The work of researchers at IMDEA Nanociencia establishes the foundations for the amount of information that can be recovered and, more importantly, the standards in coherent X-ray imaging for separating stochastic from deterministic contributions; it is notoriously hard to unscramble them as their separation would open doors to shed light on many subtle nanoscale phenomena.
Diving In: Unpacking the Stochastic Enigmas
Although coherent X-ray imaging has been a very useful technique for studying nanoscale structures and dynamics, it has had an important shortcoming: capturing the inherently stochastic behaviour of many processes at this scale. It has been traditional to generate freeze-frame images using high X-ray fluxes that might heat or even destroy the sample.
In addition to this highradiation dose, detectors have limited acquisition rates that leave fast nanoscale phenomena inaccessible. Some of you may know that stroboscopic methods have been used to take pictures during repeated, ultrafast processes (for example [3]), but these suffer from the fact that one can only reveal mean dynamics and everything related with stochastic forces – for honing in and zooming into trajectories describing chaotic systems when laboratory changes next level-up how-to make previously invisibly small at each successive iteration images now appear as seen in Fig.
Now, the researchers at IMDEA Nanociencia have devised an unprecedented method called “Coherence Isolated Diffractive Imaging” (CIDI) that uniquely obtains stochastic and deterministic contributions to a coherent X-ray scattering pattern. This enables them to acquire real-space images of the deterministic contribution and momentum spectrum of the stochastic component of nano-scale complex behaviors at an unparalleled level.
Decoding the Secrets of Quantum Materials
Indeed, stochastic processes are all-pervasive at the nano-scale, where thermal (or even quantum) effects really start to matter. For example, in quantum materials we frequently encounter classical stochastic motion of charge carriers, vortices or domain walls. Nonetheless, the (lack of) visualizability of such stochastic processes in real space [11] has kept our knowledge about these issues quite limited.
For a long time fluctuations in these systems have been studied using other techniques from which only the statistical properties can be obtained, not the image of the system itself. Although such fluctuations might be observed via single-shot measurements at free-electron lasers, that approach may not always work in other systems, she says, because of the issue of sample damage.
The appreciable advance that the technique with CIDI developed by the researchers of IMDEA Nanociencia signifies in this sense. With reconstruction methods applied to the scattering patterns, the team could also retrieve a wealth of quantitative information on separations, size and phase shifts of polaron pairs, like well as shape, size and metallic character of domain walls in an insulating matrix. These features combine to enable direct imaging of stochastic processes in the nanoscale, opening up a new level of understanding quantum materials and their rich dynamics.
Conclusion
The new CIDI method created by the team from IMDEA Nanociencia constitutes a breakthrough in coherent X-ray imaging. This decoupling of the stochastic and deterministic components in such scattering patterns has paved new ways to study a variety of complex, nanometer scale phenomena, from charge carrier dynamics in quantum materials to fluctuations of domain walls or vortices. It is a flexible methodology with unprecedented potentials to reveal, in a more thorough manner compared to those accessible so far, the hidden dynamics of fast evolving systems over an extremely wide energy and time ranges and represents therefore opens prospects for unveiling deep insight into the nanoscale world.
