A general experimental procedure for SEIRAS involves the formation of a metal layer, typically 100-200 nm of Au or Ag, on a polished ATR substrate through electrochemical deposition (86, 87), metal vapor deposition in vacuum , or electroless (chemical) deposition . The latter technique yields more stable metal films and larger islands on the surface. The enhancement factor depends on the thickness of the film, as thicker films exhibit increased IR reflectivity.