Spelling suggestions: "subject:"browth dynamics"" "subject:"bgrowth dynamics""
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Morphogenesis of nanostructures in glancing angle deposition of metal thin film coatingsBROWN, Timothy James 18 January 2011 (has links)
Atomic vapors condensed onto solid surfaces form a remarkable category of condensed matter materials, the so-called thin films, with a myriad of compositions, morphological structures, and properties.
The dynamic process of atomic condensation exhibits self-assembled pattern formation, producing morphologies with atomic-scale three-dimensional structures of seemingly limitless variety.
This study attempts to shed new light on the dynamical growth processes of thin film deposition by analyzing in detail a previously unreported specific distinct emergent structure, a crystalline triangular-shaped spike that grows within copper and silver thin films.
I explored the deposition parameters that lead to the growth of these unique structures, referred to as ``nanospikes'', fabricating approximately 55 thin films and used scanning electron microscopy and x-ray diffraction analysis.
The variation of parameters include: vapor incidence angle, film thickness, substrate temperature, deposition rate, deposition material, substrate, and source-to-substrate distance.
Microscopy analysis reveals that the silver and copper films deposited at glancing vapor incidence angles, 80 degrees and greater, have a high degree of branching interconnectivity between adjacent inclined nanorods.
Diffraction analysis reveals that the vapor incidence angle influences the sub-populations of crystallites in the films, producing two different [110] crystal texture orientations.
I hypothesize that the growth of nanospikes from nanorods is initiated by the stochastic arrival of vapor atoms and photons emitted from the deposition source at small diameter nanorods, and then driven by localized heating from vapor condensation and photon absorption.
Restricted heat flow due to nanoscale thermal conduction maintains an elevated local temperature at the nanorod, enhancing adatom diffusion and enabling fast epitaxial crystal growth, leading to the formation and growth of nanospikes.
Electron microscopy and x-ray diffraction analysis, and comparisons to related scientific literature, support this hypothesis.
I also designed a highly modular ultrahigh vacuum deposition chamber, capable of concurrently mounting several different pieces of deposition equipment, that allows for a high degree of control of the growth dynamics of deposited thin films.
I used the newly designed chamber to fabricate tailor-made nanostructured tantalum films for use in ultracapacitors, for the Cabot Corporation. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-17 15:22:47.533
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Nonlinear and Nonparametric Dynamical Methods in Economics and FinanceUddin, Gazi Salah January 2016 (has links)
The objectives of the thesis - which comprises six parts – can be summarized in i) implementing linear and nonlinear/nonparametric approaches toward detecting, measuring and analyzing the nature and directionality of causal relationships in financial markets, ii) elaborating on modern topics in financial investment analysis, iii) probing into the role of commodity futures in constructing optimal portfolios as well as iv) investigating growth dynamics via aggregated and disaggregated indices. The first paper named “Analyzing causal interactions between sectoral equity returns and commodity futures returns in the aftermath of the global financial crisis: The case of the US and EU equity returns”, aims to explore and compare the dependence and co-movement structure between commodity and various asset classes’ returns including the USA and EU stock markets via the use of linear and non-linear causality testing in a comparative context with the additional adjustment for cointegration and conditional heteroscedasticity. The findings provide important implications for optimal asset allocation and portfolio diversification with respect to various market conditions, namely both in “good” and “bad” (crisis) times. The second paper is entitled “On the time scale behaviour of Equity-Commodity links: Implications for Portfolio Management”, and has been published in the Journal of International Financial Markets, Institutions and Money (2016). The study is co-authored with Professors S. Bekiros, D.K. Nguyen, and B. Sjö. It develops a holistic framework for the investigation of the multi-horizon and intra-frequency causal directionalities of various asset classes, by means of multi-resolution analysis. The results verify the assumption that financial markets exhibit time-varying co-movement patterns, which are fundamentally important in a) generating profitable trading strategies according to different investor horizon expectations and b) decoding the financialization mechanism across various asset classes. The third paper entitled “Business Cycle (de) Synchronization in the aftermath of the Global Financial Crisis: Implications for the Euro Area”, was published at Studies in Nonlinear Dynamics and Econometrics (2015) and is co-authored with S. Bekiros, D.K Nguyen and B. Sjö. In this work, the scale-dependent time-varying (de)synchronization effects between the Eurozone and the broad Euro area business cycles are revealed, before and after the global financial crisis. The results, which point towards an increased observed comovement during the crisis period for the Euro area, could be catalytic for the introduction of a more efficient monetary policy by EU institutions and in particular by the European Central Bank. In the fourth paper, “Do financial stress and policy uncertainty have an impact on the energy and metals markets? A quantile regression approach”, which was published in the International Review of Economics and Finance (2016) and co-authored with J.C. Reboredo, the financial and policy uncertainty is investigated in relation to the price dynamics of energy and metal commodity futures’ markets. This work lead to the analysis of the asymmetric interrelationships with respect to changes in the perceptions of various risk measures, covering various periods, i.e., “normal” vs. “turbulent” such as upward or downward market episodes. The fifth paper, co-authored with P. Andreasson, S. Bekiros and D.K. Nguyen, is entitled “The impact of speculation and economic uncertainty on commodity markets”, and is published in the International Review of Financial Analysis (2016). This paper attempts a novel methodological approach to measuring speculation in commodity markets, in particular whether market speculation drives agricultural commodity prices or viceversa. The assessment of the empirical analysis demonstrates that agricultural prices are not affected by speculation. Finally, the sixth paper “Energy and Output Dynamics in Bangladesh”, co-authored with B.P. Paul, was published in Energy Economics (2011) and explores the relationship between energy utilization and economic growth in Bangladesh. Specifically, it deals with the important issue of whether energy consumption can be reduced without affecting economic growth while at the same time implicitly may lead to poverty reduction. The findings substantiate the fact that a) energy usage has become more efficient in recent times, as well as indicate that b) fluctuations in energy consumption did not have a significant impact on economic output.
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Growth Dynamics of Semiconductor Nanostructures by MOCVDFu, Kai January 2009 (has links)
Semiconductors and related low-dimensional nanostructures are extremely important in the modern world. They have been extensively studied and applied in industry/military areas such as ultraviolet optoelectronics, light emitting diodes, quantum-dot photodetectors and lasers. The knowledge of growth dynamics of semiconductor nanostructures by metalorganic chemical vapour deposition (MOCVD) is very important then. MOCVD, which is widely applied in industry, is a kind of chemical vapour deposition method of epitaxial growth for compound semiconductors. In this method, one or several of the precursors are metalorganics which contain the required elements for the deposit materials. Theoretical studies of growth mechanism by MOCVD from a realistic reactor dimension down to atomic dimensions can give fundamental guidelines to the experiment, optimize the growth conditions and improve the quality of the semiconductor-nanostructure-based devices. Two main types of study methods are applied in the present thesis in order to understand the growth dynamics of semiconductor nanostructures at the atomic level: (1) Kinetic Monte Carlo method which was adopted to simulate film growths such as diamond, Si, GaAs and InP using the chemical vapor deposition method; (2) Computational fluid dynamics method to study the distribution of species and temperature in the reactor dimension. The strain energy is introduced by short-range valence-force-field method in order to study the growth process of the hetero epitaxy. The Monte Carlo studies show that the GaN film grows on GaN substrate in a two-dimensional step mode because there is no strain over the surface during homoepitaxial growth. However, the growth of self-assembled GaSb quantum dots (QDs) on GaAs substrate follows strain-induced Stranski-Krastanov mode. The formation of GaSb nanostructures such as nanostrips and nanorings could be determined by the geometries of the initial seeds on the surface. Furthermore, the growth rate and aspect ratio of the GaSb QD are largely determined by the strain field distribution on the growth surface. / QC 20100713
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Pěstování kukuřice v praktických podmínkách zemědělského podniku / Maize growing in terms of selected agricultural companyFENCL, Lukáš January 2018 (has links)
The thesis follows up an assessment of germination and growth dynamics of maze, in relation to different processing of soil in the region of Kozojed in North Pilsen. This experiment was conducted in the year 2016. In utter overview of the thesis, we can find a description of the technological procedure of maze cultivation, and individual technological procedures of soil preparation in more detail. In the resultant part of the thesis, we find the evaluation of germination, height, number of plants per m2 (squared meter), and average number of sticks per plant; further evaluation of WTG (Weight of thousand grains) of individual growers' technologies, and the most important overall produce of maze biomass in four variants of soil processing. Examined variants in the thesis are as follows: Sowing into deeply processed soil (underlay), Sowing into stubble, Sowing into loosened soil (disk plow), Sowing into tillage. The results showed that in provided soil-climatic conditions the best came out maze that was sown into stubble. In total biomass yield was option No. 3. sowing in loosened soil, where the resulting income, 30, 21 t.ha-1. From variants No. 1. seed to uderlay it was 0,93 t.ha-1 and No. 2. sowing into stubble to 3,57 t.ha-1 less than option No. 1. The highest difference was in variant No. 4 in the plow, where the biomass yield was by 7.26 t.ha-1 lower than in variant No. 3.
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DOES THE PRESENCE OF PIKE AFFECT THE GROWTH OF JUVENILE BURBOT?Foth, Angelina January 2024 (has links)
The present study investigates the impact of northern pike (Esox Lucius) on the growth of juvenile burbot (Lota lota) in northern lake ecosystems. It is hypothesized that the presence of pike will positively affect the growth of juvenile burbot by reducing interspecific competition and increasing the abundance of benthic invertebrates. To test this hypothesis, electrofishing for juvenile burbot was conducted in the littoral zones of lakes with and without pike in the region Jämtland Härjedalen, Sweden. Data on length and age of the captured burbot were used to compare growth between the two lake types. Contrary to the initial hypothesis, the results show that juvenile burbot were significantly larger at a given age in lakes where pike was absent. This outcome suggests that juvenile burbot may reduce their foraging activity in lakes with pike to minimize predation risk. Since adult burbot has shown to be of greater size in lakes with pike, future research could investigate whether the shift towards piscivory in burbot leads to changes in how they are affected by pike.
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The Dynamics Of Root Growth And The Partitioning Of Photosynthates In Cool Desert ShrubsFernandez, Osvaldo Alberto 01 May 1974 (has links)
This study addresses the nature of physiological and phenological evolutionary strategies of root growth dynamics and energy allocation followed by Atriplex confertifolia, Ceratoides lanata, and Artemisia tridentata growing in their natural cool desert environment.
Root observation chambers with inclined Plexiglass windows were installed in monospecific desert communities of Atriplex confertifolia, Ceratoides lanata and Artemisia tridentata. Soil temperature and water potential measurements taken immediately adjacent to the observation windows indicated a minimal disturbance was caused by the presence of these chambers. For the three species initiation of root growth was observed before initiation of shoot activity, furthermore, active root growth extended over much longer periods during the year than shoot growth. Initial growth was observed for the three species in the upper soil layers in the spring. Later in the season most of the growth activity was measured at progressively greater depths in the soil. Measurable root growth was observed for Atriplexin August when the soil water potentials were in the range of -70 bars for 1972, and at water potentials of -60 bars for all three species during 1973. Detectable growth for these three species was recorded as late as January in 1974. Except for the main extension roots, individual apical meristems were seldom active for more than 2 weeks.
Atriplex confertifolia and Ceratoides lanata plots were labeled during the growth season with 14Co2 in polyethylene enclosures to study both the partitioning of photosynthates to plant parts and their total allocation of carbon at the community level. A definite seasonal pattern of partitioning of recent photoassimilates corresponding to phenological events emerged. In the spring, photoassimilates were principally directed to shoot growth, especially expanding new leaves and vegetative buds. In terms of relative energy allocated to plant parts per unit dry weight basis, it appears that Ceratoides lanata expends less energy for reproductive organs. For both species, carbon used for new stems and previous years shoot growth appears to constitute a significant sink for energy use and storage. Relative translocation of carbon to roots was minimal during the spring for both species. It increased with the progression of the season reaching a maximum in July for Atriplex and at the end of the season for Ceratoides. Energy allocation at the community level for these species showed that approximately 60 and 40 percent of the recently photoassimilated 14C for the Atriplex-dominated community in July and September, respectively, appeared localized in the new shoot growth, the remaining was distributed in nearly equal amounts between previous year's shoot growth and the root system. The scheme of energy allocation in Ceratoides showed similar patterns of carbon utilization in July and September; approximately 80 percent of the fixed carbon was al located in approximately equal amounts to roots and new shoot growth with the remainder to the previous year's shoot growth.
In the Ceratoides-dominated community 65 percent and 36 percent of 14C photoassimilated in April and July, respectively, and still remaining in the plant by September, was localized in the underground structures. Similarly, in the Atriplex community, 35 percent and 29 percent of the 14C incorporated in April and July appeared in the root system. From the total 14C photoassimilated in July for both communities, approximately 60 percent and 50 percent was retained in the plants by September in the Atriplex- and Ceratoides-dominated communities, respectively.
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Déterminisme génétique de la dynamique de croissance et de la composition isotopique du carbone chez l'Eucalyptus en réponse aux variations environnementales / Genetic determinism of growth dynamics and carbon isotope composition in Eucalyptus in response to environmental changesBartholomé, Jérôme 28 March 2014 (has links)
Les différents scénarios sur l'évolution du climat prévoient une augmentation de la fréquence et de l'intensité des sécheresses. La croissance des arbres forestiers étant fortement conditionnée par la disponibilité en eau, ces changements devraient impacter de manière significative la productivité des forêts plantées. La compréhension de l'impact des facteurs génétiques et environnementaux sur la dynamique de croissance est donc un enjeu majeur pour assurer les niveaux de production des plantations de demain. L'Eucalyptus, grâce à sa croissance rapide et à la disponibilité de ressources génétiques et génomiques, est un modèle biologique idéal pour mener ces recherches.L'objectif de cette thèse est de caractériser l'architecture génétique de la dynamique de croissance à différentes échelles de temps chez l'eucalyptus en relation avec : (i) les variations environnementales, et notamment l'évolution de la disponibilité en eau, et (ii) la composition isotopique du carbone de l'arbre (delta 13C), un caractère lié à l'efficience d'utilisation de l'eau. Pour répondre à cet objectif, un croisement interspécifique Eucalyptus urophylla x E. grandis a été étudié dans quatre dispositifs expérimentaux en République du Congo. Notre approche se base sur la cartographie des loci à effet quantitatif (QTL) et combine : (i) un génotypage haut débit, (ii) une caractérisation inter et intra-annuelle de la croissance et du delta 13C, ainsi qu'un suivi en continu des micro-variations du rayon et (iii) une caractérisation en continu des facteurs environnementaux.Ces travaux ont tout d'abord conduit à la construction des premières cartes génétiques à haute résolution chez l'Eucalyptus. L'analyse de l'architecture génétique du delta 13C a ensuite permis de mettre en évidence des gènes candidats positionnels, potentiellement impliqués dans la variation de ce caractère. Enfin, la caractérisation inter et intra-annuelle de la dynamique de croissance a permis de montrer que l'architecture génétique de la croissance, au stade adulte, est structurée par les réponses à l'environnement au stade juvénile. Ces réponses ont ensuite été analysées grâce aux profils de micro-variations du rayon, permettant ainsi de préciser leurs déterminants génétiques Nos résultats soulignent l'importance de considérer la croissance comme un caractère dynamique, non seulement pour la compréhension de ses bases génétiques, mais également à des fins de sélection de variétés adaptées à un environnement changeant. / Scenarios of climate changes forecast an increase in frequency and intensity of droughts, related to an increase of global temperatures and changes in rainfall distribution. Growth of forest trees highly depends on water availability and will be significantly impacted by these changes. The understanding of the impact of genetic and environmental factors on the growth dynamics is a major challenge to ensure production levels of future planted forests. Eucalyptus, thanks to its rapid growth and the availability of genetic and genomic resources, is a perfect model to conduct this research.The objective of this thesis is to characterize the genetic architecture of growth dynamics in Eucalyptus at different time scales, in relation with: (i) environmental changes, including changes in water availability, and (ii) isotopic composition of carbon (delta 13C), a character associated with water-use efficiency. To this end, an interspecific cross between E. urophylla x E. grandis was studied in four experimental trials in the Republic of Congo. Our approach, based on mapping of quantitative trait loci (QTL), combines (i) a high-throughput genotyping, (ii) a characterization of inter and intra-annual growth dynamics and delta 13C, as well as a continual measurement of stem radial micro-variations and (iii) a continual characterization of environmental factors.First of all, this work led to the construction of the first high-resolution genetic maps in Eucalyptus, improving the sequence of the reference genome. Then, the analysis of genetic architecture of delta 13C enabled the identification of positional candidate genes which might be involved in the variation of this trait. Finally, inter and intra-annual characterization of growth dynamics highlight that genetic architecture of adult growth is structured by responses to the environment at the juvenile stage. These responses were then analyzed using daily profiles of stem radial micro-variations, which enabled the characterization of the genetic determinants of response to the environmental factors at the juvenile stage.Our results highlight the importance of considering growth as a dynamic trait, not only to understand its genetic basis, but also to select in a changing environment.
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Growth Dynamics, Antibiotic Susceptibility and the Effect of Sublethal Ciprofloxacin Concentrations in Susceptible and Resistant Escherichia coli in Biofilm / Tillväxtdynamik, Antibiotikakänslighet och Effekten av Subletala Koncentrationer av Ciprofloxacin på Känsliga och Resistenta Escherichia coli i BiofilmFernberg, Jenny January 2019 (has links)
Instead of planktonic growth in nature, many species of bacteria form biofilm to survive in harsh conditions. Although many chronic bacterial infections are caused by bacterial species in a biofilm lifestyle, previous research has focused on studying antibiotic resistance in planktonic growth. Here we used a modified MBEC assay, i.e. biofilm growth on pegs, to determine Escherichia coli biofilm inhibitory concentrations (BIC) of ciprofloxacin, streptomycin and rifampicin and to study the minimal selective concentration (MSC) for ciprofloxacin in E. coli biofilm. We could observe high inhibitory concentrations for all antibiotics in the biofilm pre-formed in media without antibiotics compared to the biofilm formed in antibiotics. We also show preliminary result indicating that sublethal concentrations of ciprofloxacin lead to the selection of ciprofloxacin resistant mutants in biofilm and that the selection level is lower than what was observed in planktonic growing E. coli. With more knowledge in how the biofilm formation precedes in different antibiotic settings, the treatment for chronic biofilm infections used today could be evaluated and changed so that the infections could be eradicated.
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Mixed-species plantations of nitrogen-fixing and non-nitrogen-fixing treesForrester, David Ian, davidif@unimelb.edu.au January 2005 (has links)
Mixed-species plantations of eucalypts and acacias have the potential to improve stand productivity over that of respective monocultures through the facilitative effect of nitrogen-fixation by acacias, and increased resource capture through above- and belowground stratification. However, growth in mixed-species plantations may not be improved compared to that of monocultures when competitive interactions outweigh the effects of improved nutrient availability and resource capture. Careful selection of sites and species is therefore critical to successfully improving stand productivity using mixed-species plantations. This study set out to examine some of the processes and interactions that occur in mixed-species plantations, and the effect nutrient and water availability can have on the growth of mixtures.
In three out of four mixed-species field trials examined in this study, growth was not increased in mixtures compared to monocultures. However, in the fourth field trial, heights, diameters, stand volume and aboveground biomass were higher in mixtures of E. globulus and A. mearnsii from 3-4 years after planting.
The range in outcomes from mixing species in these four trials shows that a fundamental understanding of the underlying processes is required to enable a greater predictive capacity for the circumstances under which mixtures will be successful. Therefore the growth dynamics, processes and interactions were examined in the mixtures of E. globulus and A. mearnsii. The difference in productivity between mixtures and monocultures in this trial increased with time up to age 11 years, when 1:1 mixtures contained twice the aboveground biomass of E. globulus monocultures. The positive growth response of trees in mixture compared to monocultures was the result of accelerated rates of nutrient cycling, a shift in C allocation and reductions in light competition through canopy stratification.
Nitrogen contents of foliage and soil clearly showed that A. mearnsii influenced the N dynamics in this trial. If these changes in N contents were due to N fixation by A. mearnsii, then about 51 and 86 kg N ha-1 yr-1 was fixed in the 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation was also examined using the natural abundance method. The delta15N values of foliage collected at 10 years were grouped according to the mycorrhizal status of the host plant. Therefore the discrimination of 15N during transfer from mycorrhizae to the host plant appeared to vary with mycorrhizal status, and the natural abundance of 15N was not used to quantify N fixation.
Rates of N and P cycling in litterfall were significantly higher in stands containing at least 25% A. mearnsii (more than 31 kg N ha-1 yr-1 and more than 0.68 kg P ha-1 yr-1) compared to E. globulus monocultures (24 kg N ha-1 yr-1 and 0.45 kg P ha-1 yr-1). Rates of litter decomposition and N and P release were about twice as high in 1:1 mixtures compared to E. globulus monocultures and were even higher in A. mearnsii monocultures. It is therefore important to select N-fixing species that are capable of cycling nutrients quickly between the plant and soil, and that have readily decomposable litter.
The total belowground C allocation was not significantly different between mixtures and monocultures (14 to 16 Mg C ha-1 yr-1). However, since aboveground net primary production was greater in 1:1 mixtures, the changes in nutrient availability appears to have increased total productivity (both above- and belowground), and reduced the proportion of C allocated belowground in mixtures compared to E. globulus monocultures.
In a pot trial containing mixtures of E. globulus and A. mearnsii both species grew larger in mixture than in monoculture at low N levels, and mixtures were more productive than monocultures. However, at high N levels, E. globulus suppressed A. mearnsii and mixtures were less productive than E. globulus monocultures. Similar effects were found for high and low levels of P.
Therefore resource availability can have a strong influence on the interactions and growth of mixtures. The productivity of mixtures may only be increased on sites where the resource for which competition is reduced in mixture is a major limiting growth resource. For example, if N is not a limiting growth factor then an increase in N availability from N-fixation may not increase growth, and the N-fixing species may compete for other resources such as soil P, moisture or light.
This study has shown that mixtures containing a N-fixing trees and a non-N-fixing trees can be more productive than monocultures, but that this increase in productivity will only occur on certain sites. Examination of the growth, interactions and processes that occurred in mixtures in this study provide useful information that can aid the selection of species combinations and sites.
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INVESTIGATION OF Ge SURFACE DIFFUSION AND SiGe NANOSTRUCTURES BY SPECTRO-MICROSCOPY TECHNIQUESVanacore, Giovanni Maria 18 February 2011 (has links) (PDF)
SiGe nanostructures on crystalline Si substrates with (001) orientation are among the most studied system in condensed matter physics and nanoscience. This interest has been mainly driven by the important potential applications in opto and nano-electronic devices thanks to the improvement of the optical and electronic properties compared to bulk systems. These features come essentially from the possibility of engineering the strain field within the nanostructures using the lattice mismatch of ~ 4 % between Ge and Si and from the spatial confinement, capable of modifying the electronic band structure leading to an increase of the charge carrier mobility. It is obvious that these applications largely depend on the control of surface processes during the growth of the nanostructures, and their performance are strongly dependent on strain relaxation and dislocation injection. Besides the technological interest, the SiGe/Si(001) system has received much attention since it is also a model for understanding the fundamental processes occurring during 3D island formation and self-organization phenomena. In fact, the lattice mismatch between Ge and Si introduces a stress field which has dramatic effects on the growth process and is responsible for a number of structural and electronic phenomena. In particular, the stored elastic energy can be partially relieved by spontaneous formation of 3D objects of nanometric size on top of a pseudomorphic SiGe wetting layer. This growth mode, called Stranski-Krastanov (SK), is a way of easily forming self-assembled nanostructures, which can be used to obtain quantum confinement of charge carriers in nanoelectronics device applications. In recent years, considerable efforts have been devoted to the growth of hetero-epitaxial SiGe nanostructures with well controlled size, shape and positioning, and with defined stoichiometry and strain state. However, some aspects still need to be addressed for a complete understanding of this system, including: (i) the competition between kinetic and thermodynamic factors for island formation, (ii) the mechanisms governing the relative growth of individual nanostructures, (iii) the interplay between SiGe intermixing and strain relaxation mechanisms. In the present work, we carry out an experimental investigation of the relationship between morphology, elemental composition, strain state and electronic structure of self-assembled and lithographically defined SiGe nanostructures by means of several spectro-microscopy techniques. The Si and Ge diffusion dynamics and the self-organization phenomena during the growth of SiGe islands have been studied by Scanning Auger Microscopy (SAM) and Atomic Force Microscopy (AFM). Micro-Raman, SAM and Scanning Transmission Electron Microscopy coupled with Electron Energy Loss Spectroscopy (STEM-EELS) techniques have been used for the investigation of the interplay between strain relaxation mechanisms and SiGe intermixing in self-assembled islands. The effects of strain and composition on the electronic band structure in lithographically defined SiGe nanostructures, in layout very close to those used in prototype devices, have been characterized with nanoscale spatial resolution joining information from Tip Enhanced Raman Spectroscopy (TERS), nanofocused X-Ray Diffraction (XRD) and Energy-Filtered PhotoElectron Emission Microscopy (PEEM). The thesis is conceptually divided in two main parts: the first, to which belong Chapters 1, 2 and 3, deals with the experimental investigation of the Ge surface diffusion and of the self-organization phenomena of SiGe islands grown in a bottom-up approach; the second, including Chapters 4 and 5, is based on the experimental characterization of the strain state and of the strain-induced effects on the electronic band structure of lithographically defined SiGe nanostructures obtained in a top-down approach Chapter 1 presents an overview on the basic processes occurring during hetero-epitaxial growth of thin solid films. In the Chapter 2 the surface diffusion of Ge on a clean and C covered Si(001) surface promoted by annealing at high temperatures in UHV of pure Ge stripes is experimentally investigated by means of in-situ Scanning Auger Microscopy. The influence of a controlled carbon coverage on the Ge surface diffusion is quantitatively studied, showing that the diffusion coefficient presents a strong dependence on carbon coverage (see Fig. 1(a)). Chapter 3 deals with the experimental investigation of the growth process of self-assembled SiGe islands on Si(001) (see Fig. 1(b)). From the size and density evolution exhibited by the nucleated islands, we propose a scenario where the island growth is essentially driven by kinetic factors within a diffusion limited regime. Finally, we investigated the interplay among SiGe intermixing and plastic relaxation, showing that the surface thermal diffusion growth method leads to the formation of coherent islands (dislocation-free), as shown in Fig. 1(c), larger than those attainable by MBE and CVD. Chapter 4 presents the mapping with nanoscale resolution of strain, composition, local work function and valence band structure of lithographically defined SiGe embedded nano-stripes using TERS and Energy-Filtered PEEM (see Fig. 1(d) showing the Ge concentration mapping of the nano-stripes as obtained by PEEM analysis). In Chapter 5 are presented the first results of a direct characterization of the strain state of lithographically defined SiGe nano-ridges using the recently developed nanofocused XRD technique. The work presented in this thesis is the outcome of an experimental PhD research project developed at the Politecnico di Milano (Milano, Italy) in co-tutorship with the École Polytechnique (Paris, France) and the French Atomic Energy Commission (CEA-Saclay, France). SAM and AFM have been performed at Department of Physics of the Politecnico di Milano. Micro-Raman Spectroscopy has been carried out at the Materials Science Department of the Università Milano-Bicocca. PEEM measurements have been realized at CEA and during two standard experimental runs at the TEMPO beamline of SOLEIL Synchrotron (France). TERS and preliminary TEM analysis have been performed at the École Polytechnique, while more extensive TEM and STEM-EELS measurements have been developed at IMM-CNR in Catania. The nano-XRD experiment has been carried out during a standard experimental run at ID13 beamline of the European Synchrotron Radiation Facility (ESRF). The close collaboration with the laboratory L-NESS in Como made available the set of the lithographically-defined investigated samples. The experimental results have been exploited in close collaboration with a theory group at the Materials Science Department of the Università Milano-Bicocca for a deeper insight into the atomic level mechanisms during island growth process.
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