Role of surfaces and interfaces on the Raman spectra of boron carbide

The influence of surfaces and interfaces on the Raman spectra of boron carbide crystal is studied employing first-principles calculations. Surfaces based on {10-11} planes and {01-12} planes are considered. The average energy of the {01-12} surfaces (3.26 J/m2) agrees with the experimentally reported surface energy (3.21 J/m2). Two peaks are observed at ∼270 cm−1 and ∼320 cm−1 in the calculated Raman spectra for the supercells built on the {01-12} planes. This result suggests that the experimentally observed Raman peaks at these two frequencies are more likely to originate from the surface. Two Raman peaks experimentally observed at ∼1330 cm−1 and ∼1520 cm−1 in the amorphized samples were reproduced in the Raman spectra calculated for the supercells built on the {10-11} planes. Therefore, the experimentally observed new Raman activity at ∼1330 cm−1 and ∼1520 cm−1 is more likely to originate from the interface between the amorphous and crystalline regions.