Generation of carbon tripods on copper by chemical vapor deposition
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Generation of carbon tripods on copper by chemical vapor deposition F. Le Normand,a) L. Constant, G. Ehret, and C. Speisser IPCMS-GSI, UMR 1046 du CNRS, Bat 69, 23, rue du Loess, 67037 Strasbourg Cedex, FRANCE (Received 12 February 1998; accepted 20 May 1998)
We report the first observation of large graphitic capped clusters with threefold symmetry (tripods). They were generated under the diamond growth conditions by the chemical vapor deposition process activated by hot filaments on a Cu(111) surface while conditions of very poor diamond nucleation (104 –105 cm22 ) are fullfilled. They were characterized by direct high resolution imaging and selected area diffraction. Furthermore, a lot of them are connected. The behavior of hydrogen radicals to curl and to close limited-size graphitic planes is emphasized to explain their formation. These tripods appear to be readily stable carbon as they form only after other limited-size graphitic clusters such as graphite lumps or bucky onions. It is thus expected that the chemical vapor deposition process is a quite relevant preparation method to grow in a controlled way new forms of carbon with a narrow size distribution. I. INTRODUCTION
Chemical vapor deposition with an activation of the carbon precursor by means of hot filaments (HFCVD), microwave power (MWCVD), ..., has been extensively used to grow diamond films within a large range of deposition parameters (substrate temperature, carbon concentration, gas flow, and pressure) and is now well documented.1 Investigations have included many substrates which have to be stable at the high temperatures of the deposition process (823–1200 K). Among them, copper is of special interest due to the lack of both carbon dissolution and alloy formation and to a good matching of the lattice parameters between cubic diamond and fcc copper. Besides the formation of diamond islands TEM observations of the carbon deposits on copper have revealed, however, others forms of carbon such as fullerenelike onions.2 Even more, these carbon onions sometimes exhibit a new phase in the onion core,3 and it is believed that they are possible precursors for diamond nucleation, as recently proposed by Banhart et al.4,5 when focusing on them highly intense and energetic electron or ion beams. We show here that under CVD conditions another remarkable new form of carbon can be observed which is shaped by threefold oriented graphitic carbon clusters. II. EXPERIMENTAL
The TEM grids of carbon deposits on copper were prepared by a replica technique which has been elsewhere described.2 The observations were performed with a TOPCON 002B microscope operating at 200 kV. The instrumental resolution is 0.18 nm point-to-point. The electron beam current density on the sample was limited to 10 Aycm2 and the images were recorded at a)
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J. Mater. Res., Vol. 14, No. 2, Feb 1999
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