Semiconducting two-dimensional (2D) materials are studied intensively because of their promising performance in diverse applications from electronics to energy storage and catalysis. Recently, HfS₂ and ZrS₂ have emerged as potential rivals for the commonly studied 2D semiconductors such as MoS₂ and WSe₂, but their use is hindered by the difficulty of producing continuous films. Herein, we report the first atomic layer deposition (ALD) processes for HfS₂ and ZrS₂ using HfCl₄ and ZrCl₄ with H₂S as the precursors. We demonstrate the deposition of uniform and continuous films on a range of substrates with accurately controlled thicknesses ranging from a few monolayers to tens of nanometers. The use of semiconductor industry-compatible precursors and temperatures (approximately 400 °C) enables facile upscaling of the process. The deposited HfS₂ and ZrS₂ films are crystalline, smooth, and stoichiometric with oxygen as the main impurity. As an important step toward applications of HfS₂ and ZrS₂, we show that their sensitivity toward oxidation can be overcome by minimizing the impurities in the reactor and by depositing a protective Al_xSi_yO_z layer on the top without a vacuum break. Finally, we demonstrate HfS₂ and ZrS₂ photodetectors exhibiting good performance and stable operation in ambient conditions. Photoresponsivity comparable to thin films or even single flakes of HfS₂ or ZrS₂ deposited at much higher temperatures is achieved, although the response speed seems to be limited by photogating, as is common for 2D photodetectors. We expect the first ALD processes for HfS₂ and ZrS₂ to enable further exploration of these materials for various semiconductor applications.

Reliable and accurate knowledge of the physical properties of elementary point defects is crucial for predictive modeling of the evolution of radiation damage in materials employed in harsh conditions. We have applied positron annihilation spectroscopy to directly detect mono-vacancy defects created in tungsten through particle irradiation at cryogenic temperatures, as well as their recovery kinetics. We find that efficient self-healing of the primary damage takes place through Frenkel pair recombination already at 35 K, in line with an upper bound of 0.1 eV for the migration barrier of self-interstitials. Further self-interstitial migration is observed above 50 K with activation energies in the range of 0.12–0.42 eV through the release of the self-interstitial atoms from impurities and structural defects and following recombination with mono-vacancies. Mono-vacancy migration is activated at around 550 K with a migration barrier of $E_m^V=1.85\pm 0.05$ eV.