Previous investigations have shown that an array of novel CMR-B-scalar sensors based on the colossal magnetoresistance effect can be used to measure the magnetic field distribution in the vicinity of the rails of a railgun. However, the data obtained suffered from electromagnetic interference. Therefore, the measurement system was considerably improved to obtain better signal quality. In this paper, the results obtained during the dynamic operation of the ISL railgun RAFIRA are presented. The magnetic field distribution in the vicinity of the rails was measured at different armature velocities. Additional information was obtained using high-speed camera snapshots. The experimental results are compared with simulations performed with the finite element code COMSOL Multiphysics. In particular, the influence of the armature current on the measurements is discussed. It is concluded that the magnetic field distribution in the vicinity of the rails clearly indicates an increased current concentration in the rear part of the armature–rail contact interface. Moreover, the current concentration depends on the speed of the armature. Velocity-dependent skin depths at the surface of aluminum (Dural) rails for projectile velocities ranging between 750 and 1500 m/s are investigated.
We present the ptychography reconstruction of the x-ray beam formed by nanofocusing lenses (NFLs) containing a number of phase singularities (vortices) in the vicinity of the focal plane. As a test object Siemens star pattern was used with the finest features of 50 nm for ptychography measurements. The extended ptychography iterative engine (ePIE) algorithm was applied to retrieve both complex illumination and object functions from the set of diffraction patterns. The reconstruction revealed the focus size of 91.4$\pm$1.1 nm in horizontal and 70$\pm$0.3 nm in vertical direction at full width at half maximum (FWHM). The complex probe function was propagated along the optical axis of the beam revealing the evolution of the phase singularities.
NanoMAX is the first hard X-ray nanoprobe beamline at the MAX IV laboratory. It utilizes the unique properties of the world's first operational multi-bend achromat storage ring to provide an intense and coherent focused beam for experiments with several methods. In this paper we present the beamline optics design in detail, show the performance figures, and give an overview of the surrounding infrastructure and the operational diffraction endstation.
X-ray Bragg ptychography (XBP) is an experimental technique for high-resolution strain mapping in a single nano- and mesoscopic crystalline structures. In this work we discuss the conditions that allow direct interpretation of the ptychographic reconstructions in terms of the strain distribution obtained from the two dimensional (2D) XBP. Simulations of the 2D XBP experiments under realistic experimental conditions are performed with a model of InGaN/GaN core-shell nanowire with low (1%) and high (30%) Indium concentrations in the shell.
Semiconductor nanowire networks are essential elements for a variety of gate-tunable quantum applications. Their relevance, however, depends critically on the material quality. In this work we study selective area growth (SAG) of highly lattice-mismatched InAs/In$_x$Ga$_{1-x}$As nanowires on insulating GaAs(001) substrates and address two key challenges: crystalline quality and compositional uniformity. We introduce optimization steps and show how misfit dislocations are guided away from the InAs active region and how Ga-In intermixing is kinetically limited with growth temperature. The optimization process leads to a more than twofold increase in electron mobility and shows an advancement toward realizing high quality gatable quantum wire networks.
Previous investigations showed that an array of novel CMR-B-scalar sensors based on the Colossal Magnetoresistance effect can be used to measure the magnetic field distribution in the vicinity of the rails of a railgun. However, the data obtained suffered from electromagnetic interference. Therefore, the measurement system was considerably improved with respect to the signal quality. In this publication the results obtained during the dynamic operation of the ISL railgun RAFIRA are presented. The magnetic field distribution in the vicinity of the rails was measured at different armature velocities. Additional information was obtained using high-speed camera snapshots. The experimental results are compared with simulations performed with the finite element code COMSOL Multiphysics. In particular, the influence of the armature current on the measurements is discussed. It is concluded that the magnetic field distribution in the vicinity of the rails clearly indicates an increased current concentration in the rear part of the armature-rail contact interface. Moreover, the current concentration depends on the speed of the armature. Velocity-dependent skin depths at the surface of aluminum (Dural) rails for projectile velocities ranging between 750 m/s and 1500 m/s are given.
Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$. This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures.
