42 research outputs found
Coexistence of multiple silicene phases in silicon grown on Ag(111)
Silicene, the silicon equivalent of graphene, is attracting increasing
scientific and technological attention in view of the exploitation of its
exotic electronic properties. This novel material has been theoretically
predicted to exist as a free-standing layer in a low-buckled, stable form, and
can be synthesized by the deposition of Si on appropriate crystalline
substrates. By employing low-energy electron diffraction and microscopy, we
have studied the growth of Si on Ag(111) and observed a rich variety of
rotationally non-equivalent silicene structures. Our results highlight a very
complex formation diagram, reflecting the coexistence of different and nearly
degenerate silicene phases, whose relative abundance can be controlled by
varying the Si coverage and growth temperature. At variance with other studies,
we find that the formation of single-phase silicene monolayers cannot be
achieved on Ag(111)
Laterally Inhomogeneous Au Intercalation in Epitaxial Graphene on SiC(0 0 0 1): A Multimethod Electron Microscopy Study
Epitaxial graphene is of particular interest because of its tunable electronic structure. One important approach to tune the electronic properties of graphene relays on intercalating atomic species between graphene and the topmost silicon carbide layer. Here, we investigated the morphology and electronic structure of gold-intercalated epitaxial graphene using a multitechnique approach combining spectroscopic photoemission low-energy electron microscopy (SPELEEM) for chemical and structural characterization at mesoscopic length scale and with transmission electron microscopy (STEM) at the atomic level. Deposition of gold on ex situ prepared graphene on SiC(0 0 0 1) results in the partial intercalation of Au adatoms under graphene, with the formation of a buffer layer of variable thickness. Gold has also shown to aggregate in nanometer-sized clusters lying on top of the same graphene film. X-ray photo-emission electron microscopy measurements indicate that Au induces only small changes in the doping of the graphene layer, which does not develop a quasi free-standing behavior
Fragmentation of magnetism in artificial kagome dipolar spin ice
Geometrical frustration in magnetic materials often gives rise to exotic,
low-temperature states of matter, like the ones observed in spin ices. Here we
report the imaging of the magnetic states of a thermally-active artificial
magnetic ice that reveal the fingerprints of a spin fragmentation process. This
fragmentation corresponds to a splitting of the magnetic degree of freedom into
two channels and is evidenced in both real and reciprocal space. Furthermore,
the internal organization of both channels is interpreted within the framework
of a hybrid spin-charge model that directly emerges from the parent spin model
of the kagome dipolar spin ice. Our experimental and theoretical results
provide insights into the physics of frustrated magnets and deepen our
understanding of emergent fields through the use of tailor-made magnetism.Comment: 9 pages, 5 figures. Published version available on the Nat. Comm. web
site:
http://www.nature.com/ncomms/2016/160513/ncomms11446/full/ncomms11446.htm
Making ARPES Measurements on Corrugated Monolayer Crystals: Suspended Exfoliated Single-Crystal Graphene
Free-standing exfoliated monolayer graphene is an ultra-thin flexible
membrane, which exhibits out of plane deformation or corrugation. In this
paper, a technique is described to measure the band structure of such
free-standing graphene by angle-resolved photoemission. Our results show that
photoelectron coherence is limited by the crystal corrugation. However, by
combining surface morphology measurements of the graphene roughness with
angle-resolved photoemission, energy dependent quasiparticle lifetime and
bandstructure measurements can be extracted. Our measurements rely on our
development of an analytical formulation for relating the crystal corrugation
to the photoemission linewidth. Our ARPES measurements show that, despite
significant deviation from planarity of the crystal, the electronic structure
of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we
measure the Dirac point to be within 25 meV of . Further, we show that
suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle
lifetime which scales as ; comparison with other graphene and
graphite data is discussed
Magnetism in nanometer-thick magnetite
The oldest known magnetic material, magnetite, is of current interest for use
in spintronics as a thin film. An open question is how thin can magnetite films
be and still retain the robust ferrimagnetism required for many applications.
We have grown one-nanometer-thick magnetite crystals and characterized them in
situ by electron and photoelectron microscopies including selected-area x-ray
circular dichroism. Well-defined magnetic patterns are observed in individual
nano-crystals up to at least 520 K, establishing the retention of
ferrimagnetism in magnetite two-unit-cells thick.Comment: 5 pages, 4 figure
Electronic properties of single-layer tungsten disulfide on epitaxial graphene on silicon carbide
This work reports an electronic and micro-structural study of an appealing system for optoelectronics: tungsten disulphide (WS2) on epitaxial graphene (EG) on SiC(0001)
Unidirectional Nano-modulated Binding and Electron Scattering in Epitaxial Borophene
A complex interplay between the crystal structure and the electron behavior within borophene renders this material an intriguing 2D system, with many of its electronic properties still undiscovered. Experimental insight into those properties is additionally hampered by the limited capabilities of the established synthesis methods, which, in turn, inhibits the realization of potential borophene applications. In this multimethod study, photoemission spectroscopies and scanning probe techniques complemented by theoretical calculations have been used to investigate the electronic characteristics of a high-coverage, single-layer borophene on the Ir(111) substrate. Our results show that the binding of borophene to Ir(111) exhibits pronounced one-dimensional modulation and transforms borophene into a nanograting. The scattering of photoelectrons from this structural grating gives rise to the replication of the electronic bands. In addition, the binding modulation is reflected in the chemical reactivity of borophene and gives rise to its inhomogeneous aging effect. Such aging is easily reset by dissolving boron atoms in iridium at high temperature, followed by their reassembly into a fresh atomically thin borophene mesh. Besides proving electron-grating capabilities of the boron monolayer, our data provide comprehensive insight into the electronic properties of epitaxial borophene which is vital for further examination of other boron systems of reduced dimensionality