  Ice I has three forms depending on the stacking arrangements of its layers:
hexagonal ice Ih, cubic ice Ic, and stacking disordered ice Isd. Below ~60 K,
amorphous water becomes metastable, and the formation of any form of ice I is
often implicitly precluded. Using a newly developed low-temperature reflection
high-energy electron diffraction (RHEED) technique, we show that crystalline
ice with cubic stacking sequences (i.e., ice Ic) formed through Ne sublimation
from a solid H2O/Ne (1:1000 ratio) matrix at 13 K. The extent of staking
disorder (disordered cubic and hexagonal stacking sequences) in the ice formed
by Ne matrix sublimation is smaller than that in vapor-deposited ice Isd
prepared at 143 K and below the limit of detection of low-temperature RHEED.
Dependence of the resulting ice structures on the thickness of the H2O/Ne
matrix shows that amorphous water first forms in the early stages of Ne
sublimation and the cubic stacking sequence subsequently takes place. As the
cubic ice Ic formed here at a much lower temperature (13 K) than previously
observed (typically above 78 K), Ne matrix sublimation represents a novel route
to the formation of cubic ice Ic under low-temperature and low-pressure
conditions.
