AVS 51st International Symposium
    Nanometer-scale Science and Technology Thursday Sessions
       Session NS1-ThM

Paper NS1-ThM8
The Role of Hydrogen in Ultrananocrystalline Diamond Thin Film Growth

Thursday, November 18, 2004, 10:40 am, Room 213C

Session: Nanoscale Fabrication
Presenter: J.P. Birrell, Argonne National Laboratory
Authors: J.P. Birrell, Argonne National Laboratory
J.E. Gerbi, Argonne National Laboratory
O.H. Auciello, Argonne National Laboratory
J.A. Carlisle, Argonne National Laboratory
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A great deal of recent experimental studies and computer simulations have been performed to try to understand the surface stability of diamond nanocrystals. These results have yielded a number of striking conclusions that and the size of the crystallite. This study can help explain the transition of diamond thin film structure from microcrystalline to nanocrystalline with the reduction of hydrogen in the gas phase during microwave plasma enhanced chemical vapor deposition; namely, that the stability of the surface of the diamond nanoparticle is a strong function of both the hydrogen coverage uses TEM, Raman scattering, and XRD to investigate the role of hydrogen in the growth of ultrananocrystalline diamond (UNCD) thin films in two different regimes. First, we add hydrogen to the normal Ar/CH@sub 4@ gas mixture used during growth, and observe that rather than a monotonic increase in the grain size from nanocrystalline to microcrystalline, the films are clearly mixed-phase, with microcrystalline diamond inclusions that become much more prominent with added hydrogen. Second, we remove hydrogen from the plasma by changing the hydrocarbon precursor from CH@sub 4@ to C@sub 2@H@sub 2@. We observe that there is a lower limit to the amount of hydrogen that needed to sustain ultrananocrystalline diamond growth, below which a significant amount of disordered graphitic carbon is nucleated. We suggest that the reasons for these observed changes are that large amounts of hydrogen (in the form of H@super +@ ) in the plasma enables the more rapid growth of diamond microcrystals, while low concentrations of hydrogen result in unstable diamond nanocrystals and thus the nucleation of disordered carbon material. This work was supported by the DOE-Office of science-Materials Science under Contract No. W-31-109-ENG-38.