Abstract
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.
Highlights
Scattering experiments are widely used to investigate the structure and dynamics over a broad range of size and time scales in soft matter and biological materials (Narayanan et al, 2017)
In order to demonstrate the capabilities of the Eiger 500k detector for X-ray photon correlation spectroscopy (XPCS) measurements, we studied the well known Brownian dynamics of spherical colloidal particles (Berne & Pecora, 2000)
For the fastest XPCS measurements, the detector was operated in the 4 bit parallel readout mode at a frame rate of 22 kHz
Summary
Scattering experiments are widely used to investigate the structure and dynamics over a broad range of size and time scales in soft matter and biological materials (Narayanan et al, 2017). Applications of multispeckle XPCS to probe submillisecond dynamics have been limited due to the available coherent photon flux from a synchrotron source and the frame rate and resolution of two-dimensional detectors. In this respect, the Eiger single-photon-counting pixel detector developed at the Paul Scherrer Institut (PSI) is a major step forward (Dinapoli et al, 2011; Johnson et al, 2012). Basic principles of XPCS and experimental results are presented in subsequent sections
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