Black, Andrés and Jimenez, Fernando and Bernardo Gavito, Ramon and Casado, Santiago and Granados, Daniel and Vázquez De Parga, Amadeo L. (2016) Growth and characterization of 7,7,8,8-tetracyano-quinodimethane crystals on chemical vapor deposition graphene. Journal of Crystal Growth, 453. pp. 1-6. ISSN 0022-0248
TCNQ_Growth_JCG_Revised.pdf - Accepted Version
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Abstract
Chemical functionalization of graphene could pave the way for favorably modifying its already remarkable properties. Organic molecules have been utilized to this end as a way to alter graphene’s structural, chemical, electrical, optical and even magnetic properties. One such promising organic molecule is 7,7,8,8-tetracyano-quinodimethane (TCNQ), a strong electron acceptor which has been shown to be an effective p-dopant of graphene. This study explores the thermal evaporation of TCNQ onto graphene transferred onto SiO2/Si substrates. Using two different home-made thermal evaporators, a wide range of TCNQ growth regimes are explored, from thin films to crystals . The resulting graphene/TCNQ structure is characterized via optical microscopy, Raman spectroscopy and atomic force microscopy (AFM). TCNQ films are found to be comprised of TCNQ and the oxidized product of TCNQ, α,α-dicyano-p-toluoylcyanide (DCTC), which confirms the electron charge transfer from graphene to the TCNQ films. AFM measurements of these films show that after forming a rather smooth layer covering the graphene surface, small clusters start to form. For higher TCNQ coverage, the clusters agglomerate, becoming quite large in size and forming ripples or wrinkles across the surface.