Ice nucleation on hydrophilic silicon

We have used Fourier transform infrared spectroscopy to study thin water films on a hydrophilic silicon surface in the temperature range from 20 to − 20 ° C . Throughout that range, the spectra of the water adjacent to the silicon surface are consistent with that of bulk water near 25 ° C . Thicker films ( > 1 μ m ) freeze at − 11 ± 1 ° C . We reconcile the apparent paradox of a thin film of water which is quite liquidlike at a temperature where freezing of thicker films occurs by hypothesizing that the nucleation event in the thicker film is triggered by a critical ice embryo which forms at some small distance from the silicon surface, as opposed to in direct contact with it.