Biomedical subjects

JM Zuo

Publications and source records attributed to JM Zuo.

11 recordsLinked to original sources

PubMed2000

Surface structural sensitivity of convergent-beam RHEED: Si (0 0 1) 2 x 1 models compared with dynamical simulations

The aim of this work is to evaluate the sensitivity of convergent-beam RHEED for the refinement of surface atomic structure. We have compared experimental and theoretical convergent-beam RHEED patterns from the silicon (0 0 1) reconstructed surface. The experiment was carried out in a custom designed UHV diffraction camera,using a micron sized probe. Both experimental and theoretical CB-RHEED patterns show complex details, highly sensitive to the surface structure. The multiple scattering simulations were based on two experimental structural models which make different assumptions for dimer tilt, one derived from X-ray diffraction results, and another from LEED data. The simulated CB-RHEED patterns using the X-ray model were found to be in closer agreement with our experiment than the LEED model. However, the agreement is not entirely satisfactory, suggesting that further improvement on this model is necessary.

Journal Article↗

PubMed2000

Experimental measurement of electron diffuse scattering in magnetite using energy-filter and imaging plates

We have measured the diffuse scattering in magnetite as a function of temperature using the LEO 912Ohms energy-filtering electron microscope and the imaging plates. This study takes the advantage of the Koehler illumination system, energy filtering and the imaging plates for recording electron diffraction pattern over a large dynamic range. The experiment clearly shows a quantitative change in diffuse scattering distribution, which has the characteristics of one-dimensional ordering. This study clearly demonstrates the possibility for the quantitative study of diffuse scattering using electron diffraction.

Journal Article↗

PubMed1999

Lattice dynamics and Debye-Waller factors of some compounds with the sodium chloride structure.

The lattice dynamics of 19 compounds with the sodium chloride structure have been investigated using shell models. The models are compared with existing experimentally measured phonon-dispersion curves and refined using a multidimensional downhill simplex method. Debye-Waller factors for these compounds are calculated over the temperature range from 1 to 1000 K where appropriate and the results are fitted analytically using polynomial regression. The results are compared with experimentally measured room-temperature Debye-Waller factors and for most of the compounds the agreement is found to be better than 10%. At lower temperatures, it is expected that these results would be more accurate, since the harmonic approximation, which is crucial to the calculation of the Debye-Waller factors, works better. In choosing the models for particular applications, it is recommended that the model with the smallest standard error sigma is used for fitting the experimentally measured phonon-dispersion curves, or the model that shows best agreement with reliable experimental measurements of more relevant physical quantities, such as Debye-Waller factors in crystallography.

Journal Article↗

PubMed1999

Anisotropic dispersion of the band structure and formation of ring patterns in CBED.

An off-axis ring pattern was observed in the <1-11> zone-axis CBED pattern of an NiO single crystal. The pattern was interpreted as resulting from anisotropic dispersion of the band structure of the two most strongly excited free Bloch waves and strong absorption of the most tightly bound 1s Bloch state. Comparison has also been made with the case of MgO which has the same structure as NiO but weaker scattering power. The tightly bound 1s Bloch state in MgO was found to play an important role together with a strongly excited free Bloch state and a more conventional zone-axis ring pattern similar to that observed in the <001> zone-axis CBED pattern of silicon was observed.

Journal Article↗

PubMed1999

Dynamic inversion by the method of generalized projections.

A new approach to the inversion problem of dynamical transmission electron diffraction is described, based on the method of generalized projections in set theory. An algorithm is described that projects between two sets of constrained scattering matrices. This iterative process can be shown to converge, giving the required structure factors (for some choice of origin) if the sets are convex. For the dynamical inversion problem, the set topology is that of an N(2) torus, the sets are not convex, and traps are therefore sometimes encountered. These can be distinguished from solutions, allowing the algorithm to be restarted until a solution is found. Examples of successful inversion from simulated multiple-scattering data are given, which therefore solve the phase problem of electron diffraction for centrosymmetric or noncentrosymmetric crystal structures. The method may also be useful for the three-beam X-ray diffraction problem.

Journal Article↗

PubMed1992