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We report on the analysis of virtual powder-diffraction patterns from serial femtosecond crystallography (SFX) data collected at an X-ray free-electron laser. Different approaches to binning and normalizing these patterns are discussed with respect to the microstructural characteristics which each highlights. Analysis of SFX data from a powder of Pr0.5Ca0.5MnO3 in this way finds evidence of other trace phases in its microstructure which was not detectable in a standard powder-diffraction measurement. Furthermore, a comparison between two virtual powder pattern integration strategies is shown to yield different diffraction peak broadening, indicating sensitivity to different types of microstrain. This paper is a first step in developing new data analysis methods for microstructure characterization from serial crystallography data.
Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.
A transmission electron microscope (TEM) is much more than just a tool for imaging the static state of materials. To demonstrate this, we present work on studying the mechanical and electrical properties of carbon nanotube devices. Multiwall carbon nanotubes are concentrically stacked tubular sheets of graphite, where the spacing between each cylinder is simply the natural spacing of graphite. Using a custom-built in-situ nanomanipulation probe, we have shown that it is possible to slide the nanotube layers in a telescopic extension mode that exhibits low friction, demonstrating the potential of nanotubes as the ultimate synthetic nanobearing. During this telescopic extension, the electrical resistance of the nanotube devices increases, opening the possibility that these devices can also be used as nanoscale rheostats. We also briefly describe work on using electron holography inside a TEM to study the electric field distribution in nanotube field-emission devices and on using a nanotube itself as a biprism for electron holography. These measurements together demonstrate the wealth of information that can be obtained and frontiers that can be opened by putting operational nanodevices inside an electron microscope.
Iterative algorithms, which use diffracted intensities and some a-priori knowledge of an image to solve the phase problem, have been under development for many years. The promised super-resolution images, reconstructed from diffraction information alone, would be of the greatest value for molecular imaging and for the image of nonperiodic structures in materials. Using simulated data it is possible, for example, to reconstruct a complex object from a knowledge of its diffracted intensities with certain known support functions. Some success has recently been achieved reconstructing micrometer-sized non-periodic objects using coherent X-rays by the Feinup method. One favorable support function consists of two holes spanned by the coherence width of the beam, with one or both holes containing an unknown object. Our simulations, which iterate between diffracted intensities and the image, applying the known support (either completely opaque or completely transparent) and intensities in each domain, confirm that image reconstruction is possible for loose supports and noiseless data.
Cu2O and CuO are of great interest after the discovery of the high Tc superconductors. The superconductivity is believed to be dependent on charge states in CuO2 layers whose structure is similar to that of CuO. These transition-metal compounds are also important because of the different copper coordination numbers and different copper-oxygen distances, therefore these reflect different electron density distributions and bonding mechanisms. The electronic structure of cuprite has been studied extensively both theoretically and experimentally because of its symmetrical crystallographic structure (space group ) while that of CuO (space group C2/c) which has a monoclinic structure has been studied only recently. Previous experimental and theoretical results show that the valence electrons of copper in cuprite form hybrid states which is proposed by Orgel instead of spherical d10 state as in ionic copper.