No description available.

This dissertation describes research on the synthesis and characterization of extended heptazine–based, graphite–like carbon nitride materials (CNx), as well as molecular heptazine (C6N7) derivatives. Spurred on by recent triazine to heptazine conversion studies, a structural examination was performed on an amorphous nitrogen–rich carbon nitride material formed via the rapid and exothermic self-propagating decomposition of a triazine (C3N3) precursor, trichloromelamine (TCM). The thermally stable and insoluble CNxHy product was determined to be composed of heptazine repeat units. This conclusion was supported by 13C solid state NMR and isolation of molecular heptazine anions after base hydrolysis (structural deconstruction) of the CNxHy material. Modifications to the decomposition of TCM were explored. Introduction of a solid template (NaCl or silica) led to morphological changes in the TCM–CNx product, observed by scanning electron microscopy. It was found that the sodium salts, NaBr and NaN3, led to chloride exchange with TCM. The use of mixtures of NH4Cl and NaN3 also showed changes in the morphology of the material, while leading to slight changes in the IR spectra. A series of reactions between NaBH4 and TCM yield novel thermally stable boron carbon nitride (BCN) materials. Reactions between TCM and Li2C2 or aromatic organic solids led to CNx materials with increased carbon contents. Crystalline metal–heptazine precipitates were generated by cation exchange reaction with the base hydrolysis product of TCM–CNx, potassium cyamelurate. A structure solution was attempted for the crystalline copper cyamelurate salt, KCu[C6N7O3]·4H2O. Neutral molecular heptazines were also synthesized; these species included 2,5,8–tribromo–s–heptazine (TBH), 2,5,8–triphenyl–s–heptazine (TPH), 2,5,8–tris(diisopropylamino)–s–heptazine (TAmH), and 2–bis(trimethylsilyl)amido–5,8–dichloroheptazine (DCAH). These materials were sublimable and showed interesting optical absorption and emission properties. A polymeric heptazine material was synthesized by thermal decomposition of DCAH. Several attempts were made to synthesize polymeric materials from heptazine precursors. Extended solids with C6N8 and C9N7 stoichiometry were made through solid state metathesis reactions between trichloroheptazine and either lithium nitride or lithium carbide. Powder X–ray diffraction indicated that salt formation was occurring during these reactions and products had the desired stoichiometry by elemental analysis. It was generally observed that CNx materials containing excess carbon displayed increased thermal stability when compared to pure CNx.

No description available.

The factors influencing the direct nitridation of silicon, including the effects of the native oxide layer covering the surface of silicon, the effects of hydrogen contained in the nitridation gas and the catalytic effects of metals added to the raw material silicon, were investigated, using a tubular flow reactor and a fluidized-bed reactor operated at temperatures ranging from 1150��C to 1390��C in a stream of nitrogen containing 10% hydrogen. The nitridation of silicon is not initiated until the native oxide is removed by an assistance of hydrogen contained in argon during the pretreatment or in the nitridation gas mixture. An induction period is observed before the initiation of the nitridation and depends on the nitridation temperature as well as the pretreatment time, which is associated with the removal of the oxide layer. The presence of hydrogen in the nitridation atmosphere is crucial for the nitridation of silicon. When pretreated silicon grains are exposed to nitrogen without hydrogen for a time period as short as 5 minutes, the subsequent nitridation, even with hydrogen, becomes extremely slow. The concentration of hydrogen as low as 0.3% is effective for sustaining the reactivity of silicon for the nitridation. The results suggest the formation of a protective layer on the surface of silicon when silicon grains are exposed to nitrogen without hydrogen. The protective film is suspected to be silicon oxynitride, or a mixture of silicon oxynitride and silicon dioxide or silicon nitride formed from the reaction of silicon with oxygen and nitrogen, depending on the temperature of its formation. However, the protective film does not form on the native oxide layer, and the reactivity of silicon is resumed upon the removal of the native oxide. An addition of calcium (as low as 0.125%) or yttrium (1.0-2.0%) to silicon suppresses the formation of ��-silicon nitride while iron enhances the formation of silicon nitride. Copper promotes not only the nitridation but also the formation of ��-silicon nitride at 1200��C, but enhances the ��-phase formation at higher temperatures. The role of liquid phases on the formation of ��-/��-silicon nitride was also discussed based on the nitridation of silicon impregnated with copper, calcium, silver, chromium and tungsten. / Graduation date: 2003

2 ��m average sized silicon powder was nitrided with 90% N���/10% H��� in a fluidized-bed reactor, operated at 1200��C, 1250��C and 1300��C. To fluidize silicon powder, alumina particles with an average size of 300 ��m were used as an inert fluidizing conditioner. The feasibility and operating conditions of the fluidization were studied at room temperature. The effects of silicon content and operating temperature on the nitridation of silicon as well as on the formation of ��- and ��-silicon nitride were investigated in batch and semi-continuous operations. The effects of the average residence time of silicon/alumina mixtures in the fluidized-bed reactor on the nitridation process were studied in semi-continuous operations. In batch operations, a maximum mass fraction of 15 wt% silicon powder could be added to alumina particles at temperatures in the range of 1200 to 1300��C without changing the fluidization quality. When the silicon fraction was increased to 20 wt%, fluidization failed immediately. With a mass fraction of 5% silicon powder, almost 100% ��-silicon nitride, which was preferred in applications, was found in the product. ��-silicon nitride was facilitated with an increase in silicon fractions in silicon/alumina mixtures. The nitridation process was strongly affected by the reaction temperature. The overall conversion of silicon increased with an increase in reaction temperature. Higher temperature also promoted the formation of ��-silicon nitride. The overall conversion of silicon into silicon nitride was also enhanced by hydrogen concentrations. An increase in hydrogen concentration facilitated the formation of ��-form silicon nitride. In the semi-continuous operation, the nitridation of 30 wt% silicon/70 wt% alumina mixtures could be achieved without changing the fluidizing quality. Almost 100% ��-silicon nitride was found in the product when a 20 wt% silicon/80 wt% alumina mixture was nitrided at 1250��C for an average residence time of up to 4 hours. However, ��-silicon nitride was formed when the mixture was nitrided at 1300��C for an average residence time of 3 hours. A mathematical model incorporating kinetic data and carryover of silicon powder was developed to described the total conversion of silicon in batch operation. A semi-continuous model was also proposed, which successfully predicted the overall conversion of silicon powder. / Graduation date: 1997

Flash memory is one sort of non-volatile memory, focus on the dates holding and capacity. Conventional non-volatile memory applies poly-crystalline for floating gate material, because the poly-crystalline (like poly-silicon) itself is the semiconductor material, will cause leakage problem, recently, Oxide-nitride-oxide multi-layer structure is under development for the place of conventional floating gate. Because it is the insulator material, can suppress leakage current, and it contains a deeper trapping energy level, and has a partial trapped carriers phenomenon to give a multi-bits memory solution. My effort is to propose a pair of ONO three layers stack, which is located close to the beneath of D/S region and a column like. Such structure can overcome miniaturization limitation of channel length, and a somewhat depth oxide can promise good isolation and separation between the trapping layer and other area, and a reliable distance of the two trapped unit can prevent interference issue. My proposal can suppose a higher devices density and a feasible and flexible solution to develop memory devices, a cost down to be more competitive, certainly bring much favor for the future improvement.

Polyhedral boranes and carboranes have acquired their popularity for constructing meso and nano-size structures for an array of applications from pharmaceuticals to material science. These three-dimensional boranes range from 4 to 22 boron atom per molecules with delocalized bonding analogous to aromatic compounds. The unique vibrational spectroscopy of the BH function allows for possible application of these species to bioimaging. Silver nanoparticles functionalized with ortho-carboranes have been reported for bioimaging using Surface-enhanced Raman scattering (SERS). The silver nanoparticles were functionalized with antibodies specific to cancer cell receptors. Bonding thiol-substituted carboranes to these particles allowed for observation of enhanced Raman signals as the imaging mode. Here, attempts to synthesize second generation carborane molecules with additional Raman-active group such as nitrile were conducted. Hybrid diblock copolymers have the ability to self-assemble in different morphological patterns depending on the type and ratio of monomers and the compatibilities in various solvents. Linear hybrid diblock copolymers were synthesized by ring-opening metathesis polymerization (ROMP) reactions with norbornenyl-based decaborane and various amounts of norbornene and norbornenyl-ester derivative monomers. Their self-assembly behaviour in various solvents were characterized by NMR, TGA, DSC, and SEM. P(norbornene)60-b-p(norbornenyl-decaborane)40 polymers showed lamellar morphology patterns when slowly evaporated from chloroform. Based on results and the SEM images, a few of these diblock copolymers were used as ceramic precursors and pyrolyzed to elevated temperatures forming boron nitride and boron carbonitride nano-ordered ceramics

Thesis (M.S. in Combat Systems Science and Technology)--Naval Postgraduate School, December 2009. / Thesis Advisor: Haegel, Nacy M. Second Reader: Karunasiri, Gamani. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Minority charge carrier, diffusion length, GaN, nanowires, EBIC. Includes bibliographical references (p. 71-73). Also available in print.

Thesis (Ph. D.)--Lehigh University, 2003. / Includes bibliographical references and vita.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 140-141). Available also in a digital version from Dissertation Abstracts.