Book review.

Alignment of anisotropic particles along specific orientations influences the mechanical and rheological properties of a material. Small-angle scattering techniques are widely used to probe this alignment through analysis of anisotropic two-dimensional scattering intensity patterns. The anisotropy factor is the simplest and most common quantitative parameter for describing scattering anisotropy, especially in systems containing rod-like particles, and there are several methods for calculating this factor. However, there has been no systematic study comparing these methods while also evaluating the limitations imposed by non-idealities from instrumentation or polydisperse morphology. Three of the most common methods for calculating an anisotropy factor are examined here and their effectiveness for describing the orientation of a theoretical cylinder is evaluated. It is found that the maximum theoretical value of 1 for the anisotropy factor is only accessible at certain values of scattering vector q. The analysis details recommendations for q-range selection and data binning, as these influence the calculations. The theoretical results are supported by experimental small-angle neutron scattering data for a wormlike micelle solution undergoing shear, where different calculation methods yield distinct quantifications of anisotropy.

X-ray atomic pair distribution function (XPDF) measurements using a two-dimensional area detector have been of great value in studying atomic structures of materials with varying degrees of disorder. However, an area detector does not have energy resolution. Thus, incoherent inelastic Compton scattering and fluorescence are not discriminated, contaminating coherent elastic scattering. This paper investigates the effects of random noise from incoherent scattering on XPDF analysis. To conduct the study, the elastic scattering, Compton scattering and fluorescence of In0.33Ga0.67As alloy were separately measured using an intrinsic Ge solid-state detector with energy resolution. It is found that the addition of Compton scattering with a noise-to-signal ratio of about 0.8% results in the smearing of diffuse scattering in the high-Q region. Moreover, adding extra noise from fluorescence increases the smearing, overwhelming the diffuse scattering. Additionally, simulated data of elastic and Compton scattering on ferroelectric Ba(Ti0.8Zr0.2)O3 were used to investigate the evolution of noise fluctuation and its effects on the XPDF as a function of total intensity.

Density functional theory was employed to investigate the electronic structures of atomic bilayer materials that form between graphene (g-C) or graphitic silicon carbide (also known as siligraphene: g-SiC and g-SiC2) and graphitic zinc oxide (g-ZnO). The results indicate that g-C/g-ZnO bilayers have semimetallic properties with an energy band gap of zero like in graphene. For a g-SiC/g-ZnO bilayer, an ensemble of three sp2-hybridized carbon atoms periodically separated by three silicon atoms on g-ZnO has indirect and direct band gaps of 3.32 and 3.78 eV, respectively, which is suitable for use in light-emitting diode applications. For a g-SiC2/g-ZnO bilayer, an ensemble of four sp2-hybridized carbon atoms periodically separated by two silicon atoms on g-ZnO has a direct band gap of 1.15 eV, which approaches the optimal value of the band gap (Eopt ≃ 1.3 eV) for solar cell applications. The results show that increasing Si content in siligraphene can help to open the band gap of graphene and enhance the band gap of graphitic silicon carbide. The band gaps of siligraphene/g-ZnO bilayers depend on a smaller band gap from the monolayer component. Therefore, adjusting the Si content in siligraphene permits tuning of the band gap, and constructing a bilayer in the presence of a g-ZnO monolayer can slightly decrease the band gap. These results could lead to a new design of heterostructures with tunable band gaps for various applications.

An in situ study of the spatial distribution of the piezoelectric properties of an LiNb(1−x)TaxO3 crystal (⟨x⟩ = 0.088) in an external DC electric field was performed by the method of X-ray diffraction of synchrotron radiation at angles close to 180°. The variation of the d22 piezoelectric coefficient was determined with high accuracy (up to 2%) in local areas by the angular shift of the diffraction maximum under the action of the electric field (E = 1582 V mm−1) applied on the crystal along the Y axis, during scanning along the X and Z directions. A correlation between the piezoelectric strain amplitude and the concentration of tantalum obtained by X-ray fluorescence mapping has been established.

Domain configuration in epitaxial antiferroelectric films has been studied by X-ray nanoscopy, with the extraction of information about the domain sizes beyond the beam-size limit. The objective of this article is to understand how film thickness (the cases of 50 and 1000 nm are explored) and temperature (20 and 200°C) affect the nanodomain configuration of PbZrO3/SrRuO3/SrTiO3 thin films. It is found that the majority of antiferroelectric domains in both films are too small to be directly mappable, because many of them are simultaneously illuminated by the nanobeam (60 × 100 nm) most of the time. Nevertheless, these small sizes can be studied by analysing the diffraction peak width, which is, in the simplest approximation, inversely proportional to the domain size. With this approach it is identified that the characteristic (most probable) domain size does not depend on the film thickness and is ∼13 nm, while the scarcer larger domains do depend on it. An increase of the temperature to 200°C (just below the nominal antiferroelectric-to-cubic transition temperature) results in a slight increase in the characteristic size. These results are compared with those in ferroelectric films, where domain sizes are pronouncedly thickness dependent, and the relevant methodological question on the possibility of neglecting the interference of X-ray waves scattered by different nanodomains in the nanodomain assembly is also discussed.