Nonaligned Carbon Nanotubes Anchored on Porous Alumina: Formation, Process Modeling, Gas‐Phase Analysis, and Field‐Emission Properties

Abstract We have developed a chemical vapor deposition (CVD) process for the catalytic growth of carbon nanotubes (CNTs), anchored in a comose‐type structure on top of porous alumina substrates. The mass‐flow conditions of precursor and carrier gases and temperature distributions in the CVD reactor were studied by transient computational fluid dynamic simulation. Molecular‐beam quadrupole mass spectroscopy (MB‐QMS) has been used to analyze the gas phase during ferrocene CVD under reaction conditions (1073 K) in the boundary layer near the substrate. Field‐emission (FE) properties of the nonaligned CNTs were measured for various coverages and pore diameters of the alumina. Samples with more dense CNT populations provided emitter‐number densities up to 48 000 cm⁻²at an electric field of 6 V μm⁻¹. Samples with fewer but well‐anchored CNTs in 22‐nm pores yielded the highest current densities. Up to 83 mA cm⁻²at 7 V μm⁻¹in dc mode and more than 200 mA cm⁻²at 11 V μm⁻¹in pulsed diode operation have been achieved from a cathode size of 24 mm².