Spin-Polarized Scanning Tunneling Microscopy: Breakthroughs and Highlights

The principle of scanning tunneling microscopy, an imaging method with atomic resolution capability invented by Binnig and Rohrer in 1982, can be adapted for surface magnetism studies by using magnetic probe tips. The contrast mechanism of this so-called spin-polarized scanning tunneling microscopy, or SP-STM, relies on the tunneling magneto-resistance effect, i.e. the tip–sample distance as well as the differential conductance depend on the relative magnetic orientation of tip and sample. To illustrate the working principle and the unique capabilities of SP-STM, this compilation presents some key experiments which have been performed on various magnetic surfaces, such as the topological antiferromagnet Cr(001), a double-layer of Fe which exhibits a stripe- domain pattern with about 50 nm periodicity, and the Mn monolayer on W(110), where the combination of experiment and theory reveal an antiferromagnetic spin cycloid. Recent experimental results also demonstrate the suitability of SP-STM for studies of dynamic properties, such as the spin relaxation time of single magnetic nanostructures

Systematics of molecular self-assembled networks at topological insulators surfaces

The success of topological insulators (TI) in creating devices with unique functionalities is directly connected to the ability of coupling their helical spin states to well defined perturbations. However, up to now, TI-based heterostructures always resulted in very disordered interfaces, characterized by strong mesoscopic fluctuations of the chemical potential which make the spin-momentum locking ill-defined over length scales of few nanometers or even completely destroy topological states. These limitations call for the ability to control topological interfaces with atomic precision. Here, we demonstrate that molecular self-assembly processes driven by inherent interactions among the constituents offer the opportunity to create well-defined networks at TIs surfaces. Even more remarkably, we show that the symmetry of the overlayer can be finely controlled by appropriate chemical modifications. By analyzing the influence of the molecules on the TI electronic properties, we rationalize our results in terms of the charge redistribution taking place at the interface. Overall, our approach offers a precise and fast way to produce tailor-made nanoscale surface landscapes. In particular, our findings make organic materials ideal TIs counterparts, since they offer the possibility to chemically tune both electronic and magnetic properties within the same family of molecules, thereby bringing us a significant step closer towards an application of this fascinating class of materials.Comment: Nano Letters (2015

Energetic damage analysis regarding the fatigue of concrete

Due to the visco-elasto-plastic material behavior, the added energy to concrete specimens during fatigue tests is transformed into another form of energy. Besides the description of the energetic material behavior of concrete, the elastic and the plastic part of the energy as well as the dissipation energy are analyzed for different specimens. Especially the dissipation energy shows a correlation with the damage process as a result of the cyclic loading. Regarding this correlation, a new energetic damage model is introduced. With this model, a degree of damage during the tests and the development of the damage parameter over the load cycles can be determined. First tests with the developed model show good and plausible results. © 2020 fib. International Federation for Structural Concret

Coexistence of charge and ferromagnetic order in fcc Fe

Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe on Rh(001). Scanning tunneling microscopy and spectroscopy measurements reveal periodic charge order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunneling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modeled within an effective Landau theory including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena

Design eines Multiskalen-Algorithmus zur reaktiven Prozess- und Ablaufplanung

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Benzo[c][2,7]naphthyridine-5-yl-amines and Benzo[h][1,6]naphthyridine-5-yl-amines

Bei der Umsetzung von 2-Nitrobenzaldehyd mit Methylpropiolat und Ammoniumacetat in Eisessig wurden das 1,4-Dihydropyridin (DHP) 2,6-Dinor-nifedipin und als Nebenprodukt das isomere racemische 1,2-DHP gebildet. Die DHP wurden sowohl chemisch als auch durch anodische Oxidation an der rotierenden Platinelektrode mittels Differenz-Puls-Voltammetrie zu den entsprechenden Pyridinen dehydriert. Die photochemische Umsetzung der DHP lieferte die Nitrosophenylpyridin-Derivate. Aus den Dehydrierungs- und Photoprodukten wurden die tricyclischen Hydroxamsäuren vom Benzo[c][2,7]naphthyridin- und Benzo[h][1,6]naphthyridin-Typ synthetisiert. Die Desoxygenierung der Hydroxamsäuren führte zu den entsprechenden Lactamen, deren Umsetzung mit Phosphoroxychlorid zu den in 5-Position chlorierten Trizyklen führte, die als Edukte zur Darstellung von potentiellen Antimalariamitteln dienten. Die 5-Chlorbenzonaphthyridine wurden mit der Novaldiaminbase, mit sekundären Aminen sowie mit primären aromatischen Aminen zur Bildung von Amidinen umgesetzt. Die dargestellten Hydroxamsäuren wurden auf Hemmung von Lipoxygenasen und Cyclooxygenasen getestet.The reaction of 2-nitrobenzaldehyde with methyl propiolate and ammonium acetate in glacial acetic acid yielded the 1,4-dihydropyridine (DHP) 2,6-dinor-nifedipine and as a by-product the isomeric racemic 1,2-dihydropyridine. The DHP were dehydrogenated both chemically and by anodic oxidation using a rotating platinum electrode by means of differential pulse voltammetry affording the corresponding pyridines. Irradiation of the DHP with UV-A light formed the nitrosophenyl-pyridines. Products by dehydrogenation and irradiation were transformed to hydroxamic acids of the benzo[c][2,7]naphthyridine and benzo[h][1,6]naphthyridine type. The lactames, obtained from the hydroxamic acids by desoxygenation, reacted with phosphoryl chloride to give 5-chlor substituted tricycles, representing educts for potential agents against malaria. Those tricycles reacted with the novaldiamine-base, secondary aliphatic amines and primary aromatic amines to give amidines. The inhibiting potential of the hydroxamic acids against lipoxygenases and cyclooxygenases were tested

Monolayer and bilayer pentacene on Cu(111)

The morphology and electronic structure of pentacene (Pn) deposited on Cu(111) was studied using scanning tunneling microscopy (STM) and spectroscopy (STS). Deposition of a multilayer followed by annealing to reduce coverage to a monolayer results in the formation of either of two unique phases: a 2D herringbone structure previously unobserved for any linear acene, or a 'random- tiling' structure. Coverage greater than a monolayer promotes the formation of a bilayer phase similar to that observed for Pn/Ag(111). STS shows that the electronic structure of the first layer is strongly modified due to its proximity to the substrate while the second layer exhibits nearly bulk-like electronic structure