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Band Gap Opening of Graphene by Noncovalent π-π Interaction with Porphyrins  [PDF]
Arramel  , Andres Castellanos-Gomez, Bart Jan van Wees
Graphene (Graphene) , 2013, DOI: 10.4236/graphene.2013.23015
Abstract:

Graphene has been recognized as a promising 2D material with many new properties. However, pristine graphene is gapless which hinders its direct application towards graphene-based semiconducting devices. Recently, various ways have been proposed to overcome this problem. In this study, we report a robust method to open a gap in graphene via noncovalent functionalization with porphyrin molecules. Two type of porphyrins, namely, iron protoporphyrin (FePP) and zinc protoporphryin (ZnPP) were independently physisorbed on graphene grown on nickel by chemical vapour deposition (CVD) resulting in a bandgap opening in graphene. Using a statistical analysis of scanning tunneling spectroscopy (STS) measurements, we demonstrated that the magnitude of the band gap depends on the type of deposited porphyrin molecule.The π-π stacking of FePP on graphene yielded a considerably larger band gap value (0.45 eV) than physisorbed ZnPP (0.23 eV). We proposed that the origin of different band gap value is governed due to the metallic character of the respective porphyrin.

Electronic inhomogeneities in graphene: the role of the substrate interaction and chemical doping
A. Castellanos-Gomez,Arramel,M. Wojtaszek,R.H.M. Smit
Boletin del Grupo Espa?ol del Carbon , 2012,
Abstract: We probe the local inhomogeneities of the electronicproperties of graphene at the nanoscale usingscanning probe microscopy techniques. First, wefocus on the study of the electronic inhomogeneitiescaused by the graphene-substrate interaction ingraphene samples exfoliated on silicon oxide. Wefind that charged impurities, present in the graphenesubstrateinterface, perturb the carrier densitysignificantly and alter the electronic properties ofgraphene. This finding helps to understand theobserved device-to-device variation typically observedin graphene-based electronic devices. Second, weprobe the effect of chemical modification in theelectronic properties of graphene, grown by chemicalvapour deposition on nickel. We find that both thechemisorption of hydrogen and the physisorption ofporphyrin molecules strongly depress theconductance at low bias indicating the opening of abandgap in graphene, paving the way towards thechemical engineering of the electronic properties ofgraphene.
Reversible hydrogenation and band gap opening of graphene and graphite surfaces probed by scanning tunneling spectroscopy
Andres Castellanos-Gomez,Magdalena Wojtaszek,Arramel,Nikolaos Tombros,Bart J. van Wees
Physics , 2012, DOI: 10.1002/smll.201101908
Abstract: The effect of hydrogenation on the topography and the electronic properties of graphene and graphite surfaces are studied by scanning tunneling microscopy and spectroscopy. The surfaces are chemically modified using Ar/H2 plasma. Analyzing thousands of scanning tunneling spectroscopy measurements we determine that the hydrogen chemisorption on the surface of graphite/graphene opens on average an energy band gap of 0.4 eV around the Fermi level. We find that although the plasma treatment modifies the surface topography in a non-reversible way, the change in the electronic properties can be reversed by a moderate thermal annealing and the samples can be hydrogenated again yielding a similar, but slightly reduced, semiconducting behavior after the second hydrogenation.
Electronic inhomogeneities in graphene: the role of the substrate interaction and chemical doping
A. Castellanos-Gomez,Arramel,M. Wojtaszek,R. H. M. Smit,N. Tombros,N. Agra?t,B. J. van Wees,G. Rubio-Bollinger
Physics , 2012,
Abstract: We probe the local inhomogeneities of the electronic properties of graphene at the nanoscale using scanning probe microscopy techniques. First, we focus on the study of the electronic inhomogeneities caused by the graphene-substrate interaction in graphene samples exfoliated on silicon oxide. We find that charged impurities, present in the graphene-substrate interface, perturb the carrier density significantly and alter the electronic properties of graphene. This finding helps to understand the observed device-to-device variation typically observed in graphene-based electronic devices. Second, we probe the effect of chemical modification in the electronic properties of graphene, grown by chemical vapour deposition on nickel. We find that both the chemisorption of hydrogen and the physisorption of porphyrin molecules strongly depress the conductance at low bias indicating the opening of a bandgap in graphene, paving the way towards the chemical engineering of the electronic properties of graphene.
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