Splat cooling

This is a two-step procedure:
  1. Break off a piece of the melt during the regular procedure.
  2. Let the separated melt fall onto a cold surface.
In step 2, a combination of gravity and electrostatic force brings the falling melt body into swift, violent contact with a grounded surface.  Usually this surface is the stainless steel of the chamber floor, but melt particles occasionally strike the electron source (glowing hot tungsten) and produce triangular crystallites.
Step 1 is accomplished either through gravity acting on a weak target or electrostatic stress applied by high voltage between the melt and the chamber.


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Splat cooling

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polygonal boundary of origami on melt

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torn graphite drum

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graphene bubbles

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Thick shells don't buckle completely under negative hydrodynamic stress.  Freestanding graphite membranes of only several nanometers thickness are frequently observed over pockmarks.
Because the melt cools as it flows, we can expect a graphitic shell to precipitate on the interior of any pockmark.  This shell will be compressed as the melt solidifies and continues to precipitate carbon.  Apparently, enough compressive stress exists to frequently turn the graphitic pockmark lining inside-out.  The electron-transparent bubbles seen on samples of splat-cooled iron, nickel and cobalt are evidence of a resilient graphitic material.
Negative hydrodynamic stress under the top of the graphite shell can cause the shell to buckle and form pockmarks.  At the same time, longitudinal rifts may appear in the shell, around its equator.
Upon impact with a cold surface, the melt droplet rapidly deforms, cools and experiences non-uniform stress.
During freefall, the separated melt droplet briefly has the opportunity to cool and thicken the graphite shell.