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In this study we demonstrate formation of all-carbon heterostructures induced by field electron emission from diamond needle-shaped crystallites with nanoscale tips. We show that at certain experimental conditions a carbon nanoprotrusion can be formed at the apex of a diamond emitter. Staircase-like current-voltage curves observed for such emitters indicated the presence of the Coulomb blockade effect in the self-assembled all-carbon heterostructures. The mechanism of nanoprotrusion formation via the field-induced surface diffusion of carbon atoms is revealed by observing the structural transformation of the emitter material using transmission electron microscopy. We also explore how the properties of the formed heterostructures evolve with the field emission current, and show that the characteristic size of the formed nanoprotrusion depends on the dimensions of the diamond nanotip. The developed approach offers a way to reproducible fabrication of heterostructured emitters which can be applied as coherent single-electron sources in vacuum nanoelectronics and electron quantum optics. [Display omitted] [ABSTRACT FROM AUTHOR]

The Coulomb blockade effect is commonly used in solid state electronics for the control of electron flow at the single-particle level. Potentially, it allows the creation of single-electron point sources demanded for prospective electron microscopy instruments and other vacuum electronics devices. Here we realize this potential via creation of a stable point electron source composed of a carbon nanowire electrically coupled to a diamond nanotip by a tunnel junction. Using energy spectroscopy analysis, we characterize the electrons liberated from the nanometer scale carbon heterostructures in time and energy domains. Our experimental results demonstrate perfect agreement with theory prediction of Coulomb oscillations of the Fermi level in the nanowire and allow to determine the mechanisms of their suppression. Persistence of the oscillations at room temperature, high intensity field emission with currents up to 1 μA, and other characteristics of our emitters are very promising for practical realization of coherent single-electron guns. Image 1 [ABSTRACT FROM AUTHOR]

Field electron emission from the edges of large-area (∼1 cm × 1 cm) graphene films deposited onto quartz wafers was studied. The graphene was previously grown by chemical vapour deposition on copper. An extreme enhancement of electrostatic field at the edge of the films with macroscopically large lateral dimensions and with single atom thickness was achieved. This resulted in the creation of a blade type electron emitter, providing stable field emission at low-voltage with linear current density up to 0.5 mA/cm. A strong hysteresis in current–voltage characteristics and a step-like increase of the emission current during voltage ramp up were observed. These effects were explained by the local mechanical peeling of the graphene edge from the quartz substrate by the ponderomotive force during the field emission process. Specific field emission phenomena exhibited in the experimental study are explained by a unique combination of structural, electronic and mechanical properties of graphene. Various potential applications ranging from linear electron beam sources to microelectromechanical systems are discussed. [ABSTRACT FROM AUTHOR]

The nanographite (NG) films consisting of tiny graphite crystallites (nanowalls) are produced by carbon condensation from methane–hydrogen gas mixture activated by a direct current discharge. High aspect ratio and structural features of the NG crystallites provides efficient field electron emission (FE). Applicability and performance of the NG films in an electron gun (E-gun) of a solar wind thruster system with an electric sail (E-sail) is tested. The long-term tests are demonstrated suitability of E-gun assembly with the NG cathodes for the real space missions. The results of the tests are analyzed and physical mechanisms of the cathode aging and practical methods for improvement performance of the E-gun are proposed. [ABSTRACT FROM AUTHOR]

Highlights • The layered films made of hyaluronic acid (HA) and chitosan (CS) were prepared and characterized. • Formation of the CS/HA polyelectrolyte complex led to crystallization of the CS layer. • The CS/HA membranes showed high selectivity during the separation of water from the ethanol-water mixtures. • The membrane microstructure was observed to change during the pervaporation process using LVSEM. Abstract Self-supporting multilayer films containing a polyelectrolyte complex (PEC) were prepared by the sequential layering of sodium hyaluronate (HA, MW 5.4 × 104) and chitosan (CS, MW 1.6 × 105, the degree of deacetylation 0.80) in different orders. Imaging with low-voltage scanning electron microscopy (LVSEM) showed that the CS/HA films had a multilayer structure, while X-ray diffraction (XRD) indicated significant structuring of the CS layer near the PEC-CS region. Analysis of the thermal properties of the CS/HA films revealed differences in the structural organization and morphological features of the polymer layers and high thermal stability of the PEC layer. Testing of the transport properties of the CS/HA film in pervaporation (PV) separation using different compositions of ethanol-water mixtures indicated that the multilayer membrane was selective across a wide range of concentrations in the feed. Separation of an azeotropic ethanol-water mixture containing 5 wt% water yielded a permeate consisting of about 100 wt% water. LVSEM revealed that the membrane microstructure changed during the PV process due to membrane swelling and changes in the arrangement of the macromolecules during transport of the penetrant. The results support the use of CS/HA composite films as highly effective PV membranes. In addition to pervaporation separation, CS/HA multilayer films can also be used for drug delivery, tissue engineering, and wound healing applications. [ABSTRACT FROM AUTHOR]

The relationship between structure, electrical and magnetic properties of thin poly( p -xylylene) - nickel nanocomposite films with Ni concentrations from 5 to 30 vol% was studied. It was found that metal concentration strongly affects size and oxidation state of the nanoparticles and composites morphology. At nickel concentration below 5 vol% the nanoparticles are oxidized to NiO and homogeneously distributed within fine-grained polymer matrix. An increase of Ni concentration up to 10 vol% results in the development of coarse-grained morphology with preferable localization of the nanoparticles at the boundaries of polymeric grains. And finally, in the composite films with nickel concentration above 20 vol%, the fine-grained morphology is observed again, but the nanoparticles are mainly metallic. Effect of the filler content on electrical and magnetic properties of the nanocomposites was elucidated showing that they are determined by percolation phenomenon with the threshold value of about 10 vol%. The well-pronounced magnetic hysteresis as well as ferromagnetic ordering were observed at Ni content above the percolation threshold. The diagrams of magnetic properties of these composites as a function of composition and temperature were elaborated. It was demonstrated that film annealing can be used to control magnetic properties of the composites and strongly enhance magnetoresistance. [ABSTRACT FROM AUTHOR]

Squid β-chitin has been exfoliated in aqueous acrylic acid (AA), after which a composite film of chitin microfibrils in polyacrylic acid (PAA) has been prepared by in situ polymerization of the AA. The segregated chitin fibrils in the composite are 4–6 nm in diameter, with an aspect ratio >250. After drying cast films of the composites containing 1, 2 and 3% (w/w) chitin at 140 °C for four hours, there was a dramatic resistance to swelling in water, in that the dried films showed only small changes in shape and properties after four hours immersed in water.The most profound impact of the reinforcement on the mechanical properties is observed at high relative humidity (RH), when the PAA is in the rubbery state. At 97.5% RH and room temperature, the elastic moduli of the composites with 1, 2 and 3% (w/w) chitin were 150, 230 and 2100 MPa respectively, compared to 65 MPa for pure PAA. The main contribution to the filler-reinforcing effect is the high aspect ratio of fibrils and non-covalent interactions, but the stability in water suggests the presence of chemical bonding between the PAA and chitin. [ABSTRACT FROM AUTHOR]

In this study, variable-temperature grazing-incidence X-ray diffraction, transmission electron and scanning force microscopy were employed to address the semicrystalline structure and surface morphology of thin poly( p -xylylene) – silver nanocomposite films with Ag concentrations up to 12 vol.%. It was observed that the dominant crystalline modification of poly( p -xylylene) in the studied films is α -form, which is in contrast to thick poly( p -xylylene) films deposited at liquid nitrogen temperature where β -form prevails. The films exhibit planar texture that can be further enhanced on annealing. The optical properties of the films were studied by UV–vis and IR-spectroscopy. It was found that the samples display surface plasmon resonance, with the peak wavelength in the range of 435–445 nm. The peak positions undergo a redshift upon a long-term storage under ambient conditions. The IR-spectroscopy reveals the bands, which can be assigned to the vibrations of oxygen-containing groups, with intensity increasing with silver content. [ABSTRACT FROM AUTHOR]

We report cathodic deposition of birnessite oxide from permanganate alkaline solutions into porous flexible cloth consisting from carbon nanotubes. Oxide distribution in the pores is studied by means of electron microscopy, including transmission microscopy of microtom cross-sections and local elemental analysis. Oxide distribution depends on applied deposition mode. The intermittent potentiostatic mode favors the penetration of permanganate reagent into the pores of CNT cloth and allows us to fabricate more homogeneous hybrid material. We demonstrate a number of advantages of hybrid materials with oxide located mostly inside the cloth pores as compared to oxide located at external surface of the cloth. [ABSTRACT FROM AUTHOR]

We consider compositional and structural factors which can affect the activity of bixbyite α-Mn 2 O 3 towards the oxygen reduction reaction (ORR) and the stability of this oxide in alkaline solution. We compare electrochemistry of undoped, Fe and Al-doped α-Mn 2 O 3 with bixbyite structure and braunite Mn 7 SiO 12 having bixbyite-related crystal structure, using the rotating disk electrode (RDE), the rotating ring-disk electrode (RRDE), and cyclic voltammetry (CV) techniques. All manganese oxides under study are stable in the potential range between the ORR onset and ca. 0.7 V vs. Reversible Hydrogen Electrode (RHE). It is found that any changes introduced in the bixbyite structure and/or composition of α-Mn 2 O 3 lead to an activity drop in both the oxygen reduction and hydrogen peroxide reactions in this potential interval. For the hydrogen peroxide reduction reaction these modifications also result in a change in the nature of the rate-determining step. The obtained results confirm that due to its unique crystalline structure undoped α-Mn 2 O 3 is the most ORR active (among currently available) Mn oxide catalyst and favor the assumption of the key role of the (111) surface of α-Mn 2 O 3 in the very high activity of this material towards the ORR. [ABSTRACT FROM AUTHOR]