121 research outputs found
Co-sputtered MoRe thin films for carbon nanotube growth-compatible superconducting coplanar resonators
Molybdenum rhenium alloy thin films can exhibit superconductivity up to
critical temperatures of . At the same time, the films are
highly stable in the high-temperature methane / hydrogen atmosphere typically
required to grow single wall carbon nanotubes. We characterize molybdenum
rhenium alloy films deposited via simultaneous sputtering from two sources,
with respect to their composition as function of sputter parameters and their
electronic dc as well as GHz properties at low temperature. Specific emphasis
is placed on the effect of the carbon nanotube growth conditions on the film.
Superconducting coplanar waveguide resonators are defined lithographically; we
demonstrate that the resonators remain functional when undergoing nanotube
growth conditions, and characterize their properties as function of
temperature. This paves the way for ultra-clean nanotube devices grown in situ
onto superconducting coplanar waveguide circuit elements.Comment: 8 pages, 6 figure
Bioactivity and corrosion behavior of magnesium barrier membranes
In the current research, magnesium and its alloys have been intensively studied as resorbable implant materials. Magnesium materials combine their good mechanical properties with bioactivity, which make them interesting for guided bone regeneration and for the application as barrier membranes. In this study, the in vitro degradation behavior of thin magnesium films was investigated in cell medium and simulated body fluid. Three methods were applied to evaluate corrosion rates: measurements of (i) the gaseous volume evolved during immersion, (ii) volume change after immersion, and (iii) polarization curves. In this comparison, measurements of H2 development in Dulbecco's modified Eagle's medium showed to be the most appropriate method, exhibiting a corrosion rate of 0.5 mm·year−1. Observed oxide and carbon contamination have a high impact on controlled degradation, suggesting that surface treatment of thin foils is necessary. The bioactivity test showed positive results; more detailed tests in this area are of interest
Comparison of three bullet recovery systems
Comparing the marks left on questioned bullets to those left on reference bullets is the main aim of a firearm identification expertise. Thus, producing reference bullets with a questioned firearm is an essential step. Different kinds of system have been developed to safely recover bullets fired from questioned firearms. However, the performance of each system and its impact on traces left on the bullets have not been addressed.
Three bullet recovery systems – a horizontal water tank, a cotton tube and a recently designed fleece – were used to fire seven types of ammunition of various type, shape and casing. The bullets were then described and images of their surface were acquired with an automatic system to study the impact of each system on the bullets.
The water tank is the more efficient system in terms of quality of the marks. However, it cannot be used to fire every type of ammunition. Some of them, such those used by law enforcement, tend to be damaged with this system. A way to mitigate the problem is to use the cotton or the fleece-based systems, the latter being more universal. It requires a cleaning step to remove all the fibres from the surface of the bullet, but the marks left by the weapon are still of interest
Non-destructive low-temperature contacts to nanoribbon and nanotube quantum dots
Molybdenum disulfide nanoribbons and nanotubes are near-one dimensional
semiconductors with strong spin-orbit interaction, a nanomaterial highly
promising for quantum electronic applications. Here, we demonstrate that a
bismuth semimetal layer between the contact metal and this nanomaterial
strongly improves the properties of the contacts. Two-point resistances on the
order of are observed at room temperature. At cryogenic
temperature, Coulomb blockade is visible. The resulting stability diagrams
indicate a marked absence of trap states at the contacts and the corresponding
disorder, compared to previous devices using low-work function metals as
contacts. Single level quantum transport is observed at temperatures below
100mK.Comment: 7 pages, 5 figure
Spin current control of magnetism
Exploring novel strategies to manipulate the order parameter of magnetic
materials by electrical means is of great importance, not only for advancing
our understanding of fundamental magnetism, but also for unlocking potential
practical applications. A well-established concept to date uses gate voltages
to control magnetic properties, such as saturation magnetization, magnetic
anisotropies, coercive field, Curie temperature and Gilbert damping, by
modulating the charge carrier population within a capacitor structure. Note
that the induced carriers are non-spin-polarized, so the control via the
electric-field is independent of the direction of the magnetization. Here, we
show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be
reversibly modified by a spin current generated in Pt by the spin Hall effect.
The effect decreases with increasing Fe thickness, indicating that the origin
of the modification can be traced back to the interface. Uniquely, the change
in MCA due to the spin current depends not only on the polarity of the charge
current but also on the direction of magnetization, i.e. the change in MCA has
opposite sign when the direction of magnetization is reversed. The control of
magnetism by the spin current results from the modified exchange splitting of
majority- and minority-spin bands, and differs significantly from the
manipulation by gate voltages via a capacitor structure, providing a
functionality that was previously unavailable and could be useful in advanced
spintronic devices
Domain-width model for perpendicularly magnetized systems with Dzyaloshinskii-Moriya interaction
The influence of the Dzyaloshinskii-Moriya interaction (DMI) on stripe domains in perpendicularly magnetized thin ferromagnetic films is theoretically and experimentally investigated. We develop a domain spacing model describing the dependence of the stripe domain width on the magnetic properties of the sample. By including the magnetostatic energy of the domain walls the model correctly describes the transition from Bloch to Neel walls with increasing DMI constant. An approach to determine the magnitude of the DMI constant by fitting the stripe domain width as a function of the effective perpendicular anisotropy of wedge-shaped samples is developed and applied to several ultrathin multilayer samples based on Ni/Fe/Cu(001). The magnitude of the DMI constant arising from Fe/Ni and Ni/Fe interfaces is 0.3 +/- 0.14 meV/atom, indicating that the domain walls are in a pure chiral Neel state. Furthermore, phase diagrams of the skyrmionic bubble domain phase are recorded for two samples with different DMI constants, and by scaling the magnetic field a universal phase diagram for perpendicularly magnetized systems is obtained
Observation of anomalously strong penetration of terahertz electric field through terahertz-opaque gold films into a GaAs/AlGaAs quantum well
We observe an anomalously high electric field of terahertz (THz) radiation
acting on a two-dimensional electron gas (2DEG) placed beneath a thin gold
film, which, however, is supposed to be opaque at THz frequencies. We show that
the anomalously strong penetration of the THz electric field through a very
high conductive gold film emerges if two conditions are fulfilled
simultaneously: (i) the film's thickness is less than the skin depth and (ii)
the THz electric field is measured beneath the film at distances substantially
smaller than the radiation wavelength. We demonstrate that under these
conditions the strength of the field acting on a 2DEG is almost the same as it
would be in the absence of the gold film. The effect is detected for
macroscopically homogeneous perforation-free gold films illuminated by
THz-laser radiation with a spot smaller than the film area. This eliminates the
near-field of the edge diffraction as a possible cause of the anomalous
penetration. The microscopic origin of the effect remains unexplained in its
details, yet. The observed effect can be used for the development of THz
devices based on two-dimensional materials requiring robust highly conducting
top gates placed at less than nanometer distance from the electron gas
location
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