Surface topographic study of chalcogenide thin films of GexSb(As)₄₀-xS₅₀Te₁₀ glasses.
The surface topography and fractal properties of GexSb(As)40-xS50Te10 (x=10, 20, 27 at.%) films, evaporated onto glass substrates, have been studied by atomic force microscopic imaging at different scales. The surface of the chalcogenide films is smooth (<5 nm roughness), isotropic and having some particular differences in texture. All films are self-similar with Mean Fractal Dimension in the range of 2.25-2.63. The films with GexSb40-xS50Te10 composition are more uniform in terms of surface morphology (grains structure) than those with GexAs40-xS50Te10 composition for which the film surface exhibits a superimposed structure of large particles at x=10 and 20 at.%.
Advanced micromorphology study of microbial films grown on Kefir loaded with Açaí extract.
In this work, an advanced analysis of the 3D surface microtexture of the microbial films grown on Kefir loaded with Açaí extract was performed. Atomic force microscopy was used to characterize the 3D surface microtexture data in correlation with the stereometric analyses to allow a better understanding of the surface micromorphology consistent with ISO 25178-2: 2012. Two new parameters, fractal succolarity and fractal lacunarity, have been inserted for a quantitative approach to microtexture. The results revealed that the morphology was affected by the increase of the Açaí concentration in biofilms, as well as the fractal succolarity and lacunarity. Adhesive bacteria of the genus Lactobacillus were observed for the lowest concentrations of Açaí. Moreover, it was found that the surface of the biofilms has shown saturation when the concentration has changed from 4 to 6 % of Açaí. These results are of great interest in the characterization of surfaces with promising application like skin dressing.
Structural phase transitions in chalcogenide glasses.
The composition dependence of the structural and electronic properties in chalcogenide glasses suggests that there exists a structural phase transition at the average coordination number of 2.67. Materials having smaller coordination numbers are characterized by molecular structures, and oth­ erwise three-dimensional networks govern the properties. The result is discussed in light of topo­ logical and percolative arguments. I. INTRODUCTION Since Zachariasen's pioneering work! one of the long­ standing problems in condensed-matter physics has been how to grasp the structure of disordered solids. For crys­ talline materials, Bragg's equation gives, in principle, a method for uniquely determining periodic lattices, and understanding of relationships between microscopic structures and macroscopic properties has been a subject in solid-state physics. Amorphous solids, as opposed to crystals, possess no long-range order, and since we have no established techniques capable of identifying non­ periodic configurations, physics on amorphous materials is far behind that of the crystalline science. A lack of the translational regularity, however, makes it possible to change continuously the elemental ratios in glassy compounds. Hence, compositional studies seem to be vitally important for amorphous materials. It is a pur­ pose of this paper to emphasize such an approach, in which the dependence of various properties on composi­ tions for series of glassy chalcogenide semiconductors is exploited to draw a structural picture in a coherent fashion. Upon examining the amorphous structure of covalent glasses, we may classify building elements into two com­ ponents;2 one is normal bonding structure consisting of covalent bonds of densities on orders of 1022 _1023 cm - 3, which can be specified by chemical and topological na­ tures, and the other is defects, e.g., impurities, dangling bonds, valence-alternation pairs, and wrong bonds (homopolar bonds in stoichiometric alloys). The density of defective bonds is, in general, less than 10-2 of that for the covalent bonds, and therefore structural behaviors are determined mostly by the normal configurations. Further, these are primarily responsible for such elec­ tronic properties as the band-gap energy, in contrast to gap states originating from defects. Thus, consideration of glassy characters using topological concepts may give fruitful ideas similar to those obtained through the unified understanding of crystalline properties based on periodic lattices. We will discuss in the present work physical characteristics seemingly governed by the topo­ logical bonding structure, which involves a hierarchy of correlation ranges, from short to medium. Re~arding the short-range configuration extending to ~ 5 A in scale, the present status of understanding is more or less substantial. 3,4 X-ray diffraction and extend­ ed x-ray absorption fine-structure (EXAFS) studies give 39 information on radial distributions, and Raman­ scattering spectra are feasible to examine molecular clus­ ters. These investigations manifest that the short-range orders in amorphous materials are nearly the same as those in crystalline counterparts. The coordination num­ ber is preserved in covalent glasses, obeying the so-called 8 - N rule, where N is the valency of an atom. The rule suggests that the numbers of nearest-neighbor atoms for S(Se), As, and Si(Ge) are, respectively, 2, 3, and 4. The average coordination number Z of covalent bonds is a good measure representing characters of atomic units. 5 If a sample has a composition of Ge(Si)xAsyS(Se)!_x _y' then