In this research work, we have investigated the band engineering of epitaxial graphene using first principles calculations. Epitaxial graphene on SiC (0001) surface is modified by using different methods such as intercalation, doping, passivation and oxidation. The calculations are done using Density functional theory which is implemented in quantum espresso package. In the presence of H intercalation, epitaxial graphene is shown to have p type behavior with monolayer graphene. However this behavior is different for multilayer epitaxial graphene systems, and it depended on the concentration of the H atoms. When epitaxial graphene is intercalated with Ge atoms, the Ge atoms make clusters and these clusters are responsible for the electronic properties of the epitaxial graphene systems. As a result of oxidation of epitaxial SiC surface, the graphene layer is mostly stable on the surface for both silicates and oxynitrides structures. For silicate/SiC configurations, the epitaxial graphene is shown to be less n type. For oxynitrides/ SiC configurations, epitaxial graphene is shown to be neutral. In the presence of oxygen intercalation with silicate/SiC, epitaxial graphene is shown to have p type behavior. These systematic studies of epitaxial graphene will opens up great potential for electronic applications. Additionally the resultant models can be used to guide further studies.

Graphene is a promising material for chemical sensing applications and many studies have focused on incorporating graphene into \sgfet s sensors. The purpose of this work is to get a deeper understanding of the physics governing the surface interaction of graphene in \sgfet s with ions and charged molecules. With a clearer understanding of how these interactions register in the conductivity of graphene, it then may be possible to design the ultrasensitive sensors that are often predicted to be possible when using graphene. Epitaxial graphene (EG) and graphene produced by chemical vapor deposition (CVD) were used to fabricate \sgfet s that were tested under different ionic strength conditions and concentrations of charged proteins. To get a clearer picture of the electrostatic gating effect in ionic solutions, we analyzed our data combining two models: the electrical double layer model, which accounts for the distribution of ions inside the solution, and a ionization model that accounts for ionizable groups on the graphene surface. This gave us an insight into the influence of charged groups fixed to the surface on the gating effect which is fundamental to the performance of \sgfet s as sensors. Using our experimental data we were also able to estimate the density of charged impurities in two carrier density regimes. For high densities, we found a correlation between our estimated impurities and the surface charge that suggests that the ionizable groups act as impurities. For small carrier densities, we modeled the carriers using a self-consistent approximation (SCA). The impurities estimated from the SCA model do not seem to be related to the ionizable groups and so the origin of the conductivity for small density seems to be originated by the permanently charged impurities only. Our estimation of the charged impurities for our charged-protein adsorption experiments showed a relation between their values and the protein concentration. This shows that the proteins interact with the graphene as charged impurities. Overall, our experiments allowed us to gain a deeper understanding of the interaction of charged particles with graphene. The analysis performed in this work gives a guide for the development of graphene \sgfet s sensors by engineering the impurities at the surface to optimize the sensitivity. The design of receptors for specific sensing that do not require charged targets is possible with engineering the charge that the receptor presents to graphene when the analyte concentration changes.

Thermal annealing 4H-SiC(0001) substrates to produce epitaxial graphene on Si-terminated SiC was performed using five different procedures, i.e. direct and indirect current heating at different based pressures and a temperature of about 1300 . The aim is to study the effects of graphene growth under different conditions and also to produce large homogeneous graphene. To investigate the prepared samples, two surface analytical techniques, i.e. low energy electron microscopy (LEEM) and photoelectron spectroscopy (PES) have been used. LEEM was first used to observe the surface morphologies of the prepared samples. In combination with LEEM instrument, low energy electron diffraction (LEED) was used to verify the existence of graphene on SiC substrate. The number of graphene layer was determined by collecting electron reflectivity at different electron energies. The number of dips observed in the electron reflectivity curve corresponds to the number of graphene layer. The experimental results obtained from LEEM and LEED have demonstrated that a film consisting of fairly large domains of 1 and 2 monolayer (ML) graphene was obtained by direct current heating of SiC under high vacuum (HV) condition with the based pressure of 10-6 Torr. A domain size in the range of up to about 5 to 10 μm have been observed. Meanwhile another graphene film prepared by the same method and the same temperature but under ultra high vacuum (UHV) condition with the based pressure of 10-10 Torr has much smaller domain size of 1 ML graphene compared to that grown under HV condition. We therefore suggested that the based pressure during the graphene growth has a strong influence on the morphology of graphene. This is because the Si evaporation rate is suppressed when heated in a high pressure environment, which normally leads to the improvement of the surface quality. The suppression of the Si evaporation rate has also been verified by a result obtained from the other sample directly heated under much higher based pressure, i.e. in an argon (Ar) environment of 1 atm. In addition to LEEM and LEED, the existence of graphene on SiC substrate has also been verified by the PES measurement. The C1s spectrum of graphene sample grown on SiC(0001) substrate showed three components, i.e. bulk SiC, graphene (G) and the buffer layer (B) located at 283.7 eV, 284.5 eV and 285.1 eV, respectively. The intensity ratios of the three components in the C1s spectrum were also used to estimate the number of graphene layer. The estimated number of graphene layer corresponds to the result obtained from LEEM.

The objective of this research was to perform a systematic investigation of the unique structural and electrical properties of epitaxial graphene at the nanoscale. As the semiconductor industry faces increasing challenges in the production of integrated circuits, due to process complexity and scaling limitations, new materials research has come to the forefront of both science and engineering disciplines. Graphene, an atomically-thin sheet of carbon, was examined as a material which may replace or become integrated with silicon nanoelectronics. Specifically, this research was focused on epitaxial graphene produced on silicon carbide. This material system, as opposed to other types of graphene, holds great promise for large-scale manufacturing, and is therefore of wide interest to the academic and industrial community. In this work, high-quality epitaxial graphene production was optimized, followed by the process development necessary to fabricate epitaxial graphene nanoribbon transistors for electrical characterization. The structural and electrical transport properties of the nanoribbons were elucidated through a series of distinct experiments. First, the size-dependent conductivity of epitaxial graphene at the nanoscale was investigated. Next, the alleviation of the detrimental effects revealed during the size-dependent conductivity study was achieved through the selective functionalization of graphene with hydrogen. Finally, two techniques were developed to allow for the complementary doping of epitaxial graphene. All of the experiments presented herein reveal new and important aspects of epitaxial graphene at the nanoscale that must be considered if the material is to be adopted for use by the semiconductor industry.

Forests have as a of late become increasingly plagued with bark beetle infestations as a result of climate change. The damage caused by tree killing bark beetles has within recent years seen a substantial increase. Detecting and removing infested trees at an early stage is an essential part of mitigating the spread of and the damage caused by the beetle. Today, the most common way of early detection is visual detection by forestry personnel. However, this is time consuming with highly variable results. In this thesis a novel approach to tracing the European spruce bark beetle through pheromone detection is investigated. With this approach, the antennae of the beetle were paired with an epitaxial graphene chip in order to create a bioinspired smell sensor. Tests were conducted on the sensor in order to investigate how the resistance changed over the chip as a result of the sensor being exposed to the pheromone 2-methyl-3-buten-2-ol. As a result of the tests, a corelation between exposing the sensor to pheromone and an increase of the resistance over the graphene chip was noted. However, more tests need to be conducted in order to draw any definite conclusions about the efficacy of the sensor in its current form. Additionally there are opportunities to investigate further optimization alternatives regarding the design of the sensor.

For graphene to be a viable platform for nanoscale devices, high quality growth and structures are necessary. This means structuring the SiC surface to prevent graphene from having to be patterned using standard microelectronic processes. Presented in this thesis are new processes aimed at improving the graphene as well as devices based on high quality graphene nanoribbons. Amorphous carbon (aC) corrals deposited prior to graphene growth are demonstrated to control SiC step-flow. SiC steps are shown to be aligned by the presence of the corrals and can increase SiC terrace widths. aC contacts deposited and crystallized during graphene growth are shown as a way to contact graphene without metal lift-off. Observation of the Quantum Hall Effect demonstrates the high quality of the graphene grown alongside the nanocrystalline graphite contacts. Continuing the ballistic transport measurements on sidewall graphene nanoribbons, the invasive probe effect is observed using an atomic force microscope (AFM) based technique that spatially maps the invasive probe effect. Cleaning experiments demonstrate the role of scattering due to resist residues and environmental adsorbates on graphene nanoribbons. Finally, switches based on junctions formed in the graphene nanoribbons are shown as a route toward graphene based devices.

After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. Graphene is generally considered to be a strong candidate to succeed silicon as an electronic material. However, to date, it actually has not yet demonstrated capabilities that exceed standard semiconducting materials. One disadvantage of conventionally fabricated graphene devices is that nanoscopically patterned graphene tends to have disordered edges that severely reduce mobilities thereby obviating its advantage over other materials. The other disadvantage is that pristine graphene does not contain a band gap, which is critical for standard field effect transistor to operate. This thesis will show that graphene grown on structured silicon carbide surfaces overcomes the edge roughness and promises to provide an inroad into nanoscale patterning of graphene. High-quality ribbons and rings can be made using this technique.

Graphene grown epitaxially on silicon carbide provides a potential avenue toward industrial-scale graphene electronics. A predominant aspect of the multilayer graphene produced on the carbon-terminated (000 -1) face of SiC is the rotational stacking faults between graphene layers and their associated moire-pattern superlattice. We use scanning tunneling microscopy (STM) and spectroscopy (STS) in high magnetic fields to obtain detailed information about the "massless Dirac fermions" that carry charge in graphene. In agreement with prior investigations, we find that for small magnetic fields, the rotational stacking effectively decouples the electronic properties of the top graphene layer from those below. However, in maps of the wavefunction density at magnetic fields above 5 Tesla, we discover atomic-scale features that were not previously known or predicted. A phenomenological theory shows that this high-field symmetry-breaking is a consequence of small cyclotron-orbit wavefunctions, which are sensitive to the local layer stacking structures internal to the moire superlattice cell. The broken symmetry is sublattice degeneracy, predicated by atomic scale variations that derive from the sublattice polarization of graphene wavefunctions.

Graphene, a sheet of carbon atoms organized in a honeycomb lattice, is a two dimensional crystal. Even though the material has been known for a long time, only recently has it stimulated considerable interest across different research areas. Graphene is interesting not only as a platform to study fundamental physics in two dimensions, but it also has great potential for post-silicon microelectronics owing to its exceptional electronic properties. Of the several methods known to produce graphene, epitaxial growth of graphene by sublimation of silicon carbide is probably the most promising for practical applications. This thesis is a theoretical study of the growth kinetics of epitaxial graphene on SiC(0001). We propose a step-flow growth model using coarse-grained kinetic Monte Carlo (KMC) simulations and mean-field rate equations to study graphene growth on both vicinal and nano-faceted SiC surfaces. Our models are consistent with experimental observations and provide quantitative results which will allow experimenters to interpret the growth morphology and extract energy barriers from experiments. Recently, it has been shown that graphene grown epitaxially on metal surfaces may lead to potential applications such as large area transparent electrodes. To study deposition-type epitaxial growth, we investigate a new theoretical approach to this problem called the phase field method. Compared to other methods this method could be less computationally intensive, and easier to implement at large spatial scales for complicated epitaxial growth situations.

Graphene is widely considered to be a promising candidate for a new generation of electronics, but there are many outstanding fundamental issues that need to be addressed before this promise can be realized. This thesis focuses on the production and properties of graphene grown epitaxially on the carbon terminated face (C-face) of hexagonal silicon carbide leading to the construction of a novel graphene transistor structure. C-face epitaxial graphene multilayers are unique due to their rotational stacking that causes the individual layers to be electronically decoupled from each other. Well-formed C-face epitaxial graphene single layers have exceptionally high mobilities (exceeding 10,000 cm^2/Vs), which are significantly greater than those of Si-face graphene monolayers. This thesis investigates the growth and properties of C-face single layer graphene. A field effect transistor based on single layer graphene was fabricated and characterized for the first time. Aluminum oxide or boron nitride was used for the gate dielectric. Additionally, an all graphene/SiC Schottky barrier transistor on the C-face of SiC composed of 2DEG in SiC/Si2O3 interface and multilayer graphene contacts was demonstrated. A multiple growth scheme was adopted to achieve this unique structure.