Formation of high-aspect-ratio nanocavity in LiF crystal using a femtosecond of x-ray FEL pulse

TL;DR

This paper demonstrates that a single femtosecond x-ray FEL pulse can create high-aspect-ratio nanocavities in LiF, enabling deep material modifications and high-pressure phase transformations not achievable with optical lasers.

Contribution

It introduces a novel method using femtosecond x-ray pulses to form nanocavities in crystals, expanding laser processing capabilities into the hard x-ray regime.

Findings

Formation of ~1 mm long cylindrical cavities in LiF

Shock wave-induced polymorphic transformations

Potential application to semiconductors and ceramics

Abstract

Sub-picosecond optical laser processing of metals is actively utilized for modification of a heated surface layer. But for deeper modification of different materials a laser in the hard x-ray range is required. Here, we demonstrate that a single 9-keV x-ray pulse from a free-electron laser can form a um-diameter cylindrical cavity with length of ~1 mm in LiF surrounded by shock-transformed material. The plasma-generated shock wave with TPa-level pressure results in damage, melting and polymorphic transformations of any material, including transparent and non-transparent to conventional optical lasers. Moreover, cylindrical shocks can be utilized to obtain a considerable amount of exotic high-pressure polymorphs. Pressure wave propagation in LiF, radial material flow, formation of cracks and voids are analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final structure with the long cavity. Similar results can be produced with semiconductors and ceramics, which opens a new pathway for development of laser material processing with hard x-ray pulses.