Efficient field emission from coiled carbon nano/microfiber on copper substrate by dc-PECVD

Crystalline coiled carbon nano/micro fibers in thin film form have been synthesized via direct current plasma enhanced chemical vapor deposition (PECVD) on copper substrates with acetylene as a carbon precursor at 10 mbar pressure and 750 °C substrate temperature. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). XRD pattern as well as selected area electron diffraction (SAED) pattern showed that the samples were crystalline in nature. SEM and HRTEM studies showed that as synthesized coiled carbon fibers are having average diameter ∼100 nm and are several micrometers in length. The as-prepared samples showed moderately good electron field emission properties with a turn-on field as low as 1.96 V/μm for an inter-electrode distance 220 μm. The variation of field emission properties with inter-electrode distance has been studied in detail. The field emission properties of the coiled carbon fibrous thin films are compared with that of crystalline multiwalled carbon nanotubes and other carbon nanostructures.     

Enhanced field emission from Si doped nanocrystalline AlN thin films

Si doped and undoped nanocrystalline aluminum nitride thin films were deposited on various substrates by direct current sputtering technique. X-ray diffraction analysis confirmed the formation of phase pure hexagonal aluminum nitride with a single peak corresponding to (1 0 0) reflection of AlN with lattice constants, a = 0.3114 nm and c = 0.4986 nm. Energy dispersive analysis of X-rays confirmed the presence of Si in the doped AlN films. Atomic force microscopic studies showed that the average particle size of the film prepared at substrate temperature 200 °C was 9.5 nm, but when 5 at.% Si was incorporated the average particle size increased to ∼21 nm. Field emission study indicated that, with increasing Si doping concentration, the emission characteristics have been improved. The turn-on field (E_to) was 15.0 (±0.7) V/μm, 8.0 (±0.4) V/μm and 7.8 (±0.5) V/μm for undoped, 3 at.% and 5 at.% Si doped AlN films respectively and the maximum current density of 0.27 μA/cm² has been observed for 5 at.% Si doped nanocrystalline AlN film. It was also found that the dielectric properties were highly dependent on Si doping.     

Synthesis and electrochemical properties of Ni doped titanate nanotubes for lithium ion storage

Ni doped titanate nanotubes were synthesized by hydrothermal method using Ni doped rutile TiO₂ nanopowders as a starting material. The electrochemical properties were investigated by cyclic voltammmetric methods. The microstructure and morphology of the synthesized powders were characterized by XRD (X-ray diffraction), and HRTEM (high resolution transmission electron microscopy). Ni doped nanotubes were composed of H₂Ti₂O₅·H₂O with outer and inner diameter of ∼10 nm and 6 nm and showed a initial discharge capacity of 305 mAh/g with poor cycling performance. However, after firing, the Ni doped nanotubes revealed better cycling performance due to lower reaction with hydrate and smaller diameter of the tubes.     

Photoluminescence properties of powder and pulsed laser-deposited PbS nanoparticles in SiO2

Thin films of lead sulfide (PbS) nanoparticles embedded in an amorphous silica (SiO₂) host were grown on Si(1 0 0) substrates at different temperatures by the pulsed laser deposition (PLD) technique. Surface morphology and photoluminescence (PL) properties of samples were analyzed with scanning electron microscopy (SEM) and a 458 nm Ar⁺ laser, respectively. The PL data show a blue-shift from the normal emission at ∼3200 nm in PbS bulk to ∼560-700 nm in nanoparticulate PbS powders and thin films. Furthermore, the PL emission of the films was red-shifted from that of the powders at ∼560 to ∼660 nm. The blue-shifting of the emission wavelengths from 3200 to ∼560-700 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles, while the red-shift between powders and thin-film PbS nanoparticles is speculated to be due to an increase in the defect concentration. The red-shift increased slightly with an increase in deposition temperature, which suggests that there has been a relative growth in particle sizes during the PLD of the films at higher temperatures. Generally, the PL emission of the powders was more intense than that of the films, although the intensity of some of the films was improved marginally by post-deposition annealing at 400 °C. This paper compares the PL properties of powder and pulsed laser-deposited thin films of PbS nanoparticles and the effects of deposition temperatures.     

Temperature and substrate dependence of structure and growth mechanism of carbon nanofiber

The carbon nanofibers were grown on Ni/Si and Ni/Ti/Si substrates in 1 atm CH₄ atmosphere at 640 °C and 700 °C by thermal chemical vapor deposition method. The carbon nanofibers were characterized by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectrometry for morphology, microstructure, and crystallinity. The electron emission property of carbon nanofibers was also investigated by current-voltage (I-V) measurement. The results showed that the solid amorphous carbon nanofibers could be grown on Ni/Si substrate at 640 °C through tip growth mechanism, the carbon nanotubes could be grown on Ni/Si substrate at 700 °C through tip growth mechanism, and the carbon nanotubes could be grown on Ni/Ti/Si substrate at 700 °C through root growth mechanism.     

Characterization and optical property of ZnO nano-, submicro- and microrods synthesized by hydrothermal method on a large-scale

In the present paper, well-dispersed ZnO nano-, submicro- and microrods with hexagonal structure were synthesized by a simple low temperature hydrothermal process from zinc nitrate hexahydrate without using any additional surfactant, organic solvent or catalytic agent. The phase and structural analysis were carried out by X-ray diffraction (XRD), the morphological analysis was carried out by field emission scanning electron microscopy (FESEM) and the optical property was characterized by room-temperature photoluminescence (PL) spectroscopy. The results revealed the high crystal quality of ZnO powder with hexagonal (wurtzite-type) crystal structure and the formation of well-dispersed ZnO nano-, submicro- and microrods with diameters of about 50, 200 and 500 nm, and lengths of 300 nm, 1 μm and 2 μm, respectively, on a large-scale just using the different temperatures. Room-temperature PL spectrum from the ZnO nanorods reveals a strong UV emission peak at about 360 nm and no green emission band at ∼530 nm. The strong UV photoluminescence indicates the good crystallization quality of the ZnO nanorods. Room-temperature PL spectra from the ZnO submicro- and microrods reveal a weak UV emission peak at ∼400 nm and a very strong visible green emission at 530 nm, that is ascribed to the transition between V_oZn_i and valence band.     

Electrochemical synthesis of Cu/ZnO nanocomposite films and their efficient field emission behaviour

The Cu/ZnO nanocomposite films have been synthesized by cathodic electrodeposition and characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) and field emission microscope (FEM). The XRD pattern shows a set of well defined diffraction peaks, which could be indexed to the wurtzite hexagonal phase of ZnO. In addition, characteristic diffraction peaks corresponding to Cu and Zn are also observed. The SEM image shows formation of two-dimensional (2D) hexagonal sheets randomly distributed and aligned almost normal to the substrate. Uniformly distributed small clusters of Cu nanoparticles possessing average diameter of ∼25 nm, as revealed from the TEM image, are seen to be present on these 2D ZnO sheets. The selected area electron diffraction (SAED) image confirms the nanocrystalline nature of the Cu particles. From the field emission studies, carried out at the base pressure of ∼1 × 10⁻⁸ mbar, the turn-on field required for an emission current density of 0.1 μA/cm² is found to be 1.56 V/μm and emission current density of ∼100 μA/cm² has been drawn at an applied field of 3.12 V/μm. The Cu/ZnO nanocomposite film exhibits good emission current stability at the pre-set value of ∼10 μA over a duration of 5 h. The simplicity of the synthesis route coupled with the better emission properties propose the electrochemically synthesized Cu/ZnO nanocomposite film emitter as a promising electron source for high current density applications.     

Flame synthesis of carbon nanotubes for panel field emission lamp

Multi-walled carbon nanotubes (CNTs) were synthesized on the surfaces of Ni-alloy plated Fe-wires with the diameter of 2 mm using a conventional laboratory ethanol (C₂H₅OH) flame method at 560 °C. SEM showed that the product had bush-shaped micron-structures with diameters from 100 to 450 nm and lengths of over 1.0 μm. TEM revealed that the micron-structures were composed of multi-walled nanotube bundles with the diameters of about 50 nm. The test on the diode configuration field emission of the Fe-wire arrays was performed. The onset electric field was 2.95 V/μm and the emission current can reach 50 mA/cm² at an electric field of 9 V/μm. The average fluctuation of the emission current density was less than 7%. The result suggests that the field emission was uniform and the present technique was feasible to fabricate Panel Field Emission Lamp (PFEL) with arrays of carbon nanotubes. PFEL has the advantages of high luminescence as well as stability, and thus, it can be used to replace ordinary lights.     

Aligned carbon nanotubes catalytically grown on iron-based nanoparticles obtained by laser-induced CVD

Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe₂O₃ (maghemite/magnetite) particles with sizes ≤5 and 10 nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO₂/Si(1 0 0) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD process (PE-HF-CCVD). Vertically oriented and thin carbon nanotubes (CNTs) were grown with few differences between the two samples, except the diameter in relation to the initial size of the iron particles, and the density. The electron field emission of these samples exhibit quite interesting behavior with a low turn-on voltage at around 1 V/μm.     

Large-area silica nanotubes with controllable geometry on silicon substrates

The synthesis of a highly uniform, large-scale nanoarrays consisting of silica nanotubes above embedded nanohole arrays in silicon substrates is demonstrated. In situ anodized aluminium oxide (AAO) thin film masks on Si substrates were employed, and the nanotubes were fabricated by Ar ion milling through the masks. The geometries of the nanoarrays, including pore diameter, interpore distance and the length of both nanopores and nanotubes could be controlled by the process parameters, which included that the outer pore diameter of silica tube was tuned from ∼80 nm to ∼135 nm while the inner tube diameter from ∼40 nm to ∼65 nm, the interpore distance of the nanotube arrays was from 100 nm to 180 nm and the length of silica tube changed from ∼90 nm to ∼250 nm. The presented nanostructure fabrication method has strong potential for application in intensity and frequency adjustable high luminescence efficiency optoelectronic devices.     

Magnetorheology of colloidal dispersion containing Fe nanoparticles synthesized by the arc-plasma method

Spherical crystalline Fe nanoparticles, ∼100 nm in diameter, were synthesized under Ar-50% H₂ arc-plasma. These nanoparticles were dispersed in silicone oil after silane treatment on as-grown thin oxide layer (∼2 nm) to make their surfaces hydrophobic. The resulting Fe nanoparticles exhibited a high saturation magnetization of ∼190 emu/g at room temperature. The static magnetorheological behavior was measured for the colloidal dispersion (solid concentration: 15 vol%) at room temperature under magnetic flux densities of 0-0.3 T, using a parallel-plate-type commercial rheometer. The yield stress continuously increased with magnetic flux density, demonstrating the Bingham plastic behavior. Moreover, subjecting the sample to a magnetic flux density of 0.3 T increased the yield stress by ∼10². Additionally, the colloidal dispersion exhibited good stability against sedimentation.     

Photoluminescence and field emission properties of Sn-doped ZnO microrods

Sn-doped ZnO (SZO) microrods have been fabricated by a thermal evaporation method. Effect of Sn dopant on the microstructure, morphological and composition of as-prepared SZO microrods have been investigated by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The influence of the doping concentration on the morphological of the microrods has been investigated. Photoluminescence (PL) of these SZO microrods exhibits a weak ultraviolet (UV) emission peak at around 382 nm and the strong green emission peak at around 525 nm at room temperature. Field emission measurements demonstrate that the SZO possess good performance with a turn-on field of ∼1.94 V/μm and a threshold field of ∼3.23 V/μm, which have promising application as a competitive cathode material in FE microelectronic devices.     

Synthesis and field-emission of aligned SnO2 nanotubes arrays

Aligned tin dioxide (SnO₂) nanotubes have been synthesized by high-frequency inductive heating. Nanotubes with high yield were grown on silicon substrates in less than 5 min, using SnO₂ and graphite as the source powder. Scanning electron microscopy and transmission electron microscopy showed nanotube with diameters from 50 to 100 nm and lengths up to tens of mircrometers. The SnO₂ nanotubes synthesized under the optimum condition have better field-emission characteristics. The turn-on field needed to produce a current density of 10 μA/cm² is found to be 1.64 V/μm. The samples show good field-emission properties with a fairly stable emission current. This type of SnO₂ nanotubes can be applied as field emitters in displays as well as vacuum electric devices.     

Synthesis of magnetite nanoparticles for AC magnetic heating

Magnetite particles with different average diameter (D_m) suitable for magnetic fluid hyperthermia (MFH) were synthesized by controlled coprecipitation technique. In this method, the reaction pH was stabilized using the pH buffer and the average particle diameter decreased with increasing reaction pH. The size-dependent magnetic behavior of the magnetite nanoparticles was studied and the optimum size range required for magnetic fluid hyperthermia (MFH) has been arrived at. Among the samples studied, the maximum specific absorption rate of 15.7 W/g was recorded for the magnetite sample with D_m of 13 nm, when exposed to an AC magnetic field strength of 3.2 kA/m and a frequency of 600 kHz. The AC magnetic properties suggested that the size distribution of the sample was bimodal with average particle size less than ∼13 nm.     

Plasma characterization and room temperature growth of carbon nanotubes and nano-onions by excimer laser ablation

The deposition of carbon nanotubes and carbon nano-onions at room temperature using excimer laser radiation to ablate mixed graphite-metal targets is described. Our deposition conditions are in contrast to other investigations on the pulsed laser deposition of carbon nanotubes that have employed high temperatures and high pressures. We find that the formation of these carbon nanostructures is dependent on the ambient gas employed during ablation. In the presence of O₂ gas, carbon nanotubes and nano-onions are produced, while inert atmospheres such as Ar yield amorphous carbon. High-resolution, in situ, time-resolved emission spectroscopy has been used to track the evolution of species (C₂, C₃, Ni/Co) in the ablation plume. Spectral fits on low and high-resolution spectra reveal that the vibrational-rotational temperatures for C₂ produced in O₂ remain at ∼5000 K for nearly 20 μs but drop rapidly in Ar. Details of the formation of carbon nanotubes and nano-onions, and in situ time-resolved optical emission spectroscopy are described.     

Hydrogen sensors based on ZnO nanoparticles

Hydrogen sensing characteristics of thick films of nanoparticles (∼35 nm diameter) of ZnO, 3% Co doped ZnO, 1% Pt-impregnated ZnO and 1% Pt-impregnated 3% Co-ZnO have been investigated. The last composition exhibits the highest sensitivity for 10-1000 ppm H₂, reaching values upto 1700 as well as good response and recovery times at 125 °C or lower. The sensor is not affected significantly upto 50% relative humidity.     

Field emission properties of carbon nanotubes grown on silicon nanowire arrays

Carbon nanotubes are synthesized on the silicon nanowire arrays which are fabricated on silicon substrate by chemical vapor depositing SiCl₄ and H₂ gases in the presence of Au catalysts. The silicon nanowires are single-crystal with lengths up to 100 μm and diameters ranging from 50 to 500 nm. The tangled carbon nanotubes are grown directly from the surface of Si nanowires. The field emission properties of the carbon nanotubes are investigated at the gap of 200 μm. The low turn on and threshold fields are obtained. The stabilization of the emission currents is also presented.     

Field emission from ZnS nanorods synthesized by radio frequency magnetron sputtering technique

The field emission property of zinc sulphides nanorods synthesized in the thin film form on Si substrates has been studied. It is seen that ZnS nanorod thin films showed good field emission properties with a low-macroscopic turn-on field (2.9-6.3 V/μm). ZnS nanorods were synthesized by using radio frequency magnetron sputtering of a polycrystalline prefabricated ZnS target at a relatively higher pressure (10⁻¹ mbar) and at a lower substrate temperature (233-273 K) without using any catalyst. Transmission electron microscopic image showed the formation of ZnS nanorods with high aspect ratio (>60). The field emission data were analysed using Fowler-Nordhiem theory and the nearly straight-line nature of the F-N plots confirmed cold field emission of electrons. It was also found that the turn-on field decreased with the decrease of nanorod's diameters. The optical properties of the ZnS nanorods were also studied. From the measurements of transmittance of the films deposited on glass substrates, the direct allowed bandgap values have been calculated and they were in the range 3.83-4.03 eV. The thickness of the films was ∼600 nm.     

Functionalization of lamellar molybdenum disulphide nanocomposite with gold nanoparticles

This work explores the functionalization of an organic-inorganic MoS₂ lamellar compound, prepared by a chemical liquid deposition method (CLD), that has an interlamellar distance of ∼5.2 nm, using clusters of gold nanoparticles. The gold nanoparticles have a mean diameter of 1.2 nm, a stability of ∼85 days, and a zeta potential measured to be ζ = −6.8 mV (solid). The nanoparticles are localized in the hydrophilic zones, defined by the presence of amine groups of the surfactant between the lamella of MoS₂. SEM, TEM, EDAX and electron diffraction provide conclusive evidence of the interlamellar insertion of the gold nanoparticles in the MoS₂.     

Fluorescence properties of Ag nanoparticles in water, methanol and hexane

Ag nanoparticles, synthesized employing the electro-exploding wire technique, are reported. Absorption in the UV-visible region by these particles is characterized by the features reported in the literature, namely, a possible plasmon peak at ∼404 nm. For Ag nanoparticles dispersed in water, photo-excitation in the ranges 210-235 and 255-280 nm produces similar fluorescence emission at ∼300 nm, whose corresponding resonant absorption takes place at 215 and 270 nm in the excitation spectra. Further, we study the effect of the surrounding medium (solvent effect) on fluorescence from these nanoparticles by comparing fluorescence emission in methanol and hexane for photo-excitation in the same range. Compared to water, fluorescence emission in methanol is observed red-shifted at ∼310 nm, which further red-shifts to ∼325 nm in hexane. The corresponding resonant absorptions in methanol are at 225 and 275 nm. Consequence of this red-shift in a less polar solvent is discussed.