Capturing and observing 1–6-nm-sized nanocarbon particles by transmission electron microscopy during the diamond hot filament chemical vapor deposition process

Abstract

Nanocarbon particles ~1 nm in size were first suggested to exist in the gas phase in 1996, and to be the building block of diamond growth during the hot filament chemical vapor deposition process. However, only nanocarbon particles larger than ~2 nm have been captured and observed in recent research. We used single-layer graphene to capture ~1-nm-sized nanocarbon particles at 300 °C and observed them by Cs-corrected monochromated transmission electron microscopy (Cs-corrected TEM). Nanocarbon particles 1–6 nm in size were captured for 1 and 10 s with a filament temperature of 2100 °C, reactor pressure of 20 Torr, and gas mixture composition of 1 % CH4–99 % H2. According to our Cs-corrected TEM observations, most nanocarbon particles larger than 3.5 nm were crystalline, whereas most nanocarbon particles smaller than 2.0 nm were amorphous. Analysis of high-resolution TEM images and their fast Fourier transformations confirmed that most of the crystalline nanocarbon particles were i‑carbon, in contrast with a previous study reporting that they consisted of various allotropes.