N. S. Xu

GRAPHITIZATION OF NANODIAMOND POWDER ANNEALED IN ARGON AMBIENT

Nanodiamond powder was annealed at each of the following temperatures: 300, 600, 800, 1000, and 1150 °C, for an hour in flowing argon ambient. The variations of x-ray diffraction patterns and Raman spectra of the powder with different annealing temperatures were studied. While being annealed at temperatures higher than 800 °C, the powder can undergo a phase-transition process from cubic diamond to graphite. In addition, the size of nanodiamond crystallites decreased from ∼50 to ∼25 A. The physical mechanism responsible for the variation in Raman spectra is discussed using a phonon-confinement model.

Field emission of one-dimensional micro- and nanostructures of zinc oxide

A variety of one-dimensional (1D) micro- and nanostructures of zinc oxide (ZnO) were self-assembled on amorphous carbons using thermal chemical vapor transport and condensation without any metal catalysts. The low turn-on electronic field and the higher current density were achieved on these 1D ZnO micro- and nanostructural emitters. It was found that the geometry of the micro- and nanostructural emitters plays a crucial role in the field emission of ZnO.

Synthesis of crystalline alumina nanowires and nanotrees

Abstract Crystalline alumina nanowires were synthesized at elevated temperatures in a catalyst-assisted process using iron as catalyst. Nanotrees that formed by alumina nanowires were also found. SEM shows that typical nanowires are around 50 nm in diameter and around 2 μ m in length. The tree trunk of the nanotrees are around 100 nm in diameter and around 10 μ m in length. HRTEM with electron diffraction study reveals that the nanostructures are crystalline. The EDX confirms that the nanostructures contain only elements of Al and O. The XRD study shows that the nanowires are α-Al2O3. The results are explained in the light of growth mechanism based on a vapor–liquid–solid (VLS) process.

Field emission study of SiC nanowires/nanorods directly grown on SiC ceramic substrate

Single crystalline silicon carbide (SiC) nanowires were grown directly on the surface of bulk SiC ceramic substrate in a catalyst-assisted thermal heating process. The morphology of the nanowire film and the diameter of nanowires were found to be sensitive to the thickness of catalyst film and both of them had a strong effect on field emission performance. Very low turn-on and threshold fields for electron emission were observed with SiC nanowires of small diameter. A model is proposed to qualitatively explain the field emission findings, which assumes the occurrence of an insulator-to-metal-like transition in a field emitting nanowire.

Vacuum gap dependence of field electron emission properties of large area multi-walled carbon nanotube films

Field electron emission properties of aligned multi-walled carbon nanotube films were studied with variation of the vacuum gap d between anode and cathode. With d varying in the range of 0.4-2 mm, the emission current-gap voltage characteristics and the corresponding Fowler-Nordheim (FN) plots show distinct nonlinearity and regular changes with electrode separation. Three field enhancement factors may be derived from the three linear sections of a FN plot. Their variation with gap d results in different behaviours; significantly a drop of five times in the field enhancement factor is observed. The physical process responsible for our findings is suggested to be the space charge effect and both theoretical and experimental evidence is provided to support our arguments. The implication of our findings in technical applications is also discussed.

Physical origin of nonlinearity in the Fowler–Nordheim plot of field-induced emission from amorphous diamond films: Thermionic emission to field emission

Nonlinearity is observed in Fowler–Nordheim (FN) plots of field emission from nondoped and nitrogen-doped amorphous diamond films. Based on a unified electron emission equation a detailed analysis is carried out. The results from numerical calculation of the unified equation are consistent with the experimental data. It is shown that the nonlinearity in the FN plot originates from a transition from thermionic emission to field emission as the applied field increases. The electrical field ranges are derived in which the field emission and thermionic emission approximation applies.

Fabrication of vertically aligned Si nanowires and their application in a gated field emission device

A technique involving a combination of using self-assembled nanomask and anisotropic plasma etching is developed for fabricating vertically aligned single-crystalline Si nanowires (SiNWs). The SiNWs are shown to have excellent field emission performance with the turn-on field as low as 0.8MV∕m and the threshold field being 5.0MV∕m. In addition, an emission current density of 442mA∕cm2 can be obtained at an applied field of ∼14MV∕m. The technique is easily employed to fabricate arrays of SiNW-based field emission microtriodes. Mechanisms are proposed to explain the formation of the SiNWs and the observed field emission properties.

Field emission and photoluminescence of SnO2 nanograss

Two-dimensional SnO2 nanograsses were synthesized on single-crystal Si substrates by catalyst-assisted thermal evaporation. The photoluminescence spectra from the products revealed multipeaks consistent with previous reports, with the exception of a new peak at 574 nm. The large field emission current from SnO2 nanograss was observed at a high turn-on voltage, which is attributed to a shorter length and a wide emitter radius. The formation of SnO2 nanograsses at the low temperature was pursued on the basis of the vapor-liquid-solid mechanism.

Field emission display device structure based on double-gate driving principle for achieving high brightness using a variety of field emission nanoemitters

In order to apply various cold cathode nanoemitters in a field emission display (FED) and to achieve high brightness, a FED device structure with double gates and corresponding driving method have been proposed. Individual pixel addressing can be achieved by applying proper sequence of positive or negative voltage to the lower gate and upper gate, respectively. The feasibility of the device has been demonstrated by using carbon nanotube and tungsten oxide nanowire cold emitters. Display of moving images has been demonstrated and high luminance up to 2500cd∕m2 was obtained. The reported device structure is versatile for nanoemitters regardless of substrate or preparation temperature. The results are of significance to the development of FED using nanoemitters.

Enhancing electron emission from silicon tip arrays by using thin amorphous diamond coating

A thin (∼2 nm thick) amorphous diamond coating was prepared on single crystal silicon tip arrays by using a filtered vacuum arc plasma deposition technique. The coating has a microscopically uniform morphology. As compared to uncoated tips, the electron emission of the coated tip arrays is enhanced, showing an increase in the total current, lower turn-on field and a lower-slope Fowler–Nordheim plot. We propose that field-emitted electrons could tunnel through such a thin coating with few scattering events. It is shown that the low potential barrier at the interface is the major cause of the enhancing effects instead of the negative surface electron affinity of the coating.