Bonnie J. Tyler

Topography in secondary ion mass spectroscopy images

Interpretation of time-of-flight secondary ion mass spectroscopy (TOF-SIMS) images from rough samples such as particles, fibers, or biological specimens can be problematic because the images are influenced not only by the sample chemistry but also by topographical features. In this article we have investigated the influence of spherical and cylindrical features on total ion yields, relative ion yields, and feature shape. TOF-SIMS images of Pluronic coated fibers and polystyrene spheres were collected using both triple focusing time and reflectron geometry instruments and a 25keV Ga+ primary ion source. The fibers and spheres were analyzed on both conducting and insulating substrates to assess the importance of field effects. Trends in the images have been explored using principal components analysis and Poisson and multinomial mixture models. The T2 test was employed to assess the statistical significance of results. The results identify three important topographic effects. The size and shape of features ...

Analysis of biomedical polymer surfaces: polyurethanes and plasma-deposited thin films

The surface characterization of biomaterials is important for understanding the biological reactivity of surfaces and for monitoring surface reproducibility and contamination. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), contact-angle methods, vibrational spectroscopic methods, and scanning probe microscopies are briefly reviewed. Examples are presented using these methods to characterize RF plasma-deposited surfaces based upon acetone and oxygen for cell culture and Biomer¿ surfaces.

Determining depth profiles from angle dependent x‐ray photoelectron spectroscopy: The effects of analyzer lens aperture size and geometry

Lens apertures that reduce the solid angle of photoelectrons directed to the detector can be used to better resolve the variations in x‐ray photoelectron spectroscopy (XPS) signals which occur with electron takeoff angle. The effects of aperture size and geometry on angle‐dependent XPS data, and on the depth profiles calculated from the data, have been investigated. Both theoretical calculations and angle‐dependent XPS experiments have been used in this study to determine the effects of apertures. Circular and slit geometry apertures varying in size from a 6° solid collection angle to a 30° solid collection angle were studied. Samples consisting of a substrate covered by a thin, uniform overlayer were examined. At low photoelectron takeoff angles, the differences between the apertures were insignificant. At high photoelectron takeoff angles, decreasing the size of the aperture improved surface sensitivity. Decreasing the width of the aperture also sharpened the transitions between layers in a generated de...

Chemical Alteration of Biomer™ as a Result of Oxidative Degradation

We have studied the chemistry and oxidative degradation of two lots (BSP067 and BSUA001) of Biomer™, a widely used commercial poly(ether urethane) (PEU). Although transmission infrared adsorption studies revealed no differences in the bulk chemistry of the two lots, the surface chemistry, as seen by XPS and SIMS, was different. Lot BSP067 showed soft segment enrichment at the surface, which is typical of PEU. Lot BSUA001 showed no evidence of either hard or soft segment PEU components at the surface. The surface of this lot was completely covered with a non-extractable additive, identified as poly- (diisopropylaminoethyl methacrylate). To assess the susceptibility of Biomer™ to oxidative degradation, samples of each lot were exposed to concentrated hydrogen peroxide for 24 hours. The extent of degradation was assessed by using high pressure gel permeation chromatography (HPGPC), XPS and SIMS. The molecular weight of lot BSP067 increased after reaction with hydrogen peroxide but the molecular weight of lot BSUA001 decreased after reaction with hydrogen peroxide. The surfaces of both lots showed significant chemical modification following exposure to hydrogen peroxide. The chemical reactions that occurred at the surface appear to be different than the reactions that dominate in the bulk of the polymer. This work indicate that hydrogen peroxide is capable of undergoing several reactions with PEUs and that small changes in the materials can affect which reaction will dominate.