Ultra‐small‐angle X‐ray photon correlation spectroscopy using the Eiger detector

Successful implementation of the single‐photon‐counting Eiger 500k pixel array detector for sub‐millisecond X‐ray photon correlation spectroscopy (XPCS) measurements in the ultra‐small‐angle scattering region is reported. The performance is demonstrated by measuring the dynamics of dilute silica colloids in aqueous solvents when the detector is operated at different counter depths, 4, 8 and 12 bit. In the fastest mode involving 4 bit parallel readout, a stable frame rate of 22 kHz is obtained that enabled measurement of intensity–intensity autocorrelation functions with good statistics down to the 50 µs range for a sample with sufficient scattering power. The high frame rate and spatial resolution together with large number of pixels of the detector facilitate the investigation of sub‐millisecond dynamics over a broad length scale by multispeckle XPCS. This is illustrated by an example involving phoretic motion of colloids during the phase separation of the solvent. The performance of the high‐resolution fast‐photon‐counting Eiger 500k detector for sub‐millisecond X‐ray photon correlation spectroscopy measurement is demonstrated.