Graphene growth by low-pressure chemical vapor deposition on low cost copper foils shows great promise for large scale applications. It is known that the local crystallography of the foil influences the graphene growth rate. Here we find an epitaxial relationship between graphene and copper foil. Interfacial restructuring between graphene and copper drives the formation of (n10) facets on what is otherwise a mostly Cu(100) surface, and the facets in turn influence the graphene orientations from the onset of growth. Angle resolved photoemission shows that the electronic structure of the graphene is decoupled from the copper indicating a weak interaction between them. Despite this, two preferred orientations of graphene are found, ±8° from the Cu[010] direction, creating a non-uniform distribution of graphene grain boundary misorientation angles. Comparison with the model system of graphene growth on single crystal Cu(110) indicates that this orientational alignment is due to mismatch epitaxy. Despite the differences in symmetry the orientation of the graphene is defined by that of the copper. We expect these observations to not only have importance for controlling and understanding the growth process for graphene on copper, but also to have wider implications for the growth of two-dimensional materials on low cost metal substrates.
A synchrotron radiation beamline in the photon energy range of 18 -240 eV and an electron spectroscopy end station have been constructed at the 3 GeV Diamond Light Source storage ring. The instrument features a variable polarisation undulator, a high resolution monochromator, a re-focussing system to form a beam spot of 50x50 µm 2 and an end station for angle-resolved photoelectron spectroscopy (ARPES) including a 6-degrees-of-freedom cryogenic sample manipulator. The beamline design and its performance allow for a highly productive and precise use of the ARPES technique at an energy resolution of 10 -15 meV for fast k-space mapping studies with a photon flux up to 2 • 10 13 ph/sec and well below 3 meV for high resolution spectra.
We report a method of fabricating a high work function,
solution processable vanadium oxide (V2O
x(sol)) hole-extracting layer. The atmospheric processing conditions
of film preparation have a critical influence on the electronic structure
and stoichiometry of the V2O
x(sol), with a direct impact on organic photovoltaic (OPV) cell performance.
Combined Kelvin probe (KP) and ultraviolet photoemission spectroscopy
(UPS) measurements reveal a high work function, n-type character for
the thin films, analogous to previously reported thermally evaporated
transition metal oxides. Additional states within the band gap of
V2O
x(sol) are observed in the
UPS spectra and are demonstrated using X-ray photoelectron spectroscopy
(XPS) to be due to the substoichiometric nature of V2O
x(sol). The optimized V2O
x(sol) layer performance is compared directly to bare
indium–tin oxide (ITO), poly(ethyleneoxythiophene):poly(styrenesulfonate)
(PEDOT:PSS), and thermally evaporated molybdenum oxide (MoO
x
) interfaces in both small molecule/fullerene and
polymer/fullerene structures. OPV cells incorporating V2O
x(sol) are reported to achieve favorable
initial cell performance and cell stability attributes.
We investigate the growth of hexagonal boron nitride (h-BN) on copper foil by low pressure chemical vapour deposition (LP-CVD). At low pressure, h-BN growth proceeds through the nucleation and growth of triangular islands. Comparison between the orientation of the islands and the local crystallographic orientation of the polycrystalline copper foil reveals an epitaxial relation between the copper and h-BN, even on Cu(100) and Cu(110) regions whose symmetry is not matched to the h-BN. However, the growth rate is faster and the islands more uniformly oriented on Cu(111) grains. Angle resolved photoemission spectroscopy measurements reveal a well-defined band structure for the h-BN, consistent with a band gap of 6 eV, that is decoupled from the copper surface beneath. These results indicate that, despite a weak interaction between h-BN and copper, van der Waals epitaxy defines the long range ordering of h-BN even on polycrystalline copper foils and suggest that large area, single crystal, monolayer h-BN could be readily and cheaply produced.
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