Analysis of graphene synthesis on SiO₂/Si, SiC and Ti6Al4V by hot filament chemical vapor deposition

Abstract

Graphene, a material formed from one layer of graphite, was obtained for the first time in 2004 by Novoselov and Geim. The interesting properties of this two-dimensional (2D) sp² hybridized material have led to an increase in research to find the most efficient method to obtain high-quality graphene on a large industrial scale. The exceptional properties of graphene have converted it into one of the most studied materials in the 20+ years since its discovery. Graphene has high electrical conductivity, elasticity, flexibility, hardness, chemical resistance and others outstanding properties that has converted it into a promising material for advances in science and technology. Graphene, in combination or deposited on other materials, can extend its application in multiple areas, such as electronic, energy storage, aerospace, and biomedical. The most common method to grow graphene is thermal chemical vapor deposition on copper, and the carbon layer is then transferred to the desired material. This transfer process often results in wrinkles, breaks, and contamination in the graphene films. For this reason, this work proposes a method to grow graphene directly on SiO₂/Si, SiC and Ti6Al4V by hot filament chemical vapor deposition (HFCVD). The relation between the growth parameters and the graphene films characteristics are presented here. Three chapters of this dissertation are dedicated to the analysis of graphene growth on each different substrate with their respective structural, morphological and compositional characterizations.<br /> <br /> The direct synthesis of graphene on SiO₂/Si by HFCVD was conducted at low pressures (35 Torr) with a mixture of methane/hydrogen and a substrate temperature of 970 ºC followed by spontaneous cooling to room temperature. A thin copper-strip was deposited in the middle of the SiO₂/Si substrate as a catalyst. Raman spectroscopy mapping and atomic force microscopy measurements indicate the growth of few-layers of graphene over the entire SiO₂/Si substrate, far beyond the thin copper-strip, while X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) showed negligible amounts of copper next to the initially deposited strip. The scale of the graphene nanocrystals were estimated by Raman spectroscopy and scanning electron microscopy (SEM).<br /> <br /> A method to grow graphene on 6H-SiC substrates at low pressure (35 Torr) by the HFCVD technique is also presented. The graphene deposition was conducted in an atmosphere of methane and hydrogen at low substrate temperatures (950 ºC). The graphene films were analyzed by using Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X ray, and X-ray photoelectron spectroscopy. Raman mapping and AFM measurements indicated that few layer and multilayer graphene were deposited from the external carbon source depending on the growth parameter conditions. The compositional analysis confirmed the presence of graphene deposition on SiC substrates and the absence of any metals involved in the growth process.<br /> <br /> An approach to grow graphene directly on Ti6Al4V pellets by HFCVD using methane as a carbon source is presented. This work establishes an analysis of graphene deposited on the Ti6Al4V alloy with the aim of reinforcing the properties of this alloy and increasing its future use in biomedical and engineering areas. Graphene deposition on Ti6Al4V was confirmed by Raman, SEM, EDS and XPS measurements and a growth mechanism is discussed.<br /> <br /> In summary, a method for each of the graphene growth processes on SiO₂/Si, SiC and Ti6Al4V is demonstrated, allowing the possibility for graphene production by the HFCVD method, which is well established for its versatility for industrial use.