Alancherry, Surjith (2018) Development of carbon nanostructures from non-conventional resources. PhD thesis, James Cook University.

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Abstract

Carbon nanostructures (CNSs) perpetuate the scientific interest over decades due to their remarkable properties and emerging technological applications. The development of sustainable technologies for the synthesis of CNSs from natural resources grabbed immense research attention aiming to implement these high-end materials in wide range of nano electronic devices through safe and environmentally friendly routes. Even though a number of top down and bottom up approaches have been developed for the production of CNSs, most of them either aided by catalysts or involved solvent assisted multi-step process that considerably increase the cost of production and hinders the realization of low cost CNSs based commercial devices. In addition, vast majority of these techniques use high pure petroleum derived hydrocarbon gas precursors that are non-renewable and expensive. Hence, it is imperative to develop scalable techniques that can derive high quality CNSs directly on arbitrary substrates from naturally derived carbon feed stocks. This work aims to develop an environmentally benign plasma enhanced chemical vapor deposition technique for fabricating CNSs from Citrus sinensis essential oil, a bio renewable precursor, and explored the potential of these nanostructures for gas sensing application.

C. sinensis essential oil, obtained through cold extraction of orange peels is a rich source of non-synthetic hydrocarbon compounds principally limonene. Inherently volatile in nature, C. sinensis essential oil can serve as an ideal candidate material compatible to plasma enhanced chemical vapor deposition. This thesis investigated the fabrication of vertically-oriented graphene nanostructures from C.sinensis essential oil through radio frequency plasma enhanced chemical vapor deposition process, the fundamental properties, extend to which the process parameters influenced the structure and morphological features, and the suitability of the developed vertical graphene arrays for gas sensing applications. Special attention is paid to probe deep into the morphological evolution with the help of a set of advanced analytical characterization methods and multi-parameter model simulations.

In the first phase, C.sinensis vapors were subjected to low RF power glow discharge that resulted in the formation of plasma polymer thin films, and the material properties were studied as a function of input RF energy. The fundamental properties of plasma polymer thin films fabricated at different RF power level (10−75 W) were characterized with variable angle spectroscopic ellipsometry, UV-visible spectroscopy, Fourier transform infrared spectroscopy X-ray photoelectron spectroscopy and atomic force microscopy. Optical characterization showed that independent of deposition power films exhibited good transparency (~90 %) in the visible region and a refractive index of 1.55 at 500nm. The optical band gap measured around 3.60 eV and falls within the insulating region. The atomic force microscopic (AFM) images revealed that the surface is pinhole-free and smooth at nanoscale, with average surface roughness dependent on the deposition power. Film hardness increased from 0.50 GPa to 0.78 GPa as applied power increased from 10 to 75 W.

In the second phase, experiments were modified by redesigning the experimental set up in order to eliminate hydrogen from the deposits leaving only crystalline carbon. The RF power deliberately kept high, substrate temperature was raised and hydrogen gas fed into the reactor in controlled manner. A sequence of experiments were carried out by systematically changing the process parameters such as in put RF power (300-500W), hydrogen flow rate (10-50 sccm) and deposition duration (2-8 min) and analysed the structural and morphological evolution of the resulted vertical graphene nanostructure.

The structure-property correlation of vertical graphene arrays with the plasma process parameters was performed. The Raman spectra ascertained the formation of less defected multilayered graphene nanostructures and scanning electron microscopic images provided the primary evidences of morphological evolution. The potential of the novel analytical techniques such as Hough transformations, fractal dimension distributions and Minkowski connectivity for the analysis of graphene array morphology was then successfully demonstrated. Worth noting that, these advanced techniques displayed significant changes and revealed the complex morphological transformation of C. sinensis derived vertical graphene subjected to change in process conditions. Precisely, vertical graphene nanowalls obtained at 300 and 500W presented a narrow height distribution profile but much wider array formed at 400 W. Fourier and Hough transformation spectra showed a prominent change with an increase in power, thus highlighted change in the morphology with the density of nanoflakes. Similarly, 2D FFT transform spectra of vertical graphene samples also presented notable changes with increasing hydrogen flux. The most narrow height distributions, well-shaped Hough transformation spectra and distribution of fractal dimensions obtained for structures formed at 20 and 50 sccm of hydrogen flow rate. In addition to this, the principal characteristics of thus fabricated vertical graphene such as flake length (Lvg) and flake half width (Wvg) are theoretically modelled by an ad hoc model based on a large number of interaction elemental processes and correlated with the experimental results. The combination of the experimental and simulation results ensured important insights and deeper understanding of the processes that govern formation of the vertical graphene morphology.Vertical graphene nanostructures having superior structural and morphological properties were successfully fabricated at an input RF energy of 500W, hydrogen flow rate of 30 sccm and deposition duration of 6 minutes.

The third phase presented an in-depth study of the properties of C.sinensis oil derived graphene over a set of conducting (copper and nickel) and insulating substrates (silicon and quartz). The SEM images of thus fabricated graphene patterns showed the unique feature of vertically interconnected and non-agglomerated carbon nanowall structures having maze-like and petal-like networks. Moreover, the normalized height distribution function and 2-D FFT spectra analysis ascertained that vertical graphene formed on silicon substrates displayed the most uniform distribution. X-ray photoelectron spectroscopy spotted only the presence of carbon and the transmission electron microscopic studies revealed the formation of unique onion-like closed loops. The 3-D nanoporous structure of C.sinensis oil derived graphene showed high hydrophobicity and measured a water contact angle of 129°. The surface energy studies were performed using Neumann model, Owens-Wendt-Kaelble approach and van Oss- Chaudhury-Good relation and estimated within the range 35‒41 mJ/m².

Finally, plasma reformed vertical graphene from C. sinensis was integrated into a sensor device prototype to evaluate the performance in gas sensing. The chemiresistive type sensor exhibited sensing activity towards acetone. In summary, this thesis has identified a viable renewable resource and successfully developed a process that transform them into vertical graphene nanostructures. Furthermore, the fabricated graphene was integrated to real world devices and evaluated the performance. The outcomes of this investigation add knowledge base to the state-of-the-art of green chemistry approach for the synthesis of vertical graphene carbon nanostructures.

Item ID:	59139
Item Type:	Thesis (PhD)
Keywords:	Plasma polymerization, Essential oils, Organic polymer, Optical properties, Orange oil, Thin films, Graphenes
Related URLs:	https://researchonline.jcu.edu.au/54417/
Copyright Information:	Copyright © 2018 Surjith Alancherry.
Additional Information:	Publications arising from this thesis are available from the Related URLs field. The publications are: Chapter 3: Alancherry, Surjith, Bazaka, Kateryna, and Jacob, Mohan V. (2018) RF plasma polymerization of orange oil and characterization of the polymer thin films. Journal of Polymers and the Environment, 26 (7). pp. 2925-2933.
Date Deposited:	05 Aug 2019 04:11
FoR Codes:	09 ENGINEERING > 0912 Materials Engineering > 091209 Polymers and Plastics @ 50% 10 TECHNOLOGY > 1007 Nanotechnology > 100703 Nanobiotechnology @ 50%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970109 Expanding Knowledge in Engineering @ 50% 97 EXPANDING KNOWLEDGE > 970110 Expanding Knowledge in Technology @ 50%
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