(110)-oriented diamond films synthesized by microwave chemical-vapor deposition

Abstract

Bilayer diamond films were deposited on Si substrates by microwave-plasma chemical-vapor deposition (CVD) using a methane-hydrogen gas mixture. The first layer was deposited for 3 h using a reaction gas which was composed of 2.5 vol. % methane and 97.5 vol.% hydrogen. The deposited film consisted of very weakly (110)-oriented microcrystalline diamonds as well as amorphous carbon and graphite. In order to remove non-diamond carbons from the film surface, the specimen was treated in hydrogen plasma for 1 h. Finally, a second layer was deposited on the first layer for 14 h using a methane concentration of between 0.2 and 1.6 vol.%. It was found that the x-ray intensity of the (220) diffraction of the bilayer films was much greater than that of the (111) diffraction, indicating that the diamond grains in the second layer were strongly oriented with their crystallographic (110) planes parallel to the substrate surface. X-ray diffraction spectra of bilayer films in which the second layer was deposited for 7, 14, 21, and 35 h using two different methane concentrations, 0.3 and 1.2 vol.%, showed that within periods of up to 21 h, the (220) intensity increased with the deposition time much more quickly than the (111) intensity, indicating that the degree of (110) orientation was further enhanced as the second layer thickness increased. However, the (220) intensity decreased after 21 h, presumably due to thermal randomization. Results of scanning electron microscopy, electron diffraction, and Raman spectroscopy of the bilayer films are also presented.

Response

“…Our transparent carbon is also a powder, and its XRD patterns indicate that many phases of crystalline carbon are present (1). The width of our 1336 cm-1 band (70 cm`1 at half-height) is identical to those reported for 50-to 150-nm diamond powders (11,15,17,18). Also, the Raman spectra of the black carbon formed by our method shows a band at 1140 cm`(1), which is seen only in diamond samples, many of them nanocrystalline, and which has been attributed to small crystallite size or disorder in the tetrahedral carbon (3), regions of amorphous or microcrystalline diamond, or precursors to crystalline diamond (4).…”

“…." (7, p. 347 Diamond-Like Carbon Bonds width of the -1330 cm-1 region-bands in the Raman spectra of nanocrystalline diamond and diamond-like powders has been interpreted as arising from the materials being powders, not films, with far greater surface areas and surface defects (15); from many polytypes of diamond and amorphous carbon being present (11,15,(18)(19)(20); from possible overlap of the D band of sp2 carbon with the 1330-region band of the sp3 carbon present (21 ); and from reduction of the photon lifetime by an increase in the density of defects in the diamond phase (19,22). Our transparent carbon is also a powder, and its XRD patterns indicate that many phases of crystalline carbon are present (1).…”

Boron-doped diamond electrode: synthesis, characterization, functionalization and analytical applications

“…The nucleation density can be increased further if diamond growth occurs on an MCD film synthesized using a methane concentration above 1.6%. 22 The film, however, still consists of NCD particles as well as graphite and amorphous carbon, and hydrogen plasma treatment (30 torr and 800 C) is an effective way to remove such non-diamond and amorphous carbon phases. NCD films can be grown using the Ar/H 2 /CH 4 plasma and the level of argon in the plasma is critical.…”

Studies on nucleation process in diamond CVD: an overview of recent developments

“…Low gas pressures (~5 torr) [12,16], high CH 4 concentrations [16,41,42,47,122,131,132] ( Figure 8), and/or high gas flow rates [50] lead to high nucleation densities. The pressure dependence of nucleation density is explained [12] by the competition effect between β-SiC formation, which increases the diamond nucleation density, and atomic-hydrogen etching, which decreases the number of nucleation sites.…”