Low dimensional diffuse scattering

Low dimensional (LD) diffuse scattering is either due to LD order of crystals (meso-phases) or due to low dimensional cooperative disorder in basically 3D ordered (average) structures. Diffuse scattering may be of elastic or inelastic nature, i.e. the order/disorder phenomena may be of static or dynamic origin, respectively. Quasi-one-dimensional (lD) systems such as low dimensional conductors, inclusion compounds with channnel-like cavities, fiber-structures or two dimensional (2D) systems, such as graphite-like layer-structures or sheet silicates, give rise to pronounced diffuse sheets (2D-) and diffuse rods (lD-Bragg “peaks”), respectively, in reciprocal space. Apart from fundamental interest in analysing LD diffuse phenomena, there is a growing interest in LD crystals and related kinetic re-ordering processes from the viewpoint of applied research. Some examples are discussed in detail.     

Oscillatory diffuse scattering study by time-of-flight neutron scattering

The oscillatory profile of diffuse scattering of ordered crystal PbF₂ is observed by time-of-flight (TOF) neutron scattering measurement. The theoretical expression of diffuse scattering intensity including the correlation effects among the thermal displacements of atoms is used to analyze the diffuse scattering profile of PbF₂. The theoretical expression is effective for the analysis of the diffuse scattering data by the TOF measurement.     

Quasielastic electron-electron scattering and anomalous magnetoresistance

Wave function phase relaxation due to the quasielastic electron-electron collisions is shown to depend essentially on the external magnetic field. Additional contribution to anomalous magnetoresistance connected with this deoendence is discussed and found to be important in two dimensional case.     

Disorder diffuse scattering from quasicrystals

Very sharp Bragg reflections accompanied by diffuse scattering phenomena are typical for most stable quasicrystals. The correlation length of the quasiperiodic average structure can reach several micrometers as proved by high-resolution X-ray diffraction experiments. This corresponds to a structural perfection of some quasicrystals similar to that of silicon. Nevertheless, the omnipresent diffuse scattering indicates significant deviations from a strictly ordered quasiperiodic structure especially in the case of decagonal phases. These structural deviations may be caused by phason fluctuations, by disorder in the packing of the basic atomic clusters, by the formation of nanodomains, by chemical disorder, or by superstructure formation on a short-range scale. Characteristic examples of different types of structural disorder present in icosahedral and decagonal quasicrystals are reported. The diffuse scattering phenomena in decagonal Al-Co-Ni as a function of composition and temperature are discussed in more detail.     

Huang diffuse scattering of neutrons

Huang diffuse neutron scattering was measured for the first time on niobium with interstitially dissolved deuterium as well as on MgO after neutron irradiation and Li⁷F after-irradiation. With Huang diffuse scattering the strength and symmetry of the distortion field around lattice defects can be determined. Our results clearly demonstrate that this method is feasible with neutrons.The present results are compared with X-ray experiments and the advantages of using neutrons is discussed in some detail.     

On the technique of absolutization of diffuse scattering intensity measurements based on thermal diffuse scattering measurements

Features of microdefect (MD) formation in GaAs(Si) single crystals grown by horizontally oriented crystallization were studied by X-ray diffuse scattering (XRDS). Measurements were performed at room temperature (∼298 K) and near the liquid nitrogen evaporation temperature (∼85 K) using an open-flow cooling nitrogen cryostat. A practical technique for measuring XRDS using a triple-axis X-ray diffractometer was developed and applied to separate scattering on defects and thermal diffuse scattering. For a crystal with n = 2.0 × 10¹⁸ cm⁻³, the radius of detected nonspherical MDs was determined as ∼0.2 μm; thermal diffuse scattering (TDS) was experimentally separated. For a crystal with n = 3.9 × 10¹⁸ cm⁻³, nonspherical MDs ∼0.5 μm in radius were detected; TDS was found to be a negligible fraction of total XRDS. At the same time, in the case of coinciding crystal orientations and identical experimental conditions, TDS measurement data for one crystal can be used for other GaAs(Si) crystals with the same orientation.     

X-ray diffuse scattering from incommensurable structures

X-Ray diffuse scattering from a series of examples where the reason for the existence of incommensurable features is fairly well understood, is described. They include in particular non stoichiometric compounds such as [DIPS Φ₄(l₃)0.76] and such as intercalated graphite RbC₂₄. and quasi one dimensional conductors. A particular emphasis is given on various 1 - D conductors and to the relation of the incommensurability to the characteristics of the electron conduction bands.     

Localized diffuse scattering from icosahedral Ti-Mn

In diffraction from some icosahedral quasicrystals, diffuse scattering is concentrated on arcs in TEM diffraction patterns. The new Ti-Mn icosahedral phase produces much more intense arcs than previously observed in quasicrystals, allowing a significantly deeper study of them.     

On field effect and diffuse surface scattering

An electric field effect mechanism by diffuse surface scattering is proposed. This new field effect mechanism is dominant at metal oxide interfaces and due to interfacial exchange between conduction electrons and trap states in the oxide.     

Analyses of anomalous large angle inelastic alpha particle scattering

Inelastic alpha particle scatterings to selected states in²⁴Mg,²⁸Si and⁴⁰Ca are analysed. The transitions, all of which display anomalous structure in their differential cross sections at large scattering angles, are weakly, if at all, promoted by normal first order inelastic scattering reaction processes. To explain the anomalous structure, we utilize a two step reaction model in which the intermediate states are quasi-molecular. The energy variation of large angle scattering data shows that the quasi molecular intermediate states form a rotational band identical to that required to explain anomalous structure in the angular distributions of elastically scattered alpha particles.     

Magnetic diffuse scattering in AgMn spin glass alloys

Magnetic diffuse peaks observed around the $\text{(1}\text{1}\text{2}\text{± δ 0)}$ type positions in reciprocal space have been studied in AgMn spin glass alloys by using neutron diffraction techniques. The position parameter δ of AgMn alloys coincides with that for CuMn alloys with the same Mn content even though the former has a larger lattice spacing than the latter by about 10%. The results suggest that the origin of the satellite diffuse peaks comes from a Fermi surface effect such as the RKKY interaction.     

Imaging nonequilibrium atomic vibrations with x-ray diffuse scattering

We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations in the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse-acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal-acoustic phonons. In InSb the increase in TA phonon population is less directional.     

Crystallization kinetics of titanite glass from diffuse scattering

Abstract

The crystallization kinetics of iron-doped titanite glass were studied using X-ray powder diffraction and Mossbauer spectroscopy. Good agreement was observed for the crystallization kinetics determined from the diffuse and the Bragg contribution of the diffraction pattern. At 790°C both methods yielded rate constants of about 0·07h^?1. Mossbauer spectroscopy proved to be rather insensitive to the crystallization process of the titanite glass.     

Multiple scattering theory of diffuse LEED from vacancies

Previous work has shown how to make a full multiple scattering theory of DLEED from isolated adatoms. Here we investigate the complementary problem of scattering from isolated vacancies. Implementation of the theory involves two conventional LEED calculations, for the incident and exit beams and a cluster calculation, similar to that used in EXAFS, centred on the vacancy.