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Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale
Author(s) -
Schmidt Harald,
Hüger Erwin,
Chakravarty Sujoy,
Stahn Jochen,
Gutberlet Thomas,
Tietze Ursula,
Lott Dieter
Publication year - 2009
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.200800325
Subject(s) - materials science , neutron reflectometry , nanocrystalline material , amorphous solid , diffusion , crystallization , characterization (materials science) , neutron scattering , thermal diffusivity , chemical physics , analytical chemistry (journal) , small angle neutron scattering , neutron , nanotechnology , crystallography , thermodynamics , nuclear physics , chemistry , physics , chromatography
The investigation of self‐diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1 nm and below at corresponding low self‐diffusivities between 10 −25 and 10 −20 m 2 s −1 . Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non‐equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron.