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

New York University, New York NY

Investigators

Abstract

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.