SYNTHESIS OF GRAPHENE USING PULSED LASER DEPOSITION AND ITS CHARACTERIZATION

Abstract

Graphene is the two-dimensional carbon material which has gained strong research interest for more than last one decade owing to its unique properties which make it a promising material in a large number of potential applications, especially in the field of transparent electrodes, field effect transistors, solar cell, touch panels, supercapacitors, sensors, Li-ion batteries, etc. Till now, graphene has been synthesized by many physical and chemical methods that include micromechanical exfoliation, epitaxial growth on silicon carbide, chemical vapour deposition (CVD), reduction of graphite oxide, and molecular beam epitaxy (MBE). Most of these methods suffer from practical problems including high process temperature, ultra-high vacuum requirement, long growth duration, produce less perfect structure, low yield of production, and difficulties to control the number of graphene layers, which exhibit challenges for the material integration, cost, and throughput. In order to address above mentioned problems, we have proposed a new synthesis process based on pulsed laser deposition (PLD) technique for the formation of graphene layers in this thesis work. PLD technique is known to offer energetic carbon species upto a few hundred eV. However, a very limited study has been carried out on graphene fabrication by selecting appropriate substrates and PLD parameters like laser energy, laser wavelength, laser fluence, substrate temperature, cooling rate, and number of laser shots that affect the structural quality, growth, crystallinity, and the thickness of graphene films or number of graphene layers. The effect of some of these parameters is already known, but the extent of their effect in different conditions has not been explored. Knowledge of these factors will be of great significance to scientists and researchers in constructing the graphene films and to improve the structural quality, and to enhance the growth of graphene films on different substrates through PLD. Therefore, still improvement is required on some aspects of PLD-derived graphene. This thesis presents my research efforts aiming at these objectives. Recently, nickel has gained popularity as an important substrate material for graphene growth through PLD due to its higher carbon solubility and lattice mismatch, which allows growing graphene on any dielectric substrates as well as better control over the number of graphene layers. Here, by optimizing Ni and Cu pre-treatments, few- and multilayer ii graphene films have been synthesized on different substrates such as Ni/Si, quartz glass, SiO2/Si, and Cu/Si using highly ordered pyrolytic graphite (HOPG) through PLD technique. Then, their characterization have been carried out by using micro-Raman spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and two-point probe method. In this work, we have mainly focused on optimization of different experimental conditions to deposit graphene films on different substrates using highly ordered pyrolytic graphite through PLD technique and their characterization. Next, we have developed an effective and exciting route to obtain high-quality graphene films on glass substrate using some previous experimental conditions. In this study, we have grown few-layer graphene on corning glass with and without Ni films using highly ordered pyrolytic graphite through pulsed laser deposition and investigated their optical properties. Their structural characterizations were examined by Raman spectroscopy and X-ray diffraction, while the surface morphology of the as-synthesized graphene film was verified by scanning electron microscopy and optical microscopy. Likewise, carbon-carbon bond strength of graphene films was studied using X-ray photoelectron spectroscopy (XPS). Additionally, In order to achieve optical transmittance of graphene film, Ni was removed by dipping graphene sample in Ni etchant (DI water: HCl = 95:5) for 15 hours after PLD growth process. Then, the optical transmittance of PLD-derived graphene sample was measured by UV-visible spectroscopy. Finally, we have successfully grown few-layer graphene on two different types of SiO2 thickness covered Si substrates with the help of Ni film from highly ordered pyrolytic graphite through PLD technique. In this work, the influence of the buffer layer of SiO2 thickness covered Si on quality, growth, crystallinity and thickness of few-layer graphene in terms of substrate temperatures was also studied. The quality, growth, crystallinity and thickness of few-layer graphene were analyzed by Raman spectroscopy while the surface morphology of few-layer graphene was investigated using scanning electron microscopy. Moreover, Carbon-carbon bond strength and crystallinity of few-layer graphene were confirmed by X-ray photoelectron spectroscopy. The work presented in this thesis is based on six chapters.