Soft x-ray induced femtosecond solid-to-solid phase transition

Abstract

Soft x-rays were applied to induce graphitization of diamond through a non-thermal solid-tosolid phase transition. This process was observed within poly-crystalline diamond with a timeresolved experiment using ultrashort soft x-ray pulses of duration 52.5 fs and cross correlated by an optical pulse of duration 32.8 fs. This scheme enabled for the first time the measurement of a phase transition on a timescale of ~150 fs. Excellent agreement between experiment and theoretical predictions was found, using a dedicated code that followed the non-equilibrium evolution of the irradiated diamond including all transient electronic and structural changes. These observations confirm that soft x-rays can induce a non-thermal ultrafast solid-to-solid phase transition on a hundred femtosecond timescale.

Thermal and nonthermal melting of III-V compound semiconductors

“…[22], and the timeresolved kinetics of a phase transition in Ref. [23], which also validated our calculations of the optical parameters; damage thresholds in amorphous carbon and C 60 crystal were compared to experiments in Ref. [24].…”

“…Electrons, promoted across the band gap under an action of a laser pulse, populate those states, causing the materials to turn into an LDL phase. In contrast, other materials do not exhibit an LDL phase: diamond with 2p bonds graphitizes [22,23] and GaP and GaSb with 4p bonds forming the conduction band (see Fig. 8) turn into a completely disordered lowdensity phase.…”

Various damage mechanisms in carbon and silicon materials under femtosecond X-ray irradiation

“…In a series of papers, we modeled diamond under femtosecond FEL irradiation in a wide range of photon energies, using XTANT code described above 10,13,60,69,94 . We showed that at the absorbed doses above the damage threshold of ∼ 0.7 − 0.75 eV/atom, diamond undergoes a nonthermal solid-to-solid phase transition into graphite phase on an ultrashort timescale of ∼ 150 fs.…”

Generation of coherent phonons by coherent extreme ultraviolet radiation in a transient grating experiment

“…It should also be mentioned that the data quality and the ability to resolve fine features of the signal, demonstrated, for example, by Fig. 2, significantly exceed those typical for time-resolved EUV pump/optical probe measurements, [15][16][17] indicating the advantage of the background-free TG experiment, in which the diffracted optical signal vanishes in the absence of the EUV excitation. Our results indicate the promise of the TG technique for studying a wide range of phenomena initiated by femtosecond EUV pulses.…”

“…High brightness EUV and x-ray free electron lasers (FELs) now allow experiments in which femtosecond short-wavelength pulses are used to initiate dynamics probed with optical or short-wavelength radiation. [11][12][13][14][15][16][17] This report is aimed at exploring the potential of short-wavelength photon pulses for the excitation of lattice vibrations.…”