Studies of Ion-Exchange Process for Selective Placement of High-Density Carbon Nanotubes for Digital Logic Applications

纳米材料为未来电子和光子技术的革命提供了巨大的前景。尽管付出了巨大的研究努力，但将单个纳米级构建块组装成高级功能组件并最终进入系统仍然是一个挑战。纳米材料的分层集成对于需要精确放置密度极高的纳米级构建块的应用尤为重要。这种分层集成的一个重要例子包括大规模组装碳纳米管，因为它们具有实现下一代高速节能计算系统的巨大潜力。然而，在精确的位置组装高密度的纳米管一直是实现可行的纳米管技术的主要障碍。该奖项旨在通过揭示用于选择性放置纳米管的化学组装过程的基本表面科学来弥合科学和技术差距。该项目为研究生和本科生创造了新的研究和教育机会，特别是吸引了来自服务不足群体的学生。该项目的科学和技术方面，以及劳动力培训，将促进国家保持全球技术领先地位的努力。本研究项目的目标是研究基于离子交换化学的碳纳米管（cnt）选择性放置的基本表面科学。这种化学组装过程涉及纳米级的静电电荷相互作用。具体来说，电荷相互作用发生在分散在溶液中的带负电荷的表面活性剂包裹的碳纳米管和纳米级氧化铪（HfO2）沟槽中带正电荷的自组装分子之间。目前，这种离子交换化学的优化是基于一系列的试错实验，其中碳纳米管密度被用作唯一可测量的度量。为了了解这些相互作用的本质，研究了一种量化纳米尺度库仑相互作用的新方法。为此，开发了一种嵌入式四端硅场效应传感器的二维阵列，该阵列具有纳米级硅通道，可以量化小的电子电荷。然后在这些传感器上方形成HfO2沟槽，以监测不同处理参数对化学组装动力学的影响。该项目建立了高密度碳纳米管选择性放置离子交换过程动力学的定量理解。开发了一种基于硅传感器二维阵列的电化学相机，以高时空分辨率记录离子交换化学动力学。这项研究为碳纳米管在硅衬底上的高密度集成铺平了道路，从而实现高速和节能的数字逻辑应用。

Nanomaterials offer tremendous prospects to revolutionize future electronic and photonic technologies. Despite enormous research efforts, assembling individual nanoscale building blocks into high-level functional assemblies and ultimately into systems remains a challenge. The hierarchical integration of nanomaterials is particularly important for applications that require precise placement of nanoscale building blocks with exceedingly high density. An important example of such hierarchical integration includes assembling carbon nanotubes on a large scale due to their tremendous potential for realizing next-generation computing systems that are high-speed and power-efficient. However, assembling nanotubes with high density in precise locations has been a major roadblock for enabling a viable nanotube-based technology. This award aims at bridging the scientific and technological gap by uncovering the fundamental surface science of a chemical assembly process that is used for selective placement of nanotubes. The project creates new research and educational opportunities for graduate and undergraduate students, specifically engaging students from underserved groups. The scientific and technological aspects of the project, along with the workforce training, will boost the efforts of the nation in maintaining global technological leadership. The goal of this research project is to study the fundamental surface science of selective placement of carbon nanotubes (CNTs) based on ion-exchange chemistry for device applications. This chemical assembly process involves electrostatic charge interactions at the nanoscale. Specifically, the charge interactions occur between negatively charged surfactant-wrapped CNTs dispersed in a solution and positively charged self-assembled molecules in nanoscale hafnium oxide (HfO2) trenches. Currently, the optimization of this ion-exchange chemistry is based on a series of trial and error experiments in which the CNT density is used as the only measurable metric. To understand the nature of these interactions, a new methodology that quantifies the Coulombic interactions at nanoscale is studied. To this end, a two-dimensional array of embedded 4-terminal silicon field-effect sensors with nanoscale silicon channels that allow quantifying small electronic charges are developed. The HfO2 trenches are then formed above these sensors to monitor the effect of different processing parameters on the kinetics of the chemical assembly. The project establishes a quantitative understanding of the kinetics of the ion-exchange process for selective placement of high-density CNTs. It also develops a new electrochemical camera based on a 2D array of the silicon sensors for recording the dynamics of the ion-exchange chemistry with high spatiotemporal resolution. This research paves the way for high-density integration of CNTs on silicon substrates for high-speed and power-efficient digital logic applications.