Abstract
Graphene has many claims to fame: it is the thinnest possible membrane, it has unique electronic and excellent mechanical properties, and it provides the perfect model structure for studying materials science at the atomic level. However, for many practical studies and applications the ordered hexagon arrangement of carbon atoms in graphene is not directly suitable. Here, we show that the atoms can be locally either removed or rearranged into a random pattern of polygons using a focused ion beam (FIB). The atomic structure of the disordered regions is confirmed with atomic-resolution scanning transmission electron microscopy images. These structural modifications can be made on macroscopic scales with a spatial resolution determined only by the size of the ion beam. With just one processing step, three types of structures can be defined within a graphene layer: chemically inert graphene, chemically active amorphous 2D carbon, and empty areas. This, along with the changes in properties, gives promise that FIB patterning of graphene will open the way for creating all-carbon heterostructures to be used in fields ranging from nanoelectronics and chemical sensing to composite materials.
Highlights
Graphene has received enormous attention since its introduction a decade ago.[1]
Because of its two-dimensional (2D) nature, all atoms in graphene are directly exposed to external interactions through electric and magnetic fields or via chemical and physical processes
Its application on the nanoscale, requires developing a detailed atomic level understanding on irradiation effects. This is because methods for estimating ion irradiation effects in bulk materials can rarely be directly used for low-dimensional structures,[6] and the optimal irradiation parameters change drastically from bulk to nanomaterials
Summary
Fluence of ∼1016 ions/cm[2], mostly individual point defects were observed. Here, we show that perpendicular irradiation with a focused beam of Ga+ ions at 35 keV results in amorphization of suspended graphene at a dose of about 3.1 × 1015 ions/cm[2]. This yields a ratio of 91%, which indicates that the amorphized areas have approximately 9% density deficit as compared to pristine graphene Comparing this number with earlier estimations of electron irradiationamorphization of graphene[30] shows that such deficit is close to the completely disordered material, as is consistent with our atomic-resolution images. We have shown that the regular hexagon pattern of single-layer graphene can be selectively either sputtered or transformed into a random pattern of polygons ranging from pentagons to octagons and nine-membered carbon rings in a controlled manner using a focused Ga+ ion beam at 35 keV This allows defining three different kinds of areas into a graphene layer with just one processing step with the FIB: chemically inert highly conductive graphene, chemically active, presumably less conductive, amorphous 2D carbon, and empty holes.
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