UC San Diego

The use of coherent x-rays has grown recently with the development of high brilliance x-ray sources. X-ray photon correlation spectroscopy (XPCS) has proven to be a valuable tool to measure the dynamics of a wide range of systems. In this dissertation we utilized two extensions to the standard XPCS method. The first is called two-pulse XPCS. By measuring the speckle pattern from the two x-ray pulses separated in time, we can measure the dynamics of systems at much shorter time scales than conventional XPCS. To demonstrate the viability of this technique, we measured the equilibrium fluctuations of a magnetic skyrmion lattice in a FeGd multiplayer. These results showed an exponential decay in the intermediate scattering function and gave valuable insight into the dynamics of the creation and decay of the skyrmion lattice. They also demonstrated the viability of the two-pulse technique as a potential method to measure ultrafast dynamics using coherent x-rays. The second is heterodyne XPCS. This method involves interfering the sample’s scattering with a static reference signal. This interference allows the measurement of a uniform flow of scatterers. Using this technique, we have directly measured the velocity of ions inside a polymer electrolyte under an applied voltage. These results show the correlation between the ion’s velocity and the output current of the cell. There is an initial spike in the ion’s velocity as the voltage is first applied. Then an internal concentration gradient forms and the velocity decays to steady state. We show how this velocity is dependent on the applied voltage and temperature of the system. The concentration gradient is directly measured and compared with the velocity measured using heterodyne XPCS. The direct measurement of the ion’s velocity and concentration in-situ are the first of their kind for a polymer electrolyte. They provide valuable data about the transference number of the system.