The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

Abstract

The dynamics of the chemical vapor deposition (CVD) of single-walled carbon nanotubes (SWNTs) is extracted experimentally using in situ Raman spectroscopy. Nanotubes are grown using a thin À lm cobalt catalyst and À an ethanol precursor in a miniature hot walled reactor with optical access. Raman spectra at room temperature and at the growth temperature are compared for two growth temperatures. The evolution of the G-band, D-band, and radial breathing mode (RBM) is tracked at the growth temperature with time resolution of a few seconds. There are three identifiable phases in the evolution of the Raman signal intensity: an initial exponential increasing phase, a linear growth phase, and a saturation phase. In situ optical spectroscopy thus enables the study of nucleation, steady growth, and deactivation processes to be investigated separately in real time. The evolution curves for all bands (G, D, and RBM), when scaled, collapse onto the same curve, to within experimental uncertainty.

Phases of Carbon Nanotube Growth and Population Evolution from in Situ Raman Spectroscopy during Chemical Vapor Deposition

“…The easiest way to understand this is if all SWNT species evolve at the same rate, meaning that there is likely no net evolution in the diameter distribution. 6 All extracted G band, D band, and RBM band evolution curves for all growth runs at all tested temperatures are provided in the Supporting Information. Overall, the RBM tracked the G band to a reasonable approximation across all Co samples.…”

“…6 The temperature was measured by a thermocouple. A Raman spectroscopic imaging system was used to monitor the sample in plan view.…”

“…24 In this work, we study the evolution of G, D, and RBM Raman bands within a range of growth temperatures (650-900 °C) for two different "catalyst" seed particle formulations that generate different nanotube yields. A small subset of this data (two temperatures and one catalyst only) was presented in ref 6. We routinely discern four phases of CVD growth: incubation, acceleration, linear growth, and termination.…”

Thermodynamic and Energetic Effects on the Diameter and Defect Density in Single-Walled Carbon Nanotube Synthesis

“…Raman spectra were acquired using a custom built Raman spectrometer 24 with 532 nm excitation. The CNT forests were analyzed ex situ, without any modification or processing, using a2 0 × objective in plan view, looking orthogonal to the top surface of the forests (parallel to the average CNT axis).…”

Heterotapes: A Persistent, Dual‐Synthon Hydrogen‐Bonding Motif

“…Recently, we developed a pulsed CVD method that combines fast‐flowing, subsecond pulses of acetylene with in‐situ time‐resolved reflectivity (TRR) to understand the rapid growth of nanotube arrays induced by high‐partial‐pressure pulses of feedstock gas 31, 32. While considerable progress has been achieved using environmental high‐resolution transmission electron microscopy (HR‐TEM)33–42 to understand the nanoscale processes inherent in nanotube growth at low pressures, including the shape and composition of individual nanoparticles,40, 42 in‐situ diagnostics of the coordinated growth of nanotubes in arrays within typical CVD reactors are mainly based on optical techniques such as TRR,26, 43, 44 absorbance,30, 45, 46 Raman scattering,47–50 and direct video imaging 19, 51, 52. Of these techniques, only TRR has the temporal and spatial precision required to investigate pulsed CVD within subsecond gas pulses.…”