Amorphous diamond may be viewed to be sintered subnano diamond grains. In the following descriptions, amorphous diamond is portrayed as a micron thin coating material. However, in many cases, thicker coatings made by nanodiamond impregnated metal matrix may also substitute amorphous diamond coating to achieve similar applications, such as for field emitters, or even as solar cells. The mainstream solar cells are made of crystalline silicon. Although the cost for generating one KwH is 5–10 times of conventional fuel fossil power plants, crystalline silicon solar cells are thought to be environmentally friendly. However, crystalline silicon is typically produced from highly pure quartz that may be extracted from beach sand. Amorphous diamond appears to be contradictory term, like liquid crystal or glassy metal. Amorphous means non-crystalline and diamond implies crystalline. However, this terminology is meaningful because unlike silicon that forms only sp3bonds, i.e. diamond structure, carbon may form either sp2 or sp3 bond.