Charge Carrier Screening in Photoexcited Epitaxial Semiconductor Nanorods Revealed by Transient X-ray Absorption Linear Dichroism

Understanding the electronic structure and dynamics of semiconducting nanomaterials at the atomic level is crucial for the realization and optimization of devices in solar energy, catalysis, and optoelectronic applications. We report here on the use of ultrafast X-ray linear dichroism spectroscopy to monitor the carrier dynamics in epitaxial ZnO nanorods after band gap photoexcitation. By rigorously subtracting out thermal contributions and conducting ab initio calculations, we reveal an overall depletion of absorption cross sections in the transient X-ray spectra caused by photogenerated charge carriers screening the core-hole potential of the X-ray absorbing atom. At low laser excitation densities, we observe phasespace filling by excited electrons and holes separately. These results pave the way for carrier- and element-specific probing of charge transfer dynamics across heterostructured interfaces with ultrafast table-top and fourth-generation X-ray sources.

Automated summary

Understanding the electronic structure and dynamics of semiconducting nanomaterials at the atomic level is crucial for optimizing devices in solar energy, catalysis, and optoelectronic applications. The study using ultrafast X-ray linear dichroism spectroscopy reveals a depletion of absorption cross sections in transient X-ray spectra due to photogenerated charge carriers screening the core-hole potential of the X-ray absorbing atom, paving the way for future research on charge transfer dynamics across heterostructured interfaces.