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We have studied luminescent properties of a ZnO whisker array, a promising crystalline material for scintillation detectors, capable of ensuring a fast and strong response and a short afterglow time. Measurements have been performed under X-ray and UV optical excitation. We present a comparative analysis of spectral features of the near-band-edge emission of the whisker array at low (∼80 K) and room temperatures in relation to the excitation method.

In this work, we demonstrate boron nitride whisker @ graphene (BN@GE) nanohybrids with a unique morphology as a thermally conductive filler for improving the thermal conductivity of a polymer matrix. In this structure, GE sheets were applied to insulating hexagonal boron nitride (BN) whiskers via a simplified method to ensure the sheets were well separated when used in epoxy composites. The addition of GE to produce the BN@GE hybrids was found to reduce the length of the BN whiskers. In addition, separation of the sheets enhanced the three-dimensional thermally conductive networks within the composite, which improved the thermal conductivity and significantly enhanced the dielectric constant. Furthermore, the implanted insulating network of BN inhibited the charge carrier mobility on the well-separated sheets via GE fixation on the BN whiskers, and resulted in a low dielectric loss. As a result, the epoxy composite containing 40 wt% BN@GE-15 hybrid filler exhibited a thermal conductivity, dielectric constant, and ultra-low dielectric loss of 1.26 W m−1 K−1, 12.7, and 0.0051, respectively. We expect this uniquely structured hybrid filler will be suitable for the fabrication of thermal interface materials with high thermal conductivities and low dielectric losses.

Mammalian whiskers can perceive obstacles and airflows. In this study, an electronic whisker (E-whisker) sensor was designed and fabricated by setting a PVDF ring with symmetrical electrodes on the root of a fiber beam. Vibration displacements with different waveforms were applied at the free end of the E-whisker beam to study the relationship between the vibration displacements and the output signals. The E-whisker protrusion sensing ability was investigated by driving it to sweep through the surface of a base platform. A static E-whisker beam and a swinging E-whisker were then separately placed in a wind tunnel to detect the airflow perception of the sensor. The experimental results suggested that the E-whisker could sense the frequencies and amplitudes of displacements at its free end, the height and width of a platform or the heights of other irregular protrusions; the static E-whisker could sense the magnitude or direction of an impact airflow, while the swinging E-whisker could sense the magnitude of a constant airflow. Thus, this kind of E-whisker could perceive the environment and airflow through touch sensation and could be used as a physical model to study the principles and abilities of animal whiskers to perceive obstacles and airflows.

This paper prepared magnesium borate whisker reinforced aluminum matrix composites by extrusion casting, and studied the effects of the volume fraction of the reinforced phase on the mechanical properties, thermal expansion properties and microstructure of the composites. The test results show that the reinforced magnesium borate whisker in the composite can be uniformly dispersed in the aluminum matrix to improve the strength. With the increase of the volume fraction, the strength of the composite material increases and the plasticity decreases. When the whisker volume fraction is 30%, the strength of the composite material reaches the maximum, with its tensile strength reaching 244 MPa and elastic modulus 107.6 GPA. When the whisker volume fraction is 20%, the composite has the best plasticity and the fracture elongation is 0.47%. The thermal expansion curve of the composite shows that the increase of whisker volume fraction will reduce the thermal expansion coefficient of the composite.

Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction (IJJ) inside the crystal structure. In this paper, we utilized BSCCO cross-whisker (CW) junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the CW IJJ at the frequency of ∼0.7 THz, which is the first observation of a THz emission from whiskers to our knowledge. Our findings would enlarge the applicability of BSCCO superconductors for compact THz emission sources.

In this study, the titanium matrix composites (TMCs) reinforced by TiB whiskers (TiBw) were fabricated by spark plasma sintering (SPS) technique. The dynamic compression test was carried out to study the effect of TiBw content on dynamic mechanical properties of TiBw/TMCs. Results showed that the TiBw content (0.76vol%~6.84vol%) correspond to specific microstructure which affect the dynamic mechanical properties of the composites. Under high strain-rate (3100s−1), the 4.56 vol.% TiBw/TMCs showed the highest flow stress (~1968MPa) and strain (~15%). The absorbed energy increased first and then decreased with increase of TiB2 content, and the highest absorbed energy of 275.8 MJ.m−3 was achieve by TMC2. Besides, the analysis of fracture appearance indicated that TiBw dominates the failure of the TMCs, fractography of composites varies by the TiBw content of TMCs.

It has been widely confirmed that alloying significantly can mitigate the formation of tin (Sn) whiskers and consequently became a possible candidate as a lead-free alloys coating material in the microelectronics industry. In this study, the effect of 0.05 wt.% Ni addition on the formation and growth of Sn whisker in Sn-0.7Cu solder coatings have been investigated under continuous mechanically stress induced at room temperature. It is clearly found that Ni addition have significantly enhanced stress relaxation by reducing the growth rate of formation Sn whiskers in Sn-0.7Cu solder coatings. The morphology of (Cu,Ni)6Sn5 interfacial IMC was more refine and thinner with a fine scallop-shaped interfacial intermetallic layer purposely to lower the compressive stress of Sn coating and extend the nucleation period, thus mitigating the formation and growth of Sn whiskers.

A cement slurry system was designed and optimized in order to meet the strict operation and production requirements of the gas storage well cementing. System formula was G cement +1.5% filtrate reducer +1% dispersant +0.5% defoamer +10% calcium carbonate whisker +8% polychloroprene latex +0.08% polypropylene fiber +0.09%PVA fiber + water. Evaluation experiments showed that the engineering properties of cement slurry system were well, such as good rheology, low water loss, no free liquid, wide adjusted range of thickening time, good anti channeling ability and good suspension stability. The experiment results of cement mechanical strength showed that the 7 days tensile strength of the cement specimen was increased 62.3% higher than that of the neat cement grout, while the 7 days compressive strength was increased 47% and the elastic modulus was reduced 41.7% compared to the standard peak. The micro-structure and morphology of gas storage cement specimens were observed and the mechanism of cement strength enhanced by fiber, latex and calcium carbonate whisker were studied that fiber and calcium carbonate whisker bridged the cracks, reduced cracked tip stress concentration, effectively prevented the development and diffusion of cracks, enhanced cement deformability and reduced the elastic modulus; polychloroprene latex formed latex film on the surface of cement particles and fiber, which improved the cementing strength and the interface micro-structure between fiber and cement, reduced the stress concentration caused by mutant materials, improve the toughness of cement stone greatly.

Gadolinium aluminate (GdAlO3, GAP) nano whiskers were synthesized by the hydrothermal-solid state method, Fourier-transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and thermogravimetry-differential thermal analysis (TG-DTA) were employed to analyze the phase change and the nucleation mechanism of GAP during calcing process. The results show that the precursor of GAP prepared by hydrothermal is (NH4)xGdAl(OH)y(NO3)z·nH2O. When the calcination temperature is higher than 900 °C, the precursor recrystallizes, forming the needle shape GAP under the synergistic effect factors. The best preparation conditions are as follows: ammonia water as mineralizer, pH = 9, calcination temperature 1100 °C and holding time 3 h.

In order to study the effect of calcium sulfate whisker on the mechanical characteristics of Portland cement, the fluidity, initial setting time, final setting time, flexural strength and compressive strength of calcium sulfate whisker-reinforced cement with 0∼1.0% (mass fraction) were studied using experimental method. The results show that calcium sulfate whisker has little effect on the fluidity, initial setting time and final setting time. For the 28-day flexural strength and compressive strength of calcium sulfate whisker-reinforced cement, the optimum whisker content is 0.4% and 1.0% and the corresponding strength is increased by 19.54% and 35.84%, respectively. Compared with calcium carbonate whisker, the reinforcement effect of calcium sulfate whisker on the strength of Portland cement is better.

Electroplated tin (Sn)Limeited finishes are widely used in the electronics industry due to their excellent solderability, electrical conductivity and corrosion resistance. However, since prohibiting the use of lead (Pb) in electronics, the issue of tin (Sn) whisker has become one of the most imperative issues that need to be resolved. Moreover, with the increasing demand for electronics miniaturization, Sn whisker growth is a severe threat to the reliability of microelectronic device. This paper investigates the effect of electroplating current density (10, 30 and 50 mA/cm2) on whisker growth at room temperature. A simple micro- indentation test was used to accelerate continuously the growth of Sn whisker at room temperature storage for 24 h. Morphology analysis of Sn whisker growth was done using scanning electron microscope (SEM) and image-J Software. Axial length of the Sn whisker was calculated by using JEDEC Standards (JESD22-A121A).

In the present study, the effect of Si addition on the microstructure and subsequently, on the oxidation behavior of nanostructured oxide dispersion strengthened (ODS, 14YWT) ferritic steel was investigated. Two types of nanostructured ODS ferritic steel powders viz. Fe-14Cr-2W-0.3Ti-0.3Y2O3 (Si-free) and Fe-14Cr-2W-0.3Ti-1Si-0.3Y2O3 (Si-containing) were mechanically alloyed up to 50 h and consolidated via spark plasma sintering. The Si-containing sintered ODS steel contained single phase ferritic microstructure with finer grains and nanoparticles of Y2Ti2O7, SiO2, and Cr2TiO4; whereas, the Si-free one contained different phases such as ferrite, austenite, and martensite with nanoparticles of Cr2O3 and Y2Ti2O7. After performing oxidation at 850oC for 100 h, the weight gain in the Si-containing sample (1.5 mg/cm2) was ~ 18 times lower than that of the Si-free sample (27.5 mg/cm2). Analyzing the surface and cross section of the oxide layers via SEM-EDS, XRD, Rietveld refinement of XRD patterns and Raman spectroscopy, it was revealed that Si-free ODS steel consisted of outer Fe2O3 and inner FeCr2O4 layers which were porous and possessed whisker like morphology. However, the oxidized Si-containing ODS steel possessed thin, dense, adherent and strong protective outer layer of (Fe, Cr)2O3 and the inner layer consisted mixture of Cr2O3 and Fe2SiO4 oxides. Synergistic effect of the single crystal structure matrix and Si addition in the Si-containing ODS steel played a crucial role in forming a thin, dense and protective oxide layers during the oxidation process, resulting in improved oxidation resistance.

The mullite whiskers have excellent high temperature resistance and high heat characteristics, the melting point is above 2000°C, and the maximum use temperature is 1500°C to 1700°C. In this paper, mullite whiskers were prepared by in-situ growth method. High aluminum castables were prepared by injecting mullite whiskers in situ at high temperature by adding Al(NO3)3·9H2O and NH4F to high alumina castables. It is 0, 0.5 wt%, 1 wt%, 2 wt%, 4 wt%. The materials were mixed, stirred, cast, and demolded and then fired at 1400°C. By testing the bulk density, apparent porosity and residual flexural strength of the samples, the properties, microstructure and microstructure of the fired samples were analyzed and characterized by means of XRD and SEM. The study focused on AlF3 to mullite whiskers. The effect of microstructure and flexural strength. The results show that the introduction of AlF3 promotes the formation of mullite whiskers. With the increase of AlF3 content, the aspect ratio of whiskers increases first and then decreases, and when the AlF3 content is 1wt%, the aspect ratio of whiskers The maximum is 6.67. Excessive AlF3 causes the mullite whiskers to become thick and rod-shaped. The in-situ mullite whiskers form an interlocking structure, which enhances the flexural strength of mullite high-aluminum castables when AlF3 content When the weight is 1wt%, the flexural strength of the model reaches the maximum value of 35.92MPa, and the residual flexural strength of the sample after 5, 10, and 15 thermal shocks reaches the maximum, which are respectively 2.07 MPa, 1.95 MPa, 1.19. MPa.

Seals are able to use their uniquely shaped whiskers to track hydrodynamic trails generated 30 s ago and detect hydrodynamic velocities as low as 245 [Formula: see text]m s-1. The high sensibility has long thought to be related to the wavy shape of the whiskers. This work revisited the hydrodynamics of a seal whisker model in a uniform flow, and discovered a new mechanism of seal whiskers in reducing self-induced noises, which is different from the long thought-of effect of the wavy shape. It was reported that the major and minor axes of the elliptical cross-sections of seal whisker are out of phase by approximately 180 degrees. Three-dimensional numerical simulations of laminar flow (Reynolds number range: 150-500) around seal-whisker-like cylinders were performed to examine the effect of the phase-difference on hydrodynamic forces and wake structures. It was found that the phase-difference induced hairpin vortices in the wake over a wide range of geometric and flow parameters (wavelength, wavy amplitude and Reynolds number), therefore substantially reducing lift-oscillations and self-induced noises. The formation mechanism of the hairpin vortices was analyzed and is discussed in details. The results provide valuable insights into an innovative vibration reduction and hydrodynamic sensing mechanism.

Due to the transition of the electronics industry to lead-free solders, the issue of tin (Sn) whisker has become one of the most imperative issues that need to be resolved. Moreover, with the increasing demand for electronics miniaturization, Sn whisker growth is a severe threat to the reliability of microelectronic devices. Sn whisker is a conductive tin structure that grows spontaneously from tin finished surfaces, which can lead to well-documented system failures in electronics industries. Assessment of the Sn whisker growth is difficult because of the slow and unpredictable nature of the Sn whisker formation. This paper presents the results of morphology analysis of Sn whisker growth in terms of Sn whiskers shape, average density and maximum length of Sn whisker on Sn-Cu solder finished using scanning electron microscope (SEM). Micro-indentation test was used to accelerate the growth of Sn whisker at room temperature storage.

ZK60 magnesium matrix composites were prepared by a powder metallurgy method which including ball milling, hot pressing sintering and hot extrusion and reinforced with varied mass fractions of Mg2B2O5 whiskers (3%, 5%, 7%, 9%, and 15%). The effects of the precipitated phase, reinforcement and texture on the mechanical properties of the as-extruded Mg2B2O5w/ZK60 magnesium matrix composites were investigated. The results show that the 7 wt% Mg2B2O5 whiskers were uniformly distributed in the matrix, and the average grain size of α-Mg in the composites was finer than that in the as-extruded ZK60 alloy. The transmission electron microscopy images show no obvious defect although the interfacial bonding between the Mg2B2O5 whisker and the matrix was mechanical bonding. Versus the as-extruded ZK60 alloy, the texture is enhanced by the addition of Mg2B2O5 whisker into the magnesium matrix. In addition, the tensile yield strength (TYS) and the compression yield strength (CYS) of the 7 wt% Mg2B2O5 whisker-reinforced ZK60 composites increased by 14.1% and 40.3%, respectively. Hall-Petch strengthening and load transfer are the main mechanisms for 7 wt% Mg2B2O5 whisker-reinforced ZK60 composites in the composites.

Mg2B2O5w/6061Al matrix composites were fabricated through the powder metallurgy (PM) technique. The morphology of the particles, particle size and the effect of powder characteristics on densification behavior of the compacted samples were investigated. It was found that milling way, milling time, milling speed and whisker content all had different effects on powders characteristics and densification. During the low-energy milling process, the particles morphology changed from spherical to flattened shape and the reinforcement accelerated the process to some extent; during the high-energy milling process, the particles experienced the welding-fracturing process, the Al particles morphology changed from spherical to flattened shape and then back to more equiaxed morphology, the reinforcement whisker apparently accelerated the milling process. During the uniaxial cold pressing process, the particles after high-energy milling achieved better densification, the reverse for the low-energy milled powders because of whiskers clusters. A good linear correlation coefficient was obtained when the experiential data were fitted by the Panelli and Ambrosio Filho equation.

The porous ceramics with a skeleton structure of magnesium borate (Mg2B2O5) whiskers were in situ synthesized by firing a compact of high-energy ball milled mixtures containing the reactants of boric acid (H3BO3) and basic magnesium carbonate [(MgCO3)4 Mg(OH)2 5H2O] (BMC), and the transition metal oxides (Fe2O3 and NiO) sintering aids. The effect of sintering aids on the phase transformation, morphology development of Mg2B2O5 whiskers and physical properties of porous ceramics were investigated. The results demonstrated that the addition of Fe2O3 inhibited the phase transition from monoclinic Mg2B2O5 to triclinic Mg2B2O5 and promoted the increase of average aspect ratio of whiskers, while introduction of NiO retarded whisker growth. An optimal synthesis temperature for well-developed porous structure of all samples is at 850 °C. Compared with samples sintered without and with sintering aid NiO, sample sintered with Fe2O3 has higher average aspect ratio of whisker and open porosity as well as compressive strength at the same temperature.

Utilizing the purified flue gas desulfurization (FGD) gypsum as raw material and AlCl3 as crystal modifier to prepare calcium sulfate whiskers (CSWs) by hydrothermal method, the effects of the AlCl3 concentration and the pH of reaction slurry on the crystal morphology of CSW were discussed. The results show that the AlCl3 concentration and the pH of reaction slurry had a significant effect on the crystal morphology of CSWs. CSWs grown in the AlCl3-H2O slurry had diameters ranging from 2 to 6 um and aspect ratio above 80 μm, and their phase structure was calcium sulfate hemihydrate (HH).

Calcium carbonate whisker (CCW) has been widely used for its excellent mechanical and physical properties as well as low manufacturing cost and simple process. In this study, CCW was added into asphalt binder to produce modified asphalt. The morphological characteristics, thermal performance and rheological properties of CCW and the modified asphalts were studied with various experimental methods. In order to enhance the compatibility of asphalt and CCW, the silane coupling agent (2 wt%, KH-570) was used to treat the surface of CCW. Results show that the addition of CCW can improve the softening point of asphalt and decrease its penetration and ductility. In addition, the rutting resistance of the modified asphalt has been increased to some extent. As the presence of silane coupling agent, the interaction between asphalt and CCW and the storage stability of CCW modified asphalt were slightly increased.

When soldering copper-based chips in electronic industry, the growth of tin whisker on Sn/Cu interface under compressive stress was caused by nano-size intermetallic compounds (IMC), Cu6Sn5. Reactive wetting process of Cu substrate by pure Sn was observed in an experimental device, and its kinetic mechanism was investigated by performing molecular dynamics calculations. When Sn/Cu wetting was assisted with ultrasonic vibrations, the vertical growth of nano-size Cu6Sn5 particles won solid-liquid interface was inhibited, so the occurrence of a new compound Cu3Sn in ultrasonic wetting which changed the morphology of interface, was beneficial to eliminate tin whisker on Sn/Cu interface.

This paper introduces a novel shape and texture recognizing technique based on the design of bionic whisker. Whisker arrays are installed on both sides of the robot. In the experiment, the whisker sweeps around to detect the unidentified object. The center wavelength of fiber Bragg grating (FBG) pasted on the whisker shifts when the whisker touches the obstacle. Shape recognition is realized by processing and further calculating the wavelength shift data. At the same time, the whisker sweeps over the surface texture, and the texture information is obtained by processing the wavelength shift data with the time-frequency analysis method. The results show that the whisker sensor can identify the three-dimensional profile shapes of contacted objects and the texture features of touched surfaces effectively.

Experimental results of natural gas hydrates formation from ice obtained under static conditions in the batch reactor applying the method of thermal cycling have been given. Hydrate forms subdivided according to their morphological features have been shown: powder and layered growth, retained ice shapes, and whisker crystals. The conducted experiments have defined effects of the thermal cycling regime on forms of obtained hydrates: decreased rates of heating/cooling results in an increase of a share of whisker crystals. The rate of decomposition of loose retained ice shapes in the form of hydrate has been defined to be 2.3 times faster than that of powder and dense layered hydrates.

Long strips of material cut from magnetostrictive Fe-Al (alfenol) and Fe-Ga (galfenol) rolled sheets with a preferred orientation are flexible yet have a high elastic modulus. They resemble animal whiskers and are effective as flow sensors, responding with local changes in magnetization due to bending stresses induced from the drag force during fluid flow. Both tensile and compressive stresses are simultaneously applied on opposite sides of the whisker neutral axis when the whisker bent, and thus the magnetostrictive whisker sensor must be able to withstand the range of tensile and compressive stress loadings caused as the whisker bends. In this study, we investigate application-related properties of alfenol and galfenol thin sheets and carbon fiber composite-coated sheets for use in whisker flow sensors. Being able to reduce sensor thickness is important for improving flexibility as the sensors deflect. The net voltage changes in the Hall sensor were proportional to the applied tip force. Magnetostriction is strongly dependent on texture development, and this was explored for several sample thicknesses in the two alloys. Goss, (011) [100], single grain was well developed in the both of 0.32- and 0.45 mm thick sheets, while the 0.20 mm thick sample shows {113} grain growth in galfenol. For alfenol, the Goss grain was globally grown in the whole sample with the overall thicknesses. For utilization of these sensors for real situations, carbon fiber was added to the alfenol whiskers as a protective layer. Bending experiments were performed on a carbon fiber-alfenol composite with a Hall sensor to see if magnetomechanical transduction was impaired. We observed that the Hall sensor output signal from the composite was improved by about 75% from that of a bare alfenol strip. Finite element modelling showed that the composite induced more internal stresses on the alfenol strip with the same degree of bending.

In order to reduce the Tin (Sn) whisker growth phenomenon in solder alloys, the researcher all the world has studied the factor of this behaviour. However, this phenomenon still hunted the electronic devices and industries. The whiskers growth were able to cause the electrical short, which would lead to the catastrophic such as plane crush, the failure of heart pacemaker, and the lost satellite connection. This article focuses on the three factors that influence the whiskers growth in solder alloys which is stress, oxidation layer and temperature. This findings were allowed the researchers to develop various method on how to reduce the growth of the Sn whiskers.

The potential of NiO sublayers for whisker growth mitigation has been examined. A thin NiO film was applied on a Cu-coated substrate before the deposition of a thicker Sn layer. The growth of Sn whiskers was then followed by optical and scanning electron microscopy and was compared with the whisker growth on a control sample without the NiO sublayer. No whiskers were observed on the sample with the NiO layer even after 12 months, whereas the control sample developed whiskers of size and density that is generally expected, based on the vast amount of published work on the topic. The mechanisms of whisker growth and whisker growth suppression are briefly discussed as well.

A new structure for the surface illuminant X-ray source system using a low-cost aluminum-doped zinc oxide (ZnO:Al) whisker cold emitter is proposed and a prototype setup is introduced. The X-ray source was fabricated using a cold cathode that consists of an aggregation of conductive ZnO:Al whiskers. The ZnO:Al whiskers were deposited on an n-type single crystalline wafer of silicon by an atmospheric chemical-vapor-deposition method. The electron emission current from the ZnO:Al whiskers varied with the Al concentration of ZnO. The diode and triode X-ray sources generated X-rays from the tungsten target used as an anode. X-ray images of a leaf and a small sardine were taken on medical X-ray films. Clear X-ray images were obtained.

The field-emission properties of Al:ZnO whisker emitters were investigated by varying the crystallite radius of curvature. The crystallite radius of curvature could be varied by adjusting the concentration of the reactant of aluminum as a dopant. When the crystallite radius of curvature was decreased from 155 to 46 nm, the electric field necessary to obtain a current density of 100 ?A/cm2 decreased from the range of 6.1 to 8.7 to the range of 4.4 to 5.1 V/?m. In addition, when the crystallite radius of curvature was decreased to 25 nm, the electric field necessary to obtain a current density of 100 ?A/cm2 decreased to 3.6 V/?m. The crystallite radius of curvature and the crystalline density during the field emission affected the electric field necessary to obtain a cathode current density of 100 ?A/cm2.

To enhance field emission properties, magnesium oxide (MgO) thin films were coated on the top of aluminum-doped zinc oxide (ZnO:Al) whiskers. The crystalline form of MgO was used as a representative material showing a high secondary-electron-emission An electron emission experiment was performed for 1000 h using an emitter consisting of the aggregated MgO/ZnO:Al whiskers. Scanning electron microscopy was conducted to compare the emission site images obtained before and after 1000 h operation. Furthermore, in this paper, Fowler–Nordheim plots are presented to explain the changing phenomenon of the field enhancement factor and the effective work function of the emission site before and after operation. Finally, a model of the electron emission of a MgO/ZnO:Al whisker-type field emitter is proposed.

The field-emission properties of Al:ZnO whisker emitters were investigated by varying the crystallite density and length. The crystallite density could be varied by adjusting the reactant concentration or the substrate temperature under which whiskers were formed. When the crystallite density was decreased from 18 ×104 to 3 ×104/mm2 and the crystallite length was increased from 12 to 19 µm, the electric field necessary to obtain a current density of 100 µA/cm2 decreased from 7.0 to the range of 3.6 to 4.9 V/µm. After the field emission, the crystallite density of some samples decreased. The electric field necessary to obtain a cathode current density of 100 µA/cm2 decreased with increasing geometric electric field enhancement factor β.

Idiomorphic and prismatic K2Nb8O21 crystals were successfully grown by the isothermal evaporation of KCl flux. On the basis of their aspect ratio, the crystals were divided into two morphological types, that is, whisker (needle) and prism. Growth was induced by heating mixtures of KCl and Nb2O5 at 1100 °C for 60 h followed by quenching in a furnace with the electric power turned off. The obtained K2Nb8O21 crystals were colorless and transparent. Whiskers having an average size of approximately 160×11.1 µm were grown from high-temperature solutions containing Nb at 1–30 mol %. The grown crystals had roundish or prismatic one-dimensional forms, and their surfaces were very smooth. Their generation and sizes were obviously dependent on the Nb concentration of the starting mixtures. The K2Nb8O21 crystals exhibited high activity for dye adsorption and degradation. The degradation occurred via a photocatalytic process under ultraviolet light irradiation.

Nanosized tin whiskers and spheres 15 nm in diameter form on anodic aluminum oxide (AAO) templates via a two-step anodization. The driving force, residual stress released from the template at a high temperature, causes tin whiskers of uniform size to grow on AAO within a few minutes. Various thicknesses AAO templates of in nano channels were fabricated from high-purity aluminum metals. The formation of hexagonal pores on aluminum was elucidated with reference to the equilibrium surface tension at each anodic condition. During a faster heating and cooling rate, tin formed coarser whiskers on the AAO, compared with fine nanowhiskers, which prefer slower rates of tempering. A series of scanning electron microscopy (SEM) images under various conditions of fabrication are introduced. Hence, the transformation of tin whiskers to a spherical shape is presented in detail in this study as well.

Whisker growth plays an important role in determining the performance and lifetime of micro/nano electronic devices. In this work, we analyse the contribution of lattice diffusion to the whisker growth in a bilayer structure. An analytical solution of the growth rate is obtained as a function of the average chemical stress and the whisker size. The growth rate is inversely proportional to the whisker size for the growth of a whisker over a semi-infinite crystal, while it is proportional to the thickness of the surface layer for larger ratio of the whisker size to the thickness of the surface layer. The analytical result provides us a rational basis to evaluate the growth behaviour of metallic whiskers and nanowires controlled by the lattice diffusion.

Whisker structures of indium tin oxide were prepared on a glass substrate by conventional sputtering using an indium-tin alloy target. Whisker structures grew well at higher temperatures than the crystallization temperature of In2O3 and the melting temperature of the In–Sn alloy, and also under the sputtering conditions of comparatively scarce oxygen and a high sputtering rate. These sputtering conditions correspond to the transition mode of reactive sputtering. The whisker structures were categorized into a structure consisting of many needles and a structure consisting of many trunks with side branches. Each whisker was a bcc single crystal growing along the direction and had a spherical droplet-like structure on the tip. Consequently, it was revealed that In–Sn droplets acted as important cores of whisker growth. The indium tin oxide (ITO) whiskers were grown by a self-catalytic vapor–liquid–solid mechanism promoted by the supersaturation of indium vapor.

Regularities of nanowire formation by thinning silicon whiskers at high-temperature oxidation in the range 900-1050 °C were studied. The oxidation was performed in a flow of dry or wet oxygen. It is shown that a stopping of the oxidation process occurs at oxidation temperature below ~960 °C. For example, at 930 °C the oxidation process is stopped in 6 hours. It is shown that at temperature above 960 °C such a stopping mechanism does not act and a through oxidation of the whisker is possible. In the wet oxygen, similar through oxidation takes place even at 930 °C. On the other hand, during oxidation above 960 °C it is possible to prepare nanowires with diameter lower than 5 nm in relatively thick whiskers; this is convenient for further manipulation with such objects. For example, during oxidation at 1000 °C nanowires with diameter ≤5 nm in an oxide shell up to 200 nm were prepared. Also, it has been shown that gold as a separate phase segregates at the nanowire-SiO2 interface provided that no special treatments were performed. This undesirable phenomenon was avoided by a special whisker treatment before oxidation.

The present contribution reports, for the first time, the successful fabrication of α-chitin whisker-reinforced poly(vinyl alcohol) (PVA) nanocomposite nanofibres by electrospinning. The α-chitin whiskers were prepared from α-chitin flakes from shrimp shells by acid hydrolysis. The as-prepared chitin whiskers exhibited lengths in the range 231–969 nm and widths in the range 12–65 nm, with the average length and width being about 549 and 31 nm, respectively. Successful incorporation of the chitin whiskers within the as-spun PVA/chitin whisker nanocomposite nanofibres was verified by infrared spectroscopic and thermogravimetric methods. The incorporation of chitin whiskers within the as-spun nanocomposite fibre mats increased the Young's modulus by about 4–8 times over that of the neat as-spun PVA fibre mat.

We review the current status of the growth, characterization and applications of Bi-Sr-Ca-Cu-Ο (BSCCO) whiskers from the materials science point of view. Our analysis leads to the conclusion that reconsideration of the importance of the whisker studies is necessary; whiskers can play a major role in studies of the growth mechanism and defects, properties control and their understanding, and new devices and applications. Arguments favourable to the idea that BSCCO whiskers can possibly have a significant impact on future synthesis of nano-objects in this system or other high-T c superconducting systems, as well as in investigation and understanding of the growth processes under elevated magnetic fields, are discussed. Emphasis is made on superconducting whiskers, but non-superconducting ones are also briefly addressed.

We use metal–organic vapour phase epitaxy for growth investigations of epitaxial nanowires in III–V materials, such as GaAs, GaP, InAs, and InP. In this paper we focus on gold assisted growth of nanowires. The nature of the metal particle—whether it is in the solid or liquid state—is discussed. For InAs and InP we have demonstrated that gold assisted wires can only grow at temperatures where the particle is solid. We continue with a discussion concerning the kinetic aspects of nanowire growth. Under common growth conditions one observes that thinner wires grow faster than thicker wires, contrary to what was described in the early days of whisker growth. We address and resolve this discrepancy by discussing a simple transport model and comparing the supersaturations of different systems. Finally, we describe the morphology of epitaxial III–V nanowires with emphasis on the crystal structure.

C60 nano-whiskers (C60 NWs) have been synthesized by a method of liquid-liquid interfacial precipitation using a system of C60-saturated m-xylene and isopropyl alcohol, and a C60 nano-whisker based field-effect transistor (C60 NW-FET) has been fabricated by a manipulator with use of a glass micro-capillary. The transport of the C60 NW-FET exhibits n-channel normally on properties and their carrier mobility is estimated to be 2.5 × 10−2 cm2/Vs in vacuum at room temperature.

Whisker crystals and whisker structures have many possibilities for industrial applications because of their unique shape with high aspect ratios. However, their fabrication methods need a high-temperature process and a limited substrate, thereby limiting their applications. Therefore, a new fabrication method that can prepare whiskers at low cost and directly on a versatile substrate, such as a glass substrate, is required. We found that indium tin oxide coatings with well-developed whisker structures could be prepared on glass substrates heated at 300 °C using conventional DC magnetron sputtering. These whisker coatings consist of continuous underlayer and upper structures with many whiskers. Each whisker is 500 nm to 1 µm in length and 10 to 20 nm in diameter. We revealed that the whisker structures were well grown under low-oxygen sputtering conditions and these whisker coatings could be categorized into three types of whisker morphology by scanning electron microscopy (SEM) observation and X-ray diffraction analysis (XRD). Whisker coatings of the first type have many needle structures and are strongly oriented along the axis normal to the substrate. Whisker coating of the second type are increasingly oriented along the axis and show a structure consisting of many trunks with side branches like similar to fir tree. Whisker coatings of the last type are equally oriented along and axes and have many fish-bone-like whisker structures. These whisker coatings may offer many possibilities for industrial applications, for example, emitter material for field-emission displays, and surface structures for super-hydrophilic or super-hydrophobic surfaces.

We prepared a new electrorheological (ER) fluid using titanate nano-whiskers as the dispersal phase. The titanate nano-whiskers, which were easy to synthesize by a simple hydrothermal treatment of TiO2 nano-particles in alkaline solution, possessed a low apparent density of about 1.85 g cm−3, large length–diameter ratio, and layered tube-like structure bonded loosely with ions by electrostatics. The ER fluid was prepared by dispersion of nano-whiskers in silicone oil with the ultrasonic technique. It was found that the suspended stability of this nano-whisker ER fluid was much better than that of the nano-particle ER fluid when no additive was added to the fluid. No significant sedimentation was found in this nano-whisker ER fluid after several months, due to the supporting effect of the nano-whiskers with large length–diameter ratio, while sedimentation occurred in TiO2 nano-particle ER fluid due to aggregation of nano-particles. Under electric field, this nano-whisker ER fluid showed notable ER activity with dynamic yield stress of about 1.1 kPa at 3 kV mm−1 and 10% particle volume fraction, which outclassed the yield stress (80 Pa) of ER fluid made of the raw material of TiO2 nano-particles.

To investigate the detailed junction properties of intrinsic Josephson junctions (IJJs) in YBa2Cu3O7−X (YBCO) without shunted grain boundaries and with good uniformity, we fabricated sub-micron sized IJJs in a YBCO whisker by using a focused-ion-beam etching. The sub-micron sized junctions showed clear multiple branches with a hysteresis structure in the current–voltage curve, like IJJs in Bi2Sr2CaCu2O8+X. The temperature dependence of the critical current demonstrates that the junction behaviour drastically changes from that of an SNS type to an SIS type when the critical temperature is decreased. The critical current density of the junctions, in the order of 10–100 kA cm−2, corresponds to Josephson plasma frequencies from a few hundred GHz to 1–2 THz.