Three-step growth of vapor-deposited ice under mesospheric temperature and water vapor conditions

TL;DR

This study reveals that vapor-deposited ice at mesospheric temperatures grows in three distinct phases—amorphous, cubic, and hexagonal—highlighting complex phase coexistence relevant to polar mesospheric clouds.

Contribution

It demonstrates the three-step growth process of vapor-deposited ice at low temperatures, providing new insights into mesospheric ice formation and phase coexistence.

Findings

Ice grows in three phases: amorphous, cubic, and hexagonal.

The phases can coexist depending on ice thickness.

Ostwald rule of stages applies to vapor-deposited ice at 120 K.

Abstract

Polar mesospheric clouds provide clues to physicochemical processes in the mesosphere and lower thermosphere. However, the heterogeneous nucleation and growth processes of water ice under polar mesospheric conditions are poorly understood, especially at the nanoscale. This study used reflection high energy electron diffraction and infrared reflection absorption spectroscopy to analyze the structure of vapor-deposited ice at polar mesospheric temperature (120 K) under vapor pressure conditions. The ice appeared to grow in three steps during vapor deposition, being amorphous water for the first 15 nm, then cubic ice up to 50 nm, and finally hexagonal ice subsequently. This three step growth suggests that the three observed phases can coexist in polar mesospheric clouds, depending on the thickness of water ice. The finding of the three-step growth also shows that the Ostwald rule of stages can hold for vapor deposited ice at low temperature.