A versatile sample fabrication method for ultrafast electron diffraction

Integral to the exploration of nonequilibrium phenomena in solid-state systems is the study of lattice motion after photoexcitation by a femtosecond laser pulse. For the past two decades, ultrafast electron diffraction (UED) has played a critical role in this regard. Despite remarkable progress in instrumental development, this technique is still bottlenecked by a demanding sample preparation process, where ultrathin single crystals of large lateral size are typically required. In this work, we describe an efficient, versatile method that yields high-quality, laterally extended (≥ 100 µm), and thin (≤ 50 nm) single crystals on amorphous films of Si₃N₄ windows. It applies to most exfoliable materials, including those reactive in ambient conditions, and promises clean, flat surfaces. Besides the natural extension to fabricating van der Waals heterostructures, our method can also be applied to future-generation UED that enables additional control of sample parameters, such as electrostatic gating and excitation by a locally enhanced terahertz field. Our work significantly expands the type of samples for UED studies and also finds application in other time-resolved techniques such as attosecond extreme-ultraviolet absorption spectroscopy. This method hence provides further opportunities to explore photoinduced transitions and to discover novel states of matter out of equilibrium.