I. U. Hassan

Friction force microscopy study of diamond films modified by a glow discharge treatment

Abstract A glow discharge treatment technique has been developed which enables control of the surface roughness and morphology of diamond films for applications in optical and electrical components. A conventional hot filament chemical vapour deposition (CVD) system was used to deposit the diamond films onto silicon substrates via a three-step sequential process: (i) deposition under normal conditions; (ii) exposure to either a pure hydrogen plasma or 3% methane in an excess of hydrogen using DC-bias; and (iii) diamond deposition for a further 2 h under standard conditions. The frictional characteristics and roughness of the film surfaces were investigated by atomic force microscopy (AFM) and the morphology and the growth rates determined from scanning electron microscope images. Lateral force microscopy (LFM) has revealed significant differences in frictional behaviour between the high quality diamond films and those modified by a glow discharge treatment. Friction forces on the diamond films were very low, with coefficients ∼0.01 against silicon nitride probe tips in air. However, friction forces and coefficients were significantly greater on the DC-biased films indicating the presence of a mechanically weaker material such as an amorphous carbon layer. A combination of growth rate and frictional data indicated that the exposure to the H 2 plasma etched the diamond surface whereas exposure to CH 4 /H 2 plasma resulted in film growth. Re-Nucleation of diamond was possible (stage iii) after exposure to either plasma treatment. The resultant friction forces on these films were as low as on the standard diamond film.

The impact of inert gases on the structure, properties and growth of nanocrystalline diamond

For biomedical and electronic applications, it is highly desirable to deposit smooth diamond films with crystal sizes in the nanoscale range. We present experimental results of chemical vapour deposition diamond growth from CH4 with incremental substitution of H2 with He or Ar gases; the concentrations of the inert gases were varied between 0 and 98 vol%. Results show that initially the addition of either argon or helium increases the growth rate and significantly alters the film structure and crystallinity up to 60 vol%. With additions of argon or helium greater than 60 vol% in the gas phase the growth decreases and there is degradation of the crystal structure. In general, nanocrystalline diamond has been deposited at dilutions in excess of 90 vol% helium or argon.

Role of surface pre-treatment in the CVD of diamond films on copper

Abstract Diamond films have been deposited on copper substrates using hot-filament chemical vapour deposition (HFCVD). In order to improve the nucleation density, several methods of surface pre-treatment and substrate biasing have been investigated. These included polishing the substrates using a number of diamond powders and diamond pastes followed by ultrasonic cleaning. We show that the nucleation density on copper is highly dependent on the particle size in the polishing materials and on the polishing duration. Negative d.c.-biasing enhances more effectively the diamond nucleation on copper than the abrasion process. This method is also much more controllable, reliable and reproducible. High quality diamond films on copper have been produced via HFCVD using a precursor gas mixture of 1% methane in hydrogen. The as-deposited diamond films were characterised for film morphology, crystallinity, film quality and phase purity by scanning electron microscopy (SEM) and Raman spectroscopy. Raman spectroscopy analysis revealed an intense diamond peak at around 1332 cm −1 and nearly no graphite band. Diamond crystals of predominantly 〈111〉 orientation were evident from SEM analysis. Both the diamond phase purity and the nucleation density were enhanced in films deposited by the bias-enhanced nucleation (BEN) method as compared to the diamond deposited on abraded copper substrates.

Chemical vapour deposition of microdrill cutting edges for micro- and nanotechnology applications

Conventional cemented tungsten carbide-cobalt (WC-Co) microdrills generally have a low cutting efficiency and short lifetime mainly because they operate at very high cutting speeds. Since it is relatively expensive to make microtools it is highly desirable to improve their lifetime and in-service performance. Microtools used to make microelectronic and mechanical systems (M.E.M.S) devices with sharp cutting edges, such as milling or drilling tools need protective coating in order to extend life and improve performance. One method of achieving this objective is to use a suitable surface engineering technology to deposit a hard wear resistant coating, such as diamond. Diamond has excellent mechanical properties, such as ultra-high hardness and a low friction coefficient. One of the most promising surface treatment technologies for depositing diamond onto complex shaped components is chemical vapour deposition (CVD). However, CVD of diamond coatings onto the cemented WC-Co tool has proved to be problematic. Binder materials such as cobalt can suppress diamond nucleation resulting in poor adhesion between the coating and substrate. In this paper the effects of pre-treated substrate material on the coating structure are reported. The morphology and the crystallinity of the as-grown films was characterised by using scanning electron microscopy (SEM). Raman spectroscopy was used to assess the carbon-phase purity and give an indication of the stress levels in the as-grown polycrystalline diamond films. The diamond coated tools have potential applications in micro- and nanomachining of micro- and nano-sized components used in M.E.MS.

An investigation of the structural properties of diamond films deposited by pulsed bias enhanced hot filament CVD

Abstract The control of the surface roughness and morphology of diamond films is of critical importance for many applications such as for optical and electronic components. In order to produce uniform CVD diamond films with a controlled surface morphology over large areas, bias enhanced methods of nucleation offer better reproducibility than substrate pre-treatment methods such as mechanical abrasion. Hot filament chemical vapour deposition (HFCVD) with bias enhanced nucleation (BEN) has been used to increase the nucleation density of diamond films on Si{100} substrates. Optimal conditions of the nucleation step for subsequent growth of good quality diamond were a substrate temperature of 1100 K; methane/hydrogen ratio of 3%; pressure of 20 Torr; filament temperature of ∼2500 K; d.c. bias of −250 V and time of 30 min. We also demonstrate that re-nucleation of diamond is possible using short intervals of substrate biasing during normal diamond growth. The film morphology and surface roughness critically depend on the length of the bias cycle and may be controlled without reducing the diamond quality. The morphology and quality of the standard negatively biased and pulsed biased films were characterised by scanning electron microscopy and Raman spectroscopy. Atomic force microscopy was used to measure the surface roughness of the films.

Pulsed biased growth of nanocrystalline diamond by hot filament chemical vapour deposition

Abstract For many industrial applications such as biomedical instruments, optical devices and microelectromechanical systems, the control of the film structure, crystallinity and morphology is of critical importance. The crystallite size, orientation and surface roughness have a profound effect on the mechanical, optical and electrical properties of the films and therefore the final product performance. In order to reduce the crystallite size and surface roughness, inert gases were added to the methane and hydrogen mixture during chemical vapour deposition of nanocrystalline diamond films. In addition, the results on the influence of pulsed biasing on the morphology of these films are reported. Bias voltages in the range –300-0 V were investigated. Increasing the bias voltage significantly alters the crystallite size and morphology of the deposited films. Raman spectroscopy, SEM and atomic force microscopy were used to characterise the nanocrystalline diamond films. SE/501

Nanocrystalline Diamond: Deposition Routes and Clinical Applications

Diamond is one of the most advanced and most useful engineering materials in use today. The properties of synthetic diamond are very similar to that of single crystal diamond and it is well established that diamond has unique combinations of excellent physical, optical, chemical and biomedical properties. Typically, each application area for diamond requires the optimum properties of the material. The optimisation of diamond properties can only be achieved by operating on the microstructure, since it is almost impossible to alter diamond’s molecular structure or its chemical composition. This chapter discusses the use of nanocrystalline diamond for clinical applications.

Diamond Surgical Tools

Deposition technology has played a major part in the creation of today’s scientific devices. Computers, electronic equipment, biomedical implants, cutting tools, optical components, and automotive parts are all based on material structures created by thin film deposition processes. There are many coating processes ranging from the traditional electroplating to the more advanced laser or ion-assisted deposition. However, the choice of deposition technology depends upon many factors including substrates properties, component dimensions and geometry, production requirements, and the exact coating specification needed for the application of interest. For complex geometry components, small feature sizes, good reproducibility, and high product throughput, chemical vapor deposition (CVD) is a highly effective technology. For example, low pressure and plasma-assisted CVD is a well-established technology for semiconductor devices, which has very small feature sizes and complex geometrical arrangements on the surface.

Dental Tool Technology

Dental technology is a discipline of dentistry concerned with the custom manufacture of dental devices to meet the prescription of a dentist. From the earliest times missing teeth have been replaced with dentures or crowns made from a wide variety of materials including gold, human or animal teeth, bone and tusks and wood. Natural teeth were used for dentures, collected from battlefields, hospitals or by grave diggers, these were mounted in carved dentures of walrus or hippopotamus ivory or on gold. By the late eightieth century dentures fused porcelain teeth were introduced, dentures could be carved from blocks of ivory or carved fixed to a gold plate by gold pins. In the mid-ninetieth century the first artificial denture base materials were introduced, vulcanite (or hard rubber) and celluloid, superseded in the 1940s with the introduction of polymethyl methacrylate. During the twentieth century base a wide range of new materials and techniques have been introduced to dentistry, including precision lost wax casting for dental alloys, a wide range of precious metal and base metal alloys and dental ceramics. This chapter focuses on advances in dental tool technology.

Surface Engineering of Dental Tools with Diamond for Improved Life and Performance

This chapter discusses use of diamond with dental tools for improving the life and performance of these tools. The teeth reside in a harsh environment and get worn and damaged through prolonged use. In order to repair damage, add fillings, and implants, a wide range of dental burs are employed by dentists and dental technicians. This chapter discusses about these tools and the techniques that can be used to improve their life and performance. The chapter also discusses chemical vapor deposition of diamond films onto dental burs. This chapter examines hot filament CVD (HFCVD) process for diamond deposition onto the burs. The effects of process parameters on the properties of diamond films and performance of diamond coated and untreated dental burs, such as wear and lifetime, is investigated. In the studies conducted, the uncoated WC-Co burs displayed flank wear along the cutting edge of the bur. The areas of flank wear were investigated at the cutting edge of the dental bur. The investigations demonstrated that HFCVD coated burs give superior performance and reduced wear compared to uncoated and conventional burs. © 2012 Elsevier Inc. All rights reserved.