Shallow angle x-ray diffraction from in-situ silica:titania sol-gel thin films

X-ray diffraction at shallow angles of incidence has been used to examine three silica:titania sol-gel thin films. Comparison with transmission x-ray diffraction measurements of similar materials in the bulk shows a distinct increase in disorder in the silica network. An increase in porosity of the network in thin films is also likely, suggested by an increase in Si-O-H bonds. No differences in structure between samples with differing titania contents were observed using this technique

A reverse monte carlo modeling study of diamond-like carbon

Reverse Monte Carlo (RMC) modeling is a novel method of obtaining 3D information on atomic structure by combining complementary data from various experiments. X-ray and neutron diffraction data, nuclear magnetic resonance results, and chemical considerations have been used as constraints in the RMC process to model diamond-like carbon, an amorphous hydrogenated form of carbon with unusual properties. The results have given us new insight into this interesting material

Development of Ultrasmall-Angle Scattering for Studies of Colloidal Systems

Ultrasmall-angle x-ray scattering (USAXS) using the Bonse-Hart twin-crystal diffractometer system 1 on a synchrotron radiation source (SRS) is being developed as a technique for studying the structure of colloidal dispersions and other inhomogeneous materials with features in the size range 500 angstrom to 1-mu-m. The use of well-characterized colloidal samples in this range highlights the problems which must be resolved in order to obtain reliable data from the system. This paper addresses the specific problems of attenuation, absorption, detector dead time, and smearing for the USAXS configuration. The system has been used to study a variety of materials and some previously unobserved features have been found in the scattering profile of a colloidal latex. This serves to indicate the value of the improved system in the field of colloidal science

Small-Angle Scattering Studies of Meso-Scopic Structures with structures with synchrotron X-Rays

The use of small-angle X-ray scattering techniques for the study of spatial inhomogeneities over the range 20 Angstrom to 2 mu m is reviewed. The basic formalism for scattering by an inhomogeneous medium is developed with particular reference to liquid suspensions, porous solids and solid aggregates. The instrumentation available on the Synchrotron Radiation Source at the Daresbury Laboratory is briefly presented and the use of the Bonse-Hart method for studies at ultra-low scattering angles described. The extraction of structural information for a range of natural and synthetic materials is presented with particular reference to microemulsions, porous silicas, clays and composites. The complementarity of X-ray and neutron techniques is critically reviewed and prospects for future developments, particularly for the study of anisotropic systems, are discussed

A Reverse Monte-Carlo Modeling Study Of Amorphous Hydrogenated Carbon

The results of a Reverse Monte Carlo (RMC) modelling of amorphous hydrogenated carbon (a-C:H) are presented. The RMC method has been implemented with the introduction of maximum co-ordination number and ''triplet'' constraints, whilst fitting both neutron and X-ray diffraction data. The positions of 5000 ''atoms'' in a box, with full periodicity, are altered until the associated model structure factor, S(Q), and pair distribution function, G(r), agree with the analogous experimental data within the errors. Once the data has been fitted, it is possible to generate model partial pair distribution functions (i.e. those associated with C-C, C-H and H-H), bond angle distributions, co-ordination number distributions, etc. X-ray data is used to provide information on the carbon-carbon network, whilst neutrons are also sensitive to the cross-terms involving hydrogen. The fitting of both types of data simultaneously therefore provides sufficient information to generate a viable ''physical'' model for the structure of these materials. The effects of increasing the number density inside the box have also been investigated

Determination of Anisotropic Features in Porous Materials by Small-Angle X-Ray-Scattering

Some synthetic and natural materials exhibit anisotropic features due to the way that they have been fabricated. Small-angle scattering techniques with x-rays or neutrons may be used to probe this anisotropy by observation of the azimuthal variation in scattering intensity from an oriented sample. Results will be presented for a series of materials, in either fibre or disk form, which give distinctive patterns corresponding to ordered or disordered structures with spatial characteristics in the 10-2000 Angstrom range. The possible extension of the method to other materials and further development of the technique is also considered

Inhomogeneities in acid-catalyzed titania-silica and zirconia-silica xerogels as revealed by small-angle x-ray scattering

The small-angle x-ray scattering (SAXS) technique was used to investigate inhomogeneities on the scale of 10 to 600 Angstrom in acid-catalyzed titania-silica and zirconia-silica xerogels. SAXS of (TiO2)(SiO2)(1-x) and (ZrO2)(x)(SiO2)(1-x) xerogels with x 0.3 showed the presence of phase-separated regions of metal oxide, which were initially amorphous and crystallized at higher temperatures. A (TiO2)(0.18)(SiO2)(0.82) xerogel that was not initially phase separated became phase separated after heat treatment at 750 degrees C due to reduced solubility of Ti in the silica network

X-ray diffraction studies of silica:titania sol-gel glasses

X-ray diffraction has been used to study a series of powdered silica:titania sol-gel glasses with titania contents ranging from a 'pure' silica sample through to high titania levels where phase separation may have occurred. Analysis of the data reveals the change in second and third neighbour coordination numbers with increasing Ti content and confirms that for low titanium contents the sol-gels are atomically mixed

An X-ray absorption study of doped silicate glass, fibre optic preforms

Optical fibre preforms, which have their germanosilicate core regions doped with small quantities of the rare-earth element erbium, have been studied using Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) at the germanium K absorption edge. These studies were performed using a circular X-ray beam of 100 mu m diameter, allowing information to be gathered as a radial function of position across the core region of the preform. This positioning was accomplished by means of a motorized pinhole collimator and sample stage developed for use on the focused X-ray beamline 8.1, at the SRS, Daresbury Laboratory, UK. The EXAFS results are consistent with the germanium sites coordinated to surrounding oxygen atoms at a mean distance of 0.17 nm. Absorption maps of the rare-earth and germanium distribution across the core region of the preforms have also been obtained, showing a correlation between the distributions of the two atom types

Small-Angle X-Ray-Scattering Studies Of a-Si-C-H

Small-angle X-ray scattering studies have been performed on a series of four a-Si:C:H alloys, prepared by rf glow discharge decomposition of varying proportions of propane and silane, in an attempt to elucidate their mesoscopic structure. The observed broad scattering peak has been interpreted as originating from irregular, elongated voids with a repeat distance of about 20 Angstrom and correlation length of about 25 Angstrom. The implications of this result in explaining the photo-oxidation properties of the material are also discussed