R. V. Nandedkar

SWIFT HEAVY ION IRRADIATION EFFECTS IN PT/C AND NI/C MULTILAYERS

Abstract Irradiation effects of 100 MeV Ag ion irradiation on Ni/C and Pt/C multilayers have been studied using X-ray reflectivity measurements. Modifications are observed in both the multilayers at (d E /d x ) e values much below the threshold values for Ni and Pt. This effect is attributed to the discontinuous nature of the metal layers. In both the multilayers interfacial roughness increases with irradiation dose. While Ni/C multilayers exhibit large ion-beam induced intermixing, no observable intermixing is observed in the case of Pt/C multilayer. This difference in the behavior of the two systems suggests a significant role for chemically guided defect motion in the mixing process associated with swift heavy ion irradiation.

Ion-beam mixing in an immiscible Fe/Ag multilayer film

Ion-beam mixing of the thermally immiscible Fe/Ag system is studied by 90 keV Ar+-ion irradiation of Fe/Ag multilayer at 325 K and the evolution of microstructure is studied by x-ray diffraction (XRD), x-ray reflectivity, and transmission electron microscopy (TEM). XRD measurements did not show any evidence of a additional phase formation or increase in solubility due to mixing of Fe in Ag. X-ray reflectivity analysis shows an initial sharpening at the interface for a fluence of 1×1016 ions/cm2 and the destruction of multilayer periodicity is observed for higher fluences. The microstructural studies by TEM show a reduction in Ag particle size with fluence. The size of Ag nanoclusters was optimum at a fluence of 7×1016 ions/cm2 and was found to be in the range of 10–20 nm. The particle density decreases at low fluence and on further irradiation, the particle density increases at higher ion fluences. This indicates the nucleation of Ag particles presumably due to long-range transport of Ag atoms. These Ag a...

Effect of Si layer thickness on the structural properties of a Co/Si multilayer system

The nature of the interface involved and the structure characteristics of the as-deposited Co/Si multilayer system have been studied. Using the ion-beam sputtering technique, multilayers, having ten bilayers of Co and Si, were deposited. X-ray reflectivity, x-ray standing wave and wide-angle x-ray diffraction techniques were used to study the interface of the system. The x-ray reflectivity curves obtained confirm the good quality of the Co/Si stack. The presence of a silicide layer at the interface is not distinctly visible. The Co is found to be crystalline in nature and it is highly textured. This texture of the Co layer is lost as the Si layer thickness is increased above a particular value. We have performed some preliminary magneto-optical Kerr effect (MOKE) measurements at room temperature, which show that all the samples have ferromagnetic coupling between the different Co layers and that the nature of ferromagnetism is highly governed by the Si layer thickness.

Thermal stablity of nickel-carbon XUV multilayers

Abstract Thermal stability of Nickel-Carbon (Ni/C) multilayer fabricated in an electron beam deposition system, is studied under vacuum annealing using x-ray reflectivity and x-ray diffraction at 8 KeV. The bilayer periodicity is stable up to 300°C. Annealing to 100°C reduces the interfacial roughness. The bilayer periodicity increases at 350°C and at 400°C multilayer reflections vanishes. The crystallite size of nickel grows with annealing temperature. Mechanism for expansion of carbon based multilayer, is studied by coating the Ni/C multilayer with a 150A thick carbon layer.

Irradiation-induced metastable phase formation and amorphization in an immiscible Co/Ag multilayer

Co/Ag multilayers were prepared by an alternate deposition of Co and Ag metals using electron beam evaporation. These multilayers were irradiated with 130 keV argon ions at room temperature. Upon irradiation to a fluence of 7 × 1016 ions cm−2, a new metastable phase (DO19) with hcp structure having nanosized grains embedded in a matrix having an amorphous structure was observed.

Effect of tin diffusion on the optical behavior of float glass in the soft-x-ray region

The optical responses of two sides of float glass in the soft-x-ray region were studied at the Indus-1 synchrotron facility. To the best of our knowledge these are the first experimentally obtained optical data for both sides of float glass in the soft-x-ray region. Optical constants delta and beta were determined by use of angle-dependent reflectance techniques in the wavelength range 80-200 A. On the side of the glass that was tin indiffused, a significant difference in delta value from that of the non-tin-side surface was observed. The measured data were compared with Henkes tabulated value of SiO2. The surface roughness of float glass was separately determined by hard-x-ray reflectivity to minimize the number of fitting variables. The effect of a contamination layer on the determination of optical constants was avoided by an appropriate sample-cleaning method.

Study of Pt/C X-Ray Multilayer Structure as a Function of Layer Perid Using X-Ray Scattering

Pt/C x-ray multilayer, with varying period lengths d, ranging from 4.7 nm to 3.5 nm were made by dc magnetron sputtering under identical deposition conditions. The Pt layer thickness in all the cases was maintained at a nominal value of 0.37d and a total of 20 layer periods were deposited in each case. Since the morphology in the interface plane and along the growth direction is important for imaging applications, the dependence of this on the layer period has been investigated using x-ray scattering. The grazing incidence x-ray scattering technique has been used to study both the specular and diffuse scattering behaviour of these multilayer structures. The interface roughness was determined from the specular reflectivity measured over a large momentum transfer range using both 0.154 nm and 0.834 nm wavelength x-rays. The interface roughness was found to vary from ~ 0.32 nm to 0.40 nm with decreasing period. The diffuse component of scattering on the other hand was found to decrease with a decrease in layer period. The atomic ordering in the individual layers studied using high angle x-ray diffraction shows clearly the presence of crystallinity in the Pt layers, independent of the layer period.

X-Ray and Neutron Reflectivity Measurements for Characterizing Thin Gold Film X-Ray Reflectors

X-ray and neutron reflectivity of thin gold films (few hundred A) deposited on float glass has been measured. The X-ray reflectivity measurement has been done using Cu Kα radiation of 1.54 A. Neutron reflectivity measurements have been done with 4.06 A cold neutrons at Dhruva reactor, Trombay, India. The film thickness, density and root mean square roughness have been estimated by fitting the data, using dynamical theory of reflection for generating X-ray and neutron reflectivity profiles. Results of both the experiments compare well.