Transport of hydrogen isotopes through interlayer spacing in van der Waals crystals

TL;DR

This study reveals that van der Waals gaps in layered crystals enable quantum confinement of hydrogen isotopes at room temperature, affecting their transport properties and opening avenues for isotope separation and atomistic quantum studies.

Contribution

It demonstrates room-temperature quantum confinement of hydrogen isotopes in van der Waals gaps, a phenomenon previously limited to low temperatures, with implications for isotope sieving.

Findings

Protons face higher barriers than deuterons in van der Waals gaps.

Transport rates are comparable to those in water, indicating fast diffusion.

Quantum confinement effects are observable at room temperature.

Abstract

Atoms start behaving as waves rather than classical particles if confined in spaces commensurate with their de Broglie wavelength. At room temperature this length is only about one angstrom even for the lightest atom, hydrogen. This restricts quantum-confinement phenomena for atomic species to the realm of very low temperatures. Here we show that van der Waals gaps between atomic planes of layered crystals provide angstrom-size channels that make quantum confinement of protons apparent even at room temperature. Our transport measurements show that thermal protons experience a notably higher barrier than deuterons when entering van der Waals gaps in hexagonal boron nitride and molybdenum disulfide. This is attributed to the difference in de Broglie wavelength of the isotopes. Once inside the crystals, transport of both isotopes can be described by classical diffusion, albeit with unexpectedly fast rates, comparable to that of protons in water. The demonstrated angstrom-size channels can be exploited for further studies of atomistic quantum confinement and, if the technology can be scaled up, for sieving hydrogen isotopes.