Richard G. White

Surface composition, chemistry, and structure of polystyrene modified by electron-beam-generated plasma.

Polystyrene (PS) surfaces were treated by electron-beam-generated plasmas in argon/oxygen, argon/nitrogen, and argon/sulfur hexafluoride environments. The resulting modifications of the polymer surface energy, morphology, and chemical composition were analyzed by a suite of complementary analytical techniques: contact angle goniometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The plasma treatments produced only minimal increases in the surface roughness while introducing the expected chemical modifications: oxygen-based after Ar/O(2) plasma, oxygen- and nitrogen-based after Ar/N(2) plasma, and fluorine-based after Ar/SF(6) plasma. Fluorinated PS surfaces became hydrophobic and did not significantly change their properties over time. In contrast, polymer treated in Ar/O(2) and Ar/N(2) plasmas initially became hydrophilic but underwent hydrophobic recovery after 28 days of aging. The aromatic carbon chemistry in the top 1 nm of these aged surfaces clearly indicated that the hydrophobic recovery was produced by reorientation/diffusion of undamaged aromatic polymer fragments from the bulk rather than by contamination. Nondestructive depth profiles of aged plasma-treated PS films were reconstructed from parallel angle-resolved XPS (ARXPS) measurements using a maximum-entropy algorithm. The salient features of reconstructed profiles were confirmed by sputter profiles obtained with 200 eV Ar ions. Both types of depth profiles showed that the electron-beam-generated plasma modifications are confined to the topmost 3-4 nm of the polymer surface, while valence band measurements and unsaturated carbon signatures in ARXPS and REELS data indicated that much of the PS structure was preserved below 9 nm.

Segregation and crosslinking in urea formaldehyde/epoxy resins: a study by high-resolution XPS

Abstract The segregation of minor components such as flow agents, in an industrial coil coating based on epoxy resins crosslinked with a urea formaldehyde resin and applied to a hot-dipped galvanized steel (HDGS) substrate, has been investigated by high resolution XPS. The addition of a low amount of flow agent in the coating formulation leads to changes in the surface elemental composition. High-resolution monochromated XPS C1s spectra can be peak-fitted taking into account all functionalities of the respective components of the formulation. The examination of both the elemental and chemical surface compositions clearly demonstrates that the use of flow agent in the process leads to its preferential segregation towards the air–film interface. This result is interpreted in terms of minimisation of the surface free energy of the final coil coating. It is also possible to monitor the extent of crosslinking undergone within the coil coating system, using the peak-fitting in the same manner as above, and it was concluded that the system is fully crosslinked.

Surface analytical characterization of SiO2 gradient membrane coatings on gas sensor microarrays

Ion beam assisted deposition is applied to cover a gas sensor microarray of an electronic nose with an ultrathin gas-permeable SiO2 membrane varying in thickness across the array. Auger electron spectroscopy sputter depth profiles and non-Rutherford backscattering spectroscopy were used to study the uniformity of the deposition and the subsequent annealing step. The combination of spectroscopic ellipsometry for the freshly prepared membranes and line scans derived from Auger and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane is presented as a powerful quantification method for the determination of the desired SiO2 membrane thickness profiles.Ion beam assisted deposition is applied to cover a gas sensor microarray of an electronic nose with an ultrathin gas-permeable SiO2 membrane varying in thickness across the array. Auger electron spectroscopy sputter depth profiles and non-Rutherford backscattering spectroscopy were used to study the uniformity of the deposition and the subsequent annealing step. The combination of spectroscopic ellipsometry for the freshly prepared membranes and line scans derived from Auger and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane is presented as a powerful quantification method for the determination of the desired SiO2 membrane thickness profiles.

Synthesis and characterization of nanoscale Al–Si–O gradient membranes

Novel ultrathin gas-permeable Al–Si-oxide membranes have been developed by means of ion induced chemical vapor deposition in order to improve the gas analytical performance of an electronic nose. Dependent on the used precursor tailored Al∕Si concentration ratios and even concentration gradients are attainable. The diversity in chemical composition and thickness across the gas sensor microarray has been proven by the combination of ellipsometry for the freshly prepared membrane and line scans derived from Auger electron spectroscopy and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane.

Characterizing Materials for Energy Generation Using X-ray Photoelectron Spectroscopy (XPS)

In order to meet the challenges of more economical and environmentally benign energy production, a new generation of complex materials and devices are being developed, including thin film solar cells, fuel cells, and batteries. In all stages of development there is a requirement for materials characterization and analysis, from the initial development stages through to testing of the finished product. Most materials need to be analyzed for compositional homogeneity across surfaces and also for confirmation of film thickness and layer chemistry.

Characterizing New Energy Materials Using a Multi-Technique Approach

In order to meet the challenges of more economical and environmentally benign energy production, a new generation of complex materials and devices is being developed, such as thin film solar cells, fuel cells, and batteries. In all stages of development there is a requirement for materials characterization and analysis; from the initial development stages, through to testing of the finished article. Most materials need to be analyzed for compositional homogeneity across the sample surface and also for layer chemistry and thickness through the sample. It is rare that a single technique can achieve these testing requirements, and therefore a complementary approach involving several techniques is demanded.

Chemical Characterization of Material Surfaces Using X-ray Photoelectron Spectroscopy (XPS): The Perfect Complement to Electron Microscopy Techniques

Field emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM) are valuable microscopic imaging tools for characterizing the morphology and structure of solid materials. When combined with energy dispersive X-ray spectroscopy (EDS), these techniques also provide elemental composition information on the near-surface and subsurface of materials up to several micrometers deep. However, EDS gives no detailed information regarding the chemical composition within the top few nanometers of the surface. The topmost surface chemistry of materials influences their interaction with other substances in the environment and thus affects important material properties such as adhesion strength, catalytic activity, corrosion resistance, susceptibility to oxidation, and other critical chemical and physical characteristics. Knowledge of surface chemistry is therefore crucial to the successful production and optimization of innumerable advanced materials used in modern devices such as coatings, ceramics, composites, metals, nanomaterials, polymers, semiconductors, and thin films, among others. Highly developed surface sensitive techniques are required to properly and fully characterize the surfaces of complex materials and specialized products, which cannot be accomplished with electron microscopy techniques alone.