Growing graphene over large areas and the improvement of transfer techniques increase the need to control the shape and geometry of graphene once deposited onto the destination substrate. After transfer (1), graphene membranes always display unwanted ripples that limit its electrical, thermal and mechanical properties (2).Indeed, these ripples in graphene-based transistor can between other alter the electrical conductivity (2).
Nevertheless, it offers interesting ways to locally tune strain in graphene, which strongly influences its electronic, magnetic and vibrational properties (3,4,5). Local bending of graphene is a mean to induce an electrical gap or create high pseudo-magnetic fields (3), so that a locally tailor strain in graphene for controlled design of devices based on "stresstronics".
Before reaching such a stage of control, it appears necessary to understand the interaction process of polycrystalline graphene membranes onto the formation of graphene ripples during transfer. For that purpose, we investigate by spatially resolved Raman spectroscopy, the formation process of strain and ripples in CVD graphene layers, which are deposited onto a corrugated substrate formed by an array of SiO2 nano-pillars with varying spacing and apex radius. This ordered corrugated substrate defines strain domains of parallel ripples, which can reach different regimes by varying the pitch of the array and sharpness of the pillars.
We explore both limits of low-density arrays where graphene exhibits ripples domains and of very dense arrays for which no ripples are formed, and so the graphene stays fully suspended over a dense nano-pillars array. Spatially resolved Raman spectroscopy reveals uniaxial strain domains in the transferred graphene, which are induced and controlled by the array. For the tightest arrays, this technique shows the possibility to obtain macroscopically suspended graphene membranes with minimal interaction with the substrate. It also offer perspectives for electron transport and nano mechanical applications.
(1) Meyer, J. C.; Geim, A. K.; Katsnelson, M. I.; Novoselov, K. S.; Booth, T. J.; Roth, S. Nature2007, 446, 60-63.
(2) Ni, G.-X.; Zheng, Y.; Bae, S.; Kim, H. R.; Pachoud, A.; Kim, Y. S.; Tan, C.-L.; Im, D.;Ahn, J.-H.; Hong, B. H.; Ozyilmaz, B. ACS nano 2012, 6, 1158-64 ; Chen, C.-C.; Bao, W.; Theiss, J.; Dames, C.; Lau, C. N.; Cronin, S. B. Nano letters 2009, 9, 4172-6 ; Bao, W.; Myhro, K.; Zhao, Z.; Chen, Z.; Jang, W.; Jing, L.; Miao, F.; Zhang, H.; Dames, C.; Lau, C. N. Nano letters 2012, 12, 5470-4.
(3) Levy, N.; Burke, S. a.; Meaker, K. L.; Panlasigui, M.; Zettl, A.; Guinea, F.; Castro Neto, a. H.;Crommie, M. F. Science (New York, N.Y.) 2010, 329, 544-7.
(4) Frank, O.; Tsoukleri, G.; Riaz, I.; Papagelis, K.; Parthenios, J.; Ferrari, A. C.; Geim, A. K.;Novoselov, K. S.; Galiotis, C. Nature communications 2011, 2, 255.
(5) A. Reserbat-Plantey et al, Nature Nanotechnology 7, 151-155 (2012)