A simultaneous study of Auger spectra and secondary electron emission from the chemical vapor deposited diamond films under extended electron beam exposure is presented. Up to a 1.2 eV increase in energy of the carbon Auger peak accompanied by the decrease of the total secondary electron yield has been found. Exposure to hydrogen has resulted in recovery of the both Auger peak position and secondary yield. First-principles electronic structure calculations have been carried out to interpret the Auger peak shift. The effect is shown to be due to a change in the surface upper-valence band local density of states of the diamond crystal which is dependent on the extent of hydrogen coverage of the surface.

Electron field emission from diamond films was calculated using a model consisting of the projection of the energy-band surfaces in the <111>, <110> and <100> emission directions. It is found that the tunneling from bulk conduction and valance bands is negligible in p-type diamond, while emission from n-type doped diamond, surface states located near the conduction band edge, and hypothesized defect bands in the energy gap all have sufficient transmission probabilities to produce the low power-high current observed in experiments. To understand the mechanism for supplying electrons to these tunneling states, we analyze charge transport in diamond with internal fields. In particular, a Monte Carlo simulation was performed for electrons in the conduction band as a function of field and film thickness. The results predict hot electron behavior at lower fields with a transition to ballistic-like behavior for high fields (≥ 10 V/μm) and thin samples (≤0.1 μm). It is suggested that if a viable electron injection mechanism into the conduction band of a diamond-metal or diamond-semiconductor interface could be found for those faces of diamond exhibiting NEA, then a copious cold cathode electron emitter with field tunable energies is feasible.

We have developed both experimental and numerical methods to collect and analyze field emission data from diamond samples. The diamond emitters are either films prepared by low pressure chemical vapor deposition (CVD) or powders synthesized by traditional high pressure high temperature (HPHT) processes. We established a strong correlation between the electric field required for emission and the defect densities in undoped or p-type doped diamond. We further found that ultrafine diamond particulate emitters offer substantially enhanced electron field emission properties at low electric fields compared to CVD diamond emitters. When subject to appropriate processing schemes, the particulate diamond emitters exhibit extremely low emission fields, typically 1-5 V/μm for a current density of 10 mA/cm2. These are believed to be the lowest-voltage field emitters ever reported.

Cesiation of type IIB diamond (110) crystals was studied using a combination of ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and low energy electron diffraction. The diamond (110) crystal was hydrogen treated by exposure to a hydrogen microwave discharge. Although cesium was largely unreactive with the hydrogenated diamond surface, cesiation yielded a large enhancement in the secondary electron yield of the diamond surface and the negative electron affinity (NEA) condition. An increase in the downwards band bending of approximately 0.75-0.9 eV was inferred from the shift in the valence band edge following cesiation. In addition, (lx 1) LEED patterns were observed at all cesium coverages. Exposure of the cesiated diamond surface to molecular oxygen significantly reduced the NEA peak (relative to the secondary electron background); however, recovery of the NEA peak was observed when the molecular oxygen source was removed.

Microstructures of Amorphic Diamond™ films deposited by laser ablation method were investigated using transmission electron microscopy. The AD films matrix was homogeneous with a sp3-type bonding fraction of 40%∼45% confirmed by electron energy-loss spectroscopy. The sp3 bonding fraction decreased monotonically with increasing annealing temperature. The main inhomogeneity in Amorphic Diamond™ was observed to be particulates of high density (>105/cm2) distributed through the depth of the film. Particulate size ranged from ∼10nm to a few μm and most of them were identified to be graphite. Large particles (>0.5μm) were agglomerates of smaller graphite crystallites. Possible mechanisms for cold field emission are discussed based on the microstructures observed in these AD films.

Diamond exhibits high secondary-electron yields which vary strongly with sample preparation and sample treatment. In this study, we identify some of the factors that govern the secondary-electron emission yield of diamond. Comparative studies are made with polycrystalline diamond films having different dopants (boron or nitrogen), dopant concentrations and surface conditions (hydrogen-terminated or oxidized). In these studies, the total electron yield as a function of the incident-electron energy and the energy distribution of the secondary emitted electrons are measured. The results show that both electrical conductivity and hydrogen-termination play essential roles in the secondary-electron emission process. For hydrogen-terminated samples, the energy distribution shows a large and narrow peak at the onset of electron emission. The long mean-free path of the secondary electrons and the low or negative electron affinity are essential to the exceedingly high electron yield of diamond.

A study of boron diffusion into diamond lattice was performed. Diffusion was made in hydrogen atmosphere at 30 torr. Two type IIa diamonds were heated at 1200 and 1400 °C for 20 hours and 5 minutes, respectively. Boron powder was used as a dopant source. The boron concentration profiles of both samples were measured by secondary ion mass spectrometry. Based on Fick's law, the diffusion coefficients were computed.