Laser-assisted catalytic growth of single crystal GaN nanowires
Laser-assisted catalytic growth of single crystal GaN nanowires
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DOI：
10.1021/ja993713u
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发表时间：
2000-01-12
影响因子：
15
通讯作者：
Lieber, CM
中科院分区：
文献类型：
--
作者：
Duan, XF;Lieber, CM
在这里，我们报道了单晶GaN纳米线的体相合成。激光烧蚀GaN和催化金属的复合靶产生液体纳米团簇，作为反应中心限制和指导晶体纳米线的生长。场发射扫描电子显微镜(FE-SEM)表明，产物主要由线状结构组成。对块状纳米线样品的粉末X射线衍射(PXRD)分析表明，样品具有纤锌矿结构，相纯度为95%。各纳米线的透射电子显微镜、会聚束电子衍射和能量色散X射线荧光分析表明，它们是沿[100]方向生长的GaN单晶。在过去的十年里，纳米结构的GaN材料因其在光电子学方面的巨大潜力而引起了人们的广泛兴趣。1这些研究主要集中在零维(0D)量子点2-7和二维(2D)量子阱结构8-11，它们可以很容易地用现有的方法合成。一维(1D)GaN纳米线的研究由于与合成有关的困难而受到限制，因为它可以在基础和应用研究中提供独特的机会，12，13。具体地说，关于GaN纳米线生长的报道只有一篇。14、15在本工作中，以碳纳米管为模板，在GaO_2和NH_3蒸气存在下制备了GaN纳米线。我们已经利用了一种可预测的合成方法来生长GaN纳米线，称为激光辅助催化生长(LCG)。在该方法中，使用脉冲激光来汽化包含所需材料和催化剂的固体靶，在高温下形成的液体纳米团簇通过气-液-固生长机制指导生长并定义晶体纳米线的直径。这种方法的一个主要特点是，用来定义一维生长的催化剂可以从相图数据和/或化学反应知识中选择。Buhro和他的同事使用了一种名为溶液-液-固相生长的相关方法来在溶液中制备几种III-V材料的纳米线，19尽管不是氮化物。20就GaN而言，无法获得与LCG(即催化剂-Ga-N)有关的三元相图的详细信息。但是，我们可以利用成长过程的知识来理性地选择催化剂。具体地说，在纳米线生长条件下，催化剂应该与GaN形成可互溶的液相，而不是形成更稳定的固相。指导原则认为，Fe同时溶解了Ga和N，21并且不会形成比GaN更稳定的化合物，是LCG生长GaN纳米线的良好催化剂。方案1说明了激光烧蚀生成催化纳米团簇后纳米线生长的总体演变。值得注意的是，我们发现使用GaN/Fe靶的LCG产生了高产量的纳米直径的线状结构。由LCG22(图1a)制备的产物的典型FE-SEM图像显示，产物主要由一维结构组成，直径在10 nm数量级，长度大大超过1μm，即高深宽比纳米线。FE-SEM数据还表明，产物由约90%的纳米线组成，其余为纳米颗粒。我们还用X射线衍射仪(图1b)评估了块状纳米线样品的整体晶体结构和物相纯度。X射线衍射谱中所有相对尖锐的衍射峰都可以用(1)(A)Nakamura，S和…指标化为纤锌矿结构
Herein we report the bulk synthesis of single crystalline GaN nanowires. Laser ablation of a composite target of GaN and a catalytic metal generates liquid nanoclusters that serve as reactive sites confining and directing the growth of crystalline nanowires. Field emission scanning electron microscopy (FE-SEM) shows that the product primarily consists of wire-like structures. Powder X-ray diffraction (PXRD) analyses of a bulk nanowire sample can be indexed to the GaN wurtzite structure, and indicate> 95% phase purity. Transmission electron microscopy (TEM), convergent beam electron diffraction (CBED), and energy-dispersive X-ray fluorescence (EDX) analyses of individual nanowires show that they are GaN single crystals with a [100] growth direction. Nanostructured GaN materials have attracted extensive interest over the past decade due to their significant potential for optoelectronics. 1 These studies have primarily focused on zerodimensional (0D) quantum dots2-7 and two-dimensional (2D) quantum well structures, 8-11 which can be readily synthesized using established methods. Investigations of one-dimensional (1D) GaN nanowires, which could enable unique opportunities in fundamental and applied research, 12, 13 have been limited due to difficulties associated with their synthesis. Specifically, there has been only one report of GaN nanowire growth. 14, 15 In this work, carbon nanotubes were used as templates in the presence of Gaoxide and NH3 vapor to yield GaN nanowires. We have exploited the predictable synthetic approach for GaN nanowire growth called laser-assisted catalytic growth (LCG). 12, 16, 17 In this method, a pulsed laser is used to vaporize a solid target containing desired material and a catalyst, and the resulting liquid nanoclusters formed at elevated temperature direct the growth and define the diameter of crystalline nanowires through a vapor-liquid-solid growth mechanism. 12, 16-18 A key feature of this method is that the catalyst used to define 1D growth can be selected from phase diagram data and/or knowledge of chemical reactivity. A related approach termed solution-liquid-solid phase growth has been used by Buhro and co-workers to prepare nanowires of several III-V materials in solution, 19 although not nitrides. 20 In the case of GaN, detailed information on ternary phase diagrams relevant to LCG (ie, catalyst-Ga-N) is unavailable. However, we can use the knowledge of the growth process to choose a catalyst rationally. Specifically, the catalyst should form a miscible liquid phase with GaN but not form a more stable solid phase under the nanowire growth conditions. The guiding principle suggests that Fe, which dissolves both Ga and N, 21 and does not form a more stable compound than GaN will be a good catalyst for GaN nanowire growth by LCG. The overall evolution of nanowire growth following the generation of the catalytic nanocluster by laser ablation is illustrated in Scheme 1. Significantly, we find that LCG using a GaN/Fe target produces a high yield of nanometer diameter wire-like structures. A typical FE-SEM image of the product produced by LCG22 (Figure 1a) shows that the product consists primarily of 1D structures with diameters on the orders of 10 nm and lengths greatly exceeding 1 μm, that is, high aspect ratio nanowires. The FE-SEM data also show that the products consist of ca. 90% nanowires, with the remaining being nanoparticles. We have also assessed the overall crystal structure and phase purity of the bulk nanowire samples using PXRD (Figure 1b). All the relatively sharp diffraction peaks in the PXRD pattern can be indexed to a wurtzite structure with (1)(a) Nakamura, S …