Nonreactive Ambient Nitrogen Gas Significantly Suppresses the Growth Kinetics of Elementary Spiral Steps on Prism Faces of Ice Crystals

We studied the effects of ambient nitrogen (N 2 ) gas on the growth kinetics of ice crystals. We directly observed individual elementary spiral steps (0.4 nm in height) on prism faces of ice crystals under N 2 gas at 0.20–1.00 atm using our advanced optical microscope (a Laser Confocal Microscope combined with a Differential Interference contrast Microscope: LCM-DIM). We measured the lateral velocity ( v step ) of elementary spiral steps on prism faces as a function of supersaturation (σ) of water vapor under N 2 gas at different pressures ( P N 2 ). From the dependence of v step on σ, we determined the step kinetic coefficient β under different P N 2 and found that with increasing P N 2 from 0.20 to 1.00 atm, β decreases monotonically to approximately one-fourth. In addition, we also determined the step ledge free energy κ of elementary spiral steps from the relation between the spacing of adjacent spiral steps and supersaturation at crystal surfaces. Then, we found that κ shows a small maximum at P N 2 = 0.80 atm, although it is unclear whether this result holds any meaning. We discussed the reasons for the decrease in the surface growth kinetics (β) of ice crystals by considering two cases: when N 2 gas adsorbs or does not.