Liquid lubricants are delivered to sliding interfaces through a pump or by other kinds of oil delivery mechanisms, while solid lubricants have to be applied as thin films using physical vapor deposition (PVD) and/or chemical vapor deposition (CVD) methods. Due to their finite thickness, solid lubricant films wear out eventually and lose their effectiveness. They are also very sensitive to the test environments; in fact, some of them, like MoS2, will not lubricate or last long if oxygen and/or water molecules are present; indeed, graphite and boric acid will not function without humidity in the surrounding air [3]