52 research outputs found
Mapping spin-polarised transitions with atomic resolution
The coupling between Angstrom-sized electron probes and spin polarised
electronic transitions shows that the inelastically scattered probe is in a
mixed state containing electron vortices with non-zero orbital angular
momentum. These electrons create an asymmetric intensity distribution in energy
filtered diffraction patterns, giving access to maps of the magnetic moments
with atomic resolution. A feasibility experiment shows evidence of the
predicted effect. Potential applications are column-by-column maps of magnetic
ordering, and the creation of Angstrom-sized free electrons with orbital
angular momentum by inelastic scattering in a thin ferromagnetic foil
In-situ TEM annealing of amorphous Fe-24at.%W coatings and the effect of crystallization on hardness
This paper describes the crystallization which occurs upon annealing of an amorphous Fe-24at.%W coatings, electrodeposited from a glycolate-citrate plating bath. A combination of Differential Scanning Calorimetry and in-situ Transmission Electron Microscopy annealing is used to study the onset of crystallization of the amorphous coating. The in-situ TEM analyses reveal the formation of first crystallites after annealing at 400\ua0\ub0C for 30\ua0min. Upon a temperature increase to 500–600\ua0\ub0C, the crystallites develop into Fe-rich nanocrystals with ~ 40\ua0nm grain size. The nanocrystals are dispersed in the remaining amorphous Fe-W matrix, which results in the formation of a mixed nanocrystalline-amorphous structure. The observed crystallization can be held responsible for the increase in the hardness obtained upon annealing of Fe-24at.%W coatings. In fact, the hardness of the as-deposited material increases from 11 to 13\ua0GPa after annealing at 400\ua0\ub0C, and it reaches the maximum value of 16.5\ua0GPa after annealing at 600\ua0\ub0C
Preparation of Terpenoid-Invasomes with Selective Activity against S. aureus and Characterization by Cryo Transmission Electron Microscopy
Kaltschmidt B, Ennen I, Greiner J, et al. Preparation of Terpenoid-Invasomes with Selective Activity against S. aureus and Characterization by Cryo Transmission Electron Microscopy. Biomedicines. 2020;8(5): 105.Terpenoids are natural plant-derived products that are applied to treat a broad range of human diseases, such as airway infections and inflammation. However, pharmaceutical applications of terpenoids against bacterial infection remain challenging due to their poor water solubility. Here, we produce invasomes encapsulating thymol, menthol, camphor and 1,8-cineol, characterize them via cryo transmission electron microscopy and assess their bactericidal properties. While control- and cineol-invasomes are similarly distributed between unilamellar and bilamellar vesicles, a shift towards unilamellar invasomes is observable after encapsulation of thymol, menthol or camphor. Thymol- and camphor-invasomes show a size reduction, whereas menthol-invasomes are enlarged and cineol-invasomes remain unchanged compared to control. While thymol-invasomes lead to the strongest growth inhibition of S. aureus, camphor- or cineol-invasomes mediate cell death and S. aureus growth is not affected by menthol-invasomes. Flow cytometric analysis validate that invasomes comprising thymol are highly bactericidal to S. aureus. Notably, treatment with thymol-invasomes does not affect survival of Gram-negative E. coli. In summary, we successfully produce terpenoid-invasomes and demonstrate that particularly thymol-invasomes show a strong selective activity against Gram-positive bacteria. Our findings provide a promising approach to increase the bioavailability of terpenoid-based drugs and may be directly applicable for treating severe bacterial infections such as methicillin-resistant S. aureus
Reviewing Magnetic Particle Preparation: Exploring the Viability in Biosensing
Kappe D, Bondzio L, Swager J, et al. Reviewing Magnetic Particle Preparation: Exploring the Viability in Biosensing. Sensors. 2020;20(16): 4596.In this review article, we conceptually investigated the requirements of magnetic nanoparticles for their application in biosensing and related them to example systems of our thin-film portfolio. Analyzing intrinsic magnetic properties of different magnetic phases, the size range of the magnetic particles was determined, which is of potential interest for biosensor technology. Different e-beam lithography strategies are utilized to identify possible ways to realize small magnetic particles targeting this size range. Three different particle systems from 500 μm to 50 nm are produced for this purpose, aiming at tunable, vertically magnetized synthetic antiferromagnets, martensitic transformation in a single elliptical, disc-shaped Heusler Ni50Mn32.5Ga17.5 particle and nanocylinders of Co2MnSi-Heusler compound. Perspectively, new applications for these particle systems in combination with microfluidics are addressed. Using the concept of a magnetic on–off ratchet, the most suitable particle system of these three materials is validated with respect to magnetically-driven transport in a microfluidic channel. In addition, options are also discussed for improving the magnetic ratchet for larger particles
Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications
Ennen I, Kappe D, Rempel T, Glenske C, Hütten A. Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications. Sensors. 2016;16(6): 904.The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors
Magnetic tracking of protein synthesis in microfluidic environments - challenges and perspectives
Wegener M, Ennen I, Walhorn V, Anselmetti D, Hütten A, Dietz K-J. Magnetic tracking of protein synthesis in microfluidic environments - challenges and perspectives. Nanomaterials. 2019;9(4): 585.A novel technique to study protein synthesis is proposed that uses magnetic nanoparticles in combination with microfluidic devices to achieve new insights into translational regulation. Cellular protein synthesis is an energy-demanding process which is tightly controlled and is dependent on environmental and developmental requirements. Processivity and regulation of protein synthesis as part of the posttranslational nano-machinery has now moved back into the focus of cell biology, since it became apparent that multiple mechanisms are in place for fine-tuning of translation and conditional selection of transcripts. Recent methodological developments, such as ribosome foot printing, propel current research. Here we propose a strategy to open up a new field of labelling, separation, and analysis of specific polysomes using superparamagnetic particles following pharmacological arrest of translation during cell lysis and subsequent analysis. Translation occurs in polysomes, which are assemblies of specific transcripts, associated ribosomes, nascent polypeptides, and other factors. This supramolecular structure allows for unique approaches to selection of polysomes by targeting the specific transcript, ribosomes, or nascent polypeptides. Once labeled with functionalized superparamagnetic particles, such assemblies can be separated in microfluidic devices or magnetic ratchets and quantified. Insights into the dynamics of translation is obtained through quantifying large numbers of ribosomes along different locations of the polysome. Thus, an entire new concept for in vitro, ex vivo, and eventually single cell analysis will be realized and will allow for magnetic tracking of protein synthesis
Role of NiO in the nonlocal spin transport through thin NiO films on Y3Fe5 O12
In spin-transport experiments with spin currents propagating through an antiferromagnetic (AFM) material, the antiferromagnet is mainly treated as a passive spin conductor not generating nor adding any spin current to the system. The spin current transmissivity of the AFM NiO is affected by magnetic fluctuations, peaking at the Néel temperature and decreasing by lowering the temperature. To study the role of antiferromagnetism in local and nonlocal spin-transport experiments, we send spin currents through NiO of various thicknesses placed on Y3Fe5O12. The spin currents are injected either electrically or by thermal gradients and measured at a wide range of temperatures and magnetic field strengths. The transmissive role is reflected in the sign change of the local electrically injected signals and the decrease in signal strength of all other signals by lowering the temperature. The thermally generated signals, however, show an additional upturn below 100K that is unaffected by an increased NiO thickness. A change in the thermal conductivity could affect these signals. The temperature and magnetic field dependence are similar to those for bulk NiO, indicating that NiO itself contributes to thermally induced spin currents
Oriented attachment explains cobalt ferrite nanoparticle growth in bioinspired syntheses
Oriented attachment has created a great debate about the description of crystal growth throughout the last decade. This aggregationbased
model has successfully described biomineralization processes as well as forms of inorganic crystal growth, which could not
be explained by classical crystal growth theory. Understanding the nanoparticle growth is essential since physical properties, such
as the magnetic behavior, are highly dependent on the microstructure, morphology and composition of the inorganic crystals. In this
work, the underlying nanoparticle growth of cobalt ferrite nanoparticles in a bioinspired synthesis was studied. Bioinspired
syntheses have sparked great interest in recent years due to their ability to influence and alter inorganic crystal growth and therefore
tailor properties of nanoparticles. In this synthesis, a short synthetic version of the protein MMS6, involved in nanoparticle formation
within magnetotactic bacteria, was used to alter the growth of cobalt ferrite. We demonstrate that the bioinspired nanoparticle
growth can be described by the oriented attachment model. The intermediate stages proposed in the theoretical model,
including primary-building-block-like substructures as well as mesocrystal-like structures, were observed in HRTEM measurements.
These structures display regions of substantial orientation and possess the same shape and size as the resulting discs. An
increase in orientation with time was observed in electron diffraction measurements. The change of particle diameter with time
agrees with the recently proposed kinetic model for oriented attachmen
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Density-Dependence of Surface Transport in Tellurium-Enriched Nanograined Bulk Bi2Te3
Three-dimensional topological insulators (3D TI) exhibit conventional parabolic bulk bands and protected Dirac surface states. A thorough investigation of the different transport channels provided by the bulk and surface carriers using macroscopic samples may provide a path toward accessing superior surface transport properties. Bi2Te3 materials make promising 3D TI models; however, due to their complicated defect chemistry, these materials have a high number of charge carriers in the bulk that dominate the transport, even as nanograined structures. To partially control the bulk charge carrier density, herein the synthesis of Te-enriched Bi2Te3 nanoparticles is reported. The resulting nanoparticles are compacted into nanograined pellets of varying porosity to tailor the surface-to-volume ratio, thereby emphasizing the surface transport channels. The nanograined pellets are characterized by a combination of resistivity, Hall- and magneto-conductance measurements together with (THz) time-domain reflectivity measurements. Using the Hikami-Larkin-Nagaoka (HLN) model, a characteristic coherence length of ≈200 nm is reported that is considerably larger than the diameter of the nanograins. The different contributions from the bulk and surface carriers are disentangled by THz spectroscopy, thus emphasizing the dominant role of the surface carriers. The results strongly suggest that the surface transport carriers have overcome the hindrance imposed by nanoparticle boundaries
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