Related Experiment Video
Updated: May 9, 2026

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems
Published on: April 28, 2016
Observation of low energy Raman modes in twisted bilayer graphene
Rui He1, Ting-Fung Chung, Conor Delaney
1Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614, United States. rui.he@uni.edu
Abstract:
Two new Raman modes below 100 cm(-1) are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The ~94 cm(-1) mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO' mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at ~52 cm(-1), not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.
Related Concept Videos
Raman Spectroscopy: Overview
However, a small fraction of the scattered light exhibits a frequency shift due to the exchange of energy between the incident photons and the...
Raman Spectroscopy Instrumentation: Overview
The monochromatic laser source, typically using visible or near-infrared radiation, generates a highly focused beam of light. This light interacts with the molecules of the sample, scattering some of the light. Liquid and gaseous samples are usually tested in ordinary glass capillaries, while solids can be analyzed as powders packed in capillaries or as potassium...
IR Spectroscopy: Molecular Vibration Overview
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Unsymmetric Bending
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
According to Hooke's law, the vibrational frequency is directly proportional to the...

