3D growth simulation and field emission properties of vertically aligned carbon nanotubes

Abstract

[EMBARGOED UNTIL 12/01/2024] Since their discovery, carbon nanotubes (CNTs) have become a widely researched and utilized nanomaterial due to their nanoscale size and unique electrical, thermal, and mechanical properties. In particular, bulk structures of aligned CNTs, such as CNT forests, exhibit nanoscale-based properties desirable for various electrical applications. Unfortunately, the complexity of CNT systems makes the properties of CNT forests difficult to predict from synthesis conditions. Chapter 2 details the experimental investigation and 2D simulation of the piezoresistive response of CNT-coated microfibers as hairlike sensors. Electromechanical tests reveal that piezoresistivity is governed by contact resistance between measurement electrodes and the free ends of CNT 'hairs.' Hairlike sensors must be highly sensitive to external stimuli, indicating the need for a large, consistent stimulus response. Results suggest that small diameter microfibers with short CNT forests provide the highest piezoresistive sensitivity, supporting the excellent potential of CNT- coated microfibers as artificial hairlike sensors. Chapter 3 introduces a time-resolved 3D CNT forest growth simulation to serve as a diagnostic tool for designing and predicting the properties of experimental CNT forests. 3D simulated CNT forest number density and conductance results are compared against CNT forest properties determined by in situ scanning electron microscopy (SEM) growth experiments and post-growth small angle x-ray spectroscopy (SAXS) measurements. Preliminary results establish that with additional adjustments, the 3D CNT growth simulation model can provide excellent representations of CNT forest growth. Chapter 4 concerns the initial fabrication, characterization, and field emission testing of CNT-based field emission cathodes for high-power physics applications, specifically a custom-designed klystron called a 'klystrino.' Both high density forest (HDF) and patterned CNT cathodes are fabricated by fixed catalyst chemical vapor deposition (CVD). Field emission tests upon CNT HDF cathodes and CNT micropillar cathodes confirm characteristic Fowler-Nordheim emission behavior and yield emission current densities on the order of A/m2.