Deformation-Induced Transformations of Nanocrystalline Ge-Si Film During Indentation
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0924-Z03-05
Deformation-Induced Transformations of Nanocrystalline Ge-Si Film During Indentation Z.W. Xu1, A.H.W. Ngan1, J.G. Huang2, and X.K. Meng2 1 Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China, People's Republic of 2 Department of Materials Science and Engineering, Nanjing University, Nanjing, 210093, China, People's Republic of ABSTRACT Thin films of Ge-Si with a duplex nanocrystalline structure were fabricated by magnetron co-sputtering and nanoindentations were made on these films. Transmission electron microscopy and Raman spectroscopy were used to analyze the deformed microstructures in the residual indentations. Amorphization and diamond-cubic (dc) to non-diamond-cubic (non-dc) phase transformation were observed and considered as the major micromechanisms in the deformation of the Ge-Si duplex nanocrystals. INTRODUCTION The deformation micromechanisms of nanocrystalline metals involving the behaviours of dislocations and grain boundaries have been studied in some detail [1]. The deformation of nanocrystalline group-IV, III–V, and II–VI semiconductors is more complicated because a series of high-pressure and amorphous phases has been identified [2]. Although some work has been done on the indentation-induced phase transformation of bulk Ge or Si [3,4], little is known about the deformation micromechanisms of nanocrystalline semiconductors. On the other hand, duplex nanocrystalline Ge-Si exhibits visible photoluminescence and thus has potentials in applications as optoelectronic materials [5]. The present study therefore aims at to investigate the deformation micromechanisms of nanocrystalline Ge-Si. EXPERIMENTAL PROCEDURES The Ge-Si films were deposited onto Al foils without substrate heating by DC sputtering using a bi-element sputtering target. Nanoindentation tests were then carried out on the films using a Berkovich indenter of CSEM® Nanohardness Tester by the peak loads of 30 mN and 60 mN respectively, with the same loading and unloading rate of 200 mN/min. After the indentations were made, the Al substrate was etched away in the selected areas using hydrochloric acid under the observation with an optical microscope. Etching and thinning were also done on virgin areas of the as-deposited films without indentation. The etched samples were rinsed in de-ionized water and dried in air. The TEM observation was performed in a Philips Tecnai 20 and a JEOL 2010F FE-TEM microscope. Raman scattering was performed on a
JY-HR800 Raman spectrometer using a 488-nm laser source. RESULTS (a)
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Fig. 1. (a-b) TEM image and diffraction pattern of the as-deposited film. (c-f) TEM images and diffraction patterns of an indent at 30mN (c-d) and another one at 60 mN (e-f). Fig. 1(a-b) exhibits the nanocrystalline structure in the as-deposited film. Fig. 1(b) shows pairs of closely spaced diffraction rings of the Ge and Si dc structures respectively. Consistent with previous observations [5], the as-deposited state of the film had a structure consi
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