Formation of nanoscale vapour films governing thermal resistance in amorphous ice

Abstract

Among the many anomalous properties of water, the formation of amorphous ice is one of its most intriguing phenomena. When water vapour is deposited at very low temperatures, it forms an amorphous solid known as amorphous solid water (ASW). Here, we combine X-ray free-electron laser pump–probe diffraction, continuum heat-transfer modelling, and molecular dynamics simulations to investigate the transient thermal response of ASW-films on a platinum substrate. Picosecond laser pulses heat the Pt from 100 K to ~700 K and maintain elevated temperatures for several nanoseconds. Contrary to expectations based on diffusive thermal transport, the hundreds-nanometer-thick ASW layer shows no detectable structural change within tens of nanoseconds. Simulations suggest a mechanism in which a nanometric vapour layer spontaneously forms at the interface, suppressing thermal contact and insulating the ice. The experimental data are consistent with a nanometric (~6 nm) interfacial gap, indicating that the anisotropic scattering originates from a vapour-nucleated interfacial layer. This finding highlights a general non-equilibrium mechanism of interfacial thermal decoupling that may extend beyond the specific ASW–metal system studied here. Theoretical work has examined non-equilibrium interfacial transport between amorphous solid water (ASW) and metal substrates at the nanosecond timescale, but experimental insights into whether ultrafast interfacial breakdown or decoupling can suppress energy flow across a metal–ASW interface remain scarce. Here, the authors use X-ray free-electron laser pump–probe diffraction, continuum heat-transfer modelling and molecular dynamics simulations to study the transient thermal response of ASW films on a metal substrate, providing insights into non-equilibrium interfacial transport on nanosecond timescales and reporting ultrafast interfacial decoupling via a vapour-nucleated interfacial layer that suppresses energy transfer at the ASW–metal interface.