1,721,707 research outputs found
Stability and thermal reaction of GMR NiFe/Cu thin films
No full textEne CB, Schmitz G, Kirchheim R, Hütten A. Stability and thermal reaction of GMR NiFe/Cu thin films. ACTA MATERIALIA. 2005;53(12):3383-3393.Giant magneto-resistance model systems of NiFe/Cu multilayer stacks with 2 nm single layer thickness were deposited onto needle-shaped W tips using ion beam sputtering and analyzed by atom probe tomography after appropriate heat treatments. Owing to the outstanding sensitivity of the method, even minor chemical modifications on the nanometer scale can be detected. Although annealing treatments at temperatures up to 250 degrees C already result in a dramatic decrease of magneto-resistivity, no major structural or chemical transformation of the initial layer system is found. Instead, a slight decrease of the concentration slope at the interfaces is observed, which is attributed to short range interdiffusion induced by non-equilibrium point defects. Annealing at higher temperatures up to 500 degrees C/40 min still preserves a clear layer structure. However, appreciable amounts of Ni are dissolved inside the Cu layers. In the presence of grain boundaries, the onset of significant grain boundary diffusion occurs at about 350 degrees C. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Nanoanalysis of Co/Cu/NiFe thin films by tomographic atom probe
No full textSchleiwies J, Schmitz G, Heitmann S, Hütten A. Nanoanalysis of Co/Cu/NiFe thin films by tomographic atom probe. APPLIED PHYSICS LETTERS. 2001;78(22):3439-3441.Offering the possibility of improving data storage and magnetic sensoric, applications of giant magnetoresistance (GMR) in thin metallic films are of great interest. In order to study thermal reactions in such layered structures, atom probe tomography is used, which has been proven to perform a real three-dimensional analysis on the relevant length scale of several angstroms only. Co/Cu/Ni79Fe21 layered structures were deposited on tungsten substrate tips by ion beam sputtering and analyzed in the as-prepared state and after suitable heat treatments. After annealing at 250 degreesC for 30 min, Fe segregation at the Co/Cu interface inside the Co layer is clearly observed. This effect may be interpreted as an interface dusting potentially increasing the GMR. After annealing at 350 degreesC for 30 min, an additional Ni segregation inside Cu grain boundaries is observed. It is suggested that this segregation path forms the initial stage of pinhole formation and finally causes ferromagnetic bridges through the paramagnetic coupling layer. (C) 2001 American Institute of Physics
Thermal reaction and stability of NiFe/Cu thin films investigated by atom probe tomography
No full textEne CB, Schmitz G, Kirchheim R, Hütten A. Thermal reaction and stability of NiFe/Cu thin films investigated by atom probe tomography. In: Surface and Interface Analysis. SURFACE AND INTERFACE ANALYSIS. Vol 39. JOHN WILEY & SONS LTD; 2007: 227-231.NiFe/Cu multilayer stacks of 2 nm single layer thickness were deposited onto needle-shaped W tips by ion beam sputtering and analysed by atom probe tomography (TAP) after appropriate heat treatments. After annealing at 250 degrees C for 30 min, no significant structural or chemical transformation of the initial layer system is detected, although such a heat treatment appreciably reduces the magneto resistivity. A slight decrease of the concentration slope at the interfaces is attributed to a very short-range interdiffusion. Clear grain boundary diffusion is observed after annealing at 400 degrees C for 30 min. Further annealing at 500 degrees C for 20 min and 40 min still preserves the layered structure with a homogeneous solution of Ni inside the Cu layers of up to 25 at.% Ni. Copyright (C) 2007 John Wiley & Sons, Ltd
Interdiffusion and reaction of metals: The influence and relaxation of mismatch-induced stress
No full textThe early interdiffusion stages in epitaxially grown Ag/Au and Cu/Au reaction couples are investigated by high-resolution and Z-contrast electron microscopy. While the interdiffusion in the lattice-matched system Ag/Au follows Fick's diffusion laws from the very beginning. a complex two-stage reaction is observed in the lattice-mismatched Cu/Au samples. A fast diffusion at the beginning of the heat treatment produces a planar zone of lattice defects along the interface. which release most of the induced stress. This first reaction stage stops after reaching a diffusion length of about 15 am. Subsequent interdiffusion takes place by a recrystallization mechanism comprising heterogeneous nucleation of new grains and diffusion-induced grain boundary migration. During this second reaction stage, discontinuous composition profiles are determined, evidencing stress release at high-angle grain boundaries. The recrystallization mechanism also dominates the formation Of ordered intermetallics at lower reaction temperatures
The relation between the shape of the stress anomaly and the structure of Fe3Al alloys
No full textThe stress anomaly for FC3Al intermetallics exhibits various shapes in the D0(3) phase region. Two in situ TEM investigations at high temperatures were performed to explain this behaviour-the growth of D0(3) domains and the measurement of the long range order (LRO) in the D0(3) phase during aging. It is shown, that LRO depends on the depth under the surface of the specimen and changes during aging. In the light of this fact is possible to explain the various shape of stress anomaly. (C) 2002 Published by Elsevier Science Ltd
Influence of the microstructure on the interreaction of Al/Ni investigated by tomographic atom probe
No full textIn order to obtain a detailed understanding of the different stages of interreaction, tomographic atom probe (TAP) investigations were performed on Al/Ni-interreaction couples in the as-prepared state, and on couples annealed at various temperatures. To investigate the influence of the microstructure on the early interreaction stages, specimens were prepared by in situ electron beam evaporation and by sputter deposition, for comparision. Because of the outstanding resolution of the TAP, the formation of a metastable phase prior to the formation of the first intermetallic phase predicted for the equilibrium phase diagram of the Binary system Al-Ni was directly proved by chemical analysis. The observation of grain boundary penetration of Ni solute into Al in sputter deposited layers shows that the microstructure of the specimens is a very important factor in the initial phase formation during the early interreaction stages. (C) 2002 Elsevier Science B.V. All rights reserved
Thin film interreaction of Al/Ag analyzed by tomographic atom probe
No full textA nanoanalytical study of Ag/Al interreaction by atom probe tomography is presented, For thia, metallic thin films are deposited on tungsten substrate tips by ion beam sputtering. The Al/Ag reaction couple qualifies its it particularly clear model system due to its simple phase diagram and the identical lattice structure of both reacting materials, Nevertheless, the tomographical analysis demonstrates that the reaction does not proceed on a planar layer geometry. Instead. after annealing at 100 degreesC for 15 min, a three-dimensional reaction morphology develops caused by fast grain boundary transport. During further annealing, at first a metastable phase of 67 at.% Al is observed. The expected equilibrium Ag2Al is only formed in late reaction stages by a precipitation process. (C) 2002 Elsevier Science B.V. All rights reserved
Structure-controlled interdiffusion of Cu/Co/Au thin films investigated by three-dimensional atom probe
No full textThe dependence of thin-film microstructure on the curvature of the substrate is investigated by field ion microscopy (FIM) and transmission electron microscopy (TEM). For this purpose, Cu-Au multilayers were deposited on W single crystals, which are prepared both as curved (radius of curvature similar to50 nm) and as planar substrates. 3D atom probe analysis shows that the curved substrates lead to heterogeneous reaction patterns by grain boundary reaction beside planar reaction patterns. This result is explained by local variations of microstructure. Grain boundary reaction is dependent on the atomic structure of the grain boundary and can lead to the early formation of intermetallics. At temperatures too low for significant volume diffusion, interdiffusion between enriched grain boundaries and neighbored grains is observed under the formation of ordered compounds. The elastic strain, which is caused by a considerable atomic size mismatch, is found to hinder interdiffusion and to cause alloying under grain boundary motion (DIGM). The introduction of a Co diffusion barrier between Au and Cu slows down interdiffusion, resulting in higher reaction temperatures. Thus, it is possible to observe that the grain boundary reaction in the An layer disappears at elevated temperatures, at which volume diffusion of Cu in An gets possible, whereas in the Cu layer the grain boundary reaction is still observed. (C) 2002 Elsevier Science B.V. All rights reserved
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