The graphene on this splat-cooled nickel sample was too thin to
produce unsupported membranes. Pockmarks are obvious, and some of the
voids are surrounded with dendrites.
At this scale, the dendrites become visible. These
features appear to form after the melt has impacted the vacuum chamber floor,
where the melt is grounded. Unlike the thinner dendrites on the
cactus-like
samples, dendrite formation here cannot be attributed to electrostatic field
stress.
Micron-scale dendrites are surprisingly reproducible, precipitating from
splat-cooled samples of iron, nickel and cobalt. The smaller "cactus
spine" dendrites are less common and apparently associated with extremely thin
graphene deposits. The carbon-saturated samples studied so far tend to yield
graphite of micron-scale thickness. Predictable synthesis of graphene
nanostructures may require better control over the carbon concentration.
