arXiv subjects

A. Jarnac

Publications and source records attributed to A. Jarnac.

4 recordsLinked to original sources

arXiv2021

Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscope allows for local implantation and patterning down to the nanometer resolution, which is of interest for device applications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally by helium implantation. Our combined Raman, XRD and TEM study shows that the implantation causes an elongation of the BiFeO3 unit cell and ultimately a transition towards the so-called super-tetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset of amorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phase transition from the R-like to T-like BiFeO3 appears as first-order in character, with regions of phase coexistence and abrupt changes in lattice parameters.

cond-mat.mtrl-sci↗

arXiv2020

Ultrafast light-induced shear strain probed by time-resolved X-ray diffraction: the model multiferroic BiFeO$_3$ as a case study

Enabling the light-control of complex systems on ultra-short timescales gives rise to rich physics with promising applications. While crucial, the quantitative determination of both the longitudinal and shear photo-induced strains still remains challenging. Here, by scrutinizing asymmetric Bragg peaks pairs $(\pm h01)$ using picosecond time-resolved X-ray diffraction experiments in BiFeO$_3$, we simultaneously determine the longitudinal and shear strains. The relative amplitude of those strains can be explained only if both thermal and non-thermal processes contribute to the acoustic phonon photogeneration process. Importantly, we also reveal a difference of the dynamical response of the longitudinal strain with respect to the shear one due to an interplay of quasi-longitudinal and quasi-transverse acoustic modes, well reproduced by our model.

cond-mat.mtrl-sci↗

arXiv2017

Stabilizing a high-pressure phase in InSb at ambient conditions with a laser-driven pressure pulse

In this letter, we describe the stabilization of indium antimonide (InSb) in the high-pressure orthorhombic phase (InSb-III) at ambient conditions. Until now, InSb-III has only been observed above 9 GPa, or at around 3 GPa as a metastable structure during the phase transition from cubic zinc blende (InSb-I) to orthorhombic InSb-IV. The crystalline phase transition from InSb-I to InSb-III was driven by an ultrashort, laser-generated, non-hydrostatic pressure pulse. The transition occurred in preferred orientations locked to the initial orientation of the InSb-I crystal, breaking the symmetry of the InSb-I cubic cell to form the InSb-III orthorhombic cell.

cond-mat.mtrl-sci↗

arXiv2014

Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water

We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\ μ$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned.

physics.optics↗