N.A. Grigorieva

Revealing stacking sequences in inverse opals by microradian X-ray diffraction

We present the results of the structural analysis of inverse opal photonic crystals by microradian X-ray diffraction. Inverse opals based on different oxide materials (TiO2, SiO2 and Fe2O3) were fabricated by templating polystyrene colloidal crystal films grown by the vertical deposition technique. Our results suggest that most inverse opal films possess dominating twinned face-centered cubic structure accompanied by some fragments of hexagonal close-packed and random hexagonal close-packed structures. The studied samples possessed individual structures with different ratios of the above fragments. By fitting the results of the angular-dependent X-ray diffraction by the Wilson model we estimate the stacking probability α in the studied samples to be ~0.7–0.8. Microradian X-ray diffraction therefore provides detailed structural information on opal-based photonic crystals and can be applied to opaque inverse opals or the samples with a periodicity <300 nm, whose structure cannot be investigated by conventional optical methods.

Magnetic properties of a two-dimensional spatially ordered array of nickel nanowires

The structural and magnetic characteristics of two-dimensional spatially ordered arrays of magnetic nickel nanowires embedded in the anodized alumina template have been investigated. It has been shown using small-angle polarized-neutron diffraction that, there exists the samples under investigation, in a highly ordered hexagonal structure of pores and magnetic nanowires separated by a characteristic distance d = 106 ± 2 nm. An analysis has been made of different contributions to neutron scattering, such as the nonmagnetic (nuclear) contribution, the magnetic contribution dependent on the magnetic field, and the interference contribution indicating a correlation between the magnetic and nuclear structures. The performed analysis of the results obtained has demonstrated that, when the magnetic field is applied perpendicular to the longitudinal axis of the nanowire in a completely magnetized sample, there arise demagnetizing fields around each nanowire that form a regular hexagonal lattice.

SANS study of new magnetic nanocomposites embedded into the mesoporous silica

Abstract Magnetic nanocomposites embedded into mesoporous silica have been studied by Small Angle Polarized Neutron Scattering. It is well known that mesoporous silica represents a highly regular hexagonal structure of nanotubes. For the samples under study a diffraction peak in SANS at q c ≈1.7 nm −1 is observed which corresponds to a hexagonal structure with periodicity a≈3.5 nm . We found that the intercalation of iron into the silica matrix leads to some changes of the matrix itself. Additionally, the nuclear–magnetic interference in scattering of polarized neutrons was investigated. The interference reveals the absence of a periodical magnetic structure at room temperature which would be consistent with the hexagonal structure of nanotubes. The correlation between magnetic nanoparticles and pores of the matrix is revealed in the interference scattering at q⪡qc.

Analysis of the imperfection of opal-like photonic crystals synthesized on conducting substrates

The type and degree of imperfection for opal-like photonic crystals on conducting substrates have been investigated using synchrotron small-angle X-ray scattering with a microradian resolution. It has been demonstrated that self-assembly of poly(styrene) spheres by the vertical deposition method leads to the formation of a face-centered cubic structure on a mica/Au substrate and a random hexagonal close packing on a glass substrate with the In2O3(SnO2) conducting coating.