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Elisseva, Tatiana VSynthesis and Characterization of Imidazole Complexes of Silanes
Doctor of Philosophy, University of Akron, 2008, Chemistry

The aim of the research was to examine a model system for the chemistry that is involved in the biomineralization of SiO2 in certain demosponges. In particular, the interaction of a silica protein, a silicatein, with silicon reagents was modeled. The active site of silicatein contains histidine and serine amino acid side4 chains.

Several imidazole-based silane complexes of the general form SiPh3OL were synthesized as a preliminary model. In order to model the histidine-serine sites of the silicatein, the ligands were used that are bound to the silicon via Si-O linkages and also have a potentially chelating imidazole ring. The three OL ligands were derided from the alcohols ROH: 1-hydroxydecyl-imidazole (HOL1), 4-hydroxymethyl-5-methyl-imidazole (HOL2), and 6-imidazole-1-ylmethyl-pyridine-2-ylmethanol (HOL3). Synthesis of the SiPh3OL complexes from chlorosilanes was achieved in two ways. The first one is the reaction of chlorosilanes or alkoxysilanes with the same number of equivalents of ligand and triethylamine or pyridine as a base. The second method is the reaction of chlorosilanes with two equivalents of the imidazole containing ligand, where one equivalent acts as a base for the HCl generated during the reaction. Removal of the HCl by-product from the reaction of SiPh3Cl and HOL was a problematic part of the syntheses of the three SiPh3OL compounds. The use of such bases as pyridine and Et3N yielded products that were less pure than when HOL was used as the base. Compounds with a high reactivity toward hydrolysis were obtained and characterized by a variety of techniques.

The syntheses of other complexes of the OL ligands were attempted. The oil Si(OL1)4 was prepared in low yield. Attempt to prepare the compounds SiPh2(OL1)2 and SiPh2(OL2)2 from chlorosilanes and from alkoxysilanes at best gave impure compounds or very complex mixtures.

Another project included the syntheses of proposed intermediates which could form during biomineralization. These intermediates are predicted to be high coordinate species extremely sensitive to hydrolysis reactions. To investigate the possible products, the reactions of chlorosilanes: SiPhCl3 and SiCl4 with 1,1‵-methyline imidazole and methyl imidazole and HOL1, respectively were performed. The products of this reaction were solids with specific chemical shifts of 5- and 6-coordinated silicon complexes were characterized by solid state NMR due low solubility.

Committee:

Claire Tessier (Advisor); Wiley Youngs (Other); Christopher Ziegler (Other); Chrys Wesdemiotis (Other); Amy Milsted (Other)

Subjects:

Chemistry, Inorganic

Keywords:

mineralization; silicon deposition; silicon,high-coordinated silicon complexes; N-containing ogranic bases; imidazoles

Carbaugh, Daniel J.Growth and Characterization of Silicon-Based Dielectrics using Plasma Enhanced Chemical Vapor Deposition
Master of Science (MS), Ohio University, 2014, Electrical Engineering (Engineering and Technology)
Plasma Enhanced Chemical Vapor Deposition (PECVD) is widely used in industry for its low temperature growth capability, excellent conformity (step coverage) and higher deposition rates. Silicon dioxide (SiO2), silicon nitride (Si3N4) and silicon oxynitride (SiOxNy) are common dielectrics deposited using PECVD and they will be the main focus of this thesis. These common dielectrics are used in a range of different applications, from optical waveguides to photovoltaic passivation layers and from transistor fabrication to micro electromechanical systems (MEMS) devices. PECVD system parameters (temperature, pressure, power, and gas ratio) are methodically varied and the resulting thin films are characterized. This requires many different metrology techniques such as: atomic force microscopy (AFM), ellipsometry, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Optical and structural properties of the resulting thin films are analyzed via a careful design of experiments to determine which system parameter has the most significant effect and to which extent they can be varied.

Committee:

Savas Kaya, Ph.D (Advisor); Faiz Rahman, Ph.D (Committee Member); Wojciech Jadwisienczak, Ph.D (Committee Member); David Drabold, Ph.D (Committee Member)

Subjects:

Electrical Engineering; Materials Science; Nanoscience; Nanotechnology

Keywords:

PECVD; Plasma Enhanced Chemical Vapor Deposition; Silicon Dioxide; Silicon Nitride; Silicon Oxynitride; Thin Films;

Xiao, ZhigangSynthesis of Functional Multilayer Coatings by Plasma Enhanced Chemical Vapor Deposition
PhD, University of Cincinnati, 2004, Engineering : Electrical Engineering
Silicon dioxide, silicon-containing polymer, silicon nitride, metal nitride, and germanium thin films were grown by electron cyclotron resonance (ECR) microwave plasma enhanced chemical vapor deposition (PECVD), and multilayer coatings were grown for high hardness and high corrosion resistance. Silicon dioxide was grown from hexamethyldisiloxane (HMDSO), 1,3,5,7-tetramethylcyclotetrasiloxane (TOMCTS ), and octamethylcyclotetrasiloxance (OMCTS) in a oxygen plasma. The grown silicon dioxide thin films were hard and colorless. Silicon nitride was grown from hexamethyldisiloxane (HMDSO) and tetramethylsilane (TMS) in an ammonia (NH3) plasma. The silicon nitride thin films grown from HMDSO were hard and transparent while the silicon nitride thin films grown from TMS were black and hard. Silicon-containing polymer was grown from 100% OMCTS. The polymer thin films are colorless, had relatively low hardness and very good salt-fog corrosion resistance. Titanium nitride, zirconium nitride, and chromium nitride were grown from titanium (IV) isopropoxide and tetrakis(dimethylamino)titanium, zirconium 2-methyl-2-butoxide and zirconium t-butoxide, and bis(ethylbenzene)chromium in an ammonia plasma. The grown titanium nitride and zirconium nitride thin films had characteristic gold coloring and high hardness while the grown chromium nitride thin films were black gray and had high hardness. Germanium thin films were grown from tetramethylgermane (TMG) in a argon plasma. The deposited germanium films were uniform and had polished-like shining surface. X-ray photoelectron spectroscopic (XPS) analyses showed the films contained 97 % germanium atomic concentration with less than 1 % carbon, and X-ray diffraction (XRD) analyses showed the films had the crystal structure of <220>. Hard corrosion-resistant silicon-containing multilayer coatings were grown in a high-density microwave electron cyclotron resonance discharge. The multilayer coatings consist of a relatively soft silicon-containing polymer thin film as the bottom layer and a hard silicon dioxide or silicon nitride thin film as the top layer. Silicon-containing polymer thin films were grown from 100% OMCTS. Silicon dioxide and silicon nitride thin films were grown from OMCTS with O2 and HMDSO with NH3, respectively. The multilayer structures combined high surface hardnesses with good corrosion resistance, surviving 1800 to 2600 hours in an ASTM B117 salt-fog corrosion test. Multilayer coatings with a titanium nitride or zirconium nitride bottom layer and a transparent silicon-containing polymer or silicon dioxide top layer were grown in a high-density microwave electron cyclotron resonance discharge for protective or decorative coating application. The grown multilayer coatings had gold coloring and good film thickness.

Committee:

Dr. Thomas Mantei (Advisor)

Keywords:

PECVD; ECR; Multilayer Coating; Silicon Dioxide; Silicon Nitride; Silicon-Containing Polymer; TiN Thin Film; ZrN Thin Films; CrN Thin Films; Ge Thin Film; ASTM B117; and DLI

CHEN, LIA BIOINSPIRED MICRO-COMPOSITE STRUCTURE
Doctor of Philosophy, Case Western Reserve University, 2005, Civil Engineering
This thesis involves the design, fabrication and mechanical testing of a bioinspired composite structure with characteristic dimensions of the order of tens of microns. The particular microarchitecture, designed and fabricated using microelectromechanical systems (MEMS) technology, involves two distinct length scales and represents a first attempt at mimicking the crossed-lamellar microstructure of the shell of the Giant Queen Conch Strombus gigas, which contains features the dimensions of which span five distinct length scales. After giving a review of the mechanical properties of mollusks, the detailed design of a microstructure, which approximates the crossed-lamellar arrangement of Strombus gigas, is presented. Fabrication of the microstructure using multi-microfabrication methods is conducted in terms of the designed fabrication flow. The problems encountered during the processes are discussed. The measurements of the strength, stiffness and work of fracture of the fabricated microstructure are conducted using a commercially available nanoindenter. Testing results are discussed and conclusions about the mechanical behaviors of the microstructure are drawn to summarize the achievement of this thesis. Finally, future work is outlined to point out the possible directions for improving the mechanical performance of the bioinspired composite. In parallel with my thesis research, I have developed a theoretical model for the experimentally observed cyclic loading-induced strengthening in MEMS polycrystalline silicon. The model relies on atomistic calculations that predict plastic-like behavior of amorphous silicon, which depending on initial density, is associated with dilatancy or compaction. The amorphous silicon is approximated as a Drucker-Prager plastic material, whose parameters are chosen to match the predictions of the atomistic calculations. The constitutive model is used to simulate the mechanical response to cyclic loads of notched polysilicon MEMS specimens containing deforming amorphous grain boundaries. The results demonstrate that certain combinations of mean stress and alternating stress produce plastic deformation and significant residual compressive stresses at the root of the notch, and in turn an increase in nominal strength. This work is presented in Chapter 6.

Committee:

Roberto Ballarini (Advisor)

Keywords:

Photoresist; silicon; Sputtered silicon; Etching; silicon film

Maiz, Jose A.Fabrication and characterization of crystalline silicon on insulator by the tungsten strip heater method /
Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Silicon crystals;Silicon crystals

SURYAMOORTHY, SOWMYAETCHING TECHNOLOGIES IN SUPPORT OF THE DEVELOPMENT OF A COHERENT POROUS SILICON WICK FOR A MEMS LHP
MS, University of Cincinnati, 2004, Engineering : Electrical Engineering
The Coherent porous silicon (CPS) etching technology is a novel technique by which vast arrays of micrometer sized through-holes are photoelectrochemically etched into a (100) oriented silicon wafer. The fabrication steps for the CPS formation include microelectronic processes such as oxidation, diffusion, photolithography and photon pumped electrochemical etching on a 2 inch diameter N type silicon wafer with resistivities ranging from 4 ohm cm to 60 ohm cm. Anisotropic etching in 46% aqueous solution of potassium hydroxide is employed to create the inverted pyramidal etch pits that define the location of the pores. Very steep porous structures with aspect ratios (AR) varying from 40 to 100 are fabricated by the CPS etching technology. The pores facilitate an anisotropic etch profile, which is required for the desired high AR although an isotropic etch process is used. In silicon, the different low index planes etch at different rates in an anisotropic etchant. Certain formulations are favored in removing atoms from the (110) and (100) planes. This result is exploited in the post processing of the CPS sample. The porous structures are then characterized to determine the actual pore diameter, pore spacing and porosity to be used as a CPS wick housed in an evaporator of a Loop Heat Pipe (LHP).The LHP is a versatile, passive two phase heat transport device with a high effective thermal conductivity. The input heat energy is converted to latent heat of vaporization at the evaporator and this energy is carried along a vapor line to the condenser where it is converted to latent heat of condensation. The working fluid, water in the present case, is circulated back to the evaporator due to the capillary action of the fine coherent porous wick. The large thermodynamic temperature difference between the evaporator and the condenser is responsible for the circulation of the water around the LHP and this completes the cycle.

Committee:

Dr. Thurman Henderson (Advisor)

Keywords:

Silicon Electrochemical Etching; MEMS/MST fabrication; Coherent, Nanoporous Silicon;

Al-Ahmadi, Ahmad AzizCOMPLEMENTARY ORTHOGONAL STACKED METAL OXIDE SEMICONDUCTOR: A NOVEL NANOSCALE COMPLEMENTRAY METAL OXIDE SEMICONDUCTOR ARCHTECTURE
Doctor of Philosophy (PhD), Ohio University, 2006, Electrical Engineering & Computer Science (Engineering and Technology)

This dissertation presents a simulation study of a novel CMOS device architecture capable of building complementary logic operation using only a single gate stack. The new architecture, named complementary orthogonal stacked MOS (COSMOS), places the n and p-MOSFETs perpendicular to one another under a single gate. As a result of concurrent vertical and lateral integration, the COSMOS architecture can lead to dramatic savings in active device area of a conventional static CMOS pair, as well as significant reductions in R-C device parasitics. We demonstrate how the COSMOS devices may be built, operated, and optimized for symmetric operation, also verifying logic operation via 3D device simulations. The proposed COSMOS architecture is based on strained Si/SiGe on insulator (SSOI) technology that has recently become available. This work is the first comprehensive treatment of general properties of COSMOS architecture to our knowledge and should allow designers to understand and design COSMOS devices and circuits in future.

Committee:

Savas Kaya (Advisor)

Keywords:

COSMOS; Nanoscale CMOS; Silicon Germanium Alloys; Silicon on Insulator Technology; A Novel CMOS; Ultra-Large-Scale Integration

Kim, Hyoun-EeGaseous corrosion of silicon carbide and silicon nitride in hydrogen /
Doctor of Philosophy, The Ohio State University, 1987, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Silicon carbide;Silicon nitride;Hydrogen

Wiseman, Charles R.Production of silicon and silicon nitride powders by a flow reactor
Master of Science (MS), Ohio University, 1988, Mechanical Engineering (Engineering)
Production of silicon and silicon nitride powders by a flow reactor

Committee:

Khairul Alam (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Silicon; Silicon Nitride Powders; Flow Reactor

Nwugo, Chika CharlesPhysiological and Molecular Studies on Silicon-Induced Cadmium Tolerance in Rice (Oryza sativa L.)
Doctor of Philosophy, Miami University, 2008, Botany
Plant productivity is seriously limited by cadmium (Cd) toxicity. Studies suggest that silicon (Si) plays a significant role in the alleviation of Cd-stress in plants. In this study, gas exchange, chlorophyll fluorescence, growth, tissue-element content, and proteomic analysis were performed on rice plants exposed to varying Si and Cd concentrations/durations towards elucidating the mechanisms involved in Si-induced Cd tolerance in hydroponically-grown rice (Oryza sativa L.) plants. The first part of this study (chapters 1 and 2) involved the investigation of the effects of different Si concentrations (0.0, 0.2, 0.6 mM) and time of Si addition on rice plants exposed to different Cd concentrations (0.0, 2.5 μM, or 5.0 μM) and time of Cd treatment. Our results showed that Si-induced Cd tolerance is mediated by a significant inhibition of Cd-uptake, regardless of time and duration of Cd/Si exposure. Additionally, our results suggest that a late addition of 0.6 mM Si is required for the alleviation of low-level (2.5 μM) long-term Cd-mediated growth inhibition. Results also suggest that Si-induced increase in instantaneous water-use-efficiency is more significant in the alleviation of low-level long-term Cd-stress, while Si-induced increase in photosynthesis rate is more significant in the alleviation of moderate (5.0 μM) level short-term Cd-stress. Furthermore, we suggest that 0.2 mM Si might be close to an optimum Si-dose requirement for the alleviation of Cd-stress in rice plants. Chlorophyll fluorescence results also provided the first real evidence that Si alleviates Cd toxicity by improving light-use-efficiency. Studies have suggested that Si-induced Cd tolerance is mediated by a chelation mechanism. Thus, we investigated the effects of a synthetic chelator, EGTA, and Si on Cd-uptake, growth and photosynthesis of rice plants under different Cd levels and exposure durations (chapter 4). Our results suggest that EGTA enhances Si-induced Cd tolerance but the mechanisms employed by EGTA and Si towards systemic Cd-exclusion might differ. Furthermore, we suggest that in the absence of Cd, the combined effect of EGTA and Si inhibits growth and photosynthesis due to a proposed synergistic inhibition of nutrient-uptake. Finally, we combined physiological and proteomic approaches to identify the molecular mechanisms involved in Si induced Cd tolerance in rice plants (chapter 5). Our results showed that in unstressed plants, the addition of Si down-regulated five proteins including glycine dehydrogenase (decarboxylating) but in Cd-stress plants, Si up-regulated five proteins including class III peroxidase and RUBISCO. Furthermore, we observed that Si nutrition inhibited Cd-induced down-regulation of putative ferredoxin-NADP(H) oxidoreductase, a Zn-binding oxidoreductase and cysteine synthase. Taken together, in this dissertation, we proposes that Si-induced Cd tolerance in plants is a holistic process involving physiological and biochemical mechanisms, including Cd-uptake inhibition, enhancement of photosynthetic efficiency and modulation of protein expression.

Committee:

Alfredo Huerta, PhD (Advisor); Nancy Smith-Huerta, PhD (Committee Member); John Hawes, PhD (Committee Member); Martin Henry Stevens, PhD (Committee Member); Daniel Gladish, PhD (Committee Member)

Subjects:

Botany

Keywords:

cadmium-stress; chlorophyll fluorescence; EGTA; photosynthesis; proteins; silicon; stomatal conductance; silicon

PUNNAMARAJU, SRIKOUNDINYACONTRIBUTIONS TO THE DEVELOPMENT OF A NOVEL METHOD IN LOW TEMPERATURE BONDING OF SILICON-SILICON AND GLASS-GLASS
MS, University of Cincinnati, 2003, Engineering : Electrical Engineering
This work describes the development of a new low temperature bonding technique for bonding silicon-silicon and thick silicon dioxide-Pyrex glass. Silicon-silicon bonding was achieved at 300 degrees centigrade with intermediate doped silicon dioxide layer (0.5-0.7 microns thick). Pyrex glass was successfully bonded to very thick silicon dioxide (2 microns thick) at 450-500 degrees centigrade. Neither type of bonding is possible with conventional bonding techniques. A novel concept using sodium doped thermal silicon dioxide intermediate layers was utilized for achieving this bonding. Sodium doped silicon dioxide was thermally grown using wet oxidation. A minute quantity of sodium chloride was mixed in deionized water during wet oxidation to dope sodium into the thermally grown oxide. With the application of heat and voltage, the electrostatic force of attraction binds the samples together. Bond strengths in the range of 1-4MPa were achieved. The author worked with silicon dioxides that were all thicker than 0.5 microns. The author explored this new concept (developed earlier at a very cursory level in this lab) and narrowed it to a greater extent. The author also worked on other bonding issues such as Coherent Porous Silicon (CPS) bonding to thick Pyrex glass samples for micro loop heat pipe packaging, metal- metal bonding utilizing intermediate glass layers and direct bonding of two thick glass substrates. The author suggests some solutions to overcome the constraints in bonding the above-mentioned samples. Finally, the author recommends further research in this novel bonding technique and also recommends some modifications to the SUSS MicroTec SB6 bonder.

Committee:

Dr. H. Thurman Henderson (Advisor)

Keywords:

silicon-silicon bonding; glass-glass bonding; low temperature bonding; MEMS; bond strength

Huang, ZhiquanSpectroscopic Ellipsometry Studies of Thin Film a-Si:H/nc-Si:H Micromorph Solar Cell Fabrication in the p-i-n Superstrate Configuration
Doctor of Philosophy, University of Toledo, 2016, Physics
Spectroscopic ellipsometry (SE) is a non-invasive optical probe that is capable of accurately and precisely measuring the structure of thin films, such as their thicknesses and void volume fractions, and in addition their optical properties, typically defined by the index of refraction and extinction coefficient spectra. Because multichannel detection systems integrated into SE instrumentation have been available for some time now, the data acquisition time possible for complete SE spectra has been reduced significantly. As a result, real time spectroscopic ellipsometry (RTSE) has become feasible for monitoring thin film nucleation and growth during the deposition of thin films as well as during their removal in processes of thin film etching. Also because of the reduced acquisition time, mapping SE is possible by mounting an SE instrument with a multichannel detector onto a mechanical translation stage. Such an SE system is capable of mapping the thin film structure and its optical properties over the substrate area, and thereby evaluating the spatial uniformity of the component layers. In thin film photovoltaics, such structural and optical property measurements mapped over the substrate area can be applied to guide device optimization by correlating small area device performance with the associated local properties. In this thesis, a detailed ex-situ SE study of hydrogenated amorphous silicon (a Si:H) thin films and solar cells prepared by plasma enhanced chemical vapor deposition (PECVD) has been presented. An SE analysis procedure with step-by-step error minimization has been applied to obtain accurate measures of the structural and optical properties of the component layers of the solar cells. Growth evolution diagrams were developed as functions of the deposition parameters in PECVD for both p-type and n-type layers to characterize the regimes of accumulated thickness over which a-Si:H, hydrogenated nanocrystalline silicon (nc-Si:H) and mixed phase (a+nc)-Si:H thin films are obtained. The underlying materials for these depositions were newly-deposited intrinsic a-Si:H layers on thermal oxide coated crystalline silicon wafers, designed to simulate specific device configurations. As a result, these growth evolution diagrams can be applied to both p-i-n and n-i-p solar cell optimization. In this thesis, the n-layer growth evolution diagram expressed in terms of hydrogen dilution ratio was applied in correlations with the performance of p-i-n single junction devices in order to optimize these devices. Moreover, ex-situ mapping SE was also employed over the area of multilayer structures in order to achieve better statistics for solar cell optimization by correlating structural parameters locally with small area solar cell performance parameters. In the study of (a-Si:H p-i-n)/(nc-Si:H p-i-n) tandem solar cells, RTSE was successfully applied to monitor the fabrication of the top cell, and efforts to optimize the nanocrystalline p-layer and i-layer of the bottom cell were initiated.

Committee:

Robert Collins (Advisor)

Subjects:

Materials Science; Physics

Keywords:

Spectroscopic ellipsometry, real time spectroscopic ellipsometry ,optical properties, thin film nucleation and growth, photovoltaics, amorphous silicon, nanocrystalline silicon, Growth evolution diagrams, tandem solar cell

Unal, OzerInterface studies in silicon nitride/silicon carbide and gallium indium arsenide/gallium arsenide systems
Doctor of Philosophy, Case Western Reserve University, 1991, Materials Science and Engineering
CVD Si3N4 grains, which have the α-form, show preferred growth orientations on the (11overline 1) SiC surface. Two prominent orientation relationships are present at Si3N4/SiC interface: the first one is (0001) Si3N4// (101) SiC; (10overline 10) Si3N4//(11overline 1)SiC and the second one is (1overline 210) Si3N4// (101) SiC; (10overline10)Si3N4//(11overline1)SiC. These orientation relationships also occur on the inclined 111SiC planes. Examination of the α- Si3N4 and SiC crystal structures indicates that the common planar relationship involving (10overline 10) Si3N4 and (11overline 1)SiC planes is due to similarities between the SiN4 and SiC4 tetrahedra in Si3N4 and SiC, respectively. Comparison is made of microstructural and mechanical properties of hot-pressed (HPed) Si3N4/SiC composites densified with MgO and hot isostatically pressed (HIPed) pure Si3N4 and Si3N4/SiC composites free of additives. Composites with elongated β- Si3N4 grains exhibit higher toughness values than those with equiaxed grains. The mechanical properties of HPed samples show degradation over 800c ircC. The mechanical properties of HIPed samples do not deteriorate even at elevated temperatures up to 1400°C. HIPed samples show higher hardness but lower fracture toughness than the HPed counterparts. The study of deflection frequency vs crack plane/whisker axis angle indicates that there is strong bonding at the Si3N4 matrix/SiC whisker interfaceGaInAs/GaAs strained-layer superlattices (SLS) deposited on (111), (001) and (112) GaAs substrates were investigated. For the (111) substrate, the dislocation network is triangular while on the (001) substrate, the network is formed by two orthogonal sets of crossing dislocations; on (112), the network is similar to that seen on the (111) substrate.

Committee:

T. Mitchell (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Silicon nitride/Silicon carbide; Gallium indium arsenide/Gallium arsenide

Nakhmanson, Serge M.Theoretical Studies of Amorphous and Paracrystalline Silicon
Doctor of Philosophy (PhD), Ohio University, 2001, Physics (Arts and Sciences)
Until recently, structural models used to represent amorphous silicon (a-Si) in computer simulations were either perfectly fourfold connected random networks or random networks containing only miscoordinated atoms. These models are an approximation to the structure of the real material and do not uniformly comply with all the experimental data for a-Si. In this dissertation we make an attempt to go beyond this approximation and construct and examine models that have two major types of defects, encountered in real material, in their structure - nanovoids and crystalline grains. For our study of voids in a-Si we have calculated vibrational properties of structural models of a-Si with and without voids using ab initio and empirical molecular dynamics techniques. A small 216 atom and a large 4096 atom continuous random network (CRN) models for a-Si have been employed as starting points for our a-Si models with voids. Our calculations show that the presence of voids leads to an emergence of localized low-energy states in the vibrational spectrum of the model system. Moreover, it appears that these states are responsible for the anomalous behavior of system's specific heat at very low temperatures. To our knowledge these are the first numerical simulations that provide adequate agreement with experiment for the very low-temperature properties of specific heat in disordered materials within the limits of harmonic approximation. For our study of crystalline grains in a-Si we have developed a new procedure for the preparation of physically realistic models of paracrystalline silicon based on a modification of the bond-switching method of Wooten, Winer, and Weaire. Our models contain randomly oriented c-Si grains embedded in a disordered matrix. Our technique creates interfaces between the crystalline and disordered phases of Si with an extremely low concentration of coordination defects. The resulting models possess structural and vibrational properties comparable with those of good CRN models of a-Si and display realistic optical properties, correctly reproducing the electronic bandgap of a-Si. The largest of our models also shows the best agreement of any atomistic model structure with fluctuation microscopy experiments, indicating that this model has a degree of medium-range order closest to that of the real material.

Committee:

David Drabold (Advisor)

Subjects:

Physics, Condensed Matter

Keywords:

amorphous silicon; paracrystalline silicon; computer simulation; atomistic model; structural model

Alanazi, NorahCALIBRATION OF THE HEAVY FLAVOR TRACKER (HFT) DETECTOR IN STAR EXPERIMENT AT RHIC
MS, Kent State University, 2015, College of Arts and Sciences / Department of Physics
Alanazi, Norah, M.S. December 2015 NUCLEAR PHYSICS CALIBRATION OF THE HEAVY FLAVOR TRACKER (HFT) DETECTOR IN STAR EXPERIMENT AT RHIC (49 pp.) Director of Thesis: Spyridon Margetis This project is in the area of Relativistic Nuclear collisions and the commissioning of a new silicon vertex detector, the Heavy Flavor Tracker (HFT) in the STAR exper- iment at Brookhaven National Laboratory (BNL). BNL hosts RHIC, the Relativistic Heavy Ion Collider, the world’s most advanced dedicated heavy ion and polarized proton accelerator facility. Heavy Ion collisions at RHIC provide a unique probe into the understanding of several aspects of the behavior of nuclear, i.e. strongly inter- acting, matter. Among the many insights that can be provided is the description of parton interaction inside the hot and dense medium produced in the early stages of a collision. It also allows us to search for evidence for a phase transition in nuclear matter, a phase where partons [quarks and gluons] can move freely over an extended volume. Production of heavy quarks in high-energy nuclear collisions at RHIC occurs mainly during the initial collisions where energetic gluon and quark interactions can create heavy quarks. Thus, heavy flavor provides an ideal probe in studying the hot and dense medium created in the early phases of high-energy nuclear collisions. A detailed study of heavy flavor is essential to better understand the parton dynamics and select among competing theoretical approaches, however, precise measurements of heavy flavor are di¿cult to obtain due to relatively low production rates and short lifetimes of heavy flavor hadrons. The combinatorial background in nuclear collisions makes the measurement of heavy flavor a challenging task. One approach to dra- matically reduce the combinatorial background by several orders of magnitude is to separate the heavy-flavor hadron’s decay vertex from the background. This is done with the help of high resolution vertex detectors. The Heavy Flavor Tracker upgrade for the STAR experiment, which made its debut during the year 2014 RHIC run (Run14), greatly improved the experiment’s track pointing capabilities making STAR an ideal detector for heavy flavor studies. The HFT consists of three subsystems, each deploying a di¿erent silicon technology. In the heart of HFT there are two layers of 400 thin silicon pixel sensors, each sensor having about one million individual pixels. The HFT is used to extend the tracks reconstructed in the Time Projection Chamber towards the event vertex, increasing at the same time their pointing resolution from a few millimeters down to about 30 microns. The achieved resolution allow us to fully reconstruct the heavy flavor hadron’s decay vertex. In this Thesis we present work and results on HFT calibration issues using a sample of the first data taken with HFT, the Run14 data set. We will focus on event vertex resolution, alignment, particle identification and selection, and track pointing resolution. We also compare our results with previous analyses and the design goals of HFT.

Committee:

Spyridon Margetis (Advisor); Mina Katramatou (Committee Member); Declan Keane (Committee Member)

Subjects:

Nuclear Physics; Physics

Keywords:

Nuclear Physics, heavy ions, collisions, silicon detectors, pixel detectors, silicon calibration, alignment, track pointing resolution, dca resolution

Chung, JuyongElectron microscopy study of nickel disilicide, cobalt disilicide and (magnesium(x) iron(1-x)) silicon trioxide (0 less than x less than 0.12) precipitates in polycrystalline silicon
Doctor of Philosophy, Case Western Reserve University, 1995, Materials Science and Engineering
The precipitation behavior of nickel, cobalt and iron was investigated by transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and image simulations, with particular attention to the effects of intragrain, random grain boundaries and twin boundaries on the precipitation behavior. Nickel and cobalt were intentionally diffused into the specimens from a surface source between 600∼1200°C. However, in the case of iron atoms, native iron impurity was used as a diffusion source. The objective is centered on an investigation of preferential nucleation sites and phases of the precipitates. Microstructural studies showed that nickel and cobalt atoms form NiSi2 and CoSi2 precipitates, respectively. On the other hand, iron atoms combined with magnesium and oxygen atoms which are also present as native impurities, and formed (MgxFe1-x)SiO3 (0 < x < 0.12) precipitates at the random grain boundaries. NiSi2 precipitation predominantly occurred within the grains and not at random grain boundaries. However, grain boundaries were favorable sites for the nucleation of CoSi2 precipitates. The majority of nickel an d cobalt atoms were incorporated into the twin boundaries so that NiSi2 and CoSi2 precipitates formed parallel to the 111 twin planes. It is deduced that the metals at the interface with the Si matrix have 7-fold coordination with Si-Si bonding, while at the opposite twin/matrix interface they have 8-fold coordination with M-Si (M = Ni, Co) bonding. Identification of large NiSi2 and CoSi2 precipitates was confirmed by EDS (energy dispersive spectrometry), diffraction patterns and dark field images. The small precipitates were identified only by diffraction patterns including reflections which are forbidden in the silicon matrix, but are allowed in the precipitates. The structure of (MgxFe1-x)SiO3 precipitates was analyzed by diffraction patterns, moire fringes and dark field images using the precipitate reflections.

Committee:

P. Pirouz (Advisor)

Keywords:

Electron microscopy; nickel disilicide; cobalt disilicide; silicon trioxide; precipitates; polycrystalline silicon

BHADRI, PRASHANT R.IMPLEMENTATION OF A SILICON CONTROL CHIP FOR Si/SiC HYBRID OPTICALLY ACTIVATED HIGH POWER SWITCHING DEVICE
MS, University of Cincinnati, 2002, Engineering : Electrical Engineering
In avionic systems, data integrity and high data rates are necessary for stable flight control. Unfortunately, conventional electronic control systems are susceptible to electromagnetic interference (EMI) that can reduce the clarity of flight control signals. Fly-by-Light systems that use optical signals to actuate the flight control surfaces of an aircraft have been suggested as a solution to the EMI problem in avionic systems. Fly-by-Light in avionic systems reduces electromagnetic interference hence improving the clarity of the control signals. Fly-by-Light technology development involves creation of building blocks like computers, fiber optic sensors and interfaces, fiber actuator loops, an integrated system etc. The development of this technology exploits fiber optic sensor and control technology. This thesis demonstrates a hybrid approach that combines a smart silicon photoreceiver module with a SiC power transistor. The resulting device uses a 5mW optical control signal to produce a 150A current that is suitable for driving an electric motor. This is the first attempt to integrate silicon carbide devices with a smart silicon chip. The first part of the thesis deals with the various high power technologies that are in use today. Different approaches are discussed and emphasis is stressed on the silicon/silicon carbide hybrid design. Briefly discussed is the use of silicon carbide for optical switching application. Second part of the thesis involves the design, simulation and analysis of the silicon smart chip. Individual components of the smart silicon are characterized and results shown. Finally, we report the performance evaluation of this smart silicon realized in a 1.5 micron CMOS process using MOSIS foundry service.

Committee:

Dr. Fred Beyette, Jr. (Advisor)

Keywords:

optical high power switch; silicon driver; mixed signal; optoelectronics; silicon carbide

Wu, Huann-DerVapor synthesis of silicon and silicon carbide powders /
Doctor of Philosophy, The Ohio State University, 1987, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Ceramics;Powders;Silicon;Silicon carbide

PARIMI, SRINIVASPARAMETRIC EXPLORATION OF AUTOMATED FABRICATION AND ANODIC BONDING OF CPS FOR LHP APPLICATIONS
MS, University of Cincinnati, 2003, Engineering : Electrical Engineering
The present work deals with the development of a very novel and prototypical Micro Loop Heat Pipe (LHP) using the Coherent Porous Silicon (CPS) technology developed at the University of Cincinnati for different thermal and space applications. The main emphasis of this thesis is the development of an automated process for batch fabrication of Coherent Porous Silicon (CPS) wicks and development/characterization of novel anodic bonding techniques. The micro cooling of Integrated Circuits (IC), solar cells are some of the applications of LHP. In this work, it was determined that individual wafers should be given individual attention in determining the critical parameters for etching. A generalized approach, while ignoring the wafer level details has many limitations. A method to determine critical current density was established by introducing a current-voltage sweeps, before etching. Different types of etching methods are studied viz., potentiostat etching mode, galvanostat etching mode, current compensation mode and light compensation mode. In this present study, it was also determined to have a higher etch rate and uniform concentration of the etchant in the etch rig. A new flow system was developed, which would increase the temperature of the etchant, for faster etch rates. This new system would supply fresh etchant to the etching rig. Etchant level controlling logic was also implemented. One of the challenging micro processing technique needed to make a LHP package is bonding wafers producing hermetic seals. The mechanisms of formation of anodic bonds between glasses and metals are examined. Prior research works suggests electrochemical, electrostatic and thermal mechanisms for bond formation, but the dominant mechanism has not been clearly defined. The process is found to be an electrochemical analog to thermal glass-to-metal seals, where the metal surface is oxidized into the glass due to the development of large electric fields across the anodic depletion layer. A novel anodic bonding technique was developed to facilitate bonding very thick silicon dioxides to glass and silicon. Characterization studies are performed and optimization of this process was suggested. Parametric approach was used to quantify the influence of each parameter on the bond strength.

Committee:

DR. H. HENDERSON (Advisor)

Keywords:

COHERENT POROUS SILICON ETCHING; MACRO POROUS SILICON ETCHING; AUTOMATION; MEMS FABRICATION; ANODIC BONDING

Faruque, Shams OmarPower GaN FET Testing
Master of Science, University of Toledo, 2014, Electrical Engineering
The purpose of this research is to test various output parameters of gallium nitride transistors. These include the voltage-current characteristic, drain-source leakage current, dv/dt immunity, and resistance to single events and radiation hardness. The specific gallium nitride transistors tested are enhancement (normally-off) devices from Efficient Power Conversion (EPC) Corporation. These devices are in passivated die form, with land grid array solder bars. For the voltage-current characteristic, the gallium nitride device was mounted on a printed circuit board. The characteristic was compared to that of conventional devices, such as silicon and silicon carbide, at low and high temperatures. The voltage-current characteristic of gallium nitride shows an on-resistance lower then silicon or silicon carbide devices. Gallium nitride devices are also found to saturate at far lower drain-source voltages than the example silicon and silicon carbide devices, and require a lower gate voltage to turn on fully, which means that lower supply voltages are necessary to take full advantage of the device. The gallium nitride characteristic did have a greater sensitivity to temperature than the conventional devices, however. The drain-source leakage current of gallium nitride devices was also compared to conventional devices, from low to high temperatures. The leakage current for gallium nitride devices was many orders of magnitude higher than the conventional devices tested, and even though leakage current increases with increasing temperature for all the devices tested, the magnitude of the leakage currents associated with gallium nitride devices mean that they may make very good temperature sensors. Gallium nitride has superior dv/dt immunity when compared to conventional devices. The device tested withstood a dv/dt magnitude that was double the maximum dv/dt the conventional devices could withstand. The theoretical dv/dt immunity level of gallium nitride devices is nearly ten times the level of conventional devices. Gallium nitride devices have very good resistance to radiation. Tests done by the manufacturer show that gallium nitride devices can withstand larger amount of radiation than conventional power devices, and have no unwanted effects. In the testing presented in this thesis, a bank of gallium nitride devices had a high drain-source voltage and were turned off. After hundreds of hours, no single event occurred and the devices did not turn on or break at any point. As part of this testing, a substantial increase in the parasitic or noise current was observed upon exposure of the unpackaged device to continuous wave blue laser light. Even more interestingly, after removal of the laser light, the elevated current levels remained, revealing latching effect that has not been observed before in these devices. This latching effect deserves further studies to understand and prevent, or even use in potential applications.

Committee:

Daniel Georgiev (Committee Chair); Vijay Devabhaktuni (Committee Member); Roger King (Committee Member)

Subjects:

Electrical Engineering

Keywords:

GaN; Power; FET; Testing; Gallium Nitride; Si; Silicon;SiC;Silicon Carbide; IV Curve;HTRB;Leakage;dv-dt;SEB;Single Electron Burnout;Blue Light;Latch;Latching;Test;Measurment;Temperature

Kerkar, Awdhoot VasantInvestigation of steric stabilization as a route for colloidal processing of silicon carbide/silicon nitride composites
Doctor of Philosophy, Case Western Reserve University, 1990, Chemical Engineering
The final strength, uniformity, and quality of ceramic components depend on their green microstructure. One key issue is the control of the number, size and distribution of particle agglomerates and voids in the green microstructure. Colloidal engineering strategies which attempt to control the strength of the interaction between the solids when in their processing fluids may provide an effective means to improve the green body microstructure. The application of steric stabilization, a colloidal engineering strategy, for the enhanced processing of SiC/Si3N4 composites, is investigated. Steric stabilization involves adsorption of polymers onto the powders from the processing medium. The system under investigation consists of silicon powder to be processed in nonaqueous media such as benzene and trichloroethylene. Poly(methyl methacrylate), poly(styrene), and their copolymer adsorbed onto silicon powder are used as stabilizing agents. The goal of the present work was to provide an in depth understanding of the phenomenon of steric stabilization as applied to the processing of ceramic powders and fibers. Also, the various functional roles played by the adsorbed polymers during green processing are demonstrated. It has been found that steric stabilization leads to elimination of inter-particle agglomeration of silicon powder. As a result, improved control over the particle size distribution and particle packing in nonaqueous slips is possible. Adsorbed polymers offer great processing flexibility as they can be used reversibly as dispersants and flocculants. The use of steric stabilization during pressure casting yielded compacts with higher packing densities and controlled microstructures. The adsorbed polymers also exhibited excellent binder characteristics as reflected by the improvement in the green strength of the compacts. The effect of steric stabilization on subsequent reaction bonding of Si to Si3N4 was studied. Also, the role of polymers in improving the wetting characteristics of the SiC fibers with the stabilized silicon slip were studied qualitatively. These results reported herein can be used as guidelines for infiltration of SiC fiber arrays with Si slips to obtain green composites via pressure casting. The green composites were also subsequently nitrided to yield SiC fiber-reinforced/reaction bonded silicon nitride (RBSN) composites

Committee:

Donald Feke (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Steric stabilization; Colloidal engineering; Silicon carbide/silicon nitride composites

Kollarits, Matthew DavidDesign and Simulation of a Temperature-Insensitive Rail-to-Rail Comparator for Analog-to-Digital Converter Application
Master of Science, University of Akron, 2010, Electrical Engineering

A comparator with rail-to-rail input voltage range is presented. The rail-to-rail operation is achieved using two folded-cascode differential amplifiers operating in parallel as an input stage. The output of the appropriate amplifier is connected to the comparator output through a transmission-gate logic stage. Temperature-insensitivity is achieved by designing the input-stage amplifiers for zero-temperature-coefficient (ZTC) operation. The proposed comparator was simulated using 0.5µm silicon-on-insulator CMOS (SOI-CMOS) models. The circuit provides propagation delay less than 146.9ns. Over the 0V to 3.3V rail-to-rail common-mode input voltage range, the maximum input-offset voltage is less than 300µV at 27°C and less than 1.91mV over the temperature range of 27°C to 125°C.

The comparator is shown to be suitable for a successive-approximation-register analog-to-digital converter (SAR-ADC) application by a series of validation simulations. An 8-bit SAR-ADC incorporating the comparator was tested to determine its integral non-linearity (INL) and differential non-linearity (DNL). The SAR-ADC exhibited a worst-case INL of 0.6LSB and a worst-case DNL of 0.2LSB over the temperature range 27°C to 125°C. The SAR ADC is capable of completing one conversion every 15µs, which is adequate for sampling at a rate of 65 Kilo-samples per second (KSPS).

Committee:

Robert Veillette, Dr. (Advisor)

Subjects:

Electrical Engineering

Keywords:

Comparator; ADC; Analog-to-Digital Converter; ZTC; Zero-Temperature Coefficient; Rail-to-Rail; Complementary Folded Cascode; Folded Cascode; Transmission Gate; SOI; Silicon-on-Insulator

Wilson, James EdwardDesign techniques for first pass silicon in SOC radio transceivers
Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Future radio transceivers are expected to deliver much higher data rates and operate at several frequencies. In 4G wireless systems, convergence of cellular and WLAN transceiver for VoIP will require the radio to operate in multiple RF bands and with different modulation schemes ranging from BPSK to 64- and 256-QAM OFDM. There is also the challenge for low power even as the handheld is pushed to achieve additional performance. While CMOS technology scaling and innovations in platform based systems and Network-on-Chip (SOC and NOC) have resulted in great strides within the digital part (digital baseband/MAC), the radio part of a wireless solution remains a major bottleneck. In today’s radio design environment, a fully integrated CMOS radio requires several silicon spins before it meets all product specifications and often with relatively low yields. This results in significant increase in NRE cost, especially when considering that mask set costs increase exponentially as feature size scales down. Furthermore, additional spins could lead to missing important market windows, particularly with the decreasing life cycles of semiconductor products.

In addition to the complexity of highly integrated radio transceiver, RF performance is highly susceptible to random variations in process and operating conditions. Such variations do not scale with the process. Worst-case corner simulations often lead to over-design and increased power consumption. RF models, package models and design kits are based on certain assumptions that severely limit design space exploration. All these factors prohibit first-time-right silicon.

This thesis work aims to address these issues by presenting design techniques leading to first pass success and taking advantage of the increased integration of digital, analog and RF. Through the exploitation of advances in the digital baseband, this dissertation proves that it is possible to calibrate the noise of the analog and RF front end. Through careful design and circuit feedback, it is also possible to calibrate the other important parameters in the RF front end, such as input matching, gain and linearity.

Committee:

Mohammed El-Naggar (Advisor)

Keywords:

first pass design; first pass silicon; RF; LNA; calibration; nosie calibration; input match; input match calibration

Chen, LiSILICON CARBIDE PRESSURE SENSORS AND INFRA-RED EMITTERS
Doctor of Philosophy, Case Western Reserve University, 2008, Materials Science and Engineering
The potential of low-stress, heavily-nitrogen-doped, (111)-oriented polycrystalline 3C-silicon carbide (poly-SiC) formed by LPCVD as an advanced MEMS material for harsh-environment and demanding applications was studied through the development and characterization of two MEMS devices: pressure sensor and IR emitter. A research prototype of a low-cost, miniature, mass-producible sensor for measurement of high pressure at operating temperatures of 300 deg.C to 600 deg.C, e.g., in-cylinder engine pressure monitoring applications, was developed. This all-SiC capacitive sensor, i.e., a SiC diaphragm on a SiC substrate, takes advantage of the excellent harsh environment material properties of SiC and was fabricated by surface micromachining. The sensor was packaged in a high-temperature ceramic package and characterized under static pressures of up to ~5MPa (700psi) and temperatures of up to 574 deg.C in a custom chamber. An instrumentation amplifier integrated circuit was used to convert capacitance into voltage for measurements up to 300 deg.C; beyond 300 deg.C, the capacitance was measured directly from an array of identical sensor elements using a LCZ meter. After high temperature soaking and several tens of temperature/pressure cycles, packaged sensors continued to show stable operation. The sensor was also packaged in a custom probe and successfully demonstrated dynamic pressure monitoring after being inserted into the cylinder head of a research internal combustion engine. A thermal infrared emitter (blackbody) capable of fast thermal cycling was realized for pulsed operation at high frequency using free-standing poly-SiC micro-bridge elements. High emissivity, high thermal conductivity, low thermal mass and excellent mechanical robustness of poly-SiC enable this development. Poly-SiC's peak emission wavelength falls in the range of short wavelength infrared. Devices were pulsed at frequencies up to 100Hz with modulation depth near 50%. Materials analysis examining the surfaces of pre- and post-heated emitter elements was performed using Auger electron spectroscopy (AES) and showed extremely low oxidation effect up to about 700 deg.C. Poly-SiC micro-hotplate-based IR emitter platforms, including poly-SiC heating and sensing resistors, were used for a reliability study using an accelerated degradation methodology testing. For comparison, platinum (Pt) was used on another set of otherwise similar SiC micro-hotplates for the heating and sensing elements. Results show that Pt will rapidly degrade when operated above ~800 deg.C, while poly-SiC is stable up to ~1100 deg.C. In short, poly-SiC stands out for many higher-temperature applications, thanks to its outstanding material properties and chemical stability.

Committee:

Mehran Mehregany (Advisor)

Keywords:

Silicon Carbide,; Pressure Sensors,; Infra-red Emitters,; MEMS,; Harsh Environment,; High-temperature,

Cheng, Tai-TsuiLattice defects in beta-silicon carbide grown on (001) silicon by CVD
Doctor of Philosophy, Case Western Reserve University, 1990, Materials Science and Engineering
This thesis describes a study of heteroepitaxial thin films of β-SiC grown on (001) Si by chemical vapor deposition (CVD). Electronic applications of these films have been restricted by the presence of a high density of defects. In order to prevent the formation of these defects, it is necessary to understand how they arise. The objectives of this work were to study the defect microstructure and growth mechanisms experimentally and provide explanations for these observations. Two types of sample were investigated; continuous films and initial growth islands. Continuous films were characterised to determine the effects of substrate orientation, deposition sequence, and deposit thickness. Initial growth samples were produced by varying the temperature and duration of simulate "buffer" layer formation. The main experimental techniques used were transmission electron microscopy (TEM) and Nomarski differential interference contrast (DIC) microscopy. The growth of SiC on (001) Si by CVD was shown to be of the Volmer-Weber growth mode. The deposits are single crystal β-SiC with a parallel epitaxial relationship with respect to the substrate. The interface is semicoherent with arrays of edge-type misfit dislocations accommodating the lattice mismatch. The predominant defects in the films are stacking faults. Other types of defec t present include microtwins, threading dislocations, and inversion domain boundaries (IDB's). Stacking faults and microtwins are concluded to be due to incorrect deposition on the 111 facets of island nuclei. The introduction of threading dislocations is attributed to residual coherency stresses. Inversion domain boundaries (IDB's) arise from the coalescence of nuclei formed on terraces separated by demi-steps. In addition, defects have been observed in the substrates; these include facetted voids and, in some cases, helical dislocations. The former result from agglomeration of vacancies, the latter are pre-existing dislocations which are pinned and climb into a helical configuration. Both of these arise during "buffer" layer formation

Committee:

P. Pirouz (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Beta-silicon carbide defects; Chemical vapor deposit

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