Vertically aligned carbon nanotubes from natural precursors by spray pyrolysis method and their field electron emission properties

Vertically aligned carbon nanotubes have been synthesized from botanical hydrocarbons: Turpentine oil and Eucalyptus oil on Si(100) substrate using Fe catalyst by simple spray pyrolysis method at 700°C and at atmospheric pressure. The as-grown carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Raman spectroscopy. It was observed that nanotubes grown from turpentine oil have better degree of graphitization and field emission performance than eucalyptus oil grown carbon nanotubes. The turpentine oil and eucalyptus oil grown carbon nanotubes indicated that the turn-on field of about 1.7 and 1.93 V/μm, respectively, at 10 μA/cm². The threshold field was observed to be about 2.13 and 2.9 V/μm at 1 mA/cm² of nanotubes grown from turpentine oil and eucalyptus oil respectively. Moreover, turpentine oil grown carbon nanotubes show higher current density in relative to eucalyptus oil grown carbon nanotubes. The maximum current density of 15.3 mA/cm² was obtained for ∼3 V/μm corresponding to the nanotubes grown from turpentine oil. The improved field emission performance was attributed to the enhanced crystallinity, fewer defects, and greater length of turpentine oil grown carbon nanotubes.     

Diode-pumped passively Q-switched and mode-locked Nd:GGG laser at 1.3 μm with V<Superscript>3+</Superscript>:YAG saturable absorber

Using V³⁺:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3 μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps.     

Field emission from single-walled carbon nanotubes aligned on a gold plate using a self-assembly monolayer

Field emission from single-walled carbon nanotubes (SWNTs) aligned on a patterned gold surface is reported. The SWNT emitters were prepared at room temperature by a self-assembly monolayer technique. SWNTs were cut into sub-micron lengths by sonication in an acidic solution. Cut SWNTs were attached to the gold surface by the reaction between the thiol groups and the gold surface. The field-emission measurements showed that the turn-on field was 4.8 V/μm at an emission current density of 10 μA/cm². The current density was 0.5 mA/cm² at 6.6 V/μm. This approach provides a novel route for fabricating CNT-based field-emission displays. Received: 3 May 2002 / Accepted: 6 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +82-54/279-8298, E-mail: ce20047@postech.ac.kr     

Field-electron emission from polyimide-ablated films

Polyimide-ablated film was deposited by using pulsed laser ablation of a polyimide target, and field-electron emission from the film was observed for the first time. The turn-on field of the polyimide-ablated film is 12 V/μm. The current density is 0.725 mA/cm², and the emission sites density is on the order of 10⁶/cm² at the applied field of 24 V/μm. The field-electron emission measurements indicate that this kind of film could be a new cold cathode material. It is suggested that the graphite-like clusters contained in the film play an important role in the field-electron emission. Received: 2 February 2000 / Accepted: 13 March 2000 / Published online: 9 August 2000     

Synthesis and field emission of two kinds of ZnO nanotubes: taper-like and flat-roofed tubes

Two kinds of ZnO nanotubes, including taper-like and flat-roofed tubes, have been successfully fabricated using a simple aqueous solution route by changing the experimental conditions. All the obtained nanotubes have a uniform size of 500 nm in diameter, 10–50 nm in wall thickness, and 2–5 μm in length. The growth mechanism of two kinds of ZnO nanotubes was investigated. Field emission measurements showed that tapering nanotubes have the good field emission performance with a low turn-on field of ∼ 2.1 V μm^-1 and a low threshold field of ∼ 3.8 V μm^-1, which suggests the possible applications of the ZnO tubular structures in field emission microelectronic devices. PACS 73.61.Ga; 73.63. Fg; 85.45.Db     

Highly nonlinear dispersion-flattened square photonic crystal fibers with low confinement losses

A new simple structure of an index-guiding highly nonlinear dispersion-flattened square photonic crystal fiber (HNDFSPCF) with low confinement losses is proposed. The results reveal that it is possible to design five-rings HNDF-SPCFs with a flattened dispersion of 0.43 ps/(nm·km), low dispersion slope of -0:02 ps/(nm²·km), low confinement loss of approximately 10³ dB/m, and a large nonlinear coefficient of approximately 35W^-1 km^-1 at 1.55 μm. It is also observed that the confinement loss is less than 10^-1 dB/m in the wavelength range of 1.2 –1.7 μm.     

Structure,transport and field-emission properties of compound nanotubes: CN<Subscript>x</Subscript> vs. BNC<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis><0.1)

Transport and field-emission properties of as-synthesized CN_x and BNC_x (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CN_x nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas those made of BNC_x nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission properties with emitting currents per rope reaching ∼4 μA(CN_x) and ∼2 μA (BNC_x), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CN_x or BNC_x nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm² (BNC_x) and 5.5 mA/cm² (CN_x) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm² both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing the current density to 0.2–0.4 A/cm², only CN_x films continued to emit steadily, while the field emission from BNC_x nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating. Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp     

Mid-infrared laser-absorption diagnostic for vapor-phase fuel mole fraction and liquid fuel film thickness

A novel two-wavelength mid-infrared laser-absorption diagnostic has been developed for simultaneous measurements of vapor-phase fuel mole fraction and liquid fuel film thickness. The diagnostic was demonstrated for time-resolved measurements of n-dodecane liquid films in the absence and presence of n-decane vapor at 25°C and 1 atm. Laser wavelengths were selected from FTIR measurements of the C–H stretching band of vapor n-decane and liquid n-dodecane near 3.4 μm (3000 cm⁻¹). n-Dodecane film thicknesses <20 μm were accurately measured in the absence of vapor, and simultaneous measurements of n-dodecane liquid film thickness and n-decane vapor mole fraction (300 ppm) were measured with <10% uncertainty for film thicknesses <10 μm. A potential application of the measurement technique is to provide accurate values of vapor mole fraction in combustion environments where strong absorption by liquid fuel or oil films on windows make conventional direct absorption measurements of the gas problematic.     

Optimization of field emission properties from multi-walled carbon nanotubes using ceramic fillers

The field emission properties of multi-walled carbon nanotubes were examined using a screen-printed thick film with a diode-type configuration in a vacuum. The effects of various concentrations of two different ceramic fillers, indium tin oxide (ITO) powder and a glass frit, on the emission current density and turn-on field were evaluated. The emission properties of both pastes were dependent on the amount of filler. Considerably enhanced emission properties were obtained with the paste containing 5–10 wt.% of either ITO or the glass frit compared with those without a filler. The paste containing the ceramic filler showed enhanced emission properties compared with that containing the 5 wt.% Ag conventionally used, which confirmed the importance of the filler. The paste containing 10 wt.% ITO represented an emission current density of 176.4 μA/cm² at 5 V/μA, a turn-on field of 1.87 V/μA for an emission current density of 1 μA/cm² and a field enhancement factor of 7580. The paste formulation was also found to be suitable for fine patterning using UV-lithography techniques. A long-term stability test for 110 h of a paste containing 10 wt.% ITO revealed a half-life of approximately 30000 h, which is appropriate for commercial applications.     

Optoacoustic effect in dense layers of oriented carbon nanotubes: Its use for measuring the optical absorption coefficient and the film thickness

The optoacoustic effect is used to measure the coefficient of light absorption at a wavelength of 0.53 μm by a dense layer of oriented carbon nanotubes on a quartz substrate. The value of the absorption coefficient is found to be equal to 3 × 10⁶ m⁻¹. This value is compared with the theoretical estimates and the estimate obtained from the reflection coefficient with the use of the Kramers-Kronig relation. With the coefficient of light absorption being known, the optoacoustic effect allows one to measure the film thickness at any point without destroying the film. Original Russian Text Sc I.S. Grudzinskaya, Z.Ya. Kosakovskaya, O.B. Ovchinnikov, I.A. Chaban, 2006, published in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 3, pp. 330–334.     

Q-switched mode-locking femtosecond all-fiber laser based on Er3+/Yb3+ codoped phosphate fiber

A Q-switched mode-locking femtosecond all-fiber laser based on a 2 cm long homemade Er³⁺/Yb³⁺ codoped phosphate glass fiber has been reported. By using the nonlinear polarization evolution technique, a nearly 100% modulation depth of mode-locking pulse train is achieved. At a pump power of 410 mW, the energy of each Q-switched envelope, whose width is about 220 μs, is 10 μJ, while the duration of mode-locking pulse within the Q-switched envelope is 318-fs.     

Synthesis of single-walled carbon nanotubes in mesoporous silica film and their field emission property

We have succeeded in direct synthesis of single-walled carbon nanotubes (SWNTs) on a conductive substrate coated with a 3D mesoporous silica film, and observed the field emission. Co catalysts for the growth of SWNTs are deposited on the substrate by electroplating. The particle size of the catalyst is well-controlled inside defined space of the mesoporous silica film. Furthermore, the location of Co particles can be controlled in the mesopores by the electroplating method. Mono-dispersed SWNTs are grown along with the mesopores that are normal to the substrate, because Co particles are deposited at the bottom of the mesopores. It is also found that the mesoporous silica film prevents the aggregation of Co catalysts and the distortion of Au layer as the conductive substrate. The field emission measurement shows that the turn-on field is 4.2 V/μm at 10 μA/cm². The field enhancement factor is about 1500. This approach provides an efficient methodology for fabricating an SWNTs-based field emitters. PACS 73.63.Fg; 78.55.Mb     

Viscoelastic properties of multiwalled carbon nanotube solutions

We have prepared solutions of multiwalled carbon nanotubes in very low vapour pressure solvents (a mixture of chlorinated biphenyls). The solutions are stable and show no sign of precipitation for six months. Rheological measurements using a modified Birnboim apparatus with annular and Sogel-Pochetino geometries have been performed. Using time-temperature superposition we obtained the real and imaginary part of the complex viscosity coefficient in a frequency range covering eight orders of magnitude and a temperature range from 5 to 50 ^○C. The data shows unexpected changes in the solution with temperature: for T below 30 ^○C there appears to be some reorganization or clustering. This self-organization could result in a useful technique to improve the electronic properties of polymer/carbon nanotubes composites used in organic electronic devices.     

Synthesis and studies of new plasticized PVP: NaClO3 electrolyte system for battery applications

A new thin film sodium ion conducting plasticized polymer electrolyte based on poly(vinyl pyrrolidone) (PVP) complexed with NaClO₃ salt systems was prepared by the solution-cast method. The interaction of NaClO₃ salt with PVP was confirmed by Infrared (IR) study. Charge transport of these polymer electrolytes is due to ions, which was confirmed by Wagner’s polarization method. From the conductivity measurements, the highest conductivity value 6.71×10⁻⁵ S/cm was observed for the composition PVP:PEG:NaClO₃(30:60:10) at room temperature 35 °C. The redox behaviour and good reversibility of the plasiticized electrolytes are confirmed by electrochemical techniques. Electrochemical cell studies of these polymer electrolytes were analyzed from their discharge characteristics. The open-circuit voltage (OCV) and short-circuit current (SCC) were found to in the range of 2.52 V to 2.36 V and 760 μA to 1040 μA, respectively.     

1.53 μm photoluminescence from ErYb(DBM)<Subscript>3</Subscript>MA containing polymer

We investigated the optical properties of the ErYb(DBM)₃MA complexes and the ErYb(DBM)₃MA containing polymer. Absorption and photoluminescence spectra confirm that the presence of Yb³⁺ ions enhances luminescence efficiency of Er³⁺ ions. The full width at half maximum bandwidth (FWHM) is ∼80 nm wide around 1.53 μm wavelength. We also fabricated ErYb containing polymeric channel waveguides using reactive ion etching technique. As an input pump of 120 mW was used, a ∼1.53 μm spontaneous emission was obtained in a 4-mm-long waveguide. PACS 42.00.00; 42.70.Jk; 42.82.Et     

Mechanism of field emission from carbon materials

Field emission in diamond and graphite-like polycrystalline films is investigated experimentally. It is shown that the emission efficiency increases as the nondiamond carbon phase increases; for graphite-like films the threshold electric field is less than 1.5 V/μm, and at 4 V/μm the emission current reaches 1 mA/cm², while the density of emission centers exceeds 10⁶ cm⁻². A general mechanism explaining the phenomenon of electron field emission from materials containing graphite-like carbon is proposed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 56–60 (10 July 1998)     

Actively mode-locked Tm-Ho:LiYF<Subscript>4</Subscript> and Tm-Ho:BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> lasers

We report on the generation of mode-locking pulse trains with high average output powers from diode-pumped Tm-Ho:LiYF₄ and Tm-Ho:BaY₂F₈ lasers emitting at around 2 μm. The highest output power of 365 mW was obtained with the Tm-Ho:YLF₄ laser, whereas the shortest pulse duration of 120 ps and the widest tunability range of 59 nm was achieved with the Tm-Ho:BaY₂F₈ laser. PACS 42.55.Xi; 42.60.Fc; 42.72.Ai; 42.55.Rz; 42.70.Hj     

Wave mixing in nominally undoped Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> at high light intensities

The intensity dependence of the photorefractive response of Sn₂P₂S₆ is studied for the Kr⁺-laser wavelength of 647 nm and pump-beam intensities of up to 10 W/cm². A considerable enhancement of the two-beam coupling gain factor with increasing intensity at a grating spacing of ≃1 μm is attributed to a light-induced increase of the effective trap density. The large gain reached at high intensities is applied for the build up of a double phase conjugate mirror with a sub-millisecond switch-on time.     

Exposure to nanoscale particles and fibers during machining of hybrid advanced composites containing carbon nanotubes

This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 10⁶ particles cm⁻³. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm⁻³ depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.

The effect of process variables on the characteristics of carbon nanotubes obtained by spray pyrolysis

A simple spray pyrolysis setup is used to grow multi-walled carbon nanotubes (MWCNTs), from a ferrocene solution in benzene as precursor. The effects of process variables such as growth temperature, position of the aerosol generator and position in the reactor where the sample was formed were investigated. These variables have a strong influence on the graphitization degree, homogeneity, diameter and alignment of the nanotubes, as observed by TEM, SEM, XRD and Raman spectroscopy. Vertically aligned MWCNT arrays with high density were obtained in large areas (10 × 10 mm²), with high yield (2.1 mg cm⁻²) and at a growth rate at 1.43 μm min⁻¹, by a suitable choice of the experimental conditions.