Edward G. Rightor

Interferometer-controlled scanning transmission X-ray microscopes at the Advanced Light Source

Two new soft X-ray scanning transmission microscopes located at the Advanced Light Source (ALS) have been designed, built and commissioned. Interferometer control implemented in both microscopes allows the precise measurement of the transverse position of the zone plate relative to the sample. Long-term positional stability and compensation for transverse displacement during translations of the zone plate have been achieved. The interferometer also provides low-distortion orthogonal x, y imaging. Two different control systems have been developed: a digital control system using standard VXI components at beamline 7.0, and a custom feedback system based on PC AT boards at beamline 5.3.2. Both microscopes are diffraction limited with the resolution set by the quality of the zone plates. Periodic features with 30 nm half period can be resolved with a zone plate that has a 40 nm outermost zone width. One microscope is operating at an undulator beamline (7.0), while the other is operating at a novel dedicated bending-magnet beamline (5.3.2), which is designed specifically to illuminate the microscope. The undulator beamline provides count rates of the order of tens of MHz at high-energy resolution with photon energies of up to about 1000 eV. Although the brightness of a bending-magnet source is about four orders of magnitude smaller than that of an undulator source, photon statistics limited operation with intensities in excess of 3 MHz has been achieved at high energy resolution and high spatial resolution. The design and performance of these microscopes are described.

A SCANNING TRANSMISSION X-RAY MICROSCOPE FOR MATERIALS SCIENCE SPECTROMICROSCOPY AT THE ADVANCED LIGHT SOURCE

Design and performance of a scanning transmission x-ray microscope (STXM) at the Advanced Light Source is described. This instrument makes use of a high brightness undulator beamline and extends the STXM technique to new areas of research. After 2.5 years of development it is now an operational tool for research in polymer science, environmental chemistry, and magnetic materials.

X-ray spectromicroscopy of polymers and tribological surfaces at beamline X1A at the NSLS

Abstract We provide a general overview of microspectroscopy and spectromicroscopy for materials characterization at beamline X1A at the national synchrotron light source (NSLS). Two instruments, the scanning transmission X-ray microscope (STXM) and scanning photoemission microscope (SPEM), are available. The STXM has been able to provide a spatial resolution of better than 50 nm for several years and near edge X-ray absorption fine structure (NEXAFS) spectroscopy is performed in transmission from thin samples at an energy resolution of typically 0.3 eV at the carbon K-edge. Numerous applications in polymer science and biology have been performed to date. We restrict our review to polymer science applications and present new results of several polymer systems. The SPEM has a spatial resolution of about 250 nm in routine operation and was recently upgraded with a hemispherical sector analyzer to improve the data throughput. We present the latest SPEM results, which were generated from a tribological sample.

X-ray microscopy in polymer science: prospects of a ‘new’ imaging technique☆

Abstract A relatively non-invasive imaging technique, which employs highly focused, tunable X-rays, is described. This technique—scanning transmission X-ray microscopy—can be used to investigate the bulk characteristics of polymeric materials with chemical sensitivity at a spatial resolution of about 50nm. We present examples ranging from unoriented multiplase polymers to highly oriented Kevlar fibres. In the case of oriented samples, a dichroism technique is used to determine the orientation of specific chemical bonds. Extension of the technique to investigate surfaces of bulk samples is discussed.

Optimization of scanning transmission X-ray microscopy for the identification and quantitation of reinforcing particles in polyurethanes

The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a polyurethane have been investigated with scanning transmission X-ray microscopy (STXM). A detailed discussion of microscope operating procedures is presented and ways to avoid potential artifacts are discussed. Images at selected photon energies in the C 1s, N 1s and O 1s regions allow unambiguous identification of styrene-acrylonitrile-based (SAN) copolymer and polyisocyanate polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieved by fitting C 1s spectra to linear combinations of reference spectra. Regression analyses of sequences of images recorded through the chemically sensitive ranges of the C 1s, N 1s and O 1s spectra are used to generate quantitative compositional maps, which provide a fast and effective means of investigating compositional distributions over a large number of reinforcing particles. The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each type of reinforcing particle, which differ considerably, were obtained by analysis of STXM images at chemically selective energies.

Development of scanning X-ray microscopes for materials science spectromicroscopy at the Advanced Light Source

The development of two zone-plate microscopes for X-ray spectroscopic analysis of materials is described. This pair of instruments will provide imaging NEXAFS analysis of samples in transmission at atmospheric pressure and imaging XPS and NEXAFS analysis of sample surfaces in a UHV environment.

X-Ray Microscopy Of Multiphase Polymeric Materials

The authors have utilized the scanning transmission x-ray microscope at Brookhaven National Laboratory to acquire high energy resolution spectra of various polymers and to investigate the bulk characteristics of multiphasic polymeric materials with chemical sensitivity at a spatial resolution of about 50 nm. The authors present studies ranging from phase separated liquid crystalline polyesters and polyurethanes to various polymer blends. Improvements in the NEXAFS imaging and spectral acquisition protocol in the recent past provide much improved spectral fidelity and include in situ energy calibration with CO{sub 2}.

Chemical Speciation by NEXAFS Spectromicroscopy: Insights from Molecular Modelling of Polymers

Near Edge X-ray Absorption Fine Structure (NEXFAS) spectroscopy of polymers performed in a scanning transmission X-ray microscope (STXM) can provide chemical speciation with < 0.1 {micro}m spatial resolution in imaging mode. The core excitation spectra of molecular compounds that are structural analogues of polymers help interpret the NEXAFS spectra of polymers. The effect of {pi}-delocalization on polymer NEXAFS is discussed and illustrated by comparison to molecular spectra. Extended Hueckel calculations are particularly useful for providing insight into the relationship between chemical structure and the molecular and polymer spectra. The authors report the interpretation of experimental NEXAFS spectra of polyethylene terephthalate (PET). Molecular models indicate that NEXAFS will be sensitive to structural isomerization in polyester polymers. They demonstrate the capability of NEXAFS to distinguish hard-segment and soft-segment phase segregation in polyurethanes.

ESTIMATING SOURCES OF VARIATION: A CASE STUDY FROM POLYURETHANE PRODUCT RESEARCH

A case study is presented from polyurethane product research. It demonstrates the need for true replicate samples when sample-to-sample variation is not known. A first-pass analysis of an additive effect on a particular polyurethane microstructure was..

Real time study of failure events in polymers

Experimental methods have been developed so that in situ transmission electron microscope (TEM) tensile studies can be performed on bulk polymer sections, and failure processes observed; real time can be correlated with failure in bulk parts. Using specially designed support grids, polymer section geometry and in situ tensile procedures, the submicrometre failure response of polycarbonate-poly(ethylene terephthalate) phase morphology to crack propagation has been studied. This paper focuses on the design of the tensile grids, sections and procedures, which had to be devised for these studies. The techniques developed allow quantification of strain rates and crack velocities. TEM experiments performed showed that artefacts, such as vacuum or radiation damage, were not significant factors influencing the morphological response to crack propagation. A companion paper presents the failure processes found in situ and correlations with failure processes found in bulk tested parts.