Controlling the shapes and assemblages of graphene

Abstract

Carbon, a vital element in our daily lives, is still fascinating us at the nanoscale. In PNAS, Geng et al. (1) manage to synthesize ordered arrays of atom-thick hexagonal microplatelets consisting of sp2 hybridized carbon. Since the discovery of C60 (Buckminsterfullerene; an icosahedral carbon cage molecules with diameter of approximately 0.7 nm) (2), carbon nanoscience emerged, and it was witnessed that nanoscale carbon materials possessed different physicochemical properties compared with the well known bulk allotropes of carbon: graphite and diamond. During the past 20 y, other novel carbon materials have been synthesized and intensively studied: carbon nanotubes (3⇓–5) and graphene (6, 7). Graphene consists of an atom-thick sp2 hybridized carbon sheet, in which each carbon atom is bonded to three carbon atoms, thus forming a hexagonal framework with bond lengths of 1.42 A. This 2D hexagonal sheet has shown outstanding properties compared with other forms of carbon. Graphene exhibits a room-temperature quantum Hall effect (8), it is a semimetal, and it has an extremely high room temperature carrier mobility (at least two orders of magnitude greater than that of silicon) (9). Graphene could also exhibit extremely high thermal conductivity values ranging from (2.50 ± 0.44)×103 to (5.30 ± 0.48)×103 W/m⋅K (10, 11). From the mechanical standpoint, graphene is very robust and exhibits a Young modulus of approximately 1 TPa (12). It is noteworthy that the aforementioned properties of graphene systems strongly depend on, for example, the degree of crystallinity (e.g., domain size of crystalline domains and types/number of defects), edge morphology (atomically smooth edges or rough edges), and number of stacking layers (e.g., bilayer, trilayer). Individual graphene sheets were first isolated by using a repeated peeling “scotch-tape” method (6). However, alternative methods involving the thermal decomposition … [↵][1]1E-mail: mut11{at}psu.edu. [1]: #xref-corresp-1-1