Neeman Lior, Ben-Zvi Regev, Rechav Katya, Popovitz-Biro Ronit, Oron Dan, Joselevich Ernesto
Departments of Physics of Complex Systems and ‡Materials and Interfaces and §Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
Nano Lett. 2017 Feb 8;17(2):842-850. doi: 10.1021/acs.nanolett.6b04087. Epub 2017 Jan 25.
The growth of horizontal nanowires (NWs) guided by epitaxial and graphoepitaxial relations with the substrate is becoming increasingly attractive owing to the possibility of controlling their position, direction, and crystallographic orientation. In guided NWs, as opposed to the extensively characterized vertically grown NWs, there is an increasing need for understanding the relation between structure and properties, specifically the role of the epitaxial relation with the substrate. Furthermore, the uniformity of crystallographic orientation along guided NWs and over the substrate has yet to be checked. Here we perform highly sensitive second harmonic generation (SHG) polarimetry of polar and nonpolar guided ZnO NWs grown on R-plane and M-plane sapphire. We optically map large areas on the substrate in a nondestructive way and find that the crystallographic orientations of the guided NWs are highly selective and specific for each growth direction with respect to the substrate lattice. In addition, we perform SHG polarimetry along individual NWs and find that the crystallographic orientation is preserved along the NW in both polar and nonpolar NWs. While polar NWs show highly uniform SHG along their axis, nonpolar NWs show a significant change in the local nonlinear susceptibility along a few micrometers, reflected in a reduction of 40% in the ratio of the SHG along different crystal axes. We suggest that these differences may be related to strain accumulation along the nonpolar wires. We find SHG polarimetry to be a powerful tool to study both selectivity and uniformity of crystallographic orientations of guided NWs with different epitaxial relations.
由于能够控制水平纳米线（NWs）的位置、方向和晶体取向，由与衬底的外延和图形外延关系引导生长的水平纳米线正变得越来越有吸引力。与广泛研究的垂直生长纳米线不同，对于引导纳米线而言，越来越需要了解结构与性能之间的关系，特别是与衬底的外延关系所起的作用。此外，沿引导纳米线以及在衬底上晶体取向的均匀性仍有待检验。在此，我们对在R面和M面蓝宝石上生长的极性和非极性引导ZnO纳米线进行了高灵敏度的二次谐波产生（SHG）偏振测量。我们以无损方式对衬底上的大面积区域进行光学映射，发现引导纳米线的晶体取向对于相对于衬底晶格的每个生长方向具有高度选择性和特异性。此外，我们沿着单个纳米线进行SHG偏振测量，发现无论是极性纳米线还是非极性纳米线，其晶体取向在纳米线长度方向上都得以保持。极性纳米线沿其轴显示出高度均匀的SHG，而非极性纳米线在几微米的长度范围内局部非线性极化率有显著变化，这表现为沿不同晶轴的SHG比率降低了40%。我们认为这些差异可能与沿非极性纳米线的应变积累有关。我们发现SHG偏振测量是研究具有不同外延关系的引导纳米线晶体取向的选择性和均匀性的有力工具。
