Morphology and electronic structure in nitrogen-doped ultrananocrystalline diamond

Ultrananocrystalline diamond (UNCD) thin films consist of 2-5 nm grains of pure sp(3)-bonded carbon and similar to0.5-nm-wide grain boundaries with a disordered mixture of sp(2)- and sp(3)-bonded carbon. UNCD exhibits many interesting materials properties that are a direct consequence of its nanoscale morphology. In this work, we report the changes in morphology induced in UNCD by the addition of nitrogen gas to the Ar/CH4 microwave plasma, as studied using high-resolution transmission electron microscopy and nanoprobe-based electron energy-loss spectroscopy. Both the grain size and grain-boundary widths increase with the addition of N-2, but the overall bonding structure in both regions remains mostly unchanged. These results are used to explain the variation of materials properties of nitrogen-incorporated UNCD films. (C) 2002 American Institute of Physics.