TEM study of superconducting polycristalline diamond

Heavily Boron-doped MPCVD-grown (Microwave Plasma Chemical Vapour Deposition) polycrystalline diamond layers were observed to have a superconducting character depending exclusively on the growth time, i.e. grown under identical experimental conditions. To elucidate such behavior, morphology aspects are investigated using Transmission Electron Microscopy (TEM). Diffraction contrasts and High Angle Annular Dark Field (HAADF) observations show that grains are thicker and boron enrichment occur at grain boundary in the superconducting samples. Interfacial effects are the main difference between the two samples, in the nonsuperconducting ones descohesion effect is observed. In both samples boron concentration is nearly constant except in isolated grains and twins, where their crystal orientation probably influences boron incorporation during growth. In summary, as grain configuration changes along the growth, a threshold thickness should be over passed to allow an optimum transport between the diamond grains.4 page