Mimicking the earth core conditions with ultrafast laser materials interaction

Abstract

Ultrafast lasers create extreme, non-equilibrium thermodynamic conditions that can transiently reach pressures and temperatures comparable to interior core of the earth. Here we show that femtosecond excitation of amorphous silica-hafnia multilayer dielectrics drives the formation of high-pressure crystalline phases of silica including stishovite, seifertite, and the pyrite-type high density structure, within confined subsurface regions.Using TEM, SAED, and 4D-STEM, we directly map nanoscale phase evolution and identify crystalline motifs embedded inside laser generated blisters.Complementary molecular dynamics simualtions reveal the thermodynamic pathway underlying these transformations, where rapid electronic pressure initiates densification and octahedral coordination, followed by temperature driven crystallization and displacive transitions during ultrafast quenching. The resulting polymorphs reflects a dual-stage pathway inaccessible under equilibrium processing. Our results establish femtosecond laser excitation as a viable route to synthesize and stabilize ultrahigh-density high pressure silica phases under ambient conditions, without a diamond anvil cell, with implications for laser-damage mechanisms, high-energy-density materials, and planetary physics.

Figures (5)

• Figure 1: Plasma-driven blister formation and pressure-induced phase transformation in silica under ultrafast laser excitation: Schematic illustration of femtosecond laser interaction with the SiO$_2$/HfO$_2$ multilayer stack. At high intensity, multiphoton and tunnelling ionization generate a dense electron plasma, leading to rapid energy deposition and bond breaking before lattice relaxation. Subsequent electron–phonon coupling drives ultrafast heating and volumetric expansion, producing subsurface void nucleation and blister formation. Confinement of the expanding material within the multilayer stack generates transient extreme pressures and temperatures, enabling stabilization of metastable high-density silica polymorphs upon rapid quenching. For reference, the lower panel shows representative low-pressure https://doi.org/10.1029/93JB02968Yagi1976DirectMeasurementsPrecise1982CoesiteComponentsand high-pressure silica phases Kuwayama2005Andrault2014PhaseConditionsOganov2005Fischer2018EquationsSiO2.Phase diagrams are computed in matlab based on literature values and edited in Inkscape vector graphics.
• Figure 2: (a) SEM image of blister generated inside amorphous SiO2/HfO2 MLD structure interacting with a single, 25 fs ultrafast laser pulse at 1030 nm. The red shaded enclosure is drawn to identify the blistered region used for this study. (b) is FIB cutout of the blister (STEM images) (c) and (d) are the close-up view of nano cracks viewed through STEM. (e), (f) are the HRTEM image of are of used from electron diffraction whereas the (g), (h), (i) and (j) are closer view of the enclosures which show clear crystalline phases.
• Figure 3: Visual representation of high-pressure phases where the red circle are diffraction spots with matches theory and yellow circle is the representation of hkl planes
• Figure 4: (a), (b), (c) are the 4D STEM experimental data obtained at electron diffraction of nanocrystalline regions. (e), (f) is the matched pyrite type silica simulated in single crystal diffract software at [111] and [100] direction. (g) is the simulated stishovite at [111] direction. The experimental data aligns with these simulations with a deviation of less than 5$\%$
• Figure 5: (a) Temporal profile of temperature during the amorphization and crystallization of stishovite (green) and evolution of Gibbs free energy (G) and its components, enthalpy (H) and entropy (S) (shifted by a value of -40.15), calculated for several snapshots over the MD timescale by DFT simulations. Time is shifted so that the cooling starts at 0 ns. (b) Temporal evolution of the per-atom potential energy and the pressure during the first 10 ns of the equilibration. The potential energy is averaged over the whole system including the Si and O atoms. (c) Bond-angle distribution for O-Si-O and Si-O-Si angles in SiO$_6$ and OSi$_3$ units, inset (d) shows the distribution of Si-O bonds. (e) Partial RDFs of Si-Si, Si-O and O-O pairs of the obtained (a) stishovite and (b) pyrite structures compared with pristine crystals at the same density.