Nanostructuring of Multilayers by a Thermally Driven Self Assembling Process
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Nanostructuring of multilayers by a thermally driven self assembling process C. Herweg1, S. Dreyer1, P. Troche1, J. Hoffmann2, S. Sievers1, C. Lang1 and H. C. Freyhardt1,2 1 2
Institut fuer Materialphysik, Universitaet Goettingen, Windausweg 2, D-37073 Goettingen Zentrum fuer Funktionswerkstoffe ZFW gGmbH, Windausweg 2, D-37073 Goettingen
ABSTRACT Multilayers consisting of two immiscible components (e.g. Fe/Ag Fe/Au or Ni/NiO) could by transformed by an annealing process into a nanostructured system of non statistically distributed nearly spherical particles in a surrounding matrix of the complementary component. The non statistical arrangement of the particles and the dynamics of the disintegration process strongly depend on the initial interface energy, i.e. the local interface curvature and the local interfacial stress. Detailed microstructure investigations of the different systems are used to interpret the measured transport properties. INTRODUCTION Due to their prominent mechanical, optical, electrical and magnetic properties, materials structured on a nanometerscale are of great interest in modern material science and strong candidates for future applications. In contrast to other methods, the preparation of nanostructered systems by conventional thin film deposition techniques and a subsequent heat treatment is relatively easy, time- and cost-efficent. A disintegration process caused by interfacial curvature has been first observed in Nb/Cu filament superconductors [1]. Analytical solutions have only been published for cylindrically shaped filaments [2], whereas the surface and changing shapes of interfaces in multilayered films is still a matter actual research [3], [4]. Different systems (Nb/Cu, Fe/Ag, Fe/Au, Cu/Co, Co/C) were studied including multilayers consisting of metals and metaloxids as a second component (Ni/Ni0, Co/CoO) in order to get detailed information on which parameters control the disintegration temperature and the final particle distribution. The transition from an anisotropic layered system to an isotropic granular system, strongly influences the transport properties, e.g. the magnetoresistance. Therefore, these properties give an additional insight in the shape instability of multilayer structures. Au(111)
intensity [a.u.]
Fe/Au 70x(2nm/10nm)
280°C
in /m C °2 ,0 320°C
41
42
43
44
45
46
2Θ [°]
47
51 52 53
Fig. 1: XRD scans during annealing. Disintegration of a 70x(2nm Fe/10nm Au) multilayer at 320°C.
EXPERIMENTS Metal/metal multilayers were prepared in a UHV-system (background pressure < 10-8mbar) using two indepentent operatable magnetron sputtering sources (working pressure Ar, 10-3mbar) with high purity metal targets. The alternating deposition of the two components was performed by intermittent operation of the two sources, whereby the 54source not in use was switched off and shutters were employed to ensure a minimum intermixing at the interfaces. Metal/metaloxid multilayers were prepared by
W6.35.1
reactive ion-beam sputtering (Xe, 5⋅10-5bar) with Kaufmann ion s
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