Bernard F. Coll

Stability of carbon nanotubes under electric field studied by scanning electron microscopy

The influence of an applied electric field on carbon nanotubes protruding from a surface was investigated in situ using a high-resolution scanning electron microscopy. Under the applied electric field, the nanotubes flexed to orient themselves parallel to the electric field lines. For moderate field strengths below the electron field emission threshold, the flexed nanotubes relaxed back to their original shapes after the electric field was removed. However, when high electron field emission currents were extracted from the nanotubes, they were permanently deformed, leaving them aligned to the electric field direction after the electric field was removed. For high currents, the length of the carbon nanotubes were found to be shortened after field emission lasted for a period of time.

Surface modification of medical implants and surgical devices using TiN layers

Abstract The possibility of using titanium nitride as a wear-resistant coating for Ti6Al4V orthopaedic implants was investigated. TiN coatings were deposited with an arc technique under various cycle conditions to minimize the number of droplets incorporated during their formation. Pin-on-disc tests, scratch tests and metallurgical analyses were performed to characterize the more suitable TiN film in order to increase the hardness and the wear resistance in the articulating contact of the hip joints. With two different tribological systems, a pin-on-disc machine and a hip simulator, we have analysed and interpreted the wear mechanisms of the couples consisting of ultrahigh molecular weight polythylene against uncoated and TiN-coated Ti6Al4V prostheses. Wear test results indicated that the TiN film improves the surface hardness of Ti6Al4V implants. The polyethylene wear rate and the formation of TiO 2 abrasive particles are greatly reduced because of the low friction coefficient and good chemical stability of the TiN layer.

Design of vacuum arc-based sources

Vacuum arc sources can produce copious quantities of ions which can be used to engineer surfaces for tribological applications. The energetic and ionic character of arc-produced coating species can lead to unusually hard, dense, slippery and/or adherent coatings which can be applied successfully to both flat surfaces and complex shapes. Arc coating technology can take many forms with each having their own advantages and limitations. The purpose of the current review is to give the reader an overview of the wide range of options which are possible with vacuum arc technology while providing specific detailed examples to show how several of these option sets translate into actual source designs. Emphasis is given to more recent findings.

Properties of chromium nitride coatings deposited by cathodic arc evaporation

Abstract CrN coatings deposited at 200–230°C (low temperature) and 480–540°C (high temperature) onto high speed steel were investigated by determining the microhardness, surface roughness and adhesion, as well as using scanning electron microscopy and X-ray diffractometry. It was found that the coatings deposited at lower temperatures exhibit higher hardnesses than those produced at higher deposition temperatures. Both coatings exhibit good adhesion and a dense structure morphology. Bulk X-ray diffraction studies show that, in both cases, the prevalent crystallographic orientation is [220].

Towards a low-cost high-quality carbon-nanotube field-emission display

We have developed field-emission-display technology driven by chemical-vapor-deposition-grown carbon-nanotube emitters incorporated in a simple, low-cost device structure. Here, we report on frit-sealed test displays with a brightness of 3000 cd/m 2 at 3 kV and a lifetime of 9000 hours with only 45% degradation. We also demonstrate the scalability of the technology with a uniform high-brightness 6-in. QVGA that displays video images with a switching voltage of 40 V.

Amorphous diamond film by enhanced arc deposition

Abstract A new type of nonhydrogenated diamond-like carbon film defined as amorphous diamond (a-D) can be deposited from Enhanced Arc carbon source on various substrate materials such as Si, high speed steel (HSS) and WC at room temperature. The role of evaporation and condensation of highly ionized carbon plasma has been investigated in this study. Experimental results show that significant relationships exist between the energy distribution of the flux species, the particle surface interactions and the microstructure and mechanical properties of the a-D films. Films deposited in optimum conditions at growth rate of 6 μm h −1 exhibit high hardness and Youngs modulus, with peak values measured by the nanoindentation technique of around 95 GPa and 1150 GPa respectively, approaching those of natural diamond. Furthermore, the specific possibility of the modified arc technique compared with other physical vapor deposition processes leads to excellent adhesion on various substrates. Scratch test measurements reveal values of 50 N–80 N on HSS and WC substrates respectively.

Very high rate coating deposition with intense ion and/or electron bombardment

Abstract The principles of a new method of high rate coating deposition are presented which are based on a pulsed ion diode with explosive emission. The equipment is flexible and can work in three regimes: pulsed ion beams, pulsed electron beams, and the deposition of films and coatings. Coatings can be deposited with ion beam mixing (coating and/or substrate), and these can be post treated with intense pulsed electron beams which allows the properties to be extensively modified. Experimental results are presented on a variety of coatings deposited on the characteristics of the diode and on different substrate materials at different temperatures; specific examples include high temperature superconductors, TiN, TiB 2 and diamond-like carbon films.

Modelization of reaction kinetics of nitrogen and titanium during TiN arc deposition

Abstract Reactive arc deposition is a very complex non-linear process in which many parameters are involved. These parameters can be either dependent or independent variables. Consequently, it is difficult to control the process by experimental observations. Therefore, for a better understanding of reactive arc evaporation mechanisms and proper selection of appropriate plasma and deposition conditions, a simple model based on reaction kinetics and energy balance should be defined. According to this model it is possible to predict phenomena occurring at the cathode and influencing the reactive deposition at the substrate. For reactive arc deposition of TiN films, this model will deal with poisining and gettering effects of nitrogen and titanium respectively. It will emphasize their influence on the evaporation rate, deposition rate and subsequently emission and deposition of the microparticles. Experimental results and measurements on reactive arc deposition of TiN are reported and verified using the theoretical model.

Nano‐emissive display technology for large‐area HDTV

— Using nano-emissive display (NED) technology, Motorola labs has successfully developed 5-in. full-color display prototypes. Carbon-nanotube-based field-emission displays with a pixel size of 0.726 mm for a 42-in. HDTV exhibit video image quality comparable to CRT displays and demonstrate a luminance of 350 cd/m2. These novel low-drive-voltage NEDs take advantage of selective growth of CNTs to obtain the desired electron-emission performance while maintaining inexpensive manufacturing due to a simple self-focusing and self-regulating planar structure. Improved video image quality and color purity are achieved with very low power consumption and without the need for an expensive focusing grid.

63.2: High Brightness, High Voltage Color Field Emission Display Technology

We have designed nanotube-based field emission displays to operate above 6500 V. As a result, we have improved the white-screen luminance of HDTV resolution (0.726 mm pixel) field emission displays beyond 700 cd/m2. We have maintained good color purity without employing separate focusing electrodes. In addition, we demonstrate spacers operating beyond 10,000 volts on the anode without any charging that would distort the image.