Diamonds have a very powerful image with both the public and the scientific community, because of their beauty and the historic difficulty in first synthesising it. Diamond-like carbon (DLC) is much less famous, but it has a similar importance in economic terms. DLC coatings are used on razor blades, in magnetic hard-disk drives, on bar-code scanners, on PET bottles, and on some car parts. But how did we develop the underlying technology? This book gives the detailed scientific and technological answer to this question. The historical overview describes how DLC has a much shorter history than diamond itself, from the 1970s with Aisenberg and Chabot and then Holland using plasma deposition to first grow hard, amorphous carbon films. A great deal of early work was carried out by the group of Koidl in the 1980s. Meanwhile, Russian groups invented the cathodic arc and used it on carbon, and this allowed growth of a second type of hydrogen-free DLC. This material came to be known as tetrahedral amorphous carbon, which is abbreviated as ta-C or TAC, or various similar ways. This range of growth techniques allowed us to understand the range of DLCs, as I summarise in Chapter 1. The thin film growth techniques are of critical importance, because DLC is only possible as a thin film material, not as a bulk glassy solid. However, historically, proving that someone had and had not grown diamond synthetically was at least as important as the growth itself. The same applies to DLC. A specific range of characterisation techniques are employed to measure the properties and bonding of DLC, as is described in Chapter 2. Diamond is known to possess the most extreme properties of any real three dimensional solid, such as highest atomic density, highest hardness, highest Young’s modulus, highest room temperature thermal conductivity, etc. But diamond is inconvenient as a coating material, because its growth temperature is high. DLC has the huge advantage over diamond of having room temperature, rather low cost, large-area vacuum deposition methods. DLC is also amorphous which allows it to be the smoothest material known. These advantages are what gives DLC its wide range of applications noted above. DLC does however have two drawbacks; one is that its thin films tend to have a large compressive stress, and the second that it is not mechanically tough. Nevertheless the amorphous character of DLC means that it can be alloyed with metals and other elements like silicon which goes some way to solving these problems. These issues are described in Chapters 4 and 12. The main applications of DLC are as a mechanical and protective coating. This is the focus of most chapters of the book, mainly in Chapter 3 and Sections B and C. Some years ago, there were many studies of DLC trying to develop the electronic properties of DLC, as field emission or doping, but these turned out to be unsuccessful or uncompetitive with other materials. Thus the focus of DLC research now continues in the area of mechanical properties. The applications in magnetic hard-disk drives and on razors have existed for 10–25 years. The applications as coatings on tool tips and on car components are more recent, and have followed more recent advances in our understanding of tribology, thin film adhesion, and alloying. These topics are less easily found in the journal literature. This book for the first time brings together all these areas in a convenient form. This book will thereby provide an extremely useful reference for the economic developments in these areas. Engineering Department, John Robertson
Posted on: Mon, 24 Mar 2014 17:59:32 +0000
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