The
catalytic growth on transition metal surfaces provides a clean
and controllable route to obtain defect-free, monocrystalline graphene.
However, graphene’s optical and electronic properties are diminished
by the interaction with the metal substrate. One way to overcome this
obstacle is the intercalation of atoms and molecules decoupling the
graphene and restoring its electronic structure. We applied noncontact
atomic force microscopy to study the structural and electric properties
of graphene on clean Cu(111) and after the adsorption of KBr or NaCl.
By means of Kelvin probe force microscopy, a change in graphene’s
work function has been observed after the deposition of KBr, indicating
a changed graphene–substrate interaction. Further measurements
of single-electron charging events as well as X-ray photoelectron
spectroscopy confirmed an electronic decoupling of the graphene islands
by KBr intercalation. The results have been compared with density
functional theory calculations, supporting our experimental findings.
We report the synthesis of well-dispersed core-shell Au@SiO(2) nanoparticles with minimal extraneous silica particle growth. Agglomeration was suppressed through consecutive exchange of the stabilizing ligands on the gold cores from citrate to L-arginine and finally (3-mercaptopropyl)triethoxysilane. The result was a vitreophilic, stable gold suspension that could be coated with silica in a biphasic mixture through controlled hydrolysis of tetraethoxysilane under L-arginine catalysis. Unwanted condensation of silica particles without gold cores was limited by slowing the transfer across the liquid-liquid interface and reducing the concentration of the L-arginine catalyst. In-situ dynamic light scattering and optical transmission spectroscopy revealed the growth and dispersion states during synthesis. The resulting core-shell particles were characterized via dynamic light scattering, optical spectroscopy, and electron microscopy. Their cores were typically 19 nm in diameter, with a narrow size distribution, and could be coated with a silica shell in multiple steps to yield core-shell particles with diameters up to 40 nm. The approach was sufficiently controllable to allow us to target a shell thickness by choosing appropriate precursor concentrations.
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