A novel event correlation scheme for X-ray photon correlation spectroscopy

Abstract

X-ray photon correlation spectroscopy (XPCS) was employed to measure the time-dependent intermediate scattering function in an organic molecular glass former. Slow translational dynamics were probed in the glassy state and the correlation functions were calculated from two-dimensional speckle patterns recorded by a CCD detector. The image frames were analysed using a droplet algorithm together with an event correlation scheme. This method provides results analogous to standard intensity correlation algorithms but is much faster, hence addressing the recurrent problem of insufficient computing power for online analysis in XPCS. The event correlator has a wide range of potential future applications at synchrotrons and free-electron laser sources. research papers J. Appl. Cryst. (2012). 45, 807-813 Y. Chushkin et al. Event correlation in XPCS 811 Figure 6(a) The correlation function g (2) of the 2800 images measured at 220 K. Squares show the standard scheme, circles represent the event correlator, and dashed lines are fits. (b) The event correlation function g (2) of the 2800 images (circles) and the time-binned image series (squares).

Compressed correlation functions and fast aging dynamics in metallic glasses

“…Time series of up to ∼5000 images were taken with 7 s exposure time per frame and were analyzed following the procedure described in Ref. 29. No beam damage was observed and the amorphous structure of the sample was checked during the whole experiment by measuring the corresponding static structure factor of the system.…”

Revealing the fast atomic motion of network glasses

“…The data were treated and analysed following the procedure described in ref. 18 to calculate the temporal intensity auto-correlation functions…”

“…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 .…”

On the use of two-time correlation functions for X-ray photon correlation spectroscopy data analysis

“…For example, information about the ergodicity of the system may be lost if the time average is done before the ensemble average (Pusey & Van Megen, 1989), but when using area detectors the time average should be done first to preserve the speckle visibility and to be able to extract measurement errors directly from azimuthal variations of g ð2Þ ðQ; Þ (Lumma et al, 2000). However, multi-speckle dynamic light scattering (DLS)/PCS analysis is often done by performing the ensemble average first (Cipelletti & Weitz, 1999;Chushkin et al, 2012). Thus, the choice of the top or bottom formula between the braces in equation (1) depends on the case under study.…”

“…The 2-TCF is generally represented as a two-dimensional graph of the value of CorrðQ; t 1 ; t 2 Þ, GðQ; t 1 ; t 2 Þ or CðQ; t 1 ; t 2 Þ for a fixed Q, with axes t 1 and t 2 (see x2.2). Brown et al (1997) introduced an alternative coordinate system, which has subsequently been widely used in the XPCS literature (Malik et al, 1998;Brown et al, 1999;Livet et al, 2001;Sutton et al, 2003;Fluerasu et al, 2005;Ludwig et al, 2005;Fluerasu et al, 2007;Mü ller et al, 2011;Orsi et al, 2010Orsi et al, , 2012Chushkin et al, 2012;Livet & Sutton, 2012;Bikondoa et al, 2012;Ruta et al, 2012). Using this alternative coordinate system, approximated 1-TCFs are often extracted from the 2-TCF at different sample ages or observation times.…”