Room temperature PL characterization of micro and nanocrystalline diamond grown by MPCVD from Ar/H2/CH4 mixtures

A photoluminescence (PL) study at room temperature was accomplished as a complement to well-established structural and morphological characterization techniques such as μ-Raman, FTIR, XRD, XPS or SEM. Considering the wide electronic band gap of pure diamond (5.45 eV), the near ultraviolet excitation (325 nm) from an HeCd laser source was selected. The observed nanocrystalline diamond (NCD) and microcrystalline CVD diamond (MCD) samples were obtained by microwave plasma (MPCVD) from hydrogen poor Ar/H2/CH4 mixtures. The PL spectrum of both NCD and MCD samples is dominated by the 1.681 eV emission with significant intensity and energy variations. The well-known 1.681 eV band related to the Si-vacancy colour centre is much more pronounced in MCD. In addition, for NCD, the band shifts to higher energies with thickness, suggesting two mechanisms for the silicon incorporation: co-deposition from the plasma and diffusion from the substrate. The samples were further characterized by μ-Raman spectroscopy, X-ray diffraction and scanning electron microscopy, structurally and morphologically.