Diamond Cathode Research Articles

Metal-insulator-vacuum type electron emission from N-containing chemical vapor deposited diamond

This letter presents a clear explanation of the electron emission mechanism of the high-resistivity N-doped diamond cathode. Due to the very low barrier to emission of electrons from the N-doped diamond conduction band into vacuum, electrons in the conduction band of diamond can establish an appreciable leakage current at very low anode voltage. When such a current starts to flow, there is a field which is developed across the diamond bulk. This field is observed as an increase in the electric field at the back contact, causing the injected tunneling current increases exponentially. This process leads to the low threshold emission from the high resistivity N-doped diamond cathode.

Recent development of diamond microtip field emitter cathodes and devices

Recent development of diamond field emitter cathodes and devices fabricated from molding process is presented. Practical modifications involving the sp2 content, surface treatment, boron doping, and tip sharpening to further enhance diamond field emission are discussed. A new fabrication process for achieving ultrasharp diamond tips with a radius of curvature less than 5 nm has been achieved and shows significant improvement in emission characteristics. Discussion of this enhanced emission in diamond microtips is presented in accordance with analysis of emission behavior. The development of high site density of uniform diamond microtip arrays is presented. We also report the development of a new technique to fabricate self-aligned gate diamond emitter diodes, which achieve very high emission characteristics at extremely low applied voltage. The latest development aims to integrate diamond field emitters with silicon-based MEMS processing technology and achieve totally monolithic diamond field emitter devices on silicon wafers. Preliminary results in the triode configuration demonstrate promising transistor characteristics suitable for vacuum microelectronic applications.

Electronic properties of diamond thin film for planar diamond electron emitter applications

Planar electron emitters have been fabricated using diamond thin films having a micro-gap. The electronic properties of the diamond thin films were characterized on the basis of the electron emission properties from the gap in the diamond cathode. Extremely low threshold emission, as low as 10 V, was observed from the diamond emitter composed of the continuous thin films and luminescence from phosphor was clearly seen by applying a voltage of 500 V on the anode screen placed 2.5 mm above this device.

Proposal and modeling of a novel thermal microprobe using n-Si/nitrogen doped diamond cathodes

A novel thermal microprobe is proposed and its operation is theoretically analyzed. The thermal sensitivity of the microprobe is assured by a field emission diode using n-Si/nitrogen doped as a cathode. The cathode layer is placed on the atomic force microscope cantilever on the opposite side of the sharp sensing stylus, thus allowing for both mechanical and thermal maps of the sample to be obtained. A model to characterize the temperature dependence of the emission current has been developed, which shows good agreement to reported experimental data. The current-temperature exponential dependence allows a high temperature sensitivity of the microprobe. The developed model is further used to characterize the thermal microprobe properties and derive design hints.

Analysis of a pressure sensor using n-Si/nitrogen doped diamond cathodes

The purpose of this article is to analyze the operation of a pressure sensor in a diode configuration based on field emission from n-Si/nitrogen doped diamond cathodes. The device comprises a silicon membrane, which is the pressure sensing element. When the device emission current is kept constant, the membrane bending under external pressure modifies its operating voltage in a linear way. A new model has been developed to characterize field emission from n-Si/nitrogen doped diamond cathodes, showing good agreement with experimental data. The device sensitivity has been computed as function of both the silicon membrane and diamond layer parameters. Better sensor sensitivity is obtained for membranes with smaller dimensions and thinner, but the opposite trend allows to increase the measurable pressure range. The obtained modeling results can be further used for sensor design improvement.

Field emission from heterostructured nanoseeded diamond and nanocluster carbon cathodes

ABSTRACTNovel heterostructured cold cathodes made of nanoseeded diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond with varying diamond concentration was first coated on to the substrate. The nanocluster carbon films were then deposited on the nanoseeded diamond coated substrates using the cathodic arc process at room temperature. The resultant heterostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at low fields of 1.2 - 5 V/μm. Further some of the samples seem to exhibit I-V characteristics with a negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond concentration.

Field emission from gated diamond arrays

Diamond field emitter arrays have been developed for use as cold electron sources in flat panel displays and high-power tubes. Diamond was selectively deposited on patterned silicon wafers, and the common problems of field emission from the gate and the walls have been solved by innovative modifications in the processes involved. This resulted in cathodes where the gate area was completely free of diamond. The leakage currents were less than 8% of the total current. The diamond cathodes were tested in two different diode configurations in a UHV system for voltages ranging from 0–20 V. Field emission has been achieved at ultra-low onset voltages of less than 0.25 V and very high currents were obtained. For a voltage of 3 V applied to the gate, for example, corresponding to an electric field of 1.5 V/μm, emission currents of up to 1 mA have been observed and tested for several days without deterioration. At 7 V, a current of 3.5 mA was achieved in this configuration. The onset of field emission for measurements to a flat anode was 0.5 V/μm, and 3.5 mA were reached at 0.8 V/μm.

Electrochemical behavior of synthetic diamond thin film electrodes

Diamond's chemical inertness and unique electrochemical properties present great potential for a variety of applications in aggressive environments. Preliminary results have shown the widest known electrochemical window before water decomposition, allowing new possibilities for both anodic and cathodic reactions. Studies of the oxidation of organic compounds has been performed with alcohols such as isopropanol, phenol and organic acids. Cyclic voltammetry demonstrates no activity in the potential range where water is stable. In the potential region of oxygen evolution, the organic compounds are mainly oxidized to CO 2 . No deactivation or reduction in the thickness of the electrode has been observed. In addition, no fouling of the diamond surface has been detected. Furthermore, no hydrodynamic effects have been observed. Concentrated (1 M) and diluted (3×10 −4 M) cyanide solutions have been oxidized on diamond electrodes both in the presence and in the absence of chloride ions. The results show a direct oxidation with a current efficiency of about 40% for concentrated solutions. At low cyanide concentrations, the current efficiency is strongly increased by the presence of Cl − . Electrochemical reduction of cadmium and copper has been carried out on diamond electrodes. Non-adherent deposits have been obtained on diamond cathodes.

ダイヤモンドを陰極とした直流プラズマＣＶＤ法におけるダイヤモンド薄膜の高速合成の試み

ダイヤモンドを陰極とした直流プラズマＣＶＤ法におけるダイヤモンド薄膜の高速合成の試み

Emission and emittance measurements of electron beams generated from Cu and diamond photocathodes

We report on the electron emission from Cu and diamond film cathodes irradiated with two ultraviolet excimer laser beams working at 308 nm XeCl, and 222 nm KrCl. The beam emittance measurements were performed using a new experimental setup composed of two movable slit arrays. The electron beam phase space areas were determined by splitting the beam in small beamlets and measuring the beamlet direction spread via small cups and slits. The highest emission was obtained at the lowest laser wavelength. With a 4 mm2 beam spot and 0.5 mJ laser energy the maximum currents from the Cu and diamond film cathode were 370 and 410 mA, respectively, and the corresponding emittances were 18 and 27 (π mm mrad). From these values the normalized beam brightness was estimated to be 4.6×109 A(π m rad)−2 for the Cu cathode and 2.3×109 A(π m rad)−2 for the diamond cathode. By increasing the laser energy and the spot beam the maximum extracted current was 16.4 A from the Cu cathode with the KrCl laser.

Quantum Chemical Approach to Redox Reactions Including Potential Dependence: Application to a Model for Hydrogen Evolution from Diamond

The evolution of H2 from diamond cathodes according to the proposed mechanism H+(aq) + ⪫C−H + e- → H2 + ⪫C• is treated with ab initio quantum mechanics. The solvated proton and diamond surface C−H bond are modeled with molecular clusters, and the electron is introduced at selected potentials by using a remote donor molecule. The reduction occurs when the electron affinity, EA, of the surface complex increases to the ionization potential, IP, of the donor as the complex traverses its reaction coordinate. When they are equal, equilibrium is assumed and electron transfer occurs. The electrochemical potential, U, is given by U = (IP/eV − 4.6) V. For the H2 generation reaction studied, the electron transfer coincides with the transition-state structure, and the activation energy is found to decrease as the potential becomes more negative. It is shown that surface C−H bonds will re-form by H+(aq) discharge on the surface carbon radicals. The potential-dependent reduction of H+(aq) to H• is examined, too. Comparison is made with the gas-phase generation of hydrogen and surface carbon radicals. The present model employs the hydronium ion for H+(aq), methane and isobutane for surface C−H, and the self-consistent HF/STO-3G method. In general, use of an electron donor is not required. This approach should find application to many other electrochemical reactions.

A new surface electron-emission mechanism in diamond cathodes

An electron-emission mechanism for cold cathodes is described based on the enhancement of electric fields at metal–diamond–vacuum triple junctions. Unlike conventional mechanisms, in which electrons tunnel from a metal or semiconductor directly into vacuum, the electrons here tunnel from a metal into diamond surface states, where they are accelerated to energies sufficient to be ejected into vacuum. Diamond cathodes designed to optimize this mechanism exhibit some of the lowest operational voltages achieved so far.

陰極にダイヤモンドを用いた直流プラズマＣＶＤ法によるダイヤモンド薄膜の合成

陰極にダイヤモンドを用いた直流プラズマＣＶＤ法によるダイヤモンド薄膜の合成

ダイヤモンド陰極を低温にした直流放電プラズマＣＶＤ法によるダイヤモンド薄膜の合成

ダイヤモンド陰極を低温にした直流放電プラズマＣＶＤ法によるダイヤモンド薄膜の合成

Field emission measurements with μm resolution on chemical-vapor-deposited polycrystalline diamond films

The distribution of field emitting sites on polycrystalline diamond films at electrical surface fields has been investigated between 2.5 and 150 MV/m by means of a field emission scanning microscope with μm resolution. For the first time field emission scans were performed on broad-area (≊cm2) diamond cathodes with in situ scanning electron microscope analysis of the localized sites. The 2–3-μm-thick diamond films were chemical-vapor deposited on Mo substrates by the hot-filament technique. Undoped and p-type boron-doped films with low content of sp2-bonded carbons were studied. The highest emitter density of ∼2000/cm2 at 100 MV/m was detected on undoped diamond surfaces. A preliminary study of localized emitters indicated both sporadic particles of foreign materials at the emitting sites as well as intrinsic emission from diamond. In addition, the Fowler–Nordheim parameters β and S, the elemental composition, and the current stability of localized emitters were measured.

Electron Emission from Cold Cathodes

ABSTRACTNew observations are presented on the emission of electrons from n-type polycrystalline diamond and n-type boron nitride (BN) cold cathode films, both as synthesized and after post-synthesis annealing. The films have been observed to show an increase in electron emission after annealing by one to several orders of magnitude, depending upon the type of emitter and the specific surface treatment. Observations from both plasma and laser annealing treatments will be presented.The annealed BN cold cathodes have been observed to yield stable emission currents as high as 2 A cm−2 (∼4 mA total current) at fields as low as ∼30 V μm−1. This is believed to be the highest reported current density yet observed from a planar film cold cathode emitter.