W. N. Wang

Field emission conduction mechanisms in chemical vapor deposited diamond and diamondlike carbon films

Field emission properties of undoped chemical vapor deposited diamond and diamondlike carbon films have been measured for a variety of different deposition conditions. The nature and appearance of the damage site after testing, together with the mathematical form of the observed current–voltage relations, are correlated with the conductivity of the film. This is consistent with a model for the overall current which is a combination of conduction mechanisms through the bulk of the film with Fowler–Nordheim tunneling.

Field emission from chemical vapor deposited diamond and diamond-like carbon films: Investigations of surface damage and conduction mechanisms

Field emission properties of undoped chemical vapor deposited diamond and diamond-like carbon films have been measured for a variety of different deposition conditions. The nature and appearance of the damage site after testing has been investigated with scanning electron microscopy and laser Raman mapping. These observations, together with the mathematical form of the observed current–voltage relations, are correlated with the conductivity of the film. The results are consistent with a model for the overall emission current that combines conduction mechanisms through the bulk of the film with Fowler–Nordheim tunneling.

Field emission properties of diamond films of different qualities

Field emission properties of diamond films were studied by macroscopic I–V measurement. A lower turn-on field and a higher emission current were observed for diamond films produced by higher methane concentration, or with higher density of defects, introduced by ion implantation. However, diamond films of poorer quality experience a severe reliability problem. Cold implantation followed by rapid thermal or laser annealing produced diamond emitters with a turn-on field as low as 5 V/μm and the desired reliability.

THE EFFECT OF DIAMOND SURFACE TERMINATION SPECIES UPON FIELD EMISSION PROPERTIES

Abstract Undoped CVD diamond films on Si substrates have been chemically treated in order to change the surface termination species. Treatments used include hydrodrogenation, deuteration, oxidation, hydrolysis, amination, chlorination, fluorination, and metallisation, using Na, K and Cs layers. The effect of these treatments upon field emission characteristics has been measured. In general, it is found that emission currents increase and threshold voltages decrease as the electronegativity of the surface species decreases. The best field emission properties were observed for the films with metal layers, with threshold voltages of ∼15 V/μm.

Mapping crystalline quality in diamond films by micro-Raman spectroscopy

Abstract It is known that different growth sectors within diamond films grown by chemical vapor deposition can contain different concentrations of defects. The defects in the diamond can be in the form of inclusions of non-diamond carbon. The quality of the diamond can be observed by the change in the ratios of diamond and non-diamond components in the Raman spectrum and in the widths of the Diamond Raman Line. In (001) textured growth, the (001) sectors are observed to be made up of good quality diamond, whereas the neighboring (111) growth sectors have high concentrations of defects and inclusions. Because of the transparency of diamond, it is possible to map the Raman signal with a confocal microscope to depths of hundreds of microns. In this way, it has been possible to show that the regions of relatively defect-free diamond lie within inverted pyramids. The bases of these pyramids correspond to the observed square (001) facets, whereas the sides of the pyramid correspond to (111) planes. This feature of textured diamond films has been observed by transmission electron microscopy of cross-sections of such films, but this is the first time that it has been shown in-situ. The “Blue-Cross” of defect related luminescence [N.C. Burton, J.E. Butler, A.R. Lang, J.W. Steeds, Proc. R. Soc. Lond. A 449 (1995) 555–566] is observed by PL and correlates well with a mapping of the FWHM. The result demonstrates the ability of confocal micro-Raman spectroscopy to map the crystalline quality in diamond films on a micron scale. It is demonstrated for the first time that the pattern of defect densities previously observed by TEM can be observed in particular growth features of diamond films by confocal Raman spectroscopy.

Negative electron affinity observed in boron‐doped p‐type diamond films by scanning field emission spectroscopy

Field emission properties of boron‐doped diamond films were studied by combined scanning tunneling microscopy/spectroscopy and scanning field emission spectroscopy. A detailed spatial correlation between field emission sites and diamond morphology, surface work function, and diamond quality can be established by this technique. A possible indication of negative electron affinity of the (111) faces near the (111)/(111) and (111)/(100) grain boundaries and high defect sites of boron doped p‐type diamond films were observed by field emission I–V (current–voltage) measurement.

Field-emission studies of boron-doped CVD diamond films following surface treatments

Abstract The electron emission from highly twinned, undoped Chemical Vapour Deposited (CVD) diamond thin films has been found to exhibit a stable voltage threshold of 15 V μ −1 . In this study the same material has been boron-doped by ion-implantation at two different energy profiles. A number of surface treatments including, Excimer laser annealing, hydrogen passivation, argon/oxygen plasma etching and also coating with gold, were employed in an attempt to enhance the electron emission properties of the highly twinned surface. It has been found that these treatments tend to degrade the electron emission performance, promoting more surface damage and instability in the electron emission current. These results are compared against the emission performance of samples of high quality boron-doped material exhibiting both similar and dissimilar surface textures.

Production and characterisation of amorphic diamond films produced by pulsed laser ablation of graphite

Abstract Amorphic diamond (a-D) films have been grown by pulsed laser deposition using an ArF excimer laser to ablate material from a dense, ultrapure graphite rod. Deposition rates have been investigated as a function of incident pulse energy and of time. The resulting films have been analysed by scanning electron microscopy (SEM) and by laser Raman spectroscopy, and their electron emission characteristics tested. We confirm the potential of a-D films for use as a cold cathode material.

Field emission properties of diode devices based on amorphic diamond-Si heterojunctions

Microscopic and macroscopic field emission properties of amorphic diamond films on n- and p-type silicon substrates were studied by combined scanning tunneling microscopy/spectroscopy and integral field emission I–V measurements. Microscopic scanning tunneling spectroscopy showed that amorphic diamond films on n-Si have lower threshold voltage and higher emission current than amorphic diamond films on p-Si. The observed rectification characteristics suggest that amorphic diamond on n-Si is an ideal forward-biased p-n junction cold cathode emitter; however, there is no significant difference between these two structures by integral field emission I–V measurements. Conversion of the smooth amorphic diamond film into porous sp3/sp2 composites with sharp features under electric fields higher than 50 V/μm, followed by preferred electron emission from the porous composite sites of high transconductance, was believed to be the cause.

Growth and field emission properties of multiply twinned diamond films with quintuplet wedges

A unique microwave plasma chemical vapor deposition (MPCVD) technique was employed to produce multiply twinned diamond films with quintuplet wedges. Biased nucleation, nonbiased growth, and high methane/hydrogen ratio (≳5%) were used to prepare the multiply twinned diamond films. The growth parameter α was carefully controlled to be close but larger than 3/2 to allow the multiply twinned particles with quintuplets to outgrow the parent face to form the secondary crystals with uniformly distributed particle sizes and smooth surface. Since there is no need to suppress the natural growth of twins in vapor‐grown diamond, higher growth rate was achieved. Excellent field emission properties of such films compared to the normal MPCVD diamond films were also obtained.