Figure 2

a) Raman scattering spectra of treated (black) and untreated (red) asphaltene sample obtained on a Raman microscope: a) 1300 cm⁻¹, indicating the presence of nanodiamonds; b) 1600 cm⁻¹, indicating the presence of graphitic planes. b) Optical microscopy image and corresponding micro-Raman images of the remaining solid residue (treated asphaltene) observed at 1300 cm⁻¹ (green) and 1600 cm⁻¹ (purple), showing the distributions of naodiamonds and graphite, respectively. Respective micro-Raman images overlap on the optical microscopy image. It is noted that the size of nanodiamonds aggregate is smaller than that of a CCD pixel (1.2 μm) for Raman imaging.