Direct observations of multi-cyclic nanoindentation-induced phase transformations in single-crystal Ge

Koji Kosai, Jiwang Yan

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Multi-cyclic nanoindentation experiments with various holding loads were carried out on single-crystal Ge to investigate pressure-induced phase transformation behaviors. Cross-sectional transmission electron microscopic observation and laser micro-Raman spectroscopy of the indents revealed various phase transformation behaviors at different holding loads. Distinctive phase transformation behaviors were observed under various loading and unloading conditions. With a low holding load, a broad phase transformed region containing r8-Ge phase and dislocations was generated. A middle holding load promoted twinning but limited phase transformations. On the other hand, a densely transformed region containing dc-Ge, a-Ge, r8-Ge and st12-Ge was widely formed at a high holding load. In addition, the calculation results of the average contact pressure in the last unloading step verified the occurrence of these phase transformations. By integrating these results, a path diagram for phase transformations of single-crystal Ge during multi-cyclic nanoindentation was established, which is useful for understanding the subsurface damage formation in mechanical processing of the material.

Original languageEnglish
Article number075065
JournalMaterials Research Express
Issue number7
Publication statusPublished - 2019 Apr 24


  • cyclic load
  • mechanical processing
  • microstructural change
  • nanoindentation
  • phase transformation
  • single-crystal germanium
  • subsurface damage

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Polymers and Plastics
  • Metals and Alloys


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