Abstract
Catalytic decomposition of hydrocarbons on transition metals attracts a renewed interest as a route toward high-quality graphene prepared in a reproducible manner. Here we employ two growth methods for graphene on Ir(111), namely room temperature adsorption and thermal decomposition at 870–1470 K (temperature programmed growth (TPG)) as well as direct exposure of the hot substrate at 870–1320 K (chemical vapor deposition (CVD)). The temperature- and exposure-dependent growth of graphene is investigated in detail by scanning tunneling microscopy. TPG is found to yield compact graphene islands bounded by C zigzag edges. The island size may be tuned from a few to a couple of tens of nanometers through Smoluchowski ripening. In the CVD growth, the carbon in ethene molecules arriving on the Ir surface is found to convert with probability near unity to graphene. The temperature-dependent nucleation, interaction with steps and coalescence of graphene islands are analyzed and a consistent model for CVD growth is developed.
Highlights
Intense research on the electronic properties of graphene has been initiated in 2004 using both exfoliated [1] and epitaxial [2] graphene
We make the following observations: (i) graphene is exclusively located at the substrate step edges for low coverages, (ii) graphene frequently spans on both sides of the step edge, and (iii) the larger fraction of graphene is at the lower terrace (70 % for doses of 4 × 10−8 mbar s), (iv) while there are graphene flakes attached only to an ascending step edge, no graphene flakes were ever observed attached only to a descending step edge
We have investigated two complementary approaches for graphene on metal preparation, namely temperature programmed growth (TPG) and chemical vapor deposition (CVD)
Summary
Intense research on the electronic properties of graphene has been initiated in 2004 using both exfoliated [1] and epitaxial [2] graphene. While most of the experimental research on graphene still relies on exfoliated graphene, the route towards practical realization calls for reproducible methods for the production of high quality graphene single layers with macroscopic extension. To this respect, epitaxial graphene on a silicon carbide (SiC) substrate has attracted much interest. Whatever the recent progress in the preparation of graphene/SiC the charge carrier mobilities remain comparable to the first ones reported [2, 5, 6], and much lower than for exfoliated graphene [7]. A further step towards applications could involve the transfer of such graphene layers onto a non conducting substrate [3, 10]
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