银纳米线的侧向生长及其抑制研究

采用多元醇法，在不同温度，不同PVP滴加速度和加入量的条件下合成了银纳米线。利用XRD, UV-Vis, SEM和TEM对银纳米线及其侧向生长过程进行了观察和分析。UV-Vis表明银纳米线在纵向生长的同时发生了侧向生长。而且表示银纳米线侧向生长的紫外吸收光谱峰在银纳米线合成后期发生了明显的红移，由384 nm红移至约388 nm处，表明银纳米线合成后期直径迅速增长，银纳米线发生了快速的侧向生长。SEM研究表明银纳米线直径在反应前期(15～23 min)只增加了20 nm，而在反应后期(23～30 min)银纳米线直径增加了近150 nm，SEM观察结果与UV-Vis分析结论一致。同时还发现银纳米线直径不仅与晶种大小有关而且与银线外覆盖的银层厚度有关，银源以吸附在银线侧面的小银颗粒为附着点沿其侧面多点沉积导致了银纳米线的侧向生长;降低反应液温度(165 ℃降至155 ℃)，降低PVP滴加速度(67 mL·h-1减小到49 mL·h-1)以及减少银纳米线合成后期PVP加入量可抑制银纳米线的侧向生长，显著提高银纳米线长径比，银纳米线直径由200 nm减小至100 nm左右，长度仍保持在100 μm以上。

Study on the Lateral Growth of Ag Nanowires and Its Inhibition

Ag nanowires (Ag NWs) are synthesized by polyol method under the conditions of different temperature of reaction solution, different addition amount and injection rate of polyvinylpyrrolidone (PVP). The structure and the process of lateral growth of Ag NWs were observed and analyzed by X-ray diffraction (XRD), ultraviolet-visible absorption spectrum (UV-VIS), scanning electron microscopy (SEM) and transmission electron microscope (TEM). It showed that the lateral growth of Ag NWs and longitudinal growth of Ag NWs occurrs at the same time by UV-VIS. And in the later stage of synthesis of Ag NWs, the peak in UV-VIS, which indicated the lateral growth of Ag NWs, red-shifted obviously from 384 nm to 388 nm. This rapid redshift implied that the diameters of Ag NWs increased quickly. In other words, rapid lateral growth of Ag NWs occurred in the later stage of synthesis of Ag NWs. According to the SEM of Ag NWs, in the early stage of the reaction (15~23 min), the diameter of Ag NWs increased by only 20 nm, but in the later stage of reaction (23~30 min), the diameter of Ag NWs increased by nearly 150 nm. The result of SEM observation is consistent with the analysis of UV-VIS. It was also found that the lateral growth of Ag NWs is related not only to the sizes of seeds but also to the thicknesses of the outer Ag layers. Tiny Ag particles with diameters of several nanometers adsorbed onto the side facets of Ag NWs and acted as adsorption points for Ag source. The lateral growth of Ag NWs was caused by the continuous multipoint adsorption of Ag source on the side of Ag NWs. Decreasing the temperature of the reaction solution (from 165 to 155 degree), reducing the injection rate (from 67 to 49 mL·h-1) and the addition amount of PVP in the later stage could inhibit the lateral growth of Ag NWs and increase the aspect ratios of Ag NWs remarkably. The diameters of Ag NWs decreased from 200 nm to 100 nm, but their lengths still maintained above 100 μm.