Polarized Raman spectroscopy with differing angles of laser incidence on single-layer graphene

Gaeun Heo,Yong Seung Kim,Maeng-Je Seong,Seung-Hyun Chun

doi:10.1186/s11671-015-0743-4

Gaeun Heo, Yong Seung Kim + Show 2 more

Open Access

https://doi.org/10.1186/s11671-015-0743-4

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Abstract

Chemical vapor deposition (CVD)-grown single-layer graphene samples, transferred onto a transmission electron microscope (TEM) grid and onto a quartz plate, were studied using polarized Raman spectroscopy with differing angles of laser incidence (θ). Two different polarization configurations are used. In an in-plane configuration, the polarization direction of both incident and scattered light is parallel to the graphene plane. In an out-of-plane configuration, the angle between the polarization vector and the graphene plane is the same as the angle of laser incidence (θ). The normalized Raman intensity of the G-band measured in the out-of-plane configuration, with respect to that in the in-plane configuration, was analyzed as a function of θ. The normalized Raman intensity showed approximately cos2θ-dependence up to θ = 70°, which can be explained by the fact that only the electric field component of the incident and the scattered photon in the out-of-plane configuration projected onto the graphene plane can contribute to the Raman scattering process because of the perfect confinement of the electrons to the graphene plane.

Highlights

Graphene, an almost perfect two-dimensional crystal, has been intensively investigated for the last decade, since its discovery in 2004 [1,2], due to its remarkable physical properties such as high thermal conductivity, high mobility, room-temperature quantum Hall effect, outstanding flexibility, and tunable bandgap [3-11].Raman spectroscopy has played an important role in studying graphene [12,13]
The normalized Raman intensity showed approximately cos2θ-dependence up to θ = 70°, which can be explained by the fact that only the electric field component of the incident and the scattered photon in the out-of-plane configuration projected onto the graphene plane can contribute to the Raman scattering process because of the perfect confinement of the electrons to the graphene plane
For a carbon nanotube (CNT), which is a quasione-dimensional crystal, the Raman intensities of CNT vibrational modes are maximum when the polarization directions of both the incident and the scattered light are parallel to the CNT direction whereas the Raman scattering is forbidden when the polarization directions of both the incident and the scattered light are perpendicular to the CNT direction [15]

Summary

Introduction

An almost perfect two-dimensional crystal, has been intensively investigated for the last decade, since its discovery in 2004 [1,2], due to its remarkable physical properties such as high thermal conductivity, high mobility, room-temperature quantum Hall effect, outstanding flexibility, and tunable bandgap [3-11].Raman spectroscopy has played an important role in studying graphene [12,13]. A typical Raman spectrum of graphene consists of the D-band near 1,340 cm−1, the G-band near 1,585 cm−1, and the 2D-band at approximately 2,675 cm−1. By analyzing both the normalized Raman intensity of the 2D-band with respect to that of the G-band and the line-shape of the 2D-band, the number of graphene layers can be accurately determined [13]. Polarizations of the incident laser and the scattered light are important in the Raman scattering on low-dimensional crystals. The Raman intensities of the G-band and the radial breathing mode (RBM) of the CNT exhibited approximately cos2α-dependence in which α is the angle between the CNT axis and the polarization direction of the incident light [15]. Similar polarization anisotropies in polarized Raman scattering from CNTs were reported [16-19]

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