Silicon carbide, SiC, is a semiconductor material which has many diverse uses in many of today's leading technologies. The wide band-gap aspect of the material has been utilized to create power and high frequency electronics, its physical hardness enables its use for MEMS devices, and the biological compatibility make perfect for utilization in medical applications. SiC is not a chemical compound normally found in nature and must be artificially generated. One of the methods used for the creation of single crystal, high quality SiC material is provided through the use of a chemical vapor deposition reactor. The University of South Florida currently has a horizontal hot-wallLPCVD reactor used by Dr. S. E. Saddow and his group to grow epitaxial SiC material for research grants by ONR and ARL.These agencies have commissioned the construction of a second LPCVD reactor for the primary purpose of growing 3C-SiC, a specific SiC crystal polytype, and this work describes the fabrication of the new reactor, MF2. This reactor was designed using the first reactor, MF1, as a template, but the design was modified to better facilitate single crystalline growth. The environment of the reactor is a very important consideration for crystal growth, and slight variations can cause critical defect incorporation into the crystal lattice. Many conditioning runs were required to facilitate the epitaxial growth of the different polytypes of SiC, and constant switching of the primary hot-zone required for the growth of hexagonal 4H-SiC and 6H-SiC to the hot zone required for 3C-SiC consumed precious resources and time. The new reactor uses a single primary control to monitor the three most important environmental concerns; hot-zone temperature, gaseous flow, and chamber pressure. The new reactor has been designed to use 100 mm Si substrates instead of the 50mm Si substrate size currently in use by MF1. The construction, testing, and 3C-SiC epitaxial growth on Si substrate capability of a 200 mm 3C-SiC hot-wall LPCVD reactor are demonstrated through this work.

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The increasing size of the car fleet makes it important to find ways of lowering the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from emissions at cold start, in the case when gasoline is utilized, and high NOx emissions and particulates from diesel engines. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose. One way of treating the high NOx levels from diesel engines is to introduce ammonia in the exhausts and let it react with the NOx in a special catalytic converter to form nitrogen gas and water, which is called SCR (selective catalytic reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. This thesis presents the efforts made to test the SiC-based field effect sensor device both as a cold start lambda sensor for gasoline engines and as an NH3 sensor for SCR systems in diesel engines. The MISiC (metal insulator silicon carbide) lambda sensor has proven to be both sensitive and selective to lambda, and its properties have been studied in lambda stairs both in gasoline engine exhausts and in the laboratory. There is, however, a small cross-sensitivity to CO. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The metal tends to form islands by time, which decreases the catalytic activity and thereby gives the sensor, which is binary when fresh, a linear behavior. Successful attempts to prevent the restructuring through depositing a protective layer of insulator on top of the metal were made. The influence of increasing the catalytic activity in the measurement cell was also studied. It was concluded that the location of the binary switch point of MISiC lambda sensors could be moved towards the stoichiometric value if the consumption of gases in the measurement cell was increased. The MISiC NH3 sensor for SCR systems has been shown to be highly sensitive to ammonia both in laboratory and diesel engine measurements. The influence of other diesel exhaust gas components, such as NOx, water or N2O has been found to be low. In order to make the ammonia sensor more long-term stable experiments on samples with different types of co-sputtered Pt or Ir/SiO2 gas-sensitive layers were performed. These samples turned out to be sensitive to NH3 even though they were dense and NH3 detection normally requires porous films. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application. / On the day of the ublic defence of the doctoral thesis, the status of article IV was: accepted, article V was: submitted and article VII was: manuscript.

Nanostructured silicon carbide (SiC) is considered today as a good alternative to the conventional materials for various multidisciplinary applications. In this thesis, SiC nanostructures were elaborated by means of electrochemical etching and laser ablation techniques. The first part of the thesis clarifies size-dependence of optical properties as well as importance of local-field effects onto the photoinduced electronic transitions of SiC nanostructures. In the second part of the thesis strong 15-fold photoluminescence enhancement of SiC nanoparticles is ensured by their near-field interactions with multipolar localized plasmons. Further, 287-fold and 72-fold plasmon-induced enhancement factors of two-photon excited luminescence and second harmonic generation is achieved, respectively. The main physical mechanisms responsible for the observed effects were described by three-dimensional finite-difference time domain simulations. Finally, the coupling effect of luminescent SiC nanoparticles to plasmonic nanostructures is used in the enhanced labelling of biological cells on the planar structures. As a perspective, colloidal plasmonic (Au@SiO2)SiC nanohybrids were elaborated and characterized.

The aim of this study is to investigate the mechanical behavior and its relation with processing and microstructure of the silicon carbide particulate (SiCp) reinforced aluminum matrix composite. Aluminum 7075 alloy is chosen as matrix alloy, in which zinc is the main alloying element. Four different additions of SiCp were used and the weight fractions were 10%, 15%, 20% and 30%. Composites were processed by with squeeze casting and the applied pressure during casting was 80 MPa. The mould is specially designed to produce both specimens ready for tensile and three point bending tests. Both as-cast and heat treated aluminum composites were examined and T6 heat treatment was applied. Three point bending tests were performed to reveal the fracture strength of aluminum composites. 10wt% SiCp aluminum composites showed the maximum flexural strength in both as-cast and heat treated composites. The mechanical test results revealed that precipitated phases in heat treated composites, behaved like fine silicon carbide particulates and they acted as barriers to dislocation motion. Maximum flexural strength increased about 40 MPa (10%) in as-cast and 180 MPa (44%) in heat treated composites. Tensile testing was also conducted to verify the results of the three point bending tests. Hardness tests were done to find the effect of silicon carbide addition and to find the peak hardness in heat treatment. For as-cast specimens hardness values increased from 133 to 188 Vickers hardness (10 kg.) with increase in SiCp content from 0 to 30wt% and for heat treatment specimens hardness values increased from 171 to 221 Vickers hardness (10 kg.). The peak hardness values were obtained at 24 hours precipitation heat treatment. SEM studies were carried out to examine the heat treated composites, to take SEM photographs and to obtain a general elemental analysis. Theoretical volume percentage addition of SiCp was checked with Clemex Image Analyzer program. Distribution of SiCp was determined by mettalographic examination. Second phases that were formed during heat treatment was searched by x-ray analysis.

Graphene is a single sheet of graphite. While bulk graphite is semimetal, graphene is a zero bandgap semiconductor. Band structure calculations show graphene has a linear energy dispersion relation in the low energy region close to the Dirac points where the conduction band and the valence band touch. Carriers in graphene are described as massless Dirac fermions in contrast to massive carriers in normal metals and semiconductors that obey a parabolic energy dispersion relation. The uniqueness of graphene band structure indicates its peculiar electronic transport properties. In this thesis work, single- and multi-layer graphene films epitaxially grow on either the Si face or the C face of SiC substrates in a homemade induction vacuum chamber by thermal decomposition of SiC at high temperatures. The surface morphology and crystal structure of epitaxial graphene are studied with surface analysis tools. The transport properties of epitaxial graphene are studied by magnetotransport experiments. An epitaxial graphene film turns out to be a multilayered graphene because carriers in epitaxial graphene act as those in single layer graphene. Top gated and side gated epitaxial graphene field effect transistors (FETs) have also been successfully fabricated. These systematic studies unambiguously demonstrate the high quality of epitaxial graphene and the great potential of epitaxial graphene for electronic applications

Graphene, a honeycomb lattice of sp2-bonded carbon atoms, has received considerable attention in the scientific community due to its unique electronic properties. Distinct symmetries of the graphene wave functions lead to unusual quantum properties, such as a unique half-integer quantum Hall effect. As an added consequence of these symmetries, back-scattering in graphene is strongly prohibited leading to long coherence lengths of carriers. These charge carriers at low energy exhibit linear energy-momentum dispersion, much like neutrinos. Thus, carriers in graphene can be described as massless Dirac fermions. Graphene grown epitaxially on semiconducting substrates offers the possibility of large-scale production and deterministic patterning of graphene for nanoelectronics. In this work, epitaxial graphene is created on SiC(0001) by annealing in vacuum. Sequential scanning tunneling microscopy (STM) and spectroscopy (STS) are performed in ultrahigh vacuum at a temperature of 4.2 K and 300 K. These atomic-scale studies address the growth, interfacial properties, stacking order, and quasiparticle coherence in epitaxial graphene. STM topographic images show the atomic structure of successive graphene layers on the SiC substrate, as well as the character of defects and adatoms within and below the graphene plane. STS differential conductance (dI/dV) maps provide spatially and energy resolved snapshots of the local density of states. Such maps clearly show that scattering from atomic defects in graphene gives rise to energy-dependent standing wave patterns. We derive the carrier energy dispersion of epitaxial graphene from these data sets by quantifying the dominant wave vectors of the standing waves for each tunneling bias.

The deposition of hydrocarbons on silicon substrates is a topic of wide interest. This is generally related to the technological importance of silicon carbide (SiC) and a growing interest in graphene and graphitic materials. Methods for producing these materials predominantly involve high processing temperatures. In the case of SiC, these high processing temperatures often result in the formation of surface defects, which compromise the electronic properties of the material. In an effort to grow SiC films at low temperatures, a technique known as electron-beam chemical vapor deposition (EBCVD) has been developed. Most electron beam deposition techniques employ a focused beam of high-energy (20-30 keV) electrons to form nanometer-sized solid deposits on a surface. However, in an effort to deposit macroscale films, a broad beam of low-energy electrons was used. In addition to investigating the applications of low-energy electrons in semiconductor film growth, the fundamental chemical and physical processes induced by the bombardment of adsorbate-covered surfaces with low-energy electrons were examined. Specifically, the electron-stimulated desorption of various adsorbate-substrate systems such as acetylene adsorbed on silicon, graphene oxide on silicon, and ultrathin graphite films on silicon carbide have been investigated. The yields of cation and neutral desorbates as a function incident electron energy were measured, appearance thresholds were determined and mechanisms of desorption were proposed.

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.