title: 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(-2) at an electric field of 6 V microm(-1). Samples with fewer but well-anchored CNTs in 22-nm pores yielded the highest current densities. Up to 83 mA cm(-2) at 7 V microm(-1) in dc mode and more than 200 mA cm(-2) at 11 V microm(-1) in pulsed diode operation have been achieved from a cathode size of 24 mm2.
authors.affiliation: Bergische Universität Wuppertal, Fachbereich C Abt. Physik, 42097 Wuppertal, Germany.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Lysenkov
authors.forename: Jörg
authors.initials: J
authors.lastname: Engstler
authors.forename: Arti
authors.initials: A
authors.lastname: Dangwal
authors.forename: Alexander
authors.initials: A
authors.lastname: Popp
authors.forename: Günter
authors.initials: G
authors.lastname: Müller
authors.forename: Jörg J
authors.initials: JJ
authors.lastname: Schneider
authors.forename: Vinod M
authors.initials: VM
authors.lastname: Janardhanan
authors.forename: Olaf
authors.initials: O
authors.lastname: Deutschmann
authors.forename: Peter
authors.initials: P
authors.lastname: Strauch
authors.forename: Volker
authors.initials: V
authors.lastname: Ebert
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wolfrum
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D003198:Computer Simulation; D005740:Gases / Q000032:analysis / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D037742:Nanotubes, Carbon / Q000737:chemistry*; D016062:Porosity; D013696:Temperature; D014835:Volatilization
chemical_list: D005740:Gases; D037742:Nanotubes, Carbon; D000537:Aluminum Oxide