Ultrafast atomic view of laser-induced melting and breathing motion of metallic liquid clusters with MeV ultrafast electron diffraction.
Proc Natl Acad Sci U S A 2022;
119:2111949119. [PMID:
35074922 PMCID:
PMC8795546 DOI:
10.1073/pnas.2111949119]
[Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2021] [Indexed: 11/18/2022] Open
Abstract
Intense lasers can be used to drive materials into transient states far from equilibrium. Investigations of such states and processes at the atomic scale are of fundamental significance in understanding a material’s behavior under extreme conditions. Herein, an ultrafast electron diffraction technique is used to track the atomic pathway of the entire melting process of aluminum and reveal a coherent breathing motion of polyhedral clusters in transient liquid aluminum at high temperature and high pressure. The negative expansion behavior of interatomic distances in a superheated liquid state upon heating is observed. These findings provide insight into ultrafast structural transformations and transient atomic dynamics under extreme conditions.
Under the irradiation of an ultrafast intense laser, solid materials can be driven into nonequilibrium states undergoing an ultrafast solid–liquid phase transition. Understanding such nonequilibrium states is essential for scientific research and industrial applications because they exist in various processes including laser fusion and laser machining yet challenging in the sense that high resolution and single-shot capability are required for the measurements. Herein, an ultrafast diffraction technique with megaelectron-volt (MeV) electrons is used to resolve the atomic pathway over the entire laser-induced ultrafast melting process, from the initial loss of long-range order and the formation of high-density liquid to the progressive evolution of short-range order and relaxation into the metastable low-density liquid state. High-resolution measurements using electron pulse compression and a time-stamping technique reveal a coherent breathing motion of polyhedral clusters in transient liquid aluminum during the ultrafast melting process, as indicated by the oscillation of the interatomic distance between the center atom and atoms in the nearest-neighbor shell. Furthermore, contraction of interatomic distance was observed in a superheated liquid state with temperatures up to 6,000 K. The results provide an atomic view of melting accompanied with internal pressure relaxation and are critical for understanding the structures and properties of matter under extreme conditions.
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