ABSTRACT
An efficient synthesis route is proposed to obtain single phase powder ceramic of CaFe5O7. This complex structure can be described as an intergrowth between one CaFe2O4 unit and n = 3 slices of FeO Wüstite-type structure. A detailed structural study has been carried out at room temperature combining transmission electron microscopy (TEM) observations (ED, HREM), scanning transmission electron microscopy (STEM-HAADF), and X-ray diffraction data. The analysis of these data has revealed an unexpected supercell with a monoclinic symmetry. From the hkl conditions deduced from the electron diffraction study and the analysis of X-ray diffraction data by simulated annealing, a structural model considering the centrosymmetric P21/m setting can be proposed. In addition the first magnetic and electrical transport measurements are reported showing a sharp peak in magnetic susceptibility and a strong localization around 360 K, associated to a structural change from monoclinic setting to orthorhombic one.
ABSTRACT
The genesis, theoretical basis and practical application of the new electron holographic dark-field technique for mapping strain in nanostructures are presented. The development places geometric phase within a unified theoretical framework for phase measurements by electron holography. The total phase of the transmitted and diffracted beams is described as a sum of four contributions: crystalline, electrostatic, magnetic and geometric. Each contribution is outlined briefly and leads to the proposal to measure geometric phase by dark-field electron holography (DFEH). The experimental conditions, phase reconstruction and analysis are detailed for off-axis electron holography using examples from the field of semiconductors. A method for correcting for thickness variations will be proposed and demonstrated using the phase from the corresponding bright-field electron hologram.
ABSTRACT
The extended-ptychographical iterative engine (e-PIE) is a recently developed powerful phase retrieval algorithm which can be used to measure the phase transfer function of a specimen and overcome conventional lens resolution limits. The major improvement over PIE is the ability to reconstruct simultaneously both the object and illumination functions, robustness to noise and speed of convergence. The technique has proven to be successful at optical and X-ray wavelengths and we describe here experimental results in transmission electron microscopy supported by corresponding simulations. These simulations show the possibilities - even with strong phase objects - and limitations of ptychography; in particular issues arising from poorly-defined probe positions.
ABSTRACT
The distortions introduced into high-resolution transmission electron microscope (HRTEM) images by the projector lens system are an important source of systematic error for quantitative displacement and strain determination. Using geometric phase analysis of images of perfect crystals, we measured these errors for two different transmission electron microscopes. Local magnification varies by as much as 5%, and rotation can reach 2 degrees across a typical image. Our experimental results are compared with theory, and optical pincushion and spiral distortion coefficients are determined. A method for calibrating and removing these distortions is presented that enables quantification to 0.1% strain and 0.1 degrees rotation across the whole field of view. This calibration is also critical for the accurate measurement of local lattice parameters from HRTEM images.
ABSTRACT
Fusarium species are opportunistic nosocomial pathogens that often cause fatal invasive mycoses. We designed a primer pair that amplifies by PCR a fragment of a gene coding for the rRNA of Fusarium species. The DNAs of the main Fusarium species and Neocosmospora vasinfecta but not the DNAs from 11 medically important fungi were amplified by these primers. The lower limit of detection of the PCR system was 10 fg of Fusarium solani DNA by ethidium bromide staining. To test the ability of this PCR system to detect Fusarium DNA in tissues, we developed a mouse model of disseminated fusariosis. Using the PCR, we detected Fusarium DNA in mouse tissues and in spiked human blood. Furthermore, F. solani, Fusarium moniliforme, and Fusarium oxysporum were testing by random amplified polymorphic DNA (RAPD) analysis. The bands produced by RAPD analysis were purified, cloned, and sequenced. The information was used to design primer pairs that selectively amplified one or several Fusarium species. The method developed may be useful for the rapid detection and identification of Fusarium species both from culture and from clinical samples.
