Nanotwin orientation on history-dependent stress decay in Cu nanopillar under constant strain

Yu-An Shen; Li Chang; Shou-Yi Chang; Y-C Chou; K N Tu; Chih Chen

doi:10.1088/1361-6528/ac46d9

Nanotwin orientation on history-dependent stress decay in Cu nanopillar under constant strain

Nanotechnology. 2022 Jan 21;33(15). doi: 10.1088/1361-6528/ac46d9.

Authors

Yu-An Shen^{1

2

3}, Li Chang^{1

2}, Shou-Yi Chang⁴, Y-C Chou^{5

6}, K N Tu^{7

8}, Chih Chen^{1

2}

Affiliations

¹ Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan 30010, Republic of China.
² Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30010, Republic of China.
³ Department of Materials Science and Engineering, Feng Chia University, Taicuhng, Taiwan 30010, Republic of China.
⁴ Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan 30013, Republic of China.
⁵ Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan 30010, Republic of China.
⁶ Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan, Republic of China.
⁷ Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, CA 90095, United States of America.
⁸ Department of Materials Science and Engineering and Dept. of Electrical Engineering, City University of Hong Kong, Kowloon, Hong Kong.

PMID: 34965523
DOI: 10.1088/1361-6528/ac46d9

Abstract

Cu with nanotwin (NT) possesses great electrical, mechanical, and thermal properties and has potential for electronic applications. Various studies have reported the effect of NT orientation on Cu mechanical properties. However, its effect on Cu stress-relaxation behavior has not been clarified, particularly in nano-scale. In this study, Cu nanopillars with various orientations were examined by a picoindenter under constant strain and observed byin situTEM. The angles between the twin plane and the loading direction in the examined nanopillars were 0°, 60°, to 90°, and a benchmark pillar of single-crystal Cu without NT was examined. The stress drops were respectively 10%, 80%, 4%, and 50%. Owing to the interaction by NT, the dislocation behavior in nanopillars was different from that in bulk or in thin film samples. Especially, the rapid slip path of dislocations to go to the free surface of the nanopillar induced a dislocation-free zone in the 0° nanopillar, which led to work-softening. On the contrary, a high dislocation density was observed in the 90° nanopillar, which was generated by dislocation interaction and obstruction of dislocation slip by twin planes, and it led to work-hardening. The findings reveal the NT orientation in Cu nanopillars affected stress relaxation significantly.

Keywords: in situ observation; nanopillar; nanotwin Cu; stress relaxation.