscopic studies show a shift in resonance peak related with E-2g phonon modes after irradiation. This shifting is caused due to improvement in scattering and alteration of Fermi surface in implanted samples. These results are explained in correlation with the lattice disorder