Symmetry in Graph Theory

This book contains the successful invited submissions to a Special Issue of Symmetry on the subject of ""Graph Theory"". Although symmetry has always played an important role in Graph Theory, in recent years, this role has increased significantly in several branches of this field, including but not limited to Gromov hyperbolic graphs, the metric dimension of graphs, domination theory, and topological indices. This Special Issue includes contributions addressing new results on these topics, both from a theoretical and an applied point of view

The development and synthetic application of titanium-mediated carbon-heteroatom double bond hydrosilylation methodologies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1997.Includes bibliographical references.by Matthew Todd Reding.Ph.D

Immobilized Bis-Indenyl Ligands for Stable and Cost-Effective Metallocene Catalysts of Hydrogenation and Polymerization Reactions

Reactions of catalytic hydrogenations and polymerizations are widely used in industry for manufacture of fine chemicals, pharmaceuticals, and plastics. Homogeneous catalysts for the processes that have low stability and their separation is difficult. Therefore, the development of new highly active and stable catalysts for hydrogenations and polymerizations is a necessity. The objective of this research was the development of a strategy for immobilization of heterogeneous metallocene catalysts. First, a methodology of immobilization of bis-indenyl ligands on the surface of mesoporous silica gel was designed. Four bis-indenyl ligands containing functionalized tethers of various lengths with terminal alkene groups were synthesized. All bis-indenyl ligands were immobilized on the surface of mesoporous functionalized silica gel by two methods: hydrosilylation and thiol-ene coupling of the double bond. After comparing the results, the second strategy was chosen as more efficient. The materials can be used further as intermediates for synthesis of supported metallocene catalysts

Synthesis of new recoverable catalysts and their application in asymmetric reduction of ketimines with trichlrosilane

Obtaining chiral amines from ketones via imine intermediates represents an attractive strategy that opens a straightforward route to valuable building blocks for the pharmaceutical and other fine chemicals industries. Metal-free oranocatalysis can be viewed as an attractive and broadly applicable methodology in which the metal is not vital for the key bond-forming event. Previously developed in our laboratory, N-methylvaline-derived formamides IIIa,b proved to be efficient catalysts for asymmetric reduction of prochiral ketimines with trichlorosilane, (up to 98%, 95% ee).136,137 Tagging the catalyst to a fluorous ponytail IIIc, soluble and insoluble polymers IIId, or gold nanoparticles IIIe simplified the isolation procedure, while preserving high activities and stereoselectivities (up to 98%, 91% ee). The recovered catalysts could be reused at least 5 times without the loss of activity or stereoselectivity. This technology appears to be particularly suited to the small-scale parallel chemistry

Ätzen von Titannitrid mit Halogenverbindungen: Kammerreinigung mit externer Plasmaquelle

Mit zunehmender Miniaturisierung mikroelektronischer Bauelemente steigen die Anforderungen an reproduzierbare qualitätskonforme Schichten. Um die zur Herstellung notwendigen ALD/PVD/CVD-Schichtabscheideanlagen in einen zuverlässigen Zustand zu versetzen, ist eine regelmäßige Kammerreinigung notwendig. Während des Abscheideprozesses werden nicht nur das Substrat, sondern auch die umliegenden Kammerteile beschichtet. Diese Schichten wachsen mit jedem Beschichtungszyklus weiter an. Der Stress zwischen Schicht und Kammerwand steigt beständig, und es besteht das Risiko das Teile abplatzen und auf die Waferoberfläche fallen und damit die Struktur unbrauchbar machen. Um das zu verhindern, muss die Kammerwand in einen regelmäßigen Zustand versetzt werden, in dem sichergestellt ist, daß keine Schichtreste abplatzen können. In der vorliegenden Arbeit wird ein neues Verfahren zur Trockenreinigung von ALD-Titannitrid Kammern vorgestellt. Dazu wurden TiN-Stücke (hergestellt im ALD, CVD, PVD-Verfahren) auf einem temperaturgeregelten Probenhalter platziert. Eine Argon/NF3 Gasmischung wurde in einer externen Plasmaquelle (RPS) zerlegt und in die Reaktionskammer geschleust. Die Ätzung wurde mit in-situ Reflexionsmessung beobachtet. Experimente mit Chlorzugabe wurden unternommen und ein starker Einfluss auf den Ätzmechanismus beobachtet. Die Ätzraten des TiN sind exponentiell abhängig von der Temperatur und proportional abhängig von der Verfügbarkeit atomaren Fluors. Dieses wird bei der Zerlegung von NF3 frei gesetzt und steht der Reaktion zur Verfügung. Die NF3-Zerlegung in Fluor und Stickstoff wurde mit Hilfe der Massenspektrometrie (QMS) untersucht, Zerlegungsgrade größer 96% wurden erreicht. Mit Hilfe dieser Messung kann der Einfluss der Kammerreinigung auf den Treibhausgasausstoß (GWP) bestimmt werden. Mit dem Ar/NF3-Verfahren können die GWP-Emissionen um 90% im Vergleich zur RIE-Ätzung mit SF6 reduziert werden. Mit Argon/Chlor-Plasmen konnte kein Titannitrid geätzt werden, da die physikalische Sputterkomponente fehlte. Durch Hinzufügen von Chlor zu einer Ar/NF3-Gasmischung konnte die Ätzrate um bis zu 270% im Bereich niedrige Temperaturen/niedriger Druck gesteigert werden. Bei höheren Temperaturen/höherem Druck fielen die Ar/NF3/Chlor Ätzraten allerdings deutlich hinter die des Ar/NF3 zurück. Die dazu führenden Effekte werden untersucht und ausgeführt. Die Nutzung von externen Plasmaquellen bietet eine vielversprechende Alternative um Abscheideanlagen von TiN-Rückständen reinigen zu können. Bei hohen Temperaturen werden deutlich höhere Ätzraten als bei anderen Schichten (SiN, SiO2, W) erreicht. Für Anwendungen im niedrigen Temperaturbereich erlaubt die Zugabe von Chlor interessante Anwendungsmöglichkeiten.Demands on state of the art deposition technologies for semiconductor production focus on uniformity, repeatability and low defectivity. The chamber condition is a key parameter to achieve these high demands in chemical vapour deposition (CVD) processes and are even more critical to the atomic layer deposition processes (ALD). During the deposition process not only the wafer surface but other chamber parts as well are covered with a thin film. This film accumulates during the deposition cycles and is prone to fall off the walls and pollute the wafer surface. The chamber parts that are exposed to the deposition must be set back to a steady state so that no deposits fall off the walls. The chamber condition also changes uncontrolled with varying film condition on the wall. A new approach for cleaning of ALD-titanium nitride (TiN) deposition chambers was investigated. To determine etch rates TiN-samples (created by ALD, CVD and PVD) were placed on a temperature controlled sample holder. An argon/NF3 mixture was excited in an upstream remote plasma source (RPS) and then routed through the reaction chamber. No further plasma activation inside the reaction chamber was done. The etching was monitored by in-situ reflectometry and etch rates were calculated. The effect of chlorine addition was also studied and strong influence on etch rates was found. The etch rate of TiN is dependent exponentially on temperature and very low etch rates were achieved below 70◦C at a chamber pressure ranging from 20-300 Pa. It was found that this correlates very well with the vapour pressure of the reaction product TiF4. At temperatures of 300◦C etch rates up to 800 nm/min were achieved. The optimum pressure for etching was found at 100 Pa while the pressure effect was small. The etch rate was mainly dependent on the availability of activated fluorine to create TiF4 by the reaction 2 NF3 → N2 + 6 F* 2 TiN + 8 F* → 2 TiF4 + N2 The NF3 decomposition to nitrogen and fluorine was monitored by quadrupole mass spectrometry (QMS) and was found to be greater than 96%. This figure allows an estimation of the amount of Global warm potential (GWP) gas emmited by the process for environmental considerations. Using argon/NF3 or argon/fluorine mixtures in RPS devices reduces the GWP emissions by more than 90% compared to RIE plasma cleaning with SF6. No etching occurred by using argon/chlorine only mixtures as no physical etch component was involved in RPS etch. However adding chlorine to the argon/NF3 mixture accelerated the etching process. Chlorine addition to the argon/NF3 mixture increased the etch rates up to 270% in the low pressure/low temperature regime. At higher temperatures or higher pressures the etch rates dropped below the etch rates achieved solely with fluorine chemistry. It must be emphasized that there is no physical acceleration of the ionized molecules toward the etched sample in this remote plasma setup. The usage of a remote plasma offers an alternative way to remove residues from chambers running TiN deposition processes. At high temperatures the Ar/NF3 offers remarkably high etching rates for TiN compared to other films (silicon nitride, -oxide, tungsten) usually cleaned by remote plasma. For low temperature applications the chlorine enhancement offers an interesting alternative to accelerate the etch process

Ätzen von Titannitrid mit Halogenverbindungen: Kammerreinigung mit externer Plasmaquelle

Mit zunehmender Miniaturisierung mikroelektronischer Bauelemente steigen die Anforderungen an reproduzierbare qualitätskonforme Schichten. Um die zur Herstellung notwendigen ALD/PVD/CVD-Schichtabscheideanlagen in einen zuverlässigen Zustand zu versetzen, ist eine regelmäßige Kammerreinigung notwendig. Während des Abscheideprozesses werden nicht nur das Substrat, sondern auch die umliegenden Kammerteile beschichtet. Diese Schichten wachsen mit jedem Beschichtungszyklus weiter an. Der Stress zwischen Schicht und Kammerwand steigt beständig, und es besteht das Risiko das Teile abplatzen und auf die Waferoberfläche fallen und damit die Struktur unbrauchbar machen. Um das zu verhindern, muss die Kammerwand in einen regelmäßigen Zustand versetzt werden, in dem sichergestellt ist, daß keine Schichtreste abplatzen können. In der vorliegenden Arbeit wird ein neues Verfahren zur Trockenreinigung von ALD-Titannitrid Kammern vorgestellt. Dazu wurden TiN-Stücke (hergestellt im ALD, CVD, PVD-Verfahren) auf einem temperaturgeregelten Probenhalter platziert. Eine Argon/NF3 Gasmischung wurde in einer externen Plasmaquelle (RPS) zerlegt und in die Reaktionskammer geschleust. Die Ätzung wurde mit in-situ Reflexionsmessung beobachtet. Experimente mit Chlorzugabe wurden unternommen und ein starker Einfluss auf den Ätzmechanismus beobachtet. Die Ätzraten des TiN sind exponentiell abhängig von der Temperatur und proportional abhängig von der Verfügbarkeit atomaren Fluors. Dieses wird bei der Zerlegung von NF3 frei gesetzt und steht der Reaktion zur Verfügung. Die NF3-Zerlegung in Fluor und Stickstoff wurde mit Hilfe der Massenspektrometrie (QMS) untersucht, Zerlegungsgrade größer 96% wurden erreicht. Mit Hilfe dieser Messung kann der Einfluss der Kammerreinigung auf den Treibhausgasausstoß (GWP) bestimmt werden. Mit dem Ar/NF3-Verfahren können die GWP-Emissionen um 90% im Vergleich zur RIE-Ätzung mit SF6 reduziert werden. Mit Argon/Chlor-Plasmen konnte kein Titannitrid geätzt werden, da die physikalische Sputterkomponente fehlte. Durch Hinzufügen von Chlor zu einer Ar/NF3-Gasmischung konnte die Ätzrate um bis zu 270% im Bereich niedrige Temperaturen/niedriger Druck gesteigert werden. Bei höheren Temperaturen/höherem Druck fielen die Ar/NF3/Chlor Ätzraten allerdings deutlich hinter die des Ar/NF3 zurück. Die dazu führenden Effekte werden untersucht und ausgeführt. Die Nutzung von externen Plasmaquellen bietet eine vielversprechende Alternative um Abscheideanlagen von TiN-Rückständen reinigen zu können. Bei hohen Temperaturen werden deutlich höhere Ätzraten als bei anderen Schichten (SiN, SiO2, W) erreicht. Für Anwendungen im niedrigen Temperaturbereich erlaubt die Zugabe von Chlor interessante Anwendungsmöglichkeiten.Demands on state of the art deposition technologies for semiconductor production focus on uniformity, repeatability and low defectivity. The chamber condition is a key parameter to achieve these high demands in chemical vapour deposition (CVD) processes and are even more critical to the atomic layer deposition processes (ALD). During the deposition process not only the wafer surface but other chamber parts as well are covered with a thin film. This film accumulates during the deposition cycles and is prone to fall off the walls and pollute the wafer surface. The chamber parts that are exposed to the deposition must be set back to a steady state so that no deposits fall off the walls. The chamber condition also changes uncontrolled with varying film condition on the wall. A new approach for cleaning of ALD-titanium nitride (TiN) deposition chambers was investigated. To determine etch rates TiN-samples (created by ALD, CVD and PVD) were placed on a temperature controlled sample holder. An argon/NF3 mixture was excited in an upstream remote plasma source (RPS) and then routed through the reaction chamber. No further plasma activation inside the reaction chamber was done. The etching was monitored by in-situ reflectometry and etch rates were calculated. The effect of chlorine addition was also studied and strong influence on etch rates was found. The etch rate of TiN is dependent exponentially on temperature and very low etch rates were achieved below 70◦C at a chamber pressure ranging from 20-300 Pa. It was found that this correlates very well with the vapour pressure of the reaction product TiF4. At temperatures of 300◦C etch rates up to 800 nm/min were achieved. The optimum pressure for etching was found at 100 Pa while the pressure effect was small. The etch rate was mainly dependent on the availability of activated fluorine to create TiF4 by the reaction 2 NF3 → N2 + 6 F* 2 TiN + 8 F* → 2 TiF4 + N2 The NF3 decomposition to nitrogen and fluorine was monitored by quadrupole mass spectrometry (QMS) and was found to be greater than 96%. This figure allows an estimation of the amount of Global warm potential (GWP) gas emmited by the process for environmental considerations. Using argon/NF3 or argon/fluorine mixtures in RPS devices reduces the GWP emissions by more than 90% compared to RIE plasma cleaning with SF6. No etching occurred by using argon/chlorine only mixtures as no physical etch component was involved in RPS etch. However adding chlorine to the argon/NF3 mixture accelerated the etching process. Chlorine addition to the argon/NF3 mixture increased the etch rates up to 270% in the low pressure/low temperature regime. At higher temperatures or higher pressures the etch rates dropped below the etch rates achieved solely with fluorine chemistry. It must be emphasized that there is no physical acceleration of the ionized molecules toward the etched sample in this remote plasma setup. The usage of a remote plasma offers an alternative way to remove residues from chambers running TiN deposition processes. At high temperatures the Ar/NF3 offers remarkably high etching rates for TiN compared to other films (silicon nitride, -oxide, tungsten) usually cleaned by remote plasma. For low temperature applications the chlorine enhancement offers an interesting alternative to accelerate the etch process

Catalytically Enchanced Systems for Hydrogen Storage: Final Report

Previous U.S. DOE sponsored research at the University of Hawaii resulted in the development of methods of doping of sodium aluminum hydride, NaAlH4 with titanium, zirconium and other catalysts such that: dehydriding occurs at temperatures as low as 100°C; rehydriding requires less than 1 h; and >4 weight percent hydrogen can be repeatedly cycled through dehydriding/rehydriding. These materials appeared to be on the threshold of practical viability as hydrogen carriers for onboard fuel cells. However, it was apparent that further kinetic enhancement was required to achieve commercial viability. Thus, one of the primary goals of this project was to develop the requisite improved catalysts. Over the course of this project, a variety of titanium and zirconium dopant precursors were investigated. Moreover, the approach was to conduct guided search for improved catalysts by obtaining a fundamental understanding of the chemical nature of the titanium dopants and their mechanism of action. Therefore, the projected also aimed to determined the chemical nature of the titanium species that are formed upon mechanical milling of NaAlH4 with the dopant precursors through synchrotron X-ray and neutron diffraction as well as transmission electron microscopy, scanning electron microscopy, and electron paramagnetic resonance (EPR) spectroscopy. In addition to kinetic studies, insight into the mechanism of action of the dopants was gained through studies of the destabilization of hydrogen in NaAlH4 by the dopants through infrared, NMR, and anelastic spectroscopy

Topological Properties of Crystallographic Structure of Molecules

Chemical graph theory plays an important role in modeling and designing any chemical structure. The molecular topological descriptors are the numerical invariants of a molecular graph and are very useful for predicting their bioactivity. In this paper, we study the chemical graph of the crystal structure of titanium difluoride TiF2 and the crystallographic structure of cuprite Cu2O. Furthermore, we compute degree-based topological indices, mainly ABC, GA, ABC4, GA5 and general Randić indices. Furthermore, we also give exact results of these indices for the crystal structure of titanium difluoride TiF2 and the crystallographic structure of cuprite Cu2O