XPCS

Nanoscale fluctuations in soft and hard condensed matter measured with XPCS

We use and develop the technique of X-ray photon correlation spectroscopy (XPCS). XPCS is a method to measure dynamics on time scales of 1s – 10^-12 s in condensed matter systems by correlating time-resolved coherent diffraction patterns. This allows us to trace nanoscale fluctuations which are important in many soft matter systems (e.g. diffusion), glassy systems, and domain wall motion in solid-state systems. The correlation functions yield deep insights into the underlying dynamical processes. 

Currently, we are pursuing a research program (BIO-XPCS) funded by BMBF with the aim of measuring protein dynamics in crowded environments and during phase transitions. The aim of the project is to mitigate beam damage by novel setups and concepts and measure the dynamics of proteins on length scales of 100 nm down to the hydrodynamic radius of the molecule. 

A typical experimental setup of X-ray Photon Correlation Spectroscopy (XPCS) of protein solutions. Coherent X-rays are utilized, which are monochromatic and attenuated, in order to avoid beam induced effects, and focused on the sample. The sample environment usually allows control of an external parameter, such as temperature or pressure. The scattering intensity is recorded with a pixelated 2D array detector. The scattering intensity is recorded as a function of time, which fluctuates due to the changes of the speckle pattern (upper right-hand panel). By calculating the intensity correlation function g₂ one can obtain information about the dynamics. The amplitude of the correlation function relates to the speckle contrast β and the decay constant reflects the timescale of motion associated with the given momentum transfer Q.Add block

see e.g.

Low dose X-ray speckle visibility spectroscopy reveals nanoscale dynamics in radiation sensitive samples 
J. Verwohlt, M. Reiser, L. Randolph, A. Matic, A. Medina, M. Sprung, A. Zozulya, A. Madsen, and C. Gutt
Phys. Rev. Lett. 120, 168001 (2018)

X-ray photon correlation spectroscopy of protein dynamics at nearly diffraction limited storage rings J. Möller, M. Sprung, A. Madsen, and C. Gutt