北海道大学 · 材料科学
田中恵二教授の研究室では、 chalcogenideガラスの構造・電子状態の組成依存性に着目し、平均結合数2.67における構造的相転移とその物性への影響を、トポロジー的・パーコレーション的視点から解明しています。光誘起流動性や光誘起膨張、可逆的光吸収変化（photodarkening）といった光物性のメカニズムを、X線回折や光学的測定を用いて詳細に解明しており、特に光による構造制御と物性制御の可能性に注目しています。微細加工応用や光エレクトロニクスへの展開も視野に入れた、物性と構造の相関を解明する研究が中心です。
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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
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