Diffuse X-ray reflections

Certain crystals give diffuse X-ray reflections there are various possible causes for this—small crystal size, structural irregularities, or thermal movements. The consideration of these phenomena in Chapter XI leads on to a brief introduction to the interpretation of the very diffuse diffraction patterns given by non-crystalline substances. 

Wooster, W. A. Diffuse X-ray Reflections from Crystals. Clarendon Press Oxford (1962). 

The x-ray reflections of solid lipid nanoparticles are usually much broader than those of the bulk material as a result of the small particle size and, potentially, also of a decrease in crystalline order. Fine details may thus not be recognizable in the resulting, more diffuse diffractograms. Assignment of polymorphs may become increasingly difficult with the complexity of the material under investigation (e.g., ) 2005 by CRC Press LLC... 

Experimentally the PD may be studied by diffuse X-ray scattering (DXS) experiments in which the ID distortion of the chains gives rise to weak continuous lines on either side of the layer lines of strong Bragg spots.10 The periodicity of the PD may be determined from the position of the diffuse line. In contrast, 3D superstructures give rise to real satellite reflections associated with the Bragg spots. 

A large number of partially oxidized divalent cation salts of the bis(oxalato)platinates have been reported (see Table 2).63 Only the series Mx[Pt(C204)]-6H20 (MOP where M = Fe, Co, Ni, Zn, Mg and 0.80 < x < 0.85) has been extensively studied.68 83 For most of these salts detailed studies have been made of their crystal structures and optical reflectivity at room temperature, and the variation of superlattice reflections, diffuse X-ray scattering, thermopower and DC electrical conductivity with temperature. 

In CoOP above 300 K the compound exists in the Cccm space group, but with characteristic diffuse X-ray lines indicative of the Peierls modulation and no evidence of superstructure formation. Below 300 K a superstructure develops as shown by the appearance of satellite reflections on the X-ray diffraction photographs. At 280 K a phase transition to the Pccn space group occurs and associated with this are changes in the satellite pattern.78 74 Superstructure development which is commensurate with the Peierls modulation is completed about 250 K. 

NiOP already exists in the Pccn group at room temperature and weak diffuse X-ray scattering and kF and 2kF satellite reflections are observed.79 The 2kF spots disappear above 305 K and the conductivity is similar to that observed for CoOP and ZnOP.79,72... 

Figure 17 Diffuse x-ray pattern of TTF-TCNQ at 60 K. (a) Pattern showing the 2kr and 4kP one-dimensional precursors at 0.294 > and 0.59 > from the layer of Bragg reflections. They appear as interrupted diffuse lines due to the structure factor of scattering molecules, (b) Schematic representation of the diffuse lines. (From Ref. 133.)...

The direct measurement of the various important parameters of foam films (thickness, capillary pressure, contact angles, etc.) makes it possible to derive information about the thermodynamic and kinetic properties of films (disjoining pressure isotherms, potential of the diffuse electric layer, molecular characteristics of foam bilayer, such as binding energy of molecules, linear tension, etc.). Along with it certain techniques employed to reveal foam film structure, being of particular importance for black foam films, are also considered here. These are FT-IR Spectroscopy, Fluorescence Recovery after Photobleaching (FRAP), X-ray reflectivity, measurement of the lateral electrical conductivity, measurement of foam film permeability, etc. 

Because the amplitude of the lattice distortion in the Peierls insulator is very small, the X-ray scattering associated with it is weak. Furthermore the one-dimensional nature of this distortion gives rise to diffuse Bragg planes instead of the usual well-defined Bragg reflections. These two facts have led to the development of a special diffuse X-ray photographic technique often referred to as the monochromatic Laue technique or XDS (for X-ray diffuse scattering) (64). 

Diffuse X-ray and elastic neutron scattering studies revealed the presence of a structural change accompanying the metal-insulator transition In the insulating state below 53 K a set of satellite reflections was discovered with the superlattice... 

In the diffuse X-ray measurements of TTF-TCNQ the superlattice reflection was found with the wave number 4kp = 0.59 b [56]. It is observed even at room temperature and suggests the absence of the interchain correlation above 49 K. A set of superlattice reflection was found below 49 K suggesting the formation of an ordered structure of three-dimension. This superstructure is ascribed to the molecular displacement caused by the Wigner crystal of electrons through the electron-lattice interaction [67]. The 4 p structure is considered to be formed predominantly on the TTF stacks. The 2kp superstructure is rather ascribed to TCNQ stacks. This is suggested [68] by detailed analyses of the results of X-ray, neutron, EPR and NMR measurements. 

Below Tp, the static ( locked ) CDW of the conduction electrons at 2 kp (or 4 kp), couple with the other atomic or molecular electrons in the lattice, cause a slight lattice distortion, and gives rise to extra X-ray reflections. Above Tp, these CDW are mobile, with no phase locking between excitations on nearby chains one sees X-ray diffuse reflections, similar to thermal diffuse scattering, which sharpen as T is lowered. Below Tp the static distortion produces new, usually weak, reflections between reciprocal-lattice layer lines. When the band filling is a rational fraction (1/4, 1/2, 2/3,1, etc.) then these reflections overlap with certain Bragg reflections of the background lattice, and are more difficult to detect. 

Durr et al. demonstrated the first application of scaling laws to organic systems for the deposition of diindenoperylene (DIP) on Si02 [50]. They utilized x-ray reflectivity, AFM, and diffuse x-ray scattering to analyze the temporal and spatial fluctuations of the surface roughness. To do this, they used an extended version of... 

The ability to infer aspects of water structure directly at the mineral/water interface using high-resolution X-ray reflectivity is an important complement to vibrational spectroscopy methods. X-ray reflectivity and other techniques, notably X-ray standing waves, can be used to derive a well-constrained molecular-scale model of the structure and distribution of sorbed ions at or near the mineral/water interface (including physisorbed ions and those in the diffuse portion of the EDL). 

---