2D materials
1. Two-dimensional materials (structures & growth)
Chemical vapor deposition is the major way to produce large-scale high-quality graphene and h-BN with controllable thickness. We have been working on 2D materials (graphene, h-BN) on various metal subtrates since 2007. We have proposed a periodically-modulated electronic and geometric structure of graphene covering the metal substrates resulting from the interfacial interaction. The curved graphene overlayer can be used as a versatile template to prepare metal nanoparticles. Our results represent some promising steps towards fabrication of high-quality large-scale graphene and h-BN. The work was done in close collaboration with Dr. Marie-Laure Bocquet (ENS), Prof. Joost Wintterlin (LMU), Prof. Sebastian Günther (TUM), Dr. Peter Sutter, Dr. Eli Sutter (BNL), Dr. Nicolás Lorente (CIN2), Prof. Richard Berndt (Kiel), Prof. Thomas Greber (Zürich).
see Nano Lett. 13, 276 (2013); Nano Lett. 11, 1895 (2011); JPCL 2, 2341 (2011); PRL 105, 236101 (2010); PRL 104, 136102 (2010); PRL 101, 099703 (2008); Surf. Sci. 605, 1676 (2011); PCCP 10, 3530 (2008); review: Prog. Surf. Sci. 85, 435 (2010) etc.
2. Two-dimensional materials (functionalization, electronics, photonics)
The unusual properties of graphene are very sensitive to defects and impurities. We have studied point defects, impurities and grain boundaries in graphene and their effects on the chemical reactivity and electronic properties of graphene. We find that grain boundaries can enhance the chemical reactivity of graphene, which induces degradation of graphene-based electronic devices. Moreover, we proposed new strategies to heal the point defects, introduce nitrogen dopant and remove oxygen impurities. The effect of external environment on the carriers mobility of graphene has also been investigated.
Much effort
In addition to defects and impurities, we have also investigated chemical functionalization of graphene using large aromatic molecules. Thanks to a unique property of graphene on transition metal surfaces, we discovered a reversible, non-destructive functionalization strategy through a non-classic cycloaddition between a range of phthalocyanines (Fe, Co, Ni, Cu, and H2Pc) and metal supported graphene. This nexus brings together the rich chemistry of phthalocyanine and porphyrin molecules and the high charge mobility in graphene, and has promising applications in nanosensors and electrochemical devices.
has been made to study transition metal dichalcogenides (TMDCs), such as MoS2, which has a direct band gap, important for electronic and optical applications. We have shown that the band structure and optical spectrum of MoS2 vary as a function of tensile strain, and the direct band gap of monolayer MoS2 becomes indirect under tensile strain around 1%. A systematic study of photoresponse of other two-dimensional materials is undergoing. We are working closely with experimental groups at Vanderbilt Univeristy, including Prof. Kirill. I. Bolotin (Physics, Vanderbilt), Prof. Yaqiong Xu (EECS/Physics, Vanderbilt), Prof. Daniel M. Fleetwood (EECS, Vanderbilt), and Prof. Ronald D. Schrimpf (EECS, Vanderbilt).
See Scientific Report 4, 6608 (2014); Nano Lett. 13, 3626 (2013); Nature Commun. 3, 734 (2012); J. Mater. Chem. A 1, 14927 (2013); Carbon, 49, 3983 (2011); PRB 86, 165438 (2012); PRB 83, 245403 (2011); APL 101, 121601 (2012); review: MRS bulletin (2012).
