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Abstract
Through Monte Carlo simulations, we investigate how various experimental parameters can influence the quality of time-resolved scanning transmission X-ray microscopy images. In particular, the effect of the X-ray photon flux, of the thickness of the investigated samples, and of the frequency of the dynamical process under investigation on the resulting time-resolved image are investigated. The ideal sample and imaging conditions that allow for an optimal image quality are then identifed.
Highlights
The interactions between the large number of atoms that constitute real-world material systems lead to a multiplicity of collective effects with spatial and temporal scales ranging from the nanoscopic to the mesoscopic and macroscopic
Time-resolved imaging model To understand what parameters influence the quality of a TRSTXM image, we modeled each possible contribution to the TR-scanning-transmission X-ray microscopy (STXM) image and simulated them with a Monte Carlo approach
In the case of TR-STXM imaging, the most typical excitation mechanism is given by electrical signals, which can be directly employed for exciting the dynamical process [e.g. processes driven by spin–orbit torques (Finizio et al, 2019b; Litzius et al, 2017; Woo et al, 2018; Baumgartner et al, 2017)], or indirectly through the generation of oscillating magnetic fields when injecting the electrical signal across a nanostructured antenna [e.g. spin-wave processes (Wintz et al, 2016; Forster et al, 2019; Dieterle et al, 2019; Kammerer et al, 2011)]
Summary
The interactions between the large number of atoms that constitute real-world material systems lead to a multiplicity of collective effects with spatial and temporal scales ranging from the nanoscopic to the mesoscopic and macroscopic. The goal of time-resolved imaging with the pump–probe protocol is to image a reproducible dynamical process triggered by an external excitation This excitation is typically generated using high-frequency waveform generators synchronized to the master clock of the synchrotron light source. Four different contributions were identified, given by the probing beam (in our case, synchrotron plus beamline optics and the Fresnel zone plate used to focus the beam onto the sample), modeled as a photon generator with Poisson statistics, the sample, where the X-ray absorption from the magnetic material takes place, the electronic setup, generating the excitation signal that drives the dynamical process on the sample, and the APD, used to detect the X-ray photons transmitted across the sample. The model employed to describe each of the contributions introduced above will be discussed
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