Self-Diffusion in Chemically Homogeneous Multilayers Using Neutron and Nuclear Resonance Reflectivity
- PDF / 219,676 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 169 Views
Q1.7.1
Self-Diffusion in Chemically Homogeneous Multilayers Using Neutron and Nuclear Resonance Reflectivity Mukul Gupta1, Ajay Gupta2, Sujoy Chakravarty2, T. Gutberlet1, H.-C. Wille3, O. Leupold3, R. Rüffer3 1
Laboratory for Neutron Scattering, ETHZ & PSI, Paul Scherrer Institute, Villigen, CH-5232, Switzerland 2 Inter University Consortium for DAE facilities, Khandwa Road, Indore, 452017, India 3 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France ABSTRACT Neutron reflectivity is a well-established technique for studying self-diffusion in chemically homogeneous system as neutron scattering lengths are different for isotopes of an element. For x-ray there is no contrast for a multilayer with isotopic abundance. However, placing Mössbauer active nuclei in a chemically homogeneous system, self-diffusion of the constituents can be probed using nuclear resonance scattering of Mössbauer active nuclei. In the present work, we have applied the neutron reflectivity technique for studying the self-diffusion of iron and nitrogen in nano crystalline multilayers of FeN/57FeN and FeN/Fe15N and nuclear resonance reflectivity techniques for studying iron self diffusion in FeNZr/57FeNZr. Both the techniques are complementary to each other and give a unique depth resolution of the order of 0.1 nm. As compared with conventional techniques used for probing self-diffusion, neutron and nuclear resonance reflectivity techniques can be applied at significantly lower temperatures. On the basis of the obtained results the diffusion mechanism in chemically homogeneous multilayers is discussed in the present work. INTRODUCTION During recent decades amorphous and nanocrystalline metals and alloys have been investigated as an important class of materials with the possibility of tailoring their properties over a wide range by controlling the particle size and morphology [1,2,3,4]. Atomic diffusion, in particular self-diffusion is decisive for determining the long standing application of these materials. In conventional crystalline alloys a diffusion mechanism involving ‘jump’ or ‘vacancy’ is broadly responsible [5]. In an amorphous system, which is free from long range ordering, a collective type diffusion mechanism governs self-diffusion [5]. Similarly, in nanocrystalline alloys grain-boundary diffusion is responsible. When an amorphous, nano or poly crystalline alloy is prepared in the form of a thin film, additional effects come into picture due to reduced dimensionality and defects produced during preparation of thin film. Under such a situation the self-diffusion mechanism may vary [6]. The aim of the present work is to investigate the self-diffusion mechanism. In order to investigate self-diffusion in thin film multilayers, isotopic labelling is required in such a way that the contrast exists only for isotopes and chemically, the whole media is homogeneous. Therefore, such structures are termed as chemically homogeneous multilayers (CHM) [7]. In order to probe self-diffusion in nm range CHM a depth resolution
Data Loading...
