Selecting a single orientation for millimeter sized graphene sheets
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Field of view (FOV) PEEM images of graphene growth on Ir(111) at . [(a) ] Two different types of domains are observed to form. The brighter of the two is aligned with the substrate, whereas the other, darker, type of domain is rotated by approximately 30° with respect to the substrate. [(b) ] The film has fully closed to form a graphene sheet consisting of various rotational domains. (c) Relative area fractions of the two different types of domains which are visible in panels [(a) and (b)]. The majority of the graphene sheet consists of rotated domains. The exponential curve is a fit for the self-limited growth mode of the graphene on Ir(111).
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FOV PEEM images of graphene growth on Ir(111) obtained at a temperature of 1126 K. [(a) ] Several aligned and rotated domains have nucleated after the first growth cycle. [(b) ] The first etching step has completely removed all rotated domains. [(c) ] After two more etch and growth steps, the graphene film now consists of a majority of aligned domains. Rotated domains continue to nucleate at every growth step, as is visible in the image. [(d) ] The film has fully closed to form a graphene sheet. A relative fraction of 99% of the sheet consists of aligned domains. (e) Relative area fractions of the two different types of domains that are visible in panels [(a)–(d)].
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FOV LEEM images of graphene growth on Ir(111) at a temperature of 1113 K and recorded with an electron energy of 18.6 V. The dark spot in the top of the images is an image detector defect. [(a) ] Start of ethylene exposure of the surface. The Ir(111) surface has been precovered with many small graphene nuclei, appearing dark in the LEEM images. [(b) ] Several of the predeposited domains have started to grow. Those domains that have edges along the substrate crystallographic directions are not observed to grow. [(c) ] The graphene film has nearly evolved into a sheet. No rotated domains that would yield a higher intensity than the aligned domains, are observed. Several precovered domains still persist and do not grow. [(d) ] The film has fully closed to form a perfectly aligned graphene sheet. (e) A FOV STM image of the growth of the aligned phase taken after the graphene film was only partially completed. The smaller nuclei with straight edges running along substrate crystallographic directions have not grown significantly, whereas domains with edges of different orientation have ( and ). (f) pattern obtained of the closed graphene film. The orientation of the graphene is unaltered when the beam is scanned over an area of several millimeters.
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