Mechanical diamond films

Figure 5.5. Electron micrographs of different types of diamond film grown on silicon. The white bar shows the scale in micrometres (p.m) (thousandths of a millimetre), (a) The initial stages of diamond growth on a nickel substrate, showing individual diamond crystallites nucleating in scratches and crevices created on the surface by mechanical abrasion, (b) a randomly oriented him,...

Polycondensation, 10 189-190, 191 as an aging mechanism, 23 64 of polyamide plastics, 19 781-782 polyester formation by, 20 390-391 silicone polymerization via, 22 556-558 in the sol-gel process, 23 61-62 Polycrystalline alloys, 13 523 Polycrystalline diamond films, deposition of, 24 744-745... 

A.H. Deutchman and R.J. Partyka (Beam Alloy Corporation observe, "Characterization and classification of thin diamond films depend both on advanced surface-analysis techniques capable of analyzing elemental composition and microstructure (morphology and crystallinity), and on measurement of macroscopic mechanical, electrical, optical and thermal properties. Because diamond films are very thin (I to 2 micrometers or less) and grain and crystal sizes are very small, scanning electron microscopy... 

CVD diamond films are not stable on mechanically stressed metals which contain iron, chromium, or nickel and hence steel. In this case films of boron nitride are an alternative. 

Catledge, S., and Vohra, Y., Effect of nitrogen addition on the microstructure and mechanical properties of diamond films grown using high-methane concentrations. /. App. Phys. 86 (1), 698-700 (1999). 

Figure 3.24 Possible mechanism for the growth of diamond film using methane as a precursor.

Formation of twin structures on the faces of diamond crystals and films have also been studied by Koidl s group in the early stage of diamond film research [84], So, we begin with reviewing their works, which is then followed by studies of other groups. To make heteroepitaxial diamond films, it is necessary to avoid the formation of twins, and thus the studies on the formation mechanism and morphology of twins are of great importance. 

Since HOD films have flat surfaces much smoother than ordinary polycrystalline diamond films, it is expected that HOD films will be used for electronic sensors and devices as well as micro electro-mechanical systems (MEMS) in the future. To this end, a selective deposition of (lOO)-oriented HOD films was undertaken using the two-step process on a 2-inch Si(lOO) wafer, and a 0.5-pm thick Si02 film was used for a masking film [295]. It was demonstrated that a micropattern of 6-pm thick HOD films was possible, and even a 8-pm wide channel was also formed. Selective deposition using polycrystalline films has been studied before [359], but this work demonstrated that a similar fabrication is possible using HOD films. 

Diamond has a low heat capacity, a low thermal expansion coefficient, and a high mechanical and thermal stability. These properties are very useful for devices using high dynamic thermal stress such as ink-jet heads. Indeed, ink-jet heads were fabricated using diamond films [17, 422]. Figure 13.8 shows a thermal actuator... 

Gielisse, P.J. (1998). Mechanical properties of diamond, diamond films, diamondlike carbon and like-diamond materials. In Handbook of Industrial Diamonds and Diamond Films (M.A. Prelas, G. Popovici, and L.K. Bigelow, eds). Marcel Dekker, Chapter 3, pp. 49—88. 

However, not only the choice but also the pretreatment of the substrate play an essential role for the nucleation rate and the quality of the diamond films obtained. Significantly better results are observed upon mechanically pretreating the surface. A polishing with diamond powder or with another abrasive, for instance, causes many scratches that then constitute preferred nucleation centers. Where diamond grinding powder is employed, the remnant tiny diamond fragments are assumed to serve to the same purpose. This effect can also intentionally be produced by depositing suitable centers of crystallization on the substrate. These include. 

Figure 6.21 Mechanism for the deposition of nanocrystalline diamond films.

Diamond has been well-known for long for its outstanding mechanical properties like great hardness and low frictional coeffident Therefore, it was self-suggesting to examine the respective characteristics of diamond films as well. Actually the results are found to vary depending on the morphology of the film and, for polycrystalline materials, on the particle size. 

Like in any material, the mechanical properties of diamond films have chemical reasons. The basic effect underlying friction is the making and breaking of... 

Measuring the tribological properties of diamond films turns out to be rather complicated for several reasons. For running such an experiment between two diamond objects, the tip or ball of the tribometer has to be coated with diamond too, which constitutes a technological challenge. Using softer tips instead may in some cases lead to a material transfer from the tip to the diamond surface under test, resulting in a modified surface with altered mechanical properties. The surface coarseness is also complicated to measure and hard to adjust Finally, problems in the diamond film s adhesion to the substrate constitute another parameter to be controlled. 

The characteristics of monocrystalline diamond films are much more clearly defined. Still polycrystalline films are employed in most cases as the high price interferes with large scale application of the monocrystalline material. Even for thin layers there is no significant change to the essential characteristics of diamond. For this reason as well as to save further material, it is a common practice to employ coated substrates with a film the thickness of micrometers spread on their surface (Section 6.6.1). The endurance of such films against mechanical stress is essentially influenced by two factors Firstly, by delamination (peeUng off) of the film from the substrate, and secondly by normal, gradual wear. 

Figure 6.45 Mechanism for the photochemical reaction of hydrogenated diamond films with co-vinyl species rendered suitable for further reaction by carrying terminal functional groups.

Owing to remarkable mechanical properties Hke great hardness, scratch resistance and a low frictional coefficient in combination with a high tolerance for aggressive environmental conditions, diamond-coated objects have been developed soon after the first preparation of diamond films. Today the respective products are employed in many technical apphcations. 

The combination of the diamond films beneficial mechanical properties with their biocompatibility (Section 6.6.3) renders them an ideal material for coating implants and prostheses. The wear of such parts is markedly decreased, and diamond hardly evokes rejection reactions of the surrounding tissue. 

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