Plasma-polymerized hexamethyldisiloxane films characterized by variable-energy positron lifetime spectroscopy

✍ Scribed by C. L. Wang; Y. Kobayashi; H. Togashi; K. Kato; T. Hirotsu; K. Hirata; R. Suzuki; T. Ohdaira; T. Mikado

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 159 KB
• Volume: 74
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19991205)74:10<2522::aid-app21>3.0.co;2-h

✦ Synopsis

Nanometer-size holes in plasma-polymerized thin films were characterized by variable-energy positron lifetime spectroscopy for the first time. Hexamethyldisiloxane (HMDSiO) was plasma-polymerized at different discharge powers (30 -105 W) and monomer pressures (1.0 -4.9 Pa). The positron lifetime spectra of deposited films were collected at positron energies of 1 and 5 keV. All films showed a well-defined long-lived component due to pick-off annihilation of ortho-positronium (o-Ps). The o-Ps lifetime 3 , reflecting the average size of free-volume holes in the film, increased with an increasing ratio of plasma discharge power, W, and monomer flow rate, F. Based on the empirical relationship between the o-Ps lifetime and the cavity radius, hole volumes were estimated to be 0.19 -0.36 nm 3 . We also found that the o-Ps intensity, I 3 , depends strongly on the same parameter, W/F. Comparison with infrared (IR) absorption spectroscopy data showed that Ps formation is suppressed in films with fewer organic bonds and higher disorder, i.e., those increasingly inorganic in nature.