Pyrolysis and laser ablation of plasma-polymerized fluorocarbon films: Effects of gold particles

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Abstract
Plasma‐polymerized fluorocarbon (PPFC) films were analyzed by thermogravimetric analysis (TGA), direct pyrolysis/mass spectrometry, and laser‐ablation/electron‐impact mass spectrometry. Fourier transform mass spectrometry was used to detect products. The films were made by plasma polymerizing tetrafluoroethylene in an argon plasma. Two types of films were studied: with and without fine gold particles incorporated in the PPFC films. TGA showed that gold‐containing films decompose more rapidly and at lower temperature with increasing gold content. Pyrolysis products were determined as a function of temperature. The predominant positive product ions, using 20 eV electron‐impact ionization, were C2F4+, CF3+ and a distribution of higher‐mass unsaturated fluorocarbon species, CnFm+, up to at least n=14 and m≥n+1. The predominant negative ions, formed by electron attachment, were also unsaturated fluorocarbon ions which extended up to 1145 u in mass. These species are different from those observed from polytetrafluoroethylene pyrolysis. No dependence of the positive‐ion mass spectral distributions of pyrolysis products on gold content of the films was observed. However, the negative‐ion pyrograms had a dramatically different temperature dependence for films with and without gold. The results imply that the gold‐containing films have regions of lower molecular weight, and a possible formation mechanism is suggested. Laser ablation formed low‐mass neutral fluorocarbon species. Ablation of the gold‐containing film under direct laser ionization conditions (higher laser power), produced a spectrum resembling the pyrolysis spectrum, suggesting that the gold particles affect the mechanism of the ablation.