On the Effect of Monomer
Chemistry on Growth Mechanisms
of Nonfouling PEG-like Plasma Polymers
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Abstract
It has been shown that both ions and neutral species
may contribute
to plasma polymer growth. However, the relative contribution from
these mechanisms remains unclear. We present data elucidating the
importance of considering monomer structure with respect to which
the growth mechanism dominates for nonfouling PEG-like plasma polymers.
The deposition rate for saturated monomers is directly linked with
ion flux to the substrate. For unsaturated monomers, the neutral flux
also plays a role, particularly at low power. Increased fragmentation
of the monomer at high power reduces the ability of unsaturated monomers
to grow via neutral grafting. Chemical characterization by X-ray photoelectron
spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry
(ToF-SIMS) confirm the role that plasma phase fragmentation plays
in determining the deposition rate and surface chemistry of the deposited
film. The simple experimental method used here may also be used to
determine which mechanisms dominate plasma deposition for other monomers.
This knowledge may enable significant improvement in future reactor
design and process control