Tailoring the diameter of decorated CN nanotubes by temperature variations using HF-CVD

TL;DR

This study systematically investigates how substrate temperature during HF-CVD affects the morphology, diameter, and properties of nitrogenated carbon nanotubes, revealing a strong temperature dependence and novel decoration features.

Contribution

It introduces a controlled method to tailor the diameter and structure of C-N nanotubes by adjusting the substrate temperature during HF-CVD.

Findings

Nanotube diameter varies significantly with temperature.

A new decoration covering nanotubes was observed.

Field emission properties strongly depend on nanotube diameter.

Abstract

Patterned films of decorated nitrogenated carbon (C-N) nanotubes were catalytically synthesised by hot filament chemical vapour deposition (HF-CVD) in a nitrogen-methane-ammonia environment. The systematic study of a transition between different kinds of C-N nanostructures as a function of the local substrate temperature ranging from 700 up to 820C is presented. The morphology, the diameter as well as the properties of the generated tubular structures showed strong dependence on this parameter. By means of electron microscopy a new type of decoration covering all tubular structures was observed. Buckled lattice fringes revealed the disordered graphitic-like character of the hollow C-N nanotubes. Raman spectroscopy confirmed a transition in the microscopic order as a function of temperature. Furthermore field emission in vacuum was studied and showed a spectacular correlation to the deposition temperature and therefore the diameter of the C-N tubes. For arrays of tubes thinner than 50 nm an onset field below 4 V/um was observed.