Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that Na(x)CoO2*yH2O (x approximately 0.35, y approximately 1.3) is a superconductor with a T(c) of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-T(c) copper oxides, suggesting that the two systems have similar underlying physics.

Superconductors Superconductors D 8000Superconductivity in Two-Dimensional CoO 2 Layers. -NaxCoO2·yH2O (x ≈ 0.35, y ≈ 1.3) is prepared from Na0.7CoO2 by an oxidation process. The compound is a superconductor with TC = 5 K. It crystallizes in the hexagonal space group P63/mmc. The structure consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na + ions and H2O molecules. The compound is a superconductor with a T C of about 5 K. There is a marked resemblance in superconducting properties between the present material and high-TC copper oxides, suggesting that the two systems have similar underlying physics. -(TAKADA*, K.; SAKURAI, H.; TAKAYAMA-MUROMACHI, E.; IZUMI, F.; DILANIAN, R. A.; SASAKI, T.; Nature (London, UK) 422 (2003) 6927, 53-55; CREST, Japan Sci.

The measured spatial coherence characteristics of the illumination used in a diffractive imaging experiment are incorporated in an algorithm that reconstructs the complex transmission function of an object from experimental x-ray diffraction data using 1.4 keV x rays. Conventional coherent diffractive imaging, which assumes full spatial coherence, is a limiting case of our approach. Even in cases in which the deviation from full spatial coherence is small, we demonstrate a significant improvement in the quality of wave field reconstructions. Our formulation is applicable to x-ray and electron diffraction imaging techniques provided that the spatial coherence properties of the illumination are known or can be measured.

No abstract

We demonstrate coherent diffraction imaging using multiple harmonics from a high-harmonic generation source. An algorithm is presented that builds the known incident spectrum into the reconstruction procedure with the result that the useable flux is increased by more than an order of magnitude. Excellent images are obtained with a resolution of ͑165Ϯ 5͒ nm and compare very well with images from a scanning electron microscope.