Orientador: Fernando Alvarez / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T10:47:17Z (GMT). No. of bitstreams: 1 ParedezAngeles_PabloJenner_D.pdf: 4194390 bytes, checksum: 8881d83ee8bcb5a5ad4bfb23b7ff1028 (MD5) Previous issue date: 2007 / Resumo: Nesta tese são apresentados os efeitos nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico induzidos pela incorporação de nitrogênio em nanoestruturas de carbono. As nanoestruturas de carbono contendo nitrogênio foram preparadas por pulverização catódica (sputtering) de um alvo de grafite assistido, ou não, por um feixe iônico. A técnica permite atuar sobre os parâmetros de deposição induzindo mudanças nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico. O papel do hélio na formação de nanoes-truturas de carbono contendo nitrogênio foi também explorado, mostrando que o gás nobre promove maior incorporação de nitrogênio. Isto é provavelmente devido à relativa alta condutividade térmica que apresenta o hélio, propriedade que modifica a cinética do crescimento das nanoestruturas. O estudo realizado permitiu entender o mecanismo de formação das nanoestruturas, mostrando que primeiramente o carbono alcança as partículas de Ni por difusão até a saturação do metal, iniciando a formação das camadas grafíticas sobre a partícula de Ni, camadas que foram observadas por microscopia eletrônica de transmissão de alta resolução. O estudo mostra, também, que os parâmetros importantes que controlam a incorporação de nitrogênio no material são a pressão parcial de nitrogênio na câmara de deposição, assim como a energia do feixe de íons assistindo a deposição.Foram estudadas três séries de amostras preparadas em atmosferas controladas. Na primeira série foi utilizado um feixe de íons de nitrogênio como feixe de assistência, e na segunda, uma mistura composta por duas espécies iônicas, íons de nitrogênio e hidrogênio. Com o auxilio da espectroscopia de elétrons fotoemitidos por raios-X observou-se a incorporação de nitrogênio nos filmes. A microscopia de força atômica revelou a presença de estruturas do tipo domo, distribuídas de maneira uniforme na superfície das amostras, apresentando uma densidade média de ~3×10 9 domos/cm 2as da primeira série, e ~1.4×10 9 domos/cm 2as da segunda série. Tanto a distribuição como a forma seguem o padrão estabelecido pelos precursores utilizados na preparação das nanoestruturas, i.e., ilhas de níquel que agem ao mesmo tempo como catalisadores e como suporte para as nanoestruturas. Na terceira série, as nanoestruturas foram crescidas sobre um filme de nitreto de titânio, depositado sobre substratos de Si, pulverizando um alvo de grafite em atmosferas de nitrogênio e hélio-nitrogênio. A densidade dos domos encontrada para esta série foi de ~5.3×10 10 domos/cm 2 . Os espectros Raman das três séries apresentam as bandas G e D, o que indica a presença estruturas grafíticas com distorções representadas pela banda D. A incorporação de nitrogênio ocasiona o alargamento da banda G e aumento da razão das intensidades das bandas D e G, respectivamente, indicando uma redução da ordem estrutural com a incorporação de Nitrogênio. Finalmente, para as três séries de amostras, fez-se também um estudo das propriedades de emissão eletrônica por efeito de campo elétrico. A emissão é predominantemente por tunelamento quântico (as curvas de densidade de corrente vs campo elétrico seguem o modelo de Fowler-Nordheim) e dependem da concentração de nitrogênio assim como do processo usado na preparação das amostras / Abstract: The subject of this thesis is establishing a link among the synthesis, structures, and field emission properties for nanostructured carbon materials containing nitrogen. The materials were prepared by ion beam assisted deposition and ion beam sputtering. The carbon material was obtained sputtering an ultra pure graphite target by an argon ion beam. The method allows controlling the deposition parameters to induce changes in the structural, electronic, and field emission properties. Also, the role of helium on the carbon containing nitrogen nanostructures was investigated. The remarkable thermal conductance of He modifying the growing kinetics was also studied. An important goal of the work was to elucidate the mechanism of the nanostructures formation. It was found that, at first, the carbon atoms reach the Ni particles saturating the metal particle, and then, the formation of stacked graphene starts on the metal particles. The graphene layers were observed by high resolution transmission electron microscopy. The results show that mainly two parameters control the nitrogen incorporation, namely, the deposition chamber nitrogen partial pressure and the energy of the nitrogen ion beam assisting the growth. Three sample series prepared in controlled atmospheres were studied. The first series was prepared assisting the growth with a nitrogen ion beam and, the second series by a nitrogen-hydrogen ion beam. The third sample series were prepared by ion beam sputtering on silicon substrate by sequentially depositing titanium nitride thin film, nanometric nickel particles and carbon. The carbon containing nitrogen nanostructures were grown in nitrogen and helium-nitrogen atmospheres. X-ray photoelectron spectroscopy analysis indicates nitrogen incorporation and it depends predominantly on the ion beam energy or on the nitrogen partial pressure. Atomic force microscopy reveals dome-like structures uniformly distributed on the surface of the samples, with ~3×10 9 domes/cm 2 for the first series, ~1.4×10 9 domes/cm 2 for the second, and ~5.3×10 10 domes/cm 2 for the third. Both distribution and shape follow the Ni island pattern, i.e. the Ni islandsact both as a catalytic and uphold. The three samples series were also analyzed by Raman spectros-copy, showing a defined G bands around 1593 cm -1 indicating the presence of graphitic structures. Also, are observed D bands indicating structural disorder. The disorder increases with the augment of the nitrogen content, as is shown by the augment of the D and G intensities ratio. Finally, the field emission properties of the three series were studied and the electron emission depends on the growing conditions in general, and on the nitrogen content in particular. The results show that the emission is predominantly by quantum tunneling and the current density vs. electric field curves follow the Fowler-Nordheim model / Doutorado / Física / Doutor em Ciências

Impacts of land use and climate change in tropical forests on the global carbon budget are of principal interest in the recent research, as these forests amount to about 48 % of the world’s forested area. Interest has been focused on lowland tropical forests mainly, but tropical montane forests occupy about 20 % of all tropical forests. Soils of tropical montane forests are frequently waterlogged and characterised by high soil organic carbon stocks. Furthermore, along altitudinal gradients, changes in stand structure and net primary production can be observed that have not been fully explained yet. As causes reduced microbial activity and nitrogen turnover in soils of tropical montane forests have been suggested. Against the background of climate change, carbon turnover mechanisms in soils of these forests are of special interest. The present study therefore aimed at determining and quantifying relevant carbon and nitrogen pools as well as nitrogen mineralisation potentials. Furthermore, size, activity, and structure of microbial biomass were characterised. The collected data was supposed to provide basic knowledge on carbon and nitrogen cycling in tropical montane forest soils. Thus, evaluation of the susceptibility of their carbon stocks for climate change as well as nitrogen and carbon limitation of microbial organic matter decomposition was possible. Field work of this study was conducted during 2003–2005 at an altitudinal transect that in- cluded five study sites between 1 050 and 3 060 m amsl. Total soil respiration was recorded biweekly over two years, the contribution of roots to total soil CO2 efflux over one year. Soils of the study sites were sampled twice and biochemical and microbial parameters were determined.

This thesis reports an investigation of Iron Age diet in Britain using carbon and nitrogen stable isotope data obtained from skeletal material from four locations across England and southern Scotland. Both human and animal bone Collagen has been analysed from Wetwang in East Yorkshire and other sites in East Lothian, Hampshire and Cornwall. Animal bone from Dorset has also been included. The aims of the study were to characterize British Iron Age diet in general isotopic terms and also to provide a contextual base for future analysis which allows an understanding of both inter- and intra-site variation in such data for this and other periods. The comparisons across the locations allowed consideration of geographical variability within England and southern Scotland and included material from coastal sites (Cornwall and East Lothian), from sites with easy access to rivers and estuaries (Hampshire) and an inland site where access to water would have been more difficult (Wetwang). All human groups were consuming high levels of animal protein and there was very little evidence for the consumption of aquatic resources. There was significant variation in 815N values between the locations, which was reflected both in the humans and the herbivores, such that it is likely to be related to environmental rather than to dietary differences. Intra-site group comparisons at Wetwang showed very little variation within the cemetery population IM according to age, sex, subjective status category or site phase. The data were very consistent within the populations, although those for Hampshire displayed more variation in nitrogen.

The influence of tree species on forest soils has been the subject of study for at least a century. Of particular interest have been western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn ex D. Don) – two of the most common tree species in coastal and southern British Columbia, but each with a different nutrient amplitude. It has generally been found that acid, mycogeneous Mor humus forms develop in hemlock stands, while less acid and more zoogenous Mormoder, Moder, or even Mull humus forms develop in redcedar stands. The objective of this study was to determine the influence of hemlock and redcedar, growing separately and together, on forest floor nutrient properties. The questions addressed were: (1) does each stand type have unique forest floor nutrient properties? and (2) can any forest floor nutrient property discriminate between stand types?

The thesis entitled “Copper-Catalyzed Novel Oxidative Transformations: Construction of Carbon-Hetero Bonds” is divided into two main sections. Section A deals with the utility of azide as a nitrogen source for C-N bond formation, which is further divided into 4 chapters, and section B presents decarboxylative radical coupling reaction for C-heteroatom bond formation which is further divided in to two chapters. Section A Chapter 1 describes an approach for the direct synthesis of nitrile from the corresponding alcohols using azide as a nitrogen source. Nitrile functionality is a versatile and ubiquitous which occurs in a variety of natural products. Nitrile functionality can be easily transformed into a variety of functional groups and products such as aldehydes, ketones, acids, amines, amides and nitrogen-containing heterocycles, such as tetrazoles and oxazoles. In this chapter a successful attempt for developing a novel methodology to oxidize benzylic and cinnamyl alcohols to their corresponding nitriles in excellent yields has been described. This strategy uses DDQ as an oxidant and TMSN3 as a source of nitrogen in the presence of a catalytic amount of Cu(ClO4)2·6H2O. A few representative examples are highlighted in Scheme 1.1 Scheme 1. Oxidative conversion of alcohols to nitriles Second chapter represents a protocol for the synthesis of 1,5-disubstituted tetrazoles from the corresponding secondary alcohols. Among heterocyles, tetrazole and its derivatives are important class of nitrogen containing molecules. Due to their well-known biological activities as well as vast applications in pharmaceuticals and material science, they are potential targets for synthetic organic chemists. Therefore, a simple and user-friendly method for the synthesis of tetrazole is desirable. In this chapter, a mild and convenient method to synthesize 1,5-disubstituted tetrazoles using easily accessible secondary alcohols by employing TMSN3 as a nitrogen source is developed. This reaction is performed in the presence of a catalytic amount of Cu(ClO4)2·6H2O using DDQ as an oxidant under ambient conditions (Scheme 2).2 Scheme 2. Oxidative conversion of secondary alcohols to tetrazoles Third chapter presents a method for synthesizing amides from their corresponding secondary alcohols. Amide functionality is a crucial backbone in peptide chemistry, it also serve as an important precursor or intermediate for variety of organic transformations. In this contention, a mild and convenient method to synthesize amides using easily accessible secondary alcohols by employing TMSN3 as a nitrogen source is developed. This reaction is performed in the presence of a catalytic amount of Cu(ClO4)2·6H2O using DDQ as an oxidant under ambient conditions (Scheme 3).3 Scheme 3. Oxidative conversion of secondary alcohols to amides Additionally, the application of this methodology has also been revealed for the synthesis azides directly from their alcohols. Some of the representative examples are shown in the Scheme 4.3 Scheme 4. Direct conversion of alcohols to their azides. Fourth chapter describes highly chemoselective Schmidt reaction. The classical Schmidt reaction involves the formation of new carbon-nitrogen bonds in a reaction of a carbon-centred electrophile with hydrazoic acid followed by loss of nitrogen, which usually occurs via a rearrangement. It is well known that under the Schmidt reaction conditions, ketones and carboxylic acids are converted into their corresponding amides and amines respectively, whereas aldehydes furnish a mixture of formanilides and nitriles. In this chapter, Schmidt reaction of aldehydes to obtain their nitriles without formation of the corresponding formanilide is presented (Scheme 5).4 It was also observed that aromatic ketones and acids functionalities were intact under the reaction condition, unlike the conventional Schmidt reaction. Scheme 5. Highly chemoselective Schmidt reaction Section B It is divided into two chapters, describes a copper catalyzed decarboxylative radical coupling for the synthesis of vinyl sulfones and nitroolefins (Scheme 6). Scheme 6. General strategy for the second part First chapter narrates a strategy for synthesizing nitroolefins from the α,β-unsaturated carboxylic acids. Nitroolefins represent a unique class of nitro compounds, which have multifaceted utility in organic synthesis. They possess antibacterial, rodent-repelling, and antitumor activities. They serve as important intermediates in organic synthesis. Nitroolefins also react with a variety of nucleophiles, and their electron-deficient character renders them as a powerful dienophiles in Diels-Alder reactions. In our attempt to use the decarboxylative strategy, this chapter describes a method for the nitrodecarboxylation of substituted cinnamic acid derivatives to their corresponding nitroolefins. This nitrodecarboxylation reaction is performed using catalytic amount of CuCl in the presence of air using TBN as a nitrating source (Scheme 7).5 Besides, the reaction provides a useful method for the synthesis of β,β-disubstituted nitroolefin derivatives which are generally difficult to access from other conventional methods. Scheme 7. Decarboxylative nitration Second chapter presents a new protocol for the synthesis of vinyl sulfones from the α,β-unsaturated carboxylic acid. Vinyl sulfones are versatile building blocks, which find their utility as Michael acceptors and used in cycloaddition reactions. This functional group has also been shown to potently inhibit a variety of enzymatic processes, and thus provides unique properties for drug design and medicinal chemistry. Vinyl sulfones are prominent in medicinal chemistry owing to their wide presence in pharmaceutically active molecules, such as enzyme inhibitors and biological activity. In this chapter, we report a method for the construction of C-S bonds via ligand promoted decarboxylative radical sulfonylation of ,-unsaturated carboxylic acids to synthesize vinyl sulfones using Cu catalysis (Scheme 8).6 This is the first report for this particular conversion. Scheme 8. Decarboxylative sulfonation