Toward Discrete Multilayered Composite Structures: Do Hollow Networks Form in a Polycrystalline Infinite Nanoplane by the Kirkendall Effect?
Toward Discrete Multilayered Composite Structures: Do Hollow Networks Form in a Polycrystalline Infinite Nanoplane by the Kirkendall Effect?
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DOI：
10.1021/cm201446y
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发表时间：
2011-10-25
影响因子：
8.6
通讯作者：
Zacharias, Margit
中科院分区：
文献类型：
--
作者：
Gueder, Firat;Yang, Yang;Zacharias, Margit
纳米结构中的空间限制在通过Kirkendall效应使用空隙形成来制造管状和中空球形物体中是至关重要的。对于核-壳纳米线和纳米球，所产生的空位被捕获在被限制在两个（纳米线）或所有三个（纳米球）空间维度中的区域内。当空隙形成扩展到其中仅一个维度（厚度）为纳米级且其它维度无限扩展的多层薄膜时，所形成的空隙的最终形态可显著不同。使用由原子层沉积（ALD）生长的ZnO和Al 2 O3交替层组成的多层系统，我们研究了退火温度、退火时间、层厚度、多晶性、晶粒尺寸和反应空间对固态扩散过程和最终的影响。所产生的Kirkendall空洞的形态。与涂覆有无定形Al 2 O3壳的单晶ZnO纳米线相反，其仅涉及ZnO到Al 2 O3的单向转移，多层膜中的多晶ZnO层也引起Al 2 O3通过晶界扩散到ZnO层中的扩散。在700摄氏度下的温度处理通常产生具有薄组件子层的多层膜的分层空隙。这种形态即使在800摄氏度下也保存完好。相比之下，在700摄氏度下，对于具有厚子层的多层膜形成部分连续的纳米间隙形态。然而，在这种情况下，在800摄氏度下仅产生交错的空隙，因为晶界迁移诱导定向附着。这里揭示的机制允许精确的制造和设计的多孔多层复合膜与控制的空隙形态。
Spatial confinement in nanostructures is of critical importance in the fabrication of tubular and hollow spherical objects using void formation via the Kirkendall effect. For both core-shell nanowires and nanospheres, generated vacancies are trapped within an area that is confined either in two (nanowires) or all three (nanospheres) spatial dimensions. When the void formation is extended to multilayered thin films where only one dimension (thickness) is in the nanoscale and the other dimensions are infinitely extended, the final morphology of the formed voids can be significantly different. Using a multilayered system consisting of alternating layers of ZnO and Al2O3 grown by atomic layer deposition (ALD), we investigate the effects of annealing temperature, annealing duration, layer thickness, polycrystallinity, grain size, and reaction space on the solid-state diffusion process and final morphology of the produced Kirkendall voids. As opposed to single-crystal ZnO nanowires coated with an amorphous Al2O3 shell, which involves only a one-way transfer of ZnO into Al2O3, polycrystalline ZnO layers in the multilayered films also cause diffusion of Al2O3 into ZnO layers via grain boundary diffusion. Temperature treatment at 700 degrees C generally yielded layered voids for multilayered films with thin component sublayers. This morphology was well-preserved even at 800 degrees C. In contrast, partially continuous nanogap morphologies were formed for multilayered films with thick sublayers at 700 degrees C. However, only interlaced voids were produced at 800 degrees C in this case, because of grain boundary migration induced oriented attachment. The mechanisms revealed here allow precise fabrication and design of porous multilayered composite films with controlled void morphology.