Heterogeneous to homogeneous melting transition visualized with ultrafast electron diffraction

Abstract

The ultrafast laser excitation of matters leads to nonequilibrium states with complex solid-liquid phase-transition dynamics. We used electron diffraction at mega-electron volt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 to 1000 picoseconds, transitioning to homogeneous melting that occurs catastrophically within 10 to 20 picoseconds at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion coupling rate, determine the Debye temperature, and reveal the melting sensitivity to nucleation seeds.

Melting of CaSiO3 Perovskite at High Pressure

“…Homogeneous melting can be studied experimentally with special design of sample containers or energy input (Daeges et al, 1986;Mo et al, 2018). This process differs from that studied experimentally where nucleation sites, provided by sample containers and grain-grain contacts, are typically abundant.…”

“…The homogeneous melting point is always greater than the equilibrium melting temperature. Homogeneous melting can be studied experimentally with special design of sample containers or energy input (Daeges et al, 1986;Mo et al, 2018).…”

Computational Study on Homogeneous Melting of Benzene Phase I

“…In nature, melting is usually initiated heterogeneously on surfaces, and a solid material immediately transforms into a liquid that is maintained at higher than the material's melting temperature [3,4]. However, melting homogeneously occurs inside a crystal if surface melting is suppressed, which can be experimentally achieved using coating [5,6] or laser [7][8][9][10][11][12] techniques. Homogeneous melting can be defined as the phase transition from solid to liquid in the surface-and defectfree crystal, in which there is no trigger to initiate disordering except thermal fluctuations, and nucleation is equally likely to occur anywhere.…”

“…In an earlier study, the limit of superheating was predicted using two different parameters based on vibrational instability and elastic shear instability, the Lindemann [1] and Born criteria [2], respectively. Even though experimental observation of the initial stage of homogeneous melting remains challenging because of the random creation of a liquid nucleus and its subsequent fast growth [5][6][7][8][9][10][11][12][13], recent developments in computer simulation have enabled us to closely examine its microscopic details [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Using molecular-dynamics (MD) simulations for a Lennard-Jones fluid, a study by Jin et al observed that homogeneous melting is initiated by clusters of vibrationally destabilised particles by satisfying the Lindemann and Born criteria [16,28].…”

Parallel-plate waveguides for terahertz-driven MeV electron bunch compression

“…In ultrafast pump-probe experiments, the dynamics are initiated by a pump laser, then the sample is probed with an ultrashort laser pulse, electron bunch or x-ray pulse. The opportunities for ultrafast diffraction have widened due to the rapid development of sources, detectors, and instrumentation which allow for studying matter in extreme conditions [9].…”