Enhanced Field‐Emission Obtained from NiO Coated Carbon Nanotubes

Abstract

Carbon nanotubes(CNTs) have drawn much interests because of their unique electrical, mechanical properties and their potential applications in field emission displays, sensors, transistors, nano-tweezers and AFM tips. [1][2][3][4] Above all, the field emission from CNTs have been extensively studied due to the nanometer-size diameter, structural integrity, high electrical conductivity and chemical stability after first demonstration in 1995. [5] According to Fowler-Nordheim's theory the FE current density (J) is a function of the electric field E and the work function f of emitter. [6,7] For metal, with typical work function and a flat surface the threshold field is typically around 10 4 V/lm, but it can be easily generated by the field-enhancing properties of tip-like structures such as CNT. All the field emission sources rely on the field enhancement originated from the apex of a needle of height and radius. A CNT with a diameter of 10 nm and a length of 2 lm was reported to exhibit a field-enhancement factor (b) up to 400 which is equal to the ratio of height/radius and the field emission from CNTs can be generated at the apex of CNT by a very low applied field of 7.5 V/lm.In advances in research, the enhancement of the fieldemission properties was achieved by coating the emitter's tip with wide band gap materials (WBGM). Accordingly LiF, [8] CaF 2,[9] AlN [10] and c-BN [11] were applied to metal emitters to decrease the effective work function of emitters, which correspondingly increases emissivity and also MgO and SiO 2 were applied to CNT emitters. [13,14] Such a coating gives excellent emission characteristics and protection from adsorption or ion bombardment of residual gas molecules in the vacuum cavities such as display panel or field-emission lamps.In this communication, we introduce NiO coated CNT emitters for enhancing the field-emission properties in terms of electron emissivity and structure stability protective from residual gas and corrosive environment as well. Since the field emission lighting devices comprise a planar substrate with arrays or bundle of emitters (cathode) and a phosphor coated display screen (anode) that is mounted in a parallel with the cathode plate for the electron bombardment from emitters.The both cathode and anode plates are assembled with micron scale spacers in between and sealed using frit glass under high vacuum grade. The pressure inside the device panel would be 10 -6 ∼ 10 -5 Torr. The inside pressure will be always degraded by the residual gas evaporating from the inner walls of phosphor layer during device operation. Besides the ion arcing from residual gas will deteriorate the emitting CNT tips resulting in a critical reduction of brightness. The authors developed CNTs coated all around with NiO in nanoscale aiming at the enhanced field-emission and environmental inertness for long life of electron emitter. The coating of NiO around CNTs was possible employing an electroless plating technique. Figure 1 shows the X-ray diffraction pattern of multiwall(MW) CNTs as-...

Decoration of multiwalled carbon nanotubes with CoO and NiO nanoparticles and studies of their magnetism properties

“…Consequently, decorating carbon nanotubes with magnetic nanoparticles may give birth to novel chemical and physical properties and promising applications due to the combination of features of magnetic nanoparticles and carbon nanotubes. Up to now, carbon nanotubes decorated with magnetic nanoparticles such as c-Fe 2 O 3 , Fe 3 O 4 , CoO, NiO and Mn 3 O 4 via various approaches have been reported [10,14,[18][19][20][21][22]. However, most of those approaches usually involve tedious and costly preparation procedures or the assistant of surfactants.…”

Thermal oxidation of Ni films for p-type thin-film transistors

“…5(b). As the work functions of Au, Ni, and p-type NiO are B5.0, B5.2 and B4.6 eV, respectively, 13 the band diagrams before and after the formation of the device can be drawn in Fig. 5(c) and (d).…”

Effect of Infrared Oxide Catalysts on Water Splitting for Green Energy

“…The IR‐irradiated oxide catalysts comprise two crystallographic polymorphs [21,22] . They are based on iron in the ferrous form (Fe 2+ ), which, on elevated temperatures either transforms to magnetite and/or hematite mixtures with silica under oxidizing atmospheres or reduces to metallic iron under strongly reducing conditions [23–25] …”