Raman scattering from high frequency phonons in supported n-graphene layer films

TL;DR

This study investigates the Raman scattering characteristics of ultrathin graphene films on Si/SiO2 substrates, revealing layer-dependent spectral signatures and differences from bulk graphite, with implications for layer identification.

Contribution

It provides the first detailed Raman spectral analysis of supported graphene layers from 1 to 20 layers, highlighting unique layer-dependent features and differences from graphite.

Findings

G-band frequency shifts linearly with 1/n for n=1 to 20

Weak disorder bands decrease with increasing layer number

Second order bands show significant shape changes with layer number

Abstract

Results of room temperature Raman scattering studies of ultrathin graphitic films supported on Si (111)/SiO2 substrates are reported. The results are significantly different from those known for graphite. Spectra were collected using 514 nm radiation on films containing from n=1 to 20 graphene layers, as determined by atomic force microscopy. Both the 1st and 2nd order Raman spectra show unique signatures of the number of layers in the film. The nGL film analog of the Raman G-band in graphite exhibits a Lorentzian lineshape whose center frequency shifts linearly relative to graphite as ~1/n (for n=1 G-band frequency ~1588 cm-1). Three weak bands, identified with disorder-induced 1st order scattering, are observed at ~ 1350, 1450 and 1500 cm-1. The 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 2nd order bands are also observed (~2450, ~2700 and 3248 cm-1). They are analogs to those observed in graphite. However, the ~2700 cm-1 band exhibits an interesting and dramatic change of shape with n. Interestingly, for n<5 this 2nd order band is more intense than the G-band.