IDENTIFICATION OF SUBNANOMETER SURFACE-LAYERS ON POLYMER-FILMS BY SURFACE-ENHANCED INFRARED TRANSMISSION SPECTROSCOPY

Identification of subnanometre surface layers on polymer films, which are only analysable by x-ray photoelectron spectroscopy (XPS) or secondary ion mass spectrometry (SIMS), have been demonstrated by the use of transmission surface-enhanced infrared absorption (SEIRA) spectroscopy with the use of silver island films: 1.0 nm thick polydimethylsiloxane (PDMS) or 0.5 nm thick polymethylphenylsiloxane (PMPHS) surface layers, which are semisolid materials, on polyethyleneterephthalate (PET) films were successfully identifiable with the use of transmission SEIRA by measuring the PDMS or PMPHS that was transferred onto the silver-deposited BaF2 substrates under pressure. This approach completely eliminates strong spectral interference from PET films by measuring the transferred surface layer and greatly improves the signal-to-noise ratio of the surface layer absorption with the use of silver island films. The detection limit of PDMS surface layers on PET films is approximately 0.2 nm. The present method gives a considerable amount of information about surfaces, such as chemical composition and chemical structure. This is a highly promising method for analysing subnanometre surface layers which consist of liquid or semisolid materials, such as oil, lubricant, plasticizer and surface-active agent on polymer materials.