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We have performed an experiment to compare as directly as realizable the ionization production rate by HF radio wave energy versus by solar EUV. We take advantage of the commonality that ionization production by both ground‐based high‐power HF radio waves and by solar EUV is driven by primary and secondary suprathermal electrons near and above ~20 eV. Incoherent scatter radar (ISR) plasma‐line amplitudes are used as a measure of suprathermal electron fluxes for ISR wavelengths near those for 430 MHz and are indeed a clean measure of such for those fluxes sufficiently weak to have negligible self‐damping. We present data from an HF heating experiment on November 2015 at Arecibo, which even more directly confirm the only prior midlatitude estimate, of order 10% efficiency for conversion of HF energy to ionospheric ionization. We note the theoretical maximum possible is ~1/3, while ~1% or less reduces the question to near practical irrelevance. Our measurements explicitly confirm the prediction that radio‐frequency production of artificial ionospheres can be practicable, even at midlatitudes. Furthermore, that this midlatitude efficiency is comparable to efficiencies measured at high latitudes (which include enhancements unique to high latitudes including magnetic zenith effect, gyrofrequency multiples, and double resonances) requires reexamination of current theoretical thinking about soft‐electron acceleration processes in weakly magnetized plasmas. The implications are that electron acceleration by any of a variety of processes may be a fundamental underpinning to energy redistribution in space plasmas. Our measurements explicitly confirm the prediction that radio‐frequency production of artificial ionospheres is practicableArtificial ionospheres can be created even at the midlatitude site at Arecibo ObservatoryWe have confirmed 10% energy conversion‐efficiency for HF radio wave to kinetic electron‐acceleration at Arecibo Observatory

AbstractThe stability of pressure-driven liquid-liquid viscosity-stratified microchannel flow is investigated by considering the combined effects of electrical double layer (EDL) and boundary slip. The electrical streaming currents determined by the Streaming Electrical Current Balance (ECB) and the boundary slip are considered by Navier slip assumption. The stability of flow is studied by the small disturbance theory. Numerical results indicate that the effect of boundary slip on the flow stability is strongly depended on the EDL. The boundary slip stables the flow when EDL effect is weak and destabilizes the flow when EDL effect is strong. The effects of boundary slip and EDL on flow stability is also determined by viscosity ratio, the height of channel, interface position and conductivity ratio.

ABSTRACTThe effects of boundary slip on the stability of finite miscible/immiscible liquid-liquid stratified microchannel flow were investigated. In this approach, the boundary slip was considered by Navier slip assumption and the finite-miscible liquid-liquid interface was modeled by double film model. The stability of the flow was studied by the small disturbance theory. The results indicated that the effects of boundary slip on the instability of finite miscible stratified microchannel flow with different viscosity ratio, interface location and the property of interface (i.e.thickness and viscosity distribution of mixed layer) are distinct and complex. The effect intensity of upper and lower boundary slip on flow stability is determined by viscosity ratio, interface structure (different Ns) and film thickness. When the interface changes from the channel center to the wall, the critical Re number is enhanced by boundary slip and especially markedly near the critical line and after across the critical line it suddenly decreases to a small value (even to 424). The flow stability always increased by boundary slip.

The morphological manipulation, structural characterization, and photoluminescence properties of different CdSe nanocrystals are reported. Several different CdSe structures, including nanowires, nanorods, nanoparticles, and tetrapod crystals, have been grown on silicon substrates by means of simple, Si‐assisted chemical vapor deposition. By manipulating the growth driving force (i.e., the degree of supersaturation), the morphology of the CdSe nanocrystals can be varied sequentially from nanowires/nanorods to nanoparticles to tetrapod structures. The optical properties of the CdSe nanocrystals are investigated using photoluminescence spectroscopy. Some thermodynamic models are proposed to explain the results.

Single‐crystal gold nanosheets, with triangular, hexagonal, or truncated triangular shapes, from several to tens of micrometers across and tens of nanometers thick, have been successfully synthesized in high yield via a simple and low‐cost chemical route in an ethylene glycol solution, on the basis of a polyol process. The planar surfaces of the Au nanosheets are atomically flat and correspond to {111} planes; the lateral surfaces are {110} planes. The nanosheets show strong optical absorption in the near infrared region of the electromagnetic spectrum. Both the ethylene glycol and the surfactant polyvinylpyrrolidone (PVP), in the solution play important roles in the formation of the Au nanosheets. The concentrations of the precursors (PVP, HAuCl4) and the reaction temperature are also crucial to the morphology and size of the final product. The formation of such large, single‐crystal nanosheets is explained by the preferential adsorption of some species of molecules from the solution onto the {111} planes of Au nuclei, and the connection of small, triangular nanosheets. These nanosheets could be used easily, for example, in gas sensors, in the fabrication of nanodevices and substrate materials, in property studies, and also for inducing hypothermia in tumors.

High purity single crystal alpha silicon nitride (α-Si3N4) nanowires were obtained in high yield via a simple vapor phase reaction approach without the presence of catalyst. The produced α-Si3N4 nanowires have diameters mostly ranging from 30 to 100 nm and lengths of several hundred micrometers. The nanowires were grown via vapor–solid (VS) mechanism. The room-temperature dielectric properties show that the effective dielectric constants of α-Si3N4 nanowires is higher than that of the α-Si3N4 micropowders, especially at low frequencies. Analysis of the dielectric properties indicates that the small size effect of nanowires has great influence on the dielectric behavior of the samples. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnS nanostructures with different morphologies, sizes, and microstructures were synthesized by the evaporation of ZnS nanopowders. Based on the appearance of the as‐synthesized products, we show that substrate temperature and catalyst are the critical factors for controlling the size and the structure of various kinds of ZnS nanostructures, such as nanorods, nanowires, nanobelts, and nanosheets. Within a certain temperature range, products with a specific morphology can be obtained. Therefore, it may be possible to obtain ZnS nanostructures with a specific morphology by controlling the reaction temperature and catalyst. This represents an important step toward the design and control of nanostructures. High‐resolution electron microscopy revealed that most of the nanorods and nanowires grew along the [100] direction, whereas most of the nanobelts and nanosheets grew along [001]. Photoluminescence properties and growth mechanisms of these as‐synthesized ZnS nanostructures are discussed.

A large amount of one‐dimensional (1D) Ce‐doped ZnO nanostructures with different morphologies has been successfully synthesized by annealing a polymeric precursor at various temperatures. The evolution of the morphologies and microstructures was investigated by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution TEM (HRTEM). The results show that the morphologies vary drastically with increasing synthesis temperature and the photoluminescence (PL) of the products depends on both the synthesis and measurement temperatures. The CeO layer forms first and becomes a catalytic center for the ZnO growth. At a synthesis temperature lower than the boiling point of Zn, Zn and O atoms can stack epitaxially along the CeO catalytic layer and form a bicrystal nanobelt‐like structure with a trapezoid‐like end and a concave growth fault center. At a synthesis temperature higher than the boiling point of Zn, however, nanowires with an incommensurately modulated superstructure are obtained due to the high reaction rate and the formation of a periodic separation of the CeO layer. As for the room‐temperature PL of ZnO, the incorporation of donor Ce leads to the disappearance of the green band and the appearance of a purplish‐blue emission peak, whose position shifts towards the red and whose intensity decreases with increasing synthesis temperature. Analysis of this temperature‐dependent luminescence indicates that the purplish‐blue emission of nanobelts prepared at 850 °C originates from a donor‐bound exciton emission, and, contrary to the nanowires, it undergoes a change from an emission of the electron–hole plasma (EHP) to an emission of the donor‐bound exciton with decreasing measurement temperature.

α-Al2O3 Nanobelts and nanosheets with different morphologies and sizes have been successfully synthesized by a simple chemical route from H2O and Al in an argon atmosphere. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the as-synthesized α-Al2O3 nanostructures consist of nanobelts and nanosheets. We find that the temperature distribution inside the alumina tube is the critical factor determining the morphologies and sizes of the α-Al2O3 nanostructures. Photoluminescence measurements showed a blue luminescence band in the wavelength range of 400–500 nm, which can be attributed to F+ centers in the α-Al2O3 nanostructures. The growth of these products is believed to be mainly determined by growth kinetics as well as thermodynamics.

A silver nanowire array micropolarizer within an anodic alumina membrane (AAM) was fabricated by anodization of pure Al foil and electrodeposition of Ag, respectively. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations reveal that the nanowires are essentially single crystals, and have an average diameter of 90 nm. Spectrophotometer measurements show that the silver nanowire arrays embedded in the AAM can only transmit vertically polarized light to the wires. An extinction ratio of 25–26 dB and average insertion loss of 0.77 dB in the wavelength range 1–2.2 μm were obtained, respectively. Therefore the Ag nanowire/AAM can be used as a wire-grid type polarizer.

A silver nanowire array micropolarizer within an anodic alumina membrane (AAM) was fabricated by anodization of pure Al foil and electrodeposition of Ag, respectively. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations reveal that the nanowires are essentially single crystals, and have an average diameter of 90 nm. Spectrophotometer measurements show that the silver nanowire arrays embedded in the AAM can only transmit vertically polarized light to the wires. An extinction ratio of 25-26 dB and average insertion loss of 0.77 dB in the wavelength range 1-2.2 ?m were obtained, respectively. Therefore the Ag nanowire/AAM can be used as a wire-grid type polarizer.

Large-scale single-crystalline CdO nanowires have been successfully fabricated from the electrochemical deposition mixture film of Cd and Te at 450°C, and characterized by x-ray diffraction (XRD) powder, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images show that these nanowires are uniform with diameters of about 40–60 nm, length up to several tens micrometres. XRD and selected area electron diffraction analyses altogether indicate that these CdO nanowires crystallize in a NaCl cubic structure. The growth mechanism of these nanowires is also proposed as vapour–liquid–solid mechanism, in which Te serves as a liquid-forming agent.

A laminated micropolarizer of Pb nanowire arrays was fabricated within an anodic alumina membrane (AAM) by anodization of the pure Al foil and subsequent electrodeposition of Pb. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, selected‐area electron diffraction, and high‐resolution electron microscopy investigations reveal that the ordered Pb nanowires are essentially single crystal, and have an average diameter of 40 nm. Spectrophotometry measurements show that the Pb nanowire arrays embedded in AAM can only transmit polarized light vertical to the wires. An extinction ratio of 17 to 18 dB and an average insertion loss of 0.4 dB cm–1in the wavelength range of 1 to 2.2 μm were obtained, respectively. Therefore, these Pb nanowire/AAM composites can be used as a wire grid type micropolarizer.

α-Al2O3 nanowires and nanobelts have been successfully synthesized from Al pieces and SiO2 nanoparticles at 1200 °C and 1150 °C, respectively, in a flowing Ar atmosphere. The α-Al2O3 nanowires are uniform with diameters of 20−70 nm and lengths of 15−25 μm, and the nanobelts are several to tens of micrometers long, with width of 0.1−1 μm and thickness of 10−50 nm. The growth of the nanowires is controlled by a vapor−liquid−solid (VLS) growth mechanism, while the growth of the nanobelts may be due to a vapor−solid (VS) process. Infrared spectra of these nanostructures are different from that of the bulk α-Al2O3. Photoluminescence (PL) measurements under excitation at about 255 nm show that the nanowires and nanobelts have emission peaks at 394 and 392 nm, respectively. On the basis of the discussion of the thermal annealing in different atmospheres such as O2 and H2 on the behaviors of the PL spectra, we suggest that optical transitions in oxygen-related defects, F⁺ (oxygen vacancy with one electron) centers, are responsible for the observed emission.

Titanium carbide based cermets with additions of titanium nitride nanoparticles were fabricated by using ultrasonic dispersion and conventional powder metallurgy techniques. In order to characterise the microstructure, SEM and TEM have been utilised. The results show that the microstructure becomes finer with increasing additions of titanium nitride nanoparticles. The mechanical properties were also measured and the results show that the properties do not change monotonously with the amount of titanium nitride nanoparticle addition. Good properties can be obtained when the amount of TiN addition reaches 6 - 8 wt-%. The improvement of properties is mainly owing to the refinement of TiC grains as well as the deflection effect of titanium nitride nanoparticles on crack propagation.

Ordered Ni-Cu alloy nanowire arrays embedded in the hexagonally ordered nanochannels of anodic alumina membranes (AAMs) were fabricated by electrodeposition. The x-ray diffraction, x-ray energy dispersion spectrum, scanning and transmission electron microscopy were utilized to characterize the Ni-Cu alloy nanowire arrays. The results reveal that single crystalline Ni-Cu alloy nanowires are single crystal and that the atomic composition of Ni and Cu is very close to a 1 : 1 stoichiometry. Magnetic hysteresis loop shows that the Ni-Cu alloy nanowire arrays embedded in AAMs have perpendicular magnetic anisotropy, indicating their potential applications in perpendicular magnetic recording.

Single-crystalline In₂O₃ nanowires have been successfully synthesized from indium grains by a vapor–solid method at 1030 °C in 90% Ar and 10% O₂ atmosphere. These nanowires are uniform with diameters of 40–120 nm and lengths of about 15–25 µm, and crystallize in a cubic structure. The growth of these nanowires is controlled by a spiral growth mechanism. Photoluminescence (PL) measurements show a green–blue PL band in the wavelength range of 400–700 nm with a peak at 470 nm (2.64 eV), caused by oxygen vacancies in the In₂O₃ nanowires.

Ordered ferromagnetic−nonmagnetic alloy (Co−Cu, Co−Ag and Fe−Ag) nanowire arrays embedded in the nanochannels of anodic aluminum membranes (AAM) have been fabricated by electrodeposition. Scanning electron microscopy and transmission electron microscopy observations reveal that these alloy nanowires are uniform in diameter and ordered. Magnetic measurements show that the perpendicular coercivity (HC^⊥) of these ordered nanowire arrays increases dramatically, reaches their maximum, and then decreases sharply during the annealing process. However, there is not much change of the parallel coercivity (HC^∥) for these alloy nanowire arrays in the same annealing conditions. This phenomenon should be contributed to the special structure of the nanowires/AAM.

We have successfully fabricated ordered, well-crystallized Bi₂S₃ nanowire arrays embedded in the nanochannels of porous anodic aluminium oxide templates by direct current electrodeposition from a dimethylsulfoxide solution containing BiCl₃ and elemental sulfur. X-ray diffraction and selected area electron diffraction investigations demonstrate that the Bi₂S₃ nanowires have an orthorhombic uniform structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 40 nm and lengths up to 5 µm. X-ray energy dispersion analysis indicates that the atomic composition of Bi and S is very close to a 2 : 3 stoichiometry. The optical properties of these nanowires were characterized by optical absorption techniques. These studies reveal that the annealed Bi₂S₃ nanowires have an optical band edge (direct) of about 1.56 eV.

In this article, we report the fabrication of highly ordered TiO2 nanowire arrays by anodic oxidative hydrolysis of TiCl3 within a hexagonal close-packed nanochannel alumina (NCA). The single-crystalline anatase TiO2 nanowires with diameters about 15 nm and lengths about 6 μm are obtained after annealing at 500 °C. Finally, the fabrication and characterization of highly ordered Au and Ni nanowire arrays with selectable diameters are also reported.

Dititanium sulfide (Ti2S) nanofibers were synthesized through chemical reactions from gaseous reagents of TiClx, H2S, and S with the help of Ni catalysts at elevated temperature (950 °C). Highly dispersed Ni nanoparticles and H2S (or S) gases were obtained by decomposing the preintroduced NiSO4 nanoparticles confined in the pores of activated carbon in a reducing H2 atmosphere. The active Ni catalyst provides an energetically favored site for the absorption of gaseous TiClx, H2S, and S to form an ultrafine liquid alloy droplet containing Ti and S atoms. Then a vapor−liquid−solid growth was involved in the formation of Ti2S nanofibers. SEM and TEM investigations show that the Ti2S crystals grew in the form of nanofibers with diameters mainly around 20~50 nm and lengths up to several tens of micrometers. Most Ti2S nanofibers have smooth surface with a quadrilateral, triangular, or hexagonal cross section, while the others have a wavy appearance.

K2MnSn2Se6 (I), K2MnSnSe4 (II), and K2Ag2SnSe4 (III) were prepared by molten-salt (alkali-metal polyselenide flux) reactions at intermediate temperature (400−520 °C). Their crystal structures were determined by single-crystal X-ray diffraction techniques. Crystal data for I:  space group P4/ncc, a = 8.167(1), c = 19.724(4) Å, Z = 4, R1/wR2 = 0.0435/0.0722 for 592 observed reflections and 29 variables; crystal data for II:  space group P&fourmacr;n2, a = 10.574(1), c = 8.301(2) Å, Z = 2, R1/wR2 = 0.0339/0.0939 for 1208 observed reflections and 40 parameters; crystal data for III:  space group P2/c, a = 7.575(2), b = 5.920(1), c = 12.148(2) Å, β = 113.56(3)°, Z = 2, R1/wR2 = 0.0595/0.1135 for 1098 observed reflections and 45 parameters. The crystal structure of I consists of infinite %@mt;sys@% %@sx@%∞%@be@%1%@sxx@%%@mx@% [MnSn2Se6]^2- anionic chains containing [Sn2Se6^4-] units linked by tetrahedrally coordinated Mn²⁺ ions, with the K⁺ cations situated between the chains. II contains a three-dimensional framework formed by corner- and edge-sharing SnSe4 and MnSe4 tetrahedra, with large channels hosting the K⁺ cations. III is a layered compound containing %@mt;sys@% %@sx@%∞%@be@%2%@sxx@%%@mx@% [Ag2SnSe4]^2- anionic layers separated by K⁺ counterions. The anionic layer is formed by parallel SiS2-type %@mt;sys@% %@sx@%∞%@be@%1%@sxx@%%@mx@% [AgSe2]^3- chains cross-linked by tetrahedral SnSe4 via bridging selenium atoms of the chains. The results from differential scanning calorimetry (DSC) measurements show that I is stable up to 590 °C, II decomposes at about 243 °C, and III melts congruently at about 510 °C. I, II, and III are semiconductors with estimated band gaps of 2.0, 1.7, and 1.8 eV, respectively.