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Energetic ions are made to collide with atmospheric molecules. Positively charged ions of argon (Ar^+), helium (He^+), hydrogen (H_2^+ ), and protons (H^+) with energies of 50 keV to 350 keV are used as the bombarding ion. The ion beam of desired energy is produced using a linear ion accelerator at the University of Greifswald. The mass and energy distribution of sputtered particles were analysed using an Electrostatic Quadrupole SIMS (EQS) analyser. The target gases used are oxygen (O_2), sulfur hexafluoride (SF_6), and nitrogen (N_2). The ionized and fragmented particles due to collisions have been investigated. We have discovered a new process for negative ion formation in energetic ion collision with O_2 and SF_6 molecules. The process is a two body reaction between the projectile and the molecule without the need for a third particle (such as an external electron). It requires a direct charge transfer from the projectile to the molecule leaving it intact as O_2^- or SF_6^- . The process is experimentally confirmed by using a proton as projectile which does not have an electron to transfer. In comparison with positive ion fractions (O_2^+ , SF_5^+ ), the negative ions fraction is smaller by 2 orders of magnitude. This shows that the two body charge exchange process is weak due to the larger energy transfer required compared to the positive ion forming mechanisms. The two body charge exchange mechanism is not observed for ion collisions with N_2 molecule. No stable negative ion exist for N_2 molecule. The collision cross section for the ion formation during energetic ion – O_2 collision has been determined within the investigated impact energy. For SF_6 molecule the partial ion fraction of the secondary ions are determined for different projectiles involved. This kind of investigation is of great importance mainly in atmospheric physics. Energetic ions are constantly emitted from mass of the energy sources in the universe (e.g. sun). They interact with planetary objects or atmosphere on their way. A deep knowledge about the interaction processes is necessary to understand the ionospheric physics and space exploration. As second part of my thesis, a GaAs(100) surface is bombarded with 150 keV Ar^+ ion beam. From etching the surface to thin film coating, ion bombardment on solid surface found great role in the fabrication process of modern electronic and optical devices. In order to increase the knowledge on sputtering materials and because of profound importance in modern electronics, we choose GaAs(100) as our target. Among the sputtered atoms and ions, small sized cluster ions having more than 6 atoms have been identified. GaAs is a heteroatomic semiconductor containing gallium and arsenic in equal ratio. A preferential phenomenon of ’abundant sputtering’ of gallium compared to little arsenic (GaAs) has been investigated from their mass intensity. The experimental ion counts are compared with theoretically predicted relative abundance. This phenomenon of preferential sputtering is known for atomic species of sputtered GaAs but not for the sputtered cluster ions. The main reasons for this abundant sputtering of one element is attributed to the difference in ion formation energies and surface compositional change taking place during the sputtering process. Another notable characteristics is the preference in charge state among the sputtered ions. For instance, among sputtered atomic ions the ion counts of Ga^+ is 3 orders larger than As^+ ion and As^- is 2 orders larger than Ga^- ion. To get a clue for this behavior, we have investigated the energy distribution of both negatively and positively charged clusters. Different ion formation mechanisms were discussed. The energy distribution of atomic ion is partially explained by using a modified theory given by M. W. Thompson.
Multiply negatively charged aluminium clusters and fullerenes were generated in a Penning trap using the "electron-bath" technique. Aluminium monoanions were generated using a laser vaporisation source. After this, two-, three- and four-times negatively charged aluminium clusters were generated for the first time. This research marks the first observation of tetra-anionic metal clusters in the gas phase. Additionally, doubly-negatively charged fullerenes were generated. The smallest fullerene dianion observed contained 70 atoms.
The multi-cell Penning–Malmberg trap concept has been proposed as a way to accumulate and confine unprecedented numbers of antiparticles, an attractive but challenging goal. We report on the commissioning and first results (using electron plasmas) of the World's second prototype of such a trap, which builds and improves on the findings of its predecessor. Reliable alignment of both ‘master’ and ‘storage’ cells with the axial magnetic field has enabled confinement of plasmas, without use of the ‘rotating wall’ (RW) compression technique, for over an hour in the master cell and tens of seconds in the storage cells. In the master cell, attachment to background neutrals is found to be the main source of charge loss, with an overall charge-confinement time of 8.6 h. Transfer to on-axis and off-axis storage cells has been demonstrated, with an off-axis transfer rate of 50% of the initial particles, and confinement times in the storage cells in the tens of seconds (again, without RW compression). This, in turn, has enabled the first simultaneous plasma confinement in two off-axis cells, a milestone for the multi-cell trap concept.
In this doctoral thesis, algorithms are presented that are designed for the investigation in the mesopause region between the upper Mesosphere and Lower Thermosphere (MLT). The photochemical models are proposed and applied to represent the oxygen airglow and the oxygen photochemistry in the MLT. Atomic oxygen, O, in the ground state, O(3P), is of special interest because it is a reactive trace gas actively contributing to the Earth’s airglow. The retrievals of O(3P) concentrations, [O(3P)], are based on the nightglow time series of the green line emission measured remotely as in the first part of this thesis and the individual profiles of multiple nightglow emissions of O and molecular oxygen (O2) measured in situ as in the second part of this thesis. To process the complete spectral time series measured by using the satellite-borne instrument SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), an intricate set of algorithms is developed and applied with the regularized total least squares minimization approach to estimate a set of the optimal regularization parameters and to retrieve a corresponding set of vertical Volume Emission Rate (VER) profiles. Furthermore, these algorithms take emissions of another origin and the Earth's shape into account. Considering not identified states of O2, the established photochemical models are adjusted resulting in two model modifications. Both model modifications are employed to retrieve the [O(3P)] time series on the basis of the VER time series in the MLT. The model input parameters vary in the atmosphere that motivated to propose these two model modifications and to employ available sources of the input parameters. One semi-empirical model, one general circulation model and the satellite-borne instrument SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) are employed as sources of the reference [O(3P)] and input parameters time series. The SABER instrument employed as a source of the input parameters is preferred according to the comparison of the retrieved and reference [O(3P)] time series. Studying the impact of the 11-year solar cycle on O(3P) in the MLT, an algorithm is developed and applied with the Levenberg-Marquardt algorithm to estimate the optimal fit parameters step-wise. The results of the O(3P) sensitivity analysis obtained with respect to the solar activity forcing at the 11 year and 27 day time scales and the lunar gravitational forcing agree with the reference model simulations. The hypothesis regarding vertical shifts between different of Meinel bands at least partly caused by the hydroxyl radical (OH*) quenching with O(3P) is confirmed experimentally. Based on the conclusion drawn in the first part of this thesis that the data sets’ self-consistency is high as for the averaged SABER and SCIAMACHY measurements, a comprehensive set of available data with a higher level of the data sets’ self-consistency is employed in the second part of this thesis. Multiple airglow emissions measured in situ during four campaigns are employed to propose the Multiple Airglow Chemistry (MAC) model. Processed emissions are the Herzberg I, Chamberlain, Atmospheric and Infrared Atmospheric band emissions of O2 and the green line emission of O. Considering all widely known and additionally complemented reactions, the MAC model is proposed to represent the oxygen airglow and the oxygen photochemistry in the MLT. The presented MAC model is based on the hypothesis of Slanger et al. (2004) stating that higher excited states of O2 are coupled with each other through vibronic de-excitation caused by collisions among molecules of this group of O2 states in the MLT. This hypothesis is modified excluding the singlet Herzberg state of O2 from the group of O2 states considered by Slanger et al. (2004). The MAC calculations are carried out sequentially starting with higher excited O2 states to provide the retrieved output concentrations of these O2 states as the input concentrations to the next calculation steps. The final step is only based on concentrations of all species, whereas each of the earlier steps is based on a corresponding VER profile besides of the input concentrations. The oxygen photochemistry in the MLT is represented by all species considered at the final step that makes it possible to adopt the MAC reactions in a general circulation model. Four modifications of the MAC model, i.e. including or excluding the triplet Herzberg states of O2 and including or excluding ozone and odd hydrogen (hydrogen, OH* and hydroperoxy radical), lead to negligible differences in the retrieved [O(3P)] profiles. Based on the MAC calculations verified and validated on the basis of the four rocket campaigns, one of the effective modifications of the MAC model (excluding the triplet Herzberg states of O2, ozone and odd hydrogen) is further reduced to the most effective modification. This implies that for the [O(3P)] retrieval only the O2 Atmospheric band emission, temperature and concentrations of molecular nitrogen (N2) and O2 are sufficient to apply. Calculations carried out by using the most effective modification of the MAC model are verified and validated on the basis of self-consistent in situ measurements obtained simultaneously. The MAC model enables identifying precursors of (1) the three lowest O2 valence states and (2) the second excited O state responsible for (1) the Atmospheric and Infrared Atmospheric band emissions of O2 and (2) the green line emission of O, respectively. Particularly, the singlet Herzberg state of O2 is identified as the major precursor of the second excited O state resulting in the green line emission. In focus of potential further research is an extension of the MAC model with vibrationally excited states of O2 and ionized species.
Colossal magneto-resistance manganites are characterized by a complex interplay of charge, spin, orbital and lattice degrees of freedom. Formulating microscopic models for these compounds aims at meeting two conflicting objectives: sufficient simplification without excessive restrictions on the phase space. We give a detailed introduction to the electronic structure of manganites and derive a microscopic model for their low-energy physics. Focusing on short-range electron–lattice and spin–orbital correlations we supplement the modelling with numerical simulations.
Mechanical properties have been proven to be a pivotal parameter to enhance our understanding of living systems. While research during the last decades focused on cells and tissues, little is known about the role of organelle mechanics in cell function. Here, mitochondria are of specific interest due to their involvement in numerous physiological and pathological processes, e.g., in the production and homeostasis of reactive oxygen species (ROS). Using real-time fluorescence and deformability cytometry, we present a microfluidic technology that is capable to determine the mechanical properties of individual mitochondria at a throughput exceeding 100 organelles per second. Our data on several thousands of viable mitochondria isolated from rat C6 glial cells yield a homogenous population with a median deformation that scales with the applied hydrodynamic stress. In two proof-of-principle studies, we investigated the impact of exogenously and endogenously produced ROS on mitochondria mechanics. Exposing C6 cells to hydrogen peroxide (H2O2) triggers superoxide production and leads to a reduction in mitochondria size while deformation is increased. In a second study, we focused on the knockout of tafazzin, which has been associated with impaired remodeling of the mitochondrial membrane and elevated levels of ROS. Interestingly, our results reveal the same mechanical alterations as observed after the exposure to H2O2, which points to a unified biophysical mechanism of how mitochondria respond to the presence of oxidative stress. In summary, we introduce high-throughput mechanical phenotyping into the field of organelle biology with potential applications for understanding sub-cellular dynamics that have not been accessible before.
This thesis describes mass measurements at ISOLTRAP/ISOLDE/CERN in the region of the neutron-rich calcium isotopes. For the less exotic and more abundantly produced isotopes 51Ca and 52Ca the Penning trap based ToF-ICR technique could be used to validate the available mass data and to improve their precision. For the isotopes 53Ca and 54Ca, a Multi-Reflection Time-of-Flight Mass Spectrometer (MR-ToF MS) was used to determine the mass of these exotic isotopes for the first time experimentally. This also represents the first time an MR-ToF MS was applied to derive the masses of previously unknown radioactive ions from the high precision time-of-flight data that can be gathered with the device. The mass data was then used to benchmark the strength of the N=32 neutron subshell closure and at the same time to compare to state-of-the-art shell-model calculations.
Furthermore, the capability of the MR-ToF device to deliver isobarically pure beams to a subsequent experiment was developed further and studied in detail. The new technique is based on the in-trap lift, which is normally used to in- and eject ions into and from the device. With this new selective ejection technique after separation of the ion ensemble in the MR-ToF trap, no external components are required.
Additionally, a new stabilization system for voltages supplies, based on a PI-algorithm, was developed and thoroughly tested. The stabilized voltage supply was then used to supply the most sensitive mirror voltage of the MR-ToF MS to significantly increase the short term and long-term mass resolving power of the apparatus.
The triple-trap mass spectrometer ISOLTRAP at ISOLDE/CERN has demonstrated the feasibility of mass spectrometry of in-trap-decay product ions. This novel technique gives access to radionuclides, which are not produced directly at ISOL-type radioactive ion beam facilities. As a proof of principle, the in-trap decay of 37K+ has been investigated in a Penning trap filled with helium buffer gas. The half-life of the mother nuclide was confirmed and the recoiling 37Ar+ daughter ion was contained within the trap. The ions of either the mother or the daughter nuclide were transferred to a precision Penning trap, where their mass was determined.
In the present work, mass determinations of the eleven neutron-deficient nuclides (99-109)Cd, of ten neutron-rich silver nuclides (112-114,121,123)Ag, and seven neutron-rich cadmium nuclides (114,120,122-124,126,128)Cd are reported. Due to the clean production of the neutron-deficient nuclides it was possible to reduce the experimental uncertainties down to 2 keV, whereas the measurements of neutron-rich nuclides were hampered by the presence of contaminations from more stable In and Cs nuclides. In the case of 99Cd and 123Ag the masses were determined for the first time and for the other nuclides the mass uncertainties could be reduced by up to a factor of 50 as in the case of 100Cd. In the case of a potential isomeric mixture as for (115,117,119)Ag and 123Cd, where no assignment to either the ground state or the excited state was possible, the experimental results were adjusted accordingly. Afterwards all results were included in the framework of the atomic-mass evaluation and thus linked and compared with other experimental data. In the case of the neutron-deficient Cd nuclides a conflict between the mass values obtained in the present work and those published by the JYFLTRAP group could be solved by performing an atomic-mass evaluation. These mass measurements are an important step towards an understanding of the physics of the rp process that will enable a more reliable determination of the composition of the produced material at A = 99. It has been shown that the mass of 99Cd strongly affects the A = 99 production in an X-ray burst model, and that uncertainties have been significantly reduced from more than an order of magnitude to about a factor of 3. The dominant source of uncertainty is now the mass of 100In. In principle, other uncertainties will also contribute. These include those of masses of lighter Cd isotopes, where similar rp-process branchpoints occur and which might affect feeding into the 99Cd branchpoint. In addition, nuclear reaction rate uncertainties will also play a role. However, as reaction rates affect branchings in a linear fashion, while mass differences enter exponentially, mass uncertainties will tend to dominate. Also, which reaction rates are important depends largely on nuclear masses. For example, for low Sp(100In) a (p,γ)-(γ,p) equilibrium will be established between 99Cd and 100In and the 100In(p,γ) reaction rate would affect the A = 99 production, while for larger Sp(100In) the 99Cd(p,γ) reaction rate might be more relevant. Therefore, the mass uncertainties should be addressed first. The presented results are relevant for any rp-process scenario with a reaction flow through the 99Cd region. Here, an X-ray burst model has been used to investigate in detail the impact of the present measurements on such an rp process. The νp process in core collapse supernovae might be another possible scenario for an rp process in the 99Cd region. It it is planed to also explore whether in that case mass uncertainties have a similar impact on the final composition. On the neutron-rich side of the valley of stability for the Cd and Ag chains of nuclides, the r process has not yet been reached. Further technical development on suppression of contaminants are required. This includes improvements on the ISOLDE side, e.g., by improving the selectivity of the transfer line or on the ISOLTRAP setup by implementing an electrostatic ion beam trap for a fast and efficient isobaric selection. Nevertheless the obtained results contribute to the knowledge of nuclear structure. The trends in the two-neutron separation-energy S2n and the interaction between the last neutrons and last protons ΔVpn were corrected to more smooth evolutions, as already seen in other regions of the nuclear chart. The strongest corrections have been observed for even-N nuclides, were more new experimental data are available. Thus, new measurements on odd-N nuclides are suggested. This also is underlined by the trends observed in the Garvey-Kelson relations for the neutron-rich Cd nuclides. Furthermore, it has been shown, that the prominent structure of the ΔVpn for an entire chain of nuclides including inflexion points can be reproduced by using simple relations between quantum numbers of the occupied orbits. This approach connects ten values for each nuclide with only one adjusted parameter. This has been investigated for 63 ΔVpn values of even-even nuclides in the vicinity of Z = 50 and 50 ≤ N ≤ 82. The simple model works remarkably well for the elements Cd, Sn, and Te. Small deviation have been observed for the Xe and Pd nuclides which were explained with the limitations of the model to the vicinity of the close shells, where the nuclides have only few valence protons and neutrons.
Magnetooptical properties of one-dimensional aperiodic structures formed by stacking together magnetic and nonmagnetic layers according to the Kolakoski self-generation scheme are studied theoretically using the 4x4 transfer matrix method. The effect of the generation stage of the sequence, and the helicity and direction of light propagation through the magneto-photonic crystals on the transmission/reflection spectra as well as Faraday and ellipticity rotations, have been investigated. Our results reveal that this kind of aperiodic magneto-photonic crystals can be used for the fabrication of multifrequency laser cavities, and optical filters/sensors.