Synergetic Chemical Coupling Controls the Uniformity of Carbon Nanotube Microstructure Growth
Synergetic Chemical Coupling Controls the Uniformity of Carbon Nanotube Microstructure Growth
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DOI：
10.1021/nn500698z
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发表时间：
2014-06-01
期刊：
影响因子：
17.1
通讯作者：
Hart, A. John
中科院分区：
文献类型：
--
作者：
Bedewy, Mostafa;Farmer, Brittan;Hart, A. John
垂直排列的碳纳米管结构（碳纳米管“森林”）在几何形状和纳米尺度形态（密度、直径和排列）方面的均匀性控制对应用至关重要。许多研究报告了宏观碳纳米管森林高度的复杂且有时无法解释的空间变化，以及由石刻图案催化剂阵列生长的微柱之间的变化。我们提出了一个化学耦合碳纳米管生长的模型，它描述了碳纳米管微柱之间的协同生长效应的起源。通过这个模型，我们提出在底物结合的纳米颗粒上催化产生的活性物质局部增强了碳纳米管的生长。这些活性物质的局部浓度以一种空间依赖的方式调节CNTs的生长速率，这种方式由催化剂位点的扩散和局部生成/消耗驱动。通过实验和数值模拟，我们研究了碳纳米管微柱的均匀性如何受到它们在阵列内的大小和间距的影响，并通过分配活性物质的阈值浓度来预测广泛观察到的缠绕和垂直碳纳米管生长之间的突变。这个数学框架可以对碳纳米管生长的空间依赖性进行预测建模，以及设计催化剂模式以实现工程均匀性。
Control of the uniformity of vertically aligned carbon nanotube structures (CNT "forests"), in terms of both geometry and nanoscale morphology (density, diameter, and alignment), is crucial for applications. Many studies report complex and sometimes unexplained spatial variations of the height of macroscopic CNT forests, as well as variations among micropillars grown from lithographically patterned catalyst arrays. We present a model for chemically coupled CNT growth, which describes the origins of synergetic growth effects among CNT micropillars in proximity. Via this model, we propose that growth of CNTs is locally enhanced by active species that are catalytically produced at the substrate-bound nanoparticles. The local concentration of these active species modulates the growth rate of CNTs, in a spatially dependent manner driven by diffusion and local generation/consumption at the catalyst sites. Through experiments and numerical simulations, we study how the uniformity of CNT micropillars can be influenced by their size and spacing within arrays and predict the widely observed abrupt transition between tangled and vertical CNT growth by assigning a threshold concentration of active species. This mathematical framework enables predictive modeling of spatially dependent CNT growth, as well as design of catalyst patterns to achieve engineered uniformity.