In situ observation of localized metallic nanocrystal growth on carbon nanotube templates in a scanning electron microscope

摘要

Localizable templated growth of cobalt and tungsten nanocrystals on carbon nanotube (CNT) substrates using an in situ low pressure chemical vapour deposition (CVD) process in a scanning electron microscope is reported. Sparsely distributed individual nanocrystals of 8 nm minimum diameter and with growth rates up to 6.0 X 10~(-4) mum~3 min~(-1) were obtained. The growth properties depend on the precursor decomposition temperature, CNT length, thermal conductivity, convective and radiative losses, and nanotube heating characteristics, with local Joule heating of individual CNTs additionally dependent on electrical contact resistances and thermal loading compared to global substrate heating. Growth dynamics during heating necessitate moderate local CNT temperatures in order to obtain well-dispersed individual nanocrystals along the nanotube shank and preclude extraneous growth. This process is prescribed as a repeatable and localized method for high-throughput fabrication of metallic nanocrystals and films for the electrical, mechanical and magnetic functionalization of nanotubes and nanowires. It may also be employed as a tool for direct visualization and study of CVD nucleation mechanisms on nanodimensional templates and characterization of thermomechanical properties of nanostructures including internal Joule heating and phonon propagation behaviour.