Synthesis and structure of Bi₃NF₆: a member with n=3 of the Vernier phases M_nX_2n-1

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Approaches to modeling diffuse scattering from molecular crystals : Para-Terphenyl (C18H14)

Diffuse scattering is a probe of the local correlations in a crystal, whereas Bragg peaks are descriptive of the average long-range ordering. The long-range average is the result of numerous local configurations the population of which cannot be determined from the Bragg peaks. Diffuse scattering can examine this population. This is particularly the case when making use of the three-dimensional distribution of diffuse scattering from single crystals. However, diffuse scattering is very weak and broad and is often of similar intensity to the experimental background, which makes data collection demanding. Disorder can also take many forms and local configurations are not constrained by the average crystallographic symmetry. Here, three approaches to the modeling of diffuse scattering from molecular crystals will be discussed. All three approaches are based on a Monte Carlo (MC) simulation. As an example, the modeling of neutron diffuse scattering from para-terphenyl (PTP, C 18H14) will be described

Probing surfaces with thermal He atoms: scattering and microscopy with a soft touch

Helium atom scattering (HAS) is a well established technique, particularly suited for the investigation of insulating and/or fragile materials and light adsorbates including hydrogen. In contrast to other beam techniques based on Xrays or electrons, low energy (typically less than 100 meV) He atoms are scattered by the tail of the electron density distribution which spill out from a surface, therefore HAS is strictly a nonpenetrating technique without any sample damage. HAS has been used to investigate structural properties of crystalline surfaces, including precise determination of atomic step heights, for monitoring thin film growth, to study surface transitions such as surface melting and roughening and for determining the presence and properties of adsorbates. Energy resolved HAS can provide information about surface vibrations (phonons) in the meV range and surface diffusion. This chapter provides a brief introduction to HAS with an outlook on a new, promising surface science technique: Neutral Helium Microscopy