Article

Raman Scattering from High-Frequency Phonons in Supported <i>n</i>-Graphene Layer Films

A. GuptaDepartment of Physics, Electrical Engineering, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802G. ChenDepartment of Physics, Electrical Engineering, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802P. JoshiDepartment of Physics, Electrical Engineering, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802S. TadigadapaDepartment of Physics, Electrical Engineering, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802EklundDepartment of Physics, Electrical Engineering, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802

2006en

ABI

Abstract

Results of room-temperature Raman scattering studies of ultrathin graphitic films supported on Si (100)/SiO2 substrates are reported. The results are significantly different from those known for graphite. Spectra were collected using 514.5 nm radiation on films containing from n = 1 to 20 graphene layers, as determined by atomic force microscopy. Both the first- and second-order Raman spectra show unique signatures of the number of layers in the film. The nGL film analogue of the Raman G-band in graphite exhibits a Lorentzian line shape whose center frequency shifts linearly relative to graphite as approximately 1/n (for n = 1 omegaG approximately 1587 cm-1). Three weak bands, identified with disorder-induced first-order scattering, are observed at approximately 1350, 1450, and 1500 cm-1. The approximately 1500 cm-1 band is weak but relatively sharp and exhibits an interesting n-dependence. In general, the intensity of these D-bands decreases dramatically with increasing n. Three second-order bands are also observed (approximately 2450, approximately 2700, and 3248 cm-1). They are analogues to those observed in graphite. However, the approximately 2700 cm-1 band exhibits an interesting and dramatic change of shape with n. Interestingly, for n < 5 this second-order band is more intense than the G-band.

Identifiers

DOI: 10.1021/nl061420a

Citations and references

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