  Recently-reported data suggest that bubble nucleation on surfaces with
nano-sized features (cavities and posts) may occur close to the thermodynamic
saturation temperature. However, according to the traditional theory of
heterogeneous bubble nucleation, such low nucleation temperatures are possible
only for surfaces with micro-scale cavities. Motivated by this apparent
contradiction, we have used infrared thermometry to measure the nucleation
temperature of water on custom-fabricated nano- to micro-scale cavities (from
90 nm to 4.5 um in diameter) and posts (from 60 nm to 5 um in diameter),
machined on ultra-smooth and clean silicon wafers using electron beam
lithography. Our cavity data are in agreement with the predictions of the
Young-Laplace equation, thus re-affirming the correctness of the classic view
of heterogeneous bubble nucleation, at least for the water-silicon system
investigated here. The data also suggest that individual posts of any size have
an insignificant effect on bubble nucleation, as expected from theory.
  Keywords: Bubble nucleation, superheat, artificial cavities and posts,
nanosize, Young-Laplace
