Anisotropic hot carrier relaxation mediated by electron phonon scattering in TiN thin films
Abstract
Crystal orientations can shape the ultrafast energy relaxations of transition-metal nitride thin films. Here, we investigate the orientation-dependent electron-phonon (e-ph) mediated relaxation in titanium nitride (TiN) thin films along the [100], [110], and [111] directions by combining first-principles calculations with ultrafast pump-probe transient absorption spectroscopy. Using maximally localized Wannier functions, we evaluate e-ph quasiparticle scattering lifetimes near the Fermi level and identify a clear anisotropy: The TiN [111] orientation exhibits a longer e-ph scattering lifetime (15.96 fs) than [100] (13.69 fs) and [110] (11.12 fs), indicating reduced intrinsic e-ph scattering strength. Furthermore, we grew quasi-epitaxial, orientation-controlled TiN thin films on MgO substrates. Pump-probe measurements reveals that the population-level relaxation (hot-electron cooling) time also depends on orientations, with [111] films showing a significantly slower decay (110 fs) than [100] (90 fs) and [110] (80 fs). We emphasize that the calculated few-femtosecond scattering lifetimes and the measured few-hundred-femtosecond cooling time respectively represent single-event scattering and collective cooling, yet they exhibit consistent trends. These results demonstrate that crystallographic orientation provides a practical and powerful route to tune e-ph-governed relaxation in TiN thin films, offering essential design guidelines for refractory plasmonic and energy-conversion platforms.
Keywords
Cite
@article{arxiv.2607.11237,
title = {Anisotropic hot carrier relaxation mediated by electron phonon scattering in TiN thin films},
author = {Hemant Verma and Tzu-Yu Peng and Shyr-Shyan Yeh and Sheng-Chieh Huang and Pritam Sardar and Yang-Hao Chan and Yu-Jung Lu and Chao-Cheng Kaun},
journal= {arXiv preprint arXiv:2607.11237},
year = {2026}
}