291 research outputs found
Evidence for a diamondlike electronic band structure of Si multilayers on Ag(111)
Silicon multilayers on Ag(111) have been suggested to exhibit the structure of silicene, a material that has been heralded as a novel basis for microelectronic applications. However, our angle-resolved photoemission spectra (ARPES) from silicon multilayers on Ag(111) and of the silver-induced reconstruction of Si(111) demonstrate, from the close match in the valence level band structures, that the films exhibit a sp3 diamondlike structure. This refutes the interpretation o silicon multilayers on Ag(111) as silicene, a conclusion that is strengthened by the observation from core level photoemission that significant silver segregation occurs to the surface of these layers
Facile Electron Transfer in Atomically Coupled Heterointerface for Accelerated Oxygen Evolution
An efficient and cost-effective approach for the development of advanced cata-lysts has been regarded as a sustainable way for green energy utilization. The general guideline to design active and efficient catalysts for oxygen evolution reaction (OER) is to achieve high intrinsic activity and the exposure of more density of the interfacial active sites. The heterointerface is one of the most attractive ways that plays a key role in electrochemical water oxidation. Herein, atomically cluster-based heterointerface catalysts with strong metal support interaction (SMSI) between WMn2O4 and TiO2 are designed. In this case, the WMn2O4 nanoflakes are uniformly decorated by TiO2 particles to create electronic effect on WMn2O4 nanoflakes as confirmed by X-ray absorption near edge fine structure. As a result, the engineered heterointerface requires an OER onset overpotential as low as 200 mV versus reversible hydrogen electrode, which is stable for up to 30 h of test. The outstanding performance and long-term durability are due to SMSI, the exposure of interfacial active sites, and accelerated reaction kinetics. To confirm the synergistic interaction between WMn2O4 and TiO2, and the modification of the electronic structure, high-resolution transmission electron microscopy (HR-TEM), X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) are used
An Artificially Lattice Mismatched Graphene/Metal Interface: Graphene/Ni/Ir(111)
We report the structural and electronic properties of an artificial
graphene/Ni(111) system obtained by the intercalation of a monoatomic layer of
Ni in graphene/Ir(111). Upon intercalation, Ni grows epitaxially on Ir(111),
resulting in a lattice mismatched graphene/Ni system. By performing Scanning
Tunneling Microscopy (STM) measurements and Density Functional Theory (DFT)
calculations, we show that the intercalated Ni layer leads to a pronounced
buckling of the graphene film. At the same time an enhanced interaction is
measured by Angle-Resolved Photo-Emission Spectroscopy (ARPES), showing a clear
transition from a nearly-undisturbed to a strongly-hybridized graphene
-band. A comparison of the intercalation-like graphene system with flat
graphene on bulk Ni(111), and mildly corrugated graphene on Ir(111), allows to
disentangle the two key properties which lead to the observed increased
interaction, namely lattice matching and electronic interaction. Although the
latter determines the strength of the hybridization, we find an important
influence of the local carbon configuration resulting from the lattice
mismatch.Comment: 9 pages, 3 figures, Accepted for publication in Phys. Rev.
Spin Selective Evolution of Zhang-Rice State in Binary Transition Metal Oxide
The Zhang-Rice (ZR) state is a strongly hybridized bound state formed by the
transition metal and oxygen atoms. The spin-fluctuations within the ZR state
are known to play an important role in high- superconductivity in
cuprates. Here, we employ a combination of angle-resolved photoemission
spectroscopy (ARPES), X-ray photoemission spectroscopy (XPS), and {\it ab
initio} embedded dynamical mean-field theory (eDMFT) to investigate the
influence of magnetic ordering on the spectral characteristics of the valence
band and Mn 2 core-level in MnO (001) ultrathin films. Our results
demonstrate that a complex spin-selective evolution of Mn 3O 2
hybridization develops due to the long-range antiferromagnetic (AFM) ordering.
This hybridization significantly alters the spectral shape and weight of the ZR
state. Specifically, in the AFM phase, we observed the sharpening of the ZR
state and band folding with the periodicity of the AFM unit cell of MnO(001).
We also demonstrated a strong connection between the spectral evolution of the
ZR state and the non-local screening channels of the photoexcited core holes.
Further, our detailed temperature-dependent study reveals the presence of
short-range antiferromagnetic correlations that exist at much higher
temperatures than . Such comprehensive studies showing the
evolution of the ZR state across the magnetic transitions and its implication
to the core-hole screening have never been reported in any 3 binary
transition metal oxides.Comment: 8 pages, 4 figure
Absence of Dirac cones in monolayer silicene and multilayer Si films on Ag(111)
Monolayer silicene and multilayer silicon films on Ag(111) have been the subject of many investigations within the last few years. For both systems, photoemission data have been interpreted in terms of linearly dispersing bands giving rise to the characteristic Dirac cone features, similar to graphene. Here we demonstrate, on the basis of angle-resolved valence band and core level photoemission data that this assignment is not correct. The bands previously attributed to states with Dirac fermion character are shown to derive from Ag(111) interface and bulk states in the silicene monolayer and from the well-known Ag-View the MathML source(3×3)R30°-Si(111) structure in Si multilayers. These results question the validity of the claim that graphene-like silicene and silicene multilayers are in fact formed on Ag(111)
Interfacing CrOx and CuS for synergistically enhanced water oxidation catalysis
The sluggish kinetics associated with the oxygen evolution reaction (OER) limits the sustainability of fuel production and chemical synthesis. Developing catalysts based on Earth abundant elements with a reasonable
strategy could solve the challenge. Here, we present a heterostructure built from CrOx and CuS whose interface
gives rise to the advent of new functionalities in catalytic activity. Using X-ray photoelectron and absorption
spectroscopies, we identified the multiple oxidation states and low coordination number of Cr metal in CrOx-CuS
heterostructure. Benefitting from these features, CrOx-CuS generates oxygen gas through water splitting with a
low over potential of 190 mV vs RHE at a current density of 10 mA cm− 2
. The catalyst shows no evident
deactivation after a 36-hours operation in alkaline medium. The high catalytic activity, inspired by first principles calculations, and long-time durability make it one of the most effective OER electrocatalysts
Indirect chiral magnetic exchange through Dzyaloshinskii–Moriya-enhanced RKKY interactions in manganese oxide chains on Ir(100)
Localized electron spins can couple magnetically via the Ruderman–Kittel–Kasuya–Yosida interaction even if their wave functions lack direct overlap. Theory predicts that spin–orbit scattering leads to a Dzyaloshinskii–Moriya type enhancement of this indirect exchange interaction, giving rise to chiral exchange terms. Here we present a combined spin-polarized scanning tunneling microscopy, angle-resolved photoemission, and density functional theory study of MnO_2 chains on Ir(100). Whereas we find antiferromagnetic Mn–Mn coupling along the chain, the inter-chain coupling across the non-magnetic Ir substrate turns out to be chiral with a 120° rotation between adjacent MnO_2 chains. Calculations reveal that the Dzyaloshinskii–Moriya interaction results in spin spirals with a periodicity in agreement with experiment. Our findings confirm the existence of indirect chiral magnetic exchange, potentially giving rise to exotic phenomena, such as chiral spin-liquid states in spin ice systems or the emergence of new quasiparticles
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