Microwave-assisted synthesis of single-crystalline tellurium nanorods and nanowires in ionic liquids.
Microwave-assisted synthesis of single-crystalline tellurium nanorods and nanowires in ionic liquids.
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DOI：
10.1002/anie.200353101
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发表时间：
2004-03
影响因子：
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通讯作者：
Yingjie Zhu;Wei-wei Wang;Rui-Juan Qi;Xianluo Hu
中科院分区：
文献类型：
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作者：
Yingjie Zhu;Wei-wei Wang;Rui-Juan Qi;Xianluo Hu
图 2a 和 b 显示了与图 1 相同的样品（样品 1）的 TEM 显微照片，从中可以看到直径大多在 15 至 40 nm 之间（少数直径为 40 至 100 nm）、长度可达 700 nm 的碲纳米棒。每个纳米棒都是直的，并且沿其整个长度具有均匀的直径。大多数纳米棒的长径比在10至20的范围内。长径比定义为长轴的长度除以短轴的宽度。纳米棒被定义为宽度为1-100 nm、长径比大于1但小于20的结构；和纳米线是长径比大于 20 的类似结构。[31]图2c显示了直径为32 nm、长度为610 nm（长径比%19）的单个Te纳米棒，其相应的电子衍射图如图2d所示，这是通过沿[11 0]方向聚焦电子束获得的。不同纳米棒或给定单个纳米棒的不同位置上的电子衍射图案基本上相同，如图2d所示，从而表明纳米棒是单晶的。电子衍射图可以反映六方结构，这与XRD的结果一致。图2e显示了如图2c所示的同一单个纳米棒的高分辨率透射电子显微镜（HRTEM）显微照片，它提供了这些纳米棒的更详细的结构信息。 HRTEM显示纳米棒在结构上是单晶，沿纳米棒纵轴的周期性条纹间距为5.927，对应于六方Te的(001)面之间的面间距。这表明Te纳米棒具有沿[001]带轴（晶格c轴）优先生长的方向，这与其他方法制备Te纳米棒的结果一致。 [26, 29]通过控制实验参数，可以制备独特的纳米线或纳米棒。图 2f 显示了采用 MAIL 方法与样品 1 不同的程序（参见实验部分）制备的样品 2 的 TEM 显微照片。可以看到，生产的是纳米线而不是纳米棒。大多数纳米线的直径在 20 至 100 nm 之间，少数纳米线的直径在 100–500 nm 范围内。这些纳米线的长度为数十微米。图2g显示了样品2中的几条纳米线。图2g中最长的纳米线的相应电子衍射图案如图2h所示。纳米线的电子衍射图（图2h）与纳米棒的电子衍射图（图2d）基本相同，表明纳米棒和纳米线沿[001]区轴（晶格的c轴）具有相同的优先生长方向。温度对Te的形貌有显着影响。即使在室温下，NaBH4 也会与 TeO2 反应形成 Te。然而，在室温至 1308°C 之间的温度下没有观察到纳米棒或纳米线（表 1，样品 3）。在 130 至 1508°C 的温度范围内观察到 Te 纳米棒以及球形纳米颗粒（样品 4）。当温度升高到1808℃（样品1）或更高时，仅观察到纳米棒。然而，当温度高于2008℃时，纳米棒的直径显着增加。 Te纳米线的制备也存在类似的情况。因此，生产Te纳米棒或纳米线的最佳温度为1808℃左右。
Figure 2a and b show TEM micrographs for the same sample as in Figure 1 (sample 1), from which one can see Te nanorods with diameters mostly ranging from% 15 to% 40 nm (a minority of them have diameters of 40 to 100 nm) and with lengths up to% 700 nm. Each nanorod is straight and has a uniform diameter along its entire length. The aspect ratios of most nanorods are in the range from 10 to 20. The aspect ratio is defined as the length of the major axis divided by the width of the minor axis. Nanorods are defined as structures with widths of 1–100 nm and aspect ratios greater than 1 but less than 20; and nanowires are analogous structures with aspect ratios greater than 20.[31] Figure 2 c shows a single Te nanorod with a diameter of 32 nm and a length of 610 nm (aspect ratio% 19), its corresponding electron diffraction pattern is shown in Figure 2d which was obtained by focusing the electron beam along the [11 0] direction. Electron diffraction patterns on different nanorods or different positions of a given single nanorod were essentially the same as shown in Figure 2d, thus indicating that nanorods were single-crystalline. The electron diffraction pattern can be indexed to the hexagonal structure, which is consistent with the result obtained from XRD. Figure 2e shows the high-resolution transmission electron microscopy (HRTEM) micrograph of the same single nanorod as shown in Figure2c, which provides more detailed structural information on these nanorods. The HRTEM shows that the nanorod is structurally singlecrystalline with the periodic fringe spacing of 5.927 along the longitudinal axis of the nanorod, which corresponds to the interplanar spacing between the (001) planes of the hexagonal Te. This indicates that Te nanorods had the preferential growth direction along the [001] zone axis (c axis of the crystal lattice), which is consistent with the results obtained from Te nanorods prepared by other methods.[26, 29]By controlling the experimental parameters, exclusive nanowires or nanorods could be produced. Figure 2 f shows the TEM micrograph of sample 2 prepared under a different procedure (see Experimental Section) from sample 1 by the MAIL method. One can see that nanowires instead of nanorods were produced. Most of these nanowires have diameters ranging from 20 to 100 nm, and a minority has diameters in the range of 100–500 nm. The lengths of these nanowires are tens of micrometers. Figure 2 g shows several nanowires from sample 2. The corresponding electron diffraction pattern of the longest nanowire in Figure 2 g is shown in Figure 2 h. The electron diffraction pattern of the nanowire (Figure 2 h) is essentially the same as that of the nanorod (Figure2d), indicating that nanorods and nanowires have the same preferential growth direction along the [001] zone axis (c axis of the crystal lattice). The temperature has a significant influence on the morphology of Te. NaBH4 reacts with TeO2 to form Te even at room temperature. However, no nanorods or nanowires were observed at temperatures between room temperature and 1308C (Table 1, sample 3). Te nanorods as well as spherical nanoparticles were observed in the temperature range of 130 to 1508C (sample 4). When the temperature was increased to 1808C (sample 1) or higher, only nanorods were observed. However, diameters of nanorods increased significantly when the temperature was higher than 2008C. A similar situation exists for the preparation of Te nanowires. Therefore, the optimum temperature for the production of Te nanorods or nanowires is around 1808C.