We have recently developed the possibility to simultaneously probe the electrical and structural response of ferroelectric capacitors which are often closely coupled in such materials. Conventional positive-up-negative-down (PUND) sequences and other periodic elecrical pulse sequences drive the ferroelectric response of ferroelectric thin films while time-resolved x-ray diffraction (at synchrotrons) probes the structural changes (structure factor, strain, disorder and domain structure). We aim at driving ultrafast ferroelectric switching by heat and strain pulses and extend our investigations to ferroelectrics integrated on Si in collaboration with Catherine Dubourdieu (HZB & FU Berlin).
Rössle M., Leitenberger W., Reinhardt M., Koç A., Pudell J.-E., Kwamen C., and Bargheer M.
The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II
The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
Kwamen C., Rössle M., Leitenberger W., Alexe M., and Bargheer M.
Time-resolved X-ray diffraction study of the structural dynamics in an epitaxial ferroelectric thin Pb(Zr0.2Ti0.8)O3 film induced by sub-coercive fields
The electric field-dependence of structural dynamics in a tetragonal ferroelectric lead zirconate titanate thin film is investigated under subcoercive and above-coercive fields using time-resolved X-ray diffraction. The domain nucleation and growth are monitored in real time during the application of an external field to the prepoled thin film capacitor. We propose the observed broadening of the in-plane peak width of the symmetric 002 Bragg reflection as an indicator of the domain disorder and discuss the processes that change the measured peak intensity. Subcoercive field switching results in remnant disordered domain configurations.
Kwamen C., Rössle M., Reinhardt M., Leitenberger W., Zamponi F., Alexe M., and Bargheer M.
Simultaneous dynamic characterization of charge and structural motion during ferroelectric switching
Physical Review B 96, 134105 (2017).
Schick D., Bojahr A., Herzog M., Gaal P., Vrejoiu I., and Bargheer M.
Following Strain-Induced Mosaicity Changes of Ferroelectric Thin Films by Ultrafast Reciprocal Space Mapping
Physical Review Letters 110, 095502 (2013).
C. von Korff Schmising, M. Bargheer, M. Kiel, N. Zhavoronkov, M. Woerner, T. Elsaesser, I. Vrejoiu, D. Hesse and M. Alexe
Coupled Ultrafast Lattice and Polarization Dynamics in Ferroelectric Nanolayers
2007, Phys. Rev. Lett., 98, 25, 257601