Master's Defense: Simon Munch Johannsen
Comparing simulated and experimental X-ray photon correlation spectroscopy data from the European XFEL
X-ray photon correlation spectroscopy (XPCS) allows for the study of dynamics in materials by analyzing the fluctuation of the measured intensity in the form of speckle patterns. This tech-nique relies on a strong coherent beam produced at X-ray free-electron lasers (XFELs). Obtaining a beamtime at these facilities is a lengthy and difficult process that culminates in a brief beamtime; thus, generating unique samples consisting of particles that can move around could be a great advantage. It can help prepare the experimental setup and predict the results from measurements done during the beamtime. Therefore, this project attempts to replicate an XPCS experiment by creating dynamic samples, in the form of matrices, that undergo Brownian motion in Python. For the experiments, two different samples were used, one containing 20 nm silica particles with low polydispersity, the other containing 12 nm silica nanoparticles with a higher polydispersity. To further validate the XPCS results and gain complementary insights into the structure and particle distribution of the samples, small-angle X-ray scattering and dynamic light scattering were also performed. The scattering data highlighted that all three methods measured an equal radius within their uncertainties. The diffusion coefficients measured from DLS and XPCS also agreed with each other and using the XPCS data as a guide, it was possible to produce similar results through simulations in Python.