2 research outputs found
Co-catalytic Absorption Layers for Controlled Laser-Induced Chemical Vapor Deposition of Carbon Nanotubes
The concept of co-catalytic layer
structures for controlled laser-induced chemical vapor deposition
of carbon nanotubes is established, in which a thin Ta support layer
chemically aids the initial Fe catalyst reduction. This enables a
significant reduction in laser power, preventing detrimental positive
optical feedback and allowing improved growth control. Systematic
study of experimental parameters combined with simple thermostatic
modeling establishes general guidelines for the effective design of
such catalyst/absorption layer combinations. Local growth of vertically
aligned carbon nanotube forests directly on flexible polyimide substrates
is demonstrated, opening up new routes for nanodevice design and fabrication
Interdependency of Subsurface Carbon Distribution and Graphene–Catalyst Interaction
The
dynamics of the graphene–catalyst interaction during
chemical vapor deposition are investigated using in situ, time- and
depth-resolved X-ray photoelectron spectroscopy, and complementary
grand canonical Monte Carlo simulations coupled to a tight-binding
model. We thereby reveal the interdependency of the distribution of
carbon close to the catalyst surface and the strength of the graphene–catalyst
interaction. The strong interaction of epitaxial graphene with Ni(111)
causes a depletion of dissolved carbon close to the catalyst surface,
which prevents additional layer formation leading to a self-limiting
graphene growth behavior for low exposure pressures (10<sup>–6</sup>–10<sup>–3</sup> mbar). A further hydrocarbon pressure
increase (to ∼10<sup>–1</sup> mbar) leads to weakening
of the graphene–Ni(111) interaction accompanied by additional
graphene layer formation, mediated by an increased concentration of
near-surface dissolved carbon. We show that growth of more weakly
adhered, rotated graphene on Ni(111) is linked to an initially higher
level of near-surface carbon compared to the case of epitaxial graphene
growth. The key implications of these results for graphene growth
control and their relevance to carbon nanotube growth are highlighted
in the context of existing literature