Mass spectrometry imaging (MSI) is a powerful tool that provides mass-specific surface images with micron or sub-micron spatial resolutions. In a microscope MSI experiment, large sample surfaces are illuminated with a defocused laser or primary ion beam, enabling all surface molecules to be desorbed and ionised simultaneously before being electrostatically projected onto a position-sensitive imaging detector at the end of a time-of-flight mass analyser. Traditionally only the image of one mass-to-charge ratio can be obtained in a single acquisition, which limits its applicability. However, the development of event-triggered sensors, such as CMOS-based cameras, revives the microscope MSI method by allowing multi-mass imaging. Therefore, the challenges facing microscope have MSI shifted to improving its mass resolution, effective mass range, and mass accuracy. This thesis proposes effective solutions to each of them, and thus significantly improves the performance and applicability of microscope MSI. To increase the mass range, two modified post-extraction differential acceleration (PEDA) techniques, double-field PEDA and time-variable PEDA, were used to demonstrate mass-resolved stigmatic imaging over a broad m/z range. In double-field PEDA, a potential energy cusp was introduced into the ion acceleration region of an imaging mass spectrometer, creating two m/z foci that were tuned to overlap at the detector plane. This resulted in two focused m/z distributions that stretched the mass-resolved window with m/Δm >= 1000 to 165 Da without any loss in image quality; a range that doubled the 65 Da achieved under similar conditions using the original PEDA technique. In time-variable PEDA, a dynamic pulsed electric field was used to maximize the effective mass range of PEDA. By simultaneously focusing ions between 300 to 700 m/z using an exponentially rising voltage pulse, time-variable PEDA provides an effective mass range more than six times wider than the original PEDA method. Although reflectrons are widely used to improve the mass resolving power of ToF-MS, incorporating them in a microscope MSI instrument is novel. A reflectron MSI instrument was designed and implemented. Simulations demonstrated that one-stage gridless reflectrons were more compatible with the spatial imaging goal of the microscope MSI instrument than the gridded reflectrons. Preliminary experimental results showed that coupling the gridless reflectron with single-field PEDA achieved a mass resolution above 8,000 m/Δm while keeping a spatial resolution of 20 um. In conclusion, the gridless reflectron was able to triple the mass resolving power without losing any spatial imaging power. The poor mass accuracy hurdle was overcome by machine learning algorithms, which can construct clinical diagnostic models that recognise the peak pattern of biological mass spectra and classify them accurately without knowing the actual mass of each peak. After a proof of concept "experiment", where the mass spectra of dye molecules were classified by various learning algorithms, three pairs of datasets (ovarian cancer, prostate cancer, chronic fatigue and their respective controls) were used to build classifiers that accurately distinguish blood samples from controls. Possible biomarkers were also discovered by evaluating the importance of each m/z feature, which may assist further studies.

Accelerator Mass Spectrometry (AMS) is a sensitive technique for the analysis of rare isotopes. Optimizing the output of the cesium-sputter ion source is a fundamental method for improving measurement precision, efficiency, and reliability. Several strategies for improving the ion source are discussed and lead to an understanding of the electrodynamics within the ion source to inform further improvement in design and operating parameters. At the Andr´e E. Lalonde Accelerator Mass Spectrometry Laboratory (Lalonde AMS), the High Voltage Engineering Europa (HVEE) SO-110C ion source was modelled using Integrated Engineering Software (IES)’s Lorentz-2E ion trajectory simulation software. Lorentz-2E incorporates the mutual space-charge interaction between the positively charged cesium ion beam and the sputtered negative ion beam. A critical component of this work was the development of the Rijke code. Rijke communicates with Lorentz-2E to initiate, generate, and run varied sequences of simulations, as well as analyze and record the input and output data in formats convenient for timely analysis. This software and its interconnection with Lorentz- 2E is described in extensive detail for a prospective user. Initial simulation work examined the effects of modifying various electrode geometries within the source such as the extraction cone, the target aperture, a simple cratered sample model as well as examining the effects of varying the cesium ion current. The self-repulsion of cesium was found to be important at currents of 250 µA and above. At high enough cesium currents, the expansion of the cesium beam is such that parts of it impinge outside the extents of the sample material. Through both simulation and experiment, it was demonstrated that this effect can be mitigated by either recessing (translating along the axis of symmetry away from the ionizer) the target holding the sample or by adjusting the potential difference between the target and ionizer. Experimentally, at routine settings (6 kV target to ionizer potential, 115 ◦C cesium oven temperature, and 35 keV output energy), a target recess of 1 mm gave the most stable and sustained output of 12C from graphite blanks. While the peak current was less than the unrecessed case, the total measured charge from the recessed target was higher. Cesium currents at these routine settings were found to be below the theoretical space-charge limited maximum. Using 10Be standards, a multi-dimensional experimental study examined the effects of increasing the cesium current, adjusting the target-ionizer potential from 4 to 11 kV, while also examining target recesses of 0 to 4 mm. Multiple combinations of these settings produced enhanced currents of 9Be2+, measured at the high-energy offset Faraday cup, as high as 13.5 µA. This was higher than previously observed, resulting in the most precise measurement of 10Be performed to date at Lalonde AMS. The electrodynamics within the ion source can be characterized as three competing processes: a) a strong locus of positive space charge located at the centre of the sample, depending primarily on the focusing of the cesium beam, which draws negative ions across the axis of symmetry; b) a bulk positive space charge external to the negative ion beam, depending primarily on the magnitude of the cesium current, draws the outer-most negative ions away from the axis; and c) the raw field from the electrode potentials and geometry which is mainly defocusing for negative ions. These effects are mitigated the most when the cesium beam is distributed across the entire sample surface with the additional critical benefit of maximizing the sample material accessed for sputtering. This thesis work has demonstrated that both the mutual and self space-charge interaction of the cesium and negative ion beams were critically important and that the use of the simulation software can inform both improved design and operation settings of the ion source.

No description available.

Cette thèse porte sur l'étude de la production d'une source d'ionsCes travaux de thèse ont consisté à étudier la faisabilité d'une source d'ions césium brillante et de faible dispersion énergétique à partir d'atomes froids dans le but de la coupler à une optique de faisceau d'ions focalisés (FIB).Il s'agit de produire une source ionique continue, de fort courant et de plus faible dispersion en énergie que les sources actuellement utilisées. Un schéma expérimental innovant a donc été imaginé.Un flux continu d'atomes de césium est issu d'un four à recirculation. Les atomes sont ensuite collimatés et compressés en se basant su les techniques de refroidissement d'atomes par laser. Des simulations de la mélasse optique pour la collimation et du MOT-2D pour la compression sont présentées. Issus d'un jet effusif de césium produit par un four à recirculation, la collimation grâce à une mélasse optique et la compression effectuée en en utilisant un MOT-2D des atomes de césium a été étudiée. Le schéma d'ionisation des atomes de césium passe par une excitation vers un état de Rydberg puis par une ionisation par champ électrique. Les propriétés remarquables des atomes pour ces niveaux d'énergie permettent d'obtenir une ionisation des atomes en champ électrique quasi-instantanée qui permet la minimisation de la dispersion énergétique. Nous avons développer une simulation permettant d'étudier les propriétés du champ électrique nécessaire pour l'ionisation afin de choisir le niveau de Rydberg approprié. Des simulations complémentaires ont permis de définir et de concevoir les électrodes nécessaires à la production du champ électrique d'excitation et d'ionisation. Une première étude des effets coulombiens de la source d'ions lors de l'ionisation des atomes de Rydberg est présentée. Enfin, l'étude théorique du couplage de la source obtenue avec une optique de faisceaux d'ions focalisés est réalisée.Un montage expérimental vient compléter ces diverses études et a permis d'obtenir les premiers résultats. / The main goal of this thesis consists on studying the production of a bright ion cesium source with a low energy dispersion. In this work, the technology of cold atoms is used to coupled this source with optical elements of focused ion beams (FIB).A cw ionic source with high current and small energy spread is necessary to complete the performances of others available sources. A new experimenal scheme is presented here.A continuous high flux of cesium atoms is produced by a recirculating oven. The atoms are the collimated and compessed using laser cooling technology. Several simulations concerning the collimation and the compression have been made.A different way of producing ions comes from the excitation in an electric field of Rydberg atoms and then their ionization in an electric field. The remarkable properties of Rydberg atoms show the possibilty to ionize them almost instantanely reducing this way the energy spread. In the work several simulations indicate the way to choose the right Rydberg state for this application and the correct corresponding electric field.Further simulations determinate the electrdes needed for the excitation and the ionization of the Rydberg atoms from the beam. Moreover, a first study of the coulombian effects occuring in this ion source is described. Finally, a theorical study of the ion source and optic FIB coupling is shown.The description of the experimental setup and the first results complete this work.

V této práci je představeno zařízení pro ozařování MeV ionty při tandemovém urychlovači na univerzitě v Uppsale. Jsou podány základy teorie interakce iontů s pevnou látkou a modifikace materiálu pomocí iontů s vysokou energií. Zařízení tandemového urychlovače je popsáno počínaje generací iontů a konče dopadem iontů na vzorek v hlavní komoře zařízení pro iontové ozařování. Následně jsou detailně charakterizovány modifikace systému pro přesun vzorků a popsán princip jeho funkce. Pilotní aplikace upraveného systému v oblasti materiálových modifikací je prezentována na příkladu ozařování Ge kvantových teček. Homogenita rozložení iontů na vzorku při ozařování je testována pomocí simulace elektrostatického deflektoru.