Hokkaido University · Materials Science
Professor Keiji Tanaka's research lab specializes in the fundamental physics and materials science of chalcogenide glasses, focusing on light-matter interactions, structural dynamics, and electronic properties. Key research directions include photoinduced structural modifications such as fluidity, expansion, and birefringence, as well as reversible photodarkening and band-gap engineering under illumination and pressure. The lab combines advanced x-ray diffraction, optical spectroscopy, and theoretical modeling to understand the topological and configurational origins of these phenomena at the atomic level. Their work bridges amorphous materials physics with applications in microfabrication, optical devices, and functional glass technologies.
Figures are computed from collected data and may differ slightly.
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 otherwise three-dimensional networks govern the properties. The result is discussed in light of topological and percolative arguments.
It was found that chalcogenide glasses can be shaped by stressing the glass under light illumination because light illumination enhances the fluidity of the glass. The mechanism of photoinduced fluidity was found to be photoelectronic, that is, athermal. The process can be applied to microfabrication of optical fibers and glassy films with a typical dimension of 10 to 100 micrometers.
Mechanisms of photoexpansion in chalcogenide glasses have been studied in three respects. A detailed x-ray investigation of ${\mathrm{As}}_{2}{\mathrm{S}}_{3}$ shows that the photoexpansion can be connected with asymmetric broadening of the first sharp diffraction peak. Comparison between radiation-induced volume changes and density ratios of glassy-to-crystalline forms in ${\mathrm{As}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{SiO}}_{2}$ implies that ${\mathrm{As}}_{2}{\mathrm{S}}_{3}$ can expand sin
Mechanisms of the reversible photodarkening phenomenon have been studied for amorphous S and Se. These materials exhibit smaller photodarkening effects when illuminated with sub-bandgap illumination at 80 K. A configurational model is proposed for interpreting the results, and parameters characterizing the model are estimated. This model is connected with a structural model which assumes photoinduced bond twisting. By using the modified valence-forcefield constants, it is shown that the structur
Shifts in the optical-absorption edges induced by band-gap illumination and annealing under pressure have been studied for ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ and Se. Both materials, if annealed at 1 atm beforehand, undergo a decrease in the band-gap energy with illumination under pressure. This decrease is accompanied by a similar degree of densification as that induced by annealing. The ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ specimen annealed under pressure at the glass-transition temperature
Open papers in the app to read, cite, and organize with AI.
