We report a method
that uses van der Waals interactions to transfer
continuous, high-quality graphene films from Ge(110) to a different
substrate held by hexagonal boron nitride carriers in a clean, dry
environment. The transferred films are uniform and continuous with
low defect density and few charge puddles. The transfer is effective
because of the weak interfacial adhesion energy between graphene and
Ge. Based on the minimum strain energy required for the isolation
of film, the upper limit of the interfacial adhesion energy is estimated
to be 23 meV per carbon atom, which makes graphene/Ge(110) the first
as-grown graphene film that has a substrate adhesion energy lower
than that of typical van der Waals interactions between layered materials.
Our results suggest that graphene on Ge can serve as an ideal material
platform to be integrated with other material systems by a clean assembly
process.
Electrochemical reduction of carbon
dioxide (CO2) is
a promising method toward carbon recycling. Highly selective bimetallic
catalysts have been extensively demonstrated, while efforts to understand
the compositional and geometrical effects have been limited. Here,
we studied the relationship between the catalytic activity of bimetallic
Cu–Sn catalysts with their composition and geometry through
the fabrication of three-dimensional hierarchical (3D-h) Cu nanostructure
and the solution-based coating of Sn nanoparticles (NPs). As the coating
time of Sn NPs was increased from 1 to 60 s, Sn NPs with a larger
size and a higher surface density were coated onto the 3D-h Cu, thus
the surface atomic ratio of Cu/Sn gradually decreased. This compositional
change in bimetallic Cu–Sn catalysts remarkably shifted the
faradaic efficiency (FE) of carbon monoxide (CO) from 90.0 to 23.4%
at −0.6 VRHE. Moreover, we found that the catalytic
performance increases as the geometric structure becomes complex in
the order of flat, rods, and 3D-h Cu–Sn. The 3D-h Cu–Sn
began to produce CO at a low potential of −0.15 VRHE and showed the maximum FECO of 98.6% at −0.45
VRHE. This study reveals that the synergetic effects of
composition and nanoscale geometry are significant for the CO2 reduction reaction.
We successfully control the Ir(ppy)3 needle-like aggregates in small-molecule based emitting layers by solvent mixture for improving the properties of OLEDs.
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