Towards the standardization of fullerene nanofibers using Raman spectroscopy

The Raman spectra of fullerene nanofibers were acquired with different incident laser power densities in order to determine their influence in the peak position of the Ag(2) vibrational mode of the fullerene molecule. A procedure to measure the diameter of the laser beam and the power density under the objective of a Raman microscope is proposed. The uncertainties of the measurement and the spectrometer calibration are also presented

Disentangling contributions of point and line defects in the Raman spectra of graphene-related materials

International audienc

Estudo teórico e experimental de espectros infravermelho de ésteres de ácido graxo presentes na composição do biodiesel de soja

In this work, theoretical and experimental infrared spectra of fatty acid methyl esters (FAME) contained in soybean biodiesel were analyzed seeking the assignments of the relevant vibrational modes to characterize crude soybean oil and soybean biodiesel. The results showed the usefulness of infrared spectra for monitoring saturated and unsaturated compounds as well as impurities (mainly glycerol) in raw samples. This is the first step toward proposing an efficient molecular spectroscopy routine to certify biodiesel fuel

Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS₂

We report a novel mechanical response of few-layer graphene, h-BN, and MoS₂ to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS₂), but it is absent in single-layer graphene and in few-layer mica and Bi₂Se₃. We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed