Second-Order Overtone and Combination Raman Modes of Graphene Layers in the Range of 1690−2150 cm−1

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• 作者：Chunxiao Cong ; Ting Yu ; Riichiro Saito ; Gene F. Dresselhaus ; Mildred S. Dresselhaus
• 刊名：ACS Nano
• 出版年：2011
• 出版时间：March 22, 2011
• 年：2011
• 卷：5
• 期：3
• 页码：1600-1605
• 全文大小：859K
• 年卷期：0
• ISSN：1936-086X

文摘

Though graphene has been intensively studied by Raman spectroscopy, in this letter, we report a study of the second-order overtone and combination Raman modes in a mostly unexplored frequency range of 1690−2150 cm⁻¹ in nonsuspended commensurate (AB-stacked), incommensurate (folded) and suspended graphene layers. On the basis of the double resonance theory, four dominant modes in this range have been assigned to (i) the second order out-of-plane transverse mode (2oTO or M band), (ii) the combinational modes of in-plane transverse acoustic mode and longitudinal optical mode (iTA+LO), (iii) in-plane transverse optical mode and longitudinal acoustic mode (iTO+LA), and (iv) longitudinal optical mode and longitudinal acoustic mode (LO+LA). Differing from AB-stacked bilayer graphene or few layer graphene, single layer graphene shows the disappearance of the M band. Systematic analysis reveals that interlayer interaction is essential for the presence (or absence) of the M band, whereas the substrate has no effect on the presence (or absence) of the M band. Dispersive behaviors of these “new” Raman modes in graphene have been probed by laser excitation energy-dependent Raman spectroscopy. It is found that the appearance of the M band strictly depends on the AB stacking, which could be used as a fingerprint for AB-stacked bilayer graphene. This work expands upon the unique and powerful abilities of Raman spectroscopy to study graphene and provides another effective way to probe phonon dispersion, electron−phonon coupling, and to exploit the electronic band structure of graphene layers.