Paper GR+EM-TuM11
Stable Chemical Doping of Graphene: Transport, Raman Spectroscopy, SEM, and Transmittance Studies

Tuesday, November 1, 2011, 11:20 am, Room 208

Since becoming experimentally available by mechanical exfoliation, graphene has been used in various devices such as field effect transistors (FETs), Schottky based solar cells and sensing applications. Although graphene based devices with modest characteristics have been reported, in some of the device geometries a lower graphene sheet resistance with different Fermi level values is still desired. To achieve these ends, graphene’s physical properties have been adjusted by n- or p- chemical doping using AuCl₃, Br₂, N₂, and organic solutions. However, these techniques have several drawbacks which prevent their use in devices, namely: environmental instabilities, aging effects and a reduction in optical transparency. Here, we describe our use of a hydrophobic organic complex dopant with strong electronegativity, tight bonding, environmental stability and high optical transmittance which is spin cast onto CVD-prepared graphene films. We observe a typical 75% reduction in sheet resistance upon chemical modification of the graphene. Resistance vs. temperature / magnetic field and Hall measurements imply that the modified graphene sheets are doped, and time-dependent resistance measurements show excellent stability. Using a Horiba Micro Raman instrument we confirm the doping of graphene sheets from the shifts in G and 2D peak positions and intensity ratios. We show transmittance and SEM characteristics of the graphene sheets before and after doping. The presented results may serve as a guide for modification of graphene’s properties as desired for various applications.