2 research outputs found
Magnetic Patterning by Electron Beam-Assisted Carbon Lithography
We
report on the proof of principle of a scalable method for writing
the magnetic state by electron-stimulated molecular dissociative adsorption
on ultrathin Co on Re(0001). Intense microfocused low-energy electron
beams are used to promote the formation of surface carbides and graphitic
carbon through the fragmentation of carbon monoxide. Upon annealing
at the CO desorption temperature, carbon persists in the irradiated
areas, whereas the clean surface is recovered elsewhere, giving origin
to chemical patterns with nanometer-sharp edges. The accumulation
of carbon is found to induce an in-plane to out-of-plane spin reorientation
transition in Co, manifested by the appearance of striped magnetic
domains. Irradiation at doses in excess of 1000 L of CO followed by
ultrahigh vacuum annealing at 380 °C determines the formation
of a graphitic overlayer in the irradiated areas, under which Co exhibits
out-of-plane magnetic anisotropy. Domains with opposite magnetization
are separated here by chiral Neél walls. Our fabrication protocol
adds lateral control to spin reorientation transitions, permitting
to tune the magnetic anisotropy within arbitrary regions of mesoscopic
size. We envisage applications in the nano-engineering of graphene-spaced
stacks exhibiting the desired magnetic state and properties
Spectromicroscopy of a Model Water–Gas Shift Catalyst: Gold Nanoparticles Supported on Ceria
Nanometer-sized
gold particles supported on ceria are an important catalyst for the
low-temperature water–gas shift reaction. In this work, we
prepared a model system of epitaxial, ultrathin (1–2 nm thick)
CeO<sub>2–<i>x</i></sub>(111) crystallites on a Rh(111)
substrate. Low-energy electron microscopy (LEEM) and X-ray photoemission
electron microscopy (XPEEM) were employed to characterize the in situ
growth and morphology of these films, employing Ce 4f resonant photoemission
to probe the oxidation state of the ceria. The deposition of submonolayer
amounts of gold at room temperature was studied with scanning tunneling
microscopy (STM) and XPEEM. Spatially resolved, energy-selected XPEEM
at the Au 4f core level after gold adsorption indicated small shifts
to higher binding energy for the nanoparticles, with the magnitude
of the shift inversely related to the particle size. Slight reduction
of the ceria support was also observed upon increasing Au coverage.
The initial oxidation state of the ceria film was shown to influence
the Au 4f binding energy; more heavily reduced ceria promoted a larger
shift to higher binding energy. Understanding the redox behavior of
the gold/ceria system is an important step in elucidating the mechanisms
behind its catalytic activity