Structure of an Amorphous Boron Carbide Film: An Experimental and Computational Approach

An amorphous boron carbide ceramic is prepared via hot wall chemical vapor deposition at 1000 °C using a BCl3/CH4/H2 mixture. Its elemental composition is assessed by electron probe microanalysis (EPMA) and its structure studied by Raman spectroscopy, transmission electron microscopy (TEM), both X-ray diffraction (XRD) and neutron diffraction, 11B magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray absorption spectroscopy (XAS), and ab initio modeling. The atomic structure factor and pair distribution function derived from neutron diffraction data are compared to those deduced from an atomistic model obtained by a liquid quench ab initio molecular dynamics simulation. The good agreement between experimental data and simulation shows that the as-prepared material is essentially made of a random arrangement of icosahedra (B12, B11C, and B10C2) embedded in an amorphous matrix rich in trigonal (BC3 or BC2B) and tetrahedral (CB4) sites. The existence of trigonal boron environments is clearly confi...