18 research outputs found
Überörtliche Biotopverbundplanungen : eine planerische Grundlage für den Straßenbau
Anhand von drei OU im Zuge von Bundesstraßen wird dargestellt, wie die überörtliche Biotopverbundplanung dazu beitragen kann, Eingriffe nicht nur punktuell-lokal, sondern im größeren Zusammenhang der Biotopverbundsysteme zu bewerten und zu bewältigen. Die Biotopverbundplanung stellt einen Ideen- und Flächenpool bereit, Maßnahmen aus nicht ausgleichbaren Eingriffen sinnvoll zu konzentrieren und mit bestmöglicher Wirkung für Natur und Landschaft umzusetzen. Die Straßenbauverwaltung greift die Vorschläge der Biotopverbundplanung gern auf, wie weitere, bereits realisierte Vorhaben zeigen. Allerdings darf man nicht übersehen, dass Kompensationsmaßnahmen für Eingriffe an anderer Stelle bestenfalls dazu beitragen, die Qualität der Biotopverbundsysteme auf dem gegenwärtigen Stand zu erhalten
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Correlation of Work Function and Conformation of C80 Endofullerenes on h-BN/Ni(111)
Change of conformation or polarization of molecules is an expression of their functionality. If the two correlate, electric fields can change the conformation. In the case of endofullerene single-molecule magnets the conformation is linked to an electric and a magnetic dipole moment, and therefore magnetoelectric effects are envisoned. The interface system of one monolayer Sc2TbN@C80 on hexagonal boron nitride (h-BN) on Ni(111) has been studied. The molecular layer is hexagonally close packedbut incommensurate. With photoemission the polarization and the conformation of the molecules are addressed by the work function and angular intensity distributions. Valence band photoemission (ARPES) shows a temperature-induced energy shift of the C80 molecular orbitals that is parallel to a change in work function of 0.25 eV without charging the molecules. ARPES indicates a modification in molecular conformations between 30 and 300 K. This order–disorder transition involves a polarization change in the interface and is centered at 125 K as observed with high-resolution X-ray photoelectron spectroscopy (XPS). The temperature dependence is described with a thermodynamic model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. All experimental results are supported by density functional theory (DFT)
Circular Dichroism in Cu Resonant Auger Electron Diffraction
Upon a core level excitation by circularly polarized light (CPL), the angular momentum of light, i.e. helicity, is transferred to the emitted photoelectron. This phenomenon can be confirmed by the parallax shift measurement of the forward focusing peak (FFP) direction in a stereograph of the atomic arrangement. The angular momentum of the emitted photoelectron is the sum of CPL helicity and the magnetic quantum number (MQN) of the initial state that define the quantum number of the core hole final state. The core hole may decay via Auger electron emission, where in this two electron process the angular momentum has to be conserved as well. Starting from a given core hole, different Auger decay channels with different final state energies and angular momenta of the emitted Auger electrons may be populated. Here we report the observation and formulation of the angular momentum transfer of light to Auger electrons, instead of photoelectrons. We measured photoelectron and Auger electron intensity angular distributions from Cu(111) and Cu(001) surfaces as a function of photon energy and photoelectron kinetic energy. By combining Auger electron spectroscopy with the FFP shift measurements at absorption threshold, element- and MQN-specific hole states can be generated in the valence band
Surface Aligned Magnetic Moments and Hysteresis of an Endohedral Single-Molecule Magnet on a Metal
The interaction between the endohedral unit in the single-molecule magnet
DyScN@C and a rhodium (111) substrate leads to alignment of the Dy
4 orbitals. The resulting orientation of the DyScN plane parallel to the
surface is inferred from comparison of the angular anisotropy of x-ray
absorption spectra and multiplet calculations in the corresponding ligand
field. The x-ray magnetic circular dichroism (XMCD) is also angle dependent and
signals strong magnetocrystalline anisotropy. This directly relates geometric
and magnetic structure. Element specific magnetization curves from different
coverages exhibit hysteresis at a sample temperature of K. From the
measured hysteresis curves we estimate the zero field remanence life-time
during x-ray exposure of a sub-monolayer to be about 30 seconds.Comment: 5 pages, 4 figure
Steep-Slope Threshold Switch Enabled by Pulsed-Laser-Induced Phase Transformation
Super-steep two-terminal electronic devices using NbO2, which abruptly switch from insulator to metal at a threshold voltage (Vth), offer diverse strategies for energy-efficient and high-density device architecture to overcome fundamental limitation in current electronics. However, the tight control of stoichiometry and high-temperature processing limit practical implementation of NbO2 as a component of device integration. Here, we demonstrate a facile room-temperature process that uses solid-solid phase transformation induced by pulsed laser to fabricate NbO2-based threshold switches. Interestingly, pulsed laser annealing under a reducing environment facilitates a two-step nucleation pathway (a-Nb2O5 → o-Nb2O5-δ → t-NbO2) of the threshold-enabled NbO2 phase mediated by oxygen vacancies in o-Nb2O5-δ. The laser-annealed devices with embedded NbO2 crystallites exhibit excellent threshold device performance with low off-current and high on/off current ratio. Our strategy that exploits the interactions of pulsed lasers with multivalent metal oxides can guide the development of a rational route to achieve NbO2-based threshold switches that are compatible with current semiconductor fabrication technology. © 2019 American Chemical Societ
Enhanced Berry Curvature Dipole and Persistent Spin Texture in the Bi(110) Monolayer
Nonvanishing Berry curvature dipole (BCD) and persistent spin texture (PST) are intriguing physical manifestations of electronic states in noncentrosymmetric 2D materials. The former induces a nonlinear Hall conductivity while the latter offers a coherent spin current. Based on density-functional-theory (DFT) calculations, we demonstrate the coexistence of both phenomena in a Bi(110) monolayer with a distorted phosphorene structure. Both effects are concurrently enhanced due to the strong spin-orbit coupling of Bi while the structural distortion creates internal in-plane ferroelectricity with inversion asymmetry. We further succeed in fabricating a Bi(110) monolayer in the desired phosphorene structure on the NbSe2 substrate. Detailed atomic and electronic structures of the Bi(110)/NbSe2 heterostructure are characterized by scanning tunneling microscopy/spectroscopy and angle-resolved-photoemission spectroscopy. These results are consistent with DFT calculations which indicate the large BCD and PST are retained. Our results suggest the Bi(110)/NbSe2 heterostructure as a promising platform to exploit nonlinear Hall and coherent spin transport properties together.11Ysciescopu
Parallel and antiparallel angular momentum transfer of circularly polarized light to photoelectrons and Auger electrons at the Ni L3 absorption threshold
We report the investigation of the angular momentum transfer of light to photoelectrons and Auger electrons at the Ni L3 absorption threshold. Upon core-level excitation by circularly polarized light, the angular momentum of light, or helicity, is transferred to the emitted photoelectron. The angular momentum of the emitted photoelectron (mf) is the sum of the helicity (σ) and the orbital magnetic quantum number of the initial state (mi). Here the quantization axis was defined as the direction along the incident light. This can be measured by the parallax shift of the forward focusing peak (FFP) direction in the photoelectron intensity angular distribution. At the absorption threshold, the excited core-level electron is promoted to a conduction-band state and the angular momentum of the light is partially transferred to Auger electrons. We measured photoelectron and Auger electron intensity angular distributions from the Ni(111) surface at the L3 absorption threshold. We observed a significant angular circular dichroism of the [101] FFP for the L3M4,5M4,5 Auger electrons. Furthermore, we discovered non-negligible reversal angular circular dichroism contrasts for the triplet components in the case of the L3M2,3M4,5 Auger electrons, suggesting that the angular momentum of light was transferred to the emitted electron in the antiparallel way
Correlation of Work Function and Conformation of C80 Endofullerenes on h‐BN/Ni(111)
Abstract Change of conformation or polarization of molecules is an expression of their functionality. If the two correlate, electric fields can change the conformation. In the case of endofullerene single‐molecule magnets the conformation is linked to an electric and a magnetic dipole moment, and therefore magnetoelectric effects are envisoned. The interface system of one monolayer Sc2TbN@C80 on hexagonal boron nitride (h‐BN) on Ni(111) has been studied. The molecular layer is hexagonally close packedbut incommensurate. With photoemission the polarization and the conformation of the molecules are addressed by the work function and angular intensity distributions. Valence band photoemission (ARPES) shows a temperature‐induced energy shift of the C80 molecular orbitals that is parallel to a change in work function of 0.25 eV without charging the molecules. ARPES indicates a modification in molecular conformations between 30 and 300 K. This order–disorder transition involves a polarization change in the interface and is centered at 125 K as observed with high‐resolution X‐ray photoelectron spectroscopy (XPS). The temperature dependence is described with a thermodynamic model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. All experimental results are supported by density functional theory (DFT)