GHz apertureless near-field scanning optical microscopy of ferroelectric nanodomain dynamics

Nanoscale domain dynamics of (Ba,Sr)TiO(3) thin films are investigated at microwave frequencies with a home-developed GHz-frequency apertureless near-field scanning optical microscope (GHz-ANSOM). Using a microwave phase-modulation technique, we decoupled topographic artifacts from the optical signal, providing an enhanced and background-free temporal response. Interleaved acquisition of images taken at sequential time intervals provides amplitude and phase information about the electrooptic response at <50 nm spatial resolution and <10 ps temporal resolution. The local microwave response is highly nonuniform in both the amplitude and the phase.     

Probing interactions at two-dimensional heterointerfaces by boron nitride-wrapped tip

Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN,BN-molybdenum disulfide,and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory.The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107±0.062 and 0.999±0.053 times that at BN-BN interface,respectively,while increase to 1.195±0.076 and 1.085±0.075 a.u.after exposure of the tip to radiation in scanning electron microscopy,with data repeatability higher than 86%.The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method,whereas the effect of radiation comes from the introduced charges in the tip,indicating the crucial roles of both dispersion and electrostatic interactions in construction,manipulation and device application of two-dimensional heterostructures.     

On the dynamics of vortex structure in ferroelectric nanoparticles

The dynamics of vortex structure for polarizations in free-standing ferroelectric nanoparticles has been numerically investigated based on a thermodynamics-based continuum phase field approach under open-circuit boundary conditions. Both size effect and surface effect have been considered in this work: different assumptions for the extrapolation length have been made for the electric boundary condition and therefore accounting for the intrinsic size effect; the surface effect is studied by introducing the intrinsic surface stress, which causes volume mechanical balancing stress in the nanoparticles below free surfaces. The computed results are summarized in this article for square-shaped nanodots. It has been noticed that the particle size and intrinsic surface stress together play significant roles in the dynamics of vortex structure for polarizations. They affect both polarization configuration and existence conditions in ferroelectric nanoparticles.     

Photoelectron spectra of Yb-Si(100) heterointerfaces formed at room temperature

The laws of formation of the heterointerfaces formed upon ytterbium (Yb) deposition at room temperature (T=300 K) onto a (2×1)-reconstructed Si(100) surface were studied by methods of photoelectron spectroscopy (PES) with excitation by synchrotron radiation and low-energy electron diffraction (LEED). In the range of submonolayer surface coverages θ, the adsorption of Yb atoms leads to destruction of the surface dimers. This is accompanied by the formation of an amorphous film consisting of mixed Yb and Si atoms. For θ>1.5, a partly ordered metallic ytterbium film containing dissolved Si atoms is formed on the substrate surface. In all stages of deposition, there is charge transfer from Yb to Si atoms, which is manifested by a shift of the Si 2p core level. This shift is especially pronounced (reaching 1.5 eV) for silicon atoms dissolved in the metallic film.     

Individually addressable epitaxial ferroelectric nanocapacitor arrays with near Tb inch-2 density

Ferroelectric materials have emerged in recent years as an alternative to magnetic and dielectric materials for nonvolatile data-storage applications. Lithography is widely used to reduce the size of data-storage elements in ultrahigh-density memory devices. However, ferroelectric materials tend to be oxides with complex structures that are easily damaged by existing lithographic techniques, so an alternative approach is needed to fabricate ultrahigh-density ferroelectric memories. Here we report a high-temperature deposition process that can fabricate arrays of individually addressable metal/ferroelectric/metal nanocapacitors with a density of 176 Gb inch(-2). The use of an ultrathin anodic alumina membrane as a lift-off mask makes it possible to deposit the memory elements at temperatures as high as 650 degrees C, which results in excellent ferroelectric properties.     

Nanoscale ferroelectric and piezoelectric properties of Sb2S3 nanowire arrays

We report the first observation of piezoelectricity and ferroelectricity in individual Sb(2)S(3) nanowires embedded in anodic alumina templates. Switching spectroscopy-piezoresponse force microscopy (SS-PFM) measurements demonstrate that individual, c-axis-oriented Sb(2)S(3) nanowires exhibit ferroelectric as well as piezoelectric switching behavior. Sb(2)S(3) nanowires with nominal diameters of 200 and 100 nm showed d(33(eff)) values around 2 pm V(-1), while the piezo coefficient obtained for 50 nm diameter nanowires was relatively low at around 0.8 pm V(-1). A spontaneous polarization (P(s)) of approximately 1.8 μC cm(-2) was observed in the 200 and 100 nm Sb(2)S(3) nanowires, which is a 100% enhancement when compared to bulk Sb(2)S(3) and is probably due to the defect-free, single-crystalline nature of the nanowires synthesized. The 180° ferroelectric monodomains observed in Sb(2)S(3) nanowires were due to uniform polarization alignment along the polar c-axis.     

Spontaneous formation of arrays of three-dimensional islands in epitaxial layers

An analysis is made of a theoretical model of the formation of three-dimensional nanometer-size islands in molecular beam epitaxy. The kinetics of the self-organization processes are described using a lattice gas model of the adsorbate with self-consistent allowance for lateral interactions in the activation energies of the diffusion processes. It is shown that at below-critical temperatures in a certain range of thicknesses, decay of the spatially uniform state gives rise to arrays of three-dimensional nano-islands which do not participate in the coalescence process after growth has ceased. The average size of the islands, their geometric profile, and the spatial ordering depend strongly on the kinetic parameters of the model. Pis’ma Zh. Tekh. Fiz. 24, 20–26 (July 12, 1998)     

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.     

Spontaneous formation of vertical magnetic-metal-nanorod arrays during plasma-enhanced atomic layer deposition

A novel fabrication method of Co and Ni metal nanorods (NRs) without catalyst or template, based on the spontaneous formation of NRs during plasma-enhanced atomic layer deposition (PE-ALD) is developed. Pure Co and Ni NRs 9-10 nm in diameter are synthesized on SiO(2) and Si substrates by using metal-organic precursors and an NH(3) plasma mixed with a suitable amount of SiH(4) as a reactant. The lengths of the NRs are controlled on the nanometer scale by changing the number of PE-ALD growth cycles. Superconducting quantum interference device magnetometer measurements confirm the magnetic anisotropy of Co NRs caused by shape anisotropy.     

Anisotropic conductance at improper ferroelectric domain walls

Transition metal oxides hold great potential for the development of new device paradigms because of the field-tunable functionalities driven by their strong electronic correlations, combined with their earth abundance and environmental friendliness. Recently, the interfaces between transition-metal oxides have revealed striking phenomena, such as insulator-metal transitions, magnetism, magnetoresistance and superconductivity. Such oxide interfaces are usually produced by sophisticated layer-by-layer growth techniques, which can yield high-quality, epitaxial interfaces with almost monolayer control of atomic positions. The resulting interfaces, however, are fixed in space by the arrangement of the atoms. Here we demonstrate a route to overcoming this geometric limitation. We show that the electrical conductance at the interfacial ferroelectric domain walls in hexagonal ErMnO(3) is a continuous function of the domain wall orientation, with a range of an order of magnitude. We explain the observed behaviour using first-principles density functional and phenomenological theories, and relate it to the unexpected stability of head-to-head and tail-to-tail domain walls in ErMnO(3) and related hexagonal manganites. As the domain wall orientation in ferroelectrics is tunable using modest external electric fields, our finding opens a degree of freedom that is not accessible to spatially fixed interfaces.     

Artificial vortex pinning arrays in superconducting films deposited on highly ordered anodic alumina templates

A simple procedure is described for creating periodic vortex pinning centers in thin superconducting NbN films. We report on three different strategies which involve the use of highly ordered alumina templates. In this approach, NbN thin films are deposited either on the porous face of the template made of a triangular array of nanoholes or on the triangular array of bumps formed by the barrier layer or even on the top of perpendicularly oriented ferromagnetic nanowire arrays obtained by electrochemical deposition, thus forming superconductor-ferromagnet hybrids. In all cases, the ordered template allows NbN films to form a periodic pinning array during its growth. The interpore (or inter-bump) distance ranged between 50 and 100?nm and adjustable pore (or wire) diameter was varied between 30 and 60?nm. Numerous matching effects have been observed up to 2.5?T and are maintained at low temperature. These fields are considerably higher than those typical for periodic pinning arrays made by lithographic techniques, which reflects the benefits of nanostructuring superconductors by using self-organized growth to enhance vortex pinning in a large field and temperature range.     

Focusing ions by vortex jet at atmospheric pressure

A new method for focusing ions at atmospheric pressure by a strongly swirled gas jet is proposed and verified. It is shown that, using the driven swirled jet, it is possible to ensure a significant (tenfold) increase in the efficiency of distant ion sampling as compared to that in the aspiration regime. The influence of recombination losses on the efficiency of vortex-driven take-off of ionized samples is discussed.     

Electrothermal flow on electrodes arrays at physiological conductivities

AC electrothermal (ET) flow is inevitable for microfluidic systems dissipating electric energy in a conducting medium. Therefore, many practical applications of biomicrofluidics are prone to ET flow. Here, a series of observations are reported on ET flow in a microfluidic chamber that houses three electrode pairs. The observations indicate that the variations in liquid conductivity and channel height critically impact the structure and magnitude of the flow field. Observations indicate that after a critical conductivity a global ET flow is present in the chamber, while at lower conductivities a vortex is present at every electrode edge. In addition, no ET flow is observed when the chamber height is kept below a critical value at physiological conductivity (∼1.5 S/m). The experimental observations are compared with the numerical simulations of ET flow. The validity of the assumptions made in the current AC ET flow theory is also discussed in the light of the experimental data. The observations can be critical while designing microfluidic systems that involve power dissipation in conductive fluids.Inspec keywords: bioelectric phenomena, microfluidics, numerical analysis, bioMEMSOther keywords: electrode array, physiological conductivity, AC electrothermal flow, microfluidic system, electric energy, biomicrofluidics, microfluidic chamber, liquid conductivity, flow field structure, flow field magnitude, global ET flow, ET flow numerical simulation, AC ET flow theory, power dissipation, conductive fluid     

The orientational phase transition at a vortex in3He-B

The orientational phase transition in the vicinity of a single vortex in³He-B is studied. It is the phase transition from a uniformn-texture withn parallel to the magnetic field and the vortex line to ann-texture that is nonuniform near the vortex. The problem of the instability of the the uniformn-texture is equivalent to the quantum mechanical two-dimensional problem of a bound state in a field with an attractive potential 1/r ². The orientational phase transition at a vortex array is also considered. In the limit of large vortex density the orientational phase transition transforms to the phase transition studied by Gongadze et al. The theoretical results are compared with the observed phase transition at a vortex in³He-B.     

低温快烧自生乳浊釉

简述了在低温快烧条件下制备自生乳浊釉的研究思路，相关工作基础及实现的关键和难点。自生乳浊釉是通过釉熔体在烧成过程中产生一级或多级分相或析出微晶而实现乳浊效果的，打破了传统乳浊釉外的加晶粒乳浊剂的单一乳浊方式，具有良好的应用前景和经济效益。     

Toward self-assembled ferroelectric random access memories: hard-wired switching capacitor arrays with almost Tb/in.(2) densities

We report on the successful fabrication of arrays of switchable nanocapacitors made by harnessing the self-assembly of materials. The structures are composed of arrays of 20-40 nm diameter Pt nanowires, spaced 50-100 nm apart, electrodeposited through nanoporous alumina onto a thin film lower electrode on a silicon wafer. A thin film ferroelectric (both barium titanate (BTO) and lead zirconium titanate (PZT)) has been deposited on top of the nanowire array, followed by the deposition of thin film upper electrodes. The PZT nanocapacitors exhibit hysteresis loops with substantial remnant polarizations, while although the switching performance was inferior, the low-field characteristics of the BTO nanocapacitors show dielectric behavior comparable to conventional thin film heterostructures. While registration is not sufficient for commercial RAM production, this is nevertheless an embryonic form of the highest density hard-wired FRAM capacitor array reported to date and compares favorably with atomic force microscopy read-write densities.     

Effect of vortex formation on sediment transport at dual pipe intakes

Vortex formation and subsequent sediment transport into the intake due to sea water withdrawal is one of the problems in coastal engineering. The effect of vortex formation on rate of sediment transport at coastal dual pipe intakes was investigated using a scaled physical model. Experiments were performed on dual pipe intakes at three common intake withdrawal directions (vertical, horizontal and with angle of 45°). In each experiment, the class of vortex with respect to its strength was determined. Particle tracking velocimetry (PTV) was employed to measure tangential velocity of vortices. Results indicated that the rate of sediment transport was considerably affected by the strength of formed vortices. The rate of transported sediment was increased by increasing the strength of formed vortex. Moreover, amount of sediment transport was affected by angle of pipe intakes. It could be concluded that the minimum and maximum rates of sediment transport occur for inclined and horizontal intakes, respectively.     

The shape of a superfluid vortex nucleated at a sharp edge

Experiments on superfluid flow through pinholes suggest that inhomogeneous nucleation of distorted vortex half-rings at the orifice lip may account for the onset of dissipation in such flows. This paper gives a calculation of the shape of the critical vortex—one whose local self-induced velocity matches the local flow velocity. The length and energy correction for a typical geometry amounts to more than 30%.     

Optical index profile at an antiparallel ferroelectric domain wall in lithium niobate

Unexpected optical contrast at antiparallel domain walls is observed in non-stoichiometric lithium niobate. This is imaged using near-field scanning optical microscopy. A detailed modeling of the imaging process is performed, and a comparison of the experimental and simulation images is used to extract the index profile across a single antiparallel domain wall.