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Tesis sobre el tema "Secondary ion mass spectrometer"

Autor: Grafiati

Publicado: 25 de mayo de 2024

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1

Freeman, Stewart Peter Hans Thielbeer. "The radiocarbon microprobe : an imaging secondary ion accelerator mass spectrometer". Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314932.

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2

Li, Libing. "Strategies for secondary ion yield enhancements in focused ion beam secondary ion mass spectrometry". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11806.

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3

Lemire, Sharon Warford. "Rigorous analytical applications of liquid secondary ion mass spectrometry/mass spectrometry". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30026.

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4

Jones, Brian N. "The development of MeV secondary Ion mass spectrometry". Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580361.

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ABSTRACT. The main aim of the research presented in this dissertation is to develop a novel imaging mass spectrometry technique that uses molecular desorption induced by heavy ions accelerated to kinetic energies in the MeV/u regime. Upon impact with a sample, heavy ions accelerated above the Bohr velocity deposit their energy predominantly through electronic stopping and this has been shown to produce high sputtering yields from an insulating sample's surface. This interaction has been traditionally called electronic sputtering and was first put to analytical use many decades ago by a technique called Plasma Desorption Mass Spectrometry (PDMS). Despite its inability to provide spatially resolved measurements, PDMS became a popular way to analyse biomolecular samples until other techniques, such as matrix-assisted laser desorption/ionisation (MALDI), became readily available. There are many ion beam analysis (IBA) facilities currently operating throughout the world dedicated to accelerating and focusing ion beams with the required kinetic energy to induce electronic sputtering, but until this work there has not been any attempt to develop a time-of-flight secondary ion mass spectrometry (ToF-SIMS) technique that makes use of a scanning proton microprobe facility. This research, therefore, has been performed at the Surrey Ion Beam Centre to explore the benefits of exploiting electronic sputtering in imaging mass spectrometry studies using existing IBA technology and techniques. Due to its initial success, this novel imaging mass spectrometry technique has recently been recognised as "MeV -SIMS" by the international scientific community. As will be presented in the final chapter, because MeV primary ions can be focused through thin exit windows to analyse a sample without the need for a vacuum chamber, MeV-SIMS has recently been developed into a fully ambient pressure technique.

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5

Hearn, M. J. "Polymer surface studies by Secondary Ion Mass Spectrometry". Thesis, De Montfort University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380743.

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6

Coath, Christopher D. "A study of ion-optics for microbeam secondary-ion mass spectrometry". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335723.

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7

Gilmore, Ian Stuart. "Development of a measurement base for static secondary ion mass spectrometry". Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/11110.

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This work sets out a framework to provide a metrological basis for static SIMS measurements. This surface analytical technique has been is use for over thirty years but, because of the lack of an infrastructure, has not achieved its full potential in industry. To build this basis, the measurement chain is studied from the sample through to the detector and data processing. By understanding the effects of each link in the chain, repeatabilities are reduced by orders of magnitude to below 1%, the ion beam current and flux density are calibrated to better than 2%, ion beam damage in polymers is controlled and detection efficiencies calculated. Utilising these developments, a characterised and calibrated SIMS spectrometer is used to establish reference materials. An inter-laboratory study to assess the extent of spectrum variability between spectrometers was conducted involving over twenty laboratories worldwide. Analysis of the data gives the level of repeatability and reproducibility using current procedures. Repeatabilities for some laboratories are as good as 1% but many are at 10% and a few as poor as 80%. A Relative Instrument Spectral Response, RISR, is developed to facilitate the comparison of spectra from one instrument to another or library data. For most instruments reproducibilities of 14% are achievable. Additionally, the wide variety of ion beam sources and energies, presently in use, result in spectra that are only broadly comparable. A detailed study of these effects provides, for the first time, a unified method to relate the behaviour for all ion species and energies. A development of this work gives a totally new spectroscopy, known as G-SIMS or gentle-SIMS. Here, the static SIMS spectrum for a low surface plasma temperature is calculated which promotes those spectral intensities truly representative of the analysed material and reduces those caused by additional fragmentation and rearrangement mechanisms. The resulting GSIMS spectra are easier to identify and are interpreted more directly. This work provides the essential basis for the development of static SIMS. Future work will improve the consistency of library data so that the valid data for molecular identification can be uniquely extracted. The measurement base will be developed to meet the growing requirements for static SIMS analysis of complex organic and biomaterials.

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8

John, Gareth David. "Secondary ion mass spectrometry and resonant ionisation mass spectrometry studies of nickel contacts to silicon carbide". Thesis, Swansea University, 2004. https://cronfa.swan.ac.uk/Record/cronfa42495.

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Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and resonant ionisation mass spectrometry (RIMS) have been used to perform depth profile analyses on nickel (Ni) contacts to silicon carbide (SiC) to understand the interfacial properties. In particular, as-deposited Schottky contacts and high temperature annealed Ohmic contacts have been characterised. Previous literature had indicated that the chemistry of the interface controlled the electrical properties of the contact. Using the TOF-SIMS system, depth profiles have been performed with the standard duoplasmatron ion source and a newly introduced liquid metal ion gun. Sputtering conditions have been optimised enabling detailed depth profiling of Schottky and Ohmic samples. The data from these samples have indicated a distinct difference between the two contact types. Schottky samples have been shown to have an abrupt interface with any interfacial reaction appearing to be confined to the intimate interface. This region had no significant affect on ion yield. Conversely, the Ohmic samples exhibited an extended Si composition well into the Ni contact layer. Moreover, the ion yield varied substantially throughout the contact layer indicating matrix changes were present as a result of annealing to 1000&C. RIMS studied the variation of Ni atoms sputtered into the Ni ground state (a3F4) and first excited state (a3D3) to determine variation in chemical bonding as a function of depth through the contact. Using a defocused ion beam passing through an aperture, detailed depth profiles were obtained by using two-colour, two-step resonant ionisation scheme. Again, a significant variation exists between the RIMS signals from Ohmic and Schottky samples. The ratio of the excited state to ground state for Ni showed measurable variations indicative of multiple Ni-silicide phases. Models for these interfaces are proposed and support other studies performed on this material system. The success of these techniques is reviewed together with suggestions for experimental development.

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9

De, Souza Roger A. y Manfred Martin. "Secondary ion mass spectrometry and its application to diffusion in oxides". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186567.

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10

De, Souza Roger A. y Manfred Martin. "Secondary ion mass spectrometry and its application to diffusion in oxides". Diffusion fundamentals 12 (2010) 9, 2010. https://ul.qucosa.de/id/qucosa%3A13868.

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11

Balderas, Sara. "Application of coincidence ion mass spectrometry for chemical and structural analysis at the sub-micron scale". Texas A&M University, 2005. http://hdl.handle.net/1969.1/2530.

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Surfaces can be probed with a variant of secondary ion mass spectrometry (SIMS) where the bombardment is with a sequence of single keV projectiles, each resolved in time and space, coupled with the separate record of the secondary ions (SIs) ejected from each projectile impact. The goal of this study was to demonstrate an efficient mode of SIMS where one obtains valid analytical information with a minimum of projectiles and hence a minimum of sample consumption. An inspection of the ejected SIs from individual bombardment events will reveal ??super efficient?? collision cascades i.e., events, where two or more secondary ions were emitted simultaneously. It has been shown that these coincidental emissions can provide information about the chemical composition of nano-domains. Previous studies using coincidence counting mass spectrometry (CCMS) indicated an enhancement of identifying correlations between SIs which share a common origin. This variant of SIMS requires an individual projectile impact thus causing SI emission from a surface area of ~5 nm in radius. Thus, in an event where two or moreSIs are ejected from a single projectile impact, they must originate from atoms and molecules co-located within the same nano-domain. Au nanorods covered by a 16-mercaptohexadecanoic acid (MHDA) monolayer were analyzed using this methodology. A coincidence ion mass spectrum was obtained for the MHDA monolayer covered Au nanorods which yielded a peak for a Au adduct. Similar results were obtained for a sample with a MHDA monolayer on a Au coated Si wafer. A series of samples consisting of Cu aggregates and AuCu alloys were investigated by SIMS to demonstrate that this technique is appropriate for characterizing nanoparticles. The mass spectra of these samples indicated that Au200 4+ is an effective projectile to investigate the surface of the target because it was able to penetrate through the poly(vinylpyrrolidone) (PVP) stabilizer that coated the surface of these nanoparticles. Coincidence mass spectra of the Cu aggregates yielded molecules colocated within the same nano-domain. Finally, this methodology was used to investigate surface structural effects on the occurrence of ??super-efficient?? events. The results indicated that it is possible to distinguish between two phases of ??-ZrP compounds although the stoichiometry remains the same.

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12

Karahan, Mehmet Cem. "Laser-assisted secondary ion mass spectroscopy and its applications in practical surface analysis". Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/karahan/KarahanM0805.pdf.

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13

Li, Zhen. "Characterization of surface and layered films with cluster secondary ion mass spectrometry". Texas A&M University, 2007. http://hdl.handle.net/1969.1/85794.

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Cluster secondary ion mass spectrometry (SIMS) analyses of layer-by-layer thin films were performed to investigate the depth/volume of SI emission and accuracy of the SI signal. The thin-layered samples were assembled by alternate adsorption of polyethylenimine (PEI), polystyrene sulfonate (PSS), polydiallyldimethylammonium chloride (PDDA) and clay nanoparticles. The films have controlled 3-D structure to test the depth of secondary ion (SI) emission and evaluate planar homogeneity. The SI emission depth is ~ 6-9 nm with 136 keV Au400 4+ (340 eV/atom) and 26 keV C60 + (433 eV/atom) projectile impacts. The diameter of the SI emission area is ~ 15 nm by assuming a semispherical emission volume. The SI yields oscillate with the alternation of the compositions of the topmost layers, which was observed with small cluster projectiles (CsICs+ and Au3 +) as well as with the large cluster projectiles (C60 + and Au400 4+). The SI signals of C- and CH- are enhanced in the presence of metal atoms in the expanding plume. Recoiled C60 projectile fragments (m/z=12, 13, 36) are observed in the SI mass spectra. Caution must be taken when monitoring the yields of such carbon cluster ions from organic surfaces because their yields don't reflect the true surface concentration. The Au400 4+ projectile impacts produce abundant co-emission. The correlation coefficient between the co-emitted SIs can be used to evaluate the planar homogeneity. The results show that the PSS layer is more uniform than the clay layers. The effect of alkali metal ion implantation on the nature and abundance of SI emission was investigated on Cs+ or Na+ implanted glycine samples. The alkali metal implantation induces surface damage and decreases the glycine molecular ion yields. Glycine molecular ions and fragment ions (CN-, CNO-) are emitted from different depths and locations of the emission volume. The same implanted glycine sample analyzed with different cluster projectiles (Au400 4+ and C60 +) shows different trends in the yields of molecular and fragment ions, which suggest a different mechanism of SI emission with different projectile impacts. The Na+ beam induces more surface damage compared with the Cs+ at equal impact energy.

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14

Fox, Harvey Stuart. "A study of shallow implants in silicon by secondary ion mass spectrometry". Thesis, University of Warwick, 1989. http://wrap.warwick.ac.uk/99683/.

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This project investigates the analysis of shallow implants by secondary ion mass spectrometry (SIMS) and the problems that arise from it. Ion implantation is now almost exclusively used in the manufacture of modern very large scale integration devices. The quantification of these implants can be carried out very successfully by SIMS. However the distortions that are present in any SIMS analysis are emphasised when the implanted layer is less than lOOnm below the surface. In order to characterize these distortions, it is necessary to be able to accurately parameterize the implant profile. Taking moments of the data was found to be a reliable method of doing this without constructing a distribution. Once a parameterizing method was found the differential shift was investigated in silicon, with and without a Si-MBE grown capping layer. The results suggested that the differential shift may be a depth dependant phenomenon. The effect of the amorphization of a crystal on ion implantation was investigated with respect to the change in sputter rate going through the damaged region. The effect of uneven etching on this study is discussed in detail. In order to overcome this uneven etching two different raster scan units are discussed. One, is a new totally computer controlled device for use on a new SIMS instrument. The other is a modification to an existing scan unit. This second unit has been used to make craters that are flat to 0.05%.

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15

Dickinson, Michelle. "Secondary ion mass spectrometry (SIMS) analysis of the arsenic-hyperaccumulator, Pteris vittata". Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422557.

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16

Kunkel, Gary John. "Interlaboratory comparisons of fast atom bombardment and liquid secondary ion mass spectra of diquaternary pyridinium oxime salts". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/27336.

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17

Montgomery, Neil James. "Analysis of superconducting thin films and their substrates using secondary ion mass spectrometry". Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266425.

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18

Smart, K. E. "High resolution secondary ion mass spectrometry analysis of trace metals in biological materials". Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442655.

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19

Ghumman, Chaudhry Amjad Ali. "Time-of-flight secondary ion mass spectrometry: new application for urinary stones analysis". Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/8796.

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20

Wilson, Roderick Charles. "The design, construction and characterisation of an ion optical system for Sputtered Neutral and Secondary Ion Mass Spectrometry". Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334920.

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21

Piehowski, Paul D. Ewing Andrew Graham. "Investigating lipid heterogeneity in single cells using time-of-flight secondary ion mass spectrometry". [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4585/index.html.

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22

Théberge, Roger. "An investigation of the beam-induced dehalogenation process in liquid secondary ion mass spectrometry". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq26743.pdf.

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23

Cooke, Graham Alan. "The development of secondary ion mass spectrometry for two-dimensional impurity profiling in semiconductors". Thesis, University of Warwick, 1992. http://wrap.warwick.ac.uk/109531/.

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As the dimensions of devices on integrated circuits are reduced, the importance of lateral spreading of implanted impurities increases. To maintain inter-device isolation and predictable performance, knowledge of the extent and concentration of these regions is necessary. A number of computer models have been produced to predict this information, however there is a serious lack of experimental data with which to verify their results. Secondary Ion Mass Spectrometry (SIMS) has been used for many years to provide depth profiles with high sensitivity and depth resolution, however, direct application of SIMS will not yield multi-dimensional results with enough spatial resolution and sensitivity to be useful. This is because the analyte volume is very limited. This thesis describe the development of a technique that increases the volume available for analysis by means of a special sample. The sample geometry introduces an inherent magnification that permits the use of a relatively large, low energy, reactive ion probe. This in tum provides high sensitivity - due to enhanced secondary ion yields - and good depth resolution - due to the low range of the probe. Using a quadrupole SIMS instrument, and a 50 μm FWHM oxygen probe, spatial resolutions of less than 70 nm have been demonstrated with a sensitivity of better than 1017 atoms cm3 for boron implants in silicon.

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24

Eccles, Adrian John. "The design, construction and characterisation of a microfocused ion/atom gun for use in secondary ion mass spectrometry (SIMS)". Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334868.

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25

Harton, Shane Edward. "Investigation of Polymer Phase Behavior at Heterogeneous Polymer-Polymer Interfaces using Secondary Ion Mass Spectrometry". NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-03012006-131419/.

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Changes in the thermodynamic behavior of polymer blends from bulk to heterogeneous interfaces is investigated using secondary ion mass spectrometry (SIMS). The use of a magnetic sector spectrometer (CAMECA IMS-6f) is fully explored in order to determine the optimal conditions in which to probe polymer surfaces and heterogeneous interfaces using three bilayer film systems, namely polystyrene (PS) with poly(methyl methacrylate) (PMMA), poly(cyclohexyl methacrylate) (PCHMA) with PMMA, and PS with poly(2-vinylpyridine) (P2VP). Two primary ion beams have been employed, O2+ with detection of positive secondary ions, and Cs+ with detection of negative secondary ions. It was found that each polymer thin film system must be closely investigated in order to determine the optimal conditions for depth profiling using SIMS. Three types of systems were further investigated using SIMS.

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26

Moore, Katie Louise. "High resolution secondary ion mass spectrometry analysis of trace elements in cereal grain and roots". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:ab4f4a19-baca-48a7-af54-b9c5d87f3b7a.

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This thesis presents information on the subcellular localisation of two important trace elements, selenium and arsenic, in wheat, rice and rice roots for what is believed to be the first time. The general aim of this work was to illustrate the potential of using physical science techniques to solve biological problems. High resolution secondary ion mass spectrometry was undertaken using the CAMECA NanoSIMS50 with a sensitivity down to ppm concentrations and a lateral resolution of less than 100 nm. Selenium in wheat grain was found to be distributed across both the bran layer and the endosperm region with Se-rich hotspots found in the aleurone cells and a higher intensity of Se in the subaleurone region. Arsenic in rice grain was found in two key regions. In grains with high As and high dimethylarsinic acid (DMA) content, As was predominantly localised to the subaleurone region yet in lower concentration, hydroponically grown As(III)-treated grains the As was only localised to the aleurone layer near the ovular vascular trace (OVT). A combined NanoSIMS and S-XRF experiment revealed As hotspots near the OVT. A combination of high pressure freezing, high resolution secondary ion mass spectrometry and TEM was used to localise As in the roots of rice plants revealing a contrasting subcellular distribution of As and Si in the roots even though arsenite and silicic acid are transported across the plasma membranes by the same transporters. Fe plaque forms only on the root epidermis and was shown to be a strong sink for As. Colocalisation of S with As in the vacuoles of the endodermis, pericycle and xylem parenchyma supports the notion that As is stored as arsenite-phytochelatin complexes in the roots while Si is localised in the endodermis cell walls and is not strongly affected by the Lsi2 mutation.

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27

Salman, Fatma. "EXPERIMENTAL STUDY OF PROFILES OF IMPLANTED SPECIES INTO SEMICONDUCTOR MATERIALS USING SECONDARY ION MASS SPECTROMETRY". Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3056.

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ABSTRACT The study of impurity diffusion in semiconductor hosts is an important field that has both fundamental appeal and practical applications. Ion implantation is a good technique to introduce impurities deep into the semiconductor substrates at relatively low temperature and is not limited by the solubility of the dopants in the host. However ion implantation creates defects and damages to the substrate. Annealing process was used to heal these damages and to activate the dopants. In this study, we introduced several species such as alkali metals (Li, Na, K), alkali earth metals (Be, Ca,), transition metals (Ti, V, Cr, Mn) and other metals (Ga, Ge) into semiconductor substrates using ion implantation. The implantation energy varies form 70 keV to 200 keV and the dosages vary between ~ 1.0x1012 and ~5.0x1015 atoms/cm2. The samples are annealed at different temperatures from 300°C to 1000°C and for different time intervals. The redistribution behaviors of the implanted ions are studied experimentally using secondary ion mass spectrometry (SIMS). We observed some complex distribution behaviors due to the defects created during the process of ion implantation. The diffusivities of some impurities are calculated and compared to previous data. It was found that the diffusivities of implanted impurities is related to the dosages, annealing temperatures and the defects and damages caused by ion implantation. Additionally, as we go from one type of semiconductor to another, the diffusion behavior of the impurities shows a different trend.
Ph.D.
Department of Physics
Sciences
Physics PhD

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28

Alturaifi, Huriyyah. "New capabilities for molecular surface and in-depth analysis with cluster secondary ion mass spectrometry". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/new-capabilities-for-molecular-surface-and-indepth-analysis-with-cluster-secondary-ion-mass-spectrometry(997f36ca-1bd6-42a0-a731-a4ddba055510).html.

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Energetic polyatomic cluster beams are increasingly used in materials processing and surface analysis applications. In secondary ion mass spectrometry (SIMS) such beams have previously been utilised to investigate the chemical distribution of organic molecules (polymers, biological molecules and pharmaceuticals etc). One important application is in organic electronics, where the depth-distribution of organic components is important in the device performance. Massive gas cluster ion beams (GCIBs) have produced more successful depth-profiles for organic electronic devices that smaller projectiles including SF5+ and C60+. However, further work is needed to investigate and optimise experimental parameters to deliver the necessary SIMS performance. This study focused on molecular depth profiling of organic insulator (PMMA) and semiconductor (PTAA and TIPS-pentacene) materials, in single and bi-layered combinations, utilising cluster SIMS, using C60+ and Arn+, at different temperatures and energies. In general, at room temperature, the best depth resolution was obtained, using large Ar-GCIBs of low energy per atom (E/n ~10 eV), in comparison with the smaller Ar-GCIBs or with C60+ beams at the same total impact energy. On materials which sputtering under C60+ bombardment, ion and neutral yields were greatest due to the higher E/n, compared with GCIBs. Data from PMMA show that the sputter yield under C60 and Arn projectiles conform to the published 'universal' dependence of Y/n to E/n. Depth profiling of the semiconductor compounds were unsuccessful, using C60+ projectiles. For depth profiles using large GCIB projectiles, an increase in the secondary ion yield was observed at the interface with the silicon substrate - a phenomenon which was not observed for the smaller projectiles. In general, the most successful depth profiles (i.e. more constant molecular and fragment secondary ion yields, observed at pseudo-steady-state regions) and best depth resolutions were obtained at cryogenic temperatures - conditions under which corresponding sputtering yields and secondary ion yields were suppressed.

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29

Jiang, Haibo. "Exploiting stable isotope imaging with high resolution secondary ion mass spectrometry for applications in biology". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:15456362-6022-41e1-b78d-1127d6d172b0.

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This thesis presents applications of high resolution secondary ion mass spectrometry (NanoSIMS) analysis for stable isotope imaging in biological samples. These projects were designed to explore the potential applications of NanoSIMS analysis, and to develop protocols and novel methodologies to visualize and quantify biological processes. Working with collaborators in the UK and USA, I have applied NanoSIMS analysis to study 3 research areas, including molecule interactions, single cell metabolisms and lipid imaging in tissues. Antimicrobial peptides (AMPs) play important role in the immune system, and understanding how AMPs interact with cell membranes can provide useful information to design new therapies to control infection. The pore structures and dynamics of the interaction of AMPs with membranes has been visualized for the first time and confirmed with combined AFM and NanoSIMS analysis. A correlative backscattered electron (BSE) imaging and NanoSIMS analysis methodology has been developed to study glutamine metabolism in single cancer cells. This method enables us to measure the chemical information in specific organelles in these cells and can be widely applied to study metabolisms and to trace the uptake of labelled molecules in biological matrices. Quantitative analysis on the effects of hypoxic conditions and the PYGL gene were studied. Applying correlative BSE and NanoSIMS analysis, I also studied lipid uptake mechanisms in various mouse tissues, including brown adipose tissue, heart, intestines, liver and skeletal muscle, mainly focused on a recently discovered protein, GPIHBP1, and its function in the lipid uptake process. TRL margination was proved to depend on the GPIBP1-LPL complex, and 3 stages of lipid transport from capillary lumen to lipid droplets was also visualized by combined BSE and NanoSIMS analysis.

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30

Berrueta, Razo Irma. "Molecular imaging of mouse brain tissue using Cluster Time-of-Flight Secondary Ion Mass Spectrometry". Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/molecular-imaging-of-mouse-brain-tissue-using-cluster-timeofflight-secondary-ion-mass-spectrometry(a350dc50-5337-4d32-a95c-24c617bbba97).html.

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ToF-SIMS imaging has been drawing attention due to the wide range of applications in the biological and biomedical fields. These applications include the acquisition of quantitative and qualitative data that ranges in scale from single cells to organs, image visualisation and interpretation of biomarkers for diagnosis and development of pharmaceutics. This study focused on molecular imaging of mouse brain tissue sections using cluster primary ion beams. First, cluster ion beams were applied to comparative background studies of biomolecules and brain total lipid extract. Enhancement of the secondary ion signal was observed using water-containing cluster primary ion beams, especially for [M+H]+ type secondary ions. Water-containing clusters were then used to acquire ToF-SIMS images from the cerebellar area of serial mouse brain tissue sections. Again, water-containing cluster beams produced the highest secondary ion yields in both grey and white matter, gaining a new level of insight into the lipid compositions of both types of tissue in the brain. A clinical case was also evaluated with ToF-SIMS imaging, using cluster beams for the analysis of 3xTg-AD mouse brain tissue. SIMS images were registered with fluorescence microscopy images for the in situ identification and co-localisation of the Amyloid-β plaques on the SIMS images. Spectra from regions of interest were analysed to identify possible ion fragments derived from the Aβ protein. The co-localisation of cholesterol was also studied from images obtained with different primary ion beams. The results presented show that cluster ToF-SIMS can be successfully applied to brain tissue imaging. New primary ion beam technologies allow us to acquire data with more useful secondary ion yield for clinical applications and biological research. Nevertheless, future technological improvements are required for specialised applications e.g. cellular imaging. Moreover, processing the data obtained is still challenging and more data processing tools are also needed for interpretation.

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31

Van, Nuffel Sebastiaan. "Three-dimensional time-of-flight secondary ion mass spectrometry imaging of primary neuronal cell cultures". Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39644/.

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Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has proven its ability to characterise (in)organic surfaces, and is increasingly used for the characterisation of biological samples such as single cells. By combining ion imaging and molecular depth profiling it is possible to render 3D chemical images, which provides a novel, label-free way to investigate biological systems. Major challenges lie, however, in the development of data analysis tools and protocols that preserve the cell morphology. Here, we develop and employ such tools and protocols for the investigation of neuronal networks. One of the reasons 3D ToF-SIMS imaging of cells is underused is the lack of powerful data analysis tools as 3D ToF-SIMS measurements generate very large data sets. To address this issue, we developed a method that allows the application of principal component analysis (PCA) to be expanded to large 3D images making 3D ToF-SIMS image processing of whole, intact cells and cellular networks with multivariate analysis now accessible on a routine basis. Using this method, we are able to separate cellular material from the substrate and can then correct z-offsets due to the cells' topography resulting in a more accurate surface heightmap. The method also facilitates differentiation between cellular components such as lipids and amino acids allowing the cell membrane, the cytoplasm and the extracellular matrix (ECM) to be easily distinguished from one another. These developments permit us to investigate the intracellular localisation of specific native and non-native compounds label-free, not just in single cells but also in larger cellular networks. The visualisation of the cellular uptake of non-native compounds, namely fluorescent dyes, in primary rat cortical neurons and the chemical differentiation between cell types, namely primary rat cortical neurons and retinal pigment epithelium (RPE) cells, are presented as applications. Even though the dyes have distinct fragment ions in the high mass range, it was not possible to detect the fluorophores by 3D ToF-SIMS imaging of freeze-dried cells. However, it was possible to detect distinct differences in the kind of ions detected for freeze-dried primary rat cortical neurons and RPE cells albeit in the low mass range. To obtain meaningful results, however, it is paramount that sample preparation does not induce significant physical or chemical changes. We present the first comprehensive comparison between large 3D ToF-SIMS images of freeze-dried and frozen-hydrated cells using PCA to facilitate the data analysis of these large data sets. A higher degree of colocalisation of the K+ signal with cell regions is observed for frozen-hydrated cells, which indicates a lower degree of membrane damage and migration of diffusible chemical species. Frozen-hydrated cell samples are therefore considered to best reflect the native cell state, but freeze-dried cell samples allow far easier sample handling. The mass spectrum of frozen-hydrated cellular material also has increased ion intensities for higher-mass fragments, which is an additional advantage, because the poor signal-to-noise ratio of molecular species with m/z > 200 is a major bottleneck in the advancement of ToF-SIMS imaging as a diagnostic tool.

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32

Giordani, Andrew J. "A Fundamental Study on the Relocation, Uptake, and Distribution of the Cs⁺ Primary Ion Beam During the Secondary Ion Mass Spectrometry Analysis". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/64998.

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Combining cesium (Cs) bombardment with positive secondary molecular ion detection (MCs+) can extend the analysis capability of Secondary Ion Mass Spectrometry (SIMS) from the dilute limit (<1%) to matrix elements. The MCs+ technique has had great success in quantifying the sample composition of III-V semiconductors as well as dopants and/or impurities; however, it has been less effective at reducing the matrix effect for IV compounds, particularly Si-containing compounds, due to Cs overloading at the surface during the analysis from the Cs primary ion beam. The Cs overloading issue is attributable to the mobility and relocation of the implanted Cs to the surface; this effect happens almost instantaneously. Once the surface is overloaded with Cs, the excess Cs begins to reneutralize the ionization Cs and, as a result, the MCs+ technique is ineffective at reducing the matrix effect. This research provides new insights for improving the MCs+ technique and elucidating the Cs mobility. A combination of multiple experimental techniques and theoretical modeling was implemented to assess the Cs retention, up-take, and distribution differences between group III-V and IV materials. Early experiments revealed a temperature-dependent component of the Cs mobility, prompting an investigation of this phenomenon. Therefore, we designed, built, and installed a variable temperature stage for our SIMS with temperatures ranging from -150 to 300 C. This enabled us to study the temperature-dependent component of the Cs mobility and the effect it has on the secondary ion emission processes. Additionally, a method was devised to quantify the amount of neutralization and ionization due to the relocated Cs. The results allow for a more thorough understanding of the material dependence on the Cs+-sample interaction and the temperature component of the Cs mobility.
Ph. D.

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33

Kordys, Jeanette. "Investigation of biological compounds with time-of-flight secondary ion mass spectrometry using atomic, polyatomic and cluster primary ion beams". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503042.

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34

Lau, Richard Yiu-Ting. "Study of surfaces of semi-crystalline polymers by static time-of-flight secondary ion mass spectrometry /". View abstract or full-text, 2010. http://library.ust.hk/cgi/db/thesis.pl?CBME%202010%20LAU.

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35

Lee, Joanna L. S. "Time-of-flight secondary ion mass spectrometry - fundamental issues for quantitative measurements and multivariate data analysis". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:f0e4b8ff-f563-429e-9e71-9c277a5139c4.

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Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the analysis of organic surfaces and interfaces for many innovative technologies. However, despite recent developments, there are still many issues and challenges hindering the robust, validated use of ToF-SIMS for quantitative measurement. These include: the lack of metrology and fundamental understanding for the use of novel cluster primary ion beams such as C60ⁿ⁺ and Ar₂₀₀₀⁺; the need for validated and robust measurement protocols for difficult samples, such as those with significant micron scale surface topography; the lack of guidance on novel data analysis methods including multivariate analysis which have the potential to simplify many time-consuming and intensive analyses in industry; and the need to establish best practice to improve the accuracy of measurements. This thesis describes research undertaken to address the above challenges. Sample topography and field effects were evaluated experimentally using model conducting and insulating fibres and compared with computer simulations to provide recommendation to diagnose and reduce the effects. Two popular multivariate methods, principal component analysis (PCA) and multivariate curve resolution (MCR), were explored using mixed organic systems consisting of a simple polymer blend and complex hair fibres treated with a multi-component formulation to evaluate different multivariate and data preprocessing methods for the optimal identification, localisation and quantification of the chemical components. Finally, cluster ion beams C60ⁿ⁺ and Ar_500-2500⁺ were evaluated on an inorganic surface and an organic delta layer reference material respectively to elucidate the fundamental metrology of cluster ion sputtering and pave the way for their use in organic depth profiling. These studies provide the essential metrological foundation to address frontier issues in surface and nanoanalysis and extend the measurement capabilities of ToF-SIMS.

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36

Wagner, Matthew Scott. "Characterization of adsorbed protein films using time of flight secondary ion mass spectrometry and multivariate analysis /". Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/9813.

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37

Tian, Hua. "Visualisation and profiling of lipids in single biological cells using time-of-flight secondary ion mass spectrometry". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/visualisation-and-profiling-of-lipids-in-single-biological-cells-using-timeofflight-secondary-ion-mass-spectrometry(c36313be-4ffd-4809-b5c9-8fbe1f720bd1).html.

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Imaging Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) has been developed to perform 2D imaging and depth profiling of biological systems with micron or submicron scale lateral resolution, which can be attributed to the advent of polyatomic ion beam particularly C60+ and new concept of ToF-SIMS instrument, the J105 3D Chemical Imager (J105). These recent advances in ToF-SIMS have opened a new dimension for biological analysis. In this study, 2D and 3D imaging have been performed on two biological systems, Xenopus laevis (X. laevis) zygote/embryo and murine embryonic fibroblasts NIH 3T3 BXB-ER cells to explore the capability of ToF-SIMS to handle the biological samples with extreme topography and high resolution depth profiling of microdomains, which still represent major challenges for the ToF-SIMS. The study on X. laevis embryo explored the capability of ToF-SIMS to handle spherical samples (approx. 1-1.2 mm in diameter), identify lipid species in mixtures of lipid extraction from the zygotes and image of an intact embryo in 2D/3D during dynamic biological events, e.g., fertilisation and early embryo development. For the first time the J105 and conventional BioToF-SIMS instrument were employed for the study of developmental biology. The major classes of lipid were identified through multiple lipid assay in a single analytical run using ToF-SIMS. Topography effects of the embryo were assessed through imaging a single intact zygote/embryo that revealed secondary ions loss at the edge of the single cell. However, the topography effects on the mass resolution could be minimised using the J105. Moreover, in situ lipid profiling of the zygote revealed different lipid compositions and intensities on the membrane of the animal and vegetal hemispheres. Furthermore, high resolution imaging and depth profiling that performed on a single intact cell in a time course study visualised the egg-sperm fusion sites on the membrane of the zygote 10 min post-insemination and lipids arrangement on the membrane of the embryo through the early development stages. Subcellular signalling upon the fertilisation was also spatially located on the serial cryosections of a single zygote. With the NIH 3T3 BXB-ER cells, the study firstly adopted a finely focused C60+ beam to track morphological changes and rearrangement of subcellular organelle mitochondria (0.5-2 µm) in response to the activation of Raf/ERK (extracellular signal regulated kinase) pathway using the J105. The SIMS images of the unlabelled cells showed the shifting of membrane distribution and nuclei shrinking following Raf/ERK activation. The mitochondria fluorescence probe within the cells were located 3-dimensionally using confocal microscopy and ToF-SIMS, which revealed the distribution pattern of condensing in the two sides of the nuclei following the Raf/ERK activation. Coupled with scanning electron microscopy (SEM), the three imaging modes showed good agreement in cellular morphological changes and subcellular mitochondrial rearrangement without or following Raf/ERK activation, demonstrating an integrated approaching to study the biological processes at subcellular dimension.

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38

Morrison, Lindsay J. "Application of MS/MS and Ion Mobility to the Characterization of Secondary and Tertiary Protein Structure". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406193833.

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39

Oran, Umut. "Surface chemical characterization of plasma-chemically deposited polymer films by time of flight static secondary ion mass spectrometry". [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/271/index.html.

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40

Bright, Nicholas J. "The application of time-in-flight secondary ion mass spectrometry for the analysis of overlapping fingerprints and inks". Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590925.

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Using the technology available to forensic investigators today, it is not currently possible to distinguish (with certainty) whether a fingerprint is above or below a layer of ink. This has implications where a suspect's fingerprint may be found on a document, but they claim to have handled the paper before any ink was put down on the paper, e.g. "I only put the paper in the drawer". Furthermore, most of the techniques destroy the sample, which in a forens ic context is not recommended. Fundamental experiments analysing fingerprints and inks on basic substrates such as silicon and paper have been carried out. A protocol for determining the deposition order of overlapping undeveloped fingerprints and inks using time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been developed. The developed protocol is based on using the normalised standard deviation of the intensity of an ink line, where that ink line overlaps with a fin gerprint. This method produces a numerical value for the sample, thereby removing any potential human error in judgement when imaging the sample alone. After further testing it was shown that this first protocol was not robust. A new method and protocol was developed based upon using the entirety of the data produced in the secondary ion image. This new protocol is based upon using the fingerprint ridge pattern as a mask on the ink line signal, rather than using line scans, which are less representative of the data collected. Further research revealed that when samples involving a fingerprint overlapping with ink are chemically developed the ability of the protocol to identify the deposition order was affected. In some samples, the chemical development process appears to have had a positive effect on the protocol. The results presented indicate that diazafluoren-9-one immersion could be used preferentially over ninhydrin when investigating questioned documents. These results could affect the order in which forensic investigators use different chemical development techniques to analyse evidence. Currently it is common practice to use more than one technique to develop fingerprints. The results presented Summary could lead to recommendations about the order in which chemical development techniques are used. Techniques, such as ToF-SIMS, require the use of a vacuum chamber into which the sample is placed for analysis. Currently, there is no published literature on the effect that low pressures systems (such as vacuum chambers) have on the chemistry of fingerprints. This research shows that pressures as low as 2xlO·3 Torr have the ability to remove 20-26% (depending on the exact pressure) of a fingerprint's mass. This suggests it would be beneficial to develop high pressure systems in order to carry out analyses in order to detect all chemical species present in a sample. It was also found that some vacuum chambers can in fact add mass to a sample (believed to be from chemical contamination).

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41

Huber, Anne-Katrin, Sven Ole Steinmüller, Eva Mutoro, Bjoern Luerßen y Jürgen Janek. "In situ examination of Lanthanum Strontium Manganate (LSM) with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186860.

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42

Huber, Anne-Katrin, Sven Ole Steinmüller, Eva Mutoro, Bjoern Luerßen y Jürgen Janek. "In situ examination of Lanthanum Strontium Manganate (LSM) with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)". Diffusion fundamentals 12 (2010) 52, 2010. https://ul.qucosa.de/id/qucosa%3A13889.

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43

Xia, Nan. "Time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization of conformation and orientation of adsorbed protein films /". Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9869.

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44

Sansom, David Andrew. "A study of secondary ion mass spectrometry (SIMS) depth profiling of ultra-narrow doping structures in III-V semiconductors". Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268022.

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45

Svilar, Ljubica. "Structural elucidation of secondary metabolites from Hypoxylon fragiforme, using high resolution mass spectrometry and gas-phase ion-molecule reactions". Paris 6, 2012. http://www.theses.fr/2012PA066468.

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Fungi produce a wide variety of biologically active compounds/metabolites that could be used for medicinal and pharmaceutical purposes. Mitorubrines, members of the family of azaphilones, constitute a particularly interesting set of structurally diverse secondary metabolites, exhibiting a wide range of biological activities (e. G. Antimicrobial, antibacterial, antimalarial). This work describes the development of several mass spectrometry-based approaches to solve the natural structural diversity and complexity of azaphilones extracted from Hypoxylon fragiforme fungus. The first part of this manuscript is dedicated to the development and validation of an analytical methodology involving liquid chromatography coupled to high resolution mass spectrometry for the efficient and accurate detection of trace-level azaphilones in complex fungal extracts. Further collision-induced dissociation and hydrogen/deuterium exchange experiments were performed to fully elucidate and characterize the azaphilones and their nitrogenized analogues from Hypoxylon fragiforme. The second part is devoted to the application of these different analytical strategies to the in-depth characterization of a novel family of secondary metabolites derived from azaphilones, the mitorubramines. Lastly, these different secondary metabolites were further purified to confirm their chemical structures by NMR spectroscopy
Les champignons produisent une grande variété de composés/métabolites biologiquement actifs qui peuvent être utilisés à des fins médicinales et pharmaceutiques. Les mitorubrines, membres de la famille des azaphilones, constituent un ensemble particulièrement intéressant de métabolites secondaires, présentant une grande étendue d’activités biologiques (e. G. Antimicrobienne, antibactérienne, antipaludique). Ce travail présente le développement de plusieurs approches de spectrométrie de masse permettant de résoudre la diversité structurelle naturelle et la complexité des azaphilones extraits des champignons Hypoxylon fragiforme. La première partie de ce manuscrit est dédiée au développement et à la validation d’une méthodologie analytique impliquant la chromatographie liquide couplée à la spectrométrie de masse haute résolution pour la détection efficace et précise de traces d’azaphilones dans des extraits fongiques complexes. En outre, des expériences de spectrométrie de masse en mode tandem (par dissociation induite par collision, CID) et d'échange hydrogène/deutérium ont été effectuées pour élucider et caractériser les azaphilones et leurs analogues azotés chez Hypoxylon fragiforme. La deuxième partie est consacrée à l'application de ces différentes stratégies analytiques pour la caractérisation approfondie d'une nouvelle famille de métabolites secondaires dérivés des azaphilones, les mitorubramines. Enfin, ces différents métabolites secondaires ont été purifiés pour confirmer leur structure chimique par spectroscopie RMN

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46

Rabbani, Sadia. "Advances in time-of-flight secondary ion mass spectrometry for the analysis of single cells on sub-cellular scale". Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/advances-intimeofflight-secondary-ion-mass-spectrometryfor-the-analysis-of-single-cells-on-subcellular-scale(6ba231f1-f084-45ab-89cc-c4359769778f).html.

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Time-of-flight the secondary ion mass spectrometry (ToF-SIMS) is becoming a promising technique in analysis of a biological system due to its chemical specificity and the ability to perform high spatial resolution imaging. The combination of novel cluster and polyatomic beams has allowed generating images to map the distribution of biological components in tissue sections and cell surfaces. However, under these conditions the cluster beams have to be operated in the static regime, which limits sensitivity and confines the molecular imaging to 2 μm spatial resolution. The polyatomic beams offer the benefits of high yields and low sub-surface damage, allowing the analysis to be performed at high ion fluence and abandoning the static limit. This presents a new approach to molecular imaging in which 'voxels' are used rather than pixels, thus increasing sensitivity. As a result, the current SIMS instrumentation then becomes a limitation and has to be modified. A novel SIMS instrument, the J105 3D Chemical Imager has been developed with Ionoptika, which allows taking full advantage of the polyatomic primary beam, particularly the C60 by using it in a dc mode with buncher-ToF configuration. The aim of this project was to prove the concept and the potential of this new instrument. Initially standard organic samples have been used to show the current performance of the J105 for the analysis of organic samples with respect to a conventional ToF-SIMS instrument, the BioToF. The tandem MS capability of the instrument has been tested and proved using standard samples and a lipid mixture of brain extract. HeLa cells, an immortalised cell line were analysed using this instrument in 2D and 3D imaging mode. The images generated show molecular localisation on a sub-cellular scale, over a practical timeframe, whilst sustaining high mass resolution at 4000. The cells were imaged using a 40 keV C60+ dc beam and a clear differentiation between the material within the nuclei and lipid membrane can be made. Investigation of cell preparation suggested that the frozen-hydrated approach may be beneficial. The data presented in this thesis validates the new instrument concept offering the advantages of higher mass detection, increase in sensitivity, and an increase in the duty cycle while at the same time allowing imaging at sub-cellular scale with higher mass resolution.

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47

Bradley, Shawn Todd. "Investigation of AlGaN films and nickel/AlGaN Schottky diodes using depth-dependent cathodoluminescence spectroscopy and secondary ion mass spectrometry". Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078329692.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxii, 182 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Leonard J. Brillson, Dept. of Electrical Engineering. Includes bibliographical references (p. 173-182).

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48

Falk, Mareike [Verfasser]. "Investigation of surface film formation on LiNi0.5Mn1.5O4 cathodes in carbonate based liquid electrolytes using the secondary ion mass spectrometry / Mareike Falk". Gießen : Universitätsbibliothek, 2014. http://d-nb.info/1068590211/34.

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49

Lau, Khim Heng. "Development and application of high-resolution secondary ion mass spectrometry analysis of therapeutic and imaging molecules in cells and tissue sections". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543023.

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50

Swinford, Richard William. "An AFM-SIMS Nano Tomography Acquisition System". PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3485.

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An instrument, adding the capability to measure 3D volumetric chemical composition, has been constructed by me as a member of the Sánchez Nano Laboratory. The laboratory's in situ atomic force microscope (AFM) and secondary ion mass spectrometry systems (SIMS) are functional and integrated as one instrument. The SIMS utilizes a Ga focused ion beam (FIB) combined with a quadrupole mass analyzer. The AFM is comprised of a 6-axis stage, three coarse axes and three fine. The coarse stage is used for placing the AFM tip anywhere inside a (13x13x5 mm3) (xyz) volume. Thus the tip can be moved in and out of the FIB processing region with ease. The planned range for the Z-axis piezo was 60 µm, but was reduced after it was damaged from arc events. The repaired Z-axis piezo is now operated at a smaller nominal range of 18 µm (16.7 µm after pre-loading), still quite respectable for an AFM. The noise floor of the AFM is approximately 0.4 nm Rq. The voxel size for the combined instrument is targeted at 50 nm or larger. Thus 0.4 nm of xyz uncertainty is acceptable. The instrument has been used for analyzing samples using FIB beam currents of 250 pA and 5.75 nA. Coarse tip approaches can take a long time so an abbreviated technique is employed. Because of the relatively long thro of the Z piezo, the tip can be disengaged by deactivating the servo PID. Once disengaged, it can be moved laterally out of the way of the FIB-SIMS using the coarse stage. This instrument has been used to acquire volumetric data on AlTiC using AFM tip diameters of 18.9 nm and 30.6 nm. Acquisition times are very long, requiring multiple days to acquire a 50-image stack. New features to be added include auto stigmation, auto beam shift, more software automation, etc. Longer term upgrades to include a new lower voltage Z-piezo with strain-gauge feedback and a new design to extend the life for the coarse XY nano-positioners. This AFM-SIMS instrument, as constructed, has proven to be a great proof of concept vehicle. In the future it will be used to analyze micro fossils and it will also be used as a part of an intensive teaching curriculum.

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