[Show abstract][Hide abstract] ABSTRACT: The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order. We use a nanofabrication technique based on scanning tunnelling microscopy to define graphene nanoribbons with nanometre precision and well-defined crystallographic edge orientations. Although so-called 'armchair' ribbons display quantum confinement gaps, ribbons with the 'zigzag' edge structure that are narrower than 7 nanometres exhibit an electronic bandgap of about 0.2-0.3 electronvolts, which can be identified as a signature of interaction-induced spin ordering along their edges. Moreover, upon increasing the ribbon width, a semiconductor-to-metal transition is revealed, indicating the switching of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.
[Show abstract][Hide abstract] ABSTRACT: Graphene has many advantageous properties, but its lack of an electronic band gap makes this two-dimensional material impractical
for many nanoelectronic applications, for example, field-effect transistors. This problem can be circumvented by opening up
a confinement-induced gap, through the patterning of graphene into ribbons having widths of a few nanometres. The electronic
properties of such ribbons depend on both their size and the crystallographic orientation of the ribbon edges. Therefore,
etching processes that are able to differentiate between the zigzag and armchair type edge terminations of graphene are highly
sought after. In this contribution we show that such an anisotropic, dry etching reaction is possible and we use it to obtain
graphene ribbons with zigzag edges. We demonstrate that the starting positions for the carbon removal reaction can be tailored
at will with precision.
KeywordsGraphene-atomic force microscopy (AFM)-etching-nanoribbon-zigzag
Nano Research 12/2009; 3(2):110-116. · 7.39 Impact Factor