No abstract

How different plasma species influence the reactions and reactivity of each other during plasma processing is not fully understood, especially with respect to surface interactions. The goal of this study is to provide insight into the relationships between gas-phase NHx species in NH3 plasmas. Specifically, formation of NHx, their relationship with the surface during plasma processing, and the effects of charged species on these interactions are discussed. The surface reactivities of NH and NH2 radicals with different substrate materials during NH3 plasma processing were investigated using the imaging of radicals interacting with surfaces technique. Scatter coefficients, S, for NHx species were obtained as a function of applied rf power for polyimide, polytetrafluoroethylene, and platinum substrates. To investigate the role of ions on the formation of NHx radicals in the gas phase and at the surface, ions were removed (>98%) from the plasma molecular beam. Results from the “ion-free” conditions suggest that ions enhance NH2 surface generation, but suppress NH-forming mechanisms at high rf powers. Surface interaction results for NH and NH2 with and without ions provide the basis for a discussion of possible surface interaction mechanisms for the different substrates examined.

A variety of plasma treatments have been employed to achieve permanent hydrophilic surfaces throughout the membrane structure. Specifically, we have modified microporous polyethersulfone (PES) membranes using H 2 O, CO 2 , and N 2 plasma treatments to implant polar functional groups; alternatively, Ar-plasma treatment followed by grafting of hydrophilic monomers (acrylic acid and acrylamide) in the vapor phase has also been successful at modifying PES membranes. PES membranes treated with H 2 O and CO 2 plasmas as well as the grafted membranes are found to be permanently hydrophilic (for a minimum of six months), and the entire membrane cross-section is modified. Chemical changes to the modified PES membranes were determined with FTIR and XPS measurements. Furthermore, water bubble point measurements and electron microscopy results reveal that pore sizes of the modified membranes are only slightly affected, depending on the treatment. Incorporation of polar functionalities results in an increase in the glass transition temperature (T g ) and a moderate change in tensile strength of the modified membranes. Most importantly, the surfaces of the modified membrane are less susceptible to absorption by bovine serum albumin (BSA) proteins.