Bandgap engineering is used to create semiconductor heterostructure devices that perform processes such as resonant tunnelling1,2 and solar energy conversion3,4. However, the performance of such devices degrades as their size is reduced5,6. Graphene-based molecular electronics has emerged as a candidate to enable high performance down to the single-molecule scale7,8,9,10,11,12,13,14,15,16,17. Graphene nanoribbons, for example, can have widths of less than 2 nm and bandgaps that are tunable via their width and symmetry6,18,19. It has been predicted that bandgap engineering within a single graphene nanoribbon may be achieved by varying the width of covalently bonded segments within the nanoribbon20,21,22. Here, we demonstrate the bottom-up synthesis of such width-modulated armchair graphene nanoribbon heterostructures, obtained by fusing segments made from two different molecular building blocks. We study these heterojunctions at subnanometre length scales with scanning tunnelling microscopy and spectroscopy, and identify their spatially modulated electronic structure, demonstrating molecular-scale bandgap engineering, including type I heterojunction behaviour. First-principles calculations support these findings and provide insight into the microscopic electronic structure of bandgap-engineered graphene nanoribbon heterojunctions.
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Chang, L. L., Esaki, L. & Tsu, R. Resonant tunnelling in semiconductor double barriers. Appl. Phys. Lett. 24, 593 (1974).
Zwanenburg, F. A. et al. Silicon quantum electronics. Rev. Mod. Phys. 85, 961–1019 (2013).
Green, M. A., Emery, K., Hishikawa, Y., Warta, W. & Dunlop, E. D. Solar cell efficiency tables (version 40). Prog. Photovolt. Res. Appl. 20, 606–614 (2012).
Guter, W. et al. Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight. Appl. Phys. Lett. 94, 223504 (2009).
Frank, D. J. et al. Device scaling limits of Si MOSFETs and their application dependencies. Proc. IEEE 89, 259–288 (2001).
Schwierz, F. Graphene transistors. Nature Nanotech. 5, 487–496 (2010).
Van der Lit, J. et al. Suppression of electron–vibron coupling in graphene nanoribbons contacted via a single atom. Nature Commun. 4, 2023 (2013).
Bennett, P. B. et al. Bottom-up graphene nanoribbon field-effect transistors. Appl. Phys. Lett. 103, 253114 (2013).
Blankenburg, S. et al. Intraribbon heterojunction formation in ultranarrow graphene nanoribbons. ACS Nano 6, 2020–2025 (2012).
Bronner, C. et al. Aligning the band gap of graphene nanoribbons by monomer doping. Angew. Chem. Int. Ed. 52, 4422–4425 (2013).
Cai, J. et al. Atomically precise bottom-up fabrication of graphene nanoribbons. Nature 466, 470–473 (2010).
Chen, Y-C. et al. Tuning the band gap of graphene nanoribbons synthesized from molecular precursors. ACS Nano 7, 6123–6128 (2013).
Han, M., Özyilmaz, B., Zhang, Y. & Kim, P. Energy band-gap engineering of graphene nanoribbons. Phys. Rev. Lett. 98, 206805 (2007).
Koch, M., Ample, F., Joachim, C. & Grill, L. Voltage-dependent conductance of a single graphene nanoribbon. Nature Nanotech. 7, 713–717 (2012).
Li, X., Wang, X., Zhang, L., Lee, S. & Dai, H. Chemically derived, ultrasmooth graphene nanoribbon semiconductors. Science 319, 1229–1232 (2008).
Linden, S. et al. Electronic structure of spatially aligned graphene nanoribbons on Au(788). Phys. Rev. Lett. 108, 216801 (2012).
Ruffieux, P. et al. Electronic structure of atomically precise graphene nanoribbons. ACS Nano 6, 6930–6935 (2012).
Nakada, K., Fujita, M., Dresselhaus, G. & Dresselhaus, M. S. Edge state in graphene ribbons: nanometer size effect and edge shape dependence. Phys. Rev. B 54, 017954 (1996).
Son, Y-W., Cohen, M. L. & Louie, S. G. Energy gaps in graphene nanoribbons. Phys. Rev. Lett. 97, 216803 (2006).
Prezzi, D., Varsano, D., Ruini, A. & Molinari, E. Quantum dot states and optical excitations of edge-modulated graphene nanoribbons. Phys. Rev. B 84, 041401(R) (2011).
Sevinçli, H., Topsakal, M. & Ciraci, S. Superlattice structures of graphene-based armchair nanoribbons. Phys. Rev. B 78, 245402 (2008).
Xu, Z., Zheng, Q-S. & Chen, G. Elementary building blocks of graphene-nanoribbon-based electronic devices. Appl. Phys. Lett. 90, 223115 (2007).
Franc, G. & Gourdon, A. Covalent networks through on-surface chemistry in ultra-high vacuum: state-of-the-art and recent developments. Phys. Chem. Chem. Phys. 13, 14283–14292 (2011).
Ijäs, M. et al. Electronic states in finite graphene nanoribbons: effect of charging and defects. Phys. Rev. B 88, 075429 (2013).
Hod, O., Peralta, J. & Scuseria, G. Edge effects in finite elongated graphene nanoribbons. Phys. Rev. B 76, 233401 (2007).
Cai, J. et al. Graphene nanoribbon heterojunctions. Nature Nanotech. 9, 896–900 (2014).
Horcas, I. et al. WSXM: A software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 78, 013705 (2007).
Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).
Cohen, M. L., Schlüter, M., Chelikowsky, J. R. & Louie, S. G. Self-consistent pseudopotential method for localized configurations: Molecules. Phys. Rev. B 12, 5575–5579 (1975).
Troullier, N. & Martins, J. L. Efficient pseudopotentials for plane-wave calculations. Phys. Rev. B 43, 1993–2006 (1991).
This research was supported by the Office of Naval Research BRC Program (molecular synthesis and characterization), by the Director, Office of Science, Office of Basic Energy Sciences of the US Department of Energy under the Nanomachine Program at the Lawrence Berkeley National Laboratory (contract no. DE-AC02-05CH11231, STM instrumentation development, STM operation and simulations) and by National Science Foundation (NSF) awards (DMR-1206512, image analysis; DMR10-1006184, basic theory and formalism). Computational resources were provided by the NSF through XSEDE resources at the Texas Advanced Computing Center (TACC) at the University of Texas at Austin and Lawrence Berkeley National Laboratory's High Performance Computing Services. S.G.L. acknowledges the support of a Simons Foundation Fellowship in Theoretical Physics. D.H. acknowledges a research fellowship from the German Research Foundation (DFG; grant no. Ha 6946/1-1).
The authors declare no competing financial interests.
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Chen, YC., Cao, T., Chen, C. et al. Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions. Nature Nanotech 10, 156–160 (2015). https://doi.org/10.1038/nnano.2014.307
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