Neil A Fox

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.

Field emission from diamond-coated multiwalled carbon nanotube 'teepee' structures

Dense arrays of vertically aligned multiwalled carbon nanotubes (MWCNTs) have been seeded with a nanodiamond suspension in methanol using electrospray deposition. This treatment caused the tips of groups of 20–40 MWCNTs to stick together forming structures resembling “teepees.” Subsequent short chemical vapour deposition experiments using standard diamond-growing conditions allowed the nanodiamond seeds to grow into a thin continuous film, locking the teepee structures into this shape. Field emission tests show that these diamond-coated carbon nanotubes (CNTs) teepees retain the low threshold voltage of the uncoated CNTs but with greatly improved emission stability and lifetime.

Patterned diamond particle films

This article reports on a technique for patterning diamond nanogrit which utilizes commercial ink-jet printer technology. Diamond nanogrit as small as 50 nm has been successfully printed onto substrates of glass, silicon, copper, and fused quartz. The technique has been used to demonstrate a quick and simple means to seed patterned. nanocrystalline diamond films onto candidate substrates of potentially any conceivable size or shape.

Through-mask anodization of titania dot-?and pillar-like nanostructures on bulk Ti substrates using a nanoporous anodic alumina mask

Nanosized surface topography on an implant material has the capability of stimulating the acceptance of the material in its host surrounding. Fine-tuning of nanotopography feature size has been shown to trigger differentiation of mesenchymal stem cells into bone cells in vitro. For this purpose we have created well defined nanosized titania dot- and pillar-like structures on mechanically polished Ti substrates using a through-mask anodization technique with an anodic porous alumina template. The anodization technique allowed the titania structure dimensions to be precisely tuned in the range 15-140 nm in a single electrolyte system. The fabricated surfaces serve as good model surfaces for precise studies of in vitro cell behaviour. The through-mask anodization technique was used directly on bulk Ti surfaces, thus demonstrating a potential application for patterning of actual Ti implant surfaces.

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.

Electrochemical Properties of Two Dimensional Assemblies of Insulating Diamond Particles

The electrochemical properties of two-dimensional assemblies of 500 nm type Ib diamond particles are investigated as a function of their surface oxidation state. High Pressure High Temperature particles are sequentially exposed to a hot strong acid bath and to H(2) plasma in order to generate oxygen (ODP) and hydrogen surface terminations (HDP). Changes in the surface composition following the chemical treatments are confirmed by FTIR. Electrophoretic mobility measurements show that the diamond particles exhibit a negative surface charge at pH above 7 independently of the surface termination. Oxidation in the acid bath and subsequent reduction in the H(2) plasma only affects about 30% of the particle surface charge. The intrinsic negative charge allows the formation of 2D assemblies by electrostatic adsorption on poly(diallyldimethylammonium chloride) (PDADMAC) modified In-doped SnO(2) electrodes (ITO). The particle number density in the assembly was controlled by the adsorption time up to a maximum coverage of ca. 40%. Cyclic voltammetry in the absence of redox species in solution show that the acid treatment effectively removes responses associated with sp(2) carbon impurities, resulting in a potential independent capacitive signal. On the other hand, HDP assemblies are characterized by a charging process at a potential above 0.1 V vs Ag/AgCl. These responses are associated with hole-injection into the valence band edge which is shifted to approximately -4.75 eV vs vacuum upon hydrogenation. Information concerning the position of the valence band edge as well as hole number density at the HDP surface as a function of the applied potential are extracted from the electrochemical analysis.

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.