102 research outputs found
Interplay of electronic structure and atomic ordering on surfaces: Momentum-resolved measurements of Cs atoms adsorbed on a Ag(111) substrate
Surface-state mediated interactions between adsorbates on surfaces can be
exploited for the fabrication of self-organized nanostructures such as
two-dimensional superlattices of adatoms. Using angle-resolved photoemission we
provide experimental evidence that these interactions can be drastically
modified by adsorbate-induced alterations in the surface potential barrier.
This, in turn, will cause significant changes in the ordering of the
adsorbates. For the studied case example of Cs adatoms on Ag(111) our
momentum-resolved measurements reveal the surface state Fermi wave vector to be
increased by as much as 100% for coverages around 0.03 ML. Our results
unravel the origin for the hitherto puzzling and unexpectedly small lattice
constant in the adatom superlattice observed for this system.Comment: 5 pages, 4 figure
Complete determination of molecular orbitals by measurement of phase symmetry and electron density.
Several experimental methods allow measuring the spatial probability density of electrons in atoms, molecules and solids, that is, the absolute square of the respective single-particle wave function. But it is an intrinsic problem of the measurement process that the information about the phase is generally lost during the experiment. The symmetry of this phase, however, is a crucial parameter for the knowledge of the full orbital information in real space. Here, we report on a key experiment that demonstrates that the phase symmetry can be derived from a strictly experimental approach from the circular dichroism in the angular distribution of photoelectrons. In combination with the electron density derived from the same experiment, the full quantum mechanical wave function can thus be determined experimentally
Direct Observation of Interband Spin-Orbit Coupling in a Two-Dimensional Electron System
We report the direct observation of interband spin-orbit (SO) coupling in a
two-dimensional (2D) surface electron system, in addition to the anticipated
Rashba spin splitting. Using angle-resolved photoemission experiments and
first-principles calculations on Bi/Ag/Au heterostructures we show that the
effect strongly modifies the dispersion as well as the orbital and spin
character of the 2D electronic states, thus giving rise to considerable
deviations from the Rashba model. The strength of the interband SO coupling is
tuned by the thickness of the thin film structures
Влияние состава газовой среды на параметры упрочнения стали при азотировании в тлеющем разряде
В работе были исследованы процессы азотирования стальных деталей машиностроения в плазме тлеющего разряда при замене традиционного аммиака на смесь газов, состоящую из азота, аргона и метана. Проведено сравнение параметров азотированных слоев в зависимости от состава рабочей среды и длительности обработки. Оценены технологические параметры и возможности применения метода в реальном производстве.In the work, the processes of nitriding of steel parts of machine building in a glow discharge plasma were investigated when traditional ammonia was replaced by a mixture of gases consist of nitrogen, argon and methane. The parameters of the nitrided layers are compared depending on the composition of the working environment and the processing time. The technological parameters and possibilities of application of the method in real production are estimated
Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6
The compound SmB is the best established realization of a topological
Kondo insulator, in which a topological insulator state is obtained through
Kondo coherence. Recent studies have found evidence that the surface of SmB
hosts ferromagnetic domains, creating an intrinsic platform for unidirectional
ballistic transport at the domain boundaries. Here, surface-sensitive X-ray
absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS)
spectra are measured at the Sm N-edge, and used to evaluate electronic
symmetries, excitations and temperature dependence near the surface of cleaved
samples. The XAS data show that the density of large-moment atomic multiplet
states on a cleaved surface grows irreversibly over time, to a degree that
likely exceeds a related change that has recently been observed in the surface
4f orbital occupation
Geometry-induced spin-filtering in photoemission maps from WTe surface states
We demonstrate that an important quantum material WTe exhibits a new type
of geometry-induced spin-filtering effect in photoemission, stemming from low
symmetry that is responsible for its exotic transport properties. Through the
laser-driven spin-polarized angle-resolved photoemission Fermi surface mapping,
we showcase highly asymmetric spin textures of electrons photoemitted from the
surface states of WTe. Such asymmetries are not present in the initial
state spin textures, which are bound by the time-reversal and crystal lattice
mirror plane symmetries. The findings are reproduced qualitatively by
theoretical modeling within the one-step model photoemission formalism. The
effect could be understood within the free-electron final state model as an
interference due to emission from different atomic sites. The observed effect
is a manifestation of time-reversal symmetry breaking of the initial state in
the photoemission process, and as such it cannot be eliminated, but only its
magnitude influenced, by special experimental geometries.Comment: 5 pages, 3 figure
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