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Wang, Hongji. "Investigations into carbon nitrides and carbon nitride derivatives." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-165492.
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Carbon nitrides and carbon nitride derivatives are promising photocatalysts. The main focus of this thesis is the synthesis and characterization of various carbon nitrides (incompletely condensed melon, carbon nitride doped cesium titanate, ultra-long calcined melon, and OH-melem). Those carbon nitrides were then tested with regard to their photocatalytic properties.
In the first part of chapter 3 of this thesis, we focus on a material called ‘‘melem oligomer’’. Two different synthesis routes were applied (open system and half open system) and the composition and structure of this material was studied. Melem with two different crystalline structures and some amorphous residues were found in the product. We also tested the photocatalytic activity of melem oligomer and confirmed hydrogen production from water with a relatively low rate of 2 μmol g-1 h-1. In the second part of chapter 3, we synthesized ultra-long calcined melamine which may have a morphology similar to the ‘‘g-C3N4 nanosheets’’. We analyzed both the composition and structure and investigated the efficiency of the presumed g-C3N4 nanosheets for hydrogen production from water. Ultra-long calcined melamine showed the best photoactivity which is twice that of melon at 490 °C. This is most likely due to the interesting morphology and high surface area.
In chapter 4, melem oligomer was doped with cesium titanate in situ. Different calcination times were applied and various characterization techniques were used to investigate the composition, structure and morphology of the obtained materials. The efficiency of this hybrid photocatalyst for hydrogen production did not show higher photoactivity than the pure carbon nitrides except in the case of 16 h calcination which was the optimum calcination time overall.
In chapter 5, OH-melem with a composition close to 2-oxo-6,10-diamino-s-heptazine, which could be a precursor of oxygen-doped g-C3N4, was synthesized and characterized by various techniques. Crystallinity is rather low in this oxygen containing species. NMR spectra differ from melem or cyameluric acid and XPS results confirm the presence of C=O groups.
Overall, different carbon nitrides and carbon nitride derivatives were synthesized and chemically investigated to gain further knowledge on their synthesis, chemical properties and their resulting application as photocatalysts.
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Fischer, Anna. ""Reactive hard templating" : from carbon nitrides to metal nitrides." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/1977/.
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Nanostructured inorganic materials are routinely synthesized by the use of templates. Depending on the synthesis conditions of the product material, either “soft” or “hard” templates can be applied. For sol-gel processes, usually “soft” templating techniques are employed, while “hard” templates are used for high temperature synthesis pathways. In classical templating approaches, the template has the unique role of structure directing agent, in the sense that it is not participating to the chemical formation of the resulting material. This work investigates a new templating pathway to nanostructured materials, where the template is also a reagent in the formation of the final material. This concept is described as “reactive templating” and opens a synthetic path toward materials which cannot be synthesised on a nanometre scale by classical templating approaches. Metal nitrides are such kind of materials. They are usually produced by the conversion of metals or metal oxides in ammonia flow at high temperature (T > 1000°C), which make the application of classical templating techniques difficult.
Graphitic carbon nitride, g-C3N4, despite its fundamental and theoretical importance, is probably one of the most promising materials to complement carbon in material science and many efforts are put in the synthesis of this material. A simple polyaddition/elimination reaction path at high temperature (T = 550°C) allows the polymerisation of cyanamide toward graphitic carbon nitride solids. By hard templating, using nanostructured silica or aluminium oxide as nanotemplates, a variety of nanostructured graphitic carbon nitrides such as nanorods, nanotubes, meso- and macroporous powders could be obtained by nanocasting or nanocoating. Due to the special semi-conducting properties of the graphitic carbon nitride matrix, the nanostructured graphitic carbon nitrides show unexpected catalytic activity for the activation of benzene in Friedel-Crafts type reactions, making this material an interesting metal free catalyst. Furthermore, due to the chemical composition of g-C3N4 and the fact that it is totally decomposed at temperatures between 600°C and 800°C even under inert atmosphere, g-C3N4 was shown to be a good nitrogen donor for the synthesis of early transition metal nitrides at high temperatures. Thus using the nanostructured carbon nitrides as “reactive templates” or “nanoreactors”, various metal nitride nanostructures, such as nanoparticles and porous frameworks could be obtained at high temperature. In this approach the carbon nitride nanostructure played both the role of the nitrogen source and of the exotemplate, imprinting its size and shape to the resulting metal nitride nanostructure.Die Nanostrukturierung anorganischer Materialien, d.h. die Kontrolle ihrer Form und Größe auf der Nanometerebene durch unterschiedliche Herstellungsverfahren, ist ein sich immer noch erweiterndes Forschungsgebiet. Eine solche Nanostrukturierung wird oft über sogenannte Templatierungsverfahren erreicht: Hier werden Formgeber (Template) mit definierter Morphologie und Größe verwendet und deren Struktur in ein neues Material abgebildet. Templatierungsverfahren können, je nach der Beschaffenheit des Templats, zwischen „weich“ und „hart“ unterschieden werden. Die Begriffe beziehen sich dabei vor allem auf die mechanische und thermische Stabilität der Template, d.h. weiche Template sind vornehmlich organischer, harte Template anorganischer Natur. Wo weiche Template in milden chemischen Verfahren eingesetzt werden, werden harte Template zur Herstellung von Materialien bei Hochtemperaturverfahren verwendet (z. B. poröse Kohlenstoffe). Allgemein dienen Template ausschließlich als Strukturgeber und gehen in keiner Weise in Form einer chemischen Reaktion in die Synthese des gewünschten Materials mit ein. Gegenstand dieser Arbeit ist ein neues Templatierungsverfahren: Die „reaktive Templatierung“. Hierbei wird das Templat - neben seiner Funktion als Strukturgeber – auch als Reagenz für die Synthese des Produktes verwendet. Dieser Synthese-Ansatz öffnet damit neue Wege für die Synthese von nanostrukturierten Materialien, die durch klassische Templatierungsansätze schwer zugänglich sind. Hierzu zählen zum Beispiel die Metallnitride. Üblicherweise werden Metallnitride über die Umsetzung von Metallen oder Metalloxiden in einem Ammoniakstrom bei Mindesttemperaturen von 1000°C gewonnen, was die Anwendung klassischer Templatierungsverfahren beinahe unmöglich macht. Darüber hinaus sind konzentrierte Lauge oder Flusssäure, welche zur Entfernung klassischer harter Template benötigt werden auch Aufschlussmittel für Metallnitride. Graphitisches Kohlenstoffnitrid, g-C3N4, ist wohl eines der meistversprechendsten Materialien um Kohlenstoff in der Materialwissenschaft zu ergänzen. Es wurden bereits viele potentielle Syntheseansätze beschrieben. Eine durch Groenewolt M. erstellte Route ist die thermisch induzierte Polykondensation von Cyanamid (NCNH2) bei 550°C. Da g-C3N4 sich zwischen 600°C und 800°C vollständig in NH3 und CxNyH-Gase zersetzt, ist es eine geeignete Festkörper-Stickstoffquelle für die Herstellung von Metalnitriden. Daher boten sich nanostrukturierte graphitische Kohlenstoffnitride als geeignete reaktive Template oder Nanoreaktoren zur Herstellung von nano-strukturierten Metalnitriden an. Die Templatierung der g-C3N4-Matrix wurde über klassische Harttemplatierungsverfahren erreicht. So konnte eine Vielzahl nano-strukturierter g-C3N4 Materialien synthetisiert werden wie zum Beispiel Nanostäbchen, Nanoröhren, mesoporöse oder makroporöse graphitische Kohlenstoffnitride. Diese haben sich interessanterweise, als metalfreie Katalysatoren für die Aktivierung von Benzol in Friedel-Crafts-Acylierung und -Alkylierung erwiesen. Durch die Infiltrierung der nano-strukturierten g-C3N4-Materialien mit diversen Metal-Präkursoren und nachfolgendem Tempern bei 800°C unter Schutzgas, konnten entsprechende nano-strukturierte Metalnitride, als Nanoabdrücke der vorgegebenen Kohlenstoffnitrid Nanostrukturen hergestellt werden. So konnten TiN, VN, GaN, AlGaN und TiVN Nanopartikel synthetisiert werden, macroporöse TiN/Kohlenstoff Komposite sowie TiN Hohlkugeln. Die so hergestellten Materialien erwiesen sich als effektive basische Katalysatoren für Aldol-Kondensations Reaktionen.
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Shah, Syed Imran Ullah. "Synthesis of transition metal nitrides and silicon based ternary nitrides." Thesis, University of Southampton, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580538.
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Solution phase ammonolysis and sol-gel techniques that produce polymeric metal-amide precursors are of growing interest in the synthesis of nitride materials, which result from the thermal decomposition of the polymer. They can be used to control composition and to produce a large number of useful morphologies such as nanoparticles, films, monoliths, aerogels, and materials with large surface area such as foams. The synthesis of nitride materials using ammonolysis of metal amides and chlorides has so far largely focused on producing powders for applications such as catalysis, or thin films by chemical vapour deposition and related techniques. In this thesis, formation of tantalum and molybdenum nitride nanoparticles and metal-silicon nitride based nanocomposites have been synthesised using non-oxide precursors by solution phase ammonolysis and sol-gel methods respectively. For tantalum nitride nanoparticles Ta(NMe2)5 in THF was ammonolysed with ammonia at - 78 QC and the polymeric precursor was pyrolysed at various temperatures under ammonia. Amorphous TaN was obtained at 700 QC and below, while Ta3Ns was obtained at 800 QC under ammonia and also by re-annealing the amorphous samples at 800 QC under nitrogen. Molybdenum nitride powders were obtained by solution phase ammonolysis of MoCl, or Mo(NMe2)4 and further annealing the polymeric precursors on different temperatures. The chloride precursor resulted in hexagonal Mo'N, at 500 QC, or rock salt Mobl, at 700-1000 QC and mixture of both at 600 QC. The amide precursor resulted phase pure hexagonal MoNx at 600 QC and rock salt mixed with hexagonal at 1000 QC. Samples produced at 600 QC consisted mainly of nanotubes. Some decomposition to molybdenum metal was found in MoN obtained at 1000 QC from either precursor source. Co-ammonolysis of Ta(NMe2)5 or Mo(NMe2)4 with Si(NHMe)4 was carried out using sol-gel technique. Polymeric metal-silicon amide precursors were annealed at 600 or 1000 QC. The Ta/Si precursor produced amorphous nanocomposites and no phase segregation was observed even after high temperature annealing. With molybdenum the products were nanocomposites of molybdenum nitride particles, including nanotubes, supported on a silicon nitride amorphous matrix.
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Moseley, Michael William. "Study of III-nitride growth kinetics by molecular-beam epitaxy." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47641.
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Since the initial breakthroughs in structural quality and p-type conductivity in GaN during the late 1980s, the group-III nitride material system has attracted an enormous amount of interest because of its properties and applications in both electronics and optoelectronics. Although blue light-emitting diodes have been commercialized based on this success, much less progress has been made in ultraviolet emitters, green emitters, and photovoltaics. This lack of development has been attributed to insufficient structural and electrical material quality, which is directly linked to the growth of the material. The objective of this work is to expand the understanding of III-nitride growth towards the improvement of current device capabilities and the facilitation of novel device designs.
Group-III nitride thin films are grown by molecular-beam epitaxy in a pulsed, metal-rich environment. The growths of nitride binaries and ternaries are observed in situ by transient reflection high-energy electron diffraction (RHEED) intensities, which respond to the behavior of atoms on the growing surface. By analyzing and interpreting these RHEED signatures, a comprehensive understanding of nitride thin film growth is obtained.
The growth kinetics of unintentionally doped GaN by metal-rich MBE are elucidated, and a novel method of in situ growth rate measurement is discovered. This technique is expanded to InN, highlighting the similarity in molecular-beam epitaxy growth kinetics between III-nitride binaries. The growth of Mg-doped GaN is then explored to increase Mg incorporation and electrical activation. The growth of InxGa1-xN alloys are investigated with the goal of eliminating phase separation, which enables single-phase material for use in photovoltaics. Finally, the growth of unintentionally doped and Mg-doped AlGaN is investigated towards higher efficiency light emitting diodes.
These advancements in the understanding of III-nitride growth will address several critical problems and enable devices relying on consistent growth in production, single-phase material, and practical hole concentrations in materials with high carrier activation energies.
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吳誼暉 and Yee-fai Ng. "Heteroepitaxial growth of InN on GaN by molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B29797846.
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Ng, Yee-fai. "Heteroepitaxial growth of InN on GaN by molecular beam epitaxy /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25212175.
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Vacek, Petr. "Rozsáhlé defekty v nitridech Ga a Al." Doctoral thesis, Vysoké učení technické v Brně. CEITEC VUT, 2021. http://www.nusl.cz/ntk/nusl-447553.
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III-nitridy běžně krystalizují v hexagonální (wurtzitové) struktuře, zatímco kubická (sfaleritová) struktura je metastabilní a má pouze mírně vyšší energii. Jejich fyzikální vlastnosti jsou silně ovlivněny přítomností rozsáhlých defektů, které jsou v těchto dvou strukturách od sebe odlišné. U wurtzitových nitridů se jedná primárně o vláknové dislokace. Některé vláknové dislokace tvoří hluboké energetické stavy v zakázaném pásu, kterými ovlivňují elektrické a optoelektronické vlastnosti těchto materiálů. Oproti tomu, kubické nitridy obsahují množství vrstevných chyb, které představují lokální transformace do stabilnější wurtzitové struktury. Cílem této práce je charakterizovat rozsáhlé defekty v obou krystalových strukturách pomocí elektronové mikroskopie, mikroskopie atomárních sil a rentgenové difrakce. Prokázali jsme, že vzorky GaN/AlN a AlN s orientací (0001) rostlé na substrátu Si (111) pomocí epitaxe z organokovových sloučenin obsahují velkou hustotu vláknových dislokací. Nejčastější jsou dislokace s Burgersovým vektorem s komponentou ve směru a wurtzitové struktury, následované dislokacemi s Burgersovým vektorem s komponentou ve směru a+c, zatímco dislokace s Burgersovým vektorem s c komponentou jsou relativně vzácné. Pravděpodobný původ vláknových dislokací je diskutován v souvislosti s různými mechanismy růstu těchto vrstev. Prizmatické vrstevné chyby byly nalezeny v tenkých nukleačních vrstvách AlN, ale v tlustších vrstvách již nebyly přítomny. Na rozhraní AlN / Si byla nalezena amorfní vrstva složená ze SiNx a částečně taky z AlN. Navrhujeme, že by tato amorfní vrstva mohla hrát významnou roli při relaxaci misfitového napětí. Analýza elektrické aktivity rozsáhlých defektů v AlN byla provedena pomocí měření proudu indukovaného elektronovým svazkem. Zjistili jsme, že vláknové dislokace způsobují slabý pokles indukovaného proudu. Díky jejich vysoké hustotě a rovnoměrnému rozložení však mají větší vliv na elektrické vlastnosti, než mají V-defekty a jejich shluky. Topografické a krystalografické defekty byly studovány na nežíhaných a žíhaných nukleačních vrstvách kubického GaN deponovaných na 3C-SiC (001) / Si (001) substrátu. Velikost ostrůvků na nežíhaných vzorcích se zvyšuje s tloušťkou nukleační vrstvy a po žíhání se dále zvětšuje. Po žíhání se snižuje pokrytí substrátu u nejtenčích nukleačních vrstev v důsledku difúze a desorpce (nebo leptání atmosférou reaktoru). Vrstevné chyby nalezené ve vrstvách GaN, poblíž rozhraní se SiC, byly většinou identifikovány jako intrinsické a byly ohraničené Shockleyho parciálními dislokacemi. Jejich původ byl diskutován, jako i vliv parciálních dislokací na relaxaci misfitového napětí. Díky velkému množství vrstevných chyb byly podrobněji studovány jejich interakce. Na základě našich zjištění jsme vyvinuli teoretický model popisující anihilaci vrstevných chyb v kubických vrstvách GaN. Tento model dokáže předpovědět pokles hustoty vrstevných chyb se zvyšující se tloušťkou vrstvy.
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Wang, Hongji [Verfasser], and Bettina [Akademischer Betreuer] Lotsch. "Investigations into carbon nitrides and carbon nitride derivatives / Hongji Wang. Betreuer: Bettina Lotsch." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1047543478/34.
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Du, Li. "Bulk crystal growth, characterization and thermodynamic analysis of aluminum nitride and related nitrides." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8625.
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Doctor of PhilosophyDepartment of Chemical Engineering
James H. Edgar
The sublimation recondensation crystal growth of aluminum nitride, titanium nitride, and yttrium nitride were explored experimentally and theoretically. Single crystals of these nitrides are potentially suitable as substrates for AlGaInN epitaxial layers, which are employed in ultraviolet optoelectronics including UV light-emitting diodes and laser diodes, and high power high frequency electronic device applications. A thermodynamic analysis was applied to the sublimation crystal growth of aluminum nitride to predict impurities transport (oxygen, carbon, and hydrogen) and to study the aspects of impurities incorporation for different growth conditions. A source purification procedure was established to minimize the impurity concentration and avoid degradation of the crystal’s properties. More than 98% of the oxygen, 99.9% of hydrogen and 90% of carbon originally in the source was removed. The AlN crystal growth process was explored in two ways: self-seeded growth with spontaneous nucleation directly on the crucible lid or foil, and seeded growth on SiC and AlN. The oxygen concentration was 2 ~ 4 x 1018cm-3, as measured by secondary ion mass spectroscopy in the crystals produced by self-seeded growth. Crystals grown from AlN seeds have visible grain size expansion. The initial AlN growth on SiC at a low temperature range (1400°C ~1600°C) was examined to understand the factors controlling nucleation. Crystals were obtained from c-plane on-axis and off-axis, Si-face and C-face, as well as m-plane SiC seeds. In all cases, crystal growth was fastest perpendicular to the c-axis. The growth rate dependence on temperature and pressure was determined for TiN and YN crystals, and their activation energies were 775.8±29.8kJ/mol and 467.1±21.7kJ/mol respectively. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45o angle between TiN [100] and W [100], was seen for TiN crystals deposited on both (001) textured tungsten and randomly orientated tungsten. Xray diffraction confirmed that the YN crystals were rock-salt structure, with a lattice constant of 4.88Å. Cubic yttria was detected in YN sample from the oxidation upon its exposed to air for limited time by XRD, while non-cubic yttria was detected in YN sample for exposures more than one hour by Raman spectra.
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Cordes, Niklas [Verfasser], and Wolfgang [Akademischer Betreuer] Schnick. "Ammonothermal synthesis of functional nitride oxides and ternary nitrides / Niklas Cordes ; Betreuer: Wolfgang Schnick." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1192215508/34.
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Potter, Richard John. "Optical processes in dilute nitrides." Thesis, University of Essex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250073.
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Bhamra, Mohanjit Singh. "The electrochemical properties of nitrides." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309326.
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Bem, David S. (David Stanley). "Synthesis of new ternary nitrides." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11902.
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Al-Brithen, Hamad Abdulaziz. "Scanning tunneling microscopy investigation of rock-salt and zinc-blende nitrides grown by molecular beam expitaxy." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1107274641.
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Christian, George. "Photoluminescence studies of InGaN/GaN quantum well structures." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/photoluminescence-studies-of-ingangan-quantum-well-structures(aa935835-26f3-4b12-8f83-21190ffa7cb9).html.
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In this thesis, optical studies of c-plane InGaN/GaN quantum well (QW) structures are presented. The effects of a Si-doped underlayer (UL) on the optical properties of multiple quantum well (MQW) structures are investigated. The QW photoluminescence (PL) emission peak energy and radiative recombination rate decrease and increase respectively with increasing number of QWs. These observations are attributed to the increasing net electric field across the MQW structure as the strength of the surface polarisation field, which acts in the opposite sense to the piezoelectric polarisation fields across the QWs, reduces with increasing distance of the UL from the sample surface. This leads to a reduction in the electron-hole recombination energy and wavefunction overlap. It is also shown that the internal quantum efficiency of the MQW structures may decrease with increasing number of QWs due to the reducing radiative recombination rate, which could indicate that carrier losses due to thermionic emission or interface recombination are mitigated by the inclusion of an UL. Optical studies of single QW structures containing Si-doped ULs with different net electric fields across the QW are presented. The net electric field across the QW is changed by varying the thickness of the GaN cap layer. The full width at half maximum of the emission peak increases with increasing net electric field across the QW. This is attributed to the increasing variation in electron ground state energies due to the role of the electric field in the localisation of electrons at quantum well width fluctuations. For one sample, a smaller Huang-Rhys factor compared to the rest of the samples is calculated. The non-exponential PL decays detected on the low energy side of the QW emission peak from this sample are also of a different shape to the other PL decays detected at all energies for the other samples. This may be due to the reversal of the net electric field across these QW regions. Observations of a broad emission band on the high energy side of single QW structures at high excited carrier densities are presented. This band occurs in the carrier density regime at which the efficiency droop is observed. The emission band is attributed to higher energy weakly localised or delocalised electron and hole states that are populated following the saturation of the localised ground states. PL decay curves detected across this emission band exhibit plateaus where the PL intensity remains constant until the higher energy emission has decayed. These are similar to decays observed in semiconductor quantum dots, which are characteristic of Pauli state blocking.
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Simo, Saarinen. "Isotopically enriched nitrides for nuclear power." Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102148.
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Hunter, Stuart Michael. "Molybdenum nitrides : structural and reactivity studies." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3221/.
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This thesis describes the preparation, structure and activity of a range of binary, ternary and quaternary molybdenum nitrides. It has been shown that all of the samples analysed can be formed through the reaction of the respective molybdate precursor with either ammonia or 3:1 H2/N2 gas mixture. The structures of the nitrides have been studied in detail. These structural findings were then linked to the activity potential of the materials to act as stores of activated nitrogen. The main body of work focused on the ternary molybdenum nitrides of cobalt, iron and nickel with a view to understanding their differences and similarities. Full structural analysis was performed using powder X-ray diffraction (PXRD) and neutron diffraction (PND). The activity of the nitrides was examined by reaction with 3:1 H2/N2 and with 3:1 H2/Ar at various temperatures. Particular attention was paid to the reactivity of lattice nitrogen. The cobalt molybdenum nitride was shown to be special case in this regard where the nitrogen is mobile and relocates within the lattice to a different crystallographic site. This mobility and relocation is concomitant with the loss of 50% of the lattice nitrogen from the system resulting in a phase change from Co3Mo3N to the unprecedented Co6Mo6N phase. The physical and chemical properties of this novel phase have been fully characterised and studied. Interestingly, the isostructual Fe3Mo3N behaves differently and the nitrogen remains fixed and the structure and stoichiometry constant throughout the testing procedure. Further studies of the ternary molybdenum nitrides extended to nickel molybdenum nitride, which was shown to be the least active when tested under both gas mixtures, and analogously to the iron molybdenum nitride the nitrogen is fixed within the β-Mn structured nitride. Further investigations were undertaken, resulting in the successful formation of a series of quaternary nitrides (Fe3-xCoxMo3N). These materials show properties similar to the Co-Mo-N system when the material is cobalt rich and behave similarly to the Fe-Mo-N system when iron rich.
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江河 and He Jiang. "Laser spectroscopy of transition metal nitrides." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31240380.
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Dunn, Peter James. "The cycloaddition reactions of sulphur nitrides." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38294.
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Jiang, He. "Laser spectroscopy of transition metal nitrides /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21527076.
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Buterakos, Lewis A. "Bond length and bonded radii variations in nitride molecules and crystals." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040653/.
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Kucheyev, Sergei Olegovich. "Ion-beam processes in group-III nitrides." View thesis entry in Australian Digital Theses Program, 2002. http://thesis.anu.edu.au/public/adt-ANU20030211.170915/index.html.
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Kucheyev, Sergei Olegovich, and kucheyev1@llnl gov. "Ion-beam processes in group-III nitrides." The Australian National University. Research School of Physical Sciences and Engineering, 2002. http://thesis.anu.edu.au./public/adt-ANU20030211.170915.
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Group-III-nitride semiconductors (GaN, InGaN, and AlGaN) are important for the fabrication of a range of optoelectronic devices (such as blue-green light emitting diodes, laser diodes, and UV detectors) as well as devices for high-temperature/high-power electronics. In the fabrication of these devices, ion bombardment represents a very attractive technological tool. However, a successful application of ion implantation depends on an understanding of the effects of radiation damage. Hence, this thesis explores a number of fundamental aspects of radiation effects in wurtzite III-nitrides. Emphasis is given to an understanding of (i) the evolution of defect structures in III-nitrides during ion irradiation and (ii) the influence of ion bombardment on structural, mechanical, optical, and electrical properties of these materials.
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Structural characteristics of GaN bombarded with keV ions are studied by Rutherford backscattering/channeling (RBS/C) spectrometry and transmission electron microscopy (TEM). Results show that strong dynamic annealing leads to a complex dependence of the damage buildup on ion species with preferential surface disordering. Such preferential surface disordering is due to the formation of surface amorphous layers, attributed to the trapping of mobile point defects by the GaN surface. Planar defects are formed for a wide range of implant conditions during bombardment. For some irradiation regimes, bulk disorder saturates below the amorphization level, and, with increasing ion dose, amorphization proceeds layer-by-layer only from the GaN surface. In the case of light ions, chemical effects of implanted species can strongly affect damage buildup. For heavier ions, an increase in the density of collision cascades strongly increases the level of stable implantation-produced lattice disorder. Physical mechanisms of surface and bulk amorphization and various defect interaction processes in GaN are discussed.
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Structural studies by RBS/C, TEM, and atomic force microscopy (AFM) reveal anomalous swelling of implanted regions as a result of the formation of a porous structure of amorphous GaN. Results suggest that such a porous structure consists of N$_{2}$ gas bubbles embedded into a highly N-deficient amorphous GaN matrix. The evolution of the porous structure appears to be a result of stoichiometric imbalance, where N- and Ga-rich regions are produced by ion bombardment. Prior to amorphization, ion bombardment does not produce a porous structure due to efficient dynamic annealing in the crystalline phase.
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The influence of In and Al content on the accumulation of structural damage in InGaN and AlGaN under heavy-ion bombardment is studied by RBS/C and TEM. Results show that an increase in In concentration strongly suppresses dynamic annealing processes, while an increase in Al content dramatically enhances dynamic annealing. Lattice amorphization in AlN is not observed even for very large doses of keV heavy ions at -196 C. In contrast to the case of GaN, no preferential surface disordering is observed in InGaN, AlGaN, and AlN. Similar implantation-produced defect structures are revealed by TEM in GaN, InGaN, AlGaN, and AlN.
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The deformation behavior of GaN modified by ion bombardment is studied by spherical nanoindentation. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, amorphous GaN exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young's modulus compared to the values of as-grown GaN. Moreover, implantation-produced defects in crystalline GaN suppress the plastic component of deformation.
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The influence of ion-beam-produced lattice defects as well as a range of implanted species on the luminescence properties of GaN is studied by cathodoluminescence (CL). Results indicate that intrinsic lattice defects mainly act as nonradiative recombination centers and do not give rise to yellow luminescence (YL). Even relatively low dose keV light-ion bombardment results in a dramatic quenching of visible CL emission. Postimplantation annealing at temperatures up to 1050 C generally causes a partial recovery of measured CL intensities. However, CL depth profiles indicate that, in most cases, such a recovery results from CL emission from virgin GaN, beyond the implanted layer, due to a reduction in the extent of light absorption within the implanted layer. Experimental data also shows that H, C, and O are involved in the formation of YL. The chemical origin of YL is discussed based on experimental data.
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Finally, the evolution of sheet resistance of GaN epilayers irradiated with MeV light ions is studied {\it in-situ}. Results show that the threshold dose of electrical isolation linearly depends on the original free electron concentration and is inversely proportional to the number of atomic displacements produced by the ion beam. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 C. Results also show that both implantation temperature and ion beam flux can affect the process of electrical isolation. This behavior is consistent with significant dynamic annealing, which suggests a scenario where the centers responsible for electrical isolation are defect clusters and/or antisite-related defects. A qualitative model is proposed to explain temperature and flux effects.
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The work presented in this thesis has resulted in the identification and understanding of a number of both fundamental and technologically important ion-beam processes in III-nitrides. Most of the phenomena investigated are related to the nature and effects of implantation damage, such as lattice amorphization, formation of planar defects, preferential surface disordering, porosity, decomposition, and quenching of CL. These effects are often technologically undesirable, and the work of this thesis has indicated, in some cases, how such effects can be minimized or controlled. However, the thesis has also investigated one example where irradiation-produced defects can be successfully applied for a technological benefit, namely for electrical isolation of GaN-based devices. Finally, results of this thesis will clearly stimulate further research both to probe some of the mechanisms for unusual ion-induced effects and also to develop processes to avoid or repair unwanted lattice damage produced by ion bombardment.
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CHANG, YUN-CHORNG. "OPTICAL MEMORY EFFECTS IN III-V NITRIDES." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-20020107-114606.
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Optical memory effects in III-V Nitrides have been investigated. In order to have further understanding of this effect, qualitative and then quantitative measurements were performed to investigate this memory effect. A microscopic model consistent with most of the experimental observations was developed. Finally, verification of the model was performed.Experimental observations indicate that optical memory effects are flux-dependent effects, which require no lower power limit of the excitation source in order to produce them. Photoluminescence and cathodoluminescence studies indicate the yellow patterns are the result of increased yellow luminescence intensity from the sample. Heating up the samples can erase this memory effect.Blue luminescence, with an energy about 2.8 eV, is important in the explanation of the memory effect since it appears in the photoluminescence spectra of all the samples that exhibit memory effects. This leads to a model with two different transitions, yellow and blue luminescence, competing with each other to explain the memory effects. The blue luminescence is caused by electron transitions from a localized oxygen level to the deep isolated and hydrogenated gallium vacancies. Transitions from shallow silicon donor levels to the gallium vacancies result in the yellow luminescence. Intense ultraviolet light will remove hydrogen from the hydrogenated gallium vacancies and these vacancies will form complexes with neighboring oxygen atoms. These complexes will result in more yellow luminescence. Less blue luminescence and more yellow luminescence result in the yellow memory patterns observed. This model is consistent with most of the observations and several experiments strongly support this model. Potential applications for memory effects include optical data storage and optical signal processing. Further understanding of this effect could lead to the realization of all optical memory cells and could also be used to improve the quality of III-nitrides materials.
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Jalili, Yousef Seyed. "Optoelectronic properties of GaAs-based dilute nitrides." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408757.
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Siddons, Daniel James. "Synthetic routes to binary and ternary nitrides." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363637.
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Suter, Theo M. "Crystalline carbon nitrides : characterisation, intercalation and exfoliation." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10045282/.
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In recent years there has been significant interest in, and research into, carbon nitride materials for use in applications such as photocatalysis. The most commonly described C/N materials are referred to as graphitic carbon nitride (gCN), though due to the layered amorphous nature structural characterisation is difficult. Polytriazine imide (PTI) is a crystalline layered carbon nitride that is less explored within the literature compared to gCN due to its more difficult synthetic procedure. In this thesis the synthesis, characterisation, intercalation chemistry and exfoliation of PTI is explored. The synthesis of a related material, triazine based graphitic carbon nitride (TGCN) is explored and the product characterised in detail. PTI refers to the carbon, nitrogen and hydrogen framework (C6N9H3) within which different ionic intercalants can be accommodated; then give rise to several different crystalline materials with the same underlying carbon nitride backbone. The structure of these crystalline, layered PTI was synthesised by reversibly removing and replacing the intercalated ions without affecting the carbon nitride structure. The structures of these new materials was investigated and how changing the intercalant can be used to tune the structures and properties. This methodology may facilitate the fine-tuning and optimisation of carbon nitrides for a number of applications. I have also explored the exfoliation of the layered PTI materials. A number of methods have been used including intercalation and ultrasonication. Remarkably, however I found that the PTI gently, and even spontaneously dissolves to form solutions in highly polar organic solvents and even in water. This process takes place without the need for mechanical mixing, sonication or centrifugation. The resultant separated nanosheets solutions are characterised indepth. Few layer stacks of undamaged crystallites are observed. The photoluminescence of the nanosheets have been found to depend on the number of stacked layers, presenting exciting opportunities for optoelectronic devices.
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Castro, Darren T. (Darren Thomas) 1970. "Synthesis, processing, and properties of nanocrystalline nitrides." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10227.
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Galtrey, Mark John. "The mechanism of luminescence in III-nitrides." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609147.
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Kraeusel, Simon. "Native defects in the group III nitrides." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=19541.
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The promise of the broad range of direct band gaps of the (Al,Ga,In)N system is limited by the crystal quality of current material. As grown defect densities of InN, when compared with the more mature GaN, are extremely high and InN is strongly influenced by these defects. This is particularly important due to the unusual position of the charge neutrality level of InN, leading to both the well known surface charge accumulation and difficulties in p-type doping. While impurities and native defects clearly impact on the bulk carrier density in InN, the effects of threading dislocations on the electrical properties are still in dispute. Issues such as whether the dislocation line is charged or contains dangling bonds remain open. In this work an empirical Stillinger-Weber inter-atomic potential method is employed in a systematic global search for possible dislocation core reconstructions for screw and edge dislocations in GaN. The global optimisation of the dislocation cores is performed for a wide variety of core stoichiometries ranging from Ga rich to N rich. The most promising optimised core configurations are subsequently investigated using density functional theory for GaN and InN, in order to discuss relative stability under a wide range of growth conditions and their influence on the electronic properties of the bulk material.
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Lüdtke, Tobias Clemens [Verfasser], Martin [Akademischer Betreuer] Lerch, Martin [Gutachter] Lerch, and Holger [Gutachter] Kohlmann. "Metastable transition metal oxides, oxide nitrides, and nitrides / Tobias Clemens Lüdtke ; Gutachter: Martin Lerch, Holger Kohlmann ; Betreuer: Martin Lerch." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156010888/34.
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Khoshman, Jebreel M. "Spectroscopic ellipsometry charactarization of single and multilayer aluminum nitride / indium nitride thin film systems." Ohio : Ohio University, 2005. http://www.ohiolink.edu/etd/view.cgi?ohiou1129584189.
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Lind, Martin, and Cecilia Johansson. "Evaluation of the η (Eta) nitride with three laboratory melts." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176065.
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η (eta) nitride, Cr3Ni2SiN, is a precipitate found in high temperature austenitic stainless steel and is not yet included in Thermo-Calc steel database TCFE7. The aim of this thesis is to collect thermodynamic data to enable the addition of η nitride in the databases. Three laboratory melts with varying levels of silicon, chromium and nickel have been aged at 700-1000 °C for 75 h, 300 h and 1200 h and examined by Light Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Wavelength Dispersive Spectroscopy, Electron Backscattered Diffraction and X-ray Powder Diffraction. η nitride is in the studied alloys an equilibrium phase stabilized with nitrogen. Presence of η nitride was confirmed by Energy Dispersive Spectroscopy and X-ray Powder Diffraction. It was found to precipitate in four different ways, at primary grain boundaries, intragranularly, as a "skeleton-like" precipitate and as a border around the occurring Cr2N precipitates. The area fraction of η nitrides increases with longer aging times and is favored by silicon and nickel. The composition of η nitride is not changing regardless of material composition, aging temperature and aging time. The composition of η nitride in all three materials are 8.7-9.7 wt.% silicon, 47-54 wt.% chromium, 1.4-4.1 wt.% iron and 33-36 wt.% nickel. The nitrogen content 2 determined by Wavelength Dispersive Spectroscopy is 2.8-3.2 wt.%. No complete equilibrium was achieved and together with incomplete mixing of the alloying elements during melting, the microstructure is difficult to evaluate. Other precipitates found are Cr2N, π nitride, σ phase and two unidentified phases, M and N. Of these phases at least Cr2N is not an equilibrium phase as it dissolves during aging. Further aging to achieve complete equilibrium is necessary.
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So, Wai-kei. "A study of surface properties of III-nitride semiconductors by first principles total energy calculation." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38606951.
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Alevli, Mustafa. "Growth and characterezation of indium nitride layers grown by high-pressure chemical vapor deposition." unrestricted, 2008. http://etd.gsu.edu/theses/available/etd-04212008-154425/.
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Thesis (Ph. D.)--Georgia State University, 2008.Title from file title page. Nikolaus Dietz, committee chair, Brian Thoms, A. G. Unil Perera, Xiaochun He, committee members. Electronic text (215 p. : col. ill.) : digital, PDF file. Description based on contents viewed on July 14, 2008. Includes bibliographical references (p. 209-215).
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Mitra, Chandrima. "COMPUTATIONAL STUDIES OF GADOLINIUM IN NITRIDES : BULK GDN AND GD-DOPED GAN." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238690053.
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Bojdys, Michael Janus. "On new allotropes and nanostructures of carbon nitrides." Phd thesis, Universität Potsdam, 2009. http://opus.kobv.de/ubp/volltexte/2010/4123/.
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In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk.
The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C.
The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation.
The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung neuer Allotropen und Nanostrukturen von Karbonitriden und berührt einige ihrer möglichen Anwendungen. Alle gezeigten, ausgedehnten, kovalent verbundenen Karbonitridgerüste wurden in einem ionothermalen Syntheseprozess – einer Hochtemperaturbehandlung in einem eutektischen Salzgemisch als ungewöhnlichem Lösungsmittel – aus einfachen Präkursormolkülen erzeugt. Der Kondensationsmechanismus folgt einer temperaturinduzierten Deaminierung und Bildung einer ausgedehnten, aromatischen Einheit; des dreifach substituierten Heptazines. Die Dissertation folgt vier übergreifenden Themen, beginnend mit der Einleitung in Karbonitridsysteme und der Suche nach einem Material, welches einzig aus Kohlenstoff und Stickstoff aufgebaut ist – einer Suche, die 1834 mit den Beobachtungen Justus von Liebigs „über einige Stickstoffverbindungen“ begann. Der erste Abschnitt zeigt die erfolgreiche Synthese von graphitischem Karbonitrid (g-C3N4); einer Spezies, welche auf Schichten hexagonal angeordneter s-Heptazineinheiten beruht, die durch kovalente Bindungen zwischen C- und N-Atomen zusammengehalten werden, und welche in einer graphitischen, verschobenen Art und Weise gestapelt sind. Der zweite Abschnitt berührt die Vielfalt von Salzschmelzensystemen, die für die Ionothermalsynthese geeignet sind und zeigt auf, dass die bloße Veränderung der Salzschmelze eine andere Kristallphase des graphitischen Karbonitrides ergibt – das g-C3N4-mod2. Im dritten Abschnitt wird vom Graphit bekannte Interkallationschemie auf das g-C3N4 angewendet, um eine Kalliuminterkallationsverbindung des graphitischen Karbonitirdes zu erhalten (K(C6N8)3). Diese Verbindung kann in Analogie zum graphitischen System leicht exfoliiert werden, um Bündel von Karbonitridnanoschichten zu erhalten, und weist darüberhinaus interessante optische Eigenschaften auf. Der vierte und letzte Abschnitt handelt von der Einführung von Aryl- und Biphenylbrücken in das Karbonitridmaterial durch rationale Synthese der Präkursormoleküle. Diese ergeben die heptazinbasierten Frameworks, HBF-1 und HBF-2 – zwei kovalente, organische Gerüste.
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Hintze, Frauke. "Synthetic strategies to novel multinary nitrides of gallium." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-160852.
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Novel multinary nitrides of gallium are synthesized and characterized. Different synthesis approaches are shown. Novel compounds are characterized regarding their crystal structures and their properties.
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Oldham, Sophie E. "Synthesis and characterisation of intermetallic nitrides and germanides." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497063.
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Sviridov, Lev A. "Synthesis and Characterization of New Transition - Metal Nitrides." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526120.
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Baker, Charles Fielding. "Synthesis and structural studies of low dimensional nitrides." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368271.
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Bailey, Andrew Steven. "Synthesis and characterisation of layered and defect nitrides." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435363.
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Jeffs, Nicholas James. "Growth and structural characterisation of group III nitrides." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311764.
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Woodhead, K. E. "High pressure polymorphism of tantalum nitrides and oxynitrides." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1382598/.
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The investigations presented here explore the nature of the Ta-O-N system at high pressures. The techniques that are commonly used for structural determination with the diamond anvil cell (DAC) are Raman spectroscopy and synchrotron-source X-ray diffraction (XRD); these methods are supported here by energy-dispersive X-ray absorption spectroscopy (EDXAS), a technique which is in its infancy when combined with in situ DAC studies. The studies presented here are among the first to exemplify the use of EDXAS in high-pressure structural determination, and are especially useful for nitride and oxynitride studies, where the greatest changes occur in the positions of the light elements that form the local environments around the metal atoms. The refractory ceramic, ε-TaN, has previously been shown through Raman and XRD studies not to undergo any phase transition up to 58 GPa, although some interesting features were observed in both cases. Here, in situ EDXAS probes the local structure around the tantalum atoms in this material, and the movement of the nitrogen atoms from their positions can be seen up to 58 GPa. The second investigation uses Raman, XRD and EDXAS experiments to explore phase transitions of TaON; the results presented here show a phase transition occurring from the baddelyite phase to the cotunnite phase between 20-35 GPa. The known baddeylite phase of TaON is also shown to be a highly incompressible material, possessing a bulk modulus value of 328 GPa. The third investigation presents a study of the complex structural transitions undergone by orthorhmobic Ta3N5-I at pressures up to 50 GPa. Both Raman and XRD experiments show a first order phase transition at about 11 GPa to the orthorhombic Ta3N5-II phase; amorphisation and a coexistence of phases are observed at pressures above 16 GPa in the XRD patterns, and hence the subtleties of the transitions are explored by EDXAS, such as an increase in coordination number and bond length. A novel high-pressure, high-temperature synthesis route to the new Ta3N5-II phase has also been shown as viable, by laser-heating an amorphous TaxNy precursor in the DAC.
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Alshibane, Ihfaf. "Phase transformations of ternary carbides, nitrides and carbonitrides." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30702/.
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The development of novel efficient catalytic materials to improve the efficiency of industrial processes has been the driving force for many academic and industrial studies. The general approach adopted to enhance the activity of a given catalytic formulation is usually based on enhancing the structural and structural properties (e.g. crystal size and surface area) by adopting new synthesis methods, by supporting the active phase or by modifying the reactivity of the parent materials by adding dopants. However, in a less studied approach, it has been shown that the presence of interstitial species such as carbon or nitrogen can modify the electronic structure of parent metals apparently conferring, in the case of systems such as molybdenum carbide, properties akin to precious metals. This approach allows not just improvement of the catalytic activity in an incremental manner but also the design entirely new catalytic formulations. In this context, the effect of the interstitial elements carbon and nitrogen upon the activity of a range binary and ternary molybdenum based materials for ammonia synthesis and methane cracking has been investigated within this thesis. The performance of Co3Mo3N, Co3Mo3C, and Co6Mo6C for ammonia synthesis has been compared. Depending on the chemical composition, significant difference in catalytic activity was apparent. In contrast to Co3Mo3N, which is active at 400 °C, Co3Mo3C was found to be only active at a reaction temperature of 500 °C. Furthermore, in-situ NPD revealed that the catalytic activity of ternary cobalt molybdenum systems is associated with the presence of N in the 16c Wyckoff crystallographic site. Co6Mo6C was found to be inactive under the conditions tested. The same comparison between the chemical composition and the catalytic activity has been made in the context of methane cracking. Although all the prepared materials (i.e. Co3Mo3N, Co6Mo6N, Co3Mo3C, and Co6Mo6C) displayed catalytic activity, differences as a function of chemical composition were observed. Among the evaluated catalysts, the Co6Mo6N sample showed the highest activity. However, in-situ and post-reaction analysis revealed a significant phase transformation during reaction which explains the differences in terms of catalytic reactivity. In summary, this thesis details a comparison between the catalytic performance of a range of binary and ternary molybdenum based materials presenting different chemical compositions. Particular attention has been directed towards the role of, and the interconversion between, lattice C and N species with the intention of elucidating their influence upon catalytic behaviour.
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ROVAI, RICCARDO. "Synthese des nouveaux precurseurs pour les ceramiques nitrides." Université Louis Pasteur (Strasbourg) (1971-2008), 1999. http://www.theses.fr/1999STR13101.
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Le travail decrit dans cette these concerne le developpement d'une voie de synthese douce pour preparer des materiaux a base de nitride de silicium si 3n 4 et de diimide de silicium, si(nh) 2. La strategie employee est l'ammonolyse de dialkylamidosilanes. Nous avons prepare pour la premiere fois des composes tetrakis(dialkylamido)silanes partiellement ammonolyses, tels que (me 2n) 3sinh 2 et (morpholine) 3sinh 2, afin d'obtenir un meilleur degre de controle sur leur ammonolyse ulterieure en presence de catalyseur acide. En particulier, nous avons montre que les composes (me 2n) 4si et (me 2n) 3sinh 2 sont inertes vis-a-vis de l'ammoniac, mais qu'ils reagissent en presence de catalyseur acide pour former des poudres si(nh) 2. Lorsque le compose (me 2n) 3sinh 2 s'autocondense en presence de catalyseur acide, nous obtenons le trimere cyclique (me 2n) 2sinh 3. Lorsque nous realisons la reaction d'ammonolyse du compose (me 2n) 3sinh 2 dans une solution de tetrahydrofurane, nous obtenons un gel si(nh) 2. La surface specifique de ce gel peut atteindre 1000 m 2/g et la distribution de taille des pores est comparable a celle d'une silice mesoporeuse. Ce resultat represente le premier exemple de preparation d'un gel non-oxyde de grande surface specifique. Nous avons utilise la silylamine (me 2n) 3sinh 2 pour synthetiser une nouvelle classe de precurseurs monosources de ceramiques multielementaires. La deprotonation par le butyllithium conduit au sel de lithium tetramere (me 2n) 3sinh 2 4 (caracterise par crystallographie), qui peut reagir avec le trichlorure d'aluminium alcl 3 pour former le compose lia1nhsi(nhme 2) 3 4 (caracterise par crystallographie). La silylamine (me 2n) 3sinh 2 peut reagir avec des amidures metalliques pour former une serie de composes silylamides metalliques : tinhsi(nme 2) 3 4, ((me 2n) 3sinh) 2ti(nsi)nme 2) 3) 2 2 et (me 2n)bnhsi(nme 2) 3 3 2. Par reaction avec des composes organometalliques tels que a1et 3 et methylaluminoxane, nous avons obtenu les composes silylamides correspondants, a1nhsi(nme 2) 3 et (me 2n) 3sinha1o n. Certains de ces precurseurs monosources, tels que a1nhsi(nme 2) 3 et (me 2n)bnhsi(nme 2) 3 3 2, peuvent subir une ammonolyse par catalyse acide pour former des gels mixtes a base de diimide de silicium, de surface specifique elevee. D'autre part nous avons transforme le polyaluminosilazane (me 2n) 3sinha1o n en une ceramique crystalline sialon.
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Steinhoff, Georg. "Group III-nitrides for bio- and electrochemical sensors." kostenfrei, 2008. http://mediatum2.ub.tum.de/doc/646548/646548.pdf.
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Montoya, Anthony Tristan. "Synthesis of carbon nitrides and composite photocatalyst materials." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6479.
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This thesis describes the synthesis, characterization and photocatalytic applications of carbon nitride (C3N4) and titanium dioxide (TiO2) materials. C3N4 was prepared from the thermal decomposition of a trichloromelamine (TCM) precursor. Several different reactor designs and decomposition temperatures were used to produce chemically and thermally stable orange powders. These methods included a low temperature glass Schlenk reactor, a high mass scale stainless steel reactor, and decomposition at higher temperatures by the immersion of a Schlenk tube into a furnace. These products share many of the same structural and chemical properties when produced by these different methods compared to products from more common alternate precursors in the literature, determined by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis. C3N4 is capable of utilizing light for photocatalysis due to its moderate band gap (Eg), measured to be between 2.2 and 2.5 eV. This enables C3N4 to be used in the photocatalytic degradation of organic dyes and the production of hydrogen via the water-splitting reaction. C3N4 degraded methylene blue dye to less than 10% of its initial concentration in less than an hour of UV light illumination and 60% under filtered visible light in 150 minutes. It also degraded methyl orange dye to below 20% in 70 minutes under UV light and below 60% in 150 minutes under visible light. Using precious metal co-catalysts (Pt, Pd, and Ag) photo-reduced onto the surface of C3N4, hydrogen was produced from a 10% aqueous solution of triethanolamine at rates as high as 260 μmol h-1 g-1.
C3N4 was also modified by mixing the precursor with different salts (NaCl, KBr, KI, KSCN, and NH4SCN) as hard templates. Many of these salts reacted with TCM by exchanging the anion with the chlorine in TCM. The products were mostly prepared using the high temperature Schlenk tube reactor, and resulted in yellow, orange, or tan-brown products with Eg values between 2.2 and 2.7 eV. Each of these products had subtle differences in the IR spectra and elemental composition. The morphology of these C3N4 products appeared to be more porous than unmodified C3N4, and the surface area for some increased by a factor of 4. These products demonstrated increased activity for photocatalytic hydrogen evolution, with the product from TCM-KI reaching a peak rate as high as 1,300 µmol h-1 g-1. C3N4 was coated onto metal oxide supports (SiO2, Al2O3, TiO2, and WO3) with the goal of utilizing enhanced surface area of the support or synergy between two different semiconductors. These products typically required higher temperature synthesis conditions in order to fully form. The compositions of the SiO2 and Al2O3 products were richer in nitrogen and hydrogen compared to unmodified C3N4. The higher temperature reactions with C3N4 and WO3 resulted in the formation of the HxWO3 phase, and an alternate approach of coating WO3 on C3N4 was used. The degradation of methyl orange showed a significant increase in adsorption of dye for the composites with SiO2 and Al2O3, which was not seen with any of the individual components. The composite between C3N4 and TiO2 showed improved activity for hydrogen evolution compared to unmodified C3N4.
The surface of TiO2 was modified by the reductive photodeposition of several first row transition metals (Mn, Fe, Co, Ni, and Cu). This process resulted in the slight color change of the white powder to shades of light yellow, blue or grey. Bulk elemental analysis showed that these products contained between 0.04-0.6 at% of the added metal, which was lower than the targeted deposit amount. The Cu modified TiO2 had the largest enhancement of photocatalytic hydrogen evolution activity with a rate of 8,500 µmol h-1 g-1, a factor of 17 higher than unmodified TiO2.
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Seetoh, Ian Peiyuan. "Commercialization of group III nitrides-on-silicon technologies." Thesis, Massachusetts Institute of Technology, 2010. https://hdl.handle.net/1721.1/122862.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2010Cataloged from PDF version of thesis.
Includes bibliographical references (pages 35-39).
While group Ill nitride materials have been commercialized for many years, there is recent interest in growing these materials on silicon substrates as a cost effective alternative to more expensive sapphire and silicon carbide technologies. Therefore, it is necessary to determine how group Ill nitride-on-silicon technologies can be positioned in way for them to be effective in their respective applications, thereby enabling their commercialization. This thesis is a systematic evaluation of the epitaxial growth on silicon carbide, sapphire and silicon substrates, focusing on their lattice-mismatches, thermal expansion mismatches, and thermal conductivity. The subsequent analysis of important commercial applications determined that GaN-on-Si technology is ready for commercialization in the near future. These applications include the InGaN/GaN white light emitting diode and the blue laser diode, as well as the AIGaN/GaN high electron mobility transistor, each with its own unique requirements for the technology and the implementation. It was recommended that start-up firms interested in commercializing GaN-on- Si technology focus on the growth of GaN on silicon substrates and engage device manufacturers proactively. InN and In-rich nitrides can complement maturing GaN and Ga-rich nitrides technologies, resulting in new applications and products in future. While the growth of InN films is currently very challenging, it is believed that the experience and revenue obtained from the commercialization of GaN-on-Si technology can benefit InN-on-Si technology, speeding up the latter's commercialization. A brief business strategy aimed at translating the findings into a feasible approach for commercialization is also provided.
by Ian Peiyuan Seetoh.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Minj, Albert <1986>. "Nanoscale-electrical and optical properties of iii-nitrides." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5193/1/minj_albert_tesi.pdf.
Full textAbstract:
III-nitrides are wide-band gap materials that have applications in both electronics and optoelectronic devices. Because to their inherent strong polarization properties, thermal stability and higher breakdown voltage in Al(Ga,In)N/GaN heterostructures, they have emerged as strong candidates for high power high frequency transistors. Nonetheless, the use of (Al,In)GaN/GaN in solid state lighting has already proved its success by the commercialization of light-emitting diodes and lasers in blue to UV-range. However, devices based on these heterostructures suffer problems associated to structural defects. This thesis primarily focuses on the nanoscale electrical characterization and the identification of these defects, their physical origin and their effect on the electrical and optical properties of the material. Since, these defects are nano-sized, the thesis deals with the understanding of the results obtained by nano and micro-characterization techniques such as atomic force microscopy(AFM), current-AFM, scanning kelvin probe microscopy (SKPM), electron beam induced current (EBIC) and scanning tunneling microscopy (STM). This allowed us to probe individual defects (dislocations and cracks) and unveil their electrical properties. Taking further advantage of these techniques,conduction mechanism in two-dimensional electron gas heterostructures was well understood and modeled. Secondarily, origin of photoluminescence was deeply investigated. Radiative transition related to confined electrons and photoexcited holes in 2DEG heterostructures was identified and many body effects in nitrides under strong optical excitations were comprehended.