Quantum shutter approach to tunneling time scales with wave packets

The quantum shutter approach to tunneling time scales (G. Garc\'{\i }a-Calder\'{o}n and A. Rubio, Phys. Rev. A \textbf{55}, 3361 (1997)), which uses a cutoff plane wave as the initial condition, is extended in such a way that a certain type of wave packet can be used as the initial condition. An analytical expression for the time evolved wave function is derived. The time-domain resonance, the peaked structure of the probability density (as the function of time) at the exit of the barrier, originally found with the cutoff plane wave initial condition, is studied with the wave packet initial conditions. It is found that the time-domain resonance is not very sensitive to the width of the packet when the transmission process is in the tunneling regime.Comment: 6 page

Neutron reflectometry under high shear in narrow gap for tribology study

An operando analysis method has been established for evaluating the interfacial structure of an adsorbed layer formed by an additive on a metal surface under fluid lubricated conditions. A parallel-face narrow gap viscometer installed in an energy-resolved neutron reflectometer is used to evaluate the change in the interfacial structure under high shear. The viscometer was designed to operate at a high shear rate while maintaining a µm-order constant gap between two parallel surfaces. When an additive-free base oil was sandwiched in the gap, the neutron reflectivity profiles without and with upper surface rotation were the same. This demonstrates that the reflectivity profiles can be accurately measured regardless of whether the upper surface is rotated. When a base oil containing a polymethacrylate-based additive was sandwiched in the gap, both the thickness and density of the adsorbed additive layer in the rotation (shear field) condition were lower than those in the non-rotation (static) condition. This demonstrates that the proposed method can be used to analyse the structural changes in the adsorbed layer formed by an oil additive on a surface. This combination of a neutron reflectometer and narrow gap viscometer is a promising approach to near-future tribological studies

Application of precise neutron focusing mirrors for neutron reflectometry: latest results and future prospects

超精密中性子集束ミラーによる電極界面のナノ構造解析技術の実用化 --測定精度の劇的な向上に向けた大きなマイルストーン--. 京都大学プレスリリース. 2020-10-28.Neutron reflectometry (NR) is a powerful tool for providing insight into the evolution of interfacial structures, for example via operando measurements for electrode–electrolyte interfaces, with a spatial resolution of nanometres. The time resolution of NR, which ranges from seconds to minutes depending on the reflection intensity, unfortunately remains low, particularly for small samples made of state-of-the-art materials even with the latest neutron reflectometers. To overcome this problem, a large-area focusing supermirror manufactured with ultra-precision machining has been employed to enhance the neutron flux at the sample, and a gain of approximately 100% in the neutron flux was achieved. Using this mirror, a reflectivity measurement was performed on a thin cathode film on an SrTiO3 substrate in contact with an electrolyte with a small area of 15 × 15 mm. The reflectivity data obtained with the focusing mirror were consistent with those without the mirror, but the acquisition time was shortened to half that of the original, which is an important milestone for rapid measurements with a limited reciprocal space. Furthermore, a method for further upgrades that will reveal the structural evolution with a wide reciprocal space is proposed, by applying this mirror for multi-incident-angle neutron reflectometry

Novel idea of neutron polychromator and application for reflectometry and spectroscopy

Historically, two methods have been used to determine the wavelength of neutrons: (i) a timeof-flight method that separates the velocity of pulsed neutrons by the flight time; and (ii) a method utilizing Bragg reflection by a monochromator, such as a single crystal or multilayer mirror. The former cannot be applied to electromagnetic waves because the light velocity is constant and independent of the wavelength, whereas “polychromators” such as prisms and gratings, which separate wavelengths via chromatic dispersion, are typically used in the infrared to soft X-ray range. Although polychromators require collimated beams to separate wavelengths with sufficient resolution, this aspect does not affect laser and synchrotron light because they are naturally collimated. Herein, we propose a novel idea of a neutron polychromator utilizing an elliptical multilayered mirror that can be applied to a wide beam with a large beam divergence. In addition, examples of reflectometer and spectrometer applications are presented

Kinetic Process of Formation and Reconstruction of Small Unilamellar Vesicles Consisting of Long- and Short-Chain Lipids

Whereas the phase separation of normal phospholipids induces formation of microdomains on the surface of spherical vesicles, the separation of a long- and short-chain lipids can induce perforation of small unilamellar vesicles (SUVs) and transformation into bilayered micelles (bicelles) because the edges of the bilayers are stabilized by the short-chain lipid microdomain. In this study, the effect of the phase separation of lipids on the transformation behavior of SUVs consisting of a mixture of long- and short-chain lipids was investigated using small-angle neutron scattering. At the temperature jump from below to above the chain melting temperature of the long-chain lipid, <i>T</i>_c, bicelles fused together and transformed into SUVs when their size reached a critical radius. In contrast, a sequential transformation of small SUVs to small bicelles, small bicelles to large bicelles, and large bicelles to large SUVs occurred when the temperature jumped from a value far above <i>T</i>_c to one slightly above <i>T</i>_c. To the best of my knowledge, this is the first report of such reconstruction of vesicles. By considering the bending energy of the membrane, the line tension of the rim, and the perforation due to the phase separation, the mechanism of the transformation processes was clarified

Overscreening Induced by Ionic Adsorption at the Ionic Liquid/Electrode Interface Detected Using Neutron Reflectometry with a Rational Material Design

Neutron reflectometry (NR) has been utilized to study the electric double layer (EDL) of ionic liquids (ILs), however, further improvement of the sensitivity toward interfacial structure would be desirable. We recently proposed two ways to improve the NR sensitivity toward the EDL structure at the IL/electrode interface (J. Phys. Chem. C, 123 (2019) 9223). First, as the electrode, a thin film of metal (Nb) was used with the scattering length density (SLD) and thickness controlled to sensitively analyze the potential dependent EDL structure. Second, the IL cation and anion were chosen so that they have large size and large SLD difference, both of which also increase the sensitivity. In the present study, we have further explored this rational material design for the sensitivity enhancement, by changing the film metal from Nb to Bi whose SLD is closer to those for two bulk materials: Si and the IL used, trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide. We successfully observed not only the first ionic layer in the EDL but also the overlayers, revealing that the IL cation is specifically adsorbed on the electrode and that the cation-rich first layer induces overscreening in the overlayers up to the third ionic layer

Highly Swollen Adsorption Layer Formed by Polymeric Friction Modifier Providing Low Friction at Higher Temperature

To reduce friction, especially under high-temperature conditions, an oil-soluble polymeric friction modifier (polymeric FM) with a methacrylate backbone and hydroxyl groups has been developed. It was designed to have high adsorption performance and to increase in size when dissolved in base oil as the temperature is increased. To investigate the temperature dependence of the structural and tribological characteristics of the adsorbed layer formed on a metal surface by the polymeric FM, neutron reflectometry measurements and nano-to-macro tribological tests were conducted. The measurements revealed that the polymeric FM adsorbed efficiently on a Cu surface and formed a 6.0-nm-thick adsorbed layer at 23 °C. This adsorbed layer was highly swollen, and its thickness became about three times larger at 100 °C. Nanoscale friction tests using an atomic force microscope showed that the swollen-state adsorbed polymeric FM layer exhibited low-friction and surface-protection performance at 100 °C. Macroscale friction tests revealed the tribological behaviour of an adsorbed polymeric FM layer in elastohydrodynamic lubrication and mixed lubrication regimes. At higher temperatures, the increase in shear resistance due to the effect of thin-film lubrication was suppressed by the weaker segment–segment interaction, causing the boundary contact of the adsorbed polymeric FM layer to have low frictional properties on both ball and disc surfaces. The low-friction mechanism of the adsorbed polymeric FM layer at higher temperatures was justified by associating the temperature with the layer thickness

New Design of a Sample Cell for Neutron Reflectometry in Liquid&ndash;Liquid Systems and Its Application for Studying Structures at Air&ndash;Liquid and Liquid&ndash;Liquid Interfaces

Knowledge of interfacial structures in liquid&ndash;liquid systems is imperative, especially for improving two-phase biological and chemical reactions. Therefore, we developed a new sample cell for neutron reflectometry (NR), which enables us to observe the layer structure around the interface, and investigated the adsorption behavior of a typical surfactant, sodium dodecyl sulfate (SDS), on the toluene-d8-D2O interface under the new experimental conditions. The new cell was characterized by placing the PTFE frame at the bottom to produce a smooth interface and downsized compared to the conventional cell. The obtained NR profiles were readily analyzable and we determined a slight difference in the SDS adsorption layer structure at the interface between the toluene-d8-D2O and air-D2O systems. This could be owing to the difference in the adsorption behavior of the SDS molecules depending on the interfacial conditions