24 April

Watching graphene on Nickel surfaces: an STM view on the role of the substrate

Wednesday 24 April 2019, 11:00am

ICN2 Seminar Hall, ICN2 Building, UAB

By Cristina Africh, Consiglio Nazionale delle Ricerche – Istituto Officina dei Materiali (CNR-IOM), Trieste, Italy

Abstract:It is well known that the substrate plays a pivotal role in tailoring morphologic, electronic and chemical properties of supported graphene. However, this effect is typically analysed in terms of interaction between a full graphene layer and a flat underlying substrate, neglecting or underestimating their interplay during the Chemical Vapor Deposition growth process. Most of the studies focusing on the understanding of growth mechanisms at the atomic level are in fact based on the interpretation of post-growth experiments on model surfaces, which can sometimes be misleading. In our laboratory, we investigated under in-operando conditions the graphene growth process at technologically relevant temperatures (up to ≈ 700 K) by means of variable-temperature scanning tunnelling microscopy (STM), with a time resolution down to 100 ms/image, both on model surfaces and on commercially available polycrystalline Ni foils, among the most widely used substrates for industrial production. By combining the experimental results with Density Functional Theory (DFT) calculations, we can unravel transient phenomena taking place during growth, such as the action of single substrate atoms diffusing on the metal surface. These atoms drive the growth process by temporarily attaching at kink sites along the graphene flake edges and facilitating the incorporation of new C atoms in the graphene network [1]. The substrate dynamics at metal step edges and the interaction with the growing graphene flake are also key ingredients for the formation of continuous 2D carbon layers in corrugated substrate regions, as can be found at step bunches or grain boundaries on poly-crystals [2]. Segregation at the graphene/substrate interface of additional carbon atoms upon cooling, changes the carbon/metal interplay, tailoring the formation of nanostructured 1D or 2D regions of free-standing like graphene, as evidenced by combining STM and spectroscopic results and confirmed by DFT [3,4]. [1] L.L. Patera et al, Science 359 (2018) 1243-1246 [2] Z. Zou et al, Carbon 130 (2018) 441-447; Z. Zou et al, submitted [3] L.L. Patera et al, ACS Nano 7 (2013) 7901-7912; C. Africh et al, Sci. Rep. 6 (2015) 19734 [4] A. Sala et al, in preparation.

Hosted by: Dr. Jordi Fraxedas, Force Probe Microscopy and Surface Nanoengineering Group Leader at ICN2