Atomic diffusion studied with coherent X-rays

Abstract

Knowledge of atomic diffusion is a fundamental issue in synthesis and stability of materials. Direct studies of the elementary diffusion event, that is, how the individual atoms 'jump', are scarce, as the available techniques are limited to selected systems. Here we show how by monitoring the spatial and temporal variations of the scattered coherent X-ray intensity the diffusion of single atoms can be studied. This is demonstrated for the intermetallic alloy Cu(90)Au(10). By measuring along several directions in reciprocal space, we can elucidate the dynamical behaviour of single atoms as a function of their neighbourhood. This method, usually referred to as X-ray photon correlation spectroscopy (XPCS), does not rely on specific atomic species or isotopes and can thus be applied to almost any system. Thus, given the advent of the next-generation X-ray sources, XPCS has the potential to become the main method for quantitatively understanding diffusion on the atomic scale.

Atomic Migration Studies with X-Ray Photon Correlation Spectroscopy

“…for weak interactions between particles) and can be found in [12] or [13]. Our experimental results to date [14,15,16] indicate that this theory works very well and that discrepancies, if any, are negligible with nowadays available coherent beamlines.…”

Beyond simple exponential correlation functions and equilibrium dynamics in x-ray photon correlation spectroscopy

“…This result is consistent with equation (6) since S(Q, ω) and f (Q, t) are Fourier pairs. Such a characterization of diffusion with coherent scattering is an important capability [3] and indeed the ability to track diffusion at the atomic scale with XPCS has recently been demonstrated [6], thereby opening a unique window into the fundamental collective motions in materials. However, for complex dynamics in condensed matter, diffusive motion obeying equation (6) is often the exception rather than the rule.…”

Revealing the fast atomic motion of network glasses

“…Thanks to the instrumental developments in the collection of sparse scattering signals 18 and to an increased flux and coherence of X-ray beams, X-ray photon correlation spectroscopy (XPCS) has recently emerged as a very powerful technique able to follow the evolution of the dynamics at the atomic length scale in crystalline 19 and amorphous materials 8,[20][21][22] . Recent measurements on metallic glasses have revealed the existence of structural rearrangements at the atomic level, contrary to the common expectation of an almost arrested dynamics 8,20,21 .…”