Measurement of transient atomic displacements in thin films with picosecond and femtometer resolution.

M Kozina,T Hu,J Safranek,A Mehta,C Uher,J S Wittenberg,A Damodaran,J Corbett,E Szilagyi,D A Reis,T A Miller,M Trigo,L Martin,A M Lindenberg

doi:10.1063/1.4875347

Abstract

We report measurements of the transient structural response of weakly photo-excited thin films of BiFeO3, Pb(Zr,Ti)O3, and Bi and time-scales for interfacial thermal transport. Utilizing picosecond x-ray diffraction at a 1.28 MHz repetition rate with time resolution extending down to 15 ps, transient changes in the diffraction angle are recorded. These changes are associated with photo-induced lattice strains within nanolayer thin films, resolved at the part-per-million level, corresponding to a shift in the scattering angle three orders of magnitude smaller than the rocking curve width and changes in the interlayer lattice spacing of fractions of a femtometer. The combination of high brightness, repetition rate, and stability of the synchrotron, in conjunction with high time resolution, represents a novel means to probe atomic-scale, near-equilibrium dynamics.

Highlights

We report measurements of the transient structural response of weakly photoexcited thin films of BiFeO3, Pb(Zr,Ti)O3, and Bi and time-scales for interfacial thermal transport
Femtosecond to picosecond atomic-scale dynamical processes in matter have been probed using pulsed x rays from sources ranging from laboratory-scale to synchrotrons to free electron lasers
These experiments have been constrained in most cases by low repetition rates, insufficient brightness, long pulse durations, and/or large pulse-to-pulse fluctuations, necessitating the examination of systems driven far from equilibrium in order to generate a measurable signal

Summary

Introduction

We report measurements of the transient structural response of weakly photoexcited thin films of BiFeO3, Pb(Zr,Ti)O3, and Bi and time-scales for interfacial thermal transport. Phonon transport across interfaces in thin films or heterostructures intrinsically involves picosecond transport processes and resultant part-per-million strains.5,10,15,16 Here, we show that by utilizing the high brightness, repetition rate, and stability of a synchrotron, one may use x-ray scattering techniques to probe the atomic-scale dynamics and phonon conduction processes within systems close to equilibrium with 15 ps time resolution, corresponding to photo-induced lattice changes at the 10À6 level, applicable to broad diffraction peaks associated with nanoscale systems.

Results

Conclusion