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Active control of the excessively high heat and particle fluxes on the divertor target plates is of fundamental importance to the steady state operation of tokamaks, especially for fusion reactors. A series of experiments have been carried out on this critical issue to relieve the plasma-wall interactions in the experimental advanced superconducting tokamak (EAST) in the last ten years, not only contributing to the long pulse operation of EAST itself, but also providing physical understandings and potential techniques to the next-generation devices like ITER. We have characterized the power deposition pattern and broadened the divertor footprint width effectively. The plasma-wetted area is actively handled using either 3-dimentional edge magnetic topology or advanced plasma equilibrium, thereby peak heat flux around the strike point is reduced. Active control of detachment or radiation compatible with core plasma performance has progressed significantly in very recent years, with a series of active feedback control modules developed and utilized successfully, based on the divertor physics advances with both experiments and simulation. The upper divertor of EAST was upgraded from graphite to active water-cooling ITER-like tungsten in 2014, exhibiting much enhanced heat removal capability. As for the particle exhaust including both fueling and impurity particles, in addition to wall conditioning and impurity source control, the efficiency of particle flux exhaust is optimized by making full use of the divertor closure and the plasma drifts in both scrape-off layer and divertor volume. These heat and particle exhaust advances contribute greatly to a series of EAST achievements like H-mode operation over 100 s. A brief near-term plan on the integrated control of divertor plasma-wall interactions in long-time scale will also be introduced, aiming to provide favorable divertor operation solution for ITER and CFETR.

The use of non-fuel pellets is desirable for ITER due to its decoupling ELM pacing from fueling. In this paper, the Neutral Gas Shielding Model (Parks et al., Nucl, Fusion 34(1994)417) has been applied to the ablation of Li pellets in the H-mode pedestal region. The results show that the injection velocity of pellets is a more convenient parameter for one to control the deposition profile and location of the injected species in the pedestal. The information obtained from this work can further be used as input for fluid transport codes to track the trajectories of the impurity species or as input for advanced MHD codes for better understanding the non-linear destabilization of ELMs.

The transport properties and line emissions of the intrinsic carbon in the stochastic layer of the Large Helical Device have been investigated with the three-dimensional edge transport code EMC3-EIRENE. The simulations of impurity transport and emissivity have been performed to study the dedicated experiment in which the carbon emission distributions are measured by a space-resolved EUV spectrometer system. A discrepancy of the CIV impurity emission between the measurement and simulation is obtained, which is studied with the variation of the ion thermal force, friction force and the perpendicular diffusivity in the impurity transport model. An enhanced ion thermal force or a reduced friction force in the modelling can increase the CIV impurity emission at the inboard X-point region. Furthermore, the impact of the perpendicular diffusivity Dimp is studied which shows that the CIV impurity emission pattern is very sensitive to Dimp. It is found that the simulation results with the increased Dimp tend to be closer to the experimental observation. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Studies of edge plasma and impurity transport with the toroidally and poloidally localized liquid lithium limiter (LLL) on EAST have been performed by the three-dimensional (3D) edge transport code EMC3-EIRENE. The transport behavior of the Li1+ and Li2+ ions shows a non-axisymmetric distribution in the toroidal direction while an axisymmetric distribution is obtained for the Li3+ ions. The spatial structure of the charge state and excitation radiation patterns of lithium impurity can be understood by using field line tracing, which shows that the Li ions with different charge states exhibit different parallel transport behaviors. The 3D line-integrated LiII emission pattern simulated by EMC3-EIRENE shows a reasonable qualitative agreement with the experiment results measured by the CCD camera system on EAST. An unresolved issue in the LLL experiment is that the species emitting the strong visible spectrum observed around the edge plasma region cannot be distinguished by the current experimental diagnostics on EAST. The detailed numerical analysis of the carbon and deuterium emissions has been carried out to resolve this issue. The simulated deuterium emission pattern shows the same qualitative behavior as the experimental observation at the lower divertor region. The strong radiation experimentally observed at the upper divertor region is perhaps due to the mixing of the lithium and deuterium emissions.

Zinc oxide (ZnO) spherical nanoparticles (SNPs) and bitter-melon-like (BML) microparticles were synthesized by a hydrothermal route using a zinc (Zn) plate as a source and substrate at various synthesis conditions. The structural analysis confirmed the formation of ZnO with hexagonal wurtzite phase on the hexagonal Zn substrate with growth of the ZnO microparticles along the [1 0 1] direction. The UV–vis absorption spectra of the ZnO microparticles indicated absorption peaks in the UV region which can be attributed to the band gap of ZnO. The room temperature photoluminescence (PL) of the ZnO microparticles exhibited a broad emission band, which is fitted with four Gaussian peaks and were assigned to transitions involving free excitons and various defect centers. The growth model for the formation of ZnO micro- and nanoparticles is presented.

Magnesium hydroxide (Mg(OH)2) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH)2with hexagonal crystal structure. An optical band gap of 5.7 eVis determined for Mg(OH)2 nanodisks from the UV‐vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH)2 nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH)2 has been converted to MgO by calcination at 450 8C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eVand a broadband PL emission in the UV region. Mg(OH)2 and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Zirconium oxide (ZrO2) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO2 product is of pure monoclinic phase (m-ZrO2) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition,highpurity,andcrystallinity.TheRamanspectraarequantitativelyanalyzedandtheobservedpeaksareattributedtovariousvibration modes of the m-ZrO2. The UV‐vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO2 nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Vertically aligned and well interconnected NiO nanowalls with thin nanodiscs of cubic NiO as the in situ formed building blocks were fabricated via a template-free approach. The alkaline solution of ammonium hydroxide was used as a reductant and Ni foil as both source material and substrate for the nanowall synthesis. Surface morphology analysis confirmed the formation of 15 nm thick and 0.2–1.5 μm wide nanowalls. The nanowalls had the crystal structure of cubic NiO with their growth plane along the [111] direction. An optical band gap of about 3.8 eV for the NiO nanowalls was obtained from the optical absorption measurement. NiO nanowalls exhibited a broad UV emission band centered at around 390 nm. This simple, but efficient synthesis technique can facilitate the growth of well aligned 2D nanostructures with large surface area for possible applications in nanoscale devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Gram quantities of titania (TiO2) nanotubes, with a typical outside diameter about 9 nm, wall thickness of about 2.5 nm, and length of about 600 nm, were synthesized from anatase nanopowder and micropowder using the hydrothermal method. The crystallization, structure, and phase stability of the nanotubes at high temperatures were studied. A morphology change from nanotube to nanowire was observed at 650 °C. The as-prepared nanotubes were usually contaminated with sodium impurities and were poorly crystallized, but under optimized synthesis conditions the impurity phase was completely removed, resulting in highly crystallized nanotubes. The volume filling fraction of the autoclave as well as the concentration of the acid treatment were found to be particularly important for controlling the purity and crystallinity of the resulting nanotubes. The various TiO2-derived nanotube phases (sodium titanate and hydrogen titanate) reported previously by different groups were also observed under different synthesis conditions, resolving the contradiction among the previous results.

We report a simple low-temperature inverse micelle solvothermal route for the synthesis of a large quantity of single-crystalline germanium nanocrystals. X-ray diffraction measurement indicates that the as-prepared nanocrystals are composed of pure Ge with a cubic structure. The morphology, size, chemical composition, crystallinity, and structural features of the as-prepared nanocrystals were characterized by transmission electron microscopy and energy-dispersive x-ray spectroscopy.

A two-step masking technique has been developed to prepare large-scale triangular lattice arrays of uniform sub-micron islands on substrates at room temperature and at low cost by utilizing self-assembly of polystyrene microspheres. As an example, fabrication of large arrays of nickel islands with long-range periodicity and morphological uniformity is demonstrated, which is also ready to apply to fabricate periodic sub-micron islands of other materials on flat substrates in general. The islands so prepared resemble the shape of a hexagonal disc with its size determined by the size of the polystyrene spheres and its thickness variable in a wide range. These islands of various materials on different kinds of substrates can be used in a variety of applications such as catalysts to grow aligned carbon nanotubes and nanowires for 2D photonic crystals, nanoelectrode arrays for molecular devices, nanostructure building blocks for nanofabrications, etc.

Double-walled carbon nanotubes (DWCNTs) were synthesized by chemical vapour deposition using Fe–Mo catalyst supported on magnesium oxide particles. A mixture of gases of methane and hydrogen was used for the growth. The effect of gas pressure, ratio of methane to hydrogen, and growth temperature on the structure, purity, and yield of DWCNTs has been studied in detail. Transmission electron microscope studies revealed that the growth temperature is the crucial factor determining the size of the catalyst particles. Scanning electron microscope studies were also carried out to provide information on the purity and diameter of DWCNTs synthesized under various conditions.

Weak-ferromagnetic (or antiferromagnetic) resonance of Cu and electron spin resonance (ESR) of Gd are observed both in insulating GdSr2Cu2NbO8 and in superconducting GdSr2Cu2RuO8. The Cu resonance implies that the CuO2 planes are magnetic and indicates that the superconducting layer of GdSr2Cu2RuO8 is SrO (not CuO2), as in its related superconducting compound without cuprate planes, doped Sr2YRuO6.

ZnO nanowires were grown in gram quantities on graphite flakes (as collector) using the vapour transport and condensation approach. The yield, defined as the weight ratio of ZnO nanowires to the original graphite flakes, has been studied thoroughly by tuning the various growth parameters such as pressure and temperature inside the tube furnace, the amount of graphite powder in the original source, the source to collector ratio, etc. A yield as high as 200% has been achieved, equivalent to a 40% conversion of the ZnO powder in the original source. A study comparing the photoluminescence spectra of the ZnO nanowires grown on both graphite flakes and substrates with commercially available ZnO powder has been carried out.

We demonstrate here that large area periodic arrays of well-aligned carbon nanotubes can be fabricated inexpensively on Ni dots made by the process of self-assembly nanosphere lithography. These periodic arrays appear colorful due to their efficient reflection and diffraction of visible light. In addition, due to their honeycomb lattice structure, these arrays can act as photonic band gap crystals in the visible frequency range. In this report, we present the initial exploration of the optical properties of such arrays. Here we show that these potential 2D photonic band gap crystal arrays might find very important applications in optoelectronics.

Two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium- and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline-MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer-MMT nanocomposites.

Carbon nanotubes were grown directly on carbon fibers using chemical vapor deposition. When embedded in a polymer matrix, the change in length scale of carbon nanotubes relative to carbon fibers results in a multiscale composite, where individual carbon fibers are surrounded by a sheath of nanocomposite reinforcement. Single-fiber composites were fabricated to examine the influence of local nanotube reinforcement on load transfer at the fiber/matrix interface. Results of the single-fiber composite tests indicate that the nanocomposite reinforcement improves interfacial load transfer. Selective reinforcement by nanotubes at the fiber/matrix interface likely results in local stiffening of the polymer matrix near the fiber/matrix interface, thus, improving load transfer.

Microstructures of well-aligned multiwall carbon nanotubes grown on patterned nickel nanodots and uniform thin films by plasma-enhanced chemical vapor deposition have been studied by electron microscopy. It was found that growth of carbon nanotubes on patterned nickel nanodots and uniform thin films is different. During growth of carbon nanotubes, a nickel particle sits at the tip of each nanotube, and its [220] is preferentially oriented along the plasma direction, which can be explained by a channeling effect of ions coming into nickel particles in plasma. The alignment of nanotubes is induced by the electrical field direction relative to substrate surface.

GdSr 2 Cu 2 RuO 8 superconducts at an onset temperature T c ≈45 K, and exhibits a low-field magnetic resonance, which the evidence suggests is due to magnetically ordered Cu. Since Bernhard et al. [Phys. Rev. B 59 (1999) 1409] have shown that the magnetism and the superconductivity are homogeneous, it follows that if the cuprate planes are homogeneously magnetic, the superconductivity must be located, not in the cuprate planes, but in the SrO layers. Alternatively there are magnetically ordered Cu impurities on Ru sites, with a locally inhomogeneous magnetization.

Heavily overdoped epitaxial superconducting Tl 2 Ba 2 CuO 6+ δ (Tl-2201) thin films with single superconducting transition temperatures as low as 1.5 K (zero resistance) have been successfully synthesized. The films were made by “off-axis” radiofrequency magnetron sputtering and post-deposition annealing with slow cooling. Our investigations showed that the achievement of a single transition can be attributed to an off-axis configuration during sputter deposition, whereas the reduced T c results from a slow-cooling process immediately after annealing at high temperature. Transmission electron microscopy reveals that the films are pure 2201 phase with good crystallinity and modulated structure. Such samples are very much desired for detailed investigations of upper critical magnetic fields using conventional laboratory superconducting magnets, or the dc facilities at National Laboratories.

The ${}^{99}\mathrm{Ru}$ M\"ossbauer effect has been measured in the ${\mathrm{Sr}}_{2}{\mathrm{Ru}}_{x}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{O}}_{4}$ system for $x=1.0,$ 0.7, 0.5, and 0.4 at 4.2 K. The isomer shift measurements show a change of -0.05(.02) mm/s as the compound changes from a metal $(x=0.7)$ to an insulator $(x=0.5).$ This isomer shift change is the electronic signature of the metal-insulator transition. All these spectra are single line. At $x=0.4$ the compound undergoes a magnetic phase transition with the measurement of a hyperfine magnetic field of 7.2(1.5) T. The ${}^{99}\mathrm{Ru}$ M\"ossbauer effect has been measured from 1.8 to 147.5 K for ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and from these measurements the Debye temperature was estimated to be 427(50) K.

Carbon films were prepared by radio-frequency magnetron sputtering on tungsten substrates. The effect of post-irradiation (40 keV, 4×10 17 ions cm −2 ) with active nitrogen ions and inert argon ions was studied. The results show that combined irradiation with these two kinds ions can transform the carbon film into a carbide film due to induced mixing effects. X-ray diffraction and X-ray photoelectron spectroscopy were used to obtain information on the phases, composition and chemical states of elements at the specimen surface.

Zirconia–yttria films containing 7.0 wt% Y 2 O 3 were prepared by r.f. magnetron sputter deposition followed by 40 keV Ar + ion bombardment and then by electron beam heating. The characterization of the ZrO 2 –Y 2 O 3 thin film structure was carried out by Raman spectroscopy and X-ray diffraction. The Raman spectra of ZrO 2 –Y 2 O 3 films prepared by this technique revealed the monoclinic and tetragonal phase structures. The results of X-ray diffraction showed that the films go through an m–t phase transition and have a microcrystalline structure in the form of the tetragonal phase.

We have successfully synthesized multiwall carbon nanotubes by a low temperature solvothermal approach at 310 °C, in which ethoxylated alcohol polyoxyethylene (4) ether was used as carbon source. Transmission electron microscopy observations indicated that the multiwall carbon nanotubes have outer diameters between 5 and 20 nm, and inner diameters between 2 and 8 nm. The length of the multiwall carbon nanotubes is of several micrometres. A possible growth mechanism has been proposed.

Field emission from carbon nanotubes grown on carbon cloth has been studied. An extremely low electric field of less than 0.4V∕μm is required to reach an emission current density of 1mA∕cm2. This ultralow operating electric field of carbon nanotubes grown on carbon cloth is mainly due to a very high field enhancement factor of 1.882×104, which is the result of geometrical configuration of the carbon nanotubes and the substrate. In addition to the field enhancement, the highly disordered microstructure of carbon nanotubes grown on carbon cloth plays an important role to field emission. This unexpected result indicates that the roughness of the substrates on which carbon nanotubes grow is very important. This result also brings us significantly closer to practical applications such as highly efficient lamps, field emission displays, micro vacuum electron sources, etc.

This paper presents an analytical approach for investigating the dynamics and stability of an outer cylindrical shell conveying viscous fluid (i.e. water) in the annulus between the inner shell-type body and the outer shell with thermal load. The steady viscous forces that induce prestress on the shells are determined based on the time–mean Navier–Stokes equations. The shell motions are described by Flügge’s shell equations incorporating the prestress arising from the viscous effect. The shell-vibration-induced fluid forces are described by means of the potential flow theory, and the thermal loads are determined by the thermoelastic theory. The analytical model is conducted by the zero-level contour method with the aid of the weighted residual technology. The present study shows that the effect of viscosity in the annular flow renders the system more unstable. Moreover, the thermal load tends to reduce the critical flow velocity pronouncedly, for which there exists a critical temperature rise.

The length and the spacing of carbon nanotube (CNT) films are varied independently to investigate their effect on the field-emission characteristics of the vertically aligned CNT films grown by plasma-enhanced hot filament chemical vapor deposition using pulsed-current electrochemically deposited catalyst particles. It is shown that, in general, the macroscopic electric field Emac,1, defined as the electric field when the emission current density reaches 1 mA/cm2, can be reduced by increasing the length and the spacing of CNTs. However, for the very-high-density CNT films, the increase of length increases Emac,1 slightly, whereas for the very short CNT films, the increase of spacing does not effectively reduce Emac,1.

The recovery process of 20 vol.-%SiCw/6061 aluminium alloy composite chips has been investigated. The results have shown that, by selecting the proper hot compression parameters, the tensile strengths of recovered composites can reach 85% of the original composite strength. The elastic modulus remained very close to that of the original composite and the binding among the chips was good. Therefore, the recovered composite had a good re-utilisation value.

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).

The time‐varying viscosity of common grout and the nano‐composite grout are measured by rotation vis‐cometer in experiment. The time‐varying viscosity of grout is analyzed according to the characteristics in the process of anti‐seepage treatment for foundation with high pressure water. We applied the principle of effective stress for porous medium to analyze the fluid‐structure coupling in grouting. In the consideration of coupling physical variables, dynamic models of porosity, permeability and viscosity are contained. Thus the diffusion range can be defined by the foundational strain. The distribution of holes in field experiment could be arranged according to the diffusion diameter of grout. Then, the test on strength and permeability is designed to verify grout effect. Based on the results of calculation and experiment, the calculated diffusion radius coincides with experimental results, and the strength and permeability meet the requirements of the project, which is valuable for the anti‐seepage treatment in high pressure foundation.

Zirconia-yttria films containing 8.0 wt.% Y2O3 were prepared on silicon substrates by r.f. magnetron sputter deposition followed by 170 keV Ar+ ion bombardment at room temperature. The microanalyses of ion-bombarded zirconia-yttria films with different ion doses have been carried out by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy. It was found that the amorphous films deposited with r.f. magnetron sputtering were partly crystallized after Ar+ ion bombardment, and that amount of crystallization was dependent on the dose of ion bombardment. The oxidized states of Zr 3d and Y 3d XPS peaks were observed under argon ion bombardment of different doses.

Patterned growth of freestanding carbon nanotube(s) on submicron nickel dot(s) on silicon has been achieved by plasma-enhanced-hot-filament-chemical-vapor deposition (PE-HF-CVD). A thin film nickel grid was fabricated on a silicon wafer by standard microlithographic techniques, and the PE-HF-CVD was done using acetylene (C2H2) gas as the carbon source and ammonia (NH3) as a catalyst and dilution gas. Well separated, single carbon nanotubes were observed to grow on the grid. The structures had rounded base diameters of approximately 150 nm, heights ranging from 0.1 to 5 μm, and sharp pointed tips. Transmission electron microscopy cross-sectional image clearly showed that the structures are indeed hollow nanotubes. The diameter and height depend on the nickel dot size and growth time, respectively. This nanotube growth process is compatible with silicon integrated circuit processing. Using this method, devices requiring freestanding vertical carbon nanotube(s) such as scanning probe microscopy, field emissi...

TiO 2 films were prepared at room temperature by dynamic ion beam mixing where titanium was Ar + sputter deposited on iron substrates and simultaneously bombarded with argon or oxygen ion beams at an energy of 100 keV. The chemical bonding states of the elements on the surface of the films were investigated by X-ray photoelectron spectroscopy (XPS). The XPS results show that carbon on the surface of the films exhibits different states for different bombarding ion species. Argon ion beam bombardment during film deposition induced carbonization forming an O-Ti-C bonding configuration, while oxygen ion bombardment did not. A mechanism related to this phenomenon is suggested.

Zirconia films prepared with two deposition methods, a reactive ion sputter method and a dual ion beam one, were characterized with RBS, XPS, TEM, and XRD analyses. The results show that atomic ratio of [O]/[Zr] approximately constant throughout the layer, showing various zirconium oxides can be formed with the two methods by choosing suitable preparation parameters, and different phase structure can be obtained by selecting deposition method and substrate material. Comparison of optical properties for the zirconia films with these deposition methods is discussed in this paper.

Large arrays of well-aligned carbon nanotubes on glass, silicon, nickel, platinum, etc. have been successfully synthesized by plasma enhanced chemical vapor deposition at temperatures below 500 °C. Either a uniform layer of nickel made by magnetron sputtering or patterns of nickel dots made by e-beam lithography and e-beam evaporation or thermal evaporation was used as the catalyst. Acetylene and ammonia gases were used as the carbon source and dilution gas. Ammonia was also found to act as catalyst. Without ammonia, there was no growth of carbon nanotubes at that low temperature. The diameters of the carbon nanotubes range from a few nanometers to a few hundred nanometers depending on the catalytic nickel size. The length is in a range of a few thousand angstroms to a few hundred micrometers depending on the growth time. In the case of uniform nickel layer used for catalyst, the site density of carbon nanotubes range between 109 to 1012/cm2 depending on the diameters of the nanotubes. Whereas in the case...

Two kinds of distinctive field emission behaviors were observed on vertically aligned multiwall carbon nanotube ~CNT! films grown by hot filament dc-plasma enhanced chemical vapor deposition. Some samples have stable emission current for more than 60 h ~type I!, while others degrade substantially in the first 16 h ~type II!. During the field emission measurement, a brief exposure to air led an abrupt decrease of emission current of all samples. But subsequent reevacuation made type I samples recover the emission current fully, whereas type II samples were damaged permanently reflecting on the irrecoverable emission current. Microstructure studies by transmission electron microscope clearly showed that the stable emission is due to a surface passivation of CNTs by a thin layer of amorphous carbon that prevents CNTs from reacting with ambient gases, e.g., oxygen, during air exposure. © 2004 American Institute of Physics. @DOI: 10.1063/1.1642272#

A high-quality Nd3+ and Mg2+ co-doped LiTaO3 (Nd:MgO:LT) crystal was grown by the Czochralski method. The polarized absorption spectra and fluorescence spectra were studied, and the absorption cross section was calculated by Judd–Ofelt (J–O) theory. The laser performance with different sample cuts of the crystal was investigated for the first time, and it was found that Nd:MgO:LT crystal with different cutting directions (a and c) exhibits different laser properties. By optimizing a partial reflectivity mirror in the laser experimental setting, a high continuous wave output power of 3.58 W was obtained at 1092 and 1076 nm with an optical-to-optical conversion efficiency of 22.78% and slope efficiency of 26.06%. The results indicate that Nd:MgO:LT crystal is a promising candidate for the manufacture of Nd3+ doped periodically poled MgO:LiTaO3 crystal (Nd:PPMgOLT), which should have considerable applications in self-frequency doubling and optical parametric oscillation laser devices.

The RF magnetron sputtering deposited ZrO2-12wt% Y2O3 films at different temperature were post-treated by thermal annealing or electron irradiating. The results of these specimens before and after post-treatment with XRD and morphology analyses show that the phase composition and morphology of RF magnetron sputtering deposited ZrO2-12wt% Y2O3 films were not only dependent on the substrate temperature during preparation, but also related to the annealing technology.

Zirconia-yttria films containing 8.0wt% Y2O3 were prepared on a Si substrate with r.f. magnetron sputtering deposition followed by 170 KeV Ar+ ion irradiation at room temperature. The characterization of these zirconia-yttria films with different ion bombarding doses has been studied by XRD, XPS and AES. It was found that all the films consisted of three portions, the amorphous films deposited with r.f. magnetron-sputtering were partially crystallized and nontransformable tetragonal (T') phase was detected after Ar+ ion bombardment of a dose of 1×1016 ion/cm2, and the oxidized states of Zr3d, Y3d and Ols peaks of XPS were observed under the conditions of argon ion bombardment of different doses.

The oxidation behaviour of NiCoCrAlY-ZrO2·y2O3 coatings produced by using an ion-electron-atom beams combination technique (IEABCT) was studied after air exposure at 1100 °C for up to 300 hours. It was found that pores were dispersed in the coating, especially in the interface between coating and substrate, and no spallation or separation of the ceramic layer from the metallic bond layer were observed. The composition and morphology of the coatings before and after oxidation exposure in air at 1100 °C for 300 hours were examined by microscopy and electron microprobe analysis (EMPA).

We have studied the near-infrared photoluminescence properties of free-standing germanium nano-crystals (20 nm on average) and micro-crystals (60 µm on average) at 80-300 K. Two peaks were observed at ∼1.0 and ∼1.4 eV from both the nano- and micro-crystals. The integrated PL (I(PL)) intensity of the nano-crystals is about an order of magnitude stronger than that of the micro-crystals and the I(PL) is also enhanced by ageing in air for both crystals. The ∼1.0 eV peak position does not change with either the crystal size or temperature. We suggest that the deep traps located at the interfacial region between the surface GeO(2) layer and the bulk crystal Ge is responsible for the near-infrared PL.

Field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied. Iron sulfate or stainless steel was used as the catalyst, acetylene (C2H2) or methane (CH4) was used as the carbon source, and argon (Ar), hydrogen (H2), or ammonia (NH3) was used as the carrier gas. It is found that the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time. In general, higher temperature produces better field emitters than lower temperature, C2H2∕Ar is better than C2H2∕NH3, but CH4∕H2 is the best, and longer growth time normally yields longer CNTs leading to better field emitters. The best sample was made from 0.18mol∕l iron sulfate catalyst with CH4∕H2 at 860 °C for 2 h: an emission current density of 1mA∕cm2 was obtained at 0.4V∕μm corresponding to a field enhancement factor of 3.5×104.