G. Heide

Direct view of the structure of a silica glass fracture surface

Abstract The fracture minor surface of a silica glass, prepared at 1×10−11 mbar in the chamber of an ultra-high-vaccum-atomic-force microscope (UHV–AFM), was imaged at 1×10−8 mbar with high spatial resolution. The features directly seen were interatomic distances, e.g., O–O and Si–O, groupings of atoms, e.g., SiO4 tetrahedra and rings of tetrahedra, and network holes. A comparison with a structure calculated by a molecular dynamics simulation gave good coincidence. This direct view of the silica glass surface supports Zachariasens network structure model of glass.

Direct view of the structure of different glass fracture surfaces by atomic force microscopy

Abstract Silica, silicate, borosilicate and heavy metal fluoride glasses were fractured under UHV conditions. The fracture mirror surfaces then were imaged by atomic force microscopy. The atomically resolved images display a fully interconnected random network arrangement for the silica glass, modified random network geometries with percolation paths for the silicate glasses, a structure with higher connectivity with some short percolation paths only for the borosilicate glass and a strongly interconnected structure for the heavy metal fluoride glass, probably with some chain- and ring-like geometric elements. Sodium diffusion, which is supposed to follow mainly these percolation paths, is qualitatively in line with the number, length and width of these paths.

Uniformity in large area ZnO:Al films prepared by reactive midfrequency magnetron sputtering

Al-doped zinc oxide (ZnO:Al) films were deposited on glass substrates using a reactive midfrequency magnetron sputtering process. The optical transmission and reflection as well as the electrical resistivity of the films prepared on an area of 1000×600 mm2 were determined at different locations. Films with a uniform distribution of resistivity between 2.9×10−4 and 3.6×10−4 Ω cm and transmittance up to 88% in the visible spectral range were obtained. The ellipsometric spectra of the films were also analyzed using the Drude–Lorentz model. The calculated thicknesses of the films agreed well with those measured by a step profilometer. Secondary neutral mass spectrometry depth profiling showed uniform contents of Zn and O elements, while a slight periodic variation of the Al content was observed at different depths inside the film. A transition zone of 35–55 nm in width between the films and glass substrates due to the interdiffusion was also observed.

Abbe numbers and refractive indices of tektites and volcanic glasses

Knowledge of the optical properties is highly important for technical glasses. However, the optics of natural glasses are insufficiently described. Thus, Abbe numbers and refractive indices of several obsidians and tektites as well as pitchstone and synthetic obsidians with different water content are presented. Results are compared to calculated values. Refractive index measurements were in very good agreement with theoretical calculations depending on the glass chemistry. The Abbe number was found to be comparably low in the case of obsidians, but it increased after heat treatment. This is due to the high water content and magnetite particles.

Structural classification of natural non-crystalline silicates

Using wide-angle X-ray diffraction measurements, atomic force microscopy and several physical properties of natural non-crystalline silicates, a structural classification can be derived. Qualitative differences in the intermediate range structure between tektites and relaxed tektites are found, but strength changes with water content.