Dieter K. Schneider

Effect of pore structure of nanometer scale porous films on the measured elastic modulus.

The impact of pore structure of nanoporous films on the measured elastic modulus is demonstrated for silica-based nanoporous low-k films that are fabricated using an alternative manufacturing sequence which allows a separate control of porosity and matrix properties. For this purpose, different experimental techniques for measuring the elastic properties were compared, including nanoindentation, laser-induced surface acoustic wave spectroscopy (LAwave), and ellipsometric porosimetry (EP). The link between the elastic response of these nanoporous materials and their internal pore structure was investigated using positronium annihilation lifetime spectroscopy (PALS), EP, and diffusion experiments. It is shown that the absolute value of the Berkovich indentation modulus is very sensitive to the local pore structure and stiffness of the substrate and can be influenced by densification and/or anisotropic elasticity upon indentation, while on the other hand spherical indentation results are less sensitive to the local pore structure. The comparison of Berkovich and spherical indentation results combined with finite element simulations can potentially reveal changes in the internal structure of the film. For nanoporous films with porosity above the percolation threshold, the elastic modulus results obtained with LAwave and EP agree very well with spherical indentation results. On the other hand, below the percolation threshold, the elastic modulus values determined by these techniques deviate from the spherical indentation results. This was explained in terms of specific technique related effects that appear to be sensitive to the specific arrangement and morphology of the pores.

Correlated single-crystal electronic absorption spectroscopy and X-ray crystallography at NSLS beamline X26-C

The instrumentation and methods available for collecting almost simultaneous single-crystal electronic absorption correlated with X-ray diffraction data at NSLS beamline X26-C are reviewed, as well as a very brief outline of its Raman spectroscopy capability.

Single-crystal Raman spectroscopy and X-ray crystallography at beamline X26-C of the NSLS.

The collection of absorption and Raman spectroscopic data correlated with X-ray diffraction data allows investigators to understand the atomic structure as well as the electronic and vibrational characteristics of their samples, to identify transiently formed intermediates and to explore mechanistic questions. Raman spectroscopy instrumentation at beamline X26-C at the NSLS is currently available to the general user population.

Integrated software for macromolecular crystallography synchrotron beamlines II: revision, robots and a database

This manuscript chronicles the evolution of software used originally to control a diffractometer at a macromolecular crystallography beamline. The system has been augmented and rewritten. A modular and carefully organized suite of programs now handles the whole experimental environment from a single vantage point. It provides automatic logging of the experiment and communication with the user, all the way from an initial proposal to perform the work to the end of data collection. This has included construction of a relational database to organize all details of the experiment and incorporation of a robotic specimen changer to provide automation for high-throughput applications.

The use of wire chambers in structural biology

Abstract Position-sensitive neutron detectors with high detection efficiency and high spatial resolution are essential for neutron protein crystallography as well as for small-angle neutron scattering on large biological assemblies. Here we report on the performance of two wire chambers recently developed by the Brookhaven Instrumentation Division. Both detectors have a spatial resolution of about 1.3 mm, a detection efficiency of about 80%, and excellent differential and integral linearities. Using small-angle data as an example, we show that the new detectors, furthermore, have excellent temporal stability and can provide difference spectra of unparalleled accuracy. The Biology small-angle spectrometer, because of its location on the constrained reactor floor, has a short secondary flight path of 2 m. High detector resolution is therefore essential to preserve the ability to measure at small angles and to record narrowly spaced diffraction fringes. In addition, we demonstrate in detail that the state-of-the-art detector makes it possible to extend the precision and resolution of a protein single-crystal data set. By measuring beam divergence, wavelength spread, and the crystal mosaic in auxilliary experiments, a set of parameters is obtained for the calculation of a spatial filter for each diffraction spot.

Beamline X29: a novel undulator source for X-ray crystallography.

A high-flux insertion device and beamline for macromolecular crystallography has been built at the National Synchrotron Light Source (NSLS) that employs a mini-gap undulator source developed by the NSLS. The mini-gap undulator at beamline X29 is a hybrid-magnet device of period 12.5 mm operating at proven gaps of 3.3-10 mm. The beamline provides hard X-rays for macromolecular crystallography experiments from the second and third harmonics over an energy range of 5-15 keV. The X-ray optics is designed to deliver intense and highly collimated X-rays. Horizontal focusing is achieved by a cryogenically cooled sagittally focusing double-crystal monochromator with approximately 4.1:1 demagnification. A vertical focusing mirror downstream of the monochromator is used for harmonic rejection and vertical focusing. The experimental station hosts an Area Detector Systems Quantum 315 CCD detector with 2.2 s readout time between exposures and Crystal Logic goniostat for crystal rotation and detector positioning. An auto-mounter crystal changer has been installed to facilitate the high-throughput data collection required by the major users, which includes structural genomics projects and the Macromolecular Crystallography Research Resource mail-in program. X29 is 10(3) times brighter than any existing bending-magnet beamline at NSLS with an actual flux of 2.5 x 10(11) photons s(-1) through a 0.12 mm square aperture at 11.271 keV.

SANS and SAXS studies of pluronic L64 in concentrated solution

The supramolecular structure, formed by a PEO-PPO-PEO copolymer, PEO13PEO30-PEO13 or Pluronic L64, in mixtures of xylene/water, was investigated by small-angle X-ray scattering over a temperature range of 25–60°C and by small-angle neutron scattering over a temperature range of 13–29°C. The large aggregates had a hexagonally packed cylindrical structure with the interdomain spacing being in the order of ∼ 10 nm interdomain spacing increased with increasing amount of solubilized water in the large aggregates.

Fluctuations and growth of a cubic network observed in a nonionic surfactant system

We have investigated stability of a cubic lattice having a periodic-minimal surface in a nonionic surfactant system using a time resolved small-angle neutron scattering technique. The cubic lattice transformed from a lamellar phase showed polycrystalline scattering patterns and a strong fluctuation of the diffraction intensity as a function of time. The intensity distribution analysis indicates that the domain coarsening proceeds until 2000 min and then the coarsening is suppressed. At a critical temperature, such fluctuating peaks suddenly grow to a monocrystalline pattern showing no intensity fluctuations. On the contrary, in the case of the cubic lattice transformed from a hexagonal phase, the polycrystalline diffraction peaks also showed fluctuating behavior, but in this case, the domain coarsening is suppressed and the scattering intensity fluctuates around an equilibrium value. We consider that the fluctuations arise from the polycrystalline cubic network trapped in a metastable state.

Three Biomedical Beamlines at NSLS-II for Macromolecular Crystallography and Small-Angle Scattering

We report on the status of the development of three beamlines for the National Synchrotron Light Source-II (NSLS-II), two for macromolecular crystallography (MX), and one for wide- and small-angle x-ray scattering (SAXS). Funded by the National Institutes of Health, this suite of Advanced Beamlines for Biological Investigations with X-rays (ABBIX) is scheduled to begin operation by 2015. The two MX beamlines share a sector with identical canted in-vacuum undulators (IVU21). The microfocusing FMX beamline on the inboard branch employs a two-stage horizontal source demagnification scheme, will cover an energy range of 5 – 23 keV, and at 12.7 keV will focus a flux of up to 1013 ph/s into a spot of 1 μm width. The companion AMX beamline on the short outboard branch of the sector is tunable in the range of 5 – 18 keV and has a native focus of 4 μm (h) × 2 μm (v). This robust beamline will be highly automated, have high throughput capabilities, and with larger beams and low divergence will be well suited for structure determinations on large complexes. The high brightness SAXS beamline, LIX, will provide multiple dynamic and static experimental systems to support scientific programs in solution scattering, membrane structure determination, and tissue imaging. It will occupy a different sector, equipped with a single in-vacuum undulator (IVU23). It can produce beams as small as 1 μm across, and with a broad energy range of 2.1 – 18 keV it will support anomalous SAXS.

Macromolecular crystallography beamline X25 at the NSLS

A description of the upgraded beamline X25 at the NSLS, operated by the PXRR and the Photon Sciences Directorate serving the Macromolecular Crystallography community, is presented.