All entries for michael strano

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Charge Transfer at Junctions of a Single Layer of Graphene and a Metallic Single Walled Carbon Nanotube

• Authors: G.L.C. Paulus, Q.H. Wang, Z.W. Ulissi, T.P. McNicholas, A. Vijayaraghavan, C.-J. Shih, Z. Jin, M.S. Strano
• Sponsorship: 2009 US Office of Naval Research Multi University Research Initiative (MURI) grant; DOE CSGF program, Institute of Soldier Nanotechnology

In this work we fabricate and study junction between a single walled carbon nanotube (SWNT) and a monolayer of graphene for the first time^[1]. A single layer graphene (SLG) sheet grown by chemical vapor deposition (CVD) is transferred onto a SiO₂/Si wafer with aligned CVD-grown SWNTs. Raman spectroscopy is used to identify metallic-SWNT/SLG junctions, and we report a method for spectroscopic deconvolution of the overlapping G peaks of the SWNT and the SLG by making use of the polarization dependence of the SWNT^[2]. A comparison of the Raman peak positions and intensities of the individual SWNT and graphene to those of the SWNT-graphene junction indicates an electron transfer of 1.12 x 10¹³ cm^-2 from the SWNT to the graphene. This direction of charge transfer is in agreement with the work functions of the SWNT and graphene^[3]. We find that the compression of the SWNT by the graphene increases the width of the radial breathing mode (RBM) peak from 3.6 +/-0.3 to 4.6+/-0.5 cm^-1 and that of the G peak from 13+/-1 to 18+/-1 cm^-1, in reasonable agreement with our molecular dynamics simulations. However, we conclude that the RBM and G peak position shifts are primarily due to charge transfer with minimal contributions from strain. With this method, we demonstrate the ability to dope graphene with nanometer resolution.

1. G.L.C. Paulus, Q.H. Wang, Z.W. Ulissi, T.P. McNicholas, A. Vijayaraghaan, C.-J. Shih, Z. Jin, M.S. Strano, “Charge transfer at junctions of a single layer of graphene and a metallic single walled carbon nanotube,” Small, vol. 9, no. 11, pp. 1954-1963, June 2013. [↩]
2. G.S. Duesberg, I. Loa, M. Burghard, K. Syassen, S. Roth, “Polarized raman spectroscopy on isolated single-wall carbon nanotubes,” Physical Review Letters, vol. 85, no. 25, pp. 5436-5439, December 2000. [↩]
3. V. Barone, J.E. Peralta, J. Uddin, G.E. Scuseria, Journal of Chemical Physics, vol. 124, no. 2, pp. 024709 (1-5), January 2006. [↩]

Understanding and Controlling the Substrate Effect on Graphene Electron-transfer Chemistry via Reactivity Imprint Lithography

• Authors: Q. H. Wang, Z. Jin, K. K. Kim, A. J. Hilmer, G. L. C. Paulus, C.-J. Shih, M.-H. Ham, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, J. Kong, P. Jarillo-Herrero, M. S. Strano
• Sponsorship: Office of Naval Research, NSF, SRC



Figure 1: (a) Schematic of graphene supported on a chemically patterned substrate. (b) Schematic of reaction pattern in graphene induced by substrate. (c) Raman map of reaction intensity.

Graphene has exceptional electronic, optical, mechanical, and thermal properties, which provide it with great potential for use in electronic, optoelectronic and sensing applications^[1]. The chemical functionalization of graphene has been investigated with a view to controlling its electronic properties and interactions with other materials^[2]. Covalent modification of graphene by organic diazonium salts has been used to achieve these goals, but because graphene comprises only a single atomic layer, it is strongly influenced by the underlying substrate. In our work here^[3], we show a stark difference in the rate of electron-transfer reactions with organic diazonium salts for monolayer graphene supported on a variety of substrates. Reactions proceed rapidly for graphene supported on SiO₂ and Al₂O₃ (sapphire), but negligibly on alkyl-terminated and hexagonal boron nitride (hBN) surfaces, as shown by Raman spectroscopy. We also develop a model of reactivity based on substrate-induced electron–hole puddles in graphene and achieve spatial patterning of chemical reactions in graphene by patterning the substrate.

1. A. K. Geim1 and K. S. Novoselov, “The rise of graphene,” Nature Materials, vol. 6, pp. 183-191, Mar. 2007. [↩]
2. G. L. C. Paulus, Q. H. Wang, and M. S. Strano, “Covalent Electron Transfer Chemistry of Graphene with Diazonium Salts,” Accounts of Chemical Research, vol. 46, pp. 160-170, Sep. 2012. [↩]
3. Q. H. Wang, Z. Jin,  K. K. Kim, A. J. Hilmer, G. L. C. Paulus, C.-J. Shih, M.-H. Ham, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, J. Kong, P. Jarillo-Herrero, and M. S. Strano, “Understanding and controlling the substrate effect on graphene electron-transfer chemistry via reactivity imprint lithography,” Nature Chemistry, vol. 4, pp. 724-732, Aug. 2012. [↩]