Doping / Functionalization and Characterization of Mono and Few layer Graphene

Abstract

Graphene has attracted much of interest of the researchers since it was successfully isolated for the first time due to its unique mechanical, electrical, optical and thermal properties. In current work, we have focused on doping and characterization of mono and few-layer graphene (MFLG) with methyl orange (MO) and Sudan IV. The study of thickness dependent doping effect is carried out by modifying MFLG sheets with MO molecules. Importantly, Surface-enhanced Raman Scattering (SERS) identification of trace quantity Sudan IV molecules is performed by using graphene as SERS substrate for the first time. The Sudan Red dyes can cause cancer in human body if taken in large quantity and are strictly forbidden by the “International Agency for Research on Cancer”. This method can be used as economical and convenient method for detection of Sudan IV molecules and other such strictly forbidden colorants for the prevention of their usage in Food Colorants, Cosmetics and Disinfectants. The numbers of graphene layers are identified by optical microscopy, AFM and Raman Spectroscopy on oxidized silicon substrate. The optical microscopic identification based on color contrast between and oxidized silicon surface give a rough idea about the number of layers in graphene sheets but AFM measurement by step height of scanning line gave better confirmation. However, Raman Spectroscopy gives true identification of graphene layers. The surface morphology of FLG was analyzed by AFM, SEM and STM. The doping effect and induced band gap is characterized by Raman spectroscopy and UV/Vis Spectroscopy respectively. The Raman spectroscopy analysis of doped graphene shows that doping effect is thickness dependent and it is strong in mono layer graphene but decreases as the number of graphene layers increases. The UV/Vis spectroscopy analysis shows a 0.40eV increase in band gap of MO doped graphene. Furthermore, doping effect and increase in band gap are concentration dependent as well.