Measuring femtometer lattice displacements driven by free carrier diffusion in a polycrystalline semiconductor using time-resolved x-ray scattering

Abstract

We show that time-resolved x-ray scattering can be applied to polycrystalline materials for the measurement of carrier diffusion. A polycrystalline indium antimonide sample is prepared by high-intensity ultrafast laser surface melting and re-solidification under vacuum to create randomly oriented grains with an average size of 13 nm. Two static diffraction rings are simultaneously observed on a gated pixel array detector. Their centroids move following lower-intensity laser excitation, and utilizing an in-situ angular calibration, the transient lattice spacing is determined with femtometer accuracy, thereby allowing the measurement of charge carrier dynamics. Compared to bulk calculations, we find that carrier diffusion slows by more than one order of magnitude. This result provides evidence for the formation of potential energy barriers at the grain boundaries and demonstrates the capability of time-resolved x-ray scattering to probe nanoscale charge transport in materials other than near-perfect crystals.

Reduced Thermal Conductivity in Ultrafast Laser Heated Silicon Measured by Time-Resolved X-ray Diffraction

“…A direct means to measure lattice displacement due to electron and heat propagation would remove considerable ambiguity in explaining the relevant physical phenomena. During the past decade, synchrotron based time-resolved X-ray diffraction (TRXD) has become a versatile probe for characterizing various non-equilibrium phenomena, including the transmission of heat across an interface [14], charge carrier propagation across thin-film interfaces [15] and grain boundaries [16], and the production of anisotropic strain in bulk crystal [17] and multiferroic thin film [18][19][20]. Additionally, laser-based table-top X-ray diffraction methods have enabled probing dynamics at ultrafast time-scales, such as unexpected anisotropic strain development from nanograin film on substrate [21] and a nanoscale transport mechanism in metallic multilayer systems [22].…”

Structural measurement of electron-phonon coupling and electronic thermal transport across a metal-semiconductor interface

“…Fitting our numerical model to data yields an effective electron thermal conductivity of = 18.7 W m K , which is 5 times smaller than the value measured in a bulk system 18 . This discrepancy likely results from electron scattering at the grain boundaries in the polycrystalline film 37 – 39 . The effect of grain boundaries on energy relaxation and transport mechanisms in a polycrystalline metal film has been widely interpreted by the Matthiessen’s rule that describes the mean free path l of the system 40 : where and are the mean free path lengths of the electrons in a single bulk crystal and polycrystalline grain.…”

Tracing microscopic atomic displacements using polarized Raman spectroscopy: a case study on BaTiO3

“…knowledge about the atomic rearrangements in the presence of external perturbation is utmost important. Usually, x-ray diffraction (XRD), neutron diffraction, x-ray scattering and xray absorption spectroscopy are used to detect such atomic rearrangements [1,[7][8][9]. Recently, x-ray magnetic resonant scattering is used to improve the detection limit up to the order of femto-metre [10].…”