X-ray photon correlation spectroscopy (XPCS) in
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...
and
chemistry, is a novel technique that exploits a
coherent X-ray
X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...
synchrotron
A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed p ...
beam to measure the dynamics of a sample. By recording how
coherent speckle
Coherence, coherency, or coherent may refer to the following:
Physics
* Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference
* Coherence (units of measurement), a deriv ...
fluctuations in time, one can measure a time correlation function, and thus measure the timescale processes of interest (diffusion, relaxation, reorganization, etc.). XPCS is used to study the slow dynamics of various equilibrium and non-equilibrium processes occurring in
condensed matter
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the sub ...
systems.
Advantages
XPCS experiments have the advantage of providing us with the information of dynamical properties of materials (e.g. vitreous materials), while other experimental techniques can only provide information about the static structure of the material. This technique is based on the generation of a
speckle pattern
Speckle, speckle pattern, or speckle noise is a granular noise texture degrading the quality as a consequence of interference among wavefronts in coherent imaging systems, such as radar, synthetic aperture radar (SAR), medical ultrasound and o ...
by the scattered coherent light originating from a material where some spatial inhomogeneities are present. A speckle pattern is a
diffraction limited structure factor, and is typically observed when
laser light
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
is reflected from a rough surface, or from dust particles performing
Brownian motion
Brownian motion, or pedesis (from grc, πήδησις "leaping"), is the random motion of particles suspended in a medium (a liquid or a gas).
This pattern of motion typically consists of random fluctuations in a particle's position insi ...
in air. The observation of speckle patterns with
hard X-rays has just been demonstrated in the last few years. This observation is only possible now because of the development of new
synchrotron radiation
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
X-ray sources that can provide sufficient coherent
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...
.
aXPCS
A specific subgroup of these techniques is atomic-scale X-ray photon correlation spectroscopy (aXPCS).
References
{{Reflist
Sources
* P.-A. Lemieux, D.J. Duria
Investigating non-Gaussian scattering processes by using nth-order intensity correlation functions''Journal of the Optical Society of America'' 1999, 16(7), 1651–1664
doi: 10.1364/JOSAA.16.001651* Robert L. Lehen
XPCS: Nanoscale motion and rheology''Current Opinion in Colloid & Interface Science'' 2012, 17 (1), 3–12
doi: 10.1016/j.cocis.2011.11.002*Oleg G. Shpyrk
''J. Synchrotron Radiation'' 2014, 21 (5), 1057–1064
doi: 10.1107/S1600577514018232* Sunil K. Sinha, Zhang Jiang, Laurence B. Luri
X-ray Photon Correlation Spectroscopy Studies of Surfaces and Thin Films''Advanced Materials'' 2014, 26 (46), 7764–7785
doi: 10.1002/adma.201401094* Aurora Nogales, Andrei Flueras
X Ray Photon Correlation Spectroscopy for the study of polymer dynamics''European Polymer Journal'' 2016
doi: 10.1016/j.eurpolymj.2016.03.032
Synchrotron-related techniques
X-ray spectroscopy