Raman bands in microwave plasma assisted chemical vapour deposited films

Raman spectroscopy is employed to characterize thin diamond films deposited by microwave plasma assisted chemical vapour deposition technique using a gas mixture of methane and hydrogen. The surface morfology of the films was analyzed by scanning electron microscopy. We have identified submicron crystals on (100) facets of diamond crystals which gave rise to bands in the Raman spectrum centred at 1170 and 1456 cm-1

Diamond coatings on graphite for plasma facing materials

Nanocrystalline and microcrystalline diamond lms have been successfully deposited on graphite substrates for the rst time. The morphology of the lms depended on the experimental parameters used during deposition such as: gas mixture, excitation power, pressure and deposition time, along with nucleation treatments. Experiments are reported for removing non-diamond carbon material from commercial detonation nanodiamond used for seeding nucleation. Scanning Electron Microscopy (SEM), Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) techniques were used to characterise the samples. Optical Emission Spectroscopy (OES) and Mass Spectroscopy were used to analyse the species formed in the gas phase during diamond growth. We observed that the excitation power used during deposition a ects mainly the diamond crystallite size. Microcrystalline lms were obtained when the excitation power was 3.0 and 3.6 kW and nanodiamond lms were observed when 1.5 kW was used. The use of argon is essential for growing diamond on graphite and the methane content a ects the morphology, the sp3/sp2 content and the crystallite size of the lms. When using less than 5% of methane in the gas mixture, f100g faces are predominant even after long periods of deposition. Using 5% of methane results in a lm with cauli ower-like structure. Change in the morphology caused by secondary nucleation was observed after long deposition periods of time. To study the behaviour of our prepared samples under erosion conditions, diamond lms were exposed to hydrogen plasma etching and analysed in terms of lm quality (sp3/sp2 content) and growth/etching mechanisms. Finally, there is also included a study about the production of carbon bres on diamond lms during hydrogen plasma exposure in the presence of silicon

Chemical Vapour Deposition of Large-area High-quality Graphene Films for Electronic Applications

Low Pressure Chemical Vapour Deposition (LPCVD) and transfer processes are explored and optimized to obtain large-area, continuous and high quality monolayer graphene on target substrate. The size of synthesized graphene reaches up to 20 mm * 20 mm, and can be further extended by upgrading to a larger reaction chamber; the monolayer coverage rate and conductivity is better than normal commercial graphene products on the market. A novel frame-assisted method is developed to transfer graphene without introducing many defects and impurities. Annealing and acetone treatment are combined to remove PMMA residues effectively and unharmfully. A new under-etching route to fabricate graphene free-standing structure is also proposed and explored. A novel non-contact microwave examination method has been employed to simplify the sheet resistance measurement processes and to avoid the effects of metallic contacts. This method is simple and non-destructive to graphene, and can be further integrated into the graphene production line in the future. A new double-layer device is fabricated and utilized to observe the microwave field effect in graphene. The interaction between graphene and oxygen under different temperatures and oxygen partial pressures is studied and discussed. Strontium Titanate films (SrTiO3 or STO) are deposited on transferred CVD grown graphene on MgO substrates. Based on the oxidation test result, the deposition process of Strontium Titanate is optimized to minimize the defects introduced on graphene. Raman mapping data show that graphene is still continuous after the STO deposition although the D band suggests some newly formed defects.Open Acces

A fast synthesis route of boron-carbon-nitrogen ultrathin layers towards highly mixed ternary B-C-N phases

We report a direct and fast synthesis route to grow boron-carbon-nitrogen layers based on microwave-assisted plasma enhanced chemical vapour deposition (PECVD) by using methylamine borane as a single source molecular precursor. This easy and inexpensive method allows controlled and reproducible growth of B-C-N layers onto thin Cu foils. Their morphological, structural, chemical, optical and transport properties have been thoroughly characterized by a number of different microscopies, transport and spectroscopic techniques. Though disorder and segregation into C-rich and h-BN-rich domains have been observed in ultrathin flat few layers, high doping levels have been reached, inducing strong modifications of the electronic, optical and transport properties of C-rich and h-BN-rich phases. This synthesis procedure can open new routes towards the achievement of homogeneous highly mixed ternary B-C-N phase

Electron cyclotron resonance plasma enhanced chemical vapour deposition of sioxny : optical properties and applications

D.Ing. (Electrical And Electronic Engineering )Please refer to full text to view abstrac

Preparation and performance of nanostructured iron oxide thin films for solar hydrogen generation

Nowadays, energy and its resources are of prime importance at the global level. During the last few decades there have been several driving forces for the investigation of new sources of energy. Hydrogen has long been identified as one of the most promising carriers of energy. Photoelectrochemical (PEC) water splitting is one of the most promising means of producing hydrogen through a renewable source. Hematite (α-Fe2O3) is a strong candidate material as photoelectrode for PEC water splitting as it fulfils most of the selection criteria of a suitable photocatalyst material for hydrogen generation such as bandgap, chemical and photelectrochemical stability, and importantly ease of fabrication. This work has explored different preparation techniques for undoped and Si-doped iron oxide thin films using microwave-assisted and conventional preparation methods. Two distinct strategies towards improving PEC performance of hematite photoelectrodes were examined: retaining a finer nanostructure and enhancing the photocatalytic behaviour through doping. By depositing thin films using atmospheric pressure chemical vapour deposition (APCVD) and aerosol-assisted CVD (AACVD) at high temperature, it was shown that a combination of different factors (such as silicon incorporation into the hematite structure and formation of lattice defects, along with a nanostructure of small agglomerate/cluster enhancing hole transportation to the surface) were the contributing factors in improving the PEC performance in hematite films. The role of the Si-containing precursors and their consecutive effect on nanostructure of the hematite films were investigated. Further work is needed to study the decomposition pattern of precursors and consequent effects of Si additives as well as co-dopants on fundamental physical and electrical properties of hematite electrodes. In addition, the feasibility of using microwave annealing for the fabrication of iron oxide thin films prepared by electrodeposition at low temperature was also investigated. Hematite films showed improved PEC performance when microwave assisted annealing was used. Microwave heating decreased the annealing temperature by ~40% while the PEC performance was increased by two-fold. The improved performance is attributed to the lower processing temperatures and rapidity of the microwave method that help to retain the nanostructure of the thin films whilst restricting the grain coalescence to a minimum. Around 60% of the energy can be saved using this low carbon foot-print approach compared to conventional annealing procedures for the lab-scale preparation of hematite films – a trait that will have significant implications for scale-up production. The lower processing temperature requirements of the microwave process can also open up the possibility of fabricating hematite thin films on conducting, flexible, plastic electronic substrates

Copper-nanoparticle decorated graphene thin films: applications in metal-assisted etching and synthesis of next-generation graphene-based nanomaterials

Since 2006, the experimental discovery of graphene, a single-layer of carbon atoms, has spurred tremendous efforts towards new graphene-based materials. In graphene research, there is a recent trend towards next-generation materials in which graphene layers are locally modified in a controlled fashion at the nanoscale and tailored for specific applications. Examples include nanoparticle-decorated graphene thin films with surface potential tailored for nanoelectronics or advanced catalysis, graphene nanoribbons, graphene quantum dots, and the scalable fabrication of tiny pores in graphene, which are suitable to applications requiring ultrathin molecular sieving membranes. This research is focused on the development of new applications of copper-nanoparticle (Cu-np) decorated graphene thin films, towards the metal-assisted etching of graphene and the synthesis of next-generation graphene-based materials. Two different methods were utilized for Cu-np deposition: thermal evaporation – a technique operating under thermodynamic equilibrium, and DC-biased radio-frequency sputtering – a plasma-based quasi-equilibrium technique. Both methods are capable of producing ultrathin Cu layers on graphene, which can be subsequently annealed to nucleate Cu-np’s of tuneable diameter depending on the Cu layer thickness. Both techniques are suitable to be used in conjunction with large-area graphene thin films prepared by solution processing. In this thesis, three examples are presented involving the use of Cu-np’s to process graphene. In the first example, both etching and synthesis are involved: It was found that the simultaneous removal of Cu-np’s and the underlying graphene has led to the formation of graphene ribbons from corrugated graphene layers, in which nanoparticles do not deposit on ridges and wrinkles. In a second example, it was demonstrated that Cu-np-assisted etching may lead to the formation of nanoporous graphene-based membranes that are finding interesting applications as water nanofilters for the removal of impurities (e.g. Fe3+ and Mn2+) from water. In a third example, plasma-assisted synthesis of carbon on Cu-np’s was shown to lead to the growth of curved graphene quantum dots, with resistive memory effects that can find applications in data storage. These examples well represent the versatility of the Cu-np assisted processing methodology of graphene thin films, towards a large variety of next-generation carbon-based nanomaterials