14,947 research outputs found
Precision high voltage divider for the KATRIN experiment
The Karlsruhe Tritium Neutrino Experiment (KATRIN) aims to determine the
absolute mass of the electron antineutrino from a precise measurement of the
tritium beta-spectrum near its endpoint at 18.6 keV with a sensitivity of 0.2
eV. KATRIN uses an electrostatic retardation spectrometer of MAC-E filter type
for which it is crucial to monitor high voltages of up to 35 kV with a
precision and long-term stability at the ppm level. Since devices capable of
this precision are not commercially available, a new high voltage divider for
direct voltages of up to 35 kV has been designed, following the new concept of
the standard divider for direct voltages of up to 100 kV developed at the
Physikalisch-Technische Bundesanstalt (PTB). The electrical and mechanical
design of the divider, the screening procedure for the selection of the
precision resistors, and the results of the investigation and calibration at
PTB are reported here. During the latter, uncertainties at the low ppm level
have been deduced for the new divider, thus qualifying it for the precision
measurements of the KATRIN experiment.Comment: 22 pages, 12 figure
Colossal magnetocapacitance and scale-invariant dielectric response in phase-separated manganites
Thin films of strongly-correlated electron materials (SCEM) are often grown
epitaxially on planar substrates and typically have anisotropic properties that
are usually not captured by edge-mounted four-terminal electrical measurements,
which are primarily sensitive to in-plane conduction paths. Accordingly, the
correlated interactions in the out-of-plane (perpendicular) direction cannot be
measured but only inferred. We address this shortcoming and show here an
experimental technique in which the SCEM under study, in our case a 600
Angstrom-thick (La1-yPry)0.67Ca0.33MnO3 (LPCMO) film, serves as the base
electrode in a metal-insulator-metal (MIM) trilayer capacitor structure. This
unconventional arrangement allows for simultaneous determination of colossal
magnetoresistance (CMR) associated with dc transport parallel to the film
substrate and colossal magnetocapacitance (CMC) associated with ac transport in
the perpendicular direction. We distinguish two distinct strain-related
direction-dependent insulator-metal (IM) transitions and use Cole-Cole plots to
establish a heretofore unobserved collapse of the dielectric response onto a
universal scale-invariant power-law dependence over a large range of frequency,
temperature and magnetic field.Comment: 32 pages, 4 figures, Supplementary section included, Submitted to
Nature Physic
Unipolar Resistance Switching in Amorphous High-k dielectrics Based on Correlated Barrier Hopping Theory
We have proposed a kind of nonvolatile resistive switching memory based on
amorphous LaLuO3, which has already been established as a promising candidate
of high-k gate dielectric employed in transistors. Well-developed unipolar
switching behaviors in amorphous LaLuO3 make it suited for not only logic but
memory applications using the conventional semiconductor or the emerging
nano/CMOS architectures. The conduction transition between high- and low-
resistance states is attributed to the change in the separation between oxygen
vacancy sites in the light of the correlated barrier hopping theory. The mean
migration distances of vacancies responsible for the resistive switching are
demonstrated in nanoscale, which could account for the ultrafast programming
speed of 6 ns. The origin of the distributions in switching parameters in
oxides can be well understood according to the switching principle.
Furthermore, an approach has also been developed to make the operation voltages
predictable for the practical applications of resistive memories.Comment: 18 pages, 6 figure
Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges
A new traceability chain for the derivation of the farad from dc quantum Hall
effect has been implemented at INRIM. Main components of the chain are two new
coaxial transformer bridges: a resistance ratio bridge, and a quadrature
bridge, both operating at 1541 Hz. The bridges are energized and controlled
with a polyphase direct-digital-synthesizer, which permits to achieve both main
and auxiliary equilibria in an automated way; the bridges and do not include
any variable inductive divider or variable impedance box. The relative
uncertainty in the realization of the farad, at the level of 1000 pF, is
estimated to be 64E-9. A first verification of the realization is given by a
comparison with the maintained national capacitance standard, where an
agreement between measurements within their relative combined uncertainty of
420E-9 is obtained.Comment: 15 pages, 11 figures, 3 table
Impedance spectroscopy of ions at liquid-liquid interfaces
The possibility to extract properties of an interface between two immiscible
liquids, e.g., electrolyte solutions or polyelectrolyte multilayers, by means
of impedance spectroscopy is investigated theoretically within a dynamic
density functional theory which is equivalent to the Nernst-Planck-Poisson
theory. A novel approach based on a two-step fitting procedure of an equivalent
circuit to impedance spectra is proposed which allows to uniquely separate bulk
and interfacial elements. Moreover, the proposed method avoids overfitting of
the bulk properties of the two liquids in contact and underfitting of the
interfacial properties, as they might occur for standard one-step procedures.
The key idea is to determine the bulk elements of the equivalent circuit in a
first step by fitting corresponding sub-circuits to the spectra of uniform
electrolyte solutions, and afterwards fitting the full equivalent circuit with
fixed bulk elements to the impedance spectrum containing the interface. This
approach is exemplified for an equivalent circuit which leads to a physically
intuitive qualitative behavior as well as to quantitively realistic values of
the interfacial elements. The proposed method is robust such that it can be
expected to be applicable to a wide class of systems with liquid-liquid
interfaces
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