TY - JOUR
T1 - Allotropic phase transformation and photoluminescence of germanium nanograins processed by high-pressure torsion
AU - Ikoma, Yoshifumi
AU - Toyota, Takamitsu
AU - Ejiri, Yoshimasa
AU - Saito, Katsuhiko
AU - Guo, Qixin
AU - Horita, Zenji
PY - 2015/8/11
Y1 - 2015/8/11
N2 - 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.
AB - 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.
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U2 - 10.1007/s10853-015-9328-y
DO - 10.1007/s10853-015-9328-y
M3 - Article
AN - SCOPUS:84946501297
VL - 51
SP - 138
EP - 143
JO - Journal of Materials Science
JF - Journal of Materials Science
SN - 0022-2461
IS - 1
ER -