化學氣相沉積石墨烯之缺陷調控：製程控制與摻雜效應

Abstract

Defects in the CVD-derived graphene have been demonstrated to have great impacts on its optical and electrical properties. In this study, we engineered the defects in graphene by the process control in the thermal chemical vapor deposition (CVD) and by doping in both substitutional and chemical approaches. First of all, a series of graphene with different degrees of structure disorder were produced by changing the growth conditions in the CVD process. Two stages, nanocrystallization and amorphization, of amorphization trajectory for CVD-graphene were introduced and the corresponding evolution of Raman line position, line width and intensity were monitored. At the stage of nanocrystallization, grain boundaries increase and both G and 2D peaks show blue-shift. 2D peak has much larger variation than G peak, which implies the change in the paths of phonon scattering due to the variation of the electronic structure. The high I2D/IG ratio indicates the hexagonal structure of graphene is still maintained. At the stage of amorphization, the broadened D and G peaks, dramatic drop of 2D intensity, and the great upshift in G peak position indicate the localized collapse of graphitized structure due to the incorporation of amorphous phases. Secondly, the conducting polymer, PANI, was physically doped on the graphene by a self-assemble method. The PANI-modified graphene shows a dramatic decrease in its sheet resistance from ~2500 Ω/sq to ~550 Ω/sq, while maintaining its transmittance at 96%. The work function of PANI-modified graphene is comparable to that of graphite. The recovery of the sheet resistance was also observed in defected graphene. The PANI-modified process is simple, green, and scalable. It is highly appropriate for the transparent conductivity film (TCF) application. Thirdly, band gap opening and engineering is one of the high priority goal in the development of graphene electronics. To create a band gap, we co-doped B and N in large-scaled graphene films (BNG) by low-pressure chemical vapor deposition. TEM images and EELS results indicate that the segregated BN domains appeared when the concentration was over 8%. Below this concentration, BN will disperse uniformly in the graphene lattice. Based on the synchrotron-radiation XAS-XES measurements, a significant band gap (600 meV) was observed in low-BN-doped graphene which is attributed to the opening of band gap of graphene. The results of field effect transistor measurements also confirmed that the semiconductor behavior in BN-doped graphene.