Interpretation of angular symmetries in electron nanodiffraction patterns from thin amorphous specimens

The interpretation of angular symmetries in electron nanodiffraction patterns from thin amorphous specimens is discussed. It is demonstrated that dynamical scattering decreases the angular symmetry of the diffraction pattern from that obtained in the kinematical approximation, and that this effect dominates over other experimental parameters such as probe-forming lens aberrations and camera noise. The decrease in angular symmetry of the diffraction pattern is demonstrated using the phase grating and multislice formalisms. A method is demonstrated whereby the dynamical data can be corrected to recover the kinematical result.

Solution of the phase problem at non-atomic resolution by the phantom derivative method

The method of multiple phantom derivatives allows one to solve ab initio and at non-atomic resolution the crystallographic phase problem for a target structure by using random structures with the same unit cell and space-group symmetry: the composite structures, called derivatives, are devoid of experimental data. The method is also suitable for extending and refining phases obtained by other techniques.

Theoretical analysis of reflection high-energy electron diffraction (RHEED) and reflection high-energy positron diffraction (RHEPD) intensity oscillations expected for the perfect layer-by-layer growth

The importance of the phenomenon of the refraction of waves in the behaviour of the phase shift of intensity oscillations for RHEED and RHEPD is discussed using a simple model of the interference of two waves along with the precise dynamical diffraction theory.

A study of X-ray multiple diffraction by means of section topography

The theoretical and experimental study of two different cases of X-ray multiple diffraction by means of section topography for 400 diffraction in a silicon single crystal is described. Accurate computer simulations of the section topogram for the case of X-ray multiple diffraction are performed for the first time. The experiment is carried out using a laboratory source under conditions of low resolution over the azimuthal angle.

Image definition evaluation functions for X-ray crystallography: a new perspective on the phase problem

The phase problem of X-ray crystallography is surveyed from a perspective of image definition evaluation functions. The reconstructed electron-density maps are taken as the images of the real electron distribution in crystals, and two image definition evaluation functions are proposed to identify the correct phase set.

Neutron interferometric measurement and calculations of a phase shift induced by Laue transmission

In this study, the phase shift induced by Laue transmission in a perfect Si crystal blade is investigated. This `Laue phase', with a fascinating steep slope, was measured in the vicinity of the Bragg condition within a neutron interferometer.

Three new crystal structures in the Na–Pb system: solving structures without additional experimental input

Three compounds in the Na–Pb binary system are solved using the First-Principles Assisted Structure Solution method.

Hexagonal projected symmetries

A list of the three-dimensional lattices that can be projected so as to obtain a two-dimensional hexagonal pattern is established.