Electrochemical Modification of Large Area Graphene and Characterization by Vibrational Spectroscopy

Functionalized and nonfunctionalized graphene 2D sheets are technologically highly interesting for many electronic, optoelectronic, and sensing applications. Thermally stable 2D few micrometer sized graphene flakes show outstanding electrical charge carrier mobilities of up to 44,000 cm2 Vs and optical properties transmittance of 0.977 in a wide spectral range . However, micrometer sized graphene flakes are often too small and large areas, and homogeneous graphene in the square centimeter range or even higher is desired for many potential applications. Large area graphene sheets can be derived by defined preparation steps from chemical vapor deposition CVD grown graphene on metallic substrates and transferred to relevant device surfaces. In this work, we use large area graphene sheets CVD grown on Cu. Covalent functionalization of the graphene can be performed by various ways as, for example, through free radical addition, CH insertion, cycloaddition reactions, and electrochemical modifications. In this chapter, electrochemical functionalization of large area graphene is introduced as an effective method for defined graphene functionalization. Optical vibrational spectroscopy methods can offer noncontact and destruction free characterizations of graphene sheets before and after modification. Raman spectroscopy is the most used vibrational spectroscopy for studying the properties of graphene sheets. However, the sensitivity is typically too low to analyze directly the thin organic functionalization when not using resonant or enhancement conditions. Infrared IR spectroscopy can be used to analyze directly the functionalization. Beside infrared spectroscopy, for example, also nonlinear spectroscopies such as SFG and SHG can be used to investigate the modified graphene. For our characterizations, we present the cooperative use of Raman spectroscopy sensitively probing the properties and defects of the graphene sheet itself and IR spectroscopic methods such as IR ellipsometry, IR microscopy, and atomic force microscopy based infrared spectroscopy AFM IR for sensitive analysis of the organic modification. To summarize, the focus of this chapter is threefold i the CVD growth process and the subsequent transfer process are presented ii followed by the electrochemical functionalization with para N maleimido phenyl residues and modification by 4 nitrophenyl mercaptan, a S H group containing species, and iii infrared Raman spectroscopic characterization of the respective surfaces. The sensing ability of MP functionalized graphene sheets as well as aggregation of peptide nucleic acid PNA molecules on functionalized graphene surfaces is discusse