The researchers were able to force ice to form in extremely narrow gaps between a gold surface and the gold tip of a scanning tunneling microscope in an electric field as low as one million volts per meter. Previous estimates had pegged the number at one billion volts per meter.
The strength of an electric field diminishes exponentially with distance making it possible for small spaces to have high electric fields. Electric fields of one million volts per meter can be found in nanoscale electrical devices; they also form naturally in extremely small crevices in rocks, and probably in thunderclouds. A household static electric spark generates an electric field of about three million volts per meter.
[Via Smalley's Research Watch]
