Douglas A. Kirkpatrick

Analysis of field emission from three‐dimensional structures

An analysis of the field emission from emitter tips with the geometry of a prolate ellipsoid of revolution indicates that the field enhancement factor, β, and effective emission area, α, are not constant but instead depend on the applied field. The added complexity of a materials related limit on the minimum time for transition of an electron from the solid into the vacuum is also examined in the analysis. The calculated variations of α and β are as large as 35%, and in some instances could result in erroneous interpretation of measured current‐voltage (I‐V) characteristic data.

Vacuum field emission from a Si‐TaSi2 semiconductor‐metal eutectic composite

We report on measurements of vacuum field emission from ungated field emission cathode arrays fabricated from Si‐TaSi2 eutectic composite wafers. The Si‐TaSi2 material is an ideal candidate for large area field emission array cathodes due to the large density of TaSi2 fibers incorporated into the Si matrix, the high melting point of the TaSi2 material, the ease with which single‐crystal large diameter (2.5 cm) material can be fabricated, and the promise of integrability of the field emission array with conventional Si technology through the use of epitaxial Si layers grown on the cathode backplane.

Demonstration of vacuum field emission from a self-assembling biomolecular microstructure composite

We report the first demonstration of vacuum field emission from an electron source fabricated from self‐assembling biomolecular composite microstructures. Diacetylenic lipid DC8,9PC is used to form hollow, 0.5 μm diam, ≳50 μm long, tubelike structures that are subsequently plated with metal and formed into an aligned composite in an epoxy matrix. The composite material is thin‐sectioned across the axis of alignment and then etched to expose the plated tubules. The sharp edges of the exposed metal tubules produce a very large local electric field enhancement, allowing for the vacuum field emission of significant current densities at relatively low applied macroscopic fields (≤60–80 kV/cm).

High brightness electron beam sources for FEL applications

Abstract A new generation of field emitter array (FEA) cathode materials is under development at SAIC, in collaboration with NRL and GTE Laboratories. The emitter structures under consideration consist of large area ( ∼ 1 cm 2 ) arrays of large numbers ( ∼ 10 6 ) of microscopic field emitting tips. The structures can be fabricated so as to choose an emitter tip microstructure that is a solid cone, a hollow cylinder, or a variety of other shapes. These microstructures evidence very high local field enhancement factors, controllable from a factor of ∼ 200 to > 2000 . This large local field enhancement allows quantum field emission of significant current from the large area array while the applied macroscopic electric field is still quite low ( ∼ 20 kV/cm ). Single-tip, noninteracting particle, multigrid simulations indicate that the beam brightnesses B n = I/π 2 ϵ n 2 >10 10 A/cm 2 rad 2 may be possible. Beams with such high brightness allow for a greatly expanded field of FEL applications, including high gain and harmonic operation in the FIR wavelength regime. Experiments have so far demonstrated DC average current densities > 1 A/cm 2 , uniform emission, and improved characteristics when run for long periods of time ( > 100 h, DC ). Our present efforts are concentrated on optimizing the available cathode current density, measuring the actual beam brightness, and including self-field and 3-D effects in the numerical simulations.

Surface composition of Si‐TaSi2 eutectic cathodes and its effect on vacuum field emission

Our research shows that the presence of an oxide layer on the surface of a field emission cathode is deleterious to its performance and that, for successful operation, removal of this layer is necessary before overcoating with another material. We further show that once the surface oxide is removed, cathodes can be protected with a Au overcoat and run in harsh environments. We have demonstrated stable emission for a Au‐coated Si‐TaSi2 cathode for over 100 h in an O2 atmosphere at 5×10−6 Torr.

Thermal effects on the gain in free-electron lasers

Abstract The effect of an axial energy spread on the linearized gain in free-electron lasers is considered for planar wiggler configurations in both the Raman and high-gain Compton regimes in the idealized one-dimensional limit. A thermal function is obtained by a linearized Vlasov-Maxwell analysis which applies to both the fundamental and the harmonics. The electron beam is assumed to be monoenergetic with a pitch angle spread, and is described by the inclusion of nonvanishing canonical momenta by means of a Gaussian distribution. The planar wiggler configuration admits interactions at odd harmonics as well as the fundamental, and a general dispersion equation is derived which includes the thermal effect at each harmonic as well as the fundamental.

Ungated Vacuum Field Emission from Ordered Arrays of Microlithographically Defined Cylinders

A new process has been developed which allows electroless metal deposition on ordered arrays of resist structures with high aspect ratios (10–25 μm tall x 0.5–13 μm diameter). The fabricated structures have demonstrated ungated vacuum field emission at fields of 80–300 kV/cm in background pressures of 5 × 10 -6 torr. The surface composition and Interface contamination relate directly to cathode performance. Cathode performance can be optimized by controlling the chemistry at these interfaces. X-ray Photoelectron Spectroscopy depth profiles, Scanning Auger Electron Spectroscopy, and Scanning Electron Microscopy have been used to characterize this system. These structures have potential vacuum microelectronics applications such as addressable electron emitters for flat panel displays.