Two forms of nanoscale order in amorphous GexSe1−x alloys

We analyze the evolution of nanoscale order in amorphous GexSe1−x alloys using fluctuation electron microscopy. We identify two distinct structural signatures that behave independently as a function of composition. The strong signature of order at scattering vectors k ∼ 0.30 and 0.55 A−1 in Ge-rich alloys (x > 0.40) diminishes rapidly in Se-rich compositions. However, a second signature of order at scattering vector k ∼ 0.15 A−1 appears only for compositions in the middle range x = 0.30–0.53. We interpret that structural ordering occurs among pure Ge tetrahedra or among GeSe4 tetrahedra, respectively, in amorphous GexSe1−x.

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