Tailor-made inorganic nanopeapods: structural design of linear noble metal nanoparticle chains.
Tailor-made inorganic nanopeapods: structural design of linear noble metal nanoparticle chains.
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DOI：
10.1002/anie.200801931
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发表时间：
2008-09
影响因子：
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通讯作者：
Lifeng Liu;Woo-Min Lee;R. Scholz;E. Pippel;U. Gösele
中科院分区：
文献类型：
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作者：
Lifeng Liu;Woo-Min Lee;R. Scholz;E. Pippel;U. Gösele
线性贵金属纳米粒子（NP）链已在理论和实验上被证明是一维纳米光学器件（例如等离子体波导、等离子体印刷）中应用的有希望的候选者。金属纳米粒子链在衍射极限以下传输电磁能的能力对于将光学器件和组件的尺寸缩小到纳米级具有重大优势。精确控制金属纳米颗粒链中的颗粒尺寸、形状和分离是构建纳米光学器件的重要问题。传统的电子束光刻技术和扫描探针操作可以很好地控制金属纳米粒子的尺寸和位置，但既耗时又昂贵。自组装路线使金属纳米颗粒能够融入预先形成的凹槽中，但既不能控制纳米颗粒之间的分离，也不能控制它们的密度。其他制造金属纳米粒子链的方法，包括湿化学蚀刻和利用金属纳米线（NW）的瑞利不稳定性，都存在吞吐量低和可控性有限的问题。在此，我们展示了一种简便且可控的线性贵金属纳米粒子链的制造方法，其中可以轻松控制光学上感兴趣的纳米粒子的尺寸和分离。例如，Pt@CoAl2O4无机豆荚纳米结构由封装在连续CoAl2O4纳米壳中的明确Pt纳米颗粒组成，通过将钴/铂多层（ML）纳米线电沉积到纳米多孔阳极氧化铝（AAO）膜中并随后在高温下进行固态反应来实现。 Pt@CoAl2O4 无机纳米豆荚的制备如图 1a 所示。首先，通过脉冲电位电沉积将 Co/Pt ML NW 电沉积到纳米多孔 AAO 模板中。所制备的 Co/Pt ML NW 具有交替分布的 Co 和 Pt 链段，可作为后续生成 Pt@CoAl2O4 无机纳米豆的前驱体和主链（参见支持信息中的图 S1）。在此步骤中，豆荚纳米结构中 Pt“豌豆”的尺寸（直径，DPt）和间距（中心距，Dc-c）也分别由 Pt (LPt) 和 Co 段 (LCo) 的长度定义。电沉积后，Co/Pt ML NWs/AAO 复合膜在环境气氛中于 700 8C 下退火 1-5 小时。在热处理过程中，Co片段与氧化铝反应形成连续的CoAl2O4纳米壳，即“豆荚”，而大多数Pt片段聚集成球形以最小化其表面能，形成豌豆。由此，获得了豆荚纳米结构。所制备的 Pt@CoAl2O4 无机纳米豆既可以保留在多孔 AAO 模板中，也可以通过选择性去除周围的氧化铝轻松从模板中释放（参见支持信息中的图 S2a）。最近，利用金属纳米线的瑞利不稳定性被认为是创建线性金属纳米粒子链的有效“自下而上”方法。然而，这种方法只能非常有限地控制金属纳米粒子之间的分离。其控制能力严格受到最大扰动波长lmax的限制，该波长与所使用的金属纳米线的半径R0成正比，如图1c所示。比例 图 1. 豆荚纳米结构的制造。 a,b)通过基于模板的脉冲电沉积和高温固态反应制备Pt@CoAl2O4无机纳米豆荚（封装在CoAl2O4纳米壳中的Pt纳米粒子链）。 Pt 纳米颗粒 (Dc-c) 之间的间距与 Co 电沉积的脉冲持续时间 tCo 成正比，并且可以随意更改。 c）基于金属纳米线的瑞利不稳定性制造的金属纳米颗粒链。
Linear noble-metal nanoparticle (NP) chains have been demonstrated both theoretically and experimentally to be promising candidates for applications in one-dimensional nano-optical devices (e.g. plasmonic waveguides, plasmonic printing). The ability of metal NP chains to transport electromagnetic energy below the diffraction limit has major advantages for scaling down the size of optical devices and components to the nanometer scale. Precise control of particle size, shape and separation in metal NP chains is an important issue for constructing nano-optical devices. Conventional electron-beam lithographic techniques and scanning-probe manipulation have enabled excellent control over the size and position of metal NPs but are time-consuming and costly. Self-assembly routes enable metal NPs to be incorporated into preformed grooves but can control neither the separation between NPs nor their densities. Other approaches to the fabrication of metal NP chains, including wet-chemistry etching and exploitation of the Rayleigh instability of metal nanowires (NWs), suffer from low throughput and limited controllability. Herein, we show a facile and controllable route to the fabrication of linear noble-metal NP chains, in which the size and the separation of optically interesting NPs can be controlled easily. As an example, Pt@CoAl2O4 inorganic peapod nanostructures, which consist of well-defined Pt NPs encapsulated in continuous CoAl2O4 nanoshells, were realized by electrodeposition of cobalt/platinum multilayered (ML) NWs into nanoporous anodic aluminum oxide (AAO) membranes and subsequent solid-state reaction at high temperature. Fabrication of Pt@CoAl2O4 inorganic nanopeapods is schematically illustrated in Figure 1a. First, Co/Pt ML NWs were electrodeposited into the nanoporous AAO template by pulsed potential electrodeposition. As-prepared Co/Pt ML NWs with alternately distributed Co and Pt segments served as the precursors and the backbones for subsequent generation of Pt@CoAl2O4 inorganic nanopeapods (see Figure S1 in the Supporting Information). The size (diameter, DPt) and separation (center-to-center distance, Dc-c) of Pt “peas” in peapod nanostructures were also defined in this step by the lengths of Pt (LPt) and Co segments (LCo), respectively. After electrodeposition, the Co/Pt ML NWs/AAO composite membrane was annealed at 700 8C in an ambient atmosphere for 1–5 h. During heat treatment, Co segments reacted with alumina to form continuous CoAl2O4 nanoshells, that is, the “pods”, while most Pt segments agglomerated into a spherical shape to minimize their surface energy, forming the peas. Thus, the peapod nanostructures were obtained. As-prepared Pt@CoAl2O4 inorganic nanopeapods can either be kept in the porous AAO template or be easily released from the template by selectively removing the surrounding alumina (see Figure S2a in the Supporting Information). Recently, exploitation of the Rayleigh instability of metal NWs has been considered as an effective “bottom-up” approach to create linear metal NP chains. However, this method only allows very limited control of the separation between metal NPs. Its controlling capability is strictly confined by the maximum perturbation wavelength lmax, which is directly proportional to the radius R0 of the metal NWs used, as shown in Figure 1c. The proportionality Figure 1. Fabrication of peapod nanostructures. a,b) Fabrication of Pt@CoAl2O4 inorganic nanopeapods (Pt nanoparticle chains encapsulated in CoAl2O4 nanoshells) by template-based pulsed electrodeposition and high-temperature solid-state reaction. The separation between Pt nanoparticles (Dc-c) is proportional to the pulse duration for Co electrodeposition, tCo, and can be changed at will. c) Metal nanoparticle chains fabricated on the basis of the Rayleigh instability of metal nanowires.