Functionally Graded Carbon Nanotubes by Dynamic Control of Morphology during Chemical Vapor Deposition

这项资助将支持基础研究，旨在揭示排列碳纳米管制造过程的基本机制，以用于国家利益的新兴应用。碳纳米管是一种比人类头发的万分之一还小的管子，可以被认为是原子厚度的薄片，无缝地包裹在管子里。单个纳米管优越的化学和物理性质，以及通过大量排列的碳纳米管的能量和质量传输的集体独特方向性，巩固了它们在许多关键技术领域的潜力。碳纳米管的商业产量每年超过几千吨，用于依赖于各种长度和直径的随机分散纳米管成基体来增强复合材料性能的产品。然而，诸如高功率密度器件、3D纳米电子学、纳米多孔膜和结构材料等新兴应用需要更精确地控制排列碳纳米管集成的尺寸、顺序和分层形态的空间变化。这项研究希望通过对其初始成核和随后生长的新理解，生产出宽度和长度相同的垂直排列的碳纳米管大阵列。这些相同的纳米管“森林”具有优异的机械性能，可以用于新的应用领域，在这些领域中，纳米管的随机长度会导致性能不佳。该项目的研究将有助于建立工艺-结构-性能关系，推动纳米管的新兴应用更接近市场，从而提高美国的经济竞争力，同时推进大学水平的分子规模制造教育。通过YouTube频道的持续发展，向普通观众解释纳米技术相关的话题，将促进公众外展。垂直排列的碳纳米管（VACNTs）的整体特性取决于其宏观森林结构的空间变化形态。然而，目前缺乏对控制大量碳纳米管群体成核动力学的机械化学因素的理解，导致无法在数十亿碳纳米管同时生长的过程中以可重复的方式控制这些变化。该项目旨在填补这一知识空白，以精确控制通过快速热化学气相沉积（RT-CVD）生长的空间工程vacnt，并预测其性能。这将通过在周期性生长条件下的实验生长来实现，同时现场监测高度动力学，结合基于非原位x射线的形态学表征和电子显微镜，以及对基底结合的纳米催化剂的碳纳米管成核的催化活化和失活速率的随机建模。因此，该项目产生的结果将能够在与工业碳纳米管生产相关的过程中可预测地调整cvd生长的碳纳米管。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This grant will support basic research aimed at revealing the fundamental mechanisms underlying the process of manufacturing aligned carbon nanotubes for emerging applications of national interest. Carbon nanotubes are tubes that are smaller than one ten-thousandth of a human hair and can be thought of as atom-thick sheets that are wrapped seamlessly into tubes. The superior chemical and physical properties of individual nanotubes, as well as the collective unique directionality of energy and mass transport through large populations of aligned carbon nanotubes underpin their potential in many critical technological areas. The commercial production of carbon nanotubes exceeds several thousand tons per year and are used in products that rely on the random dispersion nanotubes of various lengths and diameters into a matrix to enhance the composite properties. However, emerging applications such as high power-density devices, 3D nanoelectronics, nanoporous membranes, and structural materials require more precise control of the spatial variation of sizes, order and hierarchical morphology of aligned carbon nanotube ensembles. This research looks to producing, through new understanding of their initial nucleation and subsequent growth, large arrays of vertically aligned carbon nanotubes which are all identical in width and length. These 'forests' of identical nanotubes have excellent mechanical properties and can be used in new application areas where the random length of the nanotubes would lead to poor performance. Research in this project will contribute knowledge towards building the process-structure-property relationship necessary for pushing emerging applications of nanotubes closer to market, leading to enhancing the American economic competitiveness, while advancing university-level education of molecular-scale manufacturing. Public outreach will be facilitated by the continued development of YouTube channel explaining nanotechnology-related topics to a general audience.The collective properties of vertically aligned carbon nanotubes (VACNTs) are dependent on the spatially varying morphology across their macroscopic forest-like structure. However, there is currently a lack of understanding of the mechanochemical factors governing the nucleation kinetics of large CNT populations, leading to an inability to control these variations in a repeatable fashion during the simultaneous growth of billions of CNTs. This project aims at filling this knowledge gap to enable precise control of spatially-engineered VACNTs grown by rapid thermal chemical vapor deposition (RT-CVD) and allow predicting their properties. This will be achieved by experimental growth of VACNTs under periodic growth conditions with in situ monitoring of height kinetics, combined with ex situ X-ray-based morphological characterization and electron microscopy, as well as stochastic modeling of the rates of catalytic activation and deactivation of CNTs nucleating from substrate-bound catalyst nanoparticles. Hence, the results generated from this project will enable predictably tuning CVD-grown CNTs in a process that is relevant to industrial CNT production.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.