Ultrafast X-ray induced damage and nonthermal melting in cadmium sulfide

TL;DR

This study uses advanced simulations to explore how ultrafast X-ray irradiation damages cadmium sulfide, revealing thresholds, damage mechanisms, and potential for band gap tuning.

Contribution

It introduces the XTANT-3 model to simulate nonequilibrium electronic and atomic dynamics in CdS under ultrafast X-ray irradiation, highlighting nonthermal effects.

Findings

Damage threshold dose of ~0.4-0.5 eV/atom for both phases

Damage primarily thermal, with nonthermal effects leading to melting at higher doses

Recrystallization can restore or amorphize the material, affecting bandgap

Abstract

Cadmium sulfide is a valuable material for solar cells, photovoltaic, and radiation detectors. It is thus important to evaluate the material damage mechanisms and damage threshold in response to irradiation. Here, we simulate the ultrafast XUV/X-ray irradiation of CdS with the combined model, XTANT-3. It accounts for nonequilibrium electronic and atomic dynamics, nonadiabatic coupling between the two systems, nonthermal melting and bond breaking due to electronic excitation. We find that the two phases of CdS, zinc blende and wurtzite, demonstrate very close damage threshold dose of ~0.4-0.5 eV/atom. The damage is mainly thermal, whereas with increase of the dose, nonthermal effects begin to dominate leading to nonthermal melting. The transient disordered state is a high-density liquid, which may be semiconducting or metallic depending on the dose. Later recrystallization may recover the material back to the crystalline phase, or at high doses create an amorphous phase with variable bandgap. The revealed effects may potentially allow for controllable tuning of the band gap via laser irradiation of CdS.