New opportunities with spectro-interferometry and spectro-astrometry

Latest-generation spectro-interferometric instruments combine a milliarcsecond angular resolution with spectral capabilities, resulting in an immensely increased information content. Here, I present methodological work and results that illustrate the fundamentally new scientific insights provided by spectro-interferometry with very high spectral dispersion or in multiple line transitions (Brackett and Pfund lines). In addition, I discuss some pitfalls in the interpretation of spectro-interferometric data. In the context of our recent studies on the classical Be stars {\beta} CMi and {\zeta} Tau, I present the first position-velocity diagram obtained with optical interferometry and provide a physical interpretation for a phase inversion, which has in the meantime been observed for several classical Be-stars. In the course of our study on the Herbig B[e] star V921 Sco, we combined, for the first time, spectro-interferometry and spectro-astrometry, providing a powerful and resource-efficient way to constrain the spatial distribution as well as the kinematics of the circumstellar gas with an unprecedented velocity resolution up to R = {\lambda}/{\Delta}{\lambda} = 100,000. Finally, I discuss our phase sign calibration procedure, which has allowed us to calibrate AMBER differential phases and closure phases for all spectral modes, and derive from the gained experience science-driven requirements for future instrumentation projects.Comment: 15 pages, 7 figures, published in SPIE proceedings (http://dx.doi.org/10.1117/12.926801

The interferometric view of Herbig Ae/Be stars

articleIn this contribution I review how optical interferometry has contributed to shaping our understanding of the class of Herbig Ae/Be stars and of their associated circumstellar disks. I discuss the evidence for an optically-thin cavity in the inner few astronomical units (au) and a “puffed-up rim” near the dust sublimation radius and how these observations helped to establish the current generation of irradiated disk models. Multi-wavelength interferometric observations also revealed systems with clear signatures of grain growth and dynamically-cleared disk gaps, tracing important stages of disk evolution and of ongoing planet formation. I discuss the new opportunities provided by spectro-interferometry, which enables detailed studies on the gas distribution and velocity field on sub-au scales, resulting in constrains on the accretion properties of the system and the disk excitation structure. Finally, I outline some of the open questions and loose ends in current interferometric studies, and how these might point towards new disk physics.STFC Ernest RutherfordEU-funded Marie Sklodowska Curie CI

Development of a global IT charging model for BASF Group

With ‘GS Strategy 2025’ BASF Business Services GmbH was formed to centrally steer all IT related topics of BASF group. Thus, a global charging system has to be designed, which complies to international transfer price regulations and the strategy of BASF SE. This work project develops a charging system with a following evaluation. The direct charging system benefits from its cost transparency upsides but comes with a higher administrative effort due to volume-based charging. In contrast, the indirect charging system convinces because of easy handling, which is the result of the application of suitable allocation keys. Regarding the complex group structure of BASF SE with more than 300 legal entities in 80 countries, the lower administrative effort of the indirect charging system outweighs the benefits of the direct charging model and should be used by BASF group

On-surface synthesis of sandwich-molecular wires

In this thesis, the on-surface synthesis of sandwich-molecular wires — one-dimensional chains of metal atoms and cyclic molecules in an alternating sequence — is investigated. The use of a low-symmetry substrate for the global and uniaxial alignment of these wires is introduced, making them accessible to spatially averaging techniques. Further, the effects of different types of metal atoms and molecules on the organometallic synthesis and the resulting compounds are investigated as well as their influence on the electronic and magnetic properties. First, the synthesis of a single-crystal sheet of graphene (Gr) on the two-fold symmetric substrate Ir(110) is demonstrated, which is achieved by thermal decomposition of C2H4 at 1500 K. The structure of the Gr sheet is investigated using scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED). While the bare Ir(110) substrate is strongly reconstructed, the adsorbed Gr layer is found to suppress this reconstruction and large flat terraces are observed. The two-fold symmetry of the substrate is imprinted onto the moiré of Gr with Ir(110), resulting in a clear wave pattern of nm wavelength. A strong stripe-like modulation of the electronic properties and binding energies is observed. Complementary angleresolved photoemission spectroscopy (ARPES) measurements and ab initio calculations show, that the Gr is strongly bound to the substrate and the characteristic Dirac cone in the electronic band structure is absent. This anisotropic pattern is demonstrated to enable uniaxial alignment of sandwich-molecular wires and templated adsorption of aromatic molecules. Furthermore, Gr/Ir(110) allows the on-surface synthesis of transition-metal dichalcogenide layers and the growth of epitaxial layers on unreconstructed Ir(110) under the Gr sheet. Second, the introduced two-fold symmetric Gr/Ir(110) is used for the in-depth characterization of uniaxially aligned sandwich-molecular wires consisting of the lanthanide europium (Eu) and the eight-membered carbon ring cyclooctatetraene (Cot). Using STM and LEED, the alignment effect along the [001] direction of the Ir substrate is found to persist up to several multilayers of the organometallic film. The electronic band structure of the one-dimensional wires is investigated with ARPES. A flat band 1.85 eV below the Fermi energy is found, while no π-derived bands could be observed. Using complementary density-functional theory (DFT) calculations, X-ray photoelectron spectroscopy and by exchanging the Eu within the wires by the alkaline-metal barium (Ba), this flat band could be attributed to the localized Eu 4f states. By fitting the relative position of the 4f-derived band with respect to the lower-lying σ states in the DFT calculations to the ARPES measurements, the Hubbard U of the organometallic system is derived. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) are utilized to probe the magnetic behavior of the wire film at low temperatures. An electronic configuration of 4f7 is found with a resulting magnetic spin moment of 7 µB and an easy axis magnetization along the wires. Third, the on-surface synthesis of organometallic compounds containing the rare-earth metal thulium (Tm) and Cot is reported, which are characterized using STM, XAS/XMCD and thermal desorption spectroscopy. On undoped Gr/Ir(111), a disperse phase of TmCot monomers is observed for low coverages, which for high coverages coexists with an additional island phase. Complementary DFT calculations find that the monomers bind to the substrate through charge transfer with a Tm electronic configuration of 4f12. This configuration is confirmed using XMCD measurements and an out-of plane easy axis anisotropy of the resulting magnetic moments is observed. Intriguingly, the chemical reaction pathway during the on-surface synthesis can be changed through the suppression of charge transfer into Gr by n-doping of the substrate. As a result, islands of parallelly aligned sandwich-molecular wires are formed. It is found, that the average wire length can be controlled by changing the Tm/Cot flux ratio during the organometallic synthesis, going from small wire fragments to wires exceeding 100 formula units. Finally, the on-surface synthesis of metal–Cot sandwich-molecular wires is studied for metal atoms which are electronically similar to Eu and effects of modifications to the Cot ring as well as the growth on a metal oxide substrate are investigated using STM. Similar to Eu, also Ba and the rare-earth metal ytterbium (Yb) form sandwich-molecular wires on undoped Gr/Ir(111). In both cases, islands of interlocking and parallelly aligned wires of high crystalline quality are formed. Although the growth mechanism is the same as for Eu, differences in the morphology of the resulting islands are observed. The growth of sandwich-molecular wires consisting of rareearth metals and tetramethyl-Cot was studied. In the case of Eu islands of parallel wires are found, though at a higher growth temperature compared to the synthesis using Cot. The wire islands show a strong height modulation which is explained by the additional methyl groups. Furthermore, tetramethyl-Cot leads to a weaker interaction with the substrate. Lastly, polar Eu oxide on Ir(111) was used as substrate for the synthesis of Eu–Cot wires. Although the resulting wire islands are less ordered compared to the growth on Gr/Ir(111), they were still found to be phase pure. In the scientific appendix, the intercalation of Ba and Yb under Gr/Ir(111) is presented, both forming a (√3×√3)R30° intercalation layer (for Ba with respect to Gr, and for Yb with respect to Ir). The mass spectrum of the Cot molecule and the thermal desorption spectrum of a multilayer of Cot adsorbed to Gr/Ir(111) are shown, together with STM data of an adsorbed monolayer film of Cot at low temperatures. The mass spectra of tetramethyl-Cot and Dibenzo-Cot are presented, together with thermal desorption spectra of multilayers adsorbed on Gr/Ir(111) for both molecules. Finally, the STM data of an adsorbed monolayer of Dibenzo-Cot molecules on Gr/Ir(111) are presented