  Bulk amorphous materials have been studied extensively and are widely used,
yet their atomic arrangement remains an open issue. Although they are generally
believed to be Zachariasen continuous random networks, recent experimental
evidence favours the competing crystallite model in the case of amorphous
silicon. In two-dimensional materials, however, the corresponding questions
remain unanswered. Here we report the synthesis, by laser-assisted chemical
vapour deposition, of centimetre-scale, free-standing, continuous and stable
monolayer amorphous carbon, topologically distinct from disordered graphene.
Unlike in bulk materials, the structure of monolayer amorphous carbon can be
determined by atomic-resolution imaging. Extensive characterization by Raman
and X-ray spectroscopy and transmission electron microscopy reveals the
complete absence of long-range periodicity and a threefold-coordinated
structure with a wide distribution of bond lengths, bond angles, and five-,
six-, seven- and eight-member rings. The ring distribution is not a Zachariasen
continuous random network, but resembles the competing (nano)crystallite model.
We construct a corresponding model that enables density-functional-theory
calculations of the properties of monolayer amorphous carbon, in accordance
with observations. Direct measurements confirm that it is insulating, with
resistivity values similar to those of boron nitride grown by chemical vapour
deposition. Free-standing monolayer amorphous carbon is surprisingly stable and
deforms to a high breaking strength, without crack propagation from the point
of fracture. The excellent physical properties of this stable, free-standing
monolayer amorphous carbon could prove useful for permeation and diffusion
barriers in applications such as magnetic recording devices and flexible
electronics.
