Optimization of the parameters of a carbon nanotube-based field-emission cathode

A procedure for optimizing a field-emission cathode based on carbon nanotubes (CNTs) is developed. An array of identical equidistant vertical CNTs is considered. The optimization procedure takes into account the effect of screening of an electric field by neighboring nanotubes by solving a Laplace equation and the thermal instability of nanotubes, which limits the emission current density of a nanotube, by solving a heat conduction equation. The relation between the emission current and the applied voltage is described by the Fowler-Nordheim relationship containing the CNT tip temperature as a parameter. Upon optimization, the optimum distance between CNTs that ensures the maximum emission current density is calculated. The calculation results demonstrate that this parameter depends substantially on both the applied voltage and the nanotube geometry. These dependences are weakly sensitive to the choice of the transport coefficients (thermal conductivity, electrical conductivity) of nanotubes.     

Plasma Pyrolysis of Ethanol for the Production of Carbon Nanostructures

High Energy Chemistry - An experimental and numerical study of the synthesis of carbon nanostructures by pyrolysis of alcohol in helium and nitrogen plasma jets generated by a DC plasma torch in...     

Numerical simulation of plane and spatial nonlinear stationary waves in a two-layer fluid of arbitrary depth

The solution of a model differential equation for the three-dimensional perturbations of the interface between two immiscible fluids of different densities lying between a stationary nondeformable bottom and cover is presented. It is assumed that the waves have an arbitrary length and small, though finite, amplitude. The shapes of stationary traveling internal waves, both periodic in the two horizontal coordinates and soliton-like, are presented. These shapes depend on different parameters of the problem: the direction of the perturbation wave vector and the fluid layer depth and density ratios.     

Force acting on a particle in unsteady flow of a pseudoplastic fluid

The accelerated flow of a pseudoplastic fluid around a quiescent sphere at Reynolds numbers Re = 0–200 and dimensionless acceleration Ga = 10–10⁴ is studied by numerical simulation. It is shown that the analytical expression of the added mass force for an ideal fluid is appropriate for a pseudoplastic fluid. An expression for calculating the hereditary Basset force for a pseudoplastic fluid is proposed.     

Two-parametric model of the spectrum of traffic noise in Tomsk

The technique of mapping urban noise is proposed on the basis of a two-parameter model of the acoustic noise spectrum. The acoustic noise and spatial distribution of the decay rate in Tomsk are mapped. The factors influencing the formation of the acoustic noise of traffic flow are described. Analysis is performed on how different operating modes of a vehicle??s internal combustion engine affect the background level of acoustic noise.     

Nonlinear resistance of polymer composites with carbon nanotube additives in the percolation state

The electrical properties of a polymer composite with carbon nanotube additives have been analyzed. The state of the system near the percolation threshold, when charge is transferred along a single percolation path, has been considered. For this state, the current–voltage characteristics of a percolation chain made up of carbon nanotubes have been calculated under the assumption that the contact resistance between neighboring nanotubes is much higher than the intrinsic resistance of the nanotubes. According to recent data, the distance between neighboring (contacting) nanotubes has been assumed to be randomly distributed. It has been shown that, under the given conditions, the current–voltage characteristic is essentially nonlinear. This indicates the nonohmic conductivity of the composites. The dependence of the current–voltage characteristic on the spread of the contact distribution over distances has been discussed.     

Influence of the electric field on the alignment of carbon nanotubes during their growth and emission

The problems of the electric field action on carbon nanotubes (CNTs) during their growth and under the electron field emission conditions are considered. The relations determining the growth rate of an extended structure under the action of the electric field are established. The relation connecting the angle of orientation of a CNT inclined to the substrate surface and the applied electric field is used for computing current-voltage characteristics of the cathode consisting of inclined CNTs. The degree of deviation of these characteristics from the Fowler-Nordheim classic dependence is determined, on the one hand, by the parameters characterizing the CNT spread over the angles of inclination and, on the other hand, by the value of the Young modulus characterizing the bending stiffness of a nanotube. It is shown that in zero external electric field, a certain effect on the CNT orientation can be produced by the CNT potential relative to the substrate, which is due to the effect of the contact potential difference.     

Electric field enhancement in field-emission cathodes based on carbon nanotubes

The problem of determining the field enhancement factor in field-emission cathodes based on carbon nanotubes (CNTs) is considered. The electrostatic problem of finding the field enhancement factor for nanotubes with different shapes of the tip as a function of the angle the nanotube makes with the cathode surface and of the interelectrode spacing is solved. The dependence of the electric field enhancement factor on the spacing between vertically oriented nanotubes constituting an array is derived. Making allowance for this dependence gives an optimal value of the surface density of nanotubes in the array at which the emission current density is maximal. The I—V characteristic of CNT-based cathodes is studied with regard to the statistical straggling of their orientation angles. This I—V characteristic is compared with the characteristic obtained with regard to the statistical straggling of the CNT geometrical parameters.     

Adsorption, ordering, and chemistry of nitrobenzene on Si(1 0 0)-2 × 1

Surface chemistry of nitrobenzene on Si(1 0 0)-2 × 1 has been investigated using multiple internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR), Auger electron spectroscopy (AES) and thermal desorption mass spectrometry. Molecular adsorption of nitrobenzene at submonolayer coverages is dominating at cryogenic temperatures (100 K). As the surface temperature is increased to 160 K, chemical reaction involving nitro group occurs, while the phenyl entity remains intact. Thus, a barrier of approximately 40.8 kJ/mol is established for the interaction of the nitro group of nitrobenzene with the Si(1 0 0)-2 × 1 surface. Further annealing of the silicon surface leads to the decomposition of nitrobenzene. The concentration of nitrogen and oxygen remains constant on a surface within the temperature interval studied here. AES studies also suggest that the majority of carbon-containing products remain bound to the surface at temperatures as high as 1000 K. The only chemical reaction leading to the release of the gaseous products is benzene formation around 670 K. The amount of benzene accounts only for a few percent of the surface species, while the rest of the phenyl groups connected to the silicon surface via a nitrogen linker remain stable even at elevated temperatures, opening an opportunity for stable surface coatings.     

Resonance assignment of<Superscript>13</Superscript>C−<Superscript>15</Superscript>N-labeled snake neurotoxin II from<Emphasis Type="Italic">Naja oxiana</Emphasis>

Neurotoxin II fromNaja oxiana venom is a short-chain snake curaremimetic neurotoxin containing four disulfide bonds. We obtained¹³C-¹⁵N-labeled neurotoxin II to study its internal dynamics and surface properties with atomic resolution. The recombinant protein has the native spatial structure and is biologically active. The nearly complete assignment of¹H,¹³C and¹⁵N resonances for neurotoxin II was obtained by heteronuclear triple-resonance nuclear magnetic resonance spectroscopy. Analysis of the secondary chemical shifts of the¹H^α,¹³C^α,¹³C^β and¹³CO nuclei reveal their strong correlation with the protein secondary structure.