Interesting features appear when carbon-saturated molten metal
is splat-cooled, in situ, during the usual curved
kish synthesis procedure, as this nickel sample was. The fine lines
running down the flank of this sample are rifts produced by azimuthal stress
when the the molten metal encountered the vacuum chamber floor. Closer to
the top of the sample, the negative stress produced dark spots and
even bubbles.
In this image, a rift encounters one of the dark spots.
The dark area is not a region of thicker graphite, but a hole that is only
thinly covered by a graphite membrane. The membrane is thin enough to
serve as a window for 30 keV electrons. This veiled pockmark feature
appears routinely on splat-cooled iron, nickel and cobalt samples.
This incomplete graphene bubble has a polygonal hole,
suggesting the material is crystalline, in spite of its curvature. A
certain cobalt fragment shows similar
evidence of crystalline graphene draped over a smoothly curved surface.
This electron-transparent graphene membrane has origami-like
folds, which are evidently strong enough to withstand delamination.
This "bubble wrap" structure delaminated from a splat-cooled
iron sample.
Some freestanding membranes are round. Notice the blister that is visible through the
bubble. Bubbles like this have been precipitated from iron, nickel and
cobalt. A formation mechanism is proposed on the
splat-cooling page.
