(538i) Understanding Armchair Graphene Nanoribbon Growth on Mis-Cut Ge(001) Surfaces through Experiments and Density Functional Theory Calculations
Here, we explore the impact of step edges on growth behavior of graphene nanoribbons. Experimental measurements reveal that on mis-cut Ge(001) surface, where additional step edges are created in the <110> direction, the length of the graphene nanoribbons preferentially align along step edges. Additionally, we observed that when the ribbon growth rate was increased, graphene crystals grew into larger ribbons on the flat surface and into semicircular shapes on mis-cut surfaces. To understand this behavior, we examined the interaction of graphene nanoribbons with flat and mis-cut Ge surfaces using self-consistent density functional theory (DFT) calculations. Our calculations show that a carbon-terminated edges of the graphene nanoribbons and step edges of the surface form strong bonds, which are thermodynamically unfavorable on the flat surface. We hypothesize that the strong bond between graphene and step-edge suppresses growth at this edge, and graphene crystals grow outward from this pinned edge, which explains the straight termination in one direction.
Combining experimental and theoretical methods, we offer insights into the mechanism of graphene nanoribbon alignment on Ge(001) during CVD growth. In the future, these insights carry the potential to optimize the production of graphene nanoribbon arrays for device applications.
 L. Chen, Y. Hernandez, X. Feng, and K. MÃ¼llen, âFrom Nanographene and Graphene Nanoribbons to Graphene Sheets: Chemical Synthesis,â Angew. Chemie Int. Ed., vol. 51, no. 31, pp. 7640â7654, Jul. 2012.
 R. M. Jacobberger, B. Kiraly, M. Fortin-Deschenes, P. L. Levesque, K. M. McElhinny, G. J. Brady, R. Rojas Delgado, S. Singha Roy, A. Mannix, M. G. Lagally, P. G. Evans, P. Desjardins, R. Martel, M. C. Hersam, N. P. Guisinger, and M. S. Arnold, âDirect oriented growth of armchair graphene nanoribbons on germanium,â Nat. Commun., vol. 6, p. 8006, Aug. 2015