We briefly report on progress in forming field emitter array (FEA) cones from zirconium carbide. The major advances are on high current emission from single carbide emitters. These unique carbide materials have electron emission properties making them attractive for several applications. These could include video displays, microwave applications, high current and small spot electron sources (accelerators and FELs) and for operation at tube pressures or in poor vacuums (FEAs, vacuum detectors, neutralizing beams for ion thrusters, and charge dissipation on spacecraft).

The significant recent outcomes are in high current electron emission from single emitters with and without extraction apertures. A new processing technique has been developed to allow in-situ sharpening of arced emitters. This method also yields large emitter-cone half angles yet preserves the small emitter radii of electrochemically etched emitters. So far, this geometry translates into currents as high as 15 mA dc, the highest yet measured from single emitters, and enhanced beam confinement. This geometry may also lead to new considerations in forming transition metal carbide emitter cones for FEAs.

Electron field emission and electrical conductivity of undoped and nitrogen doped DLC films have been investigated. The films were grown by the PE CVD method from CH4:H2 and CH4:H2:N2 gas mixtures, respectively. By varying nitrogen content in the gas mixture over the range 0 to 45%, corresponding concentrations of 0 to 8 % (atomic) could be achieved in the films. Three different gas pressures were used in the deposition chamber: 0.2, 0.6 and 0.8 Torr. Emission current measurements were performed at approximately 10−6 Torr using the diode method with emitter-anode spacing set at 20 gm. The current - voltage characteristics of the Si field electron emission arrays covered with DLC films show that threshold voltage (Vth) varies in a complex manner with nitrogen content. As a function of nitrogen content, Vth initially increases rapidly, then decreases and finally increases again for the highest concentration. Corresponding Fowler-Nordheim (F-N) plots follow F-N tunneling over a wide range. The F-N plots were used for determination of the work function, threshold voltage, field enhancement factor and effective emission area. For a qualitative explanation of experimental results, we treat the DLC film as a diamond-like (sp3 bonded) matrix with graphite-like inclusions.

Using photoelectron emission and Raman spectroscopy, we characterize normally unoccupied states that have an energy 2.41-2.71 eV below the conduction band of polycrystalline diamond films. The films are grown using chemical vapor deposition with methane to hydrogen gas concentrations of 0.10%, 0.20%, 0.30%, 0.45%, 0.60% and 0.70%. Photoelectron emission is performed using visible light from an argon laser. The light is focussed on a 5-10 µm diameter area of the sample. The emitted electrons are collected with high efficiency using a microchannel plate detector. Raman spectroscopy is performed simultaneously with photoelectron emission to determine the morphology and diamond versus graphite content of the photoelectron emission area. The photoelectron emission rate is observed to have a quadratic dependence on the incident light power showing that the photoelectron emission process is a two-photon process involving the excitation of electrons from normally unoccupied states. The photoelectric yield versus incident photon energy, and the photoelectric yield as a function of methane concentration are presented.

As previously demonstrated, non-diamond carbon (NDC) films deposited at low temperatures 200-300 °C on silicon tips reduced the threshold of field emission. In this paper we will present the results of the study of field emission from flat NDC films prepared by VHF CVD. Emission measurements were performed in a diode configuration at approximately 10−10 Torr. NDC films were deposited on ceramic and on c-Si substrates sputter coated with layers of Ti, Cu, Ni and Pt. The back contact material influences the emission characteristics but not as a direct correlation to work function. A model of field emission from metal-NDC film structures will be discussed.

In this work, we shall analyze the performance of a geometrical interface roughness model to estimate current from p-type silicon into insulating diamond and compare the performance of that model to experimental data. A minimum number of adjustable parameters are invoked. While the model qualitatively accounts for trends in the experimental data, in particular, the shift from negative to positive slope on a Fowler Nordheim plot of the I(V) data, it does so at the expense of demanding ellipsoid parameters that appear to be unreasonable. We therefore conclude that a simple geometrical field enhancement model of interface roughness is insufficient to account for the current observed, and thus the theory must be augmented by a more comprehensive electron transport model at the interface.