Allotropic phase transformation and photoluminescence of germanium nanograins processed by high-pressure torsion

Yoshifumi Ikoma, Takamitsu Toyota, Yoshimasa Ejiri, Katsuhiko Saito, Qixin Guo, Zenji Horita

Research output: Contribution to journalArticle

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Abstract

We report on allotropic phase transformation and nanograin refinement of Ge by severe plastic deformation using high-pressure torsion (HPT) under a pressure of 24 GPa. No appreciable formation of metastable phases occurred under compression prior to torsion, while a diamond cubic Ge-I phase and a tetragonal Ge-III phase were observed in the HPT-processed samples. The formation of the Ge-III phase was enhanced by introduction of shear strain. TEM observations revealed that HPT-processed samples consisted of micro- and nanograins. It was indicated that grain refinement occurred due to the introduction of high density of lattice defects in metallic Ge-II during HPT processing, and then Ge-II transformed not only back to Ge-I but also to metastable Ge-III upon unloading. The Ge-III phase reversely transformed to Ge-I by intense Ar-ion laser irradiation or by thermal annealing. No appreciable photoluminescence (PL) was observed from the HPT-processed sample, while a broad PL peak in the range of 600–800 nm appeared after intense laser irradiation. A similar PL peak was also observed from thermally annealed samples. These results suggest that the appearance of the PL peak arises from Ge-I nanograins.

Original languageEnglish
Pages (from-to)138-143
Number of pages6
JournalJournal of Materials Science
Volume51
Issue number1
DOIs
Publication statusPublished - Aug 11 2015

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Germanium
Torsional stress
Photoluminescence
Phase transitions
Laser beam effects
Diamond
Metastable phases
Crystal defects
Grain refinement
Shear strain
Unloading
Diamonds
Plastic deformation
Compaction
Annealing
Ions
Transmission electron microscopy
Processing

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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Allotropic phase transformation and photoluminescence of germanium nanograins processed by high-pressure torsion. / Ikoma, Yoshifumi; Toyota, Takamitsu; Ejiri, Yoshimasa; Saito, Katsuhiko; Guo, Qixin; Horita, Zenji.

In: Journal of Materials Science, Vol. 51, No. 1, 11.08.2015, p. 138-143.

Research output: Contribution to journalArticle

Ikoma, Yoshifumi ; Toyota, Takamitsu ; Ejiri, Yoshimasa ; Saito, Katsuhiko ; Guo, Qixin ; Horita, Zenji. / Allotropic phase transformation and photoluminescence of germanium nanograins processed by high-pressure torsion. In: Journal of Materials Science. 2015 ; Vol. 51, No. 1. pp. 138-143.
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