Carbon as an element constitutes the building block of some of the hardest materials (such as diamond, boron carbide and transition metal carbides) known to date. It is also a key ingredient of amorphous diamondlike carbon (DLC) and carbon nitride coatings, which offer exceptional friction and wear properties to sliding, rolling or rotating surfaces [1, 2, 3, 4, 5]. Besides diamond and DLC, other carbon-based tribo-materials (such as graphite, graphite fluoride, glassy carbon, polymer, metal or ceramic-matrix composites, and carbon-carbon or carbon-graphite composites) have also been used to combat friction and wear for quite some time [6, 7, 8, 9, 10, 11, 12]. In particular, graphite, graphite fluoride and glassy carbons are effective in reducing sliding friction and wear of machine elements and, hence, are used extensively by industry as solid lubricants [4, 5, 6, 7, 8]. Carbon-based composites are also an important class of tribo-materials, providing some of the lowest friction coefficients and high resistance to heat [11]. The low-friction carbon composites are primarily used as seal materials by the rotating equipment industry, while the high-friction carbon-carbon composites are used to make high-performance brakes for racing cars and various aircraft [13]. Figure 1 shows some of the well-known carbon nanostructures and their applications in microtribological fields.

For the past three decades or so, numerous scientists have explored carbon as a precursor for the synthesis of superhard coatings like diamond, carbonitride and DLC (see [1] for a thorough review). In particular, diamond and DLC coatings have become extremely popular, mainly because of their exceptional mechanical, thermal, electrical and tribological properties. These films are now routinely produced by a wide range of chemical and physical vapor deposition methods and are used for numerous industrial applications, ranging from razor blades to artificial biomedical implants (such as hip and knee joints) [1, 14, 15].