偏振拉曼散射研究ZnO单晶纳米压痕区内的晶格畸变分布

Polarized Micro-Raman Study of the Nanoindentation-Induced Lattice Deformation in ZnO Single Crystal

通过结合纳米压痕和偏振拉曼散射技术对压应力影响下ZnO单晶晶格出现的变化进行了研究。位错的滑移是导致ZnO单晶中出现多处塑性变形的原因而非相变。之后采用偏振拉曼Mapping成像技术以E2(high)模为对象,监视其在整个压痕区内的强度变化分布。在压痕区中心累积的应力通过位错的滑移而释放,同时导致压痕区中心处的晶格畸变程度最为严重。伴随着晶格失配的加剧,拉曼选择定则放宽,在Z(XX)Z-配置下较弱的LO得到增强,原本非拉曼活性的B1(high)模出现。此外,在Z(XY)Z-偏振下压痕区左侧的拉曼光谱中观察到位于130cm-1处的拉曼异常振动模。此峰的出现可能与压痕区左侧由刃位错所形成的应力场吸引间隙离子导致的晶格畸变有关。

Abstract： The contact-induced deformation behavior of optical phonons in ZnO single crys- tal （wurtzite） is investigated using a combination of nanoindentation with a Berkovich in- denter and polarized Raman spectroscopy. Multiple discontinuities （＂pop-in＂ events） in load-displacement curve were observed during indentation loading. After indentation, no evidence of a phase transformation was been observed by Raman scattering. Results show that the initiation of slip is identified as the major mode of plastic deformation in ZnO. Furthermore, based on the intensity Raman map of E2 （high） mode and the pressure de- pendence of the pbonon frequency for E2 （high） mode, it reveals that the greatest deforma- tions concentrated at the center of indentation, while the strain built up in this region has been relaxed through the slipping of contact-induced defects. The board band has been ob- served in Z（XX） Z geometry with the range from 500-600 cm-1. The appearance of the band is attributed to the lattice damages induced by compressive press, which confirms that this band is only related to the deformations of microstructure. Moreover, an Addi w tional mode （around 130 cm-1） in Z（XY） Z due to relaxation of Raman selection rules. spectrum is assigned to TA（M） and emerges due to relaxation of Raman selection rules.