Laser ablation in liquids : Applications in the synthesis of nanocrystals

Field emission (FE) is based on the physical phenomenon of quantum tunneling, in which electrons are injected from the surface of materials into vacuum under the influence of an applied electric field. A variety of field emission cold cathode materials have been developed to date. In this review, we shall focus on several kinds of novel cold cathode materials that have been developed in the past decade. These include materials for microfabricated field-emitter arrays, diamond and related films, carbon nanotubes, other quasi one-dimensional nanomaterials and printable composite materials. In addition, cold cathode materials have a wide range of applications such as in flat panel displays, high-power vacuum electronic devices, microwave-generation devices, vacuum microelectronic devices and vacuum nanoelectronic devices. Applications are in consumer goods, military industries and also space technology. A comprehensive overview of the various applications is presented. Recently, recognizing the strong possibility that vacuum nanoelectronic devices using quasi one-dimensional nanomaterials, such as carbon nanotubes may emit electrons with driving voltages comparable to that of a solid-state device, there is a growing interest in novel applications of such devices. With such exciting opportunities, there is now a flurry of activities to explore applications far beyond those considered for the conventional hot cathodes that operate on thermionic emission. We shall discuss the details of a number of fascinating potential applications.

Novel cold cathode materials and applications

Diamond-like carbon — present status

Ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma-enhanced chemical-vapor-deposition method using a CH4(1%)/Ar gas mixture and 1%–20% nitrogen gas added. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω−1 cm−1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films.

Synthesis and characterization of highly-conducting nitrogen-doped ultrananocrystalline diamond films

The reaction of nanoscale diamond (ND) powder with an elemental fluorine/hydrogen mixture at temperatures varying from 150 to 470 °C resulted in the high degree of ND surface fluorination yielding a fluoro-nanodiamond with up to 8.6 at. % fluorine content. The fluoro-nanodiamond was used as a precursor for preparation of the series of functionalized nanodiamonds by subsequent reactions with alkyllithium reagents, diamines, and amino acids. The fluoro-nanodiamond and corresponding alkyl-, amino-, and amino acid-nanodiamond derivatives were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), and thermal gravimetry-mass spectrometry (TG-MS) measurements. In comparison with the pristine nanodiamond, all functionalized nanodiamonds show an improved solubility in polar organic solvents, e.g., alcohols and THF, and a reduced particle agglomeration. The developed method...

Functionalization of Nanoscale Diamond Powder: Fluoro-, Alkyl-, Amino-, and Amino Acid-Nanodiamond Derivatives

Ultrananocrystalline diamond (UNCD) films 0.1–2.4 μm thick were conformally deposited on sharp single Si microtip emitters, using microwave CH4–Ar plasma-enhanced chemical vapor deposition in combination with a dielectrophoretic seeding process. Field-emission studies exhibited stable, extremely high (60–100 μA/tip) emission current, with little variation in threshold fields as a function of film thickness or Si tip radius. The electron emission properties of high aspect ratio Si microtips, coated with diamond using the hot filament chemical vapor deposition (HFCVD) process were found to be very different from those of the UNCD-coated tips. For the HFCVD process, there is a strong dependence of the emission threshold on both the diamond coating thickness and Si tip radius. Quantum photoyield measurements of the UNCD films revealed that these films have an enhanced density of states within the bulk diamond band gap that is correlated with a reduction in the threshold field for electron emission. In additio...

Electron field emission for ultrananocrystalline diamond films

Grain boundary field electron emission from CVD diamond films

Band bending formation on thin nanocrystalline diamond films and field electron emission after post-growth treatments was investigated. It was found that treatment of the diamond surface with hydrogen plasma substantially decreases the density of point defects, forms the downward band bending and enhances the field electron emission from the films. In the case of an argon plasma treated diamond surface, new point defects were induced and their energy distribution was changed. Nevertheless, the downward band bending was formed and the field electron emission was enhanced similar to the H–plasma-treated diamond surface with minor density of defects. These effects were interpreted in terms of the electrical dipole formation on the plasma treated diamond surfaces. Coating the diamond films with ultrathin metal (Ni, Ti) layers revealed the dependence of the band bending and field emission behavior on the type and thickness of the metal used. The deposition of a few monolayers of Ni on the diamond surface was f...

A.V. Karabutov

Papers

Electron field emission for ultrananocrystalline diamond films

Grain boundary field electron emission from CVD diamond films

Effects of post-growth treatment and coating with ultrathin metal layers on the band bending and field electron emission of diamond films

Diamond–carbon nanocomposites: applications for diamond film deposition and field electron emission

Diamond/sp2-bonded carbon structures: quantum well field electron emission?