Electrical determination of the valence-band discontinuity in HgTe-CdTe heterojunctions

Current-voltage behavior is studied experimentally in a Hg0.78Cd0.22Te-CdTe-Hg0.78Cd0.22Te heterostructure grown by molecular beam epitaxy. At temperatures above 160 K, energy-band diagrams suggest that the dominant low-bias current is thermionic hole emission across the CdTe barrier layer. This interpretation yields a direct determination of 390±75 meV for the HgTe-CdTe valence-band discontinuity at 300 K. Similar analyses of current-voltage data taken at 190–300 K suggest that the valence-band offset decreases at low temperatures in this heterojunction

Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton

Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin film grown on Kapton\textregistered{} has been studied by ferromagnetic resonance and glued on curved sample carrier with various radii. The results reported in this letter show that the magnetic anisotropy is drastically changed in this system by bending the thin films. This effect is attributed to the interfacial strain transmission from the substrate to the film and to the magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to determine the in-plane magnetostriction coefficient of the film, leading to a value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed.Comment: 4 pages, 4 figure

Magnetization dynamics of elastically strained nanostructures studied by coupled micromagnetic-mechanical simulations

Elastically strained ferromagnetic objects have been studied by coupled micromagnetic-mechanical numerical simulations. Both temporal evolution of the magnetization and modal frequency analysis of ferromagnetic thin films and arrays of nanostructures are presented. For this purpose, we have numerically coupled the micromagnetic equations (including magnetoelastic effects) to the ones of solid mechanics by including periodic boundary conditions. Our approach has been evaluated first on an elastically strained thin film and validated by performing in situ ferromagnetic resonance experiments. We have undertaken simulations on nanostructured arrays (modulated arrays of nanowires) and show that the heterogeneity of the strain fields and magnetic mode profiles of those strained nanostructures induce significative disparities in the magnetic mode energies, allowing applications to be foreseen where one could control in a differentiated way the spin-wave energies as a function of the applied elastic strains

Structural and magnetic properties of Co2MnSi thin films

Co2MnSi (CMS) films of different thicknesses (20, 50, and 100 nm) were grown by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays diffraction (XRD) study shows that, in all the samples, the cubic 〈110〉 CMS axis is normal to the substrate and that six well defined preferential in-plane orientations are present. Static and dynamic magnetic properties were investigated using vibrating sample magnetometry (VSM) and microstrip line ferromagnetic resonance (MS-FMR), respectively. From the resonance measurements versus the direction and the amplitude of an applied magnetic field, most of the magnetic parameters are derived, i.e.: the magnetization, the gyromagnetic factor, the exchange stiffness coefficient, and the magnetic anisotropy terms. The in-plane anisotropy results from the superposition of two terms showing a twofold and a fourfold symmetry, respectively. The observed behavior of the hysteresis loops is in agreement with this complex form of the in-plane anisotropy.International audienceCo2MnSi (CMS) films of different thicknesses (20, 50, and 100 nm) were grown by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays diffraction (XRD) study shows that, in all the samples, the cubic 〈110〉 CMS axis is normal to the substrate and that six well defined preferential in-plane orientations are present. Static and dynamic magnetic properties were investigated using vibrating sample magnetometry (VSM) and microstrip line ferromagnetic resonance (MS-FMR), respectively. From the resonance measurements versus the direction and the amplitude of an applied magnetic field, most of the magnetic parameters are derived, i.e.: the magnetization, the gyromagnetic factor, the exchange stiffness coefficient, and the magnetic anisotropy terms. The in-plane anisotropy results from the superposition of two terms showing a twofold and a fourfold symmetry, respectively. The observed behavior of the hysteresis loops is in agreement with this complex form of the in-plane anisotropy

Einsatz bioanalytischer Systeme bei der industriellen Produktion von Pharmaaminosäuren

Aminosäuren finden in den verschiedensten Bereichen vielfältigen Einsatz. Hauptanwendungsgebiete sind die Nahrungsmittel- (50%), Futtermittel (30%)- und pharmazeutische (20%) Industrie. In der pharmazeutischen Industrie werden Aminosäuren höchster Reinheit benötigt. Ein sehr wichtiges Beispiel ist die Verwendung für prä- oder postoperative parenterale Ernährung. In der Kosmetikindustrie dienen Aminosäuren als Ausgangssubstanzen für die Herstellung hochwertiger Hautcremes. Für die Gewinnung von Aminosäuren stehen diverse großtechnische Verfahren zur Verfügung: die Extraktion aus nachwachsenden Rohstoffen, die fermentative Gewinnung, die chemische Synthese und die Biotransformation. Über diese Verfahren wird eine geschätzte Jahresproduktion von weltweit ca. 3. Mrd. Tonnen hergestellt. Bei der AMINO GmbH werden Aminosäuren für den pharmazeutischen Markt aus nachwachsenden Rohstoffen wie Zuckerrübenmelasse über chromatographische Verfahren und Biotransformationen (enzymatische Katalyse) gewonnen. Hierbei ist eine On-line-Prozesskontrolle unabdingbar. Durch die optimierte Kontrolle und Führung des Bioprozesses können Ressourcen eingespart werden. Daraus ergeben sich direkt Umweltentlastungen und Kostenersparnisse. Mit den bisher erzielten Ergebnissen kann eine 20% höhere Produktkonzentration erreicht werden. Dieses entspricht – gerechnet auf die nachfolgenden Aufarbeitungsschritte – einer Ersparnis von 200 bis 300 t Dampf pro Jahr (20% der Produkt spezifischen Energiekosten). Ebenfalls einsparen lassen sich bis zu 2000 m3 Abwasser (entsprechend 0,4 t COD) pro Jahr. Letztendlich ist es das Ziel mit Hilfe der bioanalytischen Verfahren pro Jahr 3,5 t Serin und 0,5 t Indol durch eine 30% höhere Produktausbeute einsparen zu können. Es zeigt sich somit, dass der Einsatz moderner bioanalytischer Verfahren wie der 2-D-Fluoreszenzspektroskopie durchaus zu einer Verbesserung der ökonomischen als auch der ökologischen Faktoren eines industriellen Prozesses führen kann

Static and dynamic magnetic properties of epitaxial Fe1.7Ge thin films grown on Ge(111)

We have studied the magnetic properties of thin epitaxial hexagonal Fe1.7Ge films grown on Ge(111) substrates by molecular beam epitaxy. For all samples, X-ray diffraction revealed an excellent epitaxy of the Fe1.7Ge films, with crystallographic [11 (2) over bar0] and [1 (1) over bar 00] axes lying in the sample plane. The static magnetic properties were studied by Magneto-Optical Kerr Effect (MOKE) at room temperature. The dynamic magnetic properties at room temperature were investigated by Micro-Strip Ferromagnetic Resonance (MS-FMR). The frequency dependence of the spectra versus the orientation of the applied in-plane magnetic field shows that the contribution of the in-plane anisotropy to the magnetic energy density consists in two distinct terms exhibiting a twofold and a sixfold symmetry, respectively. The amplitude of the sixfold anisotropy constant is an increasing function of the film thickness. The observed angular dependence of the MOKE reduced remanent magnetization is described using a coherent rotation model. A good agreement is observed between the in-plane anisotropy values derived from MS-FMR and those obtained with MOKE Transverse Bias Initial Inverse Susceptibility and Torque data. (C) 2012 American Institute of Physics. [doi:10.1063/1.3672396

Direct observation of threading dislocations in GaN by high-resolution Z-contrast imaging

Wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers. One interesting issue concerning GaN is that the material is relatively insensitive to the presence of a density of dislocations which is six orders of magnitude higher than that for III-V arsenide and phosphide based LEDs. Although it is well known that these dislocations originate at the film-substrate interface during film growth, thread through the whole epilayer with line direction along and are perfect dislocations with Burgers vectors of a, c, or c+a, the reason why they have such a small effect on the properties of GaN is unclear. To develop a fundamental understanding of the properties of these dislocations, the core structures are studied here by high resolution Z-contrast imaging in a 300kV VG HB603 scanning transmission electron microscope (STEM) with a resolution of 0.13 nm. As the Z-contrast image is a convolution between the probe intensity profile and the specimen object function, it is possible to obtain more detailed information on the specimen object function, i.e. the structure, through maximum entropy analysis (the maximum entropy technique produces the ``most likely`` object function which is consistent with the image)