4 research outputs found
On the Onset of Coherent Phonon Motion in Peierls-Distorted Antimony by Attosecond Transient Absorption
Attosecond extreme-ultraviolet (XUV) transient absorption spectroscopy
measurements on the Peierls-distorted phase of the semimetal antimony (Sb) are
presented. After excitation by an ultrashort, broad band near-infrared (NIR)
pulse, the distortion is (partly) lifted causing the well-known coherent phonon
motion of the lattice. While the overall observed dynamics generally follow a
displacive excitation model, a delayed onset of the pump-induced carrier
dynamics due to hot-carrier thermalization is observed, as well as a large
spectral phase dependence in the coherent phonon oscillation. The observed
spectral phase dependence in the coherent motion is attributed to significantly
different carrier relaxation timescales for carrier energies above and near the
Fermi level of the semimetal. A simple theoretical model is presented that
considers the carrier relaxation timescales in the displacive phonon model to
explain the observed dynamics. The results conclusively show that the overall
displacive motion is not solely due to an abrupt displacement of carriers from
their equilibrium configuration by the pump pulse and that carrier-relaxation
effects need to be considered in the description of the phonon motion. The
results furthermore show an effect of NIR field-driven shifts of band-energies,
which is observed as a transient reshaping of the core-level absorption
features.Comment: 12 pages, 7 figures, 1 tabl
Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiOâ‚‚-Si photoanode
Metal oxide semiconductor junctions are central to most electronic and optoelectronic devices, but ultrafast measurements of carrier transport have been limited to device-average measurements. Here, charge transport and recombination kinetics in each layer of a Ni-TiOâ‚‚-Si junction is measured using the element specificity of broadband extreme ultraviolet (XUV) ultrafast pulses. After silicon photoexcitation, holes are inferred to transport from Si to Ni ballistically in ~100 fs, resulting in characteristic spectral shifts in the XUV edges. Meanwhile, the electrons remain on Si. After picoseconds, the transient hole population on Ni is observed to back-diffuse through the TiOâ‚‚, shifting the Ti spectrum to a higher oxidation state, followed by electron-hole recombination at the Si-TiOâ‚‚ interface and in the Si bulk. Electrical properties, such as the hole diffusion constant in TiOâ‚‚ and the initial hole mobility in Si, are fit from these transient spectra and match well with values reported previously