Li Fang-Hua

Image resolution enhancement by combining information from electron diffraction pattern and micrograph

Abstract An electron micrograph of chlorinated copper phthalocyanine at 2 A resolution taken on the Kyoto 500 kV electron microscope has been enhanced to 1 A resolution by incorporating the information from the corresponding electron diffraction pattern. Structure-factor amplitudes up to 1 A resolution were obtained from the electron diffraction pattern. Phases of the structure factors within 2 A resolution were derived from the Fourier transform of the electron micrograph. A phase-extension technique introduced from X-ray crystallography was then used to derive the phases between 2 and 1 A resolution. The final image was obtained by the inverse Fourier transform using the structure factor amplitudes from the electron diffraction pattern and the phases from the electron micrograph and from the phase-extension procedure.

A New Bipolar Type Transistor Created Based on Interface Effects of Integrated All Perovskite Oxides

Oxide transistor is the basic device to construct the oxide electronic circuit that is the backing to develop integrated oxide electronics with high efficiency and low power consumption. By growing the perovskite oxide integrated layers and tailoring them to lead semiconducting functions at their interfaces, the development of oxide transistors may be able to perform. We realize a kind of p-i-n type integrated layers consisting of an n-type cuprate superconductor, p-type colossal magnetoresistance manganite, and a ferroelectric barrier (i). From this, bipolar transistors were fabricated at the back-to-back p-i-n junctions, for which the Schottky emission and p-n junction barriers, as well as the ferroelectric polarization, were integrated into the interfaces to control the transport properties; a preliminary but distinct current gain greater than 1.6 at input current of microampers order was observed. These results present a real possibility to date for developing bipolar all perovskite oxide transistors.

Study of superstructure II in multiferroic BiMnO3

The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [10] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional (3D) structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.

Solving a 3-dimensional quasicrystal structure in 6-dimensional space using the direct method

A direct method was tested in solving the structure of a 3-dimensional quasicrystal in 6-dimensional space. Theoretical 3-dimensional diffraction data were used which contain Gaussian distribution errors with a mean error of about 20% for intensities. The diffraction data were firstly converted to a set of 6-dimensional structure factors. The window function used for the conversion was measured from the Patterson origin peak in pseudo space. A direct method was then applied to solve the phase problem in 6-dimensional space. Test results showed that the procedure is very efficient.

Resolution improvement of electron micrographs by the direct method for biotin-binding protein streptavidin

Direct-method phase extension has been applied to two-dimensional electron diffraction data of the protein streptavidin. Structure-factor amplitudes from electron diffraction were combined with phases from the corresponding electron micrographs. Maximum-entropy discrimination and cluster analysis were used to derive a solution from a large number of random trials. The phase extension from 0.3 to 0.25nm led to substantial improvement of the reconstructed projection image quality.

High-resolution electron microscopy studies of high-pressure synthesized mercury-based superconductor

Studies of high-pressure synthesized Hg-Ba-Ca-Cu-O superconductor by electron diffraction and high-resolution electron microscopy are reported. The results of electron diffraction indicate that two superconducting phases 1212 and 1223 exist in the sample and their cell parameters area=b=3.8 Å,c=12.7 Å anda=b=3.8 Å,c=15.8 Å, respectively. High-resolution electron micrographs were taken from the two phases Hg-1212 and Hg-1223 and from the region of the intergrowth of the two phases. The relation between the structure and superconducting transitional temperatureTc is discussed.