A @F02366@ thinner than about \(\frac{1}{4}\) @W06659@ of @VT07496@ light. Black films are often @E02181@, but equilibrium films may be considerably thicker under some conditions. In @S05721@ films, two types of @E02181@ are often observed: the one characterized by thickness of the order of \(7\ \text{nm}\) or more which varies significantly with minor changes in composition such as @I03180@ is called common black film.