Time-resolved investigation of the surface chemical modification of poly(ethylene naphthalate) by nitrogen plasma treatment

A low rf nitrogen plasma source was used to treat poly (ethylene-2, 6-naphthalate) web material. Nitrogen uptake, the N Is centroid, the N 1 s peak width, rearrangement of the ester (from the 0 1 s spectrum), and oxygen level were measured using x-ray photoelectron spectroscopy as a function of treatment time at several treatment conditions. The observed changes in surface chemistry with treatment time are roughly consistent with a dose response having a linear regime at low doses and a saturation regime at high doses (where dose is power/width/web speed). Hence. to a first approximation, the flux densities (to the web) of relevant species scale with power. As the dose increases, the distribution of nitrogen groups formed broadens and shifts toward higher N I s binding energy, suggesting that a larger fraction of the nitrogen-containing species are amines at low doses and amides at higher doses. The breadth of the distribution of nitrogen-containing species appears to be strongly correlated with the amount of nitrogen incorporated in the PEN surface. A surface sites model was applied to the measured nitrogen uptake as a function of treatment time. Phenomenological nitrogen incorporation and loss terms were determined in the context of this model. Both terms increase with treatment power and treatment pressure. The ratio, however, varies to a much smaller degree as a function of process conditions, with high powers and pressures giving the highest ratio. Further elucidation of the incorporation and loss processes should be possible with plasma diagnostic data related to species concentrations. (C) 2003 American Vacuum Society.