ISSN:
1662-9779
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Physics
Notes:
In nanostructured materials, where the density of grain- and interphase-boundaries is high,the diffusion and kinetics of surface segregation, i.e. the effective material flow is always influenced bythe contributions of these boundaries [1]. Diffusion on the nano/atomic scales in multilayers, thin filmshas many challenging features even if the role of structural defects can be neglected and ‘only’ theeffects related to the nano/atomic scale arise. Different examples for diffusional nanoscale effectsdiscovered recently by the authors will be given in this paper. We show that the continuum descriptionsof diffusion cannot be applied automatically on such short distances, the classical continuumapproximations (Fick's laws) cannot describe correctly the atomic movements. [2-4] They predict fasterkinetics than the atomistic models and the interface shift is always proportional to the square-root oftime (x ∝ t1/2 ⇒ x2 ∝ t: parabolic or Fickian kinetics). As we will show, however, the kinetics can beeven linear (x ∝ t) on the nano/atomic scale. [3, 4] Furthermore, the continuum descriptions foretellinfinitely fast kinetics as the time goes to zero (v=dx/dt∝1/t1/2), which is a long standing paradox ofdiffusion theory. We will show a possible resolution of this paradox. [5] Moreover, we will show that aninitially diffused interface can sharpen even in completely miscible systems. [6, 7]
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/24/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.129.105.pdf
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