Quantitative ToF SIMS analysis of spun-cast and solution-cast polymer films

Films of a series of monodisperse, moderately syndiotactic poly(methyl methacrylate) (PMMA) standards, with Mw ranging from 2,900–428,000, were solution-cast and spun-cast from chloroform onto clean aluminium substrates. The polymers were thoroughly characterized by conventional spectroscopic and chromatographic techniques. The films were studied using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (ToF SIMS). The effects of molecular weight and film thickness on SIMS spectra were investigated thoroughly by unit-mass and high-resolution ToF SIMS. Film thickness had a pronounced effect on the negative SIMS spectra, particularly in films a few monolayers thick. This was seen in both the total negative ion counts (m/z 31–200) and the key negative ion intensity ratios. A parallel effect was observed with respect to the effect of molecular weight. These differences are attributed to (i) the original end-group concentration in the surface which decreases with increasing molecular weight and (ii) the original end-group concentration in the surface which increases as film thickness decreases.