Casimir effect demonstrated by Raman spectroscopy on trilayer graphene intercalated into stiff layered structures of surfactant

Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by ∼40 cm−1, which result from the action of interplanar forces, of Casimir nature. The value of ∼40 cm−1 is close to the energy value associated with E2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light.