INFLUENCES OF DENSITY AND DIMENSION OF CARBON NANOTUBES ON THEIR FIELD EMISSION

The influences of density and dimension of carbon nanotubes on their electron emission from arrays are studied. The tip electric field of nanotubes, electric field enhancement factor, and optimum nanotube density are expressed by analytic equations. The theoretical analyses show that the field enhancement factor is sensitive to nanotube density, and can be sharply improved at a specific and optimum density. Some experiments have demonstrated these. Owning to electrostatic screening effect, the length of carbon nanotubes has little effect on their emission. A uniformly-distributed carbon nanotube array model is set up, and applied to analysis of carbon nanotube arrays. The results obtained here are in good agreement with the experimental data.

Field emission of carbon nanotube array with normal-gate cold cathode

A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.

Well-aligned carbon nanotube array membrane and its field emission properties

Ensembles of aligned and monodispersed carbon nanotubes (CNTs)can be prepared by templating method which involves fabrication of porous anodic aluminum oxide (AAO) template, control of catalytic iron particle size and chemical vapor deposition of carbon in the cylindrical pores of AAO. Here we show that template-synthesized CNTs can be fabricated as well-aligned nanoporous CNTs membrane, which can be directly used as an electron field emitter. A low threshold electric field of 2-4 V/μm and maximum emission current density of ～12 mA/cm2 are observed. The results also show that the electron emission current is a function of the applied electrical field and the Fowler-Nordheim (F-N) plot almost follows a linear relationship which indicates a Fowler-Nordheim tunneling mechanism, and the field enhancement factor estimated is about 1100-7500. The simple and convenient approach should be significant for the development of nanotube devices integrated into field emission displays (FEDs) technology.

Dynamic and reversible electrowetting with low voltage on the dimethicone infused carbon nanotube array in air

Unremitting efforts have been intensively making for pursuing the goal of the reversible transition of electrowetting owing to its vital importance to many practical applications,but which remains a major challenge for carbon nanotubes due to the irreversible electrochemical damage.Herein,we proposed a subtly method to prevent the CNT array from electrochemical damage by using liquid medium instead of air medium to form a liquid/liquid/solid triphase system.The dimethicone dynamically refills in CNT arrays after removing of voltage that makes the surface back to hydrophobic,which is an elegant way to not only decrease energy dissipation in electrowetting process but also obtain extra energy in reversible dewetting process.Repeated cycles of in situ experiments showed that more than four reversible electrowetting cycles could be achieved in air.It wo rth mention that the in situ reve rsible electro wetting voltage of the dimethicone infused CNT array has been lowered to 2 V from 7 V which is the electrowetting voltage for the pure CNT array.The surface of the dimethicone infused CNT array can maintain hydrophobicity with a contact angle of 145.6°after four cycles,compared with 148.1°of the initial state.Moreover,a novel perspective of theoretical simulations through the binding energy has been provided which proved that the charged CNTs preferred binding with water molecules thereby replacing the dimethicone molecules adsorbed on the CNTs,whereas reconnected with dimethicone after removing the charges.Our study provides distinct insight into dynamic reversible electrowetting on the nanostructured surface in air and supplies a way for precise control of wettability in surface chemistry,smart phase-change heat transfer enhancement,liquid lenses,microfluidics,and other chemical engineering applications.