162 research outputs found
Mid infrared near-field fingerprint spectroscopy of the 2D electron gas in LaAlO/SrTiO at low temperatures
Confined electron systems, such as 2D electron gases (2DEGs), 2D materials,
or topological insulators show great technological promise but their
susceptibility to defects often results in nanoscale inhomogeneities with
unclear origins. Scattering-type scanning near-field optical microscopy
(s-SNOM) is useful to investigate buried confined electron systems
non-destructively with nanoscale resolution, however, a clear separation of
carrier concentration and mobility was often impossible in s-SNOM. Here, we
predict a previously inaccessible characteristic "fingerprint" response of the
prototypical LaAlO/SrTiO 2DEG, and verify this using a state-of-the-art
tunable narrow-band laser in mid-infrared cryo-s-SNOM at 8 K. Our modelling
allows us to separate the influence of carrier concentration and mobility on
fingerprint spectra and to characterize 2DEG inhomogeneities on the nanoscale.
This spatially resolved information about the local electronic properties can
be used to identify the origin of inhomogeneities in confined electron systems,
making the s-SNOM fingerprint response a valuable tool for nanoelectronics and
quantum technology
Magnetic interlayer coupling between ferromagnetic SrRuO layers through a SrIrO spacer
A key element to tailor the properties of magnetic multilayers is the
coupling between the individual magnetic layers. In case of skyrmion hosting
multilayers, coupling of skyrmions across the magnetic layers is highly
desirable. Here the magnetic interlayer coupling was studied in epitaxial
all-oxide heterostructures of ferromagnetic perovskite SrRuO layers
separated by spacers of the strong spin-orbit coupling oxide SrIrO. This
combination of oxide layers is being discussed as a potential candidate system
to host N\'{e}el skyrmions. First order reversal curve (FORC) measurements were
performed in order to distinguish between magnetic switching processes of the
individual layers and to disentangle the signal of soft magnetic impurities
from the samples signal. Additionally, FORC investigations enabled to
determine whether the coupling between the magnetic layers is ferromagnetic or
antiferromagnetic. The observed interlayer coupling strength was weak for all
the heterostructures, with SrIrO spacers between 2 monolayers and 12
monolayers thick.Comment: 22 page
Origin of the hump anomalies in the Hall resistance loops of ultrathin SrRuO/SrIrO multilayers
The proposal that very small N\'eel skyrmions can form in SrRuO/SrIrO
epitaxial bilayers and that the electric field-effect can be used to manipulate
these skyrmions in gated devices strongly stimulated the recent research of
SrRuO heterostructures. A strong interfacial Dzyaloshinskii-Moriya
interaction, combined with the breaking of inversion symmetry, was considered
as the driving force for the formation of skyrmions in SrRuO/SrIrO
bilayers. Here, we investigated nominally symmetric heterostructures in which
an ultrathin ferromagnetic SrRuO layer is sandwiched between large
spin-orbit coupling SrIrO layers, for which the conditions are not
favorable for the emergence of a net interfacial Dzyaloshinskii-Moriya
interaction. Previously the formation of skyrmions in the asymmetric
SrRuO/SrIrO bilayers was inferred from anomalous Hall resistance loops
showing humplike features that resembled topological Hall effect contributions.
Symmetric SrIrO/SrRuO/SrIrO trilayers do not show hump anomalies in
the Hall loops. However, the anomalous Hall resistance loops of symmetric
multilayers, in which the trilayer is stacked several times, do exhibit the
humplike structures, similar to the asymmetric SrRuO/SrIrO bilayers.
The origin of the Hall effect loop anomalies likely resides in unavoidable
differences in the electronic and magnetic properties of the individual
SrRuO layers rather than in the formation of skyrmions
Departure from solid solution behavior in double perovskites
Mixed ionic electronic conducting oxides (MIEC) serve a plethora of electrochemical applications such as cathodes for solid oxide electrochemical cells and oxygen evolution reaction catalysts for water splitting. These applications rely to a large extent on the MIEC’s ability for electron and/or ion transfer across the solid/gas or solid/liquid interface. The efficacy of these reactions being governed by the surface defect chemistry and electronic structure, rational design of the (surface) chemistry presents itself as an auspicious path to tune these properties towards optimal device performance.
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Crystal-facet-dependent surface transformation dictates the oxygen evolution reaction activity in lanthanum nickelate
Electrocatalysts are the cornerstone in the transition to sustainable energy technologies and chemical processes. Surface transformations under operation conditions dictate the activity and stability. However, the dependence of the surface structure and transformation on the exposed crystallographic facet remains elusive, impeding rational catalyst design. We investigate the (001), (110) and (111) facets of a LaNiO3−δ electrocatalyst for water oxidation using electrochemical measurements, X-ray spectroscopy, and density functional theory calculations with a Hubbard U term. We reveal that the (111) overpotential is ≈ 30−60 mV lower than for the other facets. While a surface transformation into oxyhydroxide-like NiOO(H) may occur for all three orientations, it is more pronounced for (111). A structural mismatch of the transformed layer with the underlying perovskite for (001) and (110) influences the ratio of Ni2+ and Ni3+ to Ni4+ sites during the reaction and thereby the binding energy of reaction intermediates, resulting in the distinct catalytic activities of the transformed facets.</p
Defect-control of conventional and anomalous electron transport at complex oxide interfaces
Using low-temperature electrical measurements, the interrelation between electron transport, magnetic properties, and ionic defect structure in complex oxide interface systems is investigated, focusing on NdGaO3/SrTiO3 (100) interfaces. Field-dependent Hall characteristics (2–300 K) are obtained for samples grown at various growth pressures. In addition to multiple electron transport, interfacial magnetism is tracked exploiting the anomalous Hall effect (AHE). These two properties both contribute to a nonlinearity in the field dependence of the Hall resistance, with multiple carrier conduction evident below 30 K and AHE at temperatures ≲10  K. Considering these two sources of nonlinearity, we suggest a phenomenological model capturing the complex field dependence of the Hall characteristics in the low-temperature regime. Our model allows the extraction of the conventional transport parameters and a qualitative analysis of the magnetization. The electron mobility is found to decrease systematically with increasing growth pressure. This suggests dominant electron scattering by acceptor-type strontium vacancies incorporated during growth. The AHE scales with growth pressure. The most pronounced AHE is found at increased growth pressure and, thus, in the most defective, low-mobility samples, indicating a correlation between transport, magnetism, and cation defect concentratio
Species identification in heat processed meat products
In this work, species-specific PCR techniques were developed and optimized to identify pork, poultry and cow species in Frankfurt sausages. For pork and poultry, which are the most frequently used meats in Frankfurters, reference binary samples (pork in poultry and poultry in pork) were prepared in the laboratory. In both cases, the established conditions allowed the detection of levels as low as 0.1% of added pork/poultry meat. Real-time PCR assays based on the measurement of fluorescence increments using SYBR Green I dye were used for quantitative purposes. Several samples were acquired in the retail market and tested for their label compliance. Results showed 3 mislabelled samples regarding cow species and 2 for poultry species. Although the qualitative results showed the undeclared presence of pork meat in 2 poultry sausages samples, quantitative results showed levels < 0.1%. These low levels are probably not related to fraudulent practices, but possibly due to cross-contaminations during industrial processing
El Ocaso de los dioses
De cada obra s'ha digitalitzat un programa sencer. De la resta s'han digitalitzat les parts que són diferents.Empresa: José F. ArquerOrquestra Simfònica del Gran Teatre del Liceu, director Laszlo HalaszPrograma de la temporada d'hivern 1956-1957 corresponent a la representació de El Ocaso de los Dioses, òpera d'un pròleg i tres actes amb música i llibret de Richard Wagne
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