Anisotropic Etching and Nanoribbon Formation in Single-Layer Graphene

Abstract

, many of which can only be realized by confining graphene into nanoribbons and other nanostructures. For example, ballistic room-temperature transistors 3-5 and carbon-based spintronic devices 6-10 are two tantalizing possibilities which could one day be realized in a graphene nanodevice. First though, a reliable method must be found to controllably produce graphene nanostructures with specific sizes, geometries, and defined crystallographic edges. Theoretical predictions indicate that a graphene nanoribbon with zig-zag edges can behave as a half-metal 6, 7 which, paired with graphene's long spin relaxation time 11 , could be used to produced spin-valves and other spintronic devices. In addition, nanosized geometric structures such as triangles with zig-zag edges are predicted to have a net nonzero spin 8,9,12, 13 , furthering the potential use of graphene as a canvas for spintronic circuits. For field effect transistor applications, quantum confinement induces a band gap in the normally gapless graphene 10,14,15 , but the potential performance of the device depends strongly on the edge structure as well 4,16,17 . . Indeed, previous studies of catalytic gasification of carbon found that catalytic metal nanoparticles would sometimes etch graphite along crystallographic directions, creating both armchair and zigzag edges [27][28][29][30][31] .

Catalytic subsurface etching of nanoscale channels in graphite

“…Subsequently deposited Ni nanoparticles resting at these artificial and at the natural step edges serve as catalyst for hydrogenation of carbon when the sample is exposed to high temperature in H atmosphere (see Methods for more details). It is understood that the nanoparticle is dragged into the void where carbon atoms have been removed at the edge of the sheet, catalyses further hydrogenation of carbon and successively etches a channel from the edge into the sheet, following the main symmetry directions of carbon lattice 1,3,[5][6][7][8][9][10] (see also Fig. 1a).…”

“…In recent years it has attracted renewed attention as a possible route for nanopatterning of graphene, especially for the production of graphene nanoribbons. Metallic nanoparticles etch the surface layers of graphite [1][2][3][4][5][6][7][8] , as well as single-layer graphene sheets [9][10] . The process is anisotropic along the crystallographic highsymmetry directions, that is, the zigzag /11-20S or armchair /10-10S directions.…”

“…The process is anisotropic along the crystallographic highsymmetry directions, that is, the zigzag /11-20S or armchair /10-10S directions. Nanoparticles consisting of various metals, such as Ni 2,8,9,10 , Fe 2,7 , Pt 3 , Co 2,4,5 and Ag 6 , are known to etch channels on graphite surfaces. It was shown that the etching direction could be influenced by an external magnetic field when Co particles were used 11 .…”

The atomistic mechanism of carbon nanotube cutting catalyzed by nickel under an electron beam

“…This method enables to create a gap between the ends of the cut nanotubes in a reproducible manner without chemical contamination, with the size of the gap controlled by the size of the nickel cluster of ~1 nm, which is important for the fabrication of nanodevices. Molecular dynamics simulations based on the CompuTEM algorithm 13,30,31 confirm cutting of the (5,5) nanotube by a nickel cluster adsorbed on the hole in the nanotube sidewall prior to the cutting process. Detailed analysis of the mechanism reveals that the cutting by the 80 keV electron beam takes place over a timeframe of approximately 10 4 s and involves the ejection of 100 atoms.…”

Face the Edges: Catalytic Active Sites of Nanomaterials

“…Multi‐wall CNTs can be unzipped in the oxidative condition with H 2 SO 4 and KMnO 4 ,198 or by intercalation and exfoliation with alkali‐metal and NH 3 199. Cutting graphene with catalyst NPs like thermally activated nickel NPs can also produce smooth and orientated graphene edges 200. Other methods using electron or other beam could also be utilized to unzip the CNTs 201.…”