surface
science / reaction
dynamics
/ laser photochemistry /
laser-surface
interactions / nanotechnology
/ physical
chemistry / chemical
physics
Solidification Driven Extrusion
(Nanospikes)
Dave Mills noted that in some of the scanning electron microscopy (SEM)
images that he took of our laser ablation created silicon pillars, that a little spike formed
on the tip of the pillar. He also thought that these might be related
to ice
spikes. You can get ice spikes to form in your freezer simply by
freezing pure distilled water. A major question in nanoscience is: what
techniques to form structures scale from the macroscopic (for instance
centimeter) range into the nanoscale regime? We showed
that the physics behind ice spike formation scales down to the
nanoscale. It works for silicon pillars just like it works for ice
cubes.
In subsequent
work with germanium performed with Barada Nayak and Mool Gupta, we
found that nanospikes also form on germanium pillars, as shown on the
right.
So what do water, silicon and germanium all have in common? They all
form tetrahedrally co-ordinated solids phases and all of them expand
when they freeze. This is an unusual property but that is what makes
ice less dense than liquid water and why ice cubes float. It also means
that if the surface of liquid water, silicon or germanium freezes that
it compresses the liquid that is trapped inside. This leads to a build
up of pressure. Eventually the pressure is too much and a jet of
supercooled liquid shoots out and forms the ice spike.
For further information on related topics,
try these sites:
Labs
working in Surface
Science, Nanotechnology and Catalysis
