A. F. Myers

Electron emission from diamond coated silicon field emitters

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias‐enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Field emission from silicon and molybdenum tips coated with diamond powder by dielectrophoresis

Thin diamond layers have been formed on molybdenum and single‐crystal silicon field emitters using a dielectrophoresis coating method from a suspension of diamond powder in a nonconducting fluid. Transmission and scanning electron microscopy observation revealed a significant amount of diamond on the tips. The average thickness of the deposited diamond layer depended on the applied bias and the immersion time. Field emission from these diamond‐coated emitters exhibited significant enhancement compared to the pure emitters.

Field emission characteristics of diamond coated silicon field emitters

Single crystal silicon field emitters have been modified by surface deposition of diamond using bias‐enhanced microwave plasma chemical vapor deposition. Polycrystalline diamond with a high nucleation density (1010/cm2) and small grain size (<20 nm) was achieved on silicon field emitters. Field emission from these diamond coated emitters exhibited significant enhancement both in total emission current and stability compared to pure silicon emitters. A large effective emitting area comparable to the tip surface area was obtained from a Fowler–Nordheim analysis. The effective work function of the polycrystalline diamond coated emitter surface was found to be larger than that of a pure silicon emitter surface.

Field emission from diamond coated molybdenum field emitters

Diamond deposition onto single Mo field emitters was accomplished by two methods: microwave plasma chemical vapor deposition and a dielectrophoresis of diamond powder. Observation by transmission electron microscopy and scanning electron microscopy revealed a significant amount of deposition at the tips. The field emission characteristics were measured before and after diamond deposition on the same emitters. Field emission from diamond coated emitters yielded significant increases in emission current and lower Fowler–Nordheim slopes. We discuss a possible mechanism to explain current enhancement that depends primarily upon the Mo‐diamond interface.

Field emission from amorphous diamond coated Mo tip emitters by pulsed laser deposition

Previous studies have shown that carbon films deposited on needle-shaped Si emitters by filtered cathodic arc are amorphous with a high sp2 content. These results can be ascribed to the poor thermal conductivity inherent to this geometry. Our present studies overcome this difficulty by depositing amorphous diamond films on Mo tip emitters by pulsed laser deposition. Monitoring films were grown on sapphire substrates and appeared transparent with a resistivity greater than 1×106 Ω cm, showing a typical amorphous diamond nature. Electron energy loss spectroscopy showed that the sp3 content of the film was 50% at the apex of the tip and 30% at the shank, which was lower than on planar substrates. High resolution transmission electron microscopy images revealed that the film at the apex was much denser than that at the shank, but both film showed a nano-columnar microstructure. Selected area electron diffraction confirmed that the films were amorphous in nature. Field emission from coated Mo tip emitters show...

Electron emission from a hydrogenated diamond surface

Electron emission from a polycrystalline diamond coated silicon field emitter surface was studied using in situ exposure to various gas species during its operation. Significant enhancement of the electron emission was found after the emitting surface was exposed to hydrogen at pressures in the range 5×10−4 to 10−3 Torr. Introducing other gases such as Ne and He only suppressed the emission current. A continuous emission current was measured from such a hydrogen‐exposed surface even after the electric field was reduced to below the initial threshold for electron emission. No similar result was found for pure silicon surface when identical conditions applied. This phenomenon was interpreted as the formation of a dynamically vacuum‐stable layer by polarized hydrogen and the diamond surface. Such a surface layer may significantly lower the surface barrier and exhibit the negative electron affinity property.

Characterization of amorphous carbon coated silicon field emitters

Amorphous carbon was deposited on needle‐shaped Si field emitters by filtered cathodic arc. Electron emission was obtained from these coated cathodes, but was reduced compared to emission from uncoated Si cathodes. Electron energy loss spectroscopy indicated that the coating was a high sp2 content amorphous carbon. Au particles were found to have precipitated out of the Si emitters, which were grown by a vapor–liquid–solid technique utilizing the Au–Si eutectic during the oxidation and chemical etch sharpening of the emitters. High resolution transmission electron microscopy and selected area electron diffraction confirmed the amorphous nature of the coating and the presence of the Au particles at the Si surface. The field emission, electron energy loss spectroscopy, high resolution transmission electron microscopy, and selected area electron diffraction results are presented and discussed.

Field emission enhancement from Mo tip emitters coated with N containing amorphous diamond films

Abstract Previous studies have shown that amorphous diamond (a-D) films can be deposited on sharp Mo tip emitters at room temperature by pulsed laser deposition, to achieve a substantial improvement in field emission. We report here on the field emission performance of Mo tip emitters coated with nitrogen containing amorphous diamond (a-D:N) films by pulsed laser deposition. The a-D:N film was prepared in an N 2 pressure of 3.7 × 10 −1 Pa with a laser fluence of 25 J/cm 2 . High resolution TEM images revealed that the films had a nano-columnar microstructure which showed a continuous variation in column angle, size and density from the shank to the apex, similar to those observed from the amorphous diamond films. Field emission measurements from Mo tip emitters coated with the a-D:N film indicated a further considerable improvement in turn-on voltage and emission current as compared with those of the a-D film coated Mo emitters. Such an enhancement in field emission may be ascribed to a shallow N donor level in amorphous diamond resulting in the formation of a narrower potential barrier at the interface between the Mo and the a-D:N films.

Field emission characteristics of diamond coated molybdenum field emitters

Diamond deposition on single Mo field emitters was studied following microwave plasma CVD and biased dipping in a solution of diamond powder. TEM and SEM observation revealed a significant amount of diamond on the tip of the Mo emitter. The field emission characteristics of the Mo emitters were investigated before and after diamond deposition and data were analyzed using Fowler-Nordheim theory. After diamond coating, the emission current was found to increase by more than one order of magnitude compared to that of the same uncoated emitter. An explanation of this behavior is proposed.

Field emission from aluminum nitride and cubic boron nitride coatings

Recent studies have shown that thin layers of wide band gap materials such as silicon carbide and diamond can improve electron emission from of sharp field emitters. Aluminum and boron nitrides possess characteristics similar to those of diamond, e.g. chemical and mechanical stability, a wide band gap (from 6-7 eV), a reported negative electron affinity, and the ability to be doped p-type. There is also the possibility of n-type doping. In this study we investigate the field emission properties of these III-V nitrides deposited onto silicon and molybdenum by both reactive magnetron sputtering and by dielectrophoresis. Emission properties for diamond, AlN, and c-BN are compared and are projected to other wide band gap materials.