A new relativistic ultrafast electron diffraction and imaging (RUEDI) national facility for microscopic dynamics in the UK

Abstract text (incl. figure legends and references)
Introduction

In the last two decades, there has been rapid progress in time-resolved electron diffraction and imaging using femtosecond pulsed electron beams. While light and X-ray probes are also common, electrons can probe all of lattice, charge, spin, and electromagnetic waves with high spatial resolution. Using femtosecond laser, for example, induced dynamics of lattice, charge transfer, magnetization, polaritons, have been clarified in both reciprocal space and real space.

When the acceleration voltage is about 10- a few 100 kV, dynamics is often needed to be a reversible process with a short relaxation time in a sub 0.1 um thin specimen. The number of electrons per pulse is in the single electron regime due to the space charge effect. A long experimental time and high stability are often necessary. When it is at MeV, the number can be increased by more than one million, making it possible to observe a um thick specimen in the single shot regime. The MeV approach, on the other hand, has been realized only in diffraction but not in microscopical imaging.

Objectives

At present, the requirements to observe dynamics have become so advanced that the conventional method often do not work. They are, for example, specimens in liquid/gas phases, complex systems as battery electrode surfaces, excitations under intense laser irradiation, and sub-100 femtosecond lattice dynamics. While attosecond phenomena have been explored in electron dynamics, it has also become important to clarify the correlation between electrons, lattices and spins. In addition, it is also urgent to improve the efficiency of experimental methods and to link them with other ultrafast techniques. RUEDI [1] has been designed and developed to enable these.

Materials & Methods

RUEDI utilizes accelerator technology to generate a beam at MeV with 10 fs pulse duration and high brightness, integrates electron diffraction and electron microscope imaging, and achieve high efficiency using AI technology. For the sample environment, RUEDI has not only laser and high frequency field irradiations but also liquid/gas sample holders and in-situ, operando capabilities.

Under well-controlled environments, electron diffraction plays a key role to test hypothesis and consistency as an analytical science method. Microscopic imaging becomes important in order to do observations at nm spatial resolution and, as a field science method, to obtain an overall information from a complex system where it is difficult to discover a hypothesis.

RUEDI project focuses on five research themes. They are energy materials, materials in extreme conditions, chemical dynamics, quantum materials and in vivo life science. Some examples are, interfacial dynamics in liquid phase, photocatalytic dynamics, high-pressure and temperature materials, ultrafast chemical/molecular dynamics, and observation of biological specimens under hydration.

Results & Conclusion:

We are developing RUEDI facility to elucidate static and dynamic structures in systems those are difficult be studied with current techniques. RUEDI will be applied to systems such as thick specimens, complex sample environments, and sub-100 femtosecond dynamics.

References:

[1] RUEDI is supported by EPSRC / UK Infrastructure Fund under grant number EP/W033852/1.