서강대학교

초록/요약 도움말

Mono- and few-layer graphene which have distinctive physical properties with high carrier mobility, have attracted a great deal of interest for applications in semiconductor devices. Since Novoselov and Geim successfully established the mechanical exfoliation method for producing single and multilayer graphene in 2004, the interest in graphene-based technologies has been growing. Especially, recent studies revealed that Bernal (ABA-) or rhombohedral (ABC-) stacked multilayer graphene has a wide range of application owing to their tunable electronic properties. For instance, ABA-stacked tri-layer graphene is semi-metallic with a tunable band overlap, and ABC-stacked tri-layer graphene shows a tunable band gap under a perpendicular electric field. These promising properties, therefore, suggests that both the number of layers and stacking orders of few-layer graphene have to be characterized. Further studies have demonstrated that the number of layers as well as the stacking order of graphene can be distinguished by using Raman spectroscopy. Moreover, it has been shown that not only the number of layers has enormous impact on the peak shape of some Raman modes such as the 2D mode and N mode, but also the excitation energy has some significant influence. Consequently, the correlation between the Raman spectra of multilayer graphene and the excitation energy is of interest. We examined the number of layers in graphene using micro-Raman spectroscopy and atomic force microscopy (AFM) to understand the variations in the Raman spectrum. Various Raman features of few-layer graphene of thickness from 1 to 5 layers with different stacking orders were observed. The investigated Raman signatures of graphene are the G, G*, 2D and combination Raman modes in the range from 1450 to 2250 cm−1. We repeated the measurements using 5 different excitation sources with energies of 1.96, 2.33, 2.41, 2.54 and 2.81 eV.