Ion-beam-mixing induced amorphization of Fe/Zr multilayers

The Ar-ion-beam-mixing of the Fe/Zr multilayers is studied by conversion electron Mössbauer spectroscopy. The dependence of the amorphization process on ion dose is studied in detail for two sample thicknesses with an Fe to Zr ratio of 1 and modulation wavelength of 20 and 60 nm. Experimental results are compared with the predictions of the ballistic cascade and thermal spike models of mixing.     

Ion beam induced phase transformation in Fe–Mn bilayers: a Mössbauer study

Ion‐beam mixing of Fe–Mn bilayers induced by 100 keV krypton ions in the dose range (0.1-15)×10¹⁵ ions/cm²has been studied by means of conversion electron Mössbauer spectroscopy and X‐ray diffraction. The results indicate that a dose of about 1 ×10¹⁵ Kr⁺/cm² is sufficient to induce an appreciable mixing between the two atomic species. The α-Fe(Mn)solid solution presents a maximum at this dose, while at higher doses also the ? and γFe–Mn phases are formed in an appreciable amount. Heating of irradiated samples evidences the metastable character of ? phase and favours the growth of the terminal structures γ-Fe(Mn) and α-Mn(Fe) of the Fe–Mn equilibrium phase diagram.     

Proton irradiation and solid state reaction of Fe−Zr multilayers

The amorphization of Fe−Zr multilayers due to ion-beam mixing and solid state reaction is studied in detail using the CEMS and CXMS. The nature of the amorphous Fe−Zr phase produced by both processes is the same suggesting that diffusion of Fe is an important mechanism during ion-beam mixing.     

Influence of ion-irradiation parameters on defect formation in silicon films

It is shown that unlike bulk silicon, for which amorphization is observed at an irradiation dose of 5 × 10¹⁶ ion/cm², thin silicon films on sapphire are amorphized at lower critical doses (10¹⁵ ion/cm²). An undamaged surface layer remains when the silicon films are irradiated with Si⁺ ion beams. Its thickness depends on the current density of the incident beam. Rutherford backscattering studies show that annealing at 950°C improves the crystallinity of the irradiated silicon film. Annealing of the films at 1100°C leads to mixing of the silicon-sapphire interface.     

Magnetic anisotropy in multilayers

Magnetic anisotropy between in-plane and out of plane magnetic alignments is studied in a variety of multilayer systems using Mössbauer spectrosopy to observe the (Fe) magnetic orientation. The surface anisotropy in Fe/Au (1 1 1) multilayers is measured as K _s = 0.9 × 10^?3 Jm^?2. In Fe/Ni multilayers the dependence of magnetic orientation on external field applied normal to the layers enables volume and interface anisotropies K _v = (?5 ± 1) × 10⁴ Jm^?3 and K _s = (?0.6 ± 0.4)× 10^?3 Jm^?2 to be evaluated. In similar applied field experiments coherent rotation of the magnetic Fe and NiFe layers in Fe/Cu/NiFe/Cu multilayers was observed for intervening Cu layer thickness x = 5 Å but independent rotation for x = 50 Å. Out of plane magnetic components are observed for DyFe₂, YFe₂ thin films and DyFe₂/YFe₂ multilayers. In fields of up to 0.25 T applied inplane only the moments of the YFe₂ film showed significant rotation.     

Materials modification at zirconium–silicon interface using swift heavy ions

The reactivity of the Zr/Si interface induced by swift heavy ion beams of Au has been investigated in the present work. Zirconium was evaporated on a clean silicon substrate in ultra high vacuum (UHV) at a pressure of 10^?8 Torr by the electron beam evaporation technique and the final layer was a thin film of Au to avoid oxidation of zirconium. The Zr/Si system was irradiated by 350 MeV Au²⁶⁺ ions at liquid nitrogen temperature at different fluences (0.46×10¹⁴, 1.85×10¹⁴ and 4.62×10¹⁴ ions/cm²). Rutherford back scattering (RBS) spectroscopy using 2 MeV He ions was used to monitor the Zr and Si concentration profiles and interdiffusion at the interfaces. The irradiation at the Zr/Si interface showed mixing. X-ray diffraction measurements confirmed the formation of the ZrSi₂ phase. Thermal spike formation and melting in the tracks was found to be the dominant process at the interfaces.     

Modification of thin oxide films on Be,Si, Al,Ti, Zr,and W under bombardment by He<Superscript>+</Superscript> and Ar<Superscript>+</Superscript> ion beams with a broad energy spectrum

Data on the distribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms implanted in oxide film on metal substrates by ion mixing under the action of He⁺ and Ar⁺ ion beams with a broad energy spectrum, with average energy of 10 keV, and with radiation doses up to 1 × 10²¹ ion/cm² are presented. It is shown that layers with different concentration gradients of implanted atoms form in a thin oxide layer due to simultaneous implantation, but their concentration decreases dramatically to the background value at the oxide-metal interface. Analysis of experimental data suggests that the migration of implanted atoms takes place by means of the diffusion mechanism and is determined by the parameters of physicochemical interaction of implanted atoms with substrate atoms.     

Growth of fractal patterns during irradiation-induced amorphization in nano-sized Ni–W multilayers

In the Ni–W system, a uniform amorphous Ni–W phase was obtained by ion irradiation of the nano-sized Ni–W multilayers at liquid-nitrogen temperature. Interestingly, before undergoing complete amorphization, fractal patterns were observed at a relatively low irradiation dose (3×10¹⁴ Xe⁺/cm²), and the patterns were characterized to consist of crystalline grains of Ni-enriched solid solution. The fractal dimension was measured to be about 1.68±0.05, which was very close to that expected by the cluster diffusion-limited aggregation model. Received: 30 January 2002 / Accepted: 2 February 2002 / Published online: 3 May 2002     

Radiation damage of material surfaces under prolonged irradiation with He+ and Ar+ ions with broad energy spectra

The results of studying the redistribution of Be, Al, Ti, Fe, Cu, Zr, Mo, and W atoms incorporated in polycrystalline metal samples under irradiation with He⁺, (He⁺ + Ar⁺), and Ar⁺ ion beams with a broad energy spectrum and an average energy of 10 keV at irradiation doses of 1 × 10²¹ ion/cm² are studied. It is discovered that irradiation at doses exceeding 1 × 10¹⁹ ion/cm² results in local small-crystal formations being produced in a near-surface substrate layer. Their typical dimensions are less than 1–5 μm, and their the density is up to 1–100. They contain incorporated atoms and impurity atoms with a concentration of 0.1–10 at %. Subsequent irradiation at a dose of 1 × 10²⁰ ions/cm² or more leads to disappearance of these formations, mainly because of sputtering processes.     

Au5+ ion implantation induced structural phase transitions probed through structural,microstructural and phonon properties in BiFeO3 ceramics,using synergistic ion beam energy

Implanted Au⁵⁺-ion-induced modification in structural and phonon properties of phase pure BiFeO₃ (BFO) ceramics prepared by sol–gel method was investigated. These BFO samples were implanted by 15.8?MeV ions of Au⁵⁺ at various ion fluence ranging from 1?×?10¹⁴ to 5?×?10¹⁵?ions/cm². Effect of Au⁵⁺ ions’ implantation is explained in terms of structural phase transition coupled with amorphization/recrystallization due to ion implantation probed through XRD, SEM, EDX and Raman spectroscopy. XRD patterns show broad diffuse contributions due to amorphization in implanted samples. SEM images show grains collapsing and mounds’ formation over the surface due to mass transport. The peaks of the Raman spectra were broadened and also the peak intensities were decreased for the samples irradiated with 15.8?MeV Au⁵⁺ ions at a fluence of 5?×?10¹⁵?ion/cm². The percentage increase/decrease in amorphization and recrystallization has been estimated from Raman and XRD data, which support the synergistic effects being operative due to comparable nuclear and electronic energy losses at 15.8?MeV Au⁵⁺ ion implantation. Effect of thermal treatment on implanted samples is also probed and discussed.     

Ion induced modification in structural and magnetic properties of Pt/Cr/Co multilayers

This paper reports on the change in the magnetic and the structural properties of Pt/Cr/Co multilayers due to 1 MeV N⁺-ion irradiation at room temperature. We observe irradiation induced formation of the CoCrPt ternary alloy phase at a fluence of 1×10¹⁶ ions cm^?2. Phase formation is accompanied by an enhancement in the coercivity. The enhancement in the coercivity is attributed to inhomogeneous alloying and possible mixing-induced strain. These findings are explained in the light of ion beam induced recoil mixing and ionization events.     

热峰模型在聚碳酸酯非晶化潜径迹中的应用

为了描述快重离子在聚合物中的潜径迹行为，用不同能量的快重离子 (1158GeVFe5656,1755GeVXe136¹³⁶及2636GeVU238²³⁸) 辐照 叠层半结晶聚碳酸酯膜 (Makrofol KG型)，结合x射线衍射测量技术，在较宽的电子能损 (1 9—171keV/nm)和离子注量（5×1010¹⁰—3×1012¹² cm-2^-2）范围研究了离子在半 关键词： 离子辐照 聚碳酸酯 非晶化 潜径迹     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Effects of interfacial roughness on the magnetoresistance of Co/Cu multilayers

Using a semi-classical approach, Hood, Falicov and Penn have studied the effects of interfacial roughness on the magnetoresistance (MR) of iron based trilayers (Fe/Cr/Fe and Fe/Cu/Fe). We extend their theory to magnetic metallic multilayers composed of N bilayers ferromagnetic-normal metal. The in plane MR of Co/Cu multilayers is calculated for correlated quasiperiodic interfaces. The averaged effects due to impurities, interdiffusion, band structure, etc. are included in a simple way using two phenomenological parameters S^↑ and S^↓ for two directions of spin. MR variation with S^↑, S^↓ and relaxation time is reported. We analyse also recent experimental data giving the influence of number of bilayers on the MR of Co/Cu multilayers for different temperatures.     

The electric field gradient at 57Fe in zinc and comparisons with the conduction-electron charge-shift model

The magnitude of the electric field gradient at ⁵⁷Fe probe nuclei in Zn is measured using Mössbauer effect and the value is 2.34 × 10¹⁷ V/cm². The electric field gradients at Fe probe nuclei in Ti, Zn, Zr, Cd and Hf hosts are compared with the predictions of the conduction-electron charge-shift model.     

Swift heavy ion irradiation induced modification of BiFeO3 thin films prepared by sol-gel method

We report the preparation of multiferroic BiFeO₃ thin films on ITO coated glass substrates through sol-gel spin coating method followed by thermal annealing and their modification by swift heavy ion (SHI) irradiation. X-ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO₃ evolved on annealing the films at 550°C. Both XRD and Raman studies indicated that SHI irradiation by 200 MeV Au ions result in fragmentation of particles and progressive amorphization with increasing irradiation fluence. The average crystallite size estimated from the XRD line width decreased from 38 nm in pristine sample annealed at 550°C to 29 nm on irradiating these films by 200 MeV Au ions at 1 × 10¹¹ ions cm⁻². Complete amorphization of the rhombohedral BiFeO₃ phase occurs at a fluence of 1 × 10¹² ions.cm⁻². Irradiation by another ion (200 MeV Ag) had the similar effect. For both the ions, the electronic energy loss exceeds the threshold electronic energy loss for creation of amorphized latent tracks in BiFeO₃.     

Investigation of energetic ion-induced mixing in Bi/Ge system

The present study is carried out for the investigation of energetic ion beam mixing in the Bi/Ge system, induced by electronic excitation. The system Ge/Bi/C was deposited on Si substrate at room temperature in the high vacuum deposition system and irradiated using Au ions of 120?MeV at the fluences 1?×?10¹³, 5?×?10¹³ and 1?×?10¹⁴?ions/cm². The top layer of carbon was deposited as the protecting layer to avoid oxidation. The swift heavy ions (SHI)-induced interface mixing was studied by Rutherford backscattering spectroscopy (RBS) for depth profiles and compositions, grazing incidence X-ray diffraction (GIXRD) for phase identification and atomic force microscopy (AFM) for surface roughness. We have calculated the mixing rate, mixing efficiency and inter-diffusion coefficient for the Bi/Ge system. We observed that the thickness of the mixed region increased with increasing fluence. In the GIXRD pattern, no new crystalline phase formation was observed after irradiation, the mixed region may be in an amorphous form. The mixing effect is explained in the framework of the thermal spike model.     

Effect of ion beam irradiation on palladium (II) acetyl acetonate dispersed in polymer matrix

Composites, containing different concentrations of palladium (II) acetylacetonate in polymethyl methacrylate (PMMA) matrix were prepared by vigorous mixing. PMMA was prepared by solution polymerization technique. The composites were irradiated with a 120 MeV Ni¹⁰⁺ beam at two different fluences of 1×10¹¹ and 5×10¹² ions/cm² to study ion-induced effects on their dielectric, structural properties and surface morphology. AC electrical properties of these samples were studied in the frequency range 100 Hz to 10 MHz. The dielectric permittivity/loss shows frequency dependent behavior and it obeys the universal law of dielectric (i.e. ?α f ^n?1) for pristine and irradiated samples at high frequency. The crystalline size and crystallinity of the composites were studied by X-ray diffraction analysis. Decrease in peak intensity after irradiation signifies the amorphization which is also responsible for decrease in T _g as obtained by means of differential scanning calorimetry measurement. Fourier transform infrared spectra also support this result. Surface roughness increases upon irradiation as observed from scanning electron microscopy.     

Swift heavy ion beam mixing at V/Si interface

Vanadium silicides are of increasing interest because of applications in high temperature superconductivity and in microelectronics as contact materials due to their good electrical conductivity. In the present work ion beam induced mixing at Si/V/Si interface has been investigated using 120 MeV Au ions at 1 × 10¹³ to 1 × 10¹⁴ ions/cm² fluence at room temperature. V/Si interface was characterized by Grazing Incidence X-Ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectrometry (RBS) and Cross-sectional Transmission Electron Microscopy (XTEM) techniques before and after irradiation. It was found that the atomic mixing width increases with ion fluence. GIXRD and RBS investigations confirm the formation of V₆Si₅ silicide phase at the interface at the highest ion irradiation dose.     

A Mössbauer study on thermal dynamics of Fe atoms in the implanted CuFe solid solution

The annealing behaviour for a supersaturated solid solution of CuFe produced by ⁵⁷Fe ions implanted into a copper film has been studied by CEMS at doses of 5×10¹⁵, 1×10¹⁶, 3×10¹⁶ and 1×10¹⁷ at/cm². During annealing the transformation of the γ- Fe phase and isolated iron atoms to the α-Fe phase was observed with a dose of 1×10¹⁶ at/cm² at about 440°C. Prior to α-Fe, a ferromagnetic phase with small field occured at h higher doses. The effects of radiation defects on hyperfine parameters and phase transformation are discussed in this paper.