247 research outputs found
Are better conducting molecules more rigid?
We investigate the electronic origin of the bending stiffness of conducting
molecules. It is found that the bending stiffness associated with electronic
motion, which we refer to as electro-stiffness, , is governed by
the molecular orbital overlap and the gap width between HOMO and LUMO
levels, and behaves as . To study the
effect of doping, we analyze the electron filling-fraction dependence on
and show that doped molecules are more flexible. In addition, to
estimate the contribution of to the total stiffness, we consider
molecules under a voltage bias, and study the length contraction ratio as a
function of the voltage. The molecules are shown to be contracted or dilated,
with increasing nonlinearly with the applied bias
Surface acoustic wave generation and detection in quantum paraelectric regime of SrTiO-based heterostructure
Strontium titanate (STO), apart from being a ubiquitous substrate for
complex-oxide heterostructures, possesses a multitude of strongly-coupled
electronic and mechanical properties. Surface acoustic wave (SAW) generation
and detection offers insight into electromechanical couplings that are
sensitive to quantum paraelectricity and other structural phase transitions.
Propagating SAWs can interact with STO-based electronic nanostructures, in
particular LaAlO/SrTiO (LAO/STO). Here we report generation and
detection of SAW within LAO/STO heterointerfaces at cryogenic temperatures
(~2 K) using superconducting interdigitated transducers (IDTs). The
temperature dependence shows an increase in the SAWs quality factor that
saturates at K. The effect of backgate tuning on the SAW
resonance frequency shows the possible acoustic coupling with the ferroelastic
domain wall evolution. This method of generating SAWs provides a pathway
towards dynamic tuning of ferroelastic domain structures, which are expected to
influence electronic properties of complex-oxide nanostructures. Devices which
incorporate SAWs may in turn help to elucidate the role of ferroelastic domain
structures in mediating electronic behavior
Electrical spin injection and detection in an InAs quantum well
We demonstrate fully electrical detection of spin injection in InAs quantum
wells. A spin polarized current is injected from a NiFe thin film to a
two-dimensional electron gas (2DEG) made of InAs based epitaxial multi-layers.
Injected spins accumulate and diffuse out in the 2DEG, and the spins are
electrically detected by a neighboring NiFe electrode. The observed spin
diffusion length is 1.8 um at 20 K. The injected spin polarization across the
NiFe/InAs interface is 1.9% at 20 K and remains at 1.4% even at room
temperature. Our experimental results will contribute significantly to the
realization of a practical spin field effect transistor
Development and Characterization of Nb₃n/Al₂0₃ Superconducting Multilayers for Particle Accelerators
Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factors \u3e 1010 at 1-2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200-240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb3Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb3Sn, it has been proposed to coat Nb cavities with thin film Nb3Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb3Sn/Al2O3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al2O3 and Nb3Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology
Ultrasonographic evaluation of tracheal collapse in dogs
Tracheal ultrasonography was performed to measure the width of the tracheal ring shadow and to assess the clinical relevance of these measurements for identifying tracheal collapse. The first tracheal ring width (FTRW) and thoracic inlet tracheal ring width (TITRW) were measured on both expiration and inspiration. The mean of the FTRW width (129 dogs) was greater in expiration (10.97 ± 1.02 mm, p = 0.001) than that in inspiration (9.86 ± 1.03 mm). For 51 normal dogs, the mean of the TITRW width was greater in expiration (9.05 ± 1.52 mm, p = 0.001) than in inspiration (8.02 ± 1.43 mm). For 78 tracheal collapse dogs, the mean of the TITRW width was greater in expiration (15.89 ± 1.01 mm, p = 0.001) than in inspiration (14.85 ± 1.17 mm). The TITRW/FTRW ratio of the normal dogs was higher (p = 0.001) in expiration (0.81 ± 0.09) than that in inspiration (0.79 ± 0.10). When compared between the normal and tracheal collapse dogs, the TITRW/FTRW ratio was also increased (p = 0.001) both in expiration (1.54 ± 0.09) and inspiration (1.47 ± 0.08), respectively. Based on these results, the cutoff level of the TITRW/FTRW ratio was statistically analyzed according to the receiver operating characteristic curve and it could be set at 1.16 in expiration and at 1.13 in inspiration. We have demonstrated that tracheal ultrasonography is a useful technique for the evaluation of tracheal collapse and it can be a supportive tool together with the radiographic findings for making the correct diagnosis
A High Sensitivity Three-Dimensional-Shape Sensing Patch Prepared by Lithography and Inkjet Printing
A process combining conventional photolithography and a novel inkjet printing method for the manufacture of high sensitivity three-dimensional-shape (3DS) sensing patches was proposed and demonstrated. The supporting curvature ranges from 1.41 to 6.24 × 10−2 mm−1 and the sensing patch has a thickness of less than 130 μm and 20 × 20 mm2 dimensions. A complete finite element method (FEM) model with simulation results was calculated and performed based on the buckling of columns and the deflection equation. The results show high compatibility of the drop-on-demand (DOD) inkjet printing with photolithography and the interferometer design also supports bi-directional detection of deformation. The 3DS sensing patch can be operated remotely without any power consumption. It provides a novel and alternative option compared with other optical curvature sensors
Multiferroic Magnon Spin-Torque Based Reconfigurable Logic-In-Memory
Magnons, bosonic quasiparticles carrying angular momentum, can flow through
insulators for information transmission with minimal power dissipation.
However, it remains challenging to develop a magnon-based logic due to the lack
of efficient electrical manipulation of magnon transport. Here we present a
magnon logic-in-memory device in a spin-source/multiferroic/ferromagnet
structure, where multiferroic magnon modes can be electrically excited and
controlled. In this device, magnon information is encoded to ferromagnetic bits
by the magnon-mediated spin torque. We show that the ferroelectric polarization
can electrically modulate the magnon spin-torque by controlling the
non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin
films with coupled antiferromagnetic and ferroelectric orders. By manipulating
the two coupled non-volatile state variables (ferroelectric polarization and
magnetization), we further demonstrate reconfigurable logic-in-memory
operations in a single device. Our findings highlight the potential of
multiferroics for controlling magnon information transport and offer a pathway
towards room-temperature voltage-controlled, low-power, scalable magnonics for
in-memory computing
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