Title: Flipping growth orientation of nanographitic structures by plasma enhanced chemical vapor deposition,
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.