Real Diffraction Patterns Research Articles

The formation of diffraction gratings by the deposition of SiO2 colloidal microspheres

A simple way of fabrication of diffraction gratings with the help of deposition of SiO2 colloidal particles on vertical glass substrate has been proposed. The method is based on an intermittent, “stick–slip” motion of the suspension meniscus during liquid evaporation. The deposition was carried out at different temperatures (from 27 to 50 °C). Ethanol-based suspensions with a SiO2 concentration in the range of 0.2–0.83 g/L, both narrow-dispersed with SiO2 particle diameter of about 200–300 nm and polydisperse, were used. As a result, the structures consisting of parallel ridges of deposited SiO2 microspheres repeating with a period of 140–200 μm and empty gaps between them have been prepared. The diffraction gratings formation is possible only at temperatures higher than the critical value of about 30 °C, and their period enhances with the temperature increase. The real diffraction patterns of light have been obtained for such structures for the first time. Further modification of prepared structures with the purpose of their strengthening has been realized with the help of high-dose Ag+ implantation (4 × 1016 ions/cm2, ion energy of 30 keV) followed by sonication.

Kermesite, Sb2S2O: crystal structure revision and order–disorder interpretation

Kermesite, Sb2S2O, is a desymmetrized order-disorder (OD) structure of layers. Two data sets were recorded using twinned crystals from Pezinok, Slovakia (named as Pz21, Pz24). The primitive unit cell is triclinic, P1, Z = 4, cell parameters are a = 8.1416 (3), b = 10.6968 (3), c = 5.7835 (2) Å, α = 102.758 (3), β = 110.657 (3), γ = 101.020 (3)°, R(obs) = 0.0243 (Pz21), and a = 8.1372 (2), b = 10.6969 (2), c = 5.7840 (1) Å, α = 102.787 (2), β = 110.606 (2), γ = 100.983 (2)°, R(obs) = 0.0321 (Pz24). The structure can also be described in the non-standard pseudo-monoclinic octuple (Z = 32), F-centered (Kupčík) cell with extra points in 1/4,1/4,0; 1/4,3/4,1/2; 3/4,1/4,1/2; 3/4,3/4,0, with parameters a = 21.6466 (9), b = 8.1416 (3), c = 20.3824 (9) Å, α = 90.079 (4), β = 101.985 (5), γ = 89.948 (4)° (Pz21), and a = 21.6558 (5), b = 8.1372 (2), c = 20.3859 (8) Å, α = 90.028 (3), β = 101.994 (3), γ = 89.986 (2)° (Pz24). The structure is built of layers parallel to the bc plane, stacked along the a vector of the octuple cell, composed of ribbons parallel to the b vector: (i) ribbon of two strips of SbO5 flattened quadrangular pyramids, sharing apical edges; (ii) ribbon of edge-sharing corrugated lozenges SbO3S. Basal S atoms of pyramids share corners of lozenges. Sb atoms are displaced out of coordination polyhedra into the inter-layer space. The OD layer comprises adjacent halves of the structure building layers. The layer group is A(1)2/m1, the protocell is defined by b, c, (a/4)sin β. The MDO1 (4A) polytype is generated by repetition of the t(1,1/4,0) [or alternatively t(1,-1/4,0)] translation. The co-existence of two kinds of domains give rise to the twinning. The twin operation is 2[010], twin index 2. The total continuation of [. a2 .] generates the MDO2 (2M) polytype, space group A12/a1. Simulated and real diffraction patterns are presented. The important values (edges, angles) and displacements of atoms due to the desymmetrization were evaluated. The comparison with structures of stibnite, bismuthinite and aikinite is added.