Stacked AA graphite has been synthesized using a high-density dc plasma in hydrogen-methane mixtures. Graphene layers have been grown epitaxially with 2-1 registration between the AA graphitic edges and the (111) surface of diamond. In addition, a new graphite crystal structure containing AA(') graphene layers, where alternate planes are translated by half the hexagon width, is formed by 1-1 registry. The resulting interplanar distances of the AA graphite at the interface range from 2.20 A for the 1-1 registration to 4.40 A for the 2-1 registration and have been measured directly by high-resolution transmission electron microscopy (TEM). The appearance of the characteristic d-spacings, 3.55, 2.15, 1.80, 1.75 (not fully resolved), and 1.25 A in the selective area diffraction patterns from the TEM, are consistent with reflections from the (001), (100), (102), (002), and (110) planes of the AA graphite. Simulation of the diffraction patterns, employing the structural factors of graphene, confirms the existence of AA graphite.
This paper presents findings from a study of nanocrystalline diamond (NCD) growth in a microwave plasma chemical vapour deposition (CVD) reactor. NCD films were grown using Ar/H 2 /CH 4 and He/H 2 /CH 4 gas compositions. The resulting films were characterised using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. Analysis revealed an estimated grain size of the order of 50 nm, growth rates in the range 0.01 to 0.3 µm/h and sp 3 and sp 2 bonded carbon content consistent with that expected for NCD.The C 2 Swan band (d 3 П g ↔ a 3 П u ) was probed using cavity ring-down spectroscopy (CRDS) to measure the absolute C 2 (a) number density in the plasma during diamond film growth.The number density in the Ar/H 2 /CH 4 plasmas was in the range 2 to 4 x 10 12 cm -3 , but found to be present in quantities too low to measure in the He/H 2 /CH 4 plasmas. Optical emission 2 spectrometry (OES) was employed to determine the relative densities of the C 2 excited state (d) in the plasma.The fact that similar NCD material was grown whether using Ar or He as the carrier gas suggests that C 2 does not play a major role in the growth of nanocrystalline diamond.3
Microwave plasma deposited (100) diamond films have been thermally oxidized in dry O2 between 500 and 723 degrees C. The roughness of a single crystalline grain following oxidation is consistent with a layer-by-layer mechanism for the removal of carbon monoxide. The resulting surface exhibits infrared absorption bands at 1731 and 905 cm-1, attributed to the stretching and bending modes of a surface bonded carbonyl group. The former is within 1 cm-1 of the structurally analogous molecule 2-adamantanone. These data are consistent with the carbonyl groups being present on diamond (100) terraces.
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