Increased Carbon Chemical Vapor Deposition and Carbon Nanotube Growth on Metal Substrates in Confined Spaces

Abstract

Experimental study of carbon deposition and carbon nanotube growth between stacked metallic substrates was conducted. The batch chemical vapor deposition (CVD) reactor was used with polyethylene as the carbon precursor. Increased carbon deposition was established on surfaces between stacked nickel substrates as compared to surfaces facing to open spaces. In general case carbon films deposited between substrates were not uniform giving rise to complicated profiles. The simple diffusion-reaction scheme gives carbon film thickness profiles closely resembling those experimentally observed. This similarity is considered as evidence of homogeneous-heterogeneous reaction sequences proceeding in narrow gap between catalytically active surfaces. Increased carbon nanotube growth was believed to occur as a result of the involvement of hydrocarbon radicals generated by the catalyst surface with subsequent release into the gas phase. Radicals accelerate gas-phase reactions providing reactive intermediates. Ultimately catalytic gas phase activation in the confined space promotes increased carbon formation. An explanation of the experimental results is proposed and a practical application was demonstrated.Carbon films and layers on supporting substrates are perspective components for an increasing number of potential applications. Chemical vapor deposition (CVD) is the preferred method to produce carbon films on substrates. For carbon materials obtained by CVD process carbon species and their properties are determined by the interacting influences of hydrodynamics and chemical kinetics, which in turn depend on the reactor type, process conditions (chemical precursor, temperature, temperature gradients, pressure), surface catalytic properties and may be affected also by extrinsic factors as gas or surface impurities, surface configuration and surface morphology. The vast majority of experimental works to produce carbon films or layers has been made using the crystalline silicon as a substrate. In particular, carbon nanotubes (CNT) are frequently being synthesized on silicon with coated catalyst (Ni, Fe, Co and alloys). This is commonly justified by the need for compatibility with technologies of modern microelectronics. There exist, however, many applications for which the use of metallic substrates is preferable to other materials or essential for device performance. The considerable effort has been devoted to the synthesis of CVD diamond films on metal substrates at low temperatures and pressures. 1-3 Such films have great potential for applications in microelectronic devices, as tools, heat sinks, hard coatings, corrosion and wear resistant surfaces. CVD techniques for producing diamond films require a means of activating gas-phase carbon-containing precursor molecules. Thermal or plasma activation procedures generate hydrogen and hydrocarbon radicals which participate in surface chemical reactions resulting in film growth. In fact, the same procedures are now widely used in nanotube CVD processes to low synthesis temperature...

Surface Integrity and Carbon Chemical Vapor Deposition on Nickel Foil: Surface Abrasive Treatment

“…The graphite-like carbon is actually similar to turbostratic graphite as it was determined in Ref. 8. The coke-like phase is much more disordered graphite as it was expected.…”

“…It is unlikely that such a channel sealing with plastically deformed metal can be hermetic, so that gaseous hydrocarbons penetrating into cavities are decomposed in conditions of confined space treated in Ref. 8. As a result nickel sheets over grooves are moved apart by rapidly growing carbon phase and furrows reappear.…”

“…8 Briefly, vertical quartz tube (2 cm inner diameter and 45 cm in length) served as CVD batch reactor chamber. Two zone heating element was used to pyrolyze carbon precursor (lower zone) and to heat substrates (upper zone).…”

“…In addition, because of some carbon deposit non-uniformity inherent to such substrate array the changes in deposit thickness and carbon morphology along substrate radius can be examined in dependence on active species concentration. 8 For comparison purpose some experiments were fulfilled using nickel substrate with treated surface faced to volume of CVD reactor. Carbon deposits were produced on treated surfaces in CVD processes of different duration (1-15 min.).…”

“…Rates of carbon deposition at initial stages of surface carbon formation were determined in interrupted CVD processes of short duration (1-2 min) at two temperatures 600 and 650 • C. This choice was made to minimize the gas-phase carbon formation. Because the carbon deposition rate on substrates in stacked geometry is not uniform in general case, 8 the rates were determined as the average values assuming uniform deposit distribution. Carbon nanotubes have been grown in longer processes of 12-15 min.…”