Non-collective Josephson-Vortex Motion Induced by Pancake-Vortex Pinning in Stacked Josephson Junctions

We experimentally studied the dynamic-state characteristics of Josephson vortices (JVs) and influence of pancake vortices (PVs) on the JV dynamics in a stack of inductively coupled Bi₂Sr₂CaCuO_8+δ intrinsic Josephson junctions. In a few-tesla magnetic field range, we observed Josephson-vortex-flow branches (JVFBs) in the current–voltage characteristics. We show that the JVFBs are generated by the non-collective pinning (depinning) of Josephson vortices in individual junctions by (from) pancake vortices. Results of our study suggest a convenient means of controlling JVs for quantum-electronics applications utilizing stacked Josephson junctions.     

On the direct insulator-quantum Hall transition in two-dimensional electron systems in the vicinity of nanoscaled scatterers

A direct insulator-quantum Hall (I-QH) transition corresponds to a crossover/transition from the insulating regime to a high Landau level filling factor ν > 2 QH state. Such a transition has been attracting a great deal of both experimental and theoretical interests. In this study, we present three different two-dimensional electron systems (2DESs) which are in the vicinity of nanoscaled scatterers. All these three devices exhibit a direct I-QH transition, and the transport properties under different nanaoscaled scatterers are discussed.     

Study on the improved accuracy of strip profile using numerical formula model in continuous cold rolling with 6-high mill

The quality requirements for thickness accuracy in cold rolling continue to become more stringent. In cold rolling mill, it is very important that the rolling force calculation considers rolling conditions. The rolled strip thickness was predicted using calculated rolling force. However, the prediction of strip thickness in cold rolling is very difficult; in particular, for 6-high mill with shifted intermediate roll (IMR), the accuracy of thickness is not good. In this study, to improve the accuracy of rolled strip thickness, the roll gap flattening can be given based on Hertz contact theory, with contact between rolls and the smooth cylindrical rolls for the rolling elastic deformation. Also, the distribution of the roll gap flattening may be calculated using the contact force of unit transverse length. The strip profile at the continuous cold rolling is calculated by using the numerical analysis model considering the initial strip profile before cold rolling. Hence, we propose that the numerical model can predict the rolled strip profile more quickly and accurately and be applicable to the field. The results of the proposed numerical model were verified by FE-simulation and cold rolling experiments of 6-high mill with five stands.     

Analysis of Scanned Probe Images for Magnetic Focusing in Graphene

We have used cooled scanning probe microscopy (SPM) to study electron motion in nanoscale devices. The charged tip of the microscope was raster-scanned at constant height above the surface as the conductance of the device was measured. The image charge scatters electrons away, changing the path of electrons through the sample. Using this technique, we imaged cyclotron orbits that flow between two narrow contacts in the magnetic focusing regime for ballistic hBN–graphene–hBN devices. We present herein an analysis of our magnetic focusing imaging results based on the effects of the tip-created charge density dip on the motion of ballistic electrons. The density dip locally reduces the Fermi energy, creating a force that pushes electrons away from the tip. When the tip is above the cyclotron orbit, electrons are deflected away from the receiving contact, creating an image by reducing the transmission between contacts. The data and our analysis suggest that the graphene edge is rather rough, and electrons scattering off the edge bounce in random directions. However, when the tip is close to the edge, it can enhance transmission by bouncing electrons away from the edge, toward the receiving contact. Our results demonstrate that cooled SPM is a promising tool to investigate the motion of electrons in ballistic graphene devices.     

Hydrazine-based n-type doping process to modulate Dirac point of graphene and its application to complementary inverter

In this paper, chemical n-type doping process of graphene using hydrazine monohydrate solution (N₂H₄–H₂O) is demonstrated. This method successfully modulates the Dirac point of pristine graphene by adjusting the concentration of hydrazine solution and also provides an effective n-type doping in graphene. First, the hydrazine treated and pristine graphene films are systematically investigated by Raman and FT-IR spectroscopy. Second, with p- and n-channel FETs fabricated on both pristine and hydrazine treated n-type graphene, complementary graphene inverter is demonstrated.     

Single domain limit for NixCo1−xFe2O4 (0 ≤ x ≤ 1) nanoparticles synthesized by coprecipitation route

Ni_xCo_1−xFe₂O₄ (0 ≤ x ≤ 1) nanoparticles (sizes: 8–52 nm) were synthesized by chemical coprecipitation route. Single domain limit (d_sdl) for the nanoparticles, determined from the coercivity (H_C) versus particle-size curves, was explored as a function of nickel concentration (x). The coercivity of the particles attains a peak value at d_sdl, and it was found that coercivity decreases linearly with increasing nickel concentration in the samples. The saturation magnetization (M_S) and blocking temperature (T_b) of the system show increasing trends with increasing cobalt concentration in the nanoparticles.     

Treatment of a waste salt delivered from an electrorefining process by an oxidative precipitation of the rare earth elements

For the reuse of a waste salt from an electrorefining process of a spent oxide fuel, a separation of rare earth elements by an oxidative precipitation in a LiCl-KCl molten salt was tested without using precipitate agents. From the results obtained from the thermochemical calculations by HSC Chemistry software, the most stable rare earth compounds in the oxygen-used rare earth chlorides system were oxychlorides (EuOCl, NdOCl, PrOCl) and oxides (CeO₂, PrO₂), which coincide well with results of the Gibbs free energy of the reaction. In this study, similar to the thermochemical results, regardless of the sparging time and molten salt temperature, oxychlorides and oxides were formed as a precipitant by a reaction with oxygen. The structure of the rare earth precipitates was divided into two shapes: small cubic (oxide) and large plate-like (tetragonal) structures. The conversion efficiencies of the rare earth elements to their molten salt-insoluble precipitates were increased with the sparging time and temperature, and Ce showed the best reactivity. In the conditions of 650 °C of the molten salt temperature and 420 min of the sparging time, the final conversion efficiencies were over 99.9% for all the investigated rare earth chlorides.     

Hydrogen sensing properties of dielectrophoretically assembled SnO2 nanoparticles on CMOS-compatible micro-hotplates

We fabricated nanoparticle-based gas through in situ ac dielectrophoretical assembling of drop-coated SnO(2) nanoparticles to bridge the gap between electrodes with high aspect ratio. While the conventional dielectrophoresis (DEP) adopts a microfluidic system for continuous flow of the solution during the process, we just drop-coated a small amount of solution onto the electrodes and executed in situ DEP for a very short time. This is a very simple, cost-effective, time-saving, and highly reproducible process. We fixed the duration time and applied voltage for the DEP at 1 s and 1 V respectively and changed the frequencies from 1 up to 500 kHz. I-V characteristics of the samples were checked and it was found that DEP samples fabricated at 1 s, 1 V and 150 kHz conditions showed considerably higher connectivity of the nanoparticles. This can be attributed to the excellent step coverage achieved by ac DEP under those conditions. The devices drop-coated and dielectrophoretically assembled at other ac frequency conditions showed poor connectivity. Hydrogen gas sensing properties of the sensors fabricated under 1 s, 1 V and 150 kHz conditions were checked by flowing through 160 ppm H(2). The sensitivity reaches a maximum value of ~ 700% at 350 °C. The response time is ~ 200 s at 350 °C.     

Leakage current reduction in pentacene-based thin film transistor using asymmetric source/drain electrodes

In this work, we propose the concept of achieving a lower off-current in organic thin film transistors (OTFTs) by asymmetric source/drain with low and high work-function metals. The artificial hole barrier height (h-BH) at the drain-channel junction formed by this method prevents hole carriers transport from source to drain through the pentacene layer during the off-state. On-current is not affected by this artificially formed h-BH because the effective h-BH is reduced in the on-state. As a result, in the asymmetric Ni–Ti and Ni–Al OTFTs, the off-currents are decreased by 12 and 18.3 times, respectively, compared to that in the symmetric S/D device.     

ZnO based surface acoustic wave ultraviolet photo sensor

Ultraviolet (UV) sensor based on ZnO thin film surface acoustic wave (SAW) device is reported. ZnO films were grown using an RF magnetron sputtering technique. SAW devices were made using such ZnO films exhibiting a central frequency at ～41.2 MHz. The SAW UV sensor was fabricated by depositing a 70 nm thin photoconducting ZnO overlayer on the fabricated SAW device. The SAW UV sensor was found to exhibit interesting photoresponse behavior to UV illumination, and a downshift in frequency of ～45 kHz, and a change in insertion loss ～1.1 dB were observed under UV illumination intensity of 19 mW/cm². The changes in the frequency of operation and the insertion loss have been attributed to the acoustoelectric interaction between the photogenerated charge carriers and the potential associated with the acoustic waves. Results show the promise of ZnO for the fabrication of low cost wireless SAW UV sensors.