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Marceau, Ross Kevin William. "Design in Light Alloys by Understanding the Solute Clustering Processes During the Early Stages of Age Hardening in Al-Cu-Mg Alloys." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/4008.
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The evolution of atomistic-level nanostructure during the early stages of both standard, high-temperature T6 heat treatment, and low-temperature secondary ageing after interruption of the former (T6I4), has been investigated in rapid hardening Al-Cu-Mg alloys using a variety of microscopy and microanalytical techniques, including transmission electron microscopy (TEM), positron annihilation spectroscopy (PAS) and atom probe tomography (APT). In order to carry out this objective, quantitative data-analysis methods were developed with respect to new cluster-finding algorithms, specifically designed for use with three-dimensional APT data. Prior to this detailed characterisation work, the actual thermal impact from both heat treatment and quenching of small, lab-scale specimens was determined through correlation of both experimental results and calculations that modelled the heat transfer conditions using the lumped capacitance method. Subsequently, the maximum diffusion distance by random walk of the solute atoms was calculated for these periods, bearing significance on the propensity for these atoms to have the ability to cluster together, rather than segregate to the dislocation loops in the microstructure, which have a relatively larger interspacing distance. Age-hardening curves for the Al-1.1Cu-xMg (x = 0, 0.2, 0.5, 0.75, 1.0, 1.7 at.%) alloys at 150ºC show that the rapid hardening phenomenon (RHP) exists for Mg compositions ≥ 0.5Mg. Given that zone-like precipitate structures were unable to be detected by TEM or APT during the early stages of ageing at 150ºC, and that statistically significant dispersions of clusters were found in the APT data after ageing for 60 s, the RHP is attributed to these clustering reactions. Identification of clusters in the APT data has been achieved using the core-linkage algorithm and they have been found to be quite small, containing only a few atoms up to a couple of tens of atoms. The RHP is governed by some critical number density of both Mg clusters and Cu-Mg co-clusters of a critical size, whereas Cu clusters do not contribute significantly to the hardening mechanism. Significance testing indicates that Mg clusters are more significant at smaller clusters sizes and Cu-Mg co-clusters more important at larger cluster sizes. Hardness results also confirm the existence of rapid early hardening during secondary ageing at 65ºC in Al-1.1Cu-1.7Mg. The mechanism of secondary rapid hardening involves a combination of both secondary clustering from solute (mainly Mg atoms) residual in solution, and pre-existing amorphous primary clusters that have slower growth kinetics at the lower secondary ageing temperature. The latter occurs mainly by vacancy-assisted diffusion of Mg atoms as evidenced by the gradual increase of the Mg:Cu ratio of co-clusters. From an alloy design point of view it is important to fully understand the solute distribution in the microstructure to be able to subsequently optimise the configuration for enhanced material properties. The change in dispersion of solute atoms during ageing was determined by combining calculations of % vacancy-solute associations with detailed measurements of the dislocation loops to estimate the solute distribution within the microstructure. The implication of the balance of solute atoms segregated to the loops compared with that in the matrix is then discussed in the context of hardnening mechanisms.
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Marceau, Ross Kevin William. "Design in Light Alloys by Understanding the Solute Clustering Processes During the Early Stages of Age Hardening in Al-Cu-Mg Alloys." University of Sydney, 2008. http://hdl.handle.net/2123/4008.
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Doctor of Philosophy (PhD)The evolution of atomistic-level nanostructure during the early stages of both standard, high-temperature T6 heat treatment, and low-temperature secondary ageing after interruption of the former (T6I4), has been investigated in rapid hardening Al-Cu-Mg alloys using a variety of microscopy and microanalytical techniques, including transmission electron microscopy (TEM), positron annihilation spectroscopy (PAS) and atom probe tomography (APT). In order to carry out this objective, quantitative data-analysis methods were developed with respect to new cluster-finding algorithms, specifically designed for use with three-dimensional APT data. Prior to this detailed characterisation work, the actual thermal impact from both heat treatment and quenching of small, lab-scale specimens was determined through correlation of both experimental results and calculations that modelled the heat transfer conditions using the lumped capacitance method. Subsequently, the maximum diffusion distance by random walk of the solute atoms was calculated for these periods, bearing significance on the propensity for these atoms to have the ability to cluster together, rather than segregate to the dislocation loops in the microstructure, which have a relatively larger interspacing distance. Age-hardening curves for the Al-1.1Cu-xMg (x = 0, 0.2, 0.5, 0.75, 1.0, 1.7 at.%) alloys at 150ºC show that the rapid hardening phenomenon (RHP) exists for Mg compositions ≥ 0.5Mg. Given that zone-like precipitate structures were unable to be detected by TEM or APT during the early stages of ageing at 150ºC, and that statistically significant dispersions of clusters were found in the APT data after ageing for 60 s, the RHP is attributed to these clustering reactions. Identification of clusters in the APT data has been achieved using the core-linkage algorithm and they have been found to be quite small, containing only a few atoms up to a couple of tens of atoms. The RHP is governed by some critical number density of both Mg clusters and Cu-Mg co-clusters of a critical size, whereas Cu clusters do not contribute significantly to the hardening mechanism. Significance testing indicates that Mg clusters are more significant at smaller clusters sizes and Cu-Mg co-clusters more important at larger cluster sizes. Hardness results also confirm the existence of rapid early hardening during secondary ageing at 65ºC in Al-1.1Cu-1.7Mg. The mechanism of secondary rapid hardening involves a combination of both secondary clustering from solute (mainly Mg atoms) residual in solution, and pre-existing amorphous primary clusters that have slower growth kinetics at the lower secondary ageing temperature. The latter occurs mainly by vacancy-assisted diffusion of Mg atoms as evidenced by the gradual increase of the Mg:Cu ratio of co-clusters. From an alloy design point of view it is important to fully understand the solute distribution in the microstructure to be able to subsequently optimise the configuration for enhanced material properties. The change in dispersion of solute atoms during ageing was determined by combining calculations of % vacancy-solute associations with detailed measurements of the dislocation loops to estimate the solute distribution within the microstructure. The implication of the balance of solute atoms segregated to the loops compared with that in the matrix is then discussed in the context of hardnening mechanisms.
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Withrow, Travis P. "Computational Modeling of Atom Probe Tomography." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525763934302517.
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Engberg, David. "Atom Probe Tomography of TiSiN Thin Films." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122724.
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This thesis concerns the wear resistant coating TiSiN and the development of the analysis technique atom probe tomography (APT) applied to this materials system. The technique delivers compositional information through time-of-flight mass spectrometry, with sub-nanometer precision in 3D for a small volume of the sample. It is thus a powerful technique for imaging the local distribution of elements in micro and nanostructures. To gain the full benefits of the technique for the materials system in question, I have developed a method that combines APT with isotopic substitution, here demonstrated by substitution of natN with 15N. This alters the time-of-flight of ions with of one or more N and will thereby enable the differentiation of the otherwise inseparable isotopes 14N and 28Si. Signs of small-scale fluctuations in the data led the development of an algorithm needed to properly visualize these fluctuations. A method to identify the best sampling parameter for visualization of small-scale compositional fluctuations was added to an algorithm originally designed to find the best sampling parameters for measuring and visualizing strong compositional variations. With the identified sampling parameters, the nano-scale compositional fluctuations of Si in the metal/metalloid sub-lattice could be visualized. The existence and size of these fluctuations were corroborated by radial distribution functions, a technique independent of the previously determined sampling parameter. The radial distribution function algorithm was also developed further to ease in the interpretation. The number of curves could thereby be reduced by showing elements, rather than single and molecular ions (of which there were several different kinds). The improvement of the algorithm also allowed interpretation of signs regarding the stoichiometry of SiNy. With a combination of analytical transmission electron microscopy and APT we show Si segregation on the nanometer scale in arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N thin films. APT composition maps and proximity histograms generated from Ti-rich domains show that the TiN contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films.
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Yang, Qifeng. "Atom probe tomography research on catalytic alloys and nanoparticles." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:f3acdf37-3d23-4893-a4de-12e81712157a.
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Catalyst is a key component in the chemical industry, with more than 90% of total chemical products reliant on their use. However, the working mechanisms are in many cases still not fully understood. For heterogeneous catalysts, in which the reactions normally occur on solid phase materials, a better understanding of the catalytic surfaces, and how they evolve under reactive environments is recognised as the next step forward in the field. This work presents a study utilising atom probe tomography (APT), combined with an in-situ reaction cell, to understand the initial oxidation processes of catalytic NiFe and NiCo model alloy systems. In order to improve reliability of results, a protocol was developed to clean the sample surfaces by field ion evaporation, eliminate sample surface contamination before in-situ oxidation was then performed. APT was successfully applied to these alloys to characterise oxide development as a function of exposure time and temperature. APT also demonstrated surface enrichment induced by oxide formation remained after reduction of the alloy. The successful application of APT on the model alloys led to the next goal which was to associate the data to real catalytic particles. To achieve this, work was extended into the field of nanoparticle catalysts. Nanoparticles with similar compositions to the model alloys were fabricated by chemical synthesis and were examined initially by transmission electron microscopy (TEM). The main goal of this phase was to investigate the surface segregation behaviour of the particles, identifying common behaviours with the model alloys. However, the presence of residual complex chemical environments around the particles following synthesis made APT analysis difficult. Therefore, an alternative method of particle fabrication was explored to better control the resulting materials for easier application of atom probe for nanoparticle analyses. Metallic nanoparticles of Ag, AuCu, AuNi, and AuNiMo were made by an inert gas condensation method, deposited on suitable support materials and were subsequently analysed by APT, facilitated by an improved sample preparation method. Surface segregation on individual nanoparticles was detected. Together with other complementary surface-probing techniques, a complete understanding of these particles from micrometre down to the level of individual particles was achieved. The potential for APT is highlighted to play a key role in this approach to realise a complete understanding of the chemical order, microstructure in multimetallic nanoparticles designed for catalysis.
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McCarroll, Ingrid. "Corrosion Processes: Through the lens of atom probe tomography." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/18131.
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1 Abstract The motivation behind the current work is twofold. In the first instance it stems from a desire to understand and advance knowledge and instrumentation in the field of atom probe tomography (APT). In the second instance it is driven by the need for rapid advancements in engineered materials to keep up with the energy requirements of a continuously developing and demanding technological world. Advances in the capabilities of APT have only recently made analysis of semi- and non- conductive materials possible, opening up the APT field to the corrosion science community. The current research is divided into two projects, each focusing on the oxidation of a different alloy type: alumina-forming FeCrAl alloys and magnesium alloys. The first material analysed was the alumina-forming FeCrAl alloy. These alloys produce a very thin protective oxide layer, even when exposed to high temperature oxidising environments. Presently, the concentrated solar power industry is looking to use supercritical CO2 (s-CO2) as a heat transfer fluid. The use of s-CO2 as the heat transfer fluid would facilitate higher input temperatures at the inlet of Brayton cycle turbines, thereby increasing the efficiency of the power plants. For the implementation of s-CO2 to be successful, a material is required that is capable of maintaining its mechanical properties under thermally cyclic conditions and exposure to a high temperature, high pressure, carbon containing and oxidising environment. In a preliminary study Kanthal APM, an alumina-forming FeCrAl alloy, is characterised under isothermal and cyclic conditions in a high temperature CO2 environment. This study relates to the use of FeCrAl alloys with supercritical CO2 in concentrated solar power plants. The results show that the alumina layer is highly impermeable to carbon penetration and performs well under isothermal and cyclic conditions. The second project focused on the oxidation of magnesium alloys. Magnesium alloys offer great potential as a lighter alternative to aluminium alloys within transport industries, providing economic and environmental incentives for their use. Before they can be more readily applied to these industries, a better understanding of the corrosion mechanisms of magnesium is required. For many years corrosion scientists have been trying to understand the corrosion processes of magnesium alloys, particularly processes relating to the observed negative difference effect (NDE). Although numerous theories have been put forward as to the cause of the NDE, much debate still remains around the subject and no clear evidence of the mechanism has been provided. In order to advance understanding of magnesium corrosion, the current research takes advantage of a new in-situ vacuum transfer system between an atom probe and a catalytic reaction cell. This system allows atomically clean magnesium surfaces to be exposed to O2 and H2O (g), and then returned, via vacuum, to the atom probe for analysis of the oxidation products. Results indicate that hydrogen acts as a catalyst to the oxidation of magnesium alloys in gaseous environments at room temperature and near atmospheric pressures. Integrated into the study of each material are developments in sample preparation methods. For the preparation of atom probe samples from non-conductive materials, such as the alumina formed on an FeCrAl alloy, a focused ion beam (FIB) is required. Preparation of an atom probe tip using FIB techniques is expensive due to the high costs associated with the FIB and time-consuming, especially when considering the training required to become skilled-enough users to prepare them. Therefore, an alternative sample preparation method for non-conductive samples has been devised. This method uses a broad ion beam (BIB) to produce the initial tip shapes ready for final stage FIB annular milling. Although this new method does not completely remove the need for FIB milling, it does significantly reduce the time required on the instrument and the skills needed by the user. For adequate analysis of controlled oxidation of magnesium alloys, an entirely new apparatus was employed. The brief for this new apparatus was that an atomically clean magnesium surface could be transferred from the atom probe analysis chamber to the catalytic reaction cell, and back again, under ultra high vacuum conditions. The experiments from the magnesium oxidation have provided the first successful results from this system, and expand on current coupled exposure and analysis techniques to provide exposure capabilities at room temperature and near atmospheric conditions whilst providing high spatial and chemical resolution of the resulting oxidation products. During the APT analysis of the oxidation of FeCrAl and magnesium alloys, a number of challenges regarding interpretation of the APT data from oxide-metal interfaces had to be addressed. First, the reconstruction of oxide-metal interfaces is known to contain a number of errors relating to assumptions made in the reconstruction algorithm. Second, the mass spectrum resulting from these interfaces are often of a high complexity and require significant efforts from the analyst to decipher. Initial observations from the alumina/FeCrAl alloy interface, led to further studies of the evaporation processes of numerous oxide-metal interfaces. A method for further understanding the evaporation processes for individual tips has been devised and evidence supporting suggestions of field driven penetration of oxygen into the metal substrate have also been provided. The complexity of the resulting mass spectrum from the magnesium alloys led to the development of a systematic peak identification process. This process resulted in the detection of a significant amount of hydrogen within the data. In response to the contention around the observation of hydrogen within atom probe data, a chapter has been devoted to the analysis and discussion of hydrogen within the current magnesium mass spectra. This analysis will provide a useful reference to others in their analysis of magnesium-oxide/hydroxide mass spectra. Atom probe tomography is a characterisation technique that has been used to study a wide variety of materials with its potential application continually expanding. The current body of work focuses on the application of atom probe tomography to questions relating to processes of oxidation in two different metal alloys. Although the corrosion mechanisms and the intended application of each alloy are significantly different, the challenges relating to the application of atom probe tomography to these alloys are congruous. The overarching focus of the current study is on improving the application of atom probe tomography to the study of corrosion products.
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Araullo-Peters, Vicente James. "Advancements in atomic-scale analytical methods and their application to understanding materials." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12770.
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Atom probe tomography is a high resolution microscopy technique capable of determining the 3D location and chemical identification of individual atoms within a specimen. Though it is becoming ever more popular, a number of issues with the technique are known. First, the large amount of data created by atom probe tomography experiments requires new techniques to be developed so as to conduct effective analysis. Also, atom probe tomography is not traditionally considered a tool for crystallographic analysis even though crystallographic information is known to be present in reconstructed datasets. Though prior work has been done, the field of atom probe crystallography is underdeveloped. Furthermore, artefacts in the atom probe experiment and reconstruction are complicated and influence the resulting tomograms in subtle ways. The effects of these artefacts need to be understood so as to properly interpret atom probe results. This thesis contains seven manuscripts which discuss these issues. First, three manuscripts are presented which outline the development 3D orientation mapping of crystal grains in atom probe data, current computational approaches to atom probe data and a new framework for conducting crystallographic analysis of atom probe data. A fourth paper is presented which outlines and applies a new method to define and extract grain boundaries in atom probe datasets. Two papers are presented which discuss artefacts present in atom probe data, how they influence reconstructions and how to minimise errors resulting from these artefacts. A final manuscript is presented which applies several of the developed techniques to the analysis of the aerospace alloy, AA2198. Here, the microstructural evolution of AA2198 is characterised with particular emphasis on the strengthening T1 phase.
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Bennett, Samantha. "Nitride semiconductors studied by atom probe tomography and correlative techniques." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/236685.
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Optoelectronic devices fabricated from nitride semiconductors include blue and green light emitting diodes (LEDs) and laser diodes (LDs). To design efficient devices, the structure and composition of the constituent materials must be well-characterised. Traditional microscopy techniques used to examine nitride semiconductors include transmission electron microscopy (TEM), and atomic force microscopy (AFM). This thesis describes the study of nitride semiconductor materials using these traditional methods, as well as atom probe tomography (APT), a technique more usually applied to metals that provides three-dimensional (3D) compositional information at the atomic scale. By using both APT and correlative microscopy techniques, a more complete understanding of the material can be gained, which can potentially lead to higher-efficiency, longer-lasting devices. Defects, such as threading dislocations (TDs), can harm device performance. An AFM-based technique was used to show that TDs affect the local electrical properties of nitride materials. To investigate any compositional changes around the TD, APT studies of TDs were attempted, and evidence for oxygen enrichment near the TD was observed. The dopant level in nitride devices also affects their optoelectronic properties, and the combination of APT and TEM was used to show that Mg dopants were preferentially incorporated into pyramidal inversion domains, with a Mg content two orders of magnitude above the background level. Much debate has been focused on the microstructural origin of charge carrier localisation in InGaN. Alloy inhomogeneities have often been suggested to provide this localisation, yet APT has revealed InGaN quantum wells to be a statistically random alloy. Electron beam irradiation in the TEM caused damage to the InGaN, however, and a statistically significant deviation from a random alloy distribution was then observed by APT. The alloy homogeneity of InAlN was also studied, and this alloy system provided a unique opportunity to study gallium implantation damage to the APT sample caused during sample preparation by the focused ion beam (FIB). The combination of APT with traditional microscopy techniques made it possible to achieve a thorough understanding of a wide variety of nitride semiconductor materials.
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Chen, Yi-Sheng. "Characterisation of hydrogen trapping in steel by atom probe tomography." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:9d8ee66f-176d-4ac1-aad6-ccb33efc924d.
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Hydrogen embrittlement (HE), which results in an unpredictable failure of metals, has been a major limitation in the design of critical components for a wide range of engineering applications, given the near-ubiquitous presence of hydrogen in their service environments. However, the exact mechanisms that underpin HE failure remain poorly understood. It is known that hydrogen, when free to diffuse in these materials, can tend to concentrate at a crack tip front. In turn, this facilitates crack propagation. Hence one of the proposed strategies for mitigating HE is to limit the content of freely diffusing hydrogen within the metal atomic lattice via the introduction of microstructural hydrogen traps. Further, it is empirically known that the introduction of finely-dispersed distribution of nano-sized carbide hydrogen traps in ferritic steel matrix can improve resilience to HE. This resilience has been attributed to the effective hydrogen trapping of the carbides. However, conclusive atomic-scale experimental evidence is still lacking as to the manner by which these features can impede the movement of the hydrogen. This lack of insight limits the further progress for the optimisation of the microstructural design of this type of HE-resistant steel. In order to further understand the hydrogen trapping phenomenon of the nano-sized carbide in steel, an appropriate characterisation method is required. Atom probe tomography (APT) has been known for its powerful combination of high 3D spatial and chemical resolution for the analysis of very fine precipitates. Furthermore, previous studies have shown that the application of isotopic hydrogen (2H) loading techniques, combined with APT, facilitates the hydrogen signal associated to fine carbides to be unambiguously identified. However, the considerable experimental requirements as utilised by these previous studies, particularly the instrumental capability necessary for retention of the trapped hydrogen in the needle-shaped APT specimen, limits the study being reproduced or extended. In this APT study, a model ferritic steel with finely dispersed V-Mo-Nb carbides of 10-20 nm is investigated. Initially, existing specialised instrumentation formed the basis of a cryogenic specimen chain under vacuum, so as to retain loaded hydrogen after an electrolytic charging treatment for APT analysis. This work confirms the importance of cryogenic treatment for the retention of trapped hydrogen in APT specimen. The quality of the obtained experimental data allows a quantitative analysis on the hydrogen trapping mechanism. Thus, it is conclusively determined that interior of the carbides studied in this steel acts as the hydrogen trapping site as opposed to the carbide/matrix interface as commonly expected. This result supports the theoretical investigations proposing that the hydrogen trapping within the carbide interior is enabled by a network of carbon vacancies. Based on the established importance of the specimen cold chain in these APT experiments, this work then successfully develops a simplified approach to cryo-transfer which requires no instrumental modification. In this approach there is no requirement for the charged specimen to be transferred under vacuum conditions. The issue of environmental-induced ice contamination on the cryogenic sample surface in air transfer is resolved by its sublimation in APT vacuum chamber. Furthermore, the temperature of the transferred sample is able to be determined independently by both monitoring changes to vacuum pressure in the buffer chamber and also the thermal response of the APT sample stage in the analysis chamber. This simplified approach has the potential to open up a range of hydrogen trapping studies to any commercial atom probe instrument. Finally, as an example of the use of this simplified cryo-transfer technique, targeted studies for determining the source of hydrogen adsorption during electropolishing and electrolytic loading process are demonstrated. This research provides a critical verification of hydrogen trapping mechanism of fine carbides as well as an achievable experimental protocol for the observation of the trapping of individual hydrogen atoms in alloy microstructures. The methods developed here have the potential to underpin a wide range of possible experiments which address the HE problem, particularly for the design of new mitigation strategies to prevent this critical issue.
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Oberdorfer, Christian [Verfasser], and Guido [Akademischer Betreuer] Schmitz. "Numeric simulation of atom probe tomography / Christian Oberdorfer ; Betreuer: Guido Schmitz." Münster : Universitäts- und Landesbibliothek Münster, 2014. http://d-nb.info/1138282715/34.
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Montalvo, Delgado Stephanie Dannett. "Development and application of atom probe tomography to complex zircon grains." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/81227.
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Atom probe tomography (APT) is used to characterise the nanoscale geochemistry of complex zircon grains from different environments. New applications of APT to meteoritic, shocked and hydrothermal zircon grains are developed. The results of this project provide a new understanding of trace element modification of zircon and provides a framework for future investigations of the nanoscale geochemical and geochronological analysis of other minerals.
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Innocenti, Nicolas. "Interaction of femtosecond laser pulses with nanoscaleSi-tips for atom probe tomography." Thesis, University of Liège, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-51018.
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The atom probe is an analysis technique based on the emission of ionized species from a needle-shaped sample (apex radius < 100 nm) under the influence of a very strong electric field ( 10-50 V/nm). A DC-voltage is applied on the sample in order to generate a field slightly below the one necessary to remove atoms (in the form of ions) from its surface. An ultrashort (femtosecond) laser pulse is used to trigger the emission. The evaporated ions are accelerated in the electric field and projected onto a position sensitive detector where a magnified image of the surface is formed (magnication from 10^6 to 10^7). Time of flight mass spectrometry is used to chemically identify the evaporated atoms. The technique thus allows to analyze the composition of a 3D volume with sub-nanometer resolution. Imec conducts research in order to introduce the 3D characterization with quasi-atomic resolution capabilities of the technique to the semiconductor industry. It became quickly apparent that a detailed understanding of the laser interaction with the nanoscale samples is crucial in order to interpret the analysis results. In this work, we briefly introduce the principles of the technique and review some of its applications. We then summarize some of the currently unexplained experimental observations, taken from the literature or from experiments conducted at Imec. Based on those observations, we introduce a thermally assisted model of field evaporation that includes the electromagnetic nature of light and the semiconducting character of silicon. The optical absorption of the nanoscale sample is computed by numerical simulations using the FDTD algorithm. The temperature evolution at the tip apex is obtained by solving a coupled thermal conduction-carrier recombinations problem and the shape of the mass spectrum is deduced. We discuss the model and confront its results to experimental data. We show that the model qualitatively explains many experimental aspects of the characterization of silicon by means of an atom probe analysis. Nevertheless, we show that at this stage the model lacks quantitative accuracy and we suggest several ways to improve it.atom probe, LA-WATAP, field evaporation, femtosecond laser pulse interaction with nanoscale silicon objects, Sommerfeld's half plane problem, FDTD - Yee's scheme.
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Zhang, Yi. "Three dimensional atom probe tomography of nanoscale thin films, interfaces and particles." [Ames, Iowa : Iowa State University], 2009.
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Samudrala, Saritha Kowmudy. "Atomic scale analysis of nanocrystalline materials by advanced microscopy." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/13655.
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In this thesis, relatively new and advanced microscopy techniques are used to overcome many challenging problems in characterisation of nanocrystalline (nc-) materials. They include grain boundaries’ orientation and misorientation evaluation by transmission Kikuchi diffraction (TKD) and atomic scale analysis of segregation at grain boundaries by atom probe microscopy (APM). For each of these techniques, systematic investigations were carried out to optimise specimen preparation methods, data acquisition and analysis parameters. This resulted in fundamental knowledge that could be adopted to study a wide range of nc- materials. Two different sets of nc- materials are considered in this work: (i) bulk engineering materials (duplex stainless steels (DSS)) processed by high pressure torsion (HPT); and (ii) novel binary thin film systems including Al-O, Ni-P and Cu synthesized by direct current (DC) - magnetron sputtering and electron beam evaporation methods. In DSS samples, TKD work with the support of high resolution transmission electron microscopy has shown deformation twinning in body centred cubic ferrite phase, which is a significant experimental finding in contrast to the abundant theoretical modelling work in literature. Further, ferrite-ferrite grain boundaries and ferrite-austenite interphase boundaries are captured in APM experiments for studying segregation of alloying elements. This provided a way to calculate interfacial excess of segregating elements such as Mo, P, B, and W. Even in Al-O thin films, solute excess of O atoms and O rich clusters at grain boundaries is directly evidenced by APM and quantified by advanced computational methods. APM data also showed that O and P additions in Al-O and Ni-P led to a reduction in grain size of the as-deposited films. AP results facilitated and led to the studies of grain boundary pinning effect on stress coupled grain boundary mediated deformation mechanisms in these films.
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Zhou, Jing. "An Atom-Probe Tomography Study of Phase Separation in Fe-Cr Based Steels." Doctoral thesis, KTH, Metallografi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-150796.
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Stainless steels are very important engineering materials in a variety of applications such as in the food industry and nuclear power plants due to their combination of good mechanical properties and high corrosion resistance. However, ferrite-containing stainless steels are sensitive to the so-called ‘475°C embrittlement’, which is induced by phase separation of the ferrite phase, where it decomposes into Fe-rich ferrite (α) and Cr-rich ferrite (α'). The phase separation is accompanied with a severe loss of toughness. Therefore, the upper service temperature of ferrite-containing stainless steels in industrial applications has been limited to around 250°. In the present work, Fe-Cr based steels were mainly investigated by atom probe tomography. A new method based on the radial distribution function (RDF) was proposed to quantitatively evaluate both the wavelength and amplitude of phase separation in Fe-Cr alloys from the atom probe tomography data. Moreover, a simplified equation was derived to calculate the amplitude of phase separation. The wavelength and amplitude was compared with evaluations using the auto-correlation function (ACF) and Langer-Bar-on-Miller (LBM) method, respectively. The results show that the commonly used LBM method underestimates the amplitude of phase separation and the wavelengths obtained by RDF shows a good exponential relation with aging time which is expected from the theory. The RDF is also an effective method in detecting the phenomena of clustering and elemental partitioning. Furthermore, atom probe tomography and the developed quantitative analysis method have been applied to investigate the influence of different factors on the phase separation in Fe-Cr based alloys by the help of mainly mechanical property tests and atom probe tomography analysis. The study shows that: (1) the external tensile stress during aging enhances the phase separation in ferrite. (2) Phase separation in weld bead metals decomposes more rapidly than both the heat-affected-zone metals and the base metals mainly due to the high density of dislocations in the welding bead metals which could facilitate the diffusion. (3) The results show that Ni and Mn can enhance the phase separation comparing to the binary Fe-Cr alloy whereas Cu forms clusters during aging. (4) Initial clustering of Cr atoms was found after homogenization. Two factors, namely, clustering of Cr above the miscibility gap and clustering during quenching was suggested as the two responsible mechanisms. (5) The homogenization temperatures significantly influence the evolution of phase separation in Fe-46.5at.%Cr.QC 20140910
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La, Fontaine Alexandre Jacques. "Understanding the structure of minerals at the atomic scale: a new perspective enabled by advanced microscopy." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15484.
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From oxides to ores and rocks, minerals are the most prevalent materials on Earth. The majority of their properties are the direct result of their microstructure. The investigation of their structure at the nano and micron scale is routinely carried out using techniques such as optical and electron microscopy, X-ray diffraction or secondary ion mass spectrometry. However, these techniques are usually limited in resolution, either spatially or chemically. More recently, atom probe tomography (APT) has emerged as a powerful microscopy technique that can provide 3D maps showing the position and atomic mass of individual atoms with sub-nanometre resolution. The non-conductive character of most minerals, both thermally and electrically, makes their investigation by APT challenging, from sample preparation to data interpretation. However, with the relatively recent development of focused ion beam sample preparation techniques and ultra-violet laser-assisted local electrode atom probe, the APT study of large band gap materials such as oxides has become more successful in the last decade. Advanced microscopy techniques such as transmission Kikuchi diffraction (TKD) or electron backscattered diffraction (EBSD) can also be used in combination with APT, and bring a new perspective to the investigation of the atomic scale structure of minerals, leading to a better understanding of their structure – properties relationships. The overall purpose of this thesis is to develop and apply new methods and techniques for the characterization of the structure of minerals at the atomic scale. This is achieved by means of various advanced microscopy techniques, which are applied to a selection of important scientific questions. By using a combination of APT, TKD, EBSD and transmission electron microscopy we investigate intergranular corrosion in stainless steels, the atomic structure of dental enamel and the robustness of zircon as a geological dating accessory. In this work, intergranular corrosion mechanisms in a commercial austenitic stainless steel (ASS) were revealed using EBSD and correlative TKD/TEM. Characterization by APT of the intergranular iron-chromium spinel formed during corrosion of the ASS revealed new insights at the atomic scale on its role towards the fast corrosion rate of the ASS. With the combined use of EBSD, TKD and APT, the atomic scale distribution of trace elements within dislocations in deformed mineral zircons was investigated for the first time to review the robustness of zircon for radiogenic dating. By using APT and TEM, new structural and elemental analysis of human dental enamel at the atomic scale provided unprecedented information for our understanding of human tooth decay.
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Muller, Michael. "Performance, optimisation and applications of pulsed laser atom probe tomography for compound semiconductor analysis." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540147.
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Luo, Ting. "Study of the mechanisms of silicide formation by isotope diffusion and atom probe tomography." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0413.
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Avec la réduction de taille des composants microélectroniques, le monosiliciure de nickel (NiSi) a été largement utilisé dans les transistors CMOS (Complementary-Metal-Oxide-Semiconductor) en tant que contacts pour les sources, drains et grilles. Cependant, NiSi se dégrade lors du recuit à haute température. Il apparait essentiel d'étudier la séquence de formation de phases et la stabilité du monosilicide en présence d’éléments d'alliage. Les réactions à l'état solide entre des films de Ni allié en W et/ou Pt et un substrat de Si ont été étudiées principalement par diffraction des rayons X (DRX) in-situ et sonde atomique tomographique (SAT). L'analyse combinatoire de la réaction entre des films Ni avec différents composition gradients et le Si a permis de comprendre la séquence de formation. Les concentrations des éléments d'alliage (W et Pt) ont un impact significatif sur la séquence de formation des siliciures de Ni et sur la cinétique de formation des phases. Le mécanisme d'agglomération des films minces de NiSi a également été étudié au cours de cette thèse. Un film de Ni pur de 15 nm a été déposé sur un substrat de Si enrichi de multicouches de Si isotopique. Des analyses SAT ont été effectuées sur l'échantillon de Ni/Si (isotope) après un recuit à 600°C. En observant la distribution des isotopes de Si, un mécanisme d'agglomération de NiSi a été proposé selon que les isotopes de Si restent sous forme de multicouches ou qu'ils se mélangent. Cette étude rendue possible grâce à la capacité unique de la SAT d'observer les isotopes en 3D et à l'échelle atomique apporte une meilleure compréhension de l'agglomération de films minces poly-cristallin d'intermétalliqueWith the downscaling of microelectronic devices, NiSi has been widely used in complementary-metal-oxide-semiconductor (CMOS) transistors as contact on source, drain and gate. However, NiSi suffers from degradation upon annealing at high temperatures. Adding alloying elements is an effective method to increase the stability of nickel monosilicide but the formation sequence of Ni silicides is substantially modified. Therefore, the studies of the phase formation sequence and the stability of monosilicide are of great importance.The solid-state reactions between Ni films alloyed with W and/or Pt and Si substrates were studied mainly by in-situ X-ray diffraction (XRD) and atom probe tomography (APT) using combinatorial analysis of co-deposited gradient films. The phase sequence was monitored by in-situ XRD and APT was used to examine the silicides and reveal the redistribution of alloying elements. The content of alloying elements (W and Pt) has a large impact on the phase sequence of Ni silicides and the kinetics of phase formation. The basic agglomeration mechanism of NiSi thin films was studied. A 15nm pure Ni film was deposited on a Si substrate enriched with isotope multilayers. APT analyses were performed on the sample of Ni/Si (isotope) after an annealing at 600°C. By observing the distribution of Si isotopes (30Si, 29Si and 28Si), whether they maintain a multilayer structure or are mixed together, a mechanism of the agglomeration of NiSi was proposed. This was possible because of the unique capability of APT to observe isotopes in 3D at the atomic scale and it allows a better understanding and to control of the agglomeration of poly-crystalline compound thin films
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Bouchikhaoui, Houari [Verfasser], and Guido [Akademischer Betreuer] Schmitz. "Nanoanalysis by atom probe tomography of tunnel magnetoresistive (TMR) structures / Houari Bouchikhaoui ; Betreuer: Guido Schmitz." Münster : Universitäts- und Landesbibliothek Münster, 2016. http://d-nb.info/1141577747/34.
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Qu, Jiangtao. "Atom-Scale Insights into III-V Semiconductor Nanowires." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17851.
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As the feature size of MOSFET is scaling down to nano-size, series of problems need to be overcome to continue Moore’ Law, which seems an impossible task with traditional bulk Si technology due to the physical limitation and various negative effects being subject to small feature size. The critical issues for both further improving the devices’ performance and lowering their cost lie in the exploration of substitutions for Si and the control of morphological and compositional properties of materials. group III-V nanowires due to its unique properties are considered as the building block for next-generation electronic devices. To fulfill these commercial applications with group III-V nanowires, a fundamental and quantitative understanding of growth-structure-property relationships is central to applications where nanowires exhibit clear advantages. Therefore, this doctoral research systematically investigates three different semiconductor nanowires: Au-seeded, self-seed and planar nanowires, in terms of elemental, morphological and structural aspects by taking advantage of cutting-edge technique atom probe tomography, and endeavor to unveil the correlation between nanowires’ intrinsic properties and performance. Based on the atom probe findings, the growth mechanism of Au-seeded and self-seeded nanowire have been systematically discussed, and new model has been proposed to explain the phenomena on the basis of density functional calculation. Moreover, the doping distribution in planar nanowires has also been carefully investigated, and the results demonstrate that the dopants can diffuse into the substrate which subsequently degrade the device performance due to parasitic channel effect, and accordingly, suggestions have been given to optimize the planar nanowire growth for improved dopant distribution. The outcomes of this project are expected to theoretically support high-quality nanowire synthesis for specific applications.
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Mazumder, Baishakhi. "Physics of the field evaporation of poor conducting materials in the Laser assisted Atom Probe Tomography." Rouen, 2010. http://www.theses.fr/2010ROUES039.
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La sonde atomique assistée par laser est une technique de nano analyse 3D qui donne des informations à l'échelle atomique avec une résolution spatiale nanométrique. Les phénomènes physiques sous-jacents les mécanismes d'évaporation de ces matériaux mauvais conducteurs sont très complexes en raison de la structure électronique de ces types de matériaux. Ce travail porte sur l'étude de l'évaporation de matériaux mauvais conducteurs à partir de semi-conducteurs (Si, SiC, GaAs et InP) jusqu'aux oxydes (MgO, TiO2 et HfO2). Les atomes de la surface de l'échantillon préparé sous forme de pointe sont ionisés par un champ électrique permanent et l'interaction avec un faisceau laser femtoseconde. Cette interaction augmente la température de la pointe localement, permettant l'évaporation des atomes de surface. Des analyses ont été effectuées en variant les différents paramètres laser (longueur d'onde, énergie, etc. ) pour comprendre les mécanismes d'évaporation sous-jacents. Des modèles ont été développés pour interpréter nos résultats expérimentaux. L'influence de la longueur d'onde et de l'énergie du laser sur les mécanismes d'évaporation de semi-conducteurs et d'oxydes a été déterminée en tenant compte de l'influence de l'absorption optique, de l'effet de flexion des bandes, etc. Des études systématiques, déterminant les conditions d'analyse pour l'évaporation de matériaux mauvais conducteurs ont été effectuées afin d'aider les chercheurs travaillant dans des domaines connexes. Plus précisément l'un des ingrédients clés qui a été ajouté est l'absorption optique de surface et l'évaluation ultérieure du couplage électrons-phonons conduisant à des effets thermiques. La présente thèse marque une étape dans la compréhension de l'évaporation par effet de champ assisté par laser fs, par des résultats expérimentaux et par leur interprétationThe laser assisted atom probe tomography is a 3D nanoanalysing technique which gives information in the atomistic scale with sub nanometre spatial resolution. The physical phenomena underlying the field evaporation of poor conductive material is very complex due to the electronic structure of these types of materials. This work deals with the field evaporation study of poor conductive materials starting from semiconductors (Si, SiC, GaAs and InP= to insulating oxides (MgO, TiO2, and HfO2). The surface atoms from the tip shaped specimen are ionized by a standing electric field and the interaction of a femto-laser beam with the tip. The laser tip interaction increases the tip temperature locally, enabling the evaporation of surface atoms. Analyses are done varying different laser parameters (wavelength, energy, etc. ) to understand the underlying evaporation mechanism. Representative models have been developed to support our experimental results. The influence of wavelength and laser energy on the evaporation mechanisms of semiconductors and oxides are determined taking into account the influernce of optical absorption, band bending effect, etc. Various complex and diversified physical phenomena were observed ands understood during this study. Systematic studies, determining the analytical conditions for field evaporation of non conducting materials are evaluated to help future researchers working in related fields. Specifically one of the key factors is the surface optical absorption and the subsequent evaluation of the electron phonon coupling leading to thermal effects. The present thesis is a modest attempt to understand the field evaporation behaviour under femtosecond laser pulse and the physics involved in this framework by experimental results and corresponding interpretation
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Bilal, Huma. "Atomic Scale Microscopy of Zr-based Bulk Metallic Glasses Processed by Various Routes." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29908.
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Bulk metallic glasses (BMGs) exhibit a rare combination of strength and toughness that is difficult to achieve by other materials. These properties make them favourable for a diverse range of engineering applications. However, their disordered amorphous structure invokes catastrophic failure with shear bands localisation, limiting their industrial development as structural materials. Moreover, it is not yet clear how to quantitatively link their microstructural features to processing and mechanical properties. The aim of this thesis was to quantitatively analyse the structural features contributing to local hardness variations in thermomechanically processed zirconium (Zr)-based BMGs. Advanced atom probe tomography (APT) techniques were used to observe structural and chemical changes in these BMGs. APT operational parameters were optimised and tested for robust data outcomes. APT cluster analysis was effectively utilised in the characterisation of nanoscale heterogeneities in the BMG microstructure. The chemical composition of the nanoscale heterogeneities was roughly Zr27Cu29Al21Ni19Nb4 (at. %) in Zr63.96Cu13.36Ni10.29Al11.04Nb1.25 (at. %), and Zr22Cu29Al17Ni23Ti9 (at. %) in Zr52.5Cu17.9Ni14.6Al10Ti5 (at. %). Their chemistry was experimentally reported herein for the first time. Additionally, an ab-initio molecular dynamic (AIMD) simulation was used to simulate the atomistic distribution in a Zr-based BMG. Clusters observed in APT assigned as MRO regions were found synonymous to the shear band nucleation zones. Beyond the novel methodological rigor introduced here, the findings provide a new, independent validation of the inverse correlation between local hardness and size of the MRO regions, with their chemical compositions, providing a novel handle on the quest for understanding microstructure- property-processing relationship in BMGs.
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Yun, Fan. "Understanding the Hidden Pathways of Human Tooth Decay at the Atomic Scale." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/24957.
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Dental caries, also known as tooth decay, is the most prevalent human chronic disease worldwide. Understanding the pathways and mechanisms of human tooth decay is central to the development of both prophylaxes and treatments, but only limited information is presently available about the initiation of caries at the nanoscale.
In the present thesis, atom probe tomography 3D chemical maps and high-resolution transmission electron microscopy images managed to provide three distinct initial sites for human dental enamel dissolution: a) along the central dark line (CDL) within carbonated apatite nanocrystals, b) at organic-rich precipitates and c) along high-angle grain boundaries (HAGB).
In chapter 3, 3D maps of the atoms within hydroxyapatite nanocrystallites in sound and naturally-decayed human dental enamel reveal a higher concentration of Mg and Na in the CDL. The CDL is therefore thought to provide a pathway for the exchange of ions during demineralization and remineralization. Mg and Na enrichment of the CDL also suggests that it is associated with the ribbon-like organic-rich precursor in amelogenesis.
In chapter 4, we found that the carious region propagates from the organic-rich precipitates to surrounding crystallites after corrosion. We further showed that the organic C-F bonds have the opposite distribution to the inorganic fluoride, revealed the new insight of the pathways and positions of fluorine in human enamel.
In chapter 5, the nanoscale in-situ compression test demonstrated the low-angle grain boundary (LAGB) sliding and the resulting size effect of HAP enamel. We then distinguished that HAGBs are more susceptible to corrosion than LAGBs, independent of whether they are ordinary grain boundaries or triple junction boundaries.
The key novelties of this thesis are to provide vital new understanding and the systematic mechanisms of human tooth decay at sub-nanoscale thereby contributing to the prevention, restoration, and early diagnosis of dental caries.
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Huyan, Fei. "A study of "475°C embrittlement" in Fe-20Cr and Fe-20Cr-X (X=Ni, Cu, Mn) alloys." Thesis, KTH, Metallografi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118155.
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The “475°C embrittlement” occurring in ferritic and duplex stainless steel is considered to be detrimental and it limits the application of ferritic and duplex stainless steel at elevated temperatures, i.e., above about 300°C . In this study, the effect from alloying elements Ni, Cu and Mn on 475°C embrittlement was examined based on microhardness measurement and Charpy V-notch tests as well as atom probe tomography (APT). It was found that, after aging for 10h, 3% Ni accelerates the ferrite decomposition dramatically, 5% Mn has minor effect and no effect of 1.5% Cu was seen. The hardness increase tested at 450°C and 500°C was consistent with the observations from APT. The embrittlement based on room temperature Charpy tests was observed mainly during the first 10h. The embrittlement in Fe-20Cr-3Ni alloy was attributed to ferrite decomposition, while the other three alloys may be influenced by other phenomenon as well. A clustering effect of Cu has been observed in Fe-20Cr-1.5Cu and it was supposed to contribute to the mechanical changes.
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DeGeorge, Vincent G. "Chemical Partitioning and Resultant Effects on Structure and Electrical Properties in Co-Containing Magnetic Amorphous Nanocomposites for Electric Motors." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/885.
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chemical partitioning of Cobalt-containing soft magnetic amorphous and nanocomposite materials has been investigated with particular focus on its consequences on these materials’ nanostructure and electrical resistivity. Theory, models, experiment, and discussion in this regard are presented on this class of materials generally, and are detailed in particular on alloys of composition, (Fe65Co35)79.5+xB13Si2Nb4-xCu1.5, for X={0- 4at%}, and Co-based, Co76+YFe4Mn4-YB14Si2Nb4, for Y={0-4at%}. The context of this work is within the ongoing efforts to integrate soft magnetic metal amorphous and nanocomposite materials into electric motor applications by leveraging material properties with motor topology in order to increase the electrical efficiency and decrease the size, the usage of rare-earth permanent magnets, and the power losses of electric motors. A mass balance model derived from consideration of the partitioning of glass forming elements relates local composition to crystal state in these alloys. The ‘polymorphic burst’ onset mechanism and a Time-Temperature- Transformation diagram for secondary crystallization are also presented in relation to the partitioning of glass forming elements. Further, the intrinsic electrical resistivity of the material is related to the formation of virtual bound states due to dilute amounts of the glass forming elements. And lastly, a multiphase resistivity model for the effective composite resistivity that accounts for the amorphous, crystalline, and glass former-rich amorphous regions, each with distinct intrinsic resistivity, is also presented. The presented models are validated experimentally on the Co-containing alloys by Atom Probe Tomography performed through collaboration with Pacific Northwestern National Laboratory.
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Zelenty, Jennifer Evelyn. "Effects of nickel and manganese on the embrittlement of low-copper pressure vessel steels." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:28b9151f-1644-470b-abc7-48ff82bcffdd.
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Solute clustering is known to play a significant role in the embrittlement of reactor pressure vessel (RPV) steels. When precipitates form they impede the movement of dislocations, causing an increase in hardness and a shift in the ductile-brittle transition temperature. Over time this can cause the steel to become brittle and more susceptible to fracture. Thus, understanding precipitate formation is of great importance to the nuclear industry. The first part of this thesis aims to isolate and better understand the thermal aging component of embrittlement in low copper, model RPV steels. Currently, relatively little is known about the effects of Ni and Mn in a low copper environment. Therefore, it is of interest to determine if Ni and Mn form precipitates under these conditions. To this end, hardness measurements and atom probe tomography were utilized to link the mechanical properties to the microstructure. After 11,690 hours of thermal aging a statistically significant decrease in hardening was observed. Consistent with hardness measurements, no precipitates were present within the matrix of the thermally aged RPV steels. The local chemistry method was then applied to investigate the very early stages of solute clustering. Association was found to be statistically significant in both the thermally aged and as-received model RPV steels. Therefore, no apparent trends regarding the changes in solute association between the as-received and thermally aged RPV steels were identified. Small, non-random clusters were observed at heterogeneous nucleation sites, such as carbide/matrix interfaces and grain boundaries, within the thermally aged material. The clusters found at the carbide/matrix interfaces were all rich in Mn and approximately 90-150 atoms in size. The clusters located along the observed low-angle grain boundary, however, were significantly larger (on the order of hundreds of atoms) and rich in Ni. Lastly, copper-rich precipitates (CRPs) and Mn- and Ni-rich precipitates (MNPs) were observed within the cementite phase of a high copper and low copper RPV steel, respectively, following long term thermal aging. APT was used to characterize these precipitates and obtain more detailed chemical information. The presence of such precipitates indicates that a range of precipitation can take place within the cementite phase of thermally aged RPV steels. The second part of this thesis aims to investigate the effects of ion irradiation on the microstructure of low copper RPV steels via APT. These steels were ion irradiated with 6.4 MeV Fe3+ ions with a dose rate of 1.5 x 10-4 dpa/s at 290°C. MNPs were observed in all five of the RPV steels analyzed. These precipitates were found to have nucleated within the matrix as well as at dislocations and grain boundaries. Using the maximum separation method these MNPs were extracted and characterized. Precipitate composition, size, volume fraction, and number density were determined for each of the five samples. Lastly, several grain boundaries were characterized. Several emerging trends were observed within the samples: Ni content within the precipitates did not vary significantly once a threshold between 30-50% was reached; bulk Mn content appeared to dictate Si and Mn content within the precipitates; and samples low in bulk Ni content were characterized by a higher number density of smaller precipitates. Additionally, by regressing precipitate volume fraction against the interaction of Ni and Mn, a linear relationship was found to be statistically significant.
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He, Mengwei. "Microstructure-Property Relationships in CoCrNi-Based High Entropy Alloys: From the Atomic-Scale." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29466.
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High entropy alloys (HEAs) have attracted enormous research interest world-wide because of their intriguing compositional make-up, and because of their potential as structural materials in extreme environments such as extremes of temperature, neutron fluence, mechanical wear, and cyclic deformation A key challenge in the study of HEAs remains the desire to measure the detail of the atomic neighbourhoods. This thesis proposes a new framework for the quantification of short range order (SRO) and reveals processing-SRO-mechanical property relationships in a CoCrNi-based ternary HEA.
Having established the optimal APT operating parameters, a workflow for accurately assessing the SRO in the HEAs using APT is proposed. The influence of detector efficiency and spatial resolution on the SRO was carefully evaluated. It is suggested that this new procedure has potential to significantly enhance the ability of the atom probe to precisely study atomic coordination in HEAs and other materials. On the basis of this method, the potential for relationships between thermo-mechanical processing and SRO was investigated. The results indicate that different heat treatments do indeed change the SRO in CoCrNi alloys. Then, the new approach to measuring SRO in HEAs was applied to samples at various stages of tensile deformation via interrupted tensile tests. After different plastic strain levels, the SRO and other microstructural attributes such as the defect distributions were studied, and evidence presented that the SRO is sensitive to the amount of prior plastic deformation.
Finally, retaining a focus on the mechanical properties of the HEAs, but shifting the emphasis to wear, a new series of HEAs was designed and prepared. The results demonstrate the significant potential of combining the substitutional Sc and interstitial C elements to achieve high values for hardness, wear resistance and fracture toughness.
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Dagan, Michal. "3D field ion microscopy and atom probe tomography techniques for the atomic scale characterisation of radiation damage in tungsten." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:a575ff83-9101-499e-a54d-23d59f0d4d16.
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In this work, new reconstruction and analysis methods were developed for 3D field ion microscopy (FIM) data, motivated by the goal of atomic scale characterisation of radiation damage for fusion applications. A comparative FIM/ atom probe tomography (APT) study of radiation damage in self-implanted tungsten revealed FIM advantages in atomistic crystallographic characterisation, able to identify dislocations, large vacancy clusters, and single vacancies. While the latter is beyond the detection capabilities of APT, larger damage features were observed indirectly in APT data via trajectory aberrations and solute segregation. An automated 3DFIM reconstruction approach was developed to maintain reliable, atomistic, 3D insights into the atomic arrangements and vacancies distribution in ion-implanted tungsten. The new method was utilized for the automated âatom-by-atom' reconstruction of thousands of tungsten atoms yielding highly accurate reconstructions of atomically resolved poles but also applied to larger microstructural features such as carbides and a grain boundary, extending across larger portions of the sample. Additional tools were developed to overcome reconstruction challenges arising from the presence of crystal defects and the intrinsic distortion of FIM data. Those were employed for the automated 3D mapping of vacancies in ion-implanted tungsten, analysing their distribution in a volume extending across 50nm into the depth of the sample. The new FIM reconstruction also opened the door for more advanced analyses on FIM data. It was applied to the preliminary studies of the distortion of the reconstructed planes, found to depend on crystallographic orientation, with an increased variance in atomic positions measured in a radial direction to the centre of the poles. Additional analyses followed the subtle displacements in atomic coordinates on consecutive FIM images, to find them affected by the evaporation of atoms from the same plane. The displacements were found to increase with size as the distance to the evaporated atom decreased, and are likely to be the result of a convolution between image gas effects, surface atoms relaxation, and charge re-distribution. These measurements show potential to probe the dynamic nature of the FIM experiment and possibly resolve contributions from the different processes effecting the final image. Finally, APT characterisation was performed on bulk and pre-sharpened needles to determine the effect of sample's geometry on the resulting implantation profiles, and the extent to which pre-sharpened needles could be employed in radiation damage studies. While the ions depth profiles in needles were not found within a good match to SRIM simulations, the damage profiles exhibited closer agreement. Further, the concentration of implanted ions in bulk samples was found significantly higher than in the respective needle implanted samples, with excessive loss found for the light ion implantation.
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Chang, Yanhong [Verfasser], Dierk [Akademischer Betreuer] Raabe, and Sandra [Akademischer Betreuer] Korte-Kerzel. "Characterization of H/D in Ti and its alloys with atom probe tomography / Yanhong Chang ; Dierk Raabe, Sandra Korte-Kerzel." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1195238029/34.
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Zschiesche, Hannes. "Formation and segregation in cobalt silicide and manganese germanide thin films : correlative study by electron microscopy and atom probe tomography." Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0219.
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Dans cette thèse, des formations des germaniures de manganèse et des disiliciures de cobalt en couche minces ont été étudié comme la structure et chimie. Dans le système Mn-Ge, deux nouvelles relations entre des grains du Mn5Ge3 et (111)Ge ont été identifiées. De plus, il a été montré que la pureté du Mn5Ge3 dans les couches déposées par pulvérisation cathodique magnétron dépend du mécanisme de croissance. Une diffusion réactive donne du Mn5Ge3 presque pure tandis qu’une réaction non-diffusive donne du Mn5Ge3 qui contient la plupart des impuretés de la pulvérisation cathodique magnétron. Dans CoSi2 qui a été formé d’une configuration Co/Ti/Si, une ségrégation du Ti a été détectée dans les joints de grains du CoSi2. En outre, la distribution du Ti ségrégé a été caractérisée d’être inhomogènes. Pour étudier la ségrégation dans les joints de grains systématiquement, une méthode a été développé qui permet de corréler des investigations structurelle et chimie à l’échelle atomique sur un et le même échantillon dans les joints de grains sélectionnes. Finalement, une méthode a été proposée pour quantifier une ségrégation dans les points tripleGermanide and silicide thin films have application in different field such as thermoelectricity, magnetism and/or microelectronics. This PhD thesis study the formation, structure and chemistry of Mn5Ge3 thin films, which is interesting due to its ferromagnetic property for possible spintronic devices, and of CoSi2 thin films, which are used as contact materials. Two new epitaxial relationships between Mn5Ge3 grains and (111)Ge have been identified. The chemical purity of Mn5Ge3 has been related to the deposition by magnetron sputtering: Mn5Ge3 thin films grown by reactive-diffusion are relatively pure while the significant incorporation of impurities in Mn5Ge3 grown by non-diffusive reaction is beneficial for the ferromagnetic property. Ti segregation to CoSi2 grain boundaries has been quantified in CoSi2 grown from a Co/Ti/Si thin film. Additionally, an inhomogeneous distribution of Ti at CoSi2 grain boundary has been related to the defect density. A method has been developed for correlative structural and chemical investigations at the atomic scale on selected interfaces. Finally, a method to quantify the triple junction segregation has been proposed
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Weber, Juliane Verfasser], Dirk [Akademischer Betreuer] Bosbach, and Georg [Akademischer Betreuer] [Roth. "Fundamental insights into the radium uptake into barite by atom probe tomography and electron microscopy / Juliane Weber ; Dirk Bosbach, Georg Roth." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1157122507/34.
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Weber, Juliane [Verfasser], Dirk Akademischer Betreuer] Bosbach, and Georg [Akademischer Betreuer] [Roth. "Fundamental insights into the radium uptake into barite by atom probe tomography and electron microscopy / Juliane Weber ; Dirk Bosbach, Georg Roth." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1157122507/34.
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Lotharukpong, Chalothorn. "Defect characterisation in multi-crystalline silicon." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:a803fada-2296-41c3-9d96-864c186957a2.
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Electron beam induced current (EBIC) and atom probe tomography (APT) were used in this study to determine electrical activities and impurity compositions at extended defects in multicrystalline silicon (mc-Si) samples. The results provide, for the first time, information regarding the chemical species present at defects whose electrical activity has previously been measured. A new APT specimen fabrication process was developed with the ability to select a specific defect for APT analysis. Development of the APT specimen fabrication process proceeded by first selecting and optimising the preferential etching for nano-scale defect delineation. Three etchants were evaluated, namely Secco, Sirtl and Dash, from which the Secco etch was selected. Three parameters were optimised to produce etch pits with geometries that meet the requirements imposed by APT specimen fabrication methods. The optimum parameters were 0.05M potassium dichromate concentration, 20°C etch temperature, and 30sec etch time. In the second stage, marking techniques were developed in order for the defects to be located throughout the APT specimen fabrication process. However, it became apparent that the conventional APT specimen fabrication method could not be used to fabricate APT specimens containing selected defects in a mc-Si sample. This led to the development of a novel APT specimen fabrication approach which allowed APT specimens to be fabricated, reproducibly, containing grain boundaries and isolated dislocations. In order to evaluate accurately iron contamination in mc-Si, four atom probe parameters were optimised to maximise detection sensitivity: the evaporation rate, the laser beam energy, the pulse repetition rate and the specimen temperature. The optimisation process can be divided in to two parts. In the first part, a matrix of pre-sharpened single-crystal silicon specimens was subjected to a variety of experimental parameters. The optimised parameters were determined to be 0.3% evaporation rate, 0.5nJ beam energy, 160kHz repetition rate and 55K specimen temperature. The second part was to determine the iron detection efficiency –the percentage of detected Fe ions that can be correctly identified as Fe– and sensitivity using these parameters to analyse a specially prepared iron calibration specimen. The values were determined to be a detection efficiency of about 35% and sensitivity of 54ppm or 2.70x1018 atom/cm3. The APT specimen fabrication process and the optimised APT analysis parameters were used to analyse four extended defects in mc-Si samples subjected to three different processing conditions, namely gold-contaminated, as-grown and phosphorus diffusion gettering (PDG). The important aspects of the analysis are listed below: • Gold was not detected at the grain boundary and its associated dislocations in the gold-contaminated specimen. The binding enthalpy of gold to such defects is thus less than 0.63eV. • Iron was not detected in any specimen. • Copper was observed at the grain boundary in the as-grown specimen in the form of individual atoms as well as clusters with diameters ranging between 4nm and 9nm. The electrical activity of the grain boundary was about 58%. • Nickel and carbon were detected at the grain boundary in the post-PDG specimen with the former having platelet structures with diameters and thicknesses ranging between 4nm-7nm and 2nm-4nm, respectively. The recombination strength of the defect was about 22%. • Two nickel clusters were found at the isolated dislocation in the post-PDG specimen. The clusters were spherical with an average diameter of 10nm. The distance between the two clusters was 35nm. The recombination strength of the defect was about 4%.
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Hwang, Junyeon Kaufman M. J. "Characterization and mechanical properties of nanoscale precipitates in modified Al-Si-Cu alloys using transmission electron microscopy and 3D atom probe tomography." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-3661.
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Hwang, Junyeon. "Characterization and Mechanical Properties of Nanoscale Precipitates in Modified Al-Si-Cu Alloys Using Transmission Electron Microscopy and 3D Atom Probe Tomography." Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc3661/.
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Among the commercial aluminum alloys, aluminum 319 (Al-7wt%Si-4wt%Cu) type alloys are popularly used in automobile engine parts. These alloys have good casting characteristics and excellent mechanical properties resulting from a suitable heat treatment. To get a high strength in the 319 type alloys, grain refining, reducing the porosity, solid solution hardening, and precipitation hardening are preferred. All experimental variables such as solidification condition, composition, and heat treatment are influence on the precipitation behavior; however, precipitation hardening is the most significant because excess alloying elements from supersaturated solid solution form fine particles which act as obstacles to dislocation movement. The challenges of the 319 type alloys arise due to small size of precipitate and complex aging response caused by multi components. It is important to determine the chemical composition, crystal structure, and orientation relationship as well as precipitate morphology in order to understand the precipitation behavior and strengthening mechanism. In this study, the mechanical properties and microstructure were investigated using transmission electron microscopy and three dimensional atom probe tomography. The Mn and Mg effects on the microstructure and mechanical properties are discussed with crystallographic study on the iron intermetallic phases. The microstructural evolution and nucleation study on the precipitates in the low-Si 319 type aluminum alloys are also presented with sample preparation and analysis condition of TEM and 3DAP tomography.
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Meher, Subhashish. "Comparative Coarsening Kinetics of Gamma Prime Precipitates in Nickel and Cobalt Base Superalloys." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699871/.
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The increasing technological need to push service conditions of structural materials to higher temperatures has motivated the development of several alloy systems. Among them, superalloys are an excellent candidate for high temperature applications because of their ability to form coherent ordered precipitates, which enable the retention of high strength close to their melting temperature. The accelerated kinetics of solute diffusion, with or without an added component of mechanical stress, leads to coarsening of the precipitates, and results in microstructural degradation, limiting the durability of the materials. Hence, the coarsening of precipitates has been a classical research problem for these alloys in service. The prolonged hunt for an alternative of nickel base superalloys with superior traits has gained hope after the recent discovery of Co-Al-W based alloys, which readily form high temperature g precipitates, similar to Ni base superalloys. In the present study, coarsening behavior of g precipitates in Co-10Al-10W (at. %) has been carried out at 800°C and 900°C. This study has, for the first time, obtained critical coarsening parameters in cobalt-base alloys. Apart from this, it has incorporated atomic scale compositional information across the g/g interfaces into classical Cahn-Hilliard model for a better model of coarsening kinetics. The coarsening study of g precipitates in Ni-14Al-7 Cr (at. %) has shown the importance of temporal evolution of the compositional width of the g/g interfaces to the coarsening kinetics of g precipitates. This study has introduced a novel, reproducible characterization method of crystallographic study of ordered phase by coupling of orientation microscopy with atom probe tomography (APT). Along with the detailed analysis of field evaporation behaviors of Ni and Co superalloys in APT, the present study determines the site occupancy of various solutes within ordered g precipitates in both Ni and Co superalloys. This study has explained the role of structural and compositional gradients across the precipitates (g)/matrix (g) interfaces on the coarsening behavior of coherent precipitates in both Ni and Co-base superalloys. The observation of two interfacial widths, one corresponding to a structural order-disorder transition, and the other to the compositional transition across the interface, raises fundamental questions regarding the definition of the interfacial width in such systems. The comparative interface analysis in Co and Ni superalloy shows significant differences, which gives insights to the coarsening behaviors of g precipitates in these alloys. Hence, the principal goal of this work is to compare and contrast the Co and Ni superalloys and also, to accommodate atomic scale information related to transitions across interfaces to coarsening models for a better practical applicability of coarsening laws to various alloys.
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Mühlbacher, Marlene. "High-resolution characterization of TiN diffusion barrier layers." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-120394.
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Titanium nitride (TiN) films are widely applied as diffusion barrier layers in microelectronic devices. The continued miniaturization of such devices not only poses new challenges to material systems design, but also puts high demands on characterization techniques. To gain understanding of diffusion processes that can eventually lead to failure of the barrier layer and thus of the whole device, it is essential to develop routines to chemically and structurally investigate these layers down to the atomic scale. In the present study, model TiN diffusion barriers with a Cu overlayer acting as the diffusion source were grown by reactive magnetron sputtering on MgO(001) and thermally oxidized Si(001) substrates. Cross-sectional transmission electron microscopy (XTEM) of the pristine samples revealed epitaxial, single-crystalline growth of TiN on MgO(001), while the polycrystalline TiN grown on Si(001) exhibited a [001]-oriented columnar microstructure. Various annealing treatments were carried out to induce diffusion of Cu into the TiN layer. Subsequently, XTEM images were recorded with a high-angle annular dark field detector, which provides strong elemental contrast, to illuminate the correlation between the structure and the barrier efficiency of the single- and polycrystalline TiN layers. Particular regions of interest were investigated more closely by energy dispersive X-ray (EDX) mapping. These investigations are completed by atom probe tomography (APT) studies, which provide a three-dimensional insight into the elemental distribution at the near-interface region with atomic chemical resolution and high sensitivity. In case of the single-crystalline barrier, a uniform Cu-enriched diffusion layer of 12 nm could be detected at the interface after an annealing treatment at 1000 °C for 12 h. This excellent barrier performance can be attributed to the lack of fast diffusion paths such as grain boundaries. Moreover, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N-sublattice for the experimental N/Ti ratio. In comparison, the polycrystalline TiN layers exhibited grain boundaries reaching from the Cu-TiN interface to the substrate, thus providing direct diffusion paths for Cu. However, the microstructure of these columnar layers was still dense without open porosity or voids, so that the onset of grain boundary diffusion could only be found after annealing at 900 °C for 1 h. The present study shows how to combine two high resolution state-of-the-art methods, TEM and APT, to characterize model TiN diffusion barriers. It is shown how to correlate the microstructure with the performance of the barrier layer by two-dimensional EDX mapping and three-dimensional APT. Highly effective Cu-diffusion barrier function is thus demonstrated for single-crystal TiN(001) (up to 1000 °C) and dense polycrystalline TiN (900 °C).
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Wang, Danqi. "LOW-TEMPERATURE GAS-PHASE CARBURIZING AND NITRIDING OF 17-7 PH STAINLESS STEEL." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386165240.
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Lambeets, Sten. "Hydrogénation catalytique du CO2 sur le rhodium :étude des processus en surface et sous-surface par techniques d’émission de champ." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/263477.
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Ce travail de thèse propose une investigation des dynamiques régissant la réactiond’hydrogénation du dioxyde de carbone sur une nanoparticule modèle de rhodium àl’échelle moléculaire. Cette recherche s’inscrit dans le contexte de la valorisation du CO2 parla voie catalytique. Une meilleure compréhension de la relation entre la structurecristallographique de la surface et les mécanismes réactionnels permettrait, à terme,d’améliorer l’optimisation des matériaux catalytiques. Dans ce but, la réaction est étudiée àl’échelle moléculaire sur une nanoparticule modèle de rhodium. Sa surface est observée àl’aide de l’ensemble des techniques d’émission de champ :la microscopie d’émission dechamp (FEM), la microscopie ionique à effet de champ (FIM), la sonde atomique unidimensionnelle(1DAP) et la sonde atomique tomographique (APT). Afin d’identifier lesdifférents phénomènes observés, ces derniers sont comparés à d’autres systèmes réactifsimpliquant l’O2, le N2O et le CO, sur du rhodium, du platine et un alliage de platine rhodium(10% en masse de rhodium).Dans ce travail nous avons observé et caractérisé l’adsorption dissociative du CO2 sur lerhodium et sa réaction avec l’hydrogène. À l’aide d’études comparatives avec les autressystèmes, des phénomènes réactifs ont été identifiés. Les traitements des donnéesrecueillies indiquent qu’à 700 K, les gaz CO2 et H2 réagissent via un processus en surface etforment les produits CO(g) et H2O(g). Cette réaction est connue sous le nom de « réaction dugaz à l’eau inverse ». Cette réaction s’accompagne de transformations observables par FEM.La présence d’atomes d’oxygène adsorbés provoque une augmentation du travail de sortiedes électrons de la plupart des facettes cristallographiques de la surface de rhodium, ce quise traduit par un assombrissement global de l’image FEM. Cependant, certaines régionsparticulières correspondant aux facettes {113} présentent une tendance inverse. Grâce audéveloppement d’une nouvelle méthodologie adaptant la sonde atomique tomographique àl’étude de processus dynamiques, il a été possible de relier les observations faites par FEM àla diffusion d’atomes d’oxygène sous la surface. Cette diffusion n’est pas homogène etdépend de la structure cristallographique des facettes. L’oxygène, formé à la suite d’uneadsorption dissociative sur les facettes du type {012}, ne pénètre le coeur de phase qu’autravers de certaines régions telles que les {113}, les {011} et les {111}. La construction desdiagrammes d’adsorption du CO2 et les diagrammes de phase cinétique du systèmeH2+O2/Rh ont permis de mettre en évidence les mouvements des atomes d’oxygène entre lasurface et la sous-surface. Finalement ces observations ont été étendues à d’autresmatériaux :Le platine et l’alliage PtRh. L’accumulation d’atomes d’oxygène sur et sous lasurface peut donc être observée en temps réel et à l’échelle moléculaire.Doctorat en Sciences
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Yu, Xinghua. "Characterization and Modeling of Heat Affected Zone Microstucture in a Blast Resistant Steel." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1262201157.
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Naber, Christoph [Verfasser], Jürgen [Akademischer Betreuer] Neubauer, and Jürgen [Gutachter] Neubauer. "Hydration kinetics of tricalcium silicate: A dataset for reaction rate calculations and nanoscale analysis employing atom probe tomography / Christoph Naber ; Gutachter: Jürgen Neubauer ; Betreuer: Jürgen Neubauer." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2019. http://d-nb.info/1176809806/34.
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Eder, Katja Daniela. "Surfaces and interfaces in nano-scale and nano-structured materials." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17217.
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In this thesis, advanced characterisation methods, including atom probe tomography (APT) and transmission Kikuchi diffraction (TKD) were employed to study surface and interfaces in a range of nano-scale and nano-structured materials. These techniques were used to measure solute segregation towards grain boundaries and to explore the relationship between grain boundary segregation and grain boundary mobility. APT was also used to characterise the structure of nanoparticles used as catalysts, and the adsorption behaviour of sulphur on catalytic surfaces, to gain more information about the structure-activity relationships, and deactivation processes. This research included the development and improvement of new and existing APT sample preparation techniques, conducting the experiments, and data analysis. The first part of this thesis is concerned with nanocrystalline alloys processed by severe plastic deformation. In the second part the exceptional hardening of an 316L austenitic steel during annealing was also investigated using APT. This thesis also concentrated on the study of nanoparticles for catalysis via APT. Systematic investigations of different APT sample preparation techniques were performed in order to find a way of producing reproducible and reliable specimens. Different acquisition parameters, substrates and coatings were tested to improve the APT data quality. Experiments were conducted in which needles were dipped in thiophene. Here the aim was to investigate the phenomenon of sulphur poisoning by using APT to investigate how thiophene bonds with different metal substrates. A glovebag setup was designed for the transfer of APT samples in a controlled environment, to avoid oxidation of the samples. This allowed the comparison of oxidised and un-oxidised specimen states. In the last part of this thesis, the accuracy of crystallographic information contained within APT datasets was verified for the first time by comparing the datasets to TKD measurements.
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Chen, Hansheng. "Correlating the microstructure, magnetic domain structure, and magnetic properties of rare earth permanent magnets." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/18996.
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Rare earth permanent magnets have been broadly integrated into various applications, such as advanced electric motor technologies which partly relieve the current energy crisis worldwide by taking advantages of their extraordinary magnetic properties. Traditional approaches for increasing the intrinsic coercivity (Hci) of rare earth permanent magnets typically come at the expense of remanence, resulting in a reduction of maximum magnetic energy product [(BH)max]. Therefore, novel design and processing strategies are in urgent need to circumvent this trade-off in the advanced rare earth permanent magnets. It is well known that the Hci and (BH)max of rare earth permanent magnets can be improved via tuning their microstructure/microchemistry at the nanoscale. Furthermore, the understanding and controlling the magnetic reversal process is equivalently essential in developing high-performance rare earth permanent magnets, since the magnetic domain structure determines the magnetic properties intrinsically. It is therefore of utmost importance to understand the correlation among microstructure, magnetic domain structure, and magnetic properties of rare earth permanent magnets. The thesis consists of three major topics, which are (i) strip cast Nd-Fe-B flake; (ii) sintered Nd-Fe-B magnet, (iii) sintered Sm2Co17 type magnet. To fully understand the effects of microstructure/composition on magnetic domain structure and magnetic properties of these rare earth permanent magnets, we investigated the effects of different heat treatment approaches on magnetic structure and magnetic properties of the aforementioned rare earth permanent magnets by integrating multiple cutting-edge microscopic techniques, including scanning electron microscopy, energy dispersive x-ray spectroscopy, electron backscatter diffraction, focused ion beam, transmission electron microscopy, magnetic force microscopy and atom probe tomography, in conjunction with micromagnetic simulations.
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Xiong, Wei. "Thermodynamic and Kinetic Investigation of the Fe-Cr-Ni System Driven by Engineering Applications." Doctoral thesis, KTH, Termodynamisk modellering, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-96707.
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This work is a thermodynamic and kinetic study of the Fe-Cr-Ni system as the core of stainless steels. The Fe-Cr, Fe-Ni and Cr-Ni systems were studied intensively using both computational and experimental techniques, including CALPHAD (CALculation of PHAse Diagrams), phase field simulation, ab initio modeling, calorimetry, and atom probe tomography. The purpose of this thesis is to reveal the complexity of the phase transformations in the Fe-Cr-Ni system via the integrated techniques. Due to the importance of the binary Fe-Cr system, it was fully reassessed using the CALPHAD technique by incorporating an updated description of the lattice stability for Fe down to zero kelvin. The improved thermodynamic description was later adopted in a phase field simulation for studying the spinodal decomposition in a series of Fe-Cr binary alloys. Using atom probe tomography and phase field simulation, a new approach to analyze the composition amplitude of the spinodal decomposition was proposed by constructing an amplitude density spectrum. The magnetic phase diagram of the Fe-Ni system was reconstructed according to the results from both ab initio calculations and reported experiments. Based on the Inden-Hillert-Jarl magnetic model, the thermodynamic reassessment of the Fe-Ni system demonstrated the importance of magnetism in thermodynamic and kinetic investigations. Following this, the current magnetic model adopted in the CALPHAD community was further improved. Case studies were performed showing the advantages of the improved magnetic model. Additionally, the phase equilibria of the Fe-Cr-Ni ternary were discussed briefly showing the need of thermodynamic and kinetic studies at low temperatures. The “low temperature CALPHAD” concept was proposed and elucidated in this work showing the importance of low temperature thermodynamics and kinetics for designing the new generation of stainless steels.QC 20120612
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Zhou, Jing. "Experimental study of phase separation in Fe-Cr based alloys." Licentiate thesis, KTH, Metallografi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119230.
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Duplex stainless steels (DSSs) are important engineering materials due to their combination of good mechanical properties and corrosion resistance. However, as a consequence of their ferrite content, DSSs are sensitive to the so-called ‘475°C embrittlement’, which is induced by phase separation, namely, the ferrite decomposed into Fe-rich ferrite (α) and Cr-rich ferrite (α'), respectively. The phase separation is accompanied with a severe loss of toughness. Thus, the ‘475°C embrittlement’ phenomenon limits DSSs’ upper service temperature to around 250°C. In the present work, Fe-Cr binary model alloys and commercial DSSs from weldments were investigated for the study of phase separation in ferrite. Different techniques were employed to study the phase separation in model alloys and commercial DSSs, including atom probe tomography, transmission electron microscopy and micro-hardness test. Three different model alloys, Fe-25Cr, Fe-30Cr and Fe-35Cr (wt. %) were analyzed by atom probe tomography after different aging times. A new method based on radial distribution function was developed to evaluate the wavelength and amplitude of phase separation in these Fe-Cr binary alloys. The results were compared with the wavelengths obtained from 1D auto-correlation function and amplitudes from Langer-Bar-On-Miller method. It was found that the wavelengths from 1D auto-correlation function cannot reflect the 3D nano-scaled structures as accurate as those obtained by radial distribution function. Furthermore, the Langer-Bar-On-Miller method underestimates the amplitudes of phase separation. Commercial DSSs of SAF2205, 2304, 2507 and 25.10.4L were employed to investigate the connections between phase separation and mechanical properties from different microstructures (base metal, heat-affected-zone and welding bead) in welding. Moreover, the effect of external tensile stress during aging on phase separation of ferrite was also investigated. It was found that atom probe tomography is very useful for the analysis of phase separation in ferrite and the radial distribution function (RDF) is an effective method to compare the extent of phase separation at the very early stages. RDF is even more sensitive than frequency diagrams. In addition, the results indicate that the mechanical properties are highly connected with the phase separation in ferrite and other phenomena, such as Ni-Mn-Si-Cu clusters, that can also deteriorate the mechanical properties.QC 20130308
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Johnson, Lars. "Nanostructuring and Age Hardening in TiSCN, ZrAlN, and TiAlN Thin Films." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56221.
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This thesis explores nanostructuring in TiSiCN, ZrAlN, and TiAlN thin films deposited by cathodic arc evaporation onto cemented carbide substrates, with intended applications for cutting tools. The three systems were found to exhibit age hardening upon annealing, by different mechanisms, into the superhard regime (≥30 GPa), as determined by a combination of electron microscopy, X-ray diffraction, atom probe tomography, erda, and nanoindentation tech- niques. TiSiCN forms nanocomposite films during growth by virtue of Si segregation to the surface of TiCN nanocrystallites while simultaneously pro- moting renucleation. Thus, the common columnar microstructure of TiCN and low-Si-content (≤5 at. %) TiSiN-films is replaced by a “feather-like” nanos- tructure in high-Si-content (≥10 at. %) TiSiCN films. The presence of C promotes the formation of this structure, and results in an accelerated age hardening beginning at temperatures as low as 700 °C. The thermal stability of the TiSiCN films is, however, decreased compared to the TiSiN system by the loss of Si and interdiffusion of substrate species; C was found to ex- acerbate these processes, which became active at 900 °C. The ZrAlN system forms a two-phase nanostructure during growth consisting of cubic ZrAlN and wurtzite ZrAlN. Upon annealing to 1100 °C, the c-Zr(Al)N portion of the films recovers and semicoherent brick-like w-(Zr)AlN structures are formed. Age hardening by 36 % was obtained before overageing sets in at 1200 °C. As-deposited and annealed solid solution Ti0.33Al0.67N thin films were characterized for the first time by atom probe tomography. The as-deposited film was found to be at the very initial stage of spinodal decomposition, which continued during annealing of the film at 900 °C for 2 h. N preferentially segregates to Al-rich domains in the annealed sample, causing a compositional variation between Ti-rich and Al-rich domains, to maintain the stoichiometry for the developing AlN phase. That effect also compensates for some of the coherency strain formed between cubic domains of TiN and AlN. Finally, a possible Kirkendall effect caused by an imbalance in the metal interdiffusion during the spinodal decomposition was discovered.
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Gwalani, Bharat. "Developing Precipitation Hardenable High Entropy Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011755/.
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High entropy alloys (HEAs) is a concept wherein alloys are constructed with five or more elements mixed in equal proportions; these are also known as multi-principle elements (MPEs) or complex concentrated alloys (CCAs). This PhD thesis dissertation presents research conducted to develop precipitation-hardenable high entropy alloys using a much-studied fcc-based equi-atomic quaternary alloy (CoCrFeNi). Minor additions of aluminium make the alloy amenable for precipitating ordered intermetallic phases in an fcc matrix. Aluminum also affects grain growth kinetics and Hall-Petch hardenability.
The use of a combinatorial approach for assessing composition-microstructure-property relationships in high entropy alloys, or more broadly in complex concentrated alloys; using laser deposited compositionally graded AlxCrCuFeNi2 (0 < x < 1.5) complex concentrated alloys as a candidate system. The composition gradient has been achieved from CrCuFeNi2 to Al1.5CrCuFeNi2 over a length of ~25 mm, deposited using the laser engineered net shaping process from a blend of elemental powders. With increasing Al content, there was a gradual change from an fcc-based microstructure (including the ordered L12 phase) to a bcc-based microstructure (including the ordered B2 phase), accompanied with a progressive increase in microhardness. Based on this combinatorial assessment, two promising fcc-based precipitation strengthened systems have been identified; Al0.3CuCrFeNi2 and Al0.3CoCrFeNi, and both compositions were subsequently thermo-mechanically processed via conventional techniques. The phase stability and mechanical properties of these alloys have been investigated and will be presented. Additionally, the activation energy for grain growth as a function of Al content in these complex alloys has also been investigated.
Change in fcc grain growth kinetic was studied as a function of aluminum; the apparent activation energy for grain growth increases by about three times going from Al0.1CoCrFeNi (3% Al (at%)) to Al0.3CoCrFeNi. (7% Al (at%)). Furthermore, Al addition leads to the precipitation of highly refined ordered L12 (γ′) and B2 precipitates in Al0.3CoCrFeNi. A detailed investigation of precipitation of the ordered phases in Al0.3CoCrFeNi and their thermal stability is done using atom probe tomography (APT), transmission electron microscopy (TEM) and Synchrotron X-ray in situ and ex situ analyses.
The alloy strengthened via grain boundary strengthening following the Hall-Petch relationship offers a large increment of strength with small variation in grain size. Tensile strength of the Al0.3CoFeNi is increased by 50% on precipitation fine-scale γ′ precipitates. Furthermore, precipitation of bcc based ordered phase B2 in Al0.3CoCrFeNi can further strengthen the alloy. Fine-tuning the microstructure by thermo-mechanical treatments achieved a wide range of mechanical properties in the same alloy. The Al0.3CoCrFeNi HEA exhibited ultimate tensile strength (UTS) of ~250 MPa and ductility of ~65%; a UTS of ~1100 MPa and ductility of ~30%; and a UTS of 1850 MPa and a ductility of 5% after various thermo-mechanical treatments. Grain sizes, precipitates type and size scales manipulated in the alloy result in different strength ductility combinations. Henceforth, the alloy presents a fertile ground for development by grain boundary strengthening and precipitation strengthening, and offers very high activation energy of grain growth aptly suitable for high-temperature applications.
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Shrestha, Sachin. "Characterising the effect of Niobium-rich clusters on the microstructure-property relationships in CASTRIP® steels." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10297.
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Many properties of steels, especially those that are important for engineering purposes, are determined by their microstructures. Therefore the key driver to controlling properties of these materials lies within the characterisation and manipulation of their microstructure down to their atomic-scale structure. For industrial product development, strength and ductility are considered to be the most important properties and are highly ‘microstructure sensitive’. This thesis investigates the effect of niobium microalloying and clustering on the microstructure-property relationship of ultra-thin strip cast steels produced by the CASTRIP® steel manufacturing process using mechanical testing and advanced microanalysis techniques. The CASTRIP® process is a revolutionary new method of steel strip casting that requires significantly less energy, time, equipment, and floor space compared to conventional strip casting methods. New and improved microanalysis characterisation techniques were also developed as a part of this project in order to better characterise these steels. The work presented in this thesis will have industrial and scientific significance that is both of benefit to the CASTRIP® steel making process and its products and more generally for the microstructural characterisation of ferrous alloys, one of the most important classes of engineering materials.
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Di, russo Enrico. "Etude de biais de mesure de composition par SAT dans les matériaux semi-conducteurs." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR065/document.
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La Sonde Atomique Tomographique (SAT) assistée par laser (La-APT) est un outil puissant pour étudier la distribution atomique 3D des espèces chimiques dans une grande variété de matériaux semi-conducteurs. Cependant, des biais de composition importants affectent les analyses de sondes atomiques révélant une composition non stœchiométrique. Dans cette thèse, une étude systématique de certains semi-conducteurs binaires (GaN, GaAs, ZnO) et ternaires (AlGaN, MgZnO) a été menée afin de: (i) obtenir une description cohérente des biais de composition en APT; (ii) identifier les mécanismes physiques à l'origine de ces biais; (iii) évaluer les conditions expérimentales pour lesquelles l'analyse compositionnelle est fiable. Afin d’interpréter les résultats, l’hypothèse de l’évaporation préférentielle d’espèces métalliques (Ga, Al, Zn, Mg) à haut champ et d’émission de molécules neutres non métalliques (N2, O2) à champ bas a été proposée. Un autre objectif important de cette thèse est orienté vers la physique des matériaux. L’étude de la composition et la morphologie de certains dispositifs d’intérêt technologique, tels que les systèmes à multi-puits quantiques, est très important. Dans cette perspective, la connaissance du champ de composition 3D et de la morphologie de ces systèmes est essentielle car ces caractéristiques déterminent leurs propriétés optiques et électriques. Pour ce faire, une approche par microscopie corrélative peut être adoptée. Cette approche a été appliquée avec succès à l'étude des multi-puits quantiques ZnO/MgZnO conçus pour les lasers à cascade quantique. Les propriétés structurales, compositionnelles et optiques ont été étudiées en effectuant la tomographie par électrons (ET) - micro-photoluminescence (µ-PL) corrélative sur les mêmes échantillons de sonde atomique. Les analyses complémentaires APT et ET donnent une image claire de la structure et de la composition du système étudié, révélant d'importants phénomènes de décomposition dans l'alliage MgZnO. En particulier, La SAT s’est révélé une technique unique pour une évaluation directe de la composition locale. De plus, la µ-PL apparait extrêmement utile pour obtenir des informations relatives à la composition, en lien avec les résultats de La-APT. Enfin, nous présentons une nouvelle approche in-situ corrélative dans laquelle les mesures APT et µ-PL sont exécutées simultanément. Grâce au développement d'une sonde atomique tomographique spécialement conçue, on démontre que la µ-PL peut être mesurée avec succès sur une pointe de sonde atomique Zn :/MgZnO pendant nos analyse. Ceci est extrêmement attrayant car cela permet de corréler strictement le signal de photoluminescence avec les volumes explorés à l'échelle nanométrique. En principe, émission depuis des d'émetteurs de lumière quantiques uniques (c'est-à-dire un seul QW ou QD) peut être révélée. La nouvelle approche présentée peut être étendue à un large éventail de matériaux, ouvrant de nouvelles perspectives pour les études corrélativesLaser-assisted Atom Probe Tomography (La-APT) is a powerful tool for investigating the 3D atomic distribution of the chemical species in a wide variety of semiconductor materials. However, important compositional biases affect atom probe analyses revealing a non-stoichiometric composition. In the thesis a systematic study of selected binary (GaN, GaAs, ZnO) and ternary (AlGaN, MgZnO) semiconductors of high technological interest was developed in order to: (i) obtain a coherent description of the compositional biases in APT; (ii) identify the physical mechanisms leading to these biases; (iii) assess the experimental conditions for which the compositional analysis is reliable. In order to interpret the results, the hypothesis of preferential evaporation of metallic species (Ga, Al, Zn, Mg) at high field and emission of neutral non-metallic molecules (N2, O2) at low field has been proposed. Another important aim of this thesis is materials physics-oriented. It is indeed of utmost importance to study both composition and morphology of some devices of technological interest, such as in multi-quantum-well systems. In this perspective, the knowledge of 3D composition field and morphology is essential because these features determine the optical and electrical properties of the systems. In order to do it, a correlative microscopy approach can be adopted. This approach was successfully applied to the study of ZnO/MgZnO multi-quantum wells designed for quantum cascade lasers. Structural, compositional and optical properties were investigated performing correlative La-APT - Electron Tomography (ET) - micro-PhotoLuminescence (µ-PL) on the same atom probe tip specimens. The complementary APT and ET analyses yield a clear picture of the structure and composition of the system investigated, revealing important decomposition phenomena in the MgZnO alloy. In particular, La-APT proved to be a unique technique for a direct assessment of local composition. Moreover, µ-PL also proved to be extremely useful in order to get information related the composition, supporting La-APT results. Finally, a new correlative in-situ approach in which La-APT and µ-PL are simultaneously performed is presented. Thanks to the development of a specially designed tomographic atom probe, it is shown that µ-PL can be successfully performed on a single Zno/MgZnO atom probe tip during La-APT. This is extremely attractive and challenging because allows to strictly correlating the variation photoluminescence signal with nano-metric scale volumes of the tip evaporated during APT. In principle, the emission of single quantum light emitters (i.e. single QW or QD) can be revealed. The new approach presented can be extended to a wide range of materials, opening new perspectives for correlative studies of single atom probe tips
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El, Kousseifi Mike. "Ni silicide contacts : Diffusion and reaction in nanometric films and nanowires." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4349.
Full textAbstract:
Cette thèse porte sur l'étude des phénomènes qui se produisent lors de la réaction métal-silicium (siliciuration) en couches minces et dans des nanofils. En effet, les phénomènes tels que la germination, la croissance latérale, la croissance normale et la diffusion doivent être compris pour réaliser les contacts des futurs dispositifs de la microélectronique. La comparaison entre la siliciuration en couches minces et dans les nanofils est l'un des principaux aspects de ce travail. La distribution atomique en 3D des éléments chimiques dans les différentes siliciures de Ni a été obtenue par sonde atomique tomographique (SAT). Pour permettre l'analyse par SAT de différents types des nanofils à base de silicium, plusieurs méthodes originales de préparation des échantillons par faisceau d'ions focalisés ont été développées et testées. D'autre part, des mesures in situ et en temps réel de diffusion réactive par diffraction de rayons X ont permis de mettre en évidence l'importance de la germination dans la formation des phases et de déterminer les cinétiques de formation des siliciures de Ni allié en Pt, notamment des régimes de réaction aux interfaces et de croissance latérale. La forme caractéristique associée à la croissance latérale a été déterminée par des analyses ex situ de microscopie électronique en transmission et comparée aux modèles existants. La détermination par SAT de l'espèce qui diffuse majoritairement donne aussi des indications sur les mécanismes de formation des phases et de relaxation des contraintes dans les siliciuresThis thesis focuses on the phenomena that occur during the reaction between metal and silicon (silicide) on thin films and nanowires. Indeed, phenomena such as nucleation, lateral growth, normal growth and diffusion must be understood to make contacts for future microelectronic devices. The comparison between the silicide formation on thin films and nanowires is one of the main aspects of this work. Atomic distribution in 3D for the elements in different Ni silicide phase was obtained by atom probe tomography (APT). To enable the analysis of different types of silicon nanowires by APT, several original methods for sample preparation by focused ion beam has been developed and tested. On the other hand, in situ and real-time analysis by X-ray diffraction during the reactive diffusion helped to highlight the importance of the nucleation of a phase and to determine the kinetics of formation of Ni(Pt) silicides, including the reaction on the interfaces and the lateral growth. The characteristic shape associated with the lateral growth was determined by ex-situ transmission electron microscopy analyzes and was compared with the existing theoretical models. Moreover, the determination of the fastest diffusing species by APT provided information on the mechanisms of phase formation and stress relaxation in the silicide