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We study both experimentally and theoretically the dynamics of chemically self-propelled Janus colloids moving atop a two-dimensional crystalline surface. The surface is a hexagonally close-packed monolayer of colloidal particles of the same size as the mobile one. The dynamics of the self-propelled colloid reflects the competition between hindered diffusion due to the periodic surface and enhanced diffusion due to active motion. Which contribution dominates depends on the propulsion strength, which can be systematically tuned by changing the concentration of a chemical fuel. The mean-square displacements (MSDs) obtained from the experiment exhibit enhanced diffusion at long lag times. Our experimental data are consistent with a Langevin model for the effectively two-dimensional translational motion of an active Brownian particle in a periodic potential, combining the confining effects of gravity and the crystalline surface with the free rotational diffusion of the colloid. Approximate analytical predictions are made for theMSDdescribing the crossover from free Brownian motion at short times to active diffusion at long times. The results are in semi-quantitative agreement with numerical results of a refined Langevin model that treats translational and rotational degrees of freedom on the same footing. [ABSTRACT FROM AUTHOR]

We present the design and fabrication of a polymeric capillary fluidic interface fabricated by micro-milling. The design enables the use of glass capillaries with any kind of cross-section in complex microfluidic setups. We demonstrate two different designs of the interface; a double-inlet interface for hydrodynamic focusing and a capillary interface with integrated pneumatic valves. Both capillary interfaces are presented together with examples of practical applications. This communication shows the design optimization and presents details of the fabrication process. The capillary interface opens up for the use of complex microfluidic systems in single-use glass capillaries. They also enable simple fabrication of glass/polymer hybrid devices that can be beneficial in many research fields where a pure polymer chip negatively affects the device's performance, e.g. acoustofluidics. [ABSTRACT FROM AUTHOR]

The surface work function (WF) and substrate temperature dependence of the NaCl thin-film growth on Ag(001) have been studied by noncontact atomic force microscopy and Kelvin probe force microscopy. In the sub-monolayer range, the NaCl film is composed of large crystalline islands, which decrease in density and increase in size with increasing temperature during deposition. Each island is composed of a large base island 2 monolayers (ML) thick (for T > 343 K), which collects impinging NaCl molecules that form adislands on top. Kelvin probe force microscopy (KPFM) measurements show a reduction of the silver WF by Δφ = φAg -φNaCl/Ag = 0.69±0.03 eV with no dependence on the film thickness (1-6 ML), in agreement with recent theoretical calculations. The previously observed nanometer-sized moiré pattern on islands that are 45° rotated with respect to the silver lattice could be observed in the scanning tunneling microscopy mode. However, no contrast could be obtained in KPFM images. [ABSTRACT FROM AUTHOR]

The disordering process in crystalline GeSb2Te4 films has been studied by means of ion irradiation with 150 keV Ar+ ions. The effect of the interfaces and the role of the crystal microstructure has been investigated. The disordering path observed in a randomly oriented polycrystalline material with trigonal structure involves the transition to the disordered rocksalt structure (at fluence 7  ×  1013 cm−2) and then to the amorphous phase (at 1.5  ×  1014 cm−2). In GeSb2Te4 epitaxially grown on Si(1 1 1) the formation of the disordered rocksalt phase (DRS) occurs at much higher fluence (3  ×  1014 cm−2) and it is preceded by the conversion of the stable phase into the ordered rocksalt structure (at 5  ×  1013 cm−2), with the formation of ordered vacancy layers, associated to a local variation of the stoichiometry. Even by increasing the fluence up to 3.5  ×  1014 cm−2, the films remains mainly crystalline. The observed behaviour has been attributed to the effect of the interfaces and suggests the possibility to promote switching between the crystalline phases by interface engineering. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM) is one of the emerging technologies for the next generation of electric and optical memories. In a typical PCM device, a nanoscale amorphous interface can usually be observed. These nano amorphous interfaces are crucial because they could affect the phase transition characteristics of PCM materials, especially when the PCM devices are scaling down. In this work, according to results of our previous first-principles calculations and transmission electron microscope characterizations, we revisit the effects of three typical nano amorphous interfaces of PCM materials between different phases. We conclude that the bonding network and electronic features of the PCM material in these interfaces will be changed significantly depending on the material next to it. Different types of interface could either enhance the stability of amorphous (i.e. amorphous Si/amorphous Sb2Te3 interface) and metastable crystalline phases (i.e. amorphous GeTe/cubic Sb2Te3 interface) or promote crystallization (i.e. amorphous and crystalline Ge2Sb2Te5 interface) of the PCM materials. Therefore, a nano amorphous interface can be used to control the performance of PCM devices, such as data retention ability and crystallization speed. The present work also offers a feasible way to design novel nanoscale PCM materials based on the interface effects. [ABSTRACT FROM AUTHOR]

Among electroactive polymers (EAPs) for softactuators, conducting polymers have been intensively studied because of the large strain and stress caused by a low voltage operation. A larger deformation is desirable to extend their cycle life by reducing the operation voltage, and this is advantageous for their potential use in wider applications. The deformation is generated by the insertion of ions by electrochemical oxidation; hence, the magnitude of the strain depends on the bulkiness of the ions in the electrolytes. It is important, therefore, to clarify the structure and size of the ions during the electrochemical cycle, in order to achieve better performance of actuation. Anion and cation sizes (radii) in polypyrrole (PPy) film have been estimated using the precise measurement of strain against the amount of charge injected during the electrochemical cycles, assuming isotropic deformation of the film. The anion size was estimated using an anion-drive film, which was electrodeposited in TBABF4/methyl benzoate. The film was electrochemically cycled in sodium electrolytes, and the strain was measured simultaneously using a laser displacement meter. The cation size was obtained using a cation-drive film, being electropolymerized in aqueous dodecylbenzene sulfonic (DBS) acid. The cation-drive film was cycled in chloride electrolytes and measured the strain. The Cl−, Br−, , , and radii were found to be approximately 235, 245, 250, 270 and 290 pm, respectively. The radii of K+, Na+ and Li+ were approximately 230, 237 and 274 pm, respectively. The results were discussed and took the crystalline ion radius and hydrated ion radius (Stokes radius) into consideration. It was found that the structure and size of the anions were slightly larger than the crystalline ion radius. Contrary to the anions, the cation radii were close to the hydrated ion radius, being larger than the crystalline ion radius. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance (FMR) was used to investigate the static and dynamic magnetic properties of carbon-doped Mn5Ge3 thin films grown on Ge(1 1 1). The temperature dependence of magnetic anisotropy shows an increased perpendicular magneto-crystalline contribution at 80 K with an in-plane easy axis due to the large shape contribution. We find that our samples show a small FMR linewidth (corresponding to an intrinsic magnetic damping parameter ) which is a measure of the spin relaxation and directly related with the magnetic and structural quality of the material. In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at around 200 K for all the samples, which seems to be not correlated to the C-doping. The magnetic relaxation parameters have been determined and indicate the two-magnon scattering as the main extrinsic contribution. We observe a change in the main contribution from scattering centres in Mn5 Ge3C0.2 at low temperatures, which could be related to the minimum in linewidth. [ABSTRACT FROM AUTHOR]

A zinc oxide thin film in cubic crystalline phase, which is usually prepared under high pressure, has been grown on the MgO (001) substrate by a three-step growth using plasma-assisted molecular beam epitaxy. The cubic structure is confirmed by in-situ reflection high energy electron diffraction measurements and simulations. The x-ray photoelectron spectroscopy reveals that the outer-layer surface of the film (less than 5 nm thick) is of ZnO phase while the buffer layer above the substrate is of ZnMgO phase, which is further confirmed by the band edge transmissions at the wavelengths of about 390 nm and 280 nm, respectively. The x-ray diffraction exhibits no peaks related to wurtzite ZnO phase in the film. The cubic ZnO film is presumably considered to be of the rock-salt phase. This work suggests that the metastable cubic ZnO films, which are of applicational interest for p-type doping, can be epitaxially grown on the rock-salt substrates without the usually needed high pressure conditions. [ABSTRACT FROM AUTHOR]

This work describes, using mainly transmission electron microscopy as an investigation tool, the nature and behaviour of the crystalline defects which are present in (11-22) semipolar GaN films grown epitaxially on patterned r-sapphire substrates using a 3 step growth process. The microstructure at these different growth stages is described. The independent 3D-crystallites nucleated on the substrate surface contain threading dislocations resulting from the epitaxy on c-sapphire facets and basal stacking faults (BSFs), mainly in the  −c-wings. These defects are concentrated in a few hundred nanometre wide stripe-like regions emerging on the top facet of the islands. By a careful choice of the growth conditions, these defective regions may be overgrown by defect-free material, blocking their propagation towards the coalesced surface. However, when the 3D crystals coalesce, new dislocations together with very few BSFs are created at the coalescence boundaries. These coalescence defects propagate to the surface of the films in (0001) planes. In summary, the control of the nucleation and propagation of the crystalline defects allows obtaining large area semipolar films with very low defect densities: 7   ×   107 cm−2 for TDs and 70 cm−1 for BSFs. [ABSTRACT FROM AUTHOR]

The longitudinal spin-Seebeck effect (LSSE) has been investigated for Pt/yttrium iron garnet (YIG) bilayer systems. The magnitude of the voltage induced by the LSSE is found to be sensitive to the Pt/YIG interface condition. We observed a large LSSE voltage in a Pt/YIG system with a better crystalline interface, while the voltage decays steeply when an amorphous layer is introduced at the interface artificially. [ABSTRACT FROM AUTHOR]

We study spin and valley transports in junctions composed of silicene and topological crystalline insulators. We consider normal/magnetic/normal Dirac metal junctions where a gate electrode is attached to the magnetic region. In a normal/antiferromagnetic/normal silicene junction, we show that the current through this junction is valley and spin polarized due to the coupling between valley and spin degrees of freedom, and the valley and spin polarizations can be tuned by local application of a gate voltage. In particular, we find a fully valley and spin polarized current by applying the electric field. In a normal/ferromagnetic/normal topological crystalline insulator junction with a strain induced in the ferromagnetic segment, we investigate valley-resolved conductances and clarify how the valley polarization stemming from the strain and exchange field appears in this junction. It is found that by changing the direction of the magnetization and the potential in the ferromagnetic region, one can control the dominant valley contribution out of four valley degrees of freedom. We also review spin transport in normal/ferromagnetic/normal graphene junctions, and spin and valley transports in normal/ferromagnetic/normal silicene junctions for comparison. [ABSTRACT FROM AUTHOR]

A new high spatial resolution non-contact temperature measurement technique (thermal scanning electron microscopy, ThSEM) is demonstrated. It employs temperature dependent thermal diffuse scattering in electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM). Unlike conventional scanning thermal microscopy, which uses contact probes, ThSEM is a non-contact method. In contrast to optical temperature mapping techniques, ThSEM does not have the spatial resolution limitation that arises from the optical wavelength and theoretically can reach a resolution of <10 nm. The hardware setup is very similar to the EBSD system in an SEM, which can make the integration of temperature mapping into an SEM relatively straightforward. Moreover, multiple signals or contrast mechanisms, such as temperature distributions, grain orientation maps, topographic images and elemental maps can be obtained from the same sample area depending on the specific SEM capability. This technique thus adds a new channel—the temperature signal—to the collection of existing SEM signals. [ABSTRACT FROM AUTHOR]

We investigate the influence of Fe contamination on the minority carrier lifetimes of multi-crystalline silicon. The minority carrier lifetime is measured by the microwave photoconductive decay method. The original bulk lifetime is about 30 ms after passivation with iodine solution. After intentional Fe contamination, the bulk lifetime declines with increasing temperature. Fast cooling in air conduces to the formation of more interstitial Fe ([Fe]i). Slow cooling through the control of the furnace temperature limits the formation of more [Fe]i, but leads to the formation of precipitation. The data support the idea that the minority carrier lifetime in multi-crystalline silicon mainly depends on the distribution of Fe but not the total amount. A favorite effect of [Fe]i gettering is discovered after conventional phosphorus diffusion, and the [Fe]i concentration remaining in the silicon wafer is acceptable for solar cell applications. [ABSTRACT FROM AUTHOR]

The paper describes a robust finite element model of interface motion in media with multiple domains and junctions, as is the case in polycrystalline materials. The adopted level set framework describes each domain (grain) with a single level set function, while avoiding the creation of overlap or vacuum between these domains. The finite element mesh provides information on stored energies, calculated from a previous deformation step. Nucleation and growth of new grains are modelled by inserting additional level set functions around chosen nodes of the mesh. The kinetics and topological evolutions induced by primary recrystallization are discussed from simple test cases to more complex configurations and compared with the Johnson-Mehl-Avrami-Kolmogorov theory. [ABSTRACT FROM AUTHOR]

We report strongly magnetic field dependent transport in crystalline strontium titanate at the interface with an ion beam treated nanolayer. Microscopy shows that this interface is atomically sharp. The results obtained suggest a chemical potential driven transfer of high mobility electrons through the interface into the crystal. This phenomenon provides a strategy for device fabrication without disorder in the conduction channel. We show, for nonmagnetic metals, magnetoresistance and plateau-like Hall magneto-dependence, possibly caused by electron cyclotron effects in a strongly correlated quasi-two-dimensional Fermi gas. [ABSTRACT FROM AUTHOR]