Noncovalent chemical modification of graphene

Date

2012-08-31

Authors

Bobak, Julia

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Abstract

Low dimensional carbon allotropes presently provide an unparalleled platform to explore novel electronic properties, and with tremendous progress may one day supplant entrenched materials within the semiconductor industry. In order for graphene to continue on its extraordinary scientific and technological trajectories, many hurdles must be overcome such as reliable bandgap engineering, advances in processability, removal or mitigation of defects and so on. Noncovalent chemical modification of graphene offers a pathway to address many of these concerns and furthermore provides an opportunity to graft new functionality onto this unique material. In this work, the effects of noncovalent modification of graphene by simple polyaromatic molecules – rubrene and tetracene – are investigated. By exploiting π π interactions between the two highly conjugated systems, a simple approach to functionalize graphene devices has been developed. Optical and electron-beam lithography are used to fabricate graphene field effect transistors, which can be subsequently modified either in their entirety or in a site specific manner. In order to better understand the resulting graphene/rubrene structure, a suite of analytical tools has been employed. Raman spectroscopy and microscopy confirm the presence of the rubrene and spatially correlate observed electronic changes with surface modification while polarized Raman spectroscopy is used to investigate any long range order of rubrene on the graphene surface. Photoluminescence measurements show that rubrene emission is not quenched, and spectral analysis offers insight into rubrene film characteristics. Atomic force microscopy provides detailed information as to film thickness, and suggests that rubrene film morphology is largely disordered. Due to the simplicity of this functionalization procedure, a rubrene-based motif could be widely expanded allowing researchers to explore grafting new chemical moieties onto graphene and enabling new device opportunities. Transport measurements reveal the effects of rubrene on the graphene electronic properties. Modified devices display increased conductivity, a substantial shift in Dirac point and a moderate decrease in carrier mobility, all of which are consistent with an electronic doping mechanism whereby the rubrene acts as a hole dopant. Preliminary photoresponse measurements suggest that this graphene-molecular hybrid could act as a potential photodetector.

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Keywords

Graphene, Materials science

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