Aligned diamond nanowhiskers
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Dongryul Jeon Department of Physics, Myong Ji University, Yongin Kyunggi-do, Seoul 449-728, Korea (Received 1 October 1999; accepted 12 January 2000)
We investigated the formation of nanowhiskers by means of air plasma dry etching using diamond films of two different kinds: as-grown diamond films and films with molybdenum (Mo) deposits. As for the as-grown diamond films, nanowhiskers were found to form preferentially at grain boundaries of diamond crystals. Auger depth profile analysis of the etched films revealed a progressive enrichment by Mo toward the whisker tip, resulting from accidental sputtering of Mo substrate holder. With dry etching of diamond films with preformed Mo deposits, well-aligned whiskers 100 nm in diameter were found to form uniformly over the entire film surface with a population density of 30/m2. From these findings, it follows that Mo deposits serve as micromasks for the formation of the nanowhiskers. It was also confirmed that these whiskers showed excellent field-emission behavior.
I. INTRODUCTION
Diamond is receiving considerable attention as a promising candidate for cold cathode material due to its potential negative electron affinity, high thermal conductivity, hardness, and chemical inertness.1– 4 The potential merits of diamond cold cathode may not be utilized, however, without control of electron emission sites on the diamond film surface.5 Successful definition of electron emission sites and the concomitant effective emission have been achieved by way of shaping diamond films into macro- or microtips,6 either by a transfer mold technique using (100) Si inverted pyramidal mold7,8 or by dry etching of diamond film via sputterfaceting of silicon oxide dot mask on the diamond film.9 These processes, however, involve too-complicated and tricky semiconductor fabrication procedures for a large area fabrication. Recently, well-aligned carbon nanotubes have emerged as an attractive candidate for cold cathode due to the capability of a large electron emission engendered by the material trait of carbon combined with a characteristic geometry of high aspect ratio.10 We report here a new type of cold cathode that bears a close resemblance in geometry to a carbon nanotube but is made of crystalline diamond, hence named “diamond nanowhiskers.” We also put forward their forma-
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 4, Apr 2000
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tion mechanism in terms of the combined role of anisotropic etching and concurrent formation of micromask on diamond film.
II. EXPERIMENTAL PROCEDURE
At first, polycrystalline diamond films of about 4 m in thickness were grown on a silicon (Si) wafer by use of the hot-filament-chemical-vapor-deposition (HFCVD) method. Si wafers were pretreated by diamond powder to promote nucleation of crystalline diamonds. Hydrogen gas mixed with 5% methane was used as a source gas, which was thermally activated by tungsten filament heating at 2100 °C an
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