Flipping growth orientation of nanographitic structures by plasma enhanced chemical vapor deposition

TL;DR

This study demonstrates how plasma-enhanced chemical vapor deposition can be used to control the growth orientation of nanographitic structures by adjusting the gas mixture, affecting their morphology and structural quality.

Contribution

It introduces a method to tune nanographitic structure morphology from planar to vertical by controlling gas dilution ratios during plasma-enhanced CVD.

Findings

Vertical graphene nanosheets are favored by Ar-rich conditions.

Planar films are promoted by H2-rich conditions.

Dilution improves structural quality and turbostratic nature of NGSs.

Abstract

Nanographitic structures (NGSs) with multitude of morphological features are grown on SiO2/Si substrates by electron cyclotron resonance - plasma enhanced chemical vapor deposition (ECR-PECVD). CH4 is used as source gas with Ar and H2 as dilutants. Field emission scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy are used to study the structural and morphological features of the grown films. Herein, we demonstrate, how the morphology can be tuned from planar to vertical structure using single control parameter namely, dilution of CH4 with Ar and/or H2. Our results show that the competitive growth and etching processes dictate the morphology of the NGSs. While Ar-rich composition favors vertically oriented graphene nanosheets, H2-rich composition aids growth of planar films. Raman analysis reveals dilution of CH4 with either Ar or H2 or in combination helps to improve the structural quality of the films. Line shape analysis of Raman 2D band shows nearly symmetric Lorentzian profile which confirms the turbostratic nature of the grown NGSs. Further, this aspect is elucidated by HRTEM studies by observing elliptical diffraction pattern. Based on these experiments, a comprehensive understanding is obtained on the growth and structural properties of NGSs grown over a wide range of feedstock compositions.