Diamond growth on thin Ti wafers via chemical vapor deposition
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Diamond growth on thin Ti wafers via chemical vapor deposition Qijin Chena) and Zhangda Lin State Key Laboratory of Surface Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, People's Republic of China (Received 31 May 1995; accepted 28 July 1995) Diamond film was synthesized on thin Ti wafers (as thin as 40 /im) via hot filament chemical vapor deposition (HFCVD). The hydrogen embrittlement of the titanium substrate and the formation of a thick TiC interlayer were suppressed. A very low pressure (133 Pa) was employed to achieve high-density rapid nueleation and thus to suppress the formation of TiC. Oxygen was added to source gases to lower the growth temperature and therefore to slow down the hydrogenation of the thin Ti substrate. The role of the very low pressure during nueleation is discussed, providing insight into the nueleation mechanism of diamond on a titanium substrate. The as-grown diamond films were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and x-ray analysis.
Since Spitsyn et a/.'s report of synthesis of diamond from the gas phase,1 many methods have been developed to grow thin diamond films via chemical vapor deposition (CVD)2^1 in hopes of utilizing the various applications of CVD diamond films owing to the extraordinary properties of diamond.5 All these methods involve a nueleation stage and a subsequent growth. To get a high density of nuclei, many measures have been taken to enhance nueleation, such as scratching the substrate surface with fine diamond powder before nueleation,6 predeposition of carbonaceous precursors of non-diamond carbon,7 etc. As one of the most promising kinds of substrate, silicon has been under the most intensive research. As a matter of fact, great progress has been made in diamond synthesis on silicon. Yugo et a/.,8 Stoner et al.,9 and Jiang et al.]0'U acquired high density nueleation on mirror-polished Si by applying a negative bias to the substrate in a microwave plasma CVD (MPCVD) system and, subsequently, they achieved oriented or heteroepitaxial diamond films.10"12 In spite of all these successes, however, the nueleation mechanism is not very clear as yet, and needs further study. One of the main substrates in CVD diamond synthesis, titanium has not been given as much consideration as silicon. However, the super-high Young's modulus (1.05 X 1012 N/m 2 ) and great acoustic velocity (18.5 km/s) of diamond make it alluring to coat thin Ti films with diamond films for the use in speaker's vibrational membranes to achieve high fidelity acoustics.
"'Present address: Department of Physics, The University of Chicago, 5720 South Ellis Avenue, Chicago, Illinois 60637. J. Mater. Res., Vol. 10, No. 11, Nov 1995 http://journals.cambridge.org
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Unfortunately, diamond growth on Ti substrates, especially thin Ti films, has not been thoroughly investigated. One great problem is the severe hydrogen embrittlement of the Ti substrate due to the presence of hydrogen at high temperature during
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