Control of carbon nanotube stiffness via tunable fabrication process parameters that determine CNT geometry

Abstract

This paper presents tunable process parameters that may be used to control the geometry of multi-walled carbon nanotubes (MWCNTs). The results may be used to grow MWCNTs with desired stiffness properties. This is important to devices that rely on the compliance of MWCNTs in order to achieve specific performance requirements, e.g. deflection or stiffness. Examples of these types of devices include relays, resonators and flexural bearings for small-scale actuators. It is necessary to control the stiffness of these mechanisms because the force, stroke, and device bandwidth depend upon the stiffness of the constituent MWCNTs. For a given length MWCNT, the stiffness is controlled by the MWCNT diameter and the number of walls in the MWCNT. Herein we present a growth model that was generated via statistical and experimental analysis. The diameter and number of walls are controlled by adjusting several growth parameters temperature, catalyst film thickness, and hydrocarbon concentration. The model is then used to design a growth process for specific applications. The results of these growths show that the geometry of the CNTs can be accurately controlled to within 6% of the desired geometry. Based on the measured geometries, it was estimated that the stiffness and natural frequency can be accurately controlled to within 1.5% of the desired values.