2 research outputs found
Microscopic View on a Chemical Vapor Deposition Route to Boron-Doped Graphene Nanostructures
Single
layer boron-doped graphene layers have been grown on polycrystalline
copper foils by chemical vapor deposition using methane and diborane
as carbon and boron sources, respectively. Any attempt to deposit
doped layers in one-step has been fruitless, the reason being the
formation of very reactive boron species as a consequence of diborane
decomposition on the Cu surface, which leads to disordered nonstoichiometric
carbides. However, a two-step procedure has been optimized: as a first
step, the surface is seeded with pure graphene islands, while the
boron source is activated only in a second stage. In this case, the
nonstochiometric boron carbides formed on the bare copper areas between
preseeded graphene patches can be exploited to easily release boron,
which diffuses from the peripheral areas inward of graphene islands.
The effective substitutional doping (of the order of about 1%) has
been demonstrated by Raman and photoemission experiments. The electronic
properties of doped layers have been characterized by spatially resolved
photoemission band mapping carried out on single domain graphene flakes
using a photon beam with a spot size of 1 μm. The whole set
of experiments allow us to clarify that boron is effective at promoting
the anchoring carbon species on the surface. Taking the cue from this
basic understanding, it is possible to envisage new strategies for
the design of complex 2D graphene nanostructures with a spatially
modulated doping
Reactivity of Carbon in Lithium–Oxygen Battery Positive Electrodes
Unfortunately,
the practical applications of Li–O<sub>2</sub> batteries are
impeded by poor rechargeability. Here, for the first time we show
that superoxide radicals generated at the cathode during discharge
react with carbon that contains activated double bonds or aromatics
to form epoxy groups and carbonates, which limits the rechargeability
of Li–O<sub>2</sub> cells. Carbon materials with a low amount
of functional groups and defects demonstrate better stability thus
keeping the carbon will-o’-the-wisp lit for lithium–air
batteries